/*
 *  LibXDiff by Davide Libenzi ( File Differential Library )
 *  Copyright (C) 2003-2006 Davide Libenzi, Johannes E. Schindelin
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *  Davide Libenzi <davidel@xmailserver.org>
 *
 */

#include "xinclude.h"

typedef struct s_xdmerge {
        struct s_xdmerge *next;
        /*
         * 0 = conflict,
         * 1 = no conflict, take first,
         * 2 = no conflict, take second.
         * 3 = no conflict, take both.
         */
        int mode;
        /*
         * These point at the respective postimages.  E.g. <i1,chg1> is
         * how side #1 wants to change the common ancestor; if there is no
         * overlap, lines before i1 in the postimage of side #1 appear
         * in the merge result as a region touched by neither side.
         */
        long i1, i2;
        long chg1, chg2;
        /*
         * These point at the preimage; of course there is just one
         * preimage, that is from the shared common ancestor.
         */
        long i0;
        long chg0;
} xdmerge_t;

static int xdl_append_merge(xdmerge_t **merge, int mode,
                            long i0, long chg0,
                            long i1, long chg1,
                            long i2, long chg2)
{
        xdmerge_t *m = *merge;
        if (m && (i1 <= m->i1 + m->chg1 || i2 <= m->i2 + m->chg2)) {
                if (mode != m->mode)
                        m->mode = 0;
                m->chg0 = i0 + chg0 - m->i0;
                m->chg1 = i1 + chg1 - m->i1;
                m->chg2 = i2 + chg2 - m->i2;
        } else {
                m = xdl_malloc(sizeof(xdmerge_t));
                if (!m)
                        return -1;
                m->next = NULL;
                m->mode = mode;
                m->i0 = i0;
                m->chg0 = chg0;
                m->i1 = i1;
                m->chg1 = chg1;
                m->i2 = i2;
                m->chg2 = chg2;
                if (*merge)
                        (*merge)->next = m;
                *merge = m;
        }
        return 0;
}

static int xdl_cleanup_merge(xdmerge_t *c)
{
        int count = 0;
        xdmerge_t *next_c;

        /* were there conflicts? */
        for (; c; c = next_c) {
                if (c->mode == 0)
                        count++;
                next_c = c->next;
                free(c);
        }
        return count;
}

static int xdl_merge_cmp_lines(xdfenv_t *xe1, int i1, xdfenv_t *xe2, int i2,
                int line_count, long flags)
{
        int i;
        xrecord_t **rec1 = xe1->xdf2.recs + i1;
        xrecord_t **rec2 = xe2->xdf2.recs + i2;

        for (i = 0; i < line_count; i++) {
                int result = xdl_recmatch(rec1[i]->ptr, rec1[i]->size,
                        rec2[i]->ptr, rec2[i]->size, flags);
                if (!result)
                        return -1;
        }
        return 0;
}

static int xdl_recs_copy_0(int use_orig, xdfenv_t *xe, int i, int count, int add_nl, char *dest)
{
        xrecord_t **recs;
        int size = 0;

        recs = (use_orig ? xe->xdf1.recs : xe->xdf2.recs) + i;

        if (count < 1)
                return 0;

        for (i = 0; i < count; size += recs[i++]->size)
                if (dest)
                        memcpy(dest + size, recs[i]->ptr, recs[i]->size);
        if (add_nl) {
                i = recs[count - 1]->size;
                if (i == 0 || recs[count - 1]->ptr[i - 1] != '\n') {
                        if (dest)
                                dest[size] = '\n';
                        size++;
                }
        }
        return size;
}

static int xdl_recs_copy(xdfenv_t *xe, int i, int count, int add_nl, char *dest)
{
        return xdl_recs_copy_0(0, xe, i, count, add_nl, dest);
}

static int xdl_orig_copy(xdfenv_t *xe, int i, int count, int add_nl, char *dest)
{
        return xdl_recs_copy_0(1, xe, i, count, add_nl, dest);
}

/*
 * Returns 1 if the i'th line ends in CR/LF (if it is the last line and
 * has no eol, the preceding line, if any), 0 if it ends in LF-only, and
 * -1 if the line ending cannot be determined.
 */
static int is_eol_crlf(xdfile_t *file, int i)
{
        long size;

        if (i < file->nrec - 1)
                /* All lines before the last *must* end in LF */
                return (size = file->recs[i]->size) > 1 &&
                        file->recs[i]->ptr[size - 2] == '\r';
        if (!file->nrec)
                /* Cannot determine eol style from empty file */
                return -1;
        if ((size = file->recs[i]->size) &&
                        file->recs[i]->ptr[size - 1] == '\n')
                /* Last line; ends in LF; Is it CR/LF? */
                return size > 1 &&
                        file->recs[i]->ptr[size - 2] == '\r';
        if (!i)
                /* The only line has no eol */
                return -1;
        /* Determine eol from second-to-last line */
        return (size = file->recs[i - 1]->size) > 1 &&
                file->recs[i - 1]->ptr[size - 2] == '\r';
}

static int is_cr_needed(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m)
{
        int needs_cr;

