#include "cache.h"
#include "commit.h"
#include "diff.h"
#include "diffcore.h"
#include "quote.h"

static int uninteresting(struct diff_filepair *p)
{
        if (diff_unmodified_pair(p))
                return 1;
        if (!S_ISREG(p->one->mode) || !S_ISREG(p->two->mode))
                return 1;
        return 0;
}

static struct combine_diff_path *intersect_paths(struct combine_diff_path *curr, int n, int num_parent)
{
        struct diff_queue_struct *q = &diff_queued_diff;
        struct combine_diff_path *p;
        int i;

        if (!n) {
                struct combine_diff_path *list = NULL, **tail = &list;
                for (i = 0; i < q->nr; i++) {
                        int len;
                        const char *path;
                        if (uninteresting(q->queue[i]))
                                continue;
                        path = q->queue[i]->two->path;
                        len = strlen(path);
                        p = xmalloc(combine_diff_path_size(num_parent, len));
                        p->path = (char*) &(p->parent[num_parent]);
                        memcpy(p->path, path, len);
                        p->path[len] = 0;
                        p->len = len;
                        p->next = NULL;
                        memset(p->parent, 0,
                               sizeof(p->parent[0]) * num_parent);

                        memcpy(p->sha1, q->queue[i]->two->sha1, 20);
                        p->mode = q->queue[i]->two->mode;
                        memcpy(p->parent[n].sha1, q->queue[i]->one->sha1, 20);
                        p->parent[n].mode = q->queue[i]->one->mode;
                        *tail = p;
                        tail = &p->next;
                }
                return list;
        }

        for (p = curr; p; p = p->next) {
                int found = 0;
                if (!p->len)
                        continue;
                for (i = 0; i < q->nr; i++) {
                        const char *path;
                        int len;

                        if (uninteresting(q->queue[i]))
                                continue;
                        path = q->queue[i]->two->path;
                        len = strlen(path);
                        if (len == p->len && !memcmp(path, p->path, len)) {
                                found = 1;
                                memcpy(p->parent[n].sha1,
                                       q->queue[i]->one->sha1, 20);
                                p->parent[n].mode = q->queue[i]->one->mode;
                                break;
                        }
                }
                if (!found)
                        p->len = 0;
        }
        return curr;
}

/* Lines lost from parent */
struct lline {
        struct lline *next;
        int len;
        unsigned long parent_map;
        char line[FLEX_ARRAY];
};

/* Lines surviving in the merge result */
struct sline {
        struct lline *lost_head, **lost_tail;
        char *bol;
        int len;
        /* bit 0 up to (N-1) are on if the parent has this line (i.e.
         * we did not change it).
         * bit N is used for "interesting" lines, including context.
         */
        unsigned long flag;
        unsigned long *p_lno;
};

static char *grab_blob(const unsigned char *sha1, unsigned long *size)
{
        char *blob;
        char type[20];
        if (!memcmp(sha1, null_sha1, 20)) {
                /* deleted blob */
                *size = 0;
                return xcalloc(1, 1);
        }
        blob = read_sha1_file(sha1, type, size);
        if (strcmp(type, "blob"))
                die("object '%s' is not a blob!", sha1_to_hex(sha1));
        return blob;
}

#define TMPPATHLEN 50
#define MAXLINELEN 10240

static void write_to_temp_file(char *tmpfile, void *blob, unsigned long size)
{
        int fd = git_mkstemp(tmpfile, TMPPATHLEN, ".diff_XXXXXX");
        if (fd < 0)
                die("unable to create temp-file");
        if (write(fd, blob, size) != size)
                die("unable to write temp-file");
        close(fd);
}

static void write_temp_blob(char *tmpfile, const unsigned char *sha1)
{
        unsigned long size;
        void *blob;
        blob = grab_blob(sha1, &size);
        write_to_temp_file(tmpfile, blob, size);
        free(blob);
}

static int parse_num(char **cp_p, unsigned int *num_p)
{
        char *cp = *cp_p;
        unsigned int num = 0;
        int read_some;

        while ('0' <= *cp && *cp <= '9')
                num = num * 10 + *cp++ - '0';
        if (!(read_some = cp - *cp_p))
                return -1;
        *cp_p = cp;
        *num_p = num;
        return 0;
}

