/*
 * Builtin "git am"
 *
 * Based on git-am.sh by Junio C Hamano.
 */
#include "cache.h"
#include "builtin.h"
#include "exec_cmd.h"
#include "parse-options.h"
#include "dir.h"
#include "run-command.h"

/**
 * Like strbuf_getline(), but treats both '\n' and "\r\n" as line terminators.
 */
static int strbuf_getline_crlf(struct strbuf *sb, FILE *fp)
{
        if (strbuf_getwholeline(sb, fp, '\n'))
                return EOF;
        if (sb->buf[sb->len - 1] == '\n') {
                strbuf_setlen(sb, sb->len - 1);
                if (sb->len > 0 && sb->buf[sb->len - 1] == '\r')
                        strbuf_setlen(sb, sb->len - 1);
        }
        return 0;
}

enum patch_format {
        PATCH_FORMAT_UNKNOWN = 0,
        PATCH_FORMAT_MBOX
};

struct am_state {
        /* state directory path */
        char *dir;

        /* current and last patch numbers, 1-indexed */
        int cur;
        int last;

        /* number of digits in patch filename */
        int prec;
};

/**
 * Initializes am_state with the default values. The state directory is set to
 * dir.
 */
static void am_state_init(struct am_state *state, const char *dir)
{
        memset(state, 0, sizeof(*state));

        assert(dir);
        state->dir = xstrdup(dir);

        state->prec = 4;
}

/**
 * Releases memory allocated by an am_state.
 */
static void am_state_release(struct am_state *state)
{
        free(state->dir);
}

/**
 * Returns path relative to the am_state directory.
 */
static inline const char *am_path(const struct am_state *state, const char *path)
{
        return mkpath("%s/%s", state->dir, path);
}

/**
 * Returns 1 if there is an am session in progress, 0 otherwise.
 */
static int am_in_progress(const struct am_state *state)
{
        struct stat st;

        if (lstat(state->dir, &st) < 0 || !S_ISDIR(st.st_mode))
                return 0;
        if (lstat(am_path(state, "last"), &st) || !S_ISREG(st.st_mode))
                return 0;
        if (lstat(am_path(state, "next"), &st) || !S_ISREG(st.st_mode))
                return 0;
        return 1;
}

/**
 * Reads the contents of `file` in the `state` directory into `sb`. Returns the
 * number of bytes read on success, -1 if the file does not exist. If `trim` is
 * set, trailing whitespace will be removed.
 */
static int read_state_file(struct strbuf *sb, const struct am_state *state,
                        const char *file, int trim)
{
        strbuf_reset(sb);

        if (strbuf_read_file(sb, am_path(state, file), 0) >= 0) {
                if (trim)
                        strbuf_trim(sb);

                return sb->len;
        }

        if (errno == ENOENT)
                return -1;

        die_errno(_("could not read '%s'"), am_path(state, file));
}

/**
 * Loads state from disk.
 */
static void am_load(struct am_state *state)
{
        struct strbuf sb = STRBUF_INIT;

        if (read_state_file(&sb, state, "next", 1) < 0)
                die("BUG: state file 'next' does not exist");
        state->cur = strtol(sb.buf, NULL, 10);

        if (read_state_file(&sb, state, "last", 1) < 0)
                die("BUG: state file 'last' does not exist");
        state->last = strtol(sb.buf, NULL, 10);

        strbuf_release(&sb);
}

/**
 * Removes the am_state directory, forcefully terminating the current am
 * session.
 */
static void am_destroy(const struct am_state *state)
{
        struct strbuf sb = STRBUF_INIT;

        strbuf_addstr(&sb, state->dir);
        remove_dir_recursively(&sb, 0);
        strbuf_release(&sb);
}

/**
 * Determines if the file looks like a piece of RFC2822 mail by grabbing all
 * non-indented lines and checking if they look like they begin with valid
 * header field names.
 *
 * Returns 1 if the file looks like a piece of mail, 0 otherwise.
 */
static int is_mail(FILE *fp)
{
        const char *header_regex = "^[!-9;-~]+:";
        struct strbuf sb = STRBUF_INIT;
        regex_t regex;
        int ret = 1;

        if (fseek(fp, 0L, SEEK_SET))
                die_errno(_("fseek failed"));

        if (regcomp(&regex, header_regex, REG_NOSUB | REG_EXTENDED))
                die("invalid pattern: %s", header_regex);

        while (!strbuf_getline_crlf(&sb, fp)) {
                if (!sb.len)
                        break; /* End of header */

                /* Ignore indented folded lines */
                if (*sb.buf == '\t' || *sb.buf == ' ')
                        continue;

                /* It's a header if it matches header_regex */
                if (regexec(&regex, sb.buf, 0, NULL, 0)) {
                        ret = 0;
                        goto done;
                }
        }

done:
        regfree(&regex);
        strbuf_release(&sb);
        return ret;
}

/**
 * Attempts to detect the patch_format of the patches contained in `paths`,
 * returning the PATCH_FORMAT_* enum value. Returns PATCH_FORMAT_UNKNOWN if
 * detection fails.
 */
static int detect_patch_format(const char **paths)
{
        enum patch_format ret = PATCH_FORMAT_UNKNOWN;
        struct strbuf l1 = STRBUF_INIT;
        FILE *fp;

        /*
         * We default to mbox format if input is from stdin and for directories
         */
        if (!*paths || !strcmp(*paths, "-") || is_directory(*paths))
                return PATCH_FORMAT_MBOX;