        /* Match post-images' preceding, or first, lines' end-of-line style */
        needs_cr = is_eol_crlf(&xe1->xdf2, m->i1 ? m->i1 - 1 : 0);
        if (needs_cr)
                needs_cr = is_eol_crlf(&xe2->xdf2, m->i2 ? m->i2 - 1 : 0);
        /* Look at pre-image's first line, unless we already settled on LF */
        if (needs_cr)
                needs_cr = is_eol_crlf(&xe1->xdf1, 0);
        /* If still undecided, use LF-only */
        return needs_cr < 0 ? 0 : needs_cr;
}

static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
                              xdfenv_t *xe2, const char *name2,
                              const char *name3,
                              int size, int i, int style,
                              xdmerge_t *m, char *dest, int marker_size)
{
        int marker1_size = (name1 ? strlen(name1) + 1 : 0);
        int marker2_size = (name2 ? strlen(name2) + 1 : 0);
        int marker3_size = (name3 ? strlen(name3) + 1 : 0);
        int needs_cr = is_cr_needed(xe1, xe2, m);

        if (marker_size <= 0)
                marker_size = DEFAULT_CONFLICT_MARKER_SIZE;

        /* Before conflicting part */
        size += xdl_recs_copy(xe1, i, m->i1 - i, 0,
                              dest ? dest + size : NULL);

        if (!dest) {
                size += marker_size + 1 + needs_cr + marker1_size;
        } else {
                memset(dest + size, '<', marker_size);
                size += marker_size;
                if (marker1_size) {
                        dest[size] = ' ';
                        memcpy(dest + size + 1, name1, marker1_size - 1);
                        size += marker1_size;
                }
                if (needs_cr)
                        dest[size++] = '\r';
                dest[size++] = '\n';
        }

        /* Postimage from side #1 */
        size += xdl_recs_copy(xe1, m->i1, m->chg1, 1,
                              dest ? dest + size : NULL);

        if (style == XDL_MERGE_DIFF3) {
                /* Shared preimage */
                if (!dest) {
                        size += marker_size + 1 + needs_cr + marker3_size;
                } else {
                        memset(dest + size, '|', marker_size);
                        size += marker_size;
                        if (marker3_size) {
                                dest[size] = ' ';
                                memcpy(dest + size + 1, name3, marker3_size - 1);
                                size += marker3_size;
                        }
                        if (needs_cr)
                                dest[size++] = '\r';
                        dest[size++] = '\n';
                }
                size += xdl_orig_copy(xe1, m->i0, m->chg0, 1,
                                      dest ? dest + size : NULL);
        }

        if (!dest) {
                size += marker_size + 1 + needs_cr;
        } else {
                memset(dest + size, '=', marker_size);
                size += marker_size;
                if (needs_cr)
                        dest[size++] = '\r';
                dest[size++] = '\n';
        }

        /* Postimage from side #2 */
        size += xdl_recs_copy(xe2, m->i2, m->chg2, 1,
                              dest ? dest + size : NULL);
        if (!dest) {
                size += marker_size + 1 + needs_cr + marker2_size;
        } else {
                memset(dest + size, '>', marker_size);
                size += marker_size;
                if (marker2_size) {
                        dest[size] = ' ';
                        memcpy(dest + size + 1, name2, marker2_size - 1);
                        size += marker2_size;
                }
                if (needs_cr)
                        dest[size++] = '\r';
                dest[size++] = '\n';
        }
        return size;
}

static int xdl_fill_merge_buffer(xdfenv_t *xe1, const char *name1,
                                 xdfenv_t *xe2, const char *name2,
                                 const char *ancestor_name,
                                 int favor,
                                 xdmerge_t *m, char *dest, int style,
                                 int marker_size)
{
        int size, i;

        for (size = i = 0; m; m = m->next) {
                if (favor && !m->mode)
                        m->mode = favor;