static int parse_hunk_header(char *line, int len,
                             unsigned int *ob, unsigned int *on,
                             unsigned int *nb, unsigned int *nn)
{
        char *cp;
        cp = line + 4;
        if (parse_num(&cp, ob)) {
        bad_line:
                return error("malformed diff output: %s", line);
        }
        if (*cp == ',') {
                cp++;
                if (parse_num(&cp, on))
                        goto bad_line;
        }
        else
                *on = 1;
        if (*cp++ != ' ' || *cp++ != '+')
                goto bad_line;
        if (parse_num(&cp, nb))
                goto bad_line;
        if (*cp == ',') {
                cp++;
                if (parse_num(&cp, nn))
                        goto bad_line;
        }
        else
                *nn = 1;
        return -!!memcmp(cp, " @@", 3);
}

static void append_lost(struct sline *sline, int n, const char *line)
{
        struct lline *lline;
        int len = strlen(line);
        unsigned long this_mask = (1UL<<n);
        if (line[len-1] == '\n')
                len--;

        /* Check to see if we can squash things */
        if (sline->lost_head) {
                struct lline *last_one = NULL;
                /* We cannot squash it with earlier one */
                for (lline = sline->lost_head;
                     lline;
                     lline = lline->next)
                        if (lline->parent_map & this_mask)
                                last_one = lline;
                lline = last_one ? last_one->next : sline->lost_head;
                while (lline) {
                        if (lline->len == len &&
                            !memcmp(lline->line, line, len)) {
                                lline->parent_map |= this_mask;
                                return;
                        }
                        lline = lline->next;
                }
        }

        lline = xmalloc(sizeof(*lline) + len + 1);
        lline->len = len;
        lline->next = NULL;
        lline->parent_map = this_mask;
        memcpy(lline->line, line, len);
        lline->line[len] = 0;
        *sline->lost_tail = lline;
        sline->lost_tail = &lline->next;
}

static void combine_diff(const unsigned char *parent, const char *ourtmp,
                         struct sline *sline, int cnt, int n, int num_parent)
{
        FILE *in;
        char parent_tmp[TMPPATHLEN];
        char cmd[TMPPATHLEN * 2 + 1024];
        char line[MAXLINELEN];
        unsigned int lno, ob, on, nb, nn, p_lno;
        unsigned long nmask = (1UL << n);
        struct sline *lost_bucket = NULL;

        write_temp_blob(parent_tmp, parent);
        sprintf(cmd, "diff --unified=0 -La/x -Lb/x '%s' '%s'",
                parent_tmp, ourtmp);
        in = popen(cmd, "r");
        if (!in)
                die("cannot spawn %s", cmd);

        lno = 1;
        while (fgets(line, sizeof(line), in) != NULL) {
                int len = strlen(line);
                if (5 < len && !memcmp("@@ -", line, 4)) {
                        if (parse_hunk_header(line, len,
                                              &ob, &on, &nb, &nn))
                                break;
                        lno = nb;
                        if (!nb)
                                /* @@ -1,2 +0,0 @@ to remove the
                                 * first two lines...
                                 */
                                nb = 1;
                        if (nn == 0)
                                /* @@ -X,Y +N,0 @@ removed Y lines
                                 * that would have come *after* line N
                                 * in the result.  Our lost buckets hang
                                 * to the line after the removed lines,
                                 */
                                lost_bucket = &sline[nb];
                        else
                                lost_bucket = &sline[nb-1];
                        if (!sline[nb-1].p_lno)
                                sline[nb-1].p_lno =
                                        xcalloc(num_parent,
                                                sizeof(unsigned long));
                        sline[nb-1].p_lno[n] = ob;
                        continue;
                }
                if (!lost_bucket)
                        continue; /* not in any hunk yet */
                switch (line[0]) {
                case '-':
                        append_lost(lost_bucket, n, line+1);
                        break;
                case '+':
                        sline[lno-1].flag |= nmask;
                        lno++;
                        break;
                }
        }
        fclose(in);
        unlink(parent_tmp);

        /* Assign line numbers for this parent.
         *
         * sline[lno].p_lno[n] records the first line number
         * (counting from 1) for parent N if the final hunk display
         * started by showing sline[lno] (possibly showing the lost
         * lines attached to it first).
         */
        for (lno = 0,  p_lno = 1; lno < cnt; lno++) {
                struct lline *ll;
                sline[lno].p_lno[n] = p_lno;

