/*
 * Another stupid program, this one parsing the headers of an
 * email to figure out authorship and subject
 */
#include "cache.h"
#include "builtin.h"
#include "utf8.h"
#include "strbuf.h"

static FILE *cmitmsg, *patchfile, *fin, *fout;

static int keep_subject;
static const char *metainfo_charset;
static struct strbuf line = STRBUF_INIT;
static struct strbuf name = STRBUF_INIT;
static struct strbuf email = STRBUF_INIT;

static enum  {
        TE_DONTCARE, TE_QP, TE_BASE64,
} transfer_encoding;
static enum  {
        TYPE_TEXT, TYPE_OTHER,
} message_type;

static struct strbuf charset = STRBUF_INIT;
static int patch_lines;
static struct strbuf **p_hdr_data, **s_hdr_data;

#define MAX_HDR_PARSED 10
#define MAX_BOUNDARIES 5

static void get_sane_name(struct strbuf *out, struct strbuf *name, struct strbuf *email)
{
        struct strbuf *src = name;
        if (name->len < 3 || 60 < name->len || strchr(name->buf, '@') ||
                strchr(name->buf, '<') || strchr(name->buf, '>'))
                src = email;
        else if (name == out)
                return;
        strbuf_reset(out);
        strbuf_addbuf(out, src);
}

static void parse_bogus_from(const struct strbuf *line)
{
        /* John Doe <johndoe> */

        char *bra, *ket;
        /* This is fallback, so do not bother if we already have an
         * e-mail address.
         */
        if (email.len)
                return;

        bra = strchr(line->buf, '<');
        if (!bra)
                return;
        ket = strchr(bra, '>');
        if (!ket)
                return;

        strbuf_reset(&email);
        strbuf_add(&email, bra + 1, ket - bra - 1);

        strbuf_reset(&name);
        strbuf_add(&name, line->buf, bra - line->buf);
        strbuf_trim(&name);
        get_sane_name(&name, &name, &email);
}

static void handle_from(const struct strbuf *from)
{
        char *at;
        size_t el;
        struct strbuf f;

        strbuf_init(&f, from->len);
        strbuf_addbuf(&f, from);

        at = strchr(f.buf, '@');
        if (!at) {
                parse_bogus_from(from);
                return;
        }

        /*
         * If we already have one email, don't take any confusing lines
         */
        if (email.len && strchr(at + 1, '@')) {
                strbuf_release(&f);
                return;
        }

        /* Pick up the string around '@', possibly delimited with <>
         * pair; that is the email part.
         */
        while (at > f.buf) {
                char c = at[-1];
                if (isspace(c))
                        break;
                if (c == '<') {
                        at[-1] = ' ';
                        break;
                }
                at--;
        }
        el = strcspn(at, " \n\t\r\v\f>");
        strbuf_reset(&email);
        strbuf_add(&email, at, el);
        strbuf_remove(&f, at - f.buf, el + (at[el] ? 1 : 0));

        /* The remainder is name.  It could be "John Doe <john.doe@xz>"
         * or "john.doe@xz (John Doe)", but we have removed the
         * email part, so trim from both ends, possibly removing
         * the () pair at the end.
         */
        strbuf_trim(&f);
        if (f.buf[0] == '(' && f.len && f.buf[f.len - 1] == ')') {
                strbuf_remove(&f, 0, 1);
                strbuf_setlen(&f, f.len - 1);
        }

        get_sane_name(&name, &f, &email);
        strbuf_release(&f);
}

static void handle_header(struct strbuf **out, const struct strbuf *line)
{
        if (!*out) {
                *out = xmalloc(sizeof(struct strbuf));
                strbuf_init(*out, line->len);
        } else
                strbuf_reset(*out);

        strbuf_addbuf(*out, line);
}

/* NOTE NOTE NOTE.  We do not claim we do full MIME.  We just attempt
 * to have enough heuristics to grok MIME encoded patches often found
 * on our mailing lists.  For example, we do not even treat header lines
 * case insensitively.
 */

static int slurp_attr(const char *line, const char *name, struct strbuf *attr)
{
        const char *ends, *ap = strcasestr(line, name);
        size_t sz;

