"""
The legend module defines the Legend class, which is responsible for
drawing legends associated with axes and/or figures.

.. important::

    It is unlikely that you would ever create a Legend instance manually.
    Most users would normally create a legend via the `~.Axes.legend`
    function. For more details on legends there is also a :doc:`legend guide
    </tutorials/intermediate/legend_guide>`.

The `Legend` class is a container of legend handles and legend texts.

The legend handler map specifies how to create legend handles from artists
(lines, patches, etc.) in the axes or figures. Default legend handlers are
defined in the :mod:`~matplotlib.legend_handler` module. While not all artist
types are covered by the default legend handlers, custom legend handlers can be
defined to support arbitrary objects.

See the :doc:`legend guide </tutorials/intermediate/legend_guide>` for more
information.
"""

import itertools
import logging
import time

import numpy as np

import matplotlib as mpl
from matplotlib import _api, _docstring, colors, offsetbox
from matplotlib.artist import Artist, allow_rasterization
from matplotlib.cbook import silent_list
from matplotlib.font_manager import FontProperties
from matplotlib.lines import Line2D
from matplotlib.patches import (Patch, Rectangle, Shadow, FancyBboxPatch,
                                StepPatch)
from matplotlib.collections import (
    Collection, CircleCollection, LineCollection, PathCollection,
    PolyCollection, RegularPolyCollection)
from matplotlib.text import Text
from matplotlib.transforms import Bbox, BboxBase, TransformedBbox
from matplotlib.transforms import BboxTransformTo, BboxTransformFrom
from matplotlib.offsetbox import (
    AnchoredOffsetbox, DraggableOffsetBox,
    HPacker, VPacker,
    DrawingArea, TextArea,
)
from matplotlib.container import ErrorbarContainer, BarContainer, StemContainer
from . import legend_handler


class DraggableLegend(DraggableOffsetBox):
    def __init__(self, legend, use_blit=False, update="loc"):
        """
        Wrapper around a `.Legend` to support mouse dragging.

        Parameters
        ----------
        legend : `.Legend`
            The `.Legend` instance to wrap.
        use_blit : bool, optional
            Use blitting for faster image composition. For details see
            :ref:`func-animation`.
        update : {'loc', 'bbox'}, optional
            If "loc", update the *loc* parameter of the legend upon finalizing.
            If "bbox", update the *bbox_to_anchor* parameter.
        """
        self.legend = legend

        _api.check_in_list(["loc", "bbox"], update=update)
        self._update = update

        super().__init__(legend, legend._legend_box, use_blit=use_blit)

    def finalize_offset(self):
        if self._update == "loc":
            self._update_loc(self.get_loc_in_canvas())
        elif self._update == "bbox":
            self._update_bbox_to_anchor(self.get_loc_in_canvas())

    def _update_loc(self, loc_in_canvas):
        bbox = self.legend.get_bbox_to_anchor()
        # if bbox has zero width or height, the transformation is
        # ill-defined. Fall back to the default bbox_to_anchor.
        if bbox.width == 0 or bbox.height == 0:
            self.legend.set_bbox_to_anchor(None)
            bbox = self.legend.get_bbox_to_anchor()
        _bbox_transform = BboxTransformFrom(bbox)
        self.legend._loc = tuple(_bbox_transform.transform(loc_in_canvas))

    def _update_bbox_to_anchor(self, loc_in_canvas):
        loc_in_bbox = self.legend.axes.transAxes.transform(loc_in_canvas)
        self.legend.set_bbox_to_anchor(loc_in_bbox)


_legend_kw_doc_base = """
bbox_to_anchor : `.BboxBase`, 2-tuple, or 4-tuple of floats
    Box that is used to position the legend in conjunction with *loc*.
    Defaults to `axes.bbox` (if called as a method to `.Axes.legend`) or
    `figure.bbox` (if `.Figure.legend`).  This argument allows arbitrary
    placement of the legend.

    Bbox coordinates are interpreted in the coordinate system given by
    *bbox_transform*, with the default transform
    Axes or Figure coordinates, depending on which ``legend`` is called.

    If a 4-tuple or `.BboxBase` is given, then it specifies the bbox
    ``(x, y, width, height)`` that the legend is placed in.
    To put the legend in the best location in the bottom right
    quadrant of the axes (or figure)::

        loc='best', bbox_to_anchor=(0.5, 0., 0.5, 0.5)

    A 2-tuple ``(x, y)`` places the corner of the legend specified by *loc* at
    x, y.  For example, to put the legend's upper right-hand corner in the
    center of the axes (or figure) the following keywords can be used::

        loc='upper right', bbox_to_anchor=(0.5, 0.5)

ncols : int, default: 1
    The number of columns that the legend has.

    For backward compatibility, the spelling *ncol* is also supported
    but it is discouraged. If both are given, *ncols* takes precedence.

prop : None or `~matplotlib.font_manager.FontProperties` or dict
    The font properties of the legend. If None (default), the current
    :data:`matplotlib.rcParams` will be used.

fontsize : int or {'xx-small', 'x-small', 'small', 'medium', 'large', \
'x-large', 'xx-large'}
    The font size of the legend. If the value is numeric the size will be the
    absolute font size in points. String values are relative to the current
    default font size. This argument is only used if *prop* is not specified.

labelcolor : str or list, default: :rc:`legend.labelcolor`
    The color of the text in the legend. Either a valid color string
    (for example, 'red'), or a list of color strings. The labelcolor can
    also be made to match the color of the line or marker using 'linecolor',
    'markerfacecolor' (or 'mfc'), or 'markeredgecolor' (or 'mec').

