#include "cache.h"
#include "commit.h"
#include "refs.h"
#include "diff.h"
#include "diffcore.h"
#include "xdiff-interface.h"
#include "ll-merge.h"
#include "dir.h"
#include "notes.h"
#include "notes-merge.h"

struct notes_merge_pair {
        unsigned char obj[20], base[20], local[20], remote[20];
};

void init_notes_merge_options(struct notes_merge_options *o)
{
        memset(o, 0, sizeof(struct notes_merge_options));
        o->verbosity = NOTES_MERGE_VERBOSITY_DEFAULT;
}

#define OUTPUT(o, v, ...) \
        do { \
                if ((o)->verbosity >= (v)) { \
                        printf(__VA_ARGS__); \
                        puts(""); \
                } \
        } while (0)

static int path_to_sha1(const char *path, unsigned char *sha1)
{
        char hex_sha1[40];
        int i = 0;
        while (*path && i < 40) {
                if (*path != '/')
                        hex_sha1[i++] = *path;
                path++;
        }
        if (*path || i != 40)
                return -1;
        return get_sha1_hex(hex_sha1, sha1);
}

static int verify_notes_filepair(struct diff_filepair *p, unsigned char *sha1)
{
        switch (p->status) {
        case DIFF_STATUS_MODIFIED:
                assert(p->one->mode == p->two->mode);
                assert(!is_null_sha1(p->one->sha1));
                assert(!is_null_sha1(p->two->sha1));
                break;
        case DIFF_STATUS_ADDED:
                assert(is_null_sha1(p->one->sha1));
                break;
        case DIFF_STATUS_DELETED:
                assert(is_null_sha1(p->two->sha1));
                break;
        default:
                return -1;
        }
        assert(!strcmp(p->one->path, p->two->path));
        return path_to_sha1(p->one->path, sha1);
}

static struct notes_merge_pair *find_notes_merge_pair_pos(
                struct notes_merge_pair *list, int len, unsigned char *obj,
                int insert_new, int *occupied)
{
        /*
         * Both diff_tree_remote() and diff_tree_local() tend to process
         * merge_pairs in ascending order. Therefore, cache last returned
         * index, and search sequentially from there until the appropriate
         * position is found.
         *
         * Since inserts only happen from diff_tree_remote() (which mainly
         * _appends_), we don't care that inserting into the middle of the
         * list is expensive (using memmove()).
         */
        static int last_index;
        int i = last_index < len ? last_index : len - 1;
        int prev_cmp = 0, cmp = -1;
        while (i >= 0 && i < len) {
                cmp = hashcmp(obj, list[i].obj);
                if (!cmp) /* obj belongs @ i */
                        break;
                else if (cmp < 0 && prev_cmp <= 0) /* obj belongs < i */
                        i--;
                else if (cmp < 0) /* obj belongs between i-1 and i */
                        break;
                else if (cmp > 0 && prev_cmp >= 0) /* obj belongs > i */
                        i++;
                else /* if (cmp > 0) */ { /* obj belongs between i and i+1 */
                        i++;
                        break;
                }
                prev_cmp = cmp;
        }
        if (i < 0)
                i = 0;
        /* obj belongs at, or immediately preceding, index i (0 <= i <= len) */

        if (!cmp)
                *occupied = 1;
        else {
                *occupied = 0;
                if (insert_new && i < len) {
                        memmove(list + i + 1, list + i,
                                (len - i) * sizeof(struct notes_merge_pair));
                        memset(list + i, 0, sizeof(struct notes_merge_pair));
                }
        }
        last_index = i;
        return list + i;
}

static unsigned char uninitialized[20] =
        "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" \
        "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff";

static struct notes_merge_pair *diff_tree_remote(struct notes_merge_options *o,
                                                 const unsigned char *base,
                                                 const unsigned char *remote,
                                                 int *num_changes)
{
        struct diff_options opt;
        struct notes_merge_pair *changes;
        int i, len = 0;

        trace_printf("\tdiff_tree_remote(base = %.7s, remote = %.7s)\n",
               sha1_to_hex(base), sha1_to_hex(remote));