        if (!ap) {
                strbuf_setlen(attr, 0);
                return 0;
        }
        ap += strlen(name);
        if (*ap == '"') {
                ap++;
                ends = "\"";
        }
        else
                ends = "; \t";
        sz = strcspn(ap, ends);
        strbuf_add(attr, ap, sz);
        return 1;
}

static struct strbuf *content[MAX_BOUNDARIES];

static struct strbuf **content_top = content;

static void handle_content_type(struct strbuf *line)
{
        struct strbuf *boundary = xmalloc(sizeof(struct strbuf));
        strbuf_init(boundary, line->len);

        if (!strcasestr(line->buf, "text/"))
                 message_type = TYPE_OTHER;
        if (slurp_attr(line->buf, "boundary=", boundary)) {
                strbuf_insert(boundary, 0, "--", 2);
                if (++content_top > &content[MAX_BOUNDARIES]) {
                        fprintf(stderr, "Too many boundaries to handle\n");
                        exit(1);
                }
                *content_top = boundary;
                boundary = NULL;
        }
        if (slurp_attr(line->buf, "charset=", &charset))
                strbuf_tolower(&charset);

        if (boundary) {
                strbuf_release(boundary);
                free(boundary);
        }
}

static void handle_content_transfer_encoding(const struct strbuf *line)
{
        if (strcasestr(line->buf, "base64"))
                transfer_encoding = TE_BASE64;
        else if (strcasestr(line->buf, "quoted-printable"))
                transfer_encoding = TE_QP;
        else
                transfer_encoding = TE_DONTCARE;
}

static int is_multipart_boundary(const struct strbuf *line)
{
        return (((*content_top)->len <= line->len) &&
                !memcmp(line->buf, (*content_top)->buf, (*content_top)->len));
}

static void cleanup_subject(struct strbuf *subject)
{
        char *pos;
        size_t remove;
        while (subject->len) {
                switch (*subject->buf) {
                case 'r': case 'R':
                        if (subject->len <= 3)
                                break;
                        if (!memcmp(subject->buf + 1, "e:", 2)) {
                                strbuf_remove(subject, 0, 3);
                                continue;
                        }
                        break;
                case ' ': case '\t': case ':':
                        strbuf_remove(subject, 0, 1);
                        continue;
                case '[':
                        if ((pos = strchr(subject->buf, ']'))) {
                                remove = pos - subject->buf;
                                if (remove <= (subject->len - remove) * 2) {
                                        strbuf_remove(subject, 0, remove + 1);
                                        continue;
                                }
                        } else
                                strbuf_remove(subject, 0, 1);
                        break;
                }
                strbuf_trim(subject);
                return;
        }
}

static void cleanup_space(struct strbuf *sb)
{
        size_t pos, cnt;
        for (pos = 0; pos < sb->len; pos++) {
                if (isspace(sb->buf[pos])) {
                        sb->buf[pos] = ' ';
                        for (cnt = 0; isspace(sb->buf[pos + cnt + 1]); cnt++);
                        strbuf_remove(sb, pos + 1, cnt);
                }
        }
}

static void decode_header(struct strbuf *line);
static const char *header[MAX_HDR_PARSED] = {
        "From","Subject","Date",
};

static inline int cmp_header(const struct strbuf *line, const char *hdr)
{
        int len = strlen(hdr);
        return !strncasecmp(line->buf, hdr, len) && line->len > len &&
                        line->buf[len] == ':' && isspace(line->buf[len + 1]);
}

static int check_header(const struct strbuf *line,
                                struct strbuf *hdr_data[], int overwrite)
{
        int i, ret = 0, len;
        struct strbuf sb = STRBUF_INIT;
        /* search for the interesting parts */
        for (i = 0; header[i]; i++) {
                int len = strlen(header[i]);
                if ((!hdr_data[i] || overwrite) && cmp_header(line, header[i])) {
                        /* Unwrap inline B and Q encoding, and optionally
                         * normalize the meta information to utf8.
                         */
                        strbuf_add(&sb, line->buf + len + 2, line->len - len - 2);
                        decode_header(&sb);
                        handle_header(&hdr_data[i], &sb);
                        ret = 1;
                        goto check_header_out;
                }
        }

