"""
PyQt5 port of the `layouts/flowlayout
<https://doc.qt.io/qt-5/qtwidgets-layouts-flowlayout-example.html>`_ example
from Qt5.

"""
from PyQt5.QtCore import pyqtSignal, QPoint, QRect, QSize, Qt
from PyQt5.QtWidgets import QLayout, QSizePolicy, QSpacerItem


# https://stackoverflow.com/a/46727466

class FlowLayout(QLayout):
    """A ``QLayout`` that aranges its child widgets horizontally and
    vertically.

    If enough horizontal space is available, it looks like an ``HBoxLayout``,
    but if enough space is lacking, it automatically wraps its children into
    multiple rows.

    """
    heightChanged = pyqtSignal(int)

    def __init__(self, parent=None, margin=0, spacing=-1):
        super().__init__(parent)
        if parent is not None:
            self.setContentsMargins(margin, margin, margin, margin)
        self.setSpacing(spacing)

        self._item_list = []

    def __del__(self):
        while self.count():
            self.takeAt(0)

    def addItem(self, item):  # pylint: disable=invalid-name
        self._item_list.append(item)

    def addSpacing(self, size):  # pylint: disable=invalid-name
        self.addItem(QSpacerItem(size, 0, QSizePolicy.Fixed, QSizePolicy.Minimum))

    def count(self):
        return len(self._item_list)

    def itemAt(self, index):  # pylint: disable=invalid-name
        if 0 <= index < len(self._item_list):
            return self._item_list[index]
        return None

    def takeAt(self, index):  # pylint: disable=invalid-name
        if 0 <= index < len(self._item_list):
            return self._item_list.pop(index)
        return None

    def expandingDirections(self):  # pylint: disable=invalid-name,no-self-use
        return Qt.Orientations(Qt.Orientation(0))

    def hasHeightForWidth(self):  # pylint: disable=invalid-name,no-self-use
        return True

    def heightForWidth(self, width):  # pylint: disable=invalid-name
        height = self._do_layout(QRect(0, 0, width, 0), True)
        return height

    def setGeometry(self, rect):  # pylint: disable=invalid-name
        super().setGeometry(rect)
        self._do_layout(rect, False)

    def sizeHint(self):  # pylint: disable=invalid-name
        return self.minimumSize()

    def minimumSize(self):  # pylint: disable=invalid-name
        size = QSize()

        for item in self._item_list:
            minsize = item.minimumSize()
            extent = item.geometry().bottomRight()
            size = size.expandedTo(QSize(minsize.width(), extent.y()))

        margin = self.contentsMargins().left()
        size += QSize(2 * margin, 2 * margin)
        return size

    def _do_layout(self, rect, test_only=False):
        m = self.contentsMargins()
        effective_rect = rect.adjusted(+m.left(), +m.top(), -m.right(), -m.bottom())
        x = effective_rect.x()
        y = effective_rect.y()
        line_height = 0

        for item in self._item_list:
            wid = item.widget()

            space_x = self.spacing()
            space_y = self.spacing()
            if wid is not None:
                space_x += wid.style().layoutSpacing(
                    QSizePolicy.PushButton, QSizePolicy.PushButton, Qt.Horizontal)
                space_y += wid.style().layoutSpacing(
                    QSizePolicy.PushButton, QSizePolicy.PushButton, Qt.Vertical)

            next_x = x + item.sizeHint().width() + space_x
            if next_x - space_x > effective_rect.right() and line_height > 0:
                x = effective_rect.x()
                y = y + line_height + space_y
                next_x = x + item.sizeHint().width() + space_x
                line_height = 0

            if not test_only:
                item.setGeometry(QRect(QPoint(x, y), item.sizeHint()))

            x = next_x
            line_height = max(line_height, item.sizeHint().height())

        new_height = y + line_height - rect.y()
        self.heightChanged.emit(new_height)
        return new_height


if __name__ == '__main__':
    import sys
    from PyQt5.QtWidgets import QApplication, QPushButton, QScrollArea, QVBoxLayout, QWidget, QGroupBox

    app = QApplication(sys.argv)

    container = QWidget()
    container_layout = QVBoxLayout()
    for i in range(2):
        g = QGroupBox(f'Group {i}')
        l = FlowLayout(margin=10)
        l.heightChanged.connect(container.setMinimumHeight)
        g.setLayout(l)
        l.addWidget(QPushButton('Short'))
        l.addWidget(QPushButton('Longer'))
        l.addWidget(QPushButton('Different text'))
        l.addWidget(QPushButton('More text'))
        l.addWidget(QPushButton('Even longer button text'))
        container_layout.addWidget(g)
    container_layout.addStretch()
    container.setLayout(container_layout)

    w = QScrollArea()
    w.setWindowTitle('Flow Layout')
    w.setWidgetResizable(True)
    w.setWidget(container)
    w.show()

    sys.exit(app.exec_())