    Labelcolor can be set globally using :rc:`legend.labelcolor`. If None,
    use :rc:`text.color`.

numpoints : int, default: :rc:`legend.numpoints`
    The number of marker points in the legend when creating a legend
    entry for a `.Line2D` (line).

scatterpoints : int, default: :rc:`legend.scatterpoints`
    The number of marker points in the legend when creating
    a legend entry for a `.PathCollection` (scatter plot).

scatteryoffsets : iterable of floats, default: ``[0.375, 0.5, 0.3125]``
    The vertical offset (relative to the font size) for the markers
    created for a scatter plot legend entry. 0.0 is at the base the
    legend text, and 1.0 is at the top. To draw all markers at the
    same height, set to ``[0.5]``.

markerscale : float, default: :rc:`legend.markerscale`
    The relative size of legend markers compared to the originally drawn ones.

markerfirst : bool, default: True
    If *True*, legend marker is placed to the left of the legend label.
    If *False*, legend marker is placed to the right of the legend label.

reverse : bool, default: False
    If *True*, the legend labels are displayed in reverse order from the input.
    If *False*, the legend labels are displayed in the same order as the input.

    .. versionadded:: 3.7

frameon : bool, default: :rc:`legend.frameon`
    Whether the legend should be drawn on a patch (frame).

fancybox : bool, default: :rc:`legend.fancybox`
    Whether round edges should be enabled around the `.FancyBboxPatch` which
    makes up the legend's background.

shadow : bool, default: :rc:`legend.shadow`
    Whether to draw a shadow behind the legend.

framealpha : float, default: :rc:`legend.framealpha`
    The alpha transparency of the legend's background.
    If *shadow* is activated and *framealpha* is ``None``, the default value is
    ignored.

facecolor : "inherit" or color, default: :rc:`legend.facecolor`
    The legend's background color.
    If ``"inherit"``, use :rc:`axes.facecolor`.

edgecolor : "inherit" or color, default: :rc:`legend.edgecolor`
    The legend's background patch edge color.
    If ``"inherit"``, use take :rc:`axes.edgecolor`.

mode : {"expand", None}
    If *mode* is set to ``"expand"`` the legend will be horizontally
    expanded to fill the axes area (or *bbox_to_anchor* if defines
    the legend's size).

bbox_transform : None or `~matplotlib.transforms.Transform`
    The transform for the bounding box (*bbox_to_anchor*). For a value
    of ``None`` (default) the Axes'
    :data:`~matplotlib.axes.Axes.transAxes` transform will be used.

title : str or None
    The legend's title. Default is no title (``None``).

title_fontproperties : None or `~matplotlib.font_manager.FontProperties` or dict
    The font properties of the legend's title. If None (default), the
    *title_fontsize* argument will be used if present; if *title_fontsize* is
    also None, the current :rc:`legend.title_fontsize` will be used.

title_fontsize : int or {'xx-small', 'x-small', 'small', 'medium', 'large', \
'x-large', 'xx-large'}, default: :rc:`legend.title_fontsize`
    The font size of the legend's title.
    Note: This cannot be combined with *title_fontproperties*. If you want
    to set the fontsize alongside other font properties, use the *size*
    parameter in *title_fontproperties*.

alignment : {'center', 'left', 'right'}, default: 'center'
    The alignment of the legend title and the box of entries. The entries
    are aligned as a single block, so that markers always lined up.

borderpad : float, default: :rc:`legend.borderpad`
    The fractional whitespace inside the legend border, in font-size units.

labelspacing : float, default: :rc:`legend.labelspacing`
    The vertical space between the legend entries, in font-size units.

handlelength : float, default: :rc:`legend.handlelength`
    The length of the legend handles, in font-size units.

handleheight : float, default: :rc:`legend.handleheight`
    The height of the legend handles, in font-size units.

handletextpad : float, default: :rc:`legend.handletextpad`
    The pad between the legend handle and text, in font-size units.

borderaxespad : float, default: :rc:`legend.borderaxespad`
    The pad between the axes and legend border, in font-size units.

columnspacing : float, default: :rc:`legend.columnspacing`
    The spacing between columns, in font-size units.

handler_map : dict or None
    The custom dictionary mapping instances or types to a legend
    handler. This *handler_map* updates the default handler map
    found at `matplotlib.legend.Legend.get_legend_handler_map`.

draggable : bool, default: False
    Whether the legend can be dragged with the mouse.
"""

_loc_doc_base = """
loc : str or pair of floats, default: {default}
    The location of the legend.

    The strings ``'upper left'``, ``'upper right'``, ``'lower left'``,
    ``'lower right'`` place the legend at the corresponding corner of the
    {parent}.

    The strings ``'upper center'``, ``'lower center'``, ``'center left'``,
    ``'center right'`` place the legend at the center of the corresponding edge
    of the {parent}.

    The string ``'center'`` places the legend at the center of the {parent}.
{best}
    The location can also be a 2-tuple giving the coordinates of the lower-left
    corner of the legend in {parent} coordinates (in which case *bbox_to_anchor*
    will be ignored).

    For back-compatibility, ``'center right'`` (but no other location) can also
    be spelled ``'right'``, and each "string" location can also be given as a
    numeric value:

        ==================   =============
        Location String      Location Code
        ==================   =============
        'best' (Axes only)   0
        'upper right'        1
        'upper left'         2
        'lower left'         3
        'lower right'        4
        'right'              5
        'center left'        6
        'center right'       7
        'lower center'       8
        'upper center'       9
        'center'             10
        ==================   =============
    {outside}"""

_loc_doc_best = """
    The string ``'best'`` places the legend at the location, among the nine
    locations defined so far, with the minimum overlap with other drawn
    artists.  This option can be quite slow for plots with large amounts of
    data; your plotting speed may benefit from providing a specific location.
"""

_legend_kw_axes_st = (
    _loc_doc_base.format(parent='axes', default=':rc:`legend.loc`',
                         best=_loc_doc_best, outside='') +
    _legend_kw_doc_base)
_docstring.interpd.update(_legend_kw_axes=_legend_kw_axes_st)