                if (m->mode == 0)
                        size = fill_conflict_hunk(xe1, name1, xe2, name2,
                                                  ancestor_name,
                                                  size, i, style, m, dest,
                                                  marker_size);
                else if (m->mode & 3) {
                        /* Before conflicting part */
                        size += xdl_recs_copy(xe1, i, m->i1 - i, 0,
                                              dest ? dest + size : NULL);
                        /* Postimage from side #1 */
                        if (m->mode & 1)
                                size += xdl_recs_copy(xe1, m->i1, m->chg1, (m->mode & 2),
                                                      dest ? dest + size : NULL);
                        /* Postimage from side #2 */
                        if (m->mode & 2)
                                size += xdl_recs_copy(xe2, m->i2, m->chg2, 0,
                                                      dest ? dest + size : NULL);
                } else
                        continue;
                i = m->i1 + m->chg1;
        }
        size += xdl_recs_copy(xe1, i, xe1->xdf2.nrec - i, 0,
                              dest ? dest + size : NULL);
        return size;
}

/*
 * Sometimes, changes are not quite identical, but differ in only a few
 * lines. Try hard to show only these few lines as conflicting.
 */
static int xdl_refine_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
                xpparam_t const *xpp)
{
        for (; m; m = m->next) {
                mmfile_t t1, t2;
                xdfenv_t xe;
                xdchange_t *xscr, *x;
                int i1 = m->i1, i2 = m->i2;

                /* let's handle just the conflicts */
                if (m->mode)
                        continue;

                /* no sense refining a conflict when one side is empty */
                if (m->chg1 == 0 || m->chg2 == 0)
                        continue;

                /*
                 * This probably does not work outside git, since
                 * we have a very simple mmfile structure.
                 */
                t1.ptr = (char *)xe1->xdf2.recs[m->i1]->ptr;
                t1.size = xe1->xdf2.recs[m->i1 + m->chg1 - 1]->ptr
                        + xe1->xdf2.recs[m->i1 + m->chg1 - 1]->size - t1.ptr;
                t2.ptr = (char *)xe2->xdf2.recs[m->i2]->ptr;
                t2.size = xe2->xdf2.recs[m->i2 + m->chg2 - 1]->ptr
                        + xe2->xdf2.recs[m->i2 + m->chg2 - 1]->size - t2.ptr;
                if (xdl_do_diff(&t1, &t2, xpp, &xe) < 0)
                        return -1;
                if (xdl_change_compact(&xe.xdf1, &xe.xdf2, xpp->flags) < 0 ||
                    xdl_change_compact(&xe.xdf2, &xe.xdf1, xpp->flags) < 0 ||
                    xdl_build_script(&xe, &xscr) < 0) {
                        xdl_free_env(&xe);
                        return -1;
                }
                if (!xscr) {
                        /* If this happens, the changes are identical. */
                        xdl_free_env(&xe);
                        m->mode = 4;
                        continue;
                }
                x = xscr;
                m->i1 = xscr->i1 + i1;
                m->chg1 = xscr->chg1;
                m->i2 = xscr->i2 + i2;
                m->chg2 = xscr->chg2;
                while (xscr->next) {
                        xdmerge_t *m2 = xdl_malloc(sizeof(xdmerge_t));
                        if (!m2) {
                                xdl_free_env(&xe);
                                xdl_free_script(x);
                                return -1;
                        }
                        xscr = xscr->next;
                        m2->next = m->next;
                        m->next = m2;
                        m = m2;
                        m->mode = 0;
                        m->i1 = xscr->i1 + i1;
                        m->chg1 = xscr->chg1;
                        m->i2 = xscr->i2 + i2;
                        m->chg2 = xscr->chg2;
                }
                xdl_free_env(&xe);
                xdl_free_script(x);
        }
        return 0;
}

static int line_contains_alnum(const char *ptr, long size)
{
        while (size--)
                if (isalnum((unsigned char)*(ptr++)))
                        return 1;
        return 0;
}

static int lines_contain_alnum(xdfenv_t *xe, int i, int chg)
{
        for (; chg; chg--, i++)
                if (line_contains_alnum(xe->xdf2.recs[i]->ptr,
                                xe->xdf2.recs[i]->size))
                        return 1;
        return 0;
}

/*
 * This function merges m and m->next, marking everything between those hunks
 * as conflicting, too.
 */
static void xdl_merge_two_conflicts(xdmerge_t *m)
{
        xdmerge_t *next_m = m->next;
        m->chg1 = next_m->i1 + next_m->chg1 - m->i1;
        m->chg2 = next_m->i2 + next_m->chg2 - m->i2;
        m->next = next_m->next;
        free(next_m);
}