        diff_setup(&opt);
        DIFF_OPT_SET(&opt, RECURSIVE);
        opt.output_format = DIFF_FORMAT_NO_OUTPUT;
        if (diff_setup_done(&opt) < 0)
                die("diff_setup_done failed");
        diff_tree_sha1(base, remote, "", &opt);
        diffcore_std(&opt);

        changes = xcalloc(diff_queued_diff.nr, sizeof(struct notes_merge_pair));

        for (i = 0; i < diff_queued_diff.nr; i++) {
                struct diff_filepair *p = diff_queued_diff.queue[i];
                struct notes_merge_pair *mp;
                int occupied;
                unsigned char obj[20];

                if (verify_notes_filepair(p, obj)) {
                        trace_printf("\t\tCannot merge entry '%s' (%c): "
                               "%.7s -> %.7s. Skipping!\n", p->one->path,
                               p->status, sha1_to_hex(p->one->sha1),
                               sha1_to_hex(p->two->sha1));
                        continue;
                }
                mp = find_notes_merge_pair_pos(changes, len, obj, 1, &occupied);
                if (occupied) {
                        /* We've found an addition/deletion pair */
                        assert(!hashcmp(mp->obj, obj));
                        if (is_null_sha1(p->one->sha1)) { /* addition */
                                assert(is_null_sha1(mp->remote));
                                hashcpy(mp->remote, p->two->sha1);
                        } else if (is_null_sha1(p->two->sha1)) { /* deletion */
                                assert(is_null_sha1(mp->base));
                                hashcpy(mp->base, p->one->sha1);
                        } else
                                assert(!"Invalid existing change recorded");
                } else {
                        hashcpy(mp->obj, obj);
                        hashcpy(mp->base, p->one->sha1);
                        hashcpy(mp->local, uninitialized);
                        hashcpy(mp->remote, p->two->sha1);
                        len++;
                }
                trace_printf("\t\tStored remote change for %s: %.7s -> %.7s\n",
                       sha1_to_hex(mp->obj), sha1_to_hex(mp->base),
                       sha1_to_hex(mp->remote));
        }
        diff_flush(&opt);
        diff_tree_release_paths(&opt);

        *num_changes = len;
        return changes;
}

static void diff_tree_local(struct notes_merge_options *o,
                            struct notes_merge_pair *changes, int len,
                            const unsigned char *base,
                            const unsigned char *local)
{
        struct diff_options opt;
        int i;

        trace_printf("\tdiff_tree_local(len = %i, base = %.7s, local = %.7s)\n",
               len, sha1_to_hex(base), sha1_to_hex(local));

        diff_setup(&opt);
        DIFF_OPT_SET(&opt, RECURSIVE);
        opt.output_format = DIFF_FORMAT_NO_OUTPUT;
        if (diff_setup_done(&opt) < 0)
                die("diff_setup_done failed");
        diff_tree_sha1(base, local, "", &opt);
        diffcore_std(&opt);

        for (i = 0; i < diff_queued_diff.nr; i++) {
                struct diff_filepair *p = diff_queued_diff.queue[i];
                struct notes_merge_pair *mp;
                int match;
                unsigned char obj[20];

                if (verify_notes_filepair(p, obj)) {
                        trace_printf("\t\tCannot merge entry '%s' (%c): "
                               "%.7s -> %.7s. Skipping!\n", p->one->path,
                               p->status, sha1_to_hex(p->one->sha1),
                               sha1_to_hex(p->two->sha1));
                        continue;
                }
                mp = find_notes_merge_pair_pos(changes, len, obj, 0, &match);
                if (!match) {
                        trace_printf("\t\tIgnoring local-only change for %s: "
                               "%.7s -> %.7s\n", sha1_to_hex(obj),
                               sha1_to_hex(p->one->sha1),
                               sha1_to_hex(p->two->sha1));
                        continue;
                }

