#include "cache.h"

static int recursive = 0;
static int line_termination = '\n';

static int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base);

static void update_tree_entry(void **bufp, unsigned long *sizep)
{
        void *buf = *bufp;
        unsigned long size = *sizep;
        int len = strlen(buf) + 1 + 20;

        if (size < len)
                die("corrupt tree file");
        *bufp = buf + len;
        *sizep = size - len;
}

static const unsigned char *extract(void *tree, unsigned long size, const char **pathp, unsigned int *modep)
{
        int len = strlen(tree)+1;
        const unsigned char *sha1 = tree + len;
        const char *path = strchr(tree, ' ');

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

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

static void show_file(const char *prefix, void *tree, unsigned long size, const char *base);

/* A whole sub-tree went away or appeared */
static void show_tree(const char *prefix, void *tree, unsigned long size, const char *base)
{
        while (size) {
                show_file(prefix, tree, size, base);
                update_tree_entry(&tree, &size);
        }
}

/* A file entry went away or appeared */
static void show_file(const char *prefix, void *tree, unsigned long size, const char *base)
{
        unsigned mode;
        const char *path;
        const unsigned char *sha1 = extract(tree, size, &path, &mode);

        if (recursive && S_ISDIR(mode)) {
                char type[20];
                unsigned long size;
                char *newbase = malloc_base(base, path, strlen(path));
                void *tree;

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

                show_tree(prefix, tree, size, newbase);
                
                free(tree);
                free(newbase);
                return;
        }

        printf("%s%o\t%s\t%s\t%s%s%c", prefix, mode,
               S_ISDIR(mode) ? "tree" : "blob",
               sha1_to_hex(sha1), base, path,
               line_termination);
}

static int compare_tree_entry(void *tree1, unsigned long size1, void *tree2, unsigned long size2, const char *base)
{
        unsigned mode1, mode2;
        const char *path1, *path2;
        const unsigned char *sha1, *sha2;
        int cmp, pathlen1, pathlen2;
        char old_sha1_hex[50];

        sha1 = extract(tree1, size1, &path1, &mode1);
        sha2 = extract(tree2, size2, &path2, &mode2);

        pathlen1 = strlen(path1);
        pathlen2 = strlen(path2);
        cmp = cache_name_compare(path1, pathlen1, path2, pathlen2);
        if (cmp < 0) {
                show_file("-", tree1, size1, base);
                return -1;
        }
        if (cmp > 0) {
                show_file("+", tree2, size2, base);
                return 1;
        }
        if (!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_file("-", tree1, size1, base);
                show_file("+", tree2, size2, base);
                return 0;
        }

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

        strcpy(old_sha1_hex, sha1_to_hex(sha1));
        printf("*%o->%o\t%s\t%s->%s\t%s%s%c", mode1, mode2,
               S_ISDIR(mode1) ? "tree" : "blob",
               old_sha1_hex, sha1_to_hex(sha2), base, path1,
               line_termination);
        return 0;
}

static int diff_tree(void *tree1, unsigned long size1, void *tree2, unsigned long size2, const char *base)
{
        while (size1 | size2) {
                if (!size1) {
                        show_file("+", tree2, size2, base);
                        update_tree_entry(&tree2, &size2);
                        continue;
                }
                if (!size2) {
                        show_file("-", tree1, size1, base);
                        update_tree_entry(&tree1, &size1);
                        continue;
                }
                switch (compare_tree_entry(tree1, size1, tree2, size2, base)) {
                case -1:
                        update_tree_entry(&tree1, &size1);
                        continue;
                case 0:
                        update_tree_entry(&tree1, &size1);
                        /* Fallthrough */
                case 1:
                        update_tree_entry(&tree2, &size2);
                        continue;
                }
                die("diff-tree: internal error");
        }
        return 0;
}

static int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base)
{
        void *tree1, *tree2;
        unsigned long size1, size2;
        char type[20];
        int retval;

        tree1 = read_sha1_file(old, type, &size1);
        if (!tree1 || strcmp(type, "tree"))
                die("unable to read source tree (%s)", sha1_to_hex(old));
        tree2 = read_sha1_file(new, type, &size2);
        if (!tree2 || strcmp(type, "tree"))
                die("unable to read destination tree (%s)", sha1_to_hex(new));
        retval = diff_tree(tree1, size1, tree2, size2, base);
        free(tree1);
        free(tree2);
        return retval;
}

int main(int argc, char **argv)
{
        unsigned char old[20], new[20];

        while (argc > 3) {
                char *arg = argv[1];
                argv++;
                argc--;
                if (!strcmp(arg, "-r")) {
                        recursive = 1;
                        continue;
                }
                if (!strcmp(arg, "-z")) {
                        line_termination = '\0';
                        continue;
                }
                usage("diff-tree [-r] [-z] <tree sha1> <tree sha1>");
        }

        if (argc != 3 || get_sha1_hex(argv[1], old) || get_sha1_hex(argv[2], new))
                usage("diff-tree <tree sha1> <tree sha1>");
        return diff_tree_sha1(old, new, "");
}