                /* How many lines would this sline advance the p_lno? */
                ll = sline[lno].lost_head;
                while (ll) {
                        if (ll->parent_map & nmask)
                                p_lno++; /* '-' means parent had it */
                        ll = ll->next;
                }
                if (!(sline[lno].flag & nmask))
                        p_lno++; /* no '+' means parent had it */
        }
        sline[lno].p_lno[n] = p_lno; /* trailer */
}

static unsigned long context = 3;
static char combine_marker = '@';

static int interesting(struct sline *sline, unsigned long all_mask)
{
        /* If some parents lost lines here, or if we have added to
         * some parent, it is interesting.
         */
        return ((sline->flag & all_mask) || sline->lost_head);
}

static unsigned long adjust_hunk_tail(struct sline *sline,
                                      unsigned long all_mask,
                                      unsigned long hunk_begin,
                                      unsigned long i)
{
        /* i points at the first uninteresting line.  If the last line
         * of the hunk was interesting only because it has some
         * deletion, then it is not all that interesting for the
         * purpose of giving trailing context lines.  This is because
         * we output '-' line and then unmodified sline[i-1] itself in
         * that case which gives us one extra context line.
         */
        if ((hunk_begin + 1 <= i) && !(sline[i-1].flag & all_mask))
                i--;
        return i;
}

static unsigned long find_next(struct sline *sline,
                               unsigned long mark,
                               unsigned long i,
                               unsigned long cnt,
                               int uninteresting)
{
        /* We have examined up to i-1 and are about to look at i.
         * Find next interesting or uninteresting line.  Here,
         * "interesting" does not mean interesting(), but marked by
         * the give_context() function below (i.e. it includes context
         * lines that are not interesting to interesting() function
         * that are surrounded by interesting() ones.
         */
        while (i < cnt)
                if (uninteresting
                    ? !(sline[i].flag & mark)
                    : (sline[i].flag & mark))
                        return i;
                else
                        i++;
        return cnt;
}

static int give_context(struct sline *sline, unsigned long cnt, int num_parent)
{
        unsigned long all_mask = (1UL<<num_parent) - 1;
        unsigned long mark = (1UL<<num_parent);
        unsigned long i;

        /* Two groups of interesting lines may have a short gap of
         * unintersting lines.  Connect such groups to give them a
         * bit of context.
         *
         * We first start from what the interesting() function says,
         * and mark them with "mark", and paint context lines with the
         * mark.  So interesting() would still say false for such context
         * lines but they are treated as "interesting" in the end.
         */
        i = find_next(sline, mark, 0, cnt, 0);
        if (cnt <= i)
                return 0;

        while (i < cnt) {
                unsigned long j = (context < i) ? (i - context) : 0;
                unsigned long k;

                /* Paint a few lines before the first interesting line. */
                while (j < i)
                        sline[j++].flag |= mark;

        again:
                /* we know up to i is to be included.  where does the
                 * next uninteresting one start?
                 */
                j = find_next(sline, mark, i, cnt, 1);
                if (cnt <= j)
                        break; /* the rest are all interesting */

                /* lookahead context lines */
                k = find_next(sline, mark, j, cnt, 0);
                j = adjust_hunk_tail(sline, all_mask, i, j);

                if (k < j + context) {
                        /* k is interesting and [j,k) are not, but
                         * paint them interesting because the gap is small.
                         */
                        while (j < k)
                                sline[j++].flag |= mark;
                        i = k;
                        goto again;
                }

                /* j is the first uninteresting line and there is
                 * no overlap beyond it within context lines.  Paint
                 * the trailing edge a bit.
                 */
                i = k;
                k = (j + context < cnt) ? j + context : cnt;
                while (j < k)
                        sline[j++].flag |= mark;
        }
        return 1;
}

static int make_hunks(struct sline *sline, unsigned long cnt,
                       int num_parent, int dense)
{
        unsigned long all_mask = (1UL<<num_parent) - 1;
        unsigned long mark = (1UL<<num_parent);
        unsigned long i;
        int has_interesting = 0;

        for (i = 0; i < cnt; i++) {
                if (interesting(&sline[i], all_mask))
                        sline[i].flag |= mark;
                else
                        sline[i].flag &= ~mark;
        }
        if (!dense)
                return give_context(sline, cnt, num_parent);

