/*
 * GIT - The information manager from hell
 *
 * Copyright (C) Linus Torvalds, 2005
 */
#include "cache.h"

static char *diff_cmd = "diff -L 'a/%s' -L 'b/%s' ";
static char *diff_opts = "-p -u";
static char *diff_arg_forward  = " - '%s'";
static char *diff_arg_reverse  = " '%s' -";

static void prepare_diff_cmd(void)
{
        /*
         * Default values above are meant to match the
         * Linux kernel development style.  Examples of
         * alternative styles you can specify via environment
         * variables are:
         *
         * GIT_DIFF_CMD="diff -L '%s' -L '%s'"
         * GIT_DIFF_OPTS="-c";
         */
        diff_cmd = getenv("GIT_DIFF_CMD") ? : diff_cmd;
        diff_opts = getenv("GIT_DIFF_OPTS") ? : diff_opts;
}

/* Help to copy the thing properly quoted for the shell safety.
 * any single quote is replaced with '\'', and the caller is
 * expected to enclose the result within a single quote pair.
 *
 * E.g.
 *  original     sq_expand     result
 *  name     ==> name      ==> 'name'
 *  a b      ==> a b       ==> 'a b'
 *  a'b      ==> a'\''b    ==> 'a'\''b'
 *
 * NOTE! The returned memory belongs to this function so
 * do not free it.
 */
static char *sq_expand(char *src)
{
        static char *buf = NULL;
        int cnt, c;
        char *cp;

        /* count bytes needed to store the quoted string. */ 
        for (cnt = 1, cp = src; *cp; cnt++, cp++)
                if (*cp == '\'')
                        cnt += 3;

        if (! (buf = malloc(cnt)))
            return buf;
        cp = buf;
        while ((c = *src++)) {
                if (c != '\'')
                        *cp++ = c;
                else {
                        cp = strcpy(cp, "'\\''");
                        cp += 4;
                }
        }
        *cp = 0;
        return buf;
}

static void show_differences(char *name, char *label, void *old_contents,
                             unsigned long long old_size, int reverse)
{
        FILE *f;
        char *name_sq = sq_expand(name);
        char *label_sq = (name != label) ? sq_expand(label) : name_sq;
        char *diff_arg = reverse ? diff_arg_reverse : diff_arg_forward;
        int cmd_size = strlen(name_sq) + strlen(label_sq) * 2 +
                strlen(diff_cmd) + strlen(diff_opts) + strlen(diff_arg);
        char *cmd = malloc(cmd_size);
        int next_at;

        fflush(stdout);
        next_at = snprintf(cmd, cmd_size, diff_cmd, label_sq, label_sq);
        next_at += snprintf(cmd+next_at, cmd_size-next_at, "%s", diff_opts);
        next_at += snprintf(cmd+next_at, cmd_size-next_at, diff_arg, name_sq);
        f = popen(cmd, "w");
        if (old_size)
                fwrite(old_contents, old_size, 1, f);
        pclose(f);
        if (label_sq != name_sq)
                free(label_sq);
        free(name_sq);
        free(cmd);
}

static void show_diff_empty(struct cache_entry *ce, int reverse)
{
        char *old;
        unsigned long int size;
        unsigned char type[20];

        old = read_sha1_file(ce->sha1, type, &size);
        if (! old) {
                error("unable to read blob object for %s (%s)", ce->name,
                      sha1_to_hex(ce->sha1));
                return;
        }
        show_differences("/dev/null", ce->name, old, size, reverse);
}

static const char *show_diff_usage = "show-diff [-q] [-s] [-z] [paths...]";

static int matches_pathspec(struct cache_entry *ce, char **spec, int cnt)
{
        int i;
        int namelen = ce_namelen(ce);
        for (i = 0; i < cnt; i++) {
                int speclen = strlen(spec[i]);
                if (! strncmp(spec[i], ce->name, speclen) &&
                    speclen <= namelen &&
                    (ce->name[speclen] == 0 ||
                     ce->name[speclen] == '/'))
                        return 1;
        }
        return 0;
}

int main(int argc, char **argv)
{
        int silent = 0;
        int silent_on_nonexisting_files = 0;
        int machine_readable = 0;
        int reverse = 0;
        int entries = read_cache();
        int i;

        while (1 < argc && argv[1][0] == '-') {
                if  (!strcmp(argv[1], "-R"))
                        reverse = 1;
                else if (!strcmp(argv[1], "-s"))
                        silent_on_nonexisting_files = silent = 1;
                else if (!strcmp(argv[1], "-q"))
                        silent_on_nonexisting_files = 1;
                else if (!strcmp(argv[1], "-z"))
                        machine_readable = 1;
                else
                        usage(show_diff_usage);
                argv++; argc--;
        }

        /* At this point, if argc == 1, then we are doing everything.
         * Otherwise argv[1] .. argv[argc-1] have the explicit paths.
         */
        if (entries < 0) {
                perror("read_cache");
                exit(1);
        }
        prepare_diff_cmd();
        for (i = 0; i < entries; i++) {
                struct stat st;
                struct cache_entry *ce = active_cache[i];
                int changed;
                unsigned long size;
                char type[20];
                void *old;

                if (1 < argc &&
                    ! matches_pathspec(ce, argv+1, argc-1))
                        continue;

                if (ce_stage(ce)) {
                        if (machine_readable)
                                printf("U %s%c", ce->name, 0);
                        else
                                printf("%s: Unmerged\n",
                                       ce->name);
                        while (i < entries &&
                               !strcmp(ce->name, active_cache[i]->name))
                                i++;
                        i--; /* compensate for loop control increments */
                        continue;
                }
 
                if (stat(ce->name, &st) < 0) {
                        if (errno == ENOENT && silent_on_nonexisting_files)
                                continue;
                        if (machine_readable)
                                printf("X %s%c", ce->name, 0);
                        else {
                                printf("%s: %s\n", ce->name, strerror(errno));
                                if (errno == ENOENT)
                                        show_diff_empty(ce, reverse);
                        }
                        continue;
                }
                changed = cache_match_stat(ce, &st);
                if (!changed)
                        continue;
                if (!machine_readable)
                        printf("%s: %s\n", ce->name, sha1_to_hex(ce->sha1));
                else {
                        printf("%s %s%c", sha1_to_hex(ce->sha1), ce->name, 0);
                        continue;
                }
                if (silent)
                        continue;

                old = read_sha1_file(ce->sha1, type, &size);
                if (! old)
                        error("unable to read blob object for %s (%s)",
                              ce->name, sha1_to_hex(ce->sha1));
                else
                        show_differences(ce->name, ce->name, old, size,
                                         reverse);
                free(old);
        }
        return 0;
}