/*
 * If there are less than 3 non-conflicting lines between conflicts,
 * it appears simpler -- because it takes up less (or as many) lines --
 * if the lines are moved into the conflicts.
 */
static int xdl_simplify_non_conflicts(xdfenv_t *xe1, xdmerge_t *m,
                                      int simplify_if_no_alnum)
{
        int result = 0;

        if (!m)
                return result;
        for (;;) {
                xdmerge_t *next_m = m->next;
                int begin, end;

                if (!next_m)
                        return result;

                begin = m->i1 + m->chg1;
                end = next_m->i1;

                if (m->mode != 0 || next_m->mode != 0 ||
                    (end - begin > 3 &&
                     (!simplify_if_no_alnum ||
                      lines_contain_alnum(xe1, begin, end - begin)))) {
                        m = next_m;
                } else {
                        result++;
                        xdl_merge_two_conflicts(m);
                }
        }
}

/*
 * level == 0: mark all overlapping changes as conflict
 * level == 1: mark overlapping changes as conflict only if not identical
 * level == 2: analyze non-identical changes for minimal conflict set
 * level == 3: analyze non-identical changes for minimal conflict set, but
 *             treat hunks not containing any letter or number as conflicting
 *
 * returns < 0 on error, == 0 for no conflicts, else number of conflicts
 */
static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
                xdfenv_t *xe2, xdchange_t *xscr2,
                xmparam_t const *xmp, mmbuffer_t *result)
{
        xdmerge_t *changes, *c;
        xpparam_t const *xpp = &xmp->xpp;
        const char *const ancestor_name = xmp->ancestor;
        const char *const name1 = xmp->file1;
        const char *const name2 = xmp->file2;
        int i0, i1, i2, chg0, chg1, chg2;
        int level = xmp->level;
        int style = xmp->style;
        int favor = xmp->favor;

        if (style == XDL_MERGE_DIFF3) {
                /*
                 * "diff3 -m" output does not make sense for anything
                 * more aggressive than XDL_MERGE_EAGER.
                 */
                if (XDL_MERGE_EAGER < level)
                        level = XDL_MERGE_EAGER;
        }

        c = changes = NULL;

        while (xscr1 && xscr2) {
                if (!changes)
                        changes = c;
                if (xscr1->i1 + xscr1->chg1 < xscr2->i1) {
                        i0 = xscr1->i1;
                        i1 = xscr1->i2;
                        i2 = xscr2->i2 - xscr2->i1 + xscr1->i1;
                        chg0 = xscr1->chg1;
                        chg1 = xscr1->chg2;
                        chg2 = xscr1->chg1;
                        if (xdl_append_merge(&c, 1,
                                             i0, chg0, i1, chg1, i2, chg2)) {
                                xdl_cleanup_merge(changes);
                                return -1;
                        }
                        xscr1 = xscr1->next;
                        continue;
                }
                if (xscr2->i1 + xscr2->chg1 < xscr1->i1) {
                        i0 = xscr2->i1;
                        i1 = xscr1->i2 - xscr1->i1 + xscr2->i1;
                        i2 = xscr2->i2;
                        chg0 = xscr2->chg1;
                        chg1 = xscr2->chg1;
                        chg2 = xscr2->chg2;
                        if (xdl_append_merge(&c, 2,
                                             i0, chg0, i1, chg1, i2, chg2)) {
                                xdl_cleanup_merge(changes);
                                return -1;
                        }
                        xscr2 = xscr2->next;
                        continue;
                }
                if (level == XDL_MERGE_MINIMAL || xscr1->i1 != xscr2->i1 ||
                                xscr1->chg1 != xscr2->chg1 ||
                                xscr1->chg2 != xscr2->chg2 ||
                                xdl_merge_cmp_lines(xe1, xscr1->i2,
                                        xe2, xscr2->i2,
                                        xscr1->chg2, xpp->flags)) {
                        /* conflict */
                        int off = xscr1->i1 - xscr2->i1;
                        int ffo = off + xscr1->chg1 - xscr2->chg1;

                        i0 = xscr1->i1;
                        i1 = xscr1->i2;
                        i2 = xscr2->i2;
                        if (off > 0) {
                                i0 -= off;
                                i1 -= off;
                        }
                        else
                                i2 += off;
                        chg0 = xscr1->i1 + xscr1->chg1 - i0;
                        chg1 = xscr1->i2 + xscr1->chg2 - i1;
                        chg2 = xscr2->i2 + xscr2->chg2 - i2;
                        if (ffo < 0) {
                                chg0 -= ffo;
                                chg1 -= ffo;
                        } else
                                chg2 += ffo;
                        if (xdl_append_merge(&c, 0,
                                             i0, chg0, i1, chg1, i2, chg2)) {
                                xdl_cleanup_merge(changes);
                                return -1;
                        }
                }