_outside_doc = """
    If a figure is using the constrained layout manager, the string codes
    of the *loc* keyword argument can get better layout behaviour using the
    prefix 'outside'. There is ambiguity at the corners, so 'outside
    upper right' will make space for the legend above the rest of the
    axes in the layout, and 'outside right upper' will make space on the
    right side of the layout.  In addition to the values of *loc*
    listed above, we have 'outside right upper', 'outside right lower',
    'outside left upper', and 'outside left lower'.  See
    :doc:`/tutorials/intermediate/legend_guide` for more details.
"""

_legend_kw_figure_st = (
    _loc_doc_base.format(parent='figure', default="'upper right'",
                         best='', outside=_outside_doc) +
    _legend_kw_doc_base)
_docstring.interpd.update(_legend_kw_figure=_legend_kw_figure_st)

_legend_kw_both_st = (
    _loc_doc_base.format(parent='axes/figure',
                         default=":rc:`legend.loc` for Axes, 'upper right' for Figure",
                         best=_loc_doc_best, outside=_outside_doc) +
    _legend_kw_doc_base)
_docstring.interpd.update(_legend_kw_doc=_legend_kw_both_st)


class Legend(Artist):
    """
    Place a legend on the figure/axes.
    """

    # 'best' is only implemented for axes legends
    codes = {'best': 0, **AnchoredOffsetbox.codes}
    zorder = 5

    def __str__(self):
        return "Legend"

    @_api.make_keyword_only("3.6", "loc")
    @_docstring.dedent_interpd
    def __init__(
        self, parent, handles, labels,
        loc=None,
        numpoints=None,      # number of points in the legend line
        markerscale=None,    # relative size of legend markers vs. original
        markerfirst=True,    # left/right ordering of legend marker and label
        reverse=False,       # reverse ordering of legend marker and label
        scatterpoints=None,  # number of scatter points
        scatteryoffsets=None,
        prop=None,           # properties for the legend texts
        fontsize=None,       # keyword to set font size directly
        labelcolor=None,     # keyword to set the text color

        # spacing & pad defined as a fraction of the font-size
        borderpad=None,      # whitespace inside the legend border
        labelspacing=None,   # vertical space between the legend entries
        handlelength=None,   # length of the legend handles
        handleheight=None,   # height of the legend handles
        handletextpad=None,  # pad between the legend handle and text
        borderaxespad=None,  # pad between the axes and legend border
        columnspacing=None,  # spacing between columns

        ncols=1,     # number of columns
        mode=None,  # horizontal distribution of columns: None or "expand"

        fancybox=None,  # True: fancy box, False: rounded box, None: rcParam
        shadow=None,
        title=None,           # legend title
        title_fontsize=None,  # legend title font size
        framealpha=None,      # set frame alpha
        edgecolor=None,       # frame patch edgecolor
        facecolor=None,       # frame patch facecolor

        bbox_to_anchor=None,  # bbox to which the legend will be anchored
        bbox_transform=None,  # transform for the bbox
        frameon=None,         # draw frame
        handler_map=None,
        title_fontproperties=None,  # properties for the legend title
        alignment="center",       # control the alignment within the legend box
        *,
        ncol=1,  # synonym for ncols (backward compatibility)
        draggable=False  # whether the legend can be dragged with the mouse
    ):
        """
        Parameters
        ----------
        parent : `~matplotlib.axes.Axes` or `.Figure`
            The artist that contains the legend.

        handles : list of `.Artist`
            A list of Artists (lines, patches) to be added to the legend.

        labels : list of str
            A list of labels to show next to the artists. The length of handles
            and labels should be the same. If they are not, they are truncated
            to the length of the shorter list.

        Other Parameters
        ----------------
        %(_legend_kw_doc)s

        Attributes
        ----------
        legend_handles
            List of `.Artist` objects added as legend entries.

            .. versionadded:: 3.7
        """
        # local import only to avoid circularity
        from matplotlib.axes import Axes
        from matplotlib.figure import FigureBase

        super().__init__()

        if prop is None:
            if fontsize is not None:
                self.prop = FontProperties(size=fontsize)
            else:
                self.prop = FontProperties(
                    size=mpl.rcParams["legend.fontsize"])
        else:
            self.prop = FontProperties._from_any(prop)
            if isinstance(prop, dict) and "size" not in prop:
                self.prop.set_size(mpl.rcParams["legend.fontsize"])

        self._fontsize = self.prop.get_size_in_points()

        self.texts = []
        self.legend_handles = []
        self._legend_title_box = None

        #: A dictionary with the extra handler mappings for this Legend
        #: instance.
        self._custom_handler_map = handler_map

        def val_or_rc(val, rc_name):
            return val if val is not None else mpl.rcParams[rc_name]

        self.numpoints = val_or_rc(numpoints, 'legend.numpoints')
        self.markerscale = val_or_rc(markerscale, 'legend.markerscale')
        self.scatterpoints = val_or_rc(scatterpoints, 'legend.scatterpoints')
        self.borderpad = val_or_rc(borderpad, 'legend.borderpad')
        self.labelspacing = val_or_rc(labelspacing, 'legend.labelspacing')
        self.handlelength = val_or_rc(handlelength, 'legend.handlelength')
        self.handleheight = val_or_rc(handleheight, 'legend.handleheight')
        self.handletextpad = val_or_rc(handletextpad, 'legend.handletextpad')
        self.borderaxespad = val_or_rc(borderaxespad, 'legend.borderaxespad')
        self.columnspacing = val_or_rc(columnspacing, 'legend.columnspacing')
        self.shadow = val_or_rc(shadow, 'legend.shadow')
        # trim handles and labels if illegal label...
        _lab, _hand = [], []
        for label, handle in zip(labels, handles):
            if isinstance(label, str) and label.startswith('_'):
                _api.warn_external(f"The label {label!r} of {handle!r} starts "
                                   "with '_'. It is thus excluded from the "
                                   "legend.")
            else:
                _lab.append(label)
                _hand.append(handle)
        labels, handles = _lab, _hand

        if reverse:
            labels.reverse()
            handles.reverse()

        if len(handles) < 2:
            ncols = 1
        self._ncols = ncols if ncols != 1 else ncol

        if self.numpoints <= 0:
            raise ValueError("numpoints must be > 0; it was %d" % numpoints)