                assert(!hashcmp(mp->obj, obj));
                if (is_null_sha1(p->two->sha1)) { /* deletion */
                        /*
                         * Either this is a true deletion (1), or it is part
                         * of an A/D pair (2), or D/A pair (3):
                         *
                         * (1) mp->local is uninitialized; set it to null_sha1
                         * (2) mp->local is not uninitialized; don't touch it
                         * (3) mp->local is uninitialized; set it to null_sha1
                         *     (will be overwritten by following addition)
                         */
                        if (!hashcmp(mp->local, uninitialized))
                                hashclr(mp->local);
                } else if (is_null_sha1(p->one->sha1)) { /* addition */
                        /*
                         * Either this is a true addition (1), or it is part
                         * of an A/D pair (2), or D/A pair (3):
                         *
                         * (1) mp->local is uninitialized; set to p->two->sha1
                         * (2) mp->local is uninitialized; set to p->two->sha1
                         * (3) mp->local is null_sha1;     set to p->two->sha1
                         */
                        assert(is_null_sha1(mp->local) ||
                               !hashcmp(mp->local, uninitialized));
                        hashcpy(mp->local, p->two->sha1);
                } else { /* modification */
                        /*
                         * This is a true modification. p->one->sha1 shall
                         * match mp->base, and mp->local shall be uninitialized.
                         * Set mp->local to p->two->sha1.
                         */
                        assert(!hashcmp(p->one->sha1, mp->base));
                        assert(!hashcmp(mp->local, uninitialized));
                        hashcpy(mp->local, p->two->sha1);
                }
                trace_printf("\t\tStored local change for %s: %.7s -> %.7s\n",
                       sha1_to_hex(mp->obj), sha1_to_hex(mp->base),
                       sha1_to_hex(mp->local));
        }
        diff_flush(&opt);
        diff_tree_release_paths(&opt);
}

static void check_notes_merge_worktree(struct notes_merge_options *o)
{
        if (!o->has_worktree) {
                /*
                 * Must establish NOTES_MERGE_WORKTREE.
                 * Abort if NOTES_MERGE_WORKTREE already exists
                 */
                if (file_exists(git_path(NOTES_MERGE_WORKTREE))) {
                        if (advice_resolve_conflict)
                                die("You have not concluded your previous "
                                    "notes merge (%s exists).\nPlease, use "
                                    "'git notes merge --commit' or 'git notes "
                                    "merge --reset' to commit/abort the "
                                    "previous merge before you start a new "
                                    "notes merge.", git_path("NOTES_MERGE_*"));
                        else
                                die("You have not concluded your notes merge "
                                    "(%s exists).", git_path("NOTES_MERGE_*"));
                }

                if (safe_create_leading_directories(git_path(
                                NOTES_MERGE_WORKTREE "/.test")))
                        die_errno("unable to create directory %s",
                                  git_path(NOTES_MERGE_WORKTREE));
                o->has_worktree = 1;
        } else if (!file_exists(git_path(NOTES_MERGE_WORKTREE)))
                /* NOTES_MERGE_WORKTREE should already be established */
                die("missing '%s'. This should not happen",
                    git_path(NOTES_MERGE_WORKTREE));
}

static void write_buf_to_worktree(const unsigned char *obj,
                                  const char *buf, unsigned long size)
{
        int fd;
        char *path = git_path(NOTES_MERGE_WORKTREE "/%s", sha1_to_hex(obj));
        if (safe_create_leading_directories(path))
                die_errno("unable to create directory for '%s'", path);
        if (file_exists(path))
                die("found existing file at '%s'", path);

        fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, 0666);
        if (fd < 0)
                die_errno("failed to open '%s'", path);

        while (size > 0) {
                long ret = write_in_full(fd, buf, size);
                if (ret < 0) {
                        /* Ignore epipe */
                        if (errno == EPIPE)
                                break;
                        die_errno("notes-merge");
                } else if (!ret) {
                        die("notes-merge: disk full?");
                }
                size -= ret;
                buf += ret;
        }

        close(fd);
}

static void write_note_to_worktree(const unsigned char *obj,
                                   const unsigned char *note)
{
        enum object_type type;
        unsigned long size;
        void *buf = read_sha1_file(note, &type, &size);

        if (!buf)
                die("cannot read note %s for object %s",
                    sha1_to_hex(note), sha1_to_hex(obj));
        if (type != OBJ_BLOB)
                die("blob expected in note %s for object %s",
                    sha1_to_hex(note), sha1_to_hex(obj));
        write_buf_to_worktree(obj, buf, size);
        free(buf);
}

