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    `                 @   s   d dl mZ dd ZdS )    )defaultdictc                s   dd |  D }dd |  D }dddddd	d
dgt|t|t|t|tt x,D ]$\}} d |  d | qjW  fdd} fdd}|  || || tS )u  
    This module symmetrisatizes the source-to-target and target-to-source
    word alignment output and produces, aka. GDFA algorithm (Koehn, 2005).

    Step 1: Find the intersection of the bidirectional alignment.

    Step 2: Search for additional neighbor alignment points to be added, given
            these criteria: (i) neighbor alignments points are not in the
            intersection and (ii) neighbor alignments are in the union.

    Step 3: Add all other alignment points thats not in the intersection, not in
            the neighboring alignments that met the criteria but in the original
            foward/backward alignment outputs.

        >>> forw = ('0-0 2-1 9-2 21-3 10-4 7-5 11-6 9-7 12-8 1-9 3-10 '
        ...         '4-11 17-12 17-13 25-14 13-15 24-16 11-17 28-18')
        >>> back = ('0-0 1-9 2-9 3-10 4-11 5-12 6-6 7-5 8-6 9-7 10-4 '
        ...         '11-6 12-8 13-12 15-12 17-13 18-13 19-12 20-13 '
        ...         '21-3 22-12 23-14 24-17 25-15 26-17 27-18 28-18')
        >>> srctext = ("この よう な ハロー 白色 わい 星 の Ｌ 関数 "
        ...            "は Ｌ と 共 に 不連続 に 増加 する こと が "
        ...            "期待 さ れる こと を 示し た 。")
        >>> trgtext = ("Therefore , we expect that the luminosity function "
        ...            "of such halo white dwarfs increases discontinuously "
        ...            "with the luminosity .")
        >>> srclen = len(srctext.split())
        >>> trglen = len(trgtext.split())
        >>>
        >>> gdfa = grow_diag_final_and(srclen, trglen, forw, back)
        >>> gdfa == sorted(set([(28, 18), (6, 6), (24, 17), (2, 1), (15, 12), (13, 12),
        ...         (2, 9), (3, 10), (26, 17), (25, 15), (8, 6), (9, 7), (20,
        ...         13), (18, 13), (0, 0), (10, 4), (13, 15), (23, 14), (7, 5),
        ...         (25, 14), (1, 9), (17, 13), (4, 11), (11, 17), (9, 2), (22,
        ...         12), (27, 18), (24, 16), (21, 3), (19, 12), (17, 12), (5,
        ...         12), (11, 6), (12, 8)]))
        True

    References:
    Koehn, P., A. Axelrod, A. Birch, C. Callison, M. Osborne, and D. Talbot.
    2005. Edinburgh System Description for the 2005 IWSLT Speech
    Translation Evaluation. In MT Eval Workshop.

    :type srclen: int
    :param srclen: the number of tokens in the source language
    :type trglen: int
    :param trglen: the number of tokens in the target language
    :type e2f: str
    :param e2f: the forward word alignment outputs from source-to-target
                language (in pharaoh output format)
    :type f2e: str
    :param f2e: the backward word alignment outputs from target-to-source
                language (in pharaoh output format)
    :rtype: set(tuple(int))
    :return: the symmetrized alignment points from the GDFA algorithm
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        neighboring alignments but in the original *e2f* and *f2e* alignments
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