        # introduce y-offset for handles of the scatter plot
        if scatteryoffsets is None:
            self._scatteryoffsets = np.array([3. / 8., 4. / 8., 2.5 / 8.])
        else:
            self._scatteryoffsets = np.asarray(scatteryoffsets)
        reps = self.scatterpoints // len(self._scatteryoffsets) + 1
        self._scatteryoffsets = np.tile(self._scatteryoffsets,
                                        reps)[:self.scatterpoints]

        # _legend_box is a VPacker instance that contains all
        # legend items and will be initialized from _init_legend_box()
        # method.
        self._legend_box = None

        if isinstance(parent, Axes):
            self.isaxes = True
            self.axes = parent
            self.set_figure(parent.figure)
        elif isinstance(parent, FigureBase):
            self.isaxes = False
            self.set_figure(parent)
        else:
            raise TypeError(
                "Legend needs either Axes or FigureBase as parent"
            )
        self.parent = parent

        loc0 = loc
        self._loc_used_default = loc is None
        if loc is None:
            loc = mpl.rcParams["legend.loc"]
            if not self.isaxes and loc in [0, 'best']:
                loc = 'upper right'

        # handle outside legends:
        self._outside_loc = None
        if isinstance(loc, str):
            if loc.split()[0] == 'outside':
                # strip outside:
                loc = loc.split('outside ')[1]
                # strip "center" at the beginning
                self._outside_loc = loc.replace('center ', '')
                # strip first
                self._outside_loc = self._outside_loc.split()[0]
                locs = loc.split()
                if len(locs) > 1 and locs[0] in ('right', 'left'):
                    # locs doesn't accept "left upper", etc, so swap
                    if locs[0] != 'center':
                        locs = locs[::-1]
                    loc = locs[0] + ' ' + locs[1]
            # check that loc is in acceptable strings
            loc = _api.check_getitem(self.codes, loc=loc)

        if self.isaxes and self._outside_loc:
            raise ValueError(
                f"'outside' option for loc='{loc0}' keyword argument only "
                "works for figure legends")

        if not self.isaxes and loc == 0:
            raise ValueError(
                "Automatic legend placement (loc='best') not implemented for "
                "figure legend")

        self._mode = mode
        self.set_bbox_to_anchor(bbox_to_anchor, bbox_transform)

        # We use FancyBboxPatch to draw a legend frame. The location
        # and size of the box will be updated during the drawing time.

        if facecolor is None:
            facecolor = mpl.rcParams["legend.facecolor"]
        if facecolor == 'inherit':
            facecolor = mpl.rcParams["axes.facecolor"]

        if edgecolor is None:
            edgecolor = mpl.rcParams["legend.edgecolor"]
        if edgecolor == 'inherit':
            edgecolor = mpl.rcParams["axes.edgecolor"]

        if fancybox is None:
            fancybox = mpl.rcParams["legend.fancybox"]

        self.legendPatch = FancyBboxPatch(
            xy=(0, 0), width=1, height=1,
            facecolor=facecolor, edgecolor=edgecolor,
            # If shadow is used, default to alpha=1 (#8943).
            alpha=(framealpha if framealpha is not None
                   else 1 if shadow
                   else mpl.rcParams["legend.framealpha"]),
            # The width and height of the legendPatch will be set (in draw())
            # to the length that includes the padding. Thus we set pad=0 here.
            boxstyle=("round,pad=0,rounding_size=0.2" if fancybox
                      else "square,pad=0"),
            mutation_scale=self._fontsize,
            snap=True,
            visible=(frameon if frameon is not None
                     else mpl.rcParams["legend.frameon"])
        )
        self._set_artist_props(self.legendPatch)

        _api.check_in_list(["center", "left", "right"], alignment=alignment)
        self._alignment = alignment

        # init with null renderer
        self._init_legend_box(handles, labels, markerfirst)

        tmp = self._loc_used_default
        self._set_loc(loc)
        self._loc_used_default = tmp  # ignore changes done by _set_loc

        # figure out title font properties:
        if title_fontsize is not None and title_fontproperties is not None:
            raise ValueError(
                "title_fontsize and title_fontproperties can't be specified "
                "at the same time. Only use one of them. ")
        title_prop_fp = FontProperties._from_any(title_fontproperties)
        if isinstance(title_fontproperties, dict):
            if "size" not in title_fontproperties:
                title_fontsize = mpl.rcParams["legend.title_fontsize"]
                title_prop_fp.set_size(title_fontsize)
        elif title_fontsize is not None:
            title_prop_fp.set_size(title_fontsize)
        elif not isinstance(title_fontproperties, FontProperties):
            title_fontsize = mpl.rcParams["legend.title_fontsize"]
            title_prop_fp.set_size(title_fontsize)

        self.set_title(title, prop=title_prop_fp)

        self._draggable = None
        self.set_draggable(state=draggable)