        /* Look at each hunk, and if we have changes from only one
         * parent, or the changes are the same from all but one
         * parent, mark that uninteresting.
         */
        i = 0;
        while (i < cnt) {
                unsigned long j, hunk_begin, hunk_end;
                unsigned long same_diff;
                while (i < cnt && !(sline[i].flag & mark))
                        i++;
                if (cnt <= i)
                        break; /* No more interesting hunks */
                hunk_begin = i;
                for (j = i + 1; j < cnt; j++) {
                        if (!(sline[j].flag & mark)) {
                                /* Look beyond the end to see if there
                                 * is an interesting line after this
                                 * hunk within context span.
                                 */
                                unsigned long la; /* lookahead */
                                int contin = 0;
                                la = adjust_hunk_tail(sline, all_mask,
                                                     hunk_begin, j);
                                la = (la + context < cnt) ?
                                        (la + context) : cnt;
                                while (j <= --la) {
                                        if (sline[la].flag & mark) {
                                                contin = 1;
                                                break;
                                        }
                                }
                                if (!contin)
                                        break;
                                j = la;
                        }
                }
                hunk_end = j;

                /* [i..hunk_end) are interesting.  Now is it really
                 * interesting?  We check if there are only two versions
                 * and the result matches one of them.  That is, we look
                 * at:
                 *   (+) line, which records lines added to which parents;
                 *       this line appears in the result.
                 *   (-) line, which records from what parents the line
                 *       was removed; this line does not appear in the result.
                 * then check the set of parents the result has difference
                 * from, from all lines.  If there are lines that has
                 * different set of parents that the result has differences
                 * from, that means we have more than two versions.
                 *
                 * Even when we have only two versions, if the result does
                 * not match any of the parents, the it should be considered
                 * interesting.  In such a case, we would have all '+' line.
                 * After passing the above "two versions" test, that would
                 * appear as "the same set of parents" to be "all parents".
                 */
                same_diff = 0;
                has_interesting = 0;
                for (j = i; j < hunk_end && !has_interesting; j++) {
                        unsigned long this_diff = sline[j].flag & all_mask;
                        struct lline *ll = sline[j].lost_head;
                        if (this_diff) {
                                /* This has some changes.  Is it the
                                 * same as others?
                                 */
                                if (!same_diff)
                                        same_diff = this_diff;
                                else if (same_diff != this_diff) {
                                        has_interesting = 1;
                                        break;
                                }
                        }
                        while (ll && !has_interesting) {
                                /* Lost this line from these parents;
                                 * who are they?  Are they the same?
                                 */
                                this_diff = ll->parent_map;
                                if (!same_diff)
                                        same_diff = this_diff;
                                else if (same_diff != this_diff) {
                                        has_interesting = 1;
                                }
                                ll = ll->next;
                        }
                }

                if (!has_interesting && same_diff != all_mask) {
                        /* This hunk is not that interesting after all */
                        for (j = hunk_begin; j < hunk_end; j++)
                                sline[j].flag &= ~mark;
                }
                i = hunk_end;
        }

        has_interesting = give_context(sline, cnt, num_parent);
        return has_interesting;
}

static void show_parent_lno(struct sline *sline, unsigned long l0, unsigned long l1, unsigned long cnt, int n)
{
        l0 = sline[l0].p_lno[n];
        l1 = sline[l1].p_lno[n];
        printf(" -%lu,%lu", l0, l1-l0);
}

static void dump_sline(struct sline *sline, unsigned long cnt, int num_parent)
{
        unsigned long mark = (1UL<<num_parent);
        int i;
        unsigned long lno = 0;