        /* Content stuff */
        if (cmp_header(line, "Content-Type")) {
                len = strlen("Content-Type: ");
                strbuf_add(&sb, line->buf + len, line->len - len);
                decode_header(&sb);
                strbuf_insert(&sb, 0, "Content-Type: ", len);
                handle_content_type(&sb);
                ret = 1;
                goto check_header_out;
        }
        if (cmp_header(line, "Content-Transfer-Encoding")) {
                len = strlen("Content-Transfer-Encoding: ");
                strbuf_add(&sb, line->buf + len, line->len - len);
                decode_header(&sb);
                handle_content_transfer_encoding(&sb);
                ret = 1;
                goto check_header_out;
        }

        /* for inbody stuff */
        if (!prefixcmp(line->buf, ">From") && isspace(line->buf[5])) {
                ret = 1; /* Should this return 0? */
                goto check_header_out;
        }
        if (!prefixcmp(line->buf, "[PATCH]") && isspace(line->buf[7])) {
                for (i = 0; header[i]; i++) {
                        if (!memcmp("Subject", header[i], 7)) {
                                handle_header(&hdr_data[i], line);
                                ret = 1;
                                goto check_header_out;
                        }
                }
        }

check_header_out:
        strbuf_release(&sb);
        return ret;
}

static int is_rfc2822_header(const struct strbuf *line)
{
        /*
         * The section that defines the loosest possible
         * field name is "3.6.8 Optional fields".
         *
         * optional-field = field-name ":" unstructured CRLF
         * field-name = 1*ftext
         * ftext = %d33-57 / %59-126
         */
        int ch;
        char *cp = line->buf;

        /* Count mbox From headers as headers */
        if (!prefixcmp(cp, "From ") || !prefixcmp(cp, ">From "))
                return 1;

        while ((ch = *cp++)) {
                if (ch == ':')
                        return 1;
                if ((33 <= ch && ch <= 57) ||
                    (59 <= ch && ch <= 126))
                        continue;
                break;
        }
        return 0;
}

static int read_one_header_line(struct strbuf *line, FILE *in)
{
        /* Get the first part of the line. */
        if (strbuf_getline(line, in, '\n'))
                return 0;

        /*
         * Is it an empty line or not a valid rfc2822 header?
         * If so, stop here, and return false ("not a header")
         */
        strbuf_rtrim(line);
        if (!line->len || !is_rfc2822_header(line)) {
                /* Re-add the newline */
                strbuf_addch(line, '\n');
                return 0;
        }

        /*
         * Now we need to eat all the continuation lines..
         * Yuck, 2822 header "folding"
         */
        for (;;) {
                int peek;
                struct strbuf continuation = STRBUF_INIT;

                peek = fgetc(in); ungetc(peek, in);
                if (peek != ' ' && peek != '\t')
                        break;
                if (strbuf_getline(&continuation, in, '\n'))
                        break;
                continuation.buf[0] = '\n';
                strbuf_rtrim(&continuation);
                strbuf_addbuf(line, &continuation);
        }

        return 1;
}

static struct strbuf *decode_q_segment(const struct strbuf *q_seg, int rfc2047)
{
        const char *in = q_seg->buf;
        int c;
        struct strbuf *out = xmalloc(sizeof(struct strbuf));
        strbuf_init(out, q_seg->len);

        while ((c = *in++) != 0) {
                if (c == '=') {
                        int d = *in++;
                        if (d == '\n' || !d)
                                break; /* drop trailing newline */
                        strbuf_addch(out, (hexval(d) << 4) | hexval(*in++));
                        continue;
                }
                if (rfc2047 && c == '_') /* rfc2047 4.2 (2) */
                        c = 0x20;
                strbuf_addch(out, c);
        }
        return out;
}

static struct strbuf *decode_b_segment(const struct strbuf *b_seg)
{
        /* Decode in..ep, possibly in-place to ot */
        int c, pos = 0, acc = 0;
        const char *in = b_seg->buf;
        struct strbuf *out = xmalloc(sizeof(struct strbuf));
        strbuf_init(out, b_seg->len);