        # set the text color

        color_getters = {  # getter function depends on line or patch
            'linecolor':       ['get_color',           'get_facecolor'],
            'markerfacecolor': ['get_markerfacecolor', 'get_facecolor'],
            'mfc':             ['get_markerfacecolor', 'get_facecolor'],
            'markeredgecolor': ['get_markeredgecolor', 'get_edgecolor'],
            'mec':             ['get_markeredgecolor', 'get_edgecolor'],
        }
        if labelcolor is None:
            if mpl.rcParams['legend.labelcolor'] is not None:
                labelcolor = mpl.rcParams['legend.labelcolor']
            else:
                labelcolor = mpl.rcParams['text.color']
        if isinstance(labelcolor, str) and labelcolor in color_getters:
            getter_names = color_getters[labelcolor]
            for handle, text in zip(self.legend_handles, self.texts):
                try:
                    if handle.get_array() is not None:
                        continue
                except AttributeError:
                    pass
                for getter_name in getter_names:
                    try:
                        color = getattr(handle, getter_name)()
                        if isinstance(color, np.ndarray):
                            if (
                                    color.shape[0] == 1
                                    or np.isclose(color, color[0]).all()
                            ):
                                text.set_color(color[0])
                            else:
                                pass
                        else:
                            text.set_color(color)
                        break
                    except AttributeError:
                        pass
        elif isinstance(labelcolor, str) and labelcolor == 'none':
            for text in self.texts:
                text.set_color(labelcolor)
        elif np.iterable(labelcolor):
            for text, color in zip(self.texts,
                                   itertools.cycle(
                                       colors.to_rgba_array(labelcolor))):
                text.set_color(color)
        else:
            raise ValueError(f"Invalid labelcolor: {labelcolor!r}")

    legendHandles = _api.deprecated('3.7', alternative="legend_handles")(
        property(lambda self: self.legend_handles))

    def _set_artist_props(self, a):
        """
        Set the boilerplate props for artists added to axes.
        """
        a.set_figure(self.figure)
        if self.isaxes:
            # a.set_axes(self.axes)
            a.axes = self.axes

        a.set_transform(self.get_transform())

    def _set_loc(self, loc):
        # find_offset function will be provided to _legend_box and
        # _legend_box will draw itself at the location of the return
        # value of the find_offset.
        self._loc_used_default = False
        self._loc_real = loc
        self.stale = True
        self._legend_box.set_offset(self._findoffset)

    def set_ncols(self, ncols):
        """Set the number of columns."""
        self._ncols = ncols

    def _get_loc(self):
        return self._loc_real

    _loc = property(_get_loc, _set_loc)

    def _findoffset(self, width, height, xdescent, ydescent, renderer):
        """Helper function to locate the legend."""

        if self._loc == 0:  # "best".
            x, y = self._find_best_position(width, height, renderer)
        elif self._loc in Legend.codes.values():  # Fixed location.
            bbox = Bbox.from_bounds(0, 0, width, height)
            x, y = self._get_anchored_bbox(self._loc, bbox,
                                           self.get_bbox_to_anchor(),
                                           renderer)
        else:  # Axes or figure coordinates.
            fx, fy = self._loc
            bbox = self.get_bbox_to_anchor()
            x, y = bbox.x0 + bbox.width * fx, bbox.y0 + bbox.height * fy

        return x + xdescent, y + ydescent

    @allow_rasterization
    def draw(self, renderer):
        # docstring inherited
        if not self.get_visible():
            return

        renderer.open_group('legend', gid=self.get_gid())

        fontsize = renderer.points_to_pixels(self._fontsize)

        # if mode == fill, set the width of the legend_box to the
        # width of the parent (minus pads)
        if self._mode in ["expand"]:
            pad = 2 * (self.borderaxespad + self.borderpad) * fontsize
            self._legend_box.set_width(self.get_bbox_to_anchor().width - pad)

        # update the location and size of the legend. This needs to
        # be done in any case to clip the figure right.
        bbox = self._legend_box.get_window_extent(renderer)
        self.legendPatch.set_bounds(bbox.bounds)
        self.legendPatch.set_mutation_scale(fontsize)

        if self.shadow:
            Shadow(self.legendPatch, 2, -2).draw(renderer)

        self.legendPatch.draw(renderer)
        self._legend_box.draw(renderer)

        renderer.close_group('legend')
        self.stale = False

    # _default_handler_map defines the default mapping between plot
    # elements and the legend handlers.

    _default_handler_map = {
        StemContainer: legend_handler.HandlerStem(),
        ErrorbarContainer: legend_handler.HandlerErrorbar(),
        Line2D: legend_handler.HandlerLine2D(),
        Patch: legend_handler.HandlerPatch(),
        StepPatch: legend_handler.HandlerStepPatch(),
        LineCollection: legend_handler.HandlerLineCollection(),
        RegularPolyCollection: legend_handler.HandlerRegularPolyCollection(),
        CircleCollection: legend_handler.HandlerCircleCollection(),
        BarContainer: legend_handler.HandlerPatch(
            update_func=legend_handler.update_from_first_child),
        tuple: legend_handler.HandlerTuple(),
        PathCollection: legend_handler.HandlerPathCollection(),
        PolyCollection: legend_handler.HandlerPolyCollection()
        }

    # (get|set|update)_default_handler_maps are public interfaces to
    # modify the default handler map.

    @classmethod
    def get_default_handler_map(cls):
        """Return the global default handler map, shared by all legends."""
        return cls._default_handler_map

    @classmethod
    def set_default_handler_map(cls, handler_map):
        """Set the global default handler map, shared by all legends."""
        cls._default_handler_map = handler_map

    @classmethod
    def update_default_handler_map(cls, handler_map):
        """Update the global default handler map, shared by all legends."""
        cls._default_handler_map.update(handler_map)

    def get_legend_handler_map(self):
        """Return this legend instance's handler map."""
        default_handler_map = self.get_default_handler_map()
        return ({**default_handler_map, **self._custom_handler_map}
                if self._custom_handler_map else default_handler_map)

    @staticmethod
    def get_legend_handler(legend_handler_map, orig_handle):
        """
        Return a legend handler from *legend_handler_map* that
        corresponds to *orig_handler*.

        *legend_handler_map* should be a dictionary object (that is
        returned by the get_legend_handler_map method).