        while (1) {
                struct sline *sl = &sline[lno];
                int hunk_end;
                while (lno < cnt && !(sline[lno].flag & mark))
                        lno++;
                if (cnt <= lno)
                        break;
                for (hunk_end = lno + 1; hunk_end < cnt; hunk_end++)
                        if (!(sline[hunk_end].flag & mark))
                                break;
                for (i = 0; i <= num_parent; i++) putchar(combine_marker);
                for (i = 0; i < num_parent; i++)
                        show_parent_lno(sline, lno, hunk_end, cnt, i);
                printf(" +%lu,%lu ", lno+1, hunk_end-lno);
                for (i = 0; i <= num_parent; i++) putchar(combine_marker);
                putchar('\n');
                while (lno < hunk_end) {
                        struct lline *ll;
                        int j;
                        unsigned long p_mask;
                        sl = &sline[lno++];
                        ll = sl->lost_head;
                        while (ll) {
                                for (j = 0; j < num_parent; j++) {
                                        if (ll->parent_map & (1UL<<j))
                                                putchar('-');
                                        else
                                                putchar(' ');
                                }
                                puts(ll->line);
                                ll = ll->next;
                        }
                        p_mask = 1;
                        for (j = 0; j < num_parent; j++) {
                                if (p_mask & sl->flag)
                                        putchar('+');
                                else
                                        putchar(' ');
                                p_mask <<= 1;
                        }
                        printf("%.*s\n", sl->len, sl->bol);
                }
        }
}

static void reuse_combine_diff(struct sline *sline, unsigned long cnt,
                               int i, int j)
{
        /* We have already examined parent j and we know parent i
         * and parent j are the same, so reuse the combined result
         * of parent j for parent i.
         */
        unsigned long lno, imask, jmask;
        imask = (1UL<<i);
        jmask = (1UL<<j);

        for (lno = 0; lno < cnt; lno++) {
                struct lline *ll = sline->lost_head;
                sline->p_lno[i] = sline->p_lno[j];
                while (ll) {
                        if (ll->parent_map & jmask)
                                ll->parent_map |= imask;
                        ll = ll->next;
                }
                if (sline->flag & jmask)
                        sline->flag |= imask;
                sline++;
        }
}

int show_combined_diff(struct combine_diff_path *elem, int num_parent,
                       int dense, const char *header)
{
        unsigned long size, cnt, lno;
        char *result, *cp, *ep;
        struct sline *sline; /* survived lines */
        int mode_differs = 0;
        int i, show_hunks, shown_header = 0;
        char ourtmp_buf[TMPPATHLEN];
        char *ourtmp = ourtmp_buf;

        /* Read the result of merge first */
        if (memcmp(elem->sha1, null_sha1, 20)) {
                result = grab_blob(elem->sha1, &size);
                write_to_temp_file(ourtmp, result, size);
        }
        else {
                /* Used by diff-tree to read from the working tree */
                struct stat st;
                int fd;
                ourtmp = elem->path;
                if (0 <= (fd = open(ourtmp, O_RDONLY)) &&
                    !fstat(fd, &st)) {
                        int len = st.st_size;
                        int cnt = 0;

                        size = len;
                        result = xmalloc(len + 1);
                        while (cnt < len) {
                                int done = xread(fd, result+cnt, len-cnt);
                                if (done == 0)
                                        break;
                                if (done < 0)
                                        die("read error '%s'", ourtmp);
                                cnt += done;
                        }
                        result[len] = 0;
                }
                else {
                        /* deleted file */
                        size = 0;
                        result = xmalloc(1);
                        result[0] = 0;
                        ourtmp = "/dev/null";
                }
                if (0 <= fd)
                        close(fd);
        }

        for (cnt = 0, cp = result; cp - result < size; cp++) {
                if (*cp == '\n')
                        cnt++;
        }
        if (result[size-1] != '\n')
                cnt++; /* incomplete line */

        sline = xcalloc(cnt+1, sizeof(*sline));
        ep = result;
        sline[0].bol = result;
        for (lno = 0, cp = result; cp - result < size; cp++) {
                if (*cp == '\n') {
                        sline[lno].lost_tail = &sline[lno].lost_head;
                        sline[lno].len = cp - sline[lno].bol;
                        sline[lno].flag = 0;
                        lno++;
                        if (lno < cnt)
                                sline[lno].bol = cp + 1;
                }
        }
        if (result[size-1] != '\n') {
                sline[cnt-1].lost_tail = &sline[cnt-1].lost_head;
                sline[cnt-1].len = size - (sline[cnt-1].bol - result);
                sline[cnt-1].flag = 0;
        }

        sline[0].p_lno = xcalloc((cnt+1) * num_parent, sizeof(unsigned long));
        for (lno = 0; lno < cnt; lno++)
                sline[lno+1].p_lno = sline[lno].p_lno + num_parent;