static int ll_merge_in_worktree(struct notes_merge_options *o,
                                struct notes_merge_pair *p)
{
        mmbuffer_t result_buf;
        mmfile_t base, local, remote;
        int status;

        read_mmblob(&base, p->base);
        read_mmblob(&local, p->local);
        read_mmblob(&remote, p->remote);

        status = ll_merge(&result_buf, sha1_to_hex(p->obj), &base, NULL,
                          &local, o->local_ref, &remote, o->remote_ref, 0);

        free(base.ptr);
        free(local.ptr);
        free(remote.ptr);

        if ((status < 0) || !result_buf.ptr)
                die("Failed to execute internal merge");

        write_buf_to_worktree(p->obj, result_buf.ptr, result_buf.size);
        free(result_buf.ptr);

        return status;
}

static int merge_one_change_manual(struct notes_merge_options *o,
                                   struct notes_merge_pair *p,
                                   struct notes_tree *t)
{
        const char *lref = o->local_ref ? o->local_ref : "local version";
        const char *rref = o->remote_ref ? o->remote_ref : "remote version";

        trace_printf("\t\t\tmerge_one_change_manual(obj = %.7s, base = %.7s, "
               "local = %.7s, remote = %.7s)\n",
               sha1_to_hex(p->obj), sha1_to_hex(p->base),
               sha1_to_hex(p->local), sha1_to_hex(p->remote));

        OUTPUT(o, 2, "Auto-merging notes for %s", sha1_to_hex(p->obj));
        check_notes_merge_worktree(o);
        if (is_null_sha1(p->local)) {
                /* D/F conflict, checkout p->remote */
                assert(!is_null_sha1(p->remote));
                OUTPUT(o, 1, "CONFLICT (delete/modify): Notes for object %s "
                       "deleted in %s and modified in %s. Version from %s "
                       "left in tree.", sha1_to_hex(p->obj), lref, rref, rref);
                write_note_to_worktree(p->obj, p->remote);
        } else if (is_null_sha1(p->remote)) {
                /* D/F conflict, checkout p->local */
                assert(!is_null_sha1(p->local));
                OUTPUT(o, 1, "CONFLICT (delete/modify): Notes for object %s "
                       "deleted in %s and modified in %s. Version from %s "
                       "left in tree.", sha1_to_hex(p->obj), rref, lref, lref);
                write_note_to_worktree(p->obj, p->local);
        } else {
                /* "regular" conflict, checkout result of ll_merge() */
                const char *reason = "content";
                if (is_null_sha1(p->base))
                        reason = "add/add";
                assert(!is_null_sha1(p->local));
                assert(!is_null_sha1(p->remote));
                OUTPUT(o, 1, "CONFLICT (%s): Merge conflict in notes for "
                       "object %s", reason, sha1_to_hex(p->obj));
                ll_merge_in_worktree(o, p);
        }

        trace_printf("\t\t\tremoving from partial merge result\n");
        remove_note(t, p->obj);

        return 1;
}

static int merge_one_change(struct notes_merge_options *o,
                            struct notes_merge_pair *p, struct notes_tree *t)
{
        /*
         * Return 0 if change is successfully resolved (stored in notes_tree).
         * Return 1 is change results in a conflict (NOT stored in notes_tree,
         * but instead written to NOTES_MERGE_WORKTREE with conflict markers).
         */
        switch (o->strategy) {
        case NOTES_MERGE_RESOLVE_MANUAL:
                return merge_one_change_manual(o, p, t);
        case NOTES_MERGE_RESOLVE_OURS:
                OUTPUT(o, 2, "Using local notes for %s", sha1_to_hex(p->obj));
                /* nothing to do */
                return 0;
        case NOTES_MERGE_RESOLVE_THEIRS:
                OUTPUT(o, 2, "Using remote notes for %s", sha1_to_hex(p->obj));
                if (add_note(t, p->obj, p->remote, combine_notes_overwrite))
                        die("BUG: combine_notes_overwrite failed");
                return 0;
        case NOTES_MERGE_RESOLVE_UNION:
                OUTPUT(o, 2, "Concatenating local and remote notes for %s",
                       sha1_to_hex(p->obj));
                if (add_note(t, p->obj, p->remote, combine_notes_concatenate))
                        die("failed to concatenate notes "
                            "(combine_notes_concatenate)");
                return 0;
        }
        die("Unknown strategy (%i).", o->strategy);
}