        It first checks if the *orig_handle* itself is a key in the
        *legend_handler_map* and return the associated value.
        Otherwise, it checks for each of the classes in its
        method-resolution-order. If no matching key is found, it
        returns ``None``.
        """
        try:
            return legend_handler_map[orig_handle]
        except (TypeError, KeyError):  # TypeError if unhashable.
            pass
        for handle_type in type(orig_handle).mro():
            try:
                return legend_handler_map[handle_type]
            except KeyError:
                pass
        return None

    def _init_legend_box(self, handles, labels, markerfirst=True):
        """
        Initialize the legend_box. The legend_box is an instance of
        the OffsetBox, which is packed with legend handles and
        texts. Once packed, their location is calculated during the
        drawing time.
        """

        fontsize = self._fontsize

        # legend_box is a HPacker, horizontally packed with columns.
        # Each column is a VPacker, vertically packed with legend items.
        # Each legend item is a HPacker packed with:
        # - handlebox: a DrawingArea which contains the legend handle.
        # - labelbox: a TextArea which contains the legend text.

        text_list = []  # the list of text instances
        handle_list = []  # the list of handle instances
        handles_and_labels = []

        # The approximate height and descent of text. These values are
        # only used for plotting the legend handle.
        descent = 0.35 * fontsize * (self.handleheight - 0.7)  # heuristic.
        height = fontsize * self.handleheight - descent
        # each handle needs to be drawn inside a box of (x, y, w, h) =
        # (0, -descent, width, height).  And their coordinates should
        # be given in the display coordinates.

        # The transformation of each handle will be automatically set
        # to self.get_transform(). If the artist does not use its
        # default transform (e.g., Collections), you need to
        # manually set their transform to the self.get_transform().
        legend_handler_map = self.get_legend_handler_map()

        for orig_handle, label in zip(handles, labels):
            handler = self.get_legend_handler(legend_handler_map, orig_handle)
            if handler is None:
                _api.warn_external(
                             "Legend does not support handles for {0} "
                             "instances.\nA proxy artist may be used "
                             "instead.\nSee: https://matplotlib.org/"
                             "stable/tutorials/intermediate/legend_guide.html"
                             "#controlling-the-legend-entries".format(
                                 type(orig_handle).__name__))
                # No handle for this artist, so we just defer to None.
                handle_list.append(None)
            else:
                textbox = TextArea(label, multilinebaseline=True,
                                   textprops=dict(
                                       verticalalignment='baseline',
                                       horizontalalignment='left',
                                       fontproperties=self.prop))
                handlebox = DrawingArea(width=self.handlelength * fontsize,
                                        height=height,
                                        xdescent=0., ydescent=descent)

                text_list.append(textbox._text)
                # Create the artist for the legend which represents the
                # original artist/handle.
                handle_list.append(handler.legend_artist(self, orig_handle,
                                                         fontsize, handlebox))
                handles_and_labels.append((handlebox, textbox))

        columnbox = []
        # array_split splits n handles_and_labels into ncols columns, with the
        # first n%ncols columns having an extra entry.  filter(len, ...)
        # handles the case where n < ncols: the last ncols-n columns are empty
        # and get filtered out.
        for handles_and_labels_column in filter(
                len, np.array_split(handles_and_labels, self._ncols)):
            # pack handlebox and labelbox into itembox
            itemboxes = [HPacker(pad=0,
                                 sep=self.handletextpad * fontsize,
                                 children=[h, t] if markerfirst else [t, h],
                                 align="baseline")
                         for h, t in handles_and_labels_column]
            # pack columnbox
            alignment = "baseline" if markerfirst else "right"
            columnbox.append(VPacker(pad=0,
                                     sep=self.labelspacing * fontsize,
                                     align=alignment,
                                     children=itemboxes))

        mode = "expand" if self._mode == "expand" else "fixed"
        sep = self.columnspacing * fontsize
        self._legend_handle_box = HPacker(pad=0,
                                          sep=sep, align="baseline",
                                          mode=mode,
                                          children=columnbox)
        self._legend_title_box = TextArea("")
        self._legend_box = VPacker(pad=self.borderpad * fontsize,
                                   sep=self.labelspacing * fontsize,
                                   align=self._alignment,
                                   children=[self._legend_title_box,
                                             self._legend_handle_box])
        self._legend_box.set_figure(self.figure)
        self._legend_box.axes = self.axes
        self.texts = text_list
        self.legend_handles = handle_list

    def _auto_legend_data(self):
        """
        Return display coordinates for hit testing for "best" positioning.

        Returns
        -------
        bboxes
            List of bounding boxes of all patches.
        lines
            List of `.Path` corresponding to each line.
        offsets
            List of (x, y) offsets of all collection.
        """
        assert self.isaxes  # always holds, as this is only called internally
        bboxes = []
        lines = []
        offsets = []
        for artist in self.parent._children:
            if isinstance(artist, Line2D):
                lines.append(
                    artist.get_transform().transform_path(artist.get_path()))
            elif isinstance(artist, Rectangle):
                bboxes.append(
                    artist.get_bbox().transformed(artist.get_data_transform()))
            elif isinstance(artist, Patch):
                lines.append(
                    artist.get_transform().transform_path(artist.get_path()))
            elif isinstance(artist, Collection):
                transform, transOffset, hoffsets, _ = artist._prepare_points()
                if len(hoffsets):
                    for offset in transOffset.transform(hoffsets):
                        offsets.append(offset)

        return bboxes, lines, offsets

    def get_children(self):
        # docstring inherited
        return [self._legend_box, self.get_frame()]

    def get_frame(self):
        """Return the `~.patches.Rectangle` used to frame the legend."""
        return self.legendPatch

    def get_lines(self):
        r"""Return the list of `~.lines.Line2D`\s in the legend."""
        return [h for h in self.legend_handles if isinstance(h, Line2D)]

    def get_patches(self):
        r"""Return the list of `~.patches.Patch`\s in the legend."""
        return silent_list('Patch',
                           [h for h in self.legend_handles
                            if isinstance(h, Patch)])

    def get_texts(self):
        r"""Return the list of `~.text.Text`\s in the legend."""
        return silent_list('Text', self.texts)

    def set_alignment(self, alignment):
        """
        Set the alignment of the legend title and the box of entries.

