/*
 * Helper functions for tree diff generation
 */
#include "cache.h"
#include "diff.h"

// What paths are we interested in?
static int nr_paths = 0;
static const char **paths = NULL;
static int *pathlens = NULL;

void update_tree_entry(struct tree_desc *desc)
{
        void *buf = desc->buf;
        unsigned long size = desc->size;
        int len = strlen(buf) + 1 + 20;

        if (size < len)
                die("corrupt tree file");
        desc->buf = buf + len;
        desc->size = size - len;
}

const unsigned char *tree_entry_extract(struct tree_desc *desc, const char **pathp, unsigned int *modep)
{
        void *tree = desc->buf;
        unsigned long size = desc->size;
        int len = strlen(tree)+1;
        const unsigned char *sha1 = tree + len;
        const char *path = strchr(tree, ' ');
        unsigned int mode;

        if (!path || size < len + 20 || sscanf(tree, "%o", &mode) != 1)
                die("corrupt tree file");
        *pathp = path+1;
        *modep = DIFF_FILE_CANON_MODE(mode);
        return sha1;
}

static char *malloc_base(const char *base, const char *path, int pathlen)
{
        int baselen = strlen(base);
        char *newbase = xmalloc(baselen + pathlen + 2);
        memcpy(newbase, base, baselen);
        memcpy(newbase + baselen, path, pathlen);
        memcpy(newbase + baselen + pathlen, "/", 2);
        return newbase;
}

static int show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base);

static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
{
        unsigned mode1, mode2;
        const char *path1, *path2;
        const unsigned char *sha1, *sha2;
        int cmp, pathlen1, pathlen2;

        sha1 = tree_entry_extract(t1, &path1, &mode1);
        sha2 = tree_entry_extract(t2, &path2, &mode2);

        pathlen1 = strlen(path1);
        pathlen2 = strlen(path2);
        cmp = base_name_compare(path1, pathlen1, mode1, path2, pathlen2, mode2);
        if (cmp < 0) {
                show_entry(opt, "-", t1, base);
                return -1;
        }
        if (cmp > 0) {
                show_entry(opt, "+", t2, base);
                return 1;
        }
        if (!opt->find_copies_harder &&
            !memcmp(sha1, sha2, 20) && mode1 == mode2)
                return 0;

        /*
         * If the filemode has changed to/from a directory from/to a regular
         * file, we need to consider it a remove and an add.
         */
        if (S_ISDIR(mode1) != S_ISDIR(mode2)) {
                show_entry(opt, "-", t1, base);
                show_entry(opt, "+", t2, base);
                return 0;
        }

        if (opt->recursive && S_ISDIR(mode1)) {
                int retval;
                char *newbase = malloc_base(base, path1, pathlen1);
                if (opt->tree_in_recursive)
                        opt->change(opt, mode1, mode2,
                                    sha1, sha2, base, path1);
                retval = diff_tree_sha1(sha1, sha2, newbase, opt);
                free(newbase);
                return retval;
        }

        opt->change(opt, mode1, mode2, sha1, sha2, base, path1);
        return 0;
}

static int interesting(struct tree_desc *desc, const char *base)
{
        const char *path;
        unsigned mode;
        int i;
        int baselen, pathlen;

        if (!nr_paths)
                return 1;

        (void)tree_entry_extract(desc, &path, &mode);

        pathlen = strlen(path);
        baselen = strlen(base);

        for (i=0; i < nr_paths; i++) {
                const char *match = paths[i];
                int matchlen = pathlens[i];

                if (baselen >= matchlen) {
                        /* If it doesn't match, move along... */
                        if (strncmp(base, match, matchlen))
                                continue;

                        /* The base is a subdirectory of a path which was specified. */
                        return 1;
                }

                /* Does the base match? */
                if (strncmp(base, match, baselen))
                        continue;

                match += baselen;
                matchlen -= baselen;

                if (pathlen > matchlen)
                        continue;

                if (matchlen > pathlen) {
                        if (match[pathlen] != '/')
                                continue;
                        if (!S_ISDIR(mode))
                                continue;
                }

                if (strncmp(path, match, pathlen))
                        continue;

                return 1;
        }
        return 0; /* No matches */
}

/* A whole sub-tree went away or appeared */
static void show_tree(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base)
{
        while (desc->size) {
                if (interesting(desc, base))
                        show_entry(opt, prefix, desc, base);
                update_tree_entry(desc);
        }
}

/* A file entry went away or appeared */
static int show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base)
{
        unsigned mode;
        const char *path;
        const unsigned char *sha1 = tree_entry_extract(desc, &path, &mode);

        if (opt->recursive && S_ISDIR(mode)) {
                char type[20];
                char *newbase = malloc_base(base, path, strlen(path));
                struct tree_desc inner;
                void *tree;

                tree = read_sha1_file(sha1, type, &inner.size);
                if (!tree || strcmp(type, "tree"))
                        die("corrupt tree sha %s", sha1_to_hex(sha1));

                inner.buf = tree;
                show_tree(opt, prefix, &inner, newbase);

                free(tree);
                free(newbase);
                return 0;
        }

        opt->add_remove(opt, prefix[0], mode, sha1, base, path);
        return 0;
}

int diff_tree(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
{
        while (t1->size | t2->size) {
                if (nr_paths && t1->size && !interesting(t1, base)) {
                        update_tree_entry(t1);
                        continue;
                }
                if (nr_paths && t2->size && !interesting(t2, base)) {
                        update_tree_entry(t2);
                        continue;
                }
                if (!t1->size) {
                        show_entry(opt, "+", t2, base);
                        update_tree_entry(t2);
                        continue;
                }
                if (!t2->size) {
                        show_entry(opt, "-", t1, base);
                        update_tree_entry(t1);
                        continue;
                }
                switch (compare_tree_entry(t1, t2, base, opt)) {
                case -1:
                        update_tree_entry(t1);
                        continue;
                case 0:
                        update_tree_entry(t1);
                        /* Fallthrough */
                case 1:
                        update_tree_entry(t2);
                        continue;
                }
                die("git-diff-tree: internal error");
        }
        return 0;
}

int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base, struct diff_options *opt)
{
        void *tree1, *tree2;
        struct tree_desc t1, t2;
        int retval;

        tree1 = read_object_with_reference(old, "tree", &t1.size, NULL);
        if (!tree1)
                die("unable to read source tree (%s)", sha1_to_hex(old));
        tree2 = read_object_with_reference(new, "tree", &t2.size, NULL);
        if (!tree2)
                die("unable to read destination tree (%s)", sha1_to_hex(new));
        t1.buf = tree1;
        t2.buf = tree2;
        retval = diff_tree(&t1, &t2, base, opt);
        free(tree1);
        free(tree2);
        return retval;
}

static int count_paths(const char **paths)
{
        int i = 0;
        while (*paths++)
                i++;
        return i;
}

void diff_tree_setup_paths(const char **p)
{
        if (p) {
                int i;

                paths = p;
                nr_paths = count_paths(paths);
                if (nr_paths == 0) {
                        pathlens = NULL;
                        return;
                }
                pathlens = xmalloc(nr_paths * sizeof(int));
                for (i=0; i<nr_paths; i++)
                        pathlens[i] = strlen(paths[i]);
        }
}