                i1 = xscr1->i1 + xscr1->chg1;
                i2 = xscr2->i1 + xscr2->chg1;

                if (i1 >= i2)
                        xscr2 = xscr2->next;
                if (i2 >= i1)
                        xscr1 = xscr1->next;
        }
        while (xscr1) {
                if (!changes)
                        changes = c;
                i0 = xscr1->i1;
                i1 = xscr1->i2;
                i2 = xscr1->i1 + xe2->xdf2.nrec - xe2->xdf1.nrec;
                chg0 = xscr1->chg1;
                chg1 = xscr1->chg2;
                chg2 = xscr1->chg1;
                if (xdl_append_merge(&c, 1,
                                     i0, chg0, i1, chg1, i2, chg2)) {
                        xdl_cleanup_merge(changes);
                        return -1;
                }
                xscr1 = xscr1->next;
        }
        while (xscr2) {
                if (!changes)
                        changes = c;
                i0 = xscr2->i1;
                i1 = xscr2->i1 + xe1->xdf2.nrec - xe1->xdf1.nrec;
                i2 = xscr2->i2;
                chg0 = xscr2->chg1;
                chg1 = xscr2->chg1;
                chg2 = xscr2->chg2;
                if (xdl_append_merge(&c, 2,
                                     i0, chg0, i1, chg1, i2, chg2)) {
                        xdl_cleanup_merge(changes);
                        return -1;
                }
                xscr2 = xscr2->next;
        }
        if (!changes)
                changes = c;
        /* refine conflicts */
        if (XDL_MERGE_ZEALOUS <= level &&
            (xdl_refine_conflicts(xe1, xe2, changes, xpp) < 0 ||
             xdl_simplify_non_conflicts(xe1, changes,
                                        XDL_MERGE_ZEALOUS < level) < 0)) {
                xdl_cleanup_merge(changes);
                return -1;
        }
        /* output */
        if (result) {
                int marker_size = xmp->marker_size;
                int size = xdl_fill_merge_buffer(xe1, name1, xe2, name2,
                                                 ancestor_name,
                                                 favor, changes, NULL, style,
                                                 marker_size);
                result->ptr = xdl_malloc(size);
                if (!result->ptr) {
                        xdl_cleanup_merge(changes);
                        return -1;
                }
                result->size = size;
                xdl_fill_merge_buffer(xe1, name1, xe2, name2,
                                      ancestor_name, favor, changes,
                                      result->ptr, style, marker_size);
        }
        return xdl_cleanup_merge(changes);
}

int xdl_merge(mmfile_t *orig, mmfile_t *mf1, mmfile_t *mf2,
                xmparam_t const *xmp, mmbuffer_t *result)
{
        xdchange_t *xscr1, *xscr2;
        xdfenv_t xe1, xe2;
        int status;
        xpparam_t const *xpp = &xmp->xpp;

        result->ptr = NULL;
        result->size = 0;

        if (xdl_do_diff(orig, mf1, xpp, &xe1) < 0 ||
                        xdl_do_diff(orig, mf2, xpp, &xe2) < 0) {
                return -1;
        }
        if (xdl_change_compact(&xe1.xdf1, &xe1.xdf2, xpp->flags) < 0 ||
            xdl_change_compact(&xe1.xdf2, &xe1.xdf1, xpp->flags) < 0 ||
            xdl_build_script(&xe1, &xscr1) < 0) {
                xdl_free_env(&xe1);
                return -1;
        }
        if (xdl_change_compact(&xe2.xdf1, &xe2.xdf2, xpp->flags) < 0 ||
            xdl_change_compact(&xe2.xdf2, &xe2.xdf1, xpp->flags) < 0 ||
            xdl_build_script(&xe2, &xscr2) < 0) {
                xdl_free_env(&xe2);
                return -1;
        }
        status = 0;
        if (!xscr1) {
                result->ptr = xdl_malloc(mf2->size);
                memcpy(result->ptr, mf2->ptr, mf2->size);
                result->size = mf2->size;
        } else if (!xscr2) {
                result->ptr = xdl_malloc(mf1->size);
                memcpy(result->ptr, mf1->ptr, mf1->size);
                result->size = mf1->size;
        } else {
                status = xdl_do_merge(&xe1, xscr1,
                                      &xe2, xscr2,
                                      xmp, result);
        }
        xdl_free_script(xscr1);
        xdl_free_script(xscr2);

        xdl_free_env(&xe1);
        xdl_free_env(&xe2);

        return status;
}