        The entries are aligned as a single block, so that markers always
        lined up.

        Parameters
        ----------
        alignment : {'center', 'left', 'right'}.

        """
        _api.check_in_list(["center", "left", "right"], alignment=alignment)
        self._alignment = alignment
        self._legend_box.align = alignment

    def get_alignment(self):
        """Get the alignment value of the legend box"""
        return self._legend_box.align

    def set_title(self, title, prop=None):
        """
        Set legend title and title style.

        Parameters
        ----------
        title : str
            The legend title.

        prop : `.font_manager.FontProperties` or `str` or `pathlib.Path`
            The font properties of the legend title.
            If a `str`, it is interpreted as a fontconfig pattern parsed by
            `.FontProperties`.  If a `pathlib.Path`, it is interpreted as the
            absolute path to a font file.

        """
        self._legend_title_box._text.set_text(title)
        if title:
            self._legend_title_box._text.set_visible(True)
            self._legend_title_box.set_visible(True)
        else:
            self._legend_title_box._text.set_visible(False)
            self._legend_title_box.set_visible(False)

        if prop is not None:
            self._legend_title_box._text.set_fontproperties(prop)

        self.stale = True

    def get_title(self):
        """Return the `.Text` instance for the legend title."""
        return self._legend_title_box._text

    def get_window_extent(self, renderer=None):
        # docstring inherited
        if renderer is None:
            renderer = self.figure._get_renderer()
        return self._legend_box.get_window_extent(renderer=renderer)

    def get_tightbbox(self, renderer=None):
        # docstring inherited
        return self._legend_box.get_window_extent(renderer)

    def get_frame_on(self):
        """Get whether the legend box patch is drawn."""
        return self.legendPatch.get_visible()

    def set_frame_on(self, b):
        """
        Set whether the legend box patch is drawn.

        Parameters
        ----------
        b : bool
        """
        self.legendPatch.set_visible(b)
        self.stale = True

    draw_frame = set_frame_on  # Backcompat alias.

    def get_bbox_to_anchor(self):
        """Return the bbox that the legend will be anchored to."""
        if self._bbox_to_anchor is None:
            return self.parent.bbox
        else:
            return self._bbox_to_anchor

    def set_bbox_to_anchor(self, bbox, transform=None):
        """
        Set the bbox that the legend will be anchored to.

        Parameters
        ----------
        bbox : `~matplotlib.transforms.BboxBase` or tuple
            The bounding box can be specified in the following ways:

            - A `.BboxBase` instance
            - A tuple of ``(left, bottom, width, height)`` in the given
              transform (normalized axes coordinate if None)
            - A tuple of ``(left, bottom)`` where the width and height will be
              assumed to be zero.
            - *None*, to remove the bbox anchoring, and use the parent bbox.

        transform : `~matplotlib.transforms.Transform`, optional
            A transform to apply to the bounding box. If not specified, this
            will use a transform to the bounding box of the parent.
        """
        if bbox is None:
            self._bbox_to_anchor = None
            return
        elif isinstance(bbox, BboxBase):
            self._bbox_to_anchor = bbox
        else:
            try:
                l = len(bbox)
            except TypeError as err:
                raise ValueError(f"Invalid bbox: {bbox}") from err

            if l == 2:
                bbox = [bbox[0], bbox[1], 0, 0]

            self._bbox_to_anchor = Bbox.from_bounds(*bbox)

        if transform is None:
            transform = BboxTransformTo(self.parent.bbox)

        self._bbox_to_anchor = TransformedBbox(self._bbox_to_anchor,
                                               transform)
        self.stale = True

    def _get_anchored_bbox(self, loc, bbox, parentbbox, renderer):
        """
        Place the *bbox* inside the *parentbbox* according to a given
        location code. Return the (x, y) coordinate of the bbox.

        Parameters
        ----------
        loc : int
            A location code in range(1, 11). This corresponds to the possible
            values for ``self._loc``, excluding "best".
        bbox : `~matplotlib.transforms.Bbox`
            bbox to be placed, in display coordinates.
        parentbbox : `~matplotlib.transforms.Bbox`
            A parent box which will contain the bbox, in display coordinates.
        """
        return offsetbox._get_anchored_bbox(
            loc, bbox, parentbbox,
            self.borderaxespad * renderer.points_to_pixels(self._fontsize))

    def _find_best_position(self, width, height, renderer, consider=None):
        """
        Determine the best location to place the legend.

        *consider* is a list of ``(x, y)`` pairs to consider as a potential
        lower-left corner of the legend. All are display coords.
        """
        assert self.isaxes  # always holds, as this is only called internally

        start_time = time.perf_counter()

        bboxes, lines, offsets = self._auto_legend_data()

        bbox = Bbox.from_bounds(0, 0, width, height)
        if consider is None:
            consider = [self._get_anchored_bbox(x, bbox,
                                                self.get_bbox_to_anchor(),
                                                renderer)
                        for x in range(1, len(self.codes))]

        candidates = []
        for idx, (l, b) in enumerate(consider):
            legendBox = Bbox.from_bounds(l, b, width, height)
            badness = 0
            # XXX TODO: If markers are present, it would be good to take them
            # into account when checking vertex overlaps in the next line.
            badness = (sum(legendBox.count_contains(line.vertices)
                           for line in lines)
                       + legendBox.count_contains(offsets)
                       + legendBox.count_overlaps(bboxes)
                       + sum(line.intersects_bbox(legendBox, filled=False)
                             for line in lines))
            if badness == 0:
                return l, b
            # Include the index to favor lower codes in case of a tie.
            candidates.append((badness, idx, (l, b)))

        _, _, (l, b) = min(candidates)

        if self._loc_used_default and time.perf_counter() - start_time > 1:
            _api.warn_external(
                'Creating legend with loc="best" can be slow with large '
                'amounts of data.')

        return l, b

    def contains(self, event):
        inside, info = self._default_contains(event)
        if inside is not None:
            return inside, info
        return self.legendPatch.contains(event)

    def set_draggable(self, state, use_blit=False, update='loc'):
        """
        Enable or disable mouse dragging support of the legend.