        while ((c = *in++) != 0) {
                if (c == '+')
                        c = 62;
                else if (c == '/')
                        c = 63;
                else if ('A' <= c && c <= 'Z')
                        c -= 'A';
                else if ('a' <= c && c <= 'z')
                        c -= 'a' - 26;
                else if ('0' <= c && c <= '9')
                        c -= '0' - 52;
                else if (c == '=') {
                        /* padding is almost like (c == 0), except we do
                         * not output NUL resulting only from it;
                         * for now we just trust the data.
                         */
                        c = 0;
                }
                else
                        continue; /* garbage */
                switch (pos++) {
                case 0:
                        acc = (c << 2);
                        break;
                case 1:
                        strbuf_addch(out, (acc | (c >> 4)));
                        acc = (c & 15) << 4;
                        break;
                case 2:
                        strbuf_addch(out, (acc | (c >> 2)));
                        acc = (c & 3) << 6;
                        break;
                case 3:
                        strbuf_addch(out, (acc | c));
                        acc = pos = 0;
                        break;
                }
        }
        return out;
}

/*
 * When there is no known charset, guess.
 *
 * Right now we assume that if the target is UTF-8 (the default),
 * and it already looks like UTF-8 (which includes US-ASCII as its
 * subset, of course) then that is what it is and there is nothing
 * to do.
 *
 * Otherwise, we default to assuming it is Latin1 for historical
 * reasons.
 */
static const char *guess_charset(const struct strbuf *line, const char *target_charset)
{
        if (is_encoding_utf8(target_charset)) {
                if (is_utf8(line->buf))
                        return NULL;
        }
        return "latin1";
}

static void convert_to_utf8(struct strbuf *line, const char *charset)
{
        char *out;

        if (!charset || !*charset) {
                charset = guess_charset(line, metainfo_charset);
                if (!charset)
                        return;
        }

        if (!strcmp(metainfo_charset, charset))
                return;
        out = reencode_string(line->buf, metainfo_charset, charset);
        if (!out)
                die("cannot convert from %s to %s\n",
                    charset, metainfo_charset);
        strbuf_attach(line, out, strlen(out), strlen(out));
}

static int decode_header_bq(struct strbuf *it)
{
        char *in, *ep, *cp;
        struct strbuf outbuf = STRBUF_INIT, *dec;
        struct strbuf charset_q = STRBUF_INIT, piecebuf = STRBUF_INIT;
        int rfc2047 = 0;

        in = it->buf;
        while (in - it->buf <= it->len && (ep = strstr(in, "=?")) != NULL) {
                int encoding;
                strbuf_reset(&charset_q);
                strbuf_reset(&piecebuf);
                rfc2047 = 1;

                if (in != ep) {
                        strbuf_add(&outbuf, in, ep - in);
                        in = ep;
                }
                /* E.g.
                 * ep : "=?iso-2022-jp?B?GyR...?= foo"
                 * ep : "=?ISO-8859-1?Q?Foo=FCbar?= baz"
                 */
                ep += 2;

                if (ep - it->buf >= it->len || !(cp = strchr(ep, '?')))
                        goto decode_header_bq_out;

                if (cp + 3 - it->buf > it->len)
                        goto decode_header_bq_out;
                strbuf_add(&charset_q, ep, cp - ep);
                strbuf_tolower(&charset_q);

                encoding = cp[1];
                if (!encoding || cp[2] != '?')
                        goto decode_header_bq_out;
                ep = strstr(cp + 3, "?=");
                if (!ep)
                        goto decode_header_bq_out;
                strbuf_add(&piecebuf, cp + 3, ep - cp - 3);
                switch (tolower(encoding)) {
                default:
                        goto decode_header_bq_out;
                case 'b':
                        dec = decode_b_segment(&piecebuf);
                        break;
                case 'q':
                        dec = decode_q_segment(&piecebuf, 1);
                        break;
                }
                if (metainfo_charset)
                        convert_to_utf8(dec, charset_q.buf);

                strbuf_addbuf(&outbuf, dec);
                strbuf_release(dec);
                free(dec);
                in = ep + 2;
        }
        strbuf_addstr(&outbuf, in);
        strbuf_reset(it);
        strbuf_addbuf(it, &outbuf);
decode_header_bq_out:
        strbuf_release(&outbuf);
        strbuf_release(&charset_q);
        strbuf_release(&piecebuf);
        return rfc2047;
}

