#include <ctype.h>
#include "cache.h"
#include "diff.h"

static int silent = 0;
static int ignore_merges = 1;
static int recursive = 0;
static int read_stdin = 0;
static int line_termination = '\n';
static int generate_patch = 0;
static const char *header = NULL;

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

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 = xmalloc(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 (header) {
                printf("%s", header);
                header = NULL;
        }

        if (silent)
                return;

        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;
        }

        if (generate_patch) {
                if (!S_ISDIR(mode))
                        diff_addremove(prefix[0], mode, sha1, base, path);
        }
        else
                printf("%s%06o\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;
        }

        if (header) {
                printf("%s", header);
                header = NULL;
        }
        if (silent)
                return 0;

        if (generate_patch) {
                if (!S_ISDIR(mode1))
                        diff_change(mode1, mode2, sha1, sha2, base, path1);
        }
        else {
                strcpy(old_sha1_hex, sha1_to_hex(sha1));
                printf("*%06o->%06o\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 interesting(void *tree, unsigned long size, const char *base)
{
        const char *path;
        unsigned mode;
        int i;
        int baselen, pathlen;

        if (!nr_paths)
                return 1;

        (void)extract(tree, size, &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 (strncmp(path, match, pathlen))
                        continue;

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

static int diff_tree(void *tree1, unsigned long size1, void *tree2, unsigned long size2, const char *base)
{
        while (size1 | size2) {
                if (nr_paths && size1 && !interesting(tree1, size1, base)) {
                        update_tree_entry(&tree1, &size1);
                        continue;
                }
                if (nr_paths && size2 && !interesting(tree2, size2, base)) {
                        update_tree_entry(&tree2, &size2);
                        continue;
                }
                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;
        int retval;

        tree1 = read_object_with_reference(old, "tree", &size1, 0);
        if (!tree1)
                die("unable to read source tree (%s)", sha1_to_hex(old));
        tree2 = read_object_with_reference(new, "tree", &size2, 0);
        if (!tree2)
                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;
}

static int diff_tree_stdin(char *line)
{
        int len = strlen(line);
        unsigned char commit[20], parent[20];
        unsigned long size, offset;
        static char this_header[100];
        char *buf;

        if (!len || line[len-1] != '\n')
                return -1;
        line[len-1] = 0;
        if (get_sha1_hex(line, commit))
                return -1;
        if (isspace(line[40]) && !get_sha1_hex(line+41, parent)) {
                line[40] = 0;
                line[81] = 0;
                sprintf(this_header, "%s (from %s)\n", line, line+41);
                header = this_header;
                return diff_tree_sha1(parent, commit, "");
        }
        buf = read_object_with_reference(commit, "commit", &size, NULL);
        if (!buf)
                return -1;

        /* More than one parent? */
        if (ignore_merges) {
                if (!memcmp(buf + 46 + 48, "parent ", 7))
                        return 0;
        }

        line[40] = 0;
        offset = 46;
        while (offset + 48 < size && !memcmp(buf + offset, "parent ", 7)) {
                if (get_sha1_hex(buf + offset + 7, parent))
                        return -1;
                sprintf(this_header, "%s (from %s)\n", line, sha1_to_hex(parent));
                header = this_header;
                diff_tree_sha1(parent, commit, "");
                offset += 48;
        }
        return -1;
}

static char *diff_tree_usage = "diff-tree [-p] [-r] [-z] <tree sha1> <tree sha1>";

int main(int argc, char **argv)
{
        char line[1000];
        unsigned char old[20], new[20];

        for (;;) {
                char *arg;

                argv++;
                argc--;
                arg = *argv;
                if (!arg || *arg != '-')
                        break;

                if (!strcmp(arg, "-")) {
                        argv++;
                        argc--;
                        break;
                }
                if (!strcmp(arg, "-r")) {
                        recursive = 1;
                        continue;
                }
                if (!strcmp(arg, "-p")) {
                        recursive = generate_patch = 1;
                        continue;
                }
                if (!strcmp(arg, "-z")) {
                        line_termination = '\0';
                        continue;
                }
                if (!strcmp(arg, "-m")) {
                        ignore_merges = 0;
                        continue;
                }
                if (!strcmp(arg, "-s")) {
                        silent = 1;
                        continue;
                }
                if (!strcmp(arg, "--stdin")) {
                        read_stdin = 1;
                        continue;
                }
                usage(diff_tree_usage);
        }

        if (!read_stdin) {
                if (argc < 2 || get_sha1(argv[0], old) || get_sha1(argv[1], new))
                        usage(diff_tree_usage);
                argv += 2;
                argc -= 2;
        }

        if (argc > 0) {
                int i;

                paths = argv;
                nr_paths = argc;
                pathlens = xmalloc(nr_paths * sizeof(int));
                for (i=0; i<nr_paths; i++)
                        pathlens[i] = strlen(paths[i]);
        }

        if (!read_stdin)
                return diff_tree_sha1(old, new, "");

        while (fgets(line, sizeof(line), stdin))
                diff_tree_stdin(line);

        return 0;
}