        Parameters
        ----------
        state : bool
            Whether mouse dragging is enabled.
        use_blit : bool, optional
            Use blitting for faster image composition. For details see
            :ref:`func-animation`.
        update : {'loc', 'bbox'}, optional
            The legend parameter to be changed when dragged:

            - 'loc': update the *loc* parameter of the legend
            - 'bbox': update the *bbox_to_anchor* parameter of the legend

        Returns
        -------
        `.DraggableLegend` or *None*
            If *state* is ``True`` this returns the `.DraggableLegend` helper
            instance. Otherwise this returns *None*.
        """
        if state:
            if self._draggable is None:
                self._draggable = DraggableLegend(self,
                                                  use_blit,
                                                  update=update)
        else:
            if self._draggable is not None:
                self._draggable.disconnect()
            self._draggable = None
        return self._draggable

    def get_draggable(self):
        """Return ``True`` if the legend is draggable, ``False`` otherwise."""
        return self._draggable is not None


# Helper functions to parse legend arguments for both `figure.legend` and
# `axes.legend`:
def _get_legend_handles(axs, legend_handler_map=None):
    """Yield artists that can be used as handles in a legend."""
    handles_original = []
    for ax in axs:
        handles_original += [
            *(a for a in ax._children
              if isinstance(a, (Line2D, Patch, Collection, Text))),
            *ax.containers]
        # support parasite axes:
        if hasattr(ax, 'parasites'):
            for axx in ax.parasites:
                handles_original += [
                    *(a for a in axx._children
                      if isinstance(a, (Line2D, Patch, Collection, Text))),
                    *axx.containers]

    handler_map = {**Legend.get_default_handler_map(),
                   **(legend_handler_map or {})}
    has_handler = Legend.get_legend_handler
    for handle in handles_original:
        label = handle.get_label()
        if label != '_nolegend_' and has_handler(handler_map, handle):
            yield handle
        elif (label and not label.startswith('_') and
                not has_handler(handler_map, handle)):
            _api.warn_external(
                             "Legend does not support handles for {0} "
                             "instances.\nSee: https://matplotlib.org/stable/"
                             "tutorials/intermediate/legend_guide.html"
                             "#implementing-a-custom-legend-handler".format(
                                 type(handle).__name__))
            continue


def _get_legend_handles_labels(axs, legend_handler_map=None):
    """Return handles and labels for legend."""
    handles = []
    labels = []
    for handle in _get_legend_handles(axs, legend_handler_map):
        label = handle.get_label()
        if label and not label.startswith('_'):
            handles.append(handle)
            labels.append(label)
    return handles, labels


def _parse_legend_args(axs, *args, handles=None, labels=None, **kwargs):
    """
    Get the handles and labels from the calls to either ``figure.legend``
    or ``axes.legend``.

    The parser is a bit involved because we support::

        legend()
        legend(labels)
        legend(handles, labels)
        legend(labels=labels)
        legend(handles=handles)
        legend(handles=handles, labels=labels)

    The behavior for a mixture of positional and keyword handles and labels
    is undefined and issues a warning.

    Parameters
    ----------
    axs : list of `.Axes`
        If handles are not given explicitly, the artists in these Axes are
        used as handles.
    *args : tuple
        Positional parameters passed to ``legend()``.
    handles
        The value of the keyword argument ``legend(handles=...)``, or *None*
        if that keyword argument was not used.
    labels
        The value of the keyword argument ``legend(labels=...)``, or *None*
        if that keyword argument was not used.
    **kwargs
        All other keyword arguments passed to ``legend()``.

    Returns
    -------
    handles : list of `.Artist`
        The legend handles.
    labels : list of str
        The legend labels.
    extra_args : tuple
        *args* with positional handles and labels removed.
    kwargs : dict
        *kwargs* with keywords handles and labels removed.

    """
    log = logging.getLogger(__name__)

    handlers = kwargs.get('handler_map')
    extra_args = ()

    if (handles is not None or labels is not None) and args:
        _api.warn_external("You have mixed positional and keyword arguments, "
                           "some input may be discarded.")

    # if got both handles and labels as kwargs, make same length
    if handles and labels:
        handles, labels = zip(*zip(handles, labels))

    elif handles is not None and labels is None:
        labels = [handle.get_label() for handle in handles]

    elif labels is not None and handles is None:
        # Get as many handles as there are labels.
        handles = [handle for handle, label
                   in zip(_get_legend_handles(axs, handlers), labels)]

    # No arguments - automatically detect labels and handles.
    elif len(args) == 0:
        handles, labels = _get_legend_handles_labels(axs, handlers)
        if not handles:
            log.warning(
                "No artists with labels found to put in legend.  Note that "
                "artists whose label start with an underscore are ignored "
                "when legend() is called with no argument.")

    # One argument. User defined labels - automatic handle detection.
    elif len(args) == 1:
        labels, = args
        if any(isinstance(l, Artist) for l in labels):
            raise TypeError("A single argument passed to legend() must be a "
                            "list of labels, but found an Artist in there.")

        # Get as many handles as there are labels.
        handles = [handle for handle, label
                   in zip(_get_legend_handles(axs, handlers), labels)]

    # Two arguments:
    #   * user defined handles and labels
    elif len(args) >= 2:
        handles, labels = args[:2]
        extra_args = args[2:]

    else:
        raise TypeError('Invalid arguments to legend.')

    return handles, labels, extra_args, kwargs