        /*
         * Otherwise, check the first few lines of the first patch, starting
         * from the first non-blank line, to try to detect its format.
         */

        fp = xfopen(*paths, "r");

        while (!strbuf_getline_crlf(&l1, fp)) {
                if (l1.len)
                        break;
        }

        if (starts_with(l1.buf, "From ") || starts_with(l1.buf, "From: ")) {
                ret = PATCH_FORMAT_MBOX;
                goto done;
        }

        if (l1.len && is_mail(fp)) {
                ret = PATCH_FORMAT_MBOX;
                goto done;
        }

done:
        fclose(fp);
        strbuf_release(&l1);
        return ret;
}

/**
 * Splits out individual email patches from `paths`, where each path is either
 * a mbox file or a Maildir. Returns 0 on success, -1 on failure.
 */
static int split_mail_mbox(struct am_state *state, const char **paths)
{
        struct child_process cp = CHILD_PROCESS_INIT;
        struct strbuf last = STRBUF_INIT;

        cp.git_cmd = 1;
        argv_array_push(&cp.args, "mailsplit");
        argv_array_pushf(&cp.args, "-d%d", state->prec);
        argv_array_pushf(&cp.args, "-o%s", state->dir);
        argv_array_push(&cp.args, "-b");
        argv_array_push(&cp.args, "--");
        argv_array_pushv(&cp.args, paths);

        if (capture_command(&cp, &last, 8))
                return -1;

        state->cur = 1;
        state->last = strtol(last.buf, NULL, 10);

        return 0;
}

/**
 * Splits a list of files/directories into individual email patches. Each path
 * in `paths` must be a file/directory that is formatted according to
 * `patch_format`.
 *
 * Once split out, the individual email patches will be stored in the state
 * directory, with each patch's filename being its index, padded to state->prec
 * digits.
 *
 * state->cur will be set to the index of the first mail, and state->last will
 * be set to the index of the last mail.
 *
 * Returns 0 on success, -1 on failure.
 */
static int split_mail(struct am_state *state, enum patch_format patch_format,
                        const char **paths)
{
        switch (patch_format) {
        case PATCH_FORMAT_MBOX:
                return split_mail_mbox(state, paths);
        default:
                die("BUG: invalid patch_format");
        }
        return -1;
}

/**
 * Setup a new am session for applying patches
 */
static void am_setup(struct am_state *state, enum patch_format patch_format,
                        const char **paths)
{
        if (!patch_format)
                patch_format = detect_patch_format(paths);

        if (!patch_format) {
                fprintf_ln(stderr, _("Patch format detection failed."));
                exit(128);
        }

        if (mkdir(state->dir, 0777) < 0 && errno != EEXIST)
                die_errno(_("failed to create directory '%s'"), state->dir);

        if (split_mail(state, patch_format, paths) < 0) {
                am_destroy(state);
                die(_("Failed to split patches."));
        }

        /*
         * NOTE: Since the "next" and "last" files determine if an am_state
         * session is in progress, they should be written last.
         */

        write_file(am_path(state, "next"), 1, "%d", state->cur);

        write_file(am_path(state, "last"), 1, "%d", state->last);
}

/**
 * Increments the patch pointer, and cleans am_state for the application of the
 * next patch.
 */
static void am_next(struct am_state *state)
{
        state->cur++;
        write_file(am_path(state, "next"), 1, "%d", state->cur);
}

/**
 * Applies all queued mail.
 */
static void am_run(struct am_state *state)
{
        while (state->cur <= state->last) {

                /* NEEDSWORK: Patch application not implemented yet */

                am_next(state);
        }

        am_destroy(state);
}

/**
 * parse_options() callback that validates and sets opt->value to the
 * PATCH_FORMAT_* enum value corresponding to `arg`.
 */
static int parse_opt_patchformat(const struct option *opt, const char *arg, int unset)
{
        int *opt_value = opt->value;

        if (!strcmp(arg, "mbox"))
                *opt_value = PATCH_FORMAT_MBOX;
        else
                return error(_("Invalid value for --patch-format: %s"), arg);
        return 0;
}

int cmd_am(int argc, const char **argv, const char *prefix)
{
        struct am_state state;
        int patch_format = PATCH_FORMAT_UNKNOWN;

        const char * const usage[] = {
                N_("git am [options] [(<mbox>|<Maildir>)...]"),
                NULL
        };

        struct option options[] = {
                OPT_CALLBACK(0, "patch-format", &patch_format, N_("format"),
                        N_("format the patch(es) are in"),
                        parse_opt_patchformat),
                OPT_END()
        };

        /*
         * NEEDSWORK: Once all the features of git-am.sh have been
         * re-implemented in builtin/am.c, this preamble can be removed.
         */
        if (!getenv("_GIT_USE_BUILTIN_AM")) {
                const char *path = mkpath("%s/git-am", git_exec_path());

                if (sane_execvp(path, (char **)argv) < 0)
                        die_errno("could not exec %s", path);
        } else {
                prefix = setup_git_directory();
                trace_repo_setup(prefix);
                setup_work_tree();
        }

        git_config(git_default_config, NULL);

        am_state_init(&state, git_path("rebase-apply"));

        argc = parse_options(argc, argv, prefix, options, usage, 0);

        if (am_in_progress(&state))
                am_load(&state);
        else {
                struct argv_array paths = ARGV_ARRAY_INIT;
                int i;

                for (i = 0; i < argc; i++) {
                        if (is_absolute_path(argv[i]) || !prefix)
                                argv_array_push(&paths, argv[i]);
                        else
                                argv_array_push(&paths, mkpath("%s/%s", prefix, argv[i]));
                }

                am_setup(&state, patch_format, paths.argv);

                argv_array_clear(&paths);
        }

        am_run(&state);

        am_state_release(&state);

        return 0;
}