static int merge_changes(struct notes_merge_options *o,
                         struct notes_merge_pair *changes, int *num_changes,
                         struct notes_tree *t)
{
        int i, conflicts = 0;

        trace_printf("\tmerge_changes(num_changes = %i)\n", *num_changes);
        for (i = 0; i < *num_changes; i++) {
                struct notes_merge_pair *p = changes + i;
                trace_printf("\t\t%.7s: %.7s -> %.7s/%.7s\n",
                       sha1_to_hex(p->obj), sha1_to_hex(p->base),
                       sha1_to_hex(p->local), sha1_to_hex(p->remote));

                if (!hashcmp(p->base, p->remote)) {
                        /* no remote change; nothing to do */
                        trace_printf("\t\t\tskipping (no remote change)\n");
                } else if (!hashcmp(p->local, p->remote)) {
                        /* same change in local and remote; nothing to do */
                        trace_printf("\t\t\tskipping (local == remote)\n");
                } else if (!hashcmp(p->local, uninitialized) ||
                           !hashcmp(p->local, p->base)) {
                        /* no local change; adopt remote change */
                        trace_printf("\t\t\tno local change, adopted remote\n");
                        if (add_note(t, p->obj, p->remote,
                                     combine_notes_overwrite))
                                die("BUG: combine_notes_overwrite failed");
                } else {
                        /* need file-level merge between local and remote */
                        trace_printf("\t\t\tneed content-level merge\n");
                        conflicts += merge_one_change(o, p, t);
                }
        }

        return conflicts;
}

static int merge_from_diffs(struct notes_merge_options *o,
                            const unsigned char *base,
                            const unsigned char *local,
                            const unsigned char *remote, struct notes_tree *t)
{
        struct notes_merge_pair *changes;
        int num_changes, conflicts;

        trace_printf("\tmerge_from_diffs(base = %.7s, local = %.7s, "
               "remote = %.7s)\n", sha1_to_hex(base), sha1_to_hex(local),
               sha1_to_hex(remote));

        changes = diff_tree_remote(o, base, remote, &num_changes);
        diff_tree_local(o, changes, num_changes, base, local);

        conflicts = merge_changes(o, changes, &num_changes, t);
        free(changes);

        OUTPUT(o, 4, "Merge result: %i unmerged notes and a %s notes tree",
               conflicts, t->dirty ? "dirty" : "clean");

        return conflicts ? -1 : 1;
}

void create_notes_commit(struct notes_tree *t, struct commit_list *parents,
                         const char *msg, unsigned char *result_sha1)
{
        unsigned char tree_sha1[20];

        assert(t->initialized);

        if (write_notes_tree(t, tree_sha1))
                die("Failed to write notes tree to database");

        if (!parents) {
                /* Deduce parent commit from t->ref */
                unsigned char parent_sha1[20];
                if (!read_ref(t->ref, parent_sha1)) {
                        struct commit *parent = lookup_commit(parent_sha1);
                        if (!parent || parse_commit(parent))
                                die("Failed to find/parse commit %s", t->ref);
                        commit_list_insert(parent, &parents);
                }
                /* else: t->ref points to nothing, assume root/orphan commit */
        }

        if (commit_tree(msg, tree_sha1, parents, result_sha1, NULL))
                die("Failed to commit notes tree to database");
}

int notes_merge(struct notes_merge_options *o,
                struct notes_tree *local_tree,
                unsigned char *result_sha1)
{
        unsigned char local_sha1[20], remote_sha1[20];
        struct commit *local, *remote;
        struct commit_list *bases = NULL;
        const unsigned char *base_sha1, *base_tree_sha1;
        int result = 0;

        assert(o->local_ref && o->remote_ref);
        assert(!strcmp(o->local_ref, local_tree->ref));
        hashclr(result_sha1);

        trace_printf("notes_merge(o->local_ref = %s, o->remote_ref = %s)\n",
               o->local_ref, o->remote_ref);