static void decode_header(struct strbuf *it)
{
        if (decode_header_bq(it))
                return;
        /* otherwise "it" is a straight copy of the input.
         * This can be binary guck but there is no charset specified.
         */
        if (metainfo_charset)
                convert_to_utf8(it, "");
}

static void decode_transfer_encoding(struct strbuf *line)
{
        struct strbuf *ret;

        switch (transfer_encoding) {
        case TE_QP:
                ret = decode_q_segment(line, 0);
                break;
        case TE_BASE64:
                ret = decode_b_segment(line);
                break;
        case TE_DONTCARE:
        default:
                return;
        }
        strbuf_reset(line);
        strbuf_addbuf(line, ret);
        strbuf_release(ret);
        free(ret);
}

static void handle_filter(struct strbuf *line);

static int find_boundary(void)
{
        while (!strbuf_getline(&line, fin, '\n')) {
                if (*content_top && is_multipart_boundary(&line))
                        return 1;
        }
        return 0;
}

static int handle_boundary(void)
{
        struct strbuf newline = STRBUF_INIT;

        strbuf_addch(&newline, '\n');
again:
        if (line.len >= (*content_top)->len + 2 &&
            !memcmp(line.buf + (*content_top)->len, "--", 2)) {
                /* we hit an end boundary */
                /* pop the current boundary off the stack */
                strbuf_release(*content_top);
                free(*content_top);
                *content_top = NULL;

                /* technically won't happen as is_multipart_boundary()
                   will fail first.  But just in case..
                 */
                if (--content_top < content) {
                        fprintf(stderr, "Detected mismatched boundaries, "
                                        "can't recover\n");
                        exit(1);
                }
                handle_filter(&newline);
                strbuf_release(&newline);

                /* skip to the next boundary */
                if (!find_boundary())
                        return 0;
                goto again;
        }

        /* set some defaults */
        transfer_encoding = TE_DONTCARE;
        strbuf_reset(&charset);
        message_type = TYPE_TEXT;

        /* slurp in this section's info */
        while (read_one_header_line(&line, fin))
                check_header(&line, p_hdr_data, 0);

        strbuf_release(&newline);
        /* replenish line */
        if (strbuf_getline(&line, fin, '\n'))
                return 0;
        strbuf_addch(&line, '\n');
        return 1;
}

static inline int patchbreak(const struct strbuf *line)
{
        size_t i;

        /* Beginning of a "diff -" header? */
        if (!prefixcmp(line->buf, "diff -"))
                return 1;

        /* CVS "Index: " line? */
        if (!prefixcmp(line->buf, "Index: "))
                return 1;

        /*
         * "--- <filename>" starts patches without headers
         * "---<sp>*" is a manual separator
         */
        if (line->len < 4)
                return 0;

        if (!prefixcmp(line->buf, "---")) {
                /* space followed by a filename? */
                if (line->buf[3] == ' ' && !isspace(line->buf[4]))
                        return 1;
                /* Just whitespace? */
                for (i = 3; i < line->len; i++) {
                        unsigned char c = line->buf[i];
                        if (c == '\n')
                                return 1;
                        if (!isspace(c))
                                break;
                }
                return 0;
        }
        return 0;
}

static int handle_commit_msg(struct strbuf *line)
{
        static int still_looking = 1;

        if (!cmitmsg)
                return 0;

        if (still_looking) {
                strbuf_ltrim(line);
                if (!line->len)
                        return 0;
                if ((still_looking = check_header(line, s_hdr_data, 0)) != 0)
                        return 0;
        }

        /* normalize the log message to UTF-8. */
        if (metainfo_charset)
                convert_to_utf8(line, charset.buf);

        if (patchbreak(line)) {
                fclose(cmitmsg);
                cmitmsg = NULL;
                return 1;
        }

        fputs(line->buf, cmitmsg);
        return 0;
}

static void handle_patch(const struct strbuf *line)
{
        fwrite(line->buf, 1, line->len, patchfile);
        patch_lines++;
}

static void