        for (i = 0; i < num_parent; i++) {
                int j;
                for (j = 0; j < i; j++) {
                        if (!memcmp(elem->parent[i].sha1,
                                    elem->parent[j].sha1, 20)) {
                                reuse_combine_diff(sline, cnt, i, j);
                                break;
                        }
                }
                if (i <= j)
                        combine_diff(elem->parent[i].sha1, ourtmp, sline,
                                     cnt, i, num_parent);
                if (elem->parent[i].mode != elem->mode)
                        mode_differs = 1;
        }

        show_hunks = make_hunks(sline, cnt, num_parent, dense);

        if (show_hunks || mode_differs) {
                const char *abb;
                char null_abb[DEFAULT_ABBREV + 1];

                memset(null_abb, '0', DEFAULT_ABBREV);
                null_abb[DEFAULT_ABBREV] = 0;
                if (header) {
                        shown_header++;
                        puts(header);
                }
                printf("diff --%s ", dense ? "cc" : "combined");
                if (quote_c_style(elem->path, NULL, NULL, 0))
                        quote_c_style(elem->path, NULL, stdout, 0);
                else
                        printf("%s", elem->path);
                putchar('\n');
                printf("index ");
                for (i = 0; i < num_parent; i++) {
                        if (elem->parent[i].mode != elem->mode)
                                mode_differs = 1;
                        if (memcmp(elem->parent[i].sha1, null_sha1, 20))
                                abb = find_unique_abbrev(elem->parent[i].sha1,
                                                         DEFAULT_ABBREV);
                        else
                                abb = null_abb;
                        printf("%s%s", i ? "," : "", abb);
                }
                if (memcmp(elem->sha1, null_sha1, 20))
                        abb = find_unique_abbrev(elem->sha1, DEFAULT_ABBREV);
                else
                        abb = null_abb;
                printf("..%s\n", abb);

                if (mode_differs) {
                        printf("mode ");
                        for (i = 0; i < num_parent; i++) {
                                printf("%s%06o", i ? "," : "",
                                       elem->parent[i].mode);
                        }
                        printf("..%06o\n", elem->mode);
                }
                /* if (show_hunks) perhaps */
                dump_sline(sline, cnt, num_parent);
        }
        if (ourtmp == ourtmp_buf)
                unlink(ourtmp);
        free(result);

        for (i = 0; i < cnt; i++) {
                if (sline[i].lost_head) {
                        struct lline *ll = sline[i].lost_head;
                        while (ll) {
                                struct lline *tmp = ll;
                                ll = ll->next;
                                free(tmp);
                        }
                }
        }
        free(sline[0].p_lno);
        free(sline);
        return shown_header;
}

int diff_tree_combined_merge(const unsigned char *sha1,
                             const char *header, int dense)
{
        struct commit *commit = lookup_commit(sha1);
        struct diff_options diffopts;
        struct commit_list *parents;
        struct combine_diff_path *p, *paths = NULL;
        int num_parent, i, num_paths;

        diff_setup(&diffopts);
        diffopts.output_format = DIFF_FORMAT_NO_OUTPUT;
        diffopts.recursive = 1;

        /* count parents */
        for (parents = commit->parents, num_parent = 0;
             parents;
             parents = parents->next, num_parent++)
                ; /* nothing */

        /* find set of paths that everybody touches */
        for (parents = commit->parents, i = 0;
             parents;
             parents = parents->next, i++) {
                struct commit *parent = parents->item;
                diff_tree_sha1(parent->object.sha1, commit->object.sha1, "",
                               &diffopts);
                paths = intersect_paths(paths, i, num_parent);
                diff_flush(&diffopts);
        }

        /* find out surviving paths */
        for (num_paths = 0, p = paths; p; p = p->next) {
                if (p->len)
                        num_paths++;
        }
        if (num_paths) {
                for (p = paths; p; p = p->next) {
                        if (!p->len)
                                continue;
                        if (show_combined_diff(p, num_parent, dense, header))
                                header = NULL;
                }
        }

        /* Clean things up */
        while (paths) {
                struct combine_diff_path *tmp = paths;
                paths = paths->next;
                free(tmp);
        }
        return 0;
}