        /* Dereference o->local_ref into local_sha1 */
        if (!resolve_ref(o->local_ref, local_sha1, 0, NULL))
                die("Failed to resolve local notes ref '%s'", o->local_ref);
        else if (!check_ref_format(o->local_ref) && is_null_sha1(local_sha1))
                local = NULL; /* local_sha1 == null_sha1 indicates unborn ref */
        else if (!(local = lookup_commit_reference(local_sha1)))
                die("Could not parse local commit %s (%s)",
                    sha1_to_hex(local_sha1), o->local_ref);
        trace_printf("\tlocal commit: %.7s\n", sha1_to_hex(local_sha1));

        /* Dereference o->remote_ref into remote_sha1 */
        if (get_sha1(o->remote_ref, remote_sha1)) {
                /*
                 * Failed to get remote_sha1. If o->remote_ref looks like an
                 * unborn ref, perform the merge using an empty notes tree.
                 */
                if (!check_ref_format(o->remote_ref)) {
                        hashclr(remote_sha1);
                        remote = NULL;
                } else {
                        die("Failed to resolve remote notes ref '%s'",
                            o->remote_ref);
                }
        } else if (!(remote = lookup_commit_reference(remote_sha1))) {
                die("Could not parse remote commit %s (%s)",
                    sha1_to_hex(remote_sha1), o->remote_ref);
        }
        trace_printf("\tremote commit: %.7s\n", sha1_to_hex(remote_sha1));

        if (!local && !remote)
                die("Cannot merge empty notes ref (%s) into empty notes ref "
                    "(%s)", o->remote_ref, o->local_ref);
        if (!local) {
                /* result == remote commit */
                hashcpy(result_sha1, remote_sha1);
                goto found_result;
        }
        if (!remote) {
                /* result == local commit */
                hashcpy(result_sha1, local_sha1);
                goto found_result;
        }
        assert(local && remote);

        /* Find merge bases */
        bases = get_merge_bases(local, remote, 1);
        if (!bases) {
                base_sha1 = null_sha1;
                base_tree_sha1 = (unsigned char *)EMPTY_TREE_SHA1_BIN;
                OUTPUT(o, 4, "No merge base found; doing history-less merge");
        } else if (!bases->next) {
                base_sha1 = bases->item->object.sha1;
                base_tree_sha1 = bases->item->tree->object.sha1;
                OUTPUT(o, 4, "One merge base found (%.7s)",
                       sha1_to_hex(base_sha1));
        } else {
                /* TODO: How to handle multiple merge-bases? */
                base_sha1 = bases->item->object.sha1;
                base_tree_sha1 = bases->item->tree->object.sha1;
                OUTPUT(o, 3, "Multiple merge bases found. Using the first "
                       "(%.7s)", sha1_to_hex(base_sha1));
        }

        OUTPUT(o, 4, "Merging remote commit %.7s into local commit %.7s with "
               "merge-base %.7s", sha1_to_hex(remote->object.sha1),
               sha1_to_hex(local->object.sha1), sha1_to_hex(base_sha1));

        if (!hashcmp(remote->object.sha1, base_sha1)) {
                /* Already merged; result == local commit */
                OUTPUT(o, 2, "Already up-to-date!");
                hashcpy(result_sha1, local->object.sha1);
                goto found_result;
        }
        if (!hashcmp(local->object.sha1, base_sha1)) {
                /* Fast-forward; result == remote commit */
                OUTPUT(o, 2, "Fast-forward");
                hashcpy(result_sha1, remote->object.sha1);
                goto found_result;
        }

        result = merge_from_diffs(o, base_tree_sha1, local->tree->object.sha1,
                                  remote->tree->object.sha1, local_tree);

        if (result != 0) { /* non-trivial merge (with or without conflicts) */
                /* Commit (partial) result */
                struct commit_list *parents = NULL;
                commit_list_insert(remote, &parents); /* LIFO order */
                commit_list_insert(local, &parents);
                create_notes_commit(local_tree, parents, o->commit_msg,
                                    result_sha1);
        }

found_result:
        free_commit_list(bases);
        trace_printf("notes_merge(): result = %i, result_sha1 = %.7s\n",
               result, sha1_to_hex(result_sha1));
        return result;
}