# coding: utf-8

# Copyright (c) Jupyter Development Team.
# Distributed under the terms of the Modified BSD License.

from __future__ import unicode_literals

from difflib import SequenceMatcher
from ..diff_format import SequenceDiffBuilder


__all__ = ["diff_sequence_difflib"]


def opcodes_to_diff(a, b, opcodes):
    "Convert difflib opcodes to nbdime diff format."
    di = SequenceDiffBuilder()
    for opcode in opcodes:
        action, abegin, aend, bbegin, bend = opcode
        asize = aend - abegin
        #bsize = bend - bbegin
        if action == "equal":
            # Unlike difflib we don't represent equal stretches explicitly
            pass
        elif action == "replace":
            di.removerange(abegin, asize)
            di.addrange(abegin, b[bbegin:bend])
        elif action == "insert":
            di.addrange(abegin, b[bbegin:bend])
        elif action == "delete":
            di.removerange(abegin, asize)
        else:
            raise RuntimeError("Unknown action {}".format(action))
    return di.validated()


def diff_sequence_difflib(a, b):
    """Compute the diff of two sequences.

    This implementation uses SequenceMatcher from the builtin Python difflib.

    By the difflib documentation this should work for sequences of
    hashable objects, i.e. the elements of the sequences are only
    compared for full equality. Therefore this function does not take
    a custom compare function like the other diff_sequence_* variants.
    """
    assert not any(isinstance(x, (list, dict)) for x in a)
    assert not any(isinstance(x, (list, dict)) for x in b)
    s = SequenceMatcher(None, a, b, autojunk=False)
    return opcodes_to_diff(a, b, s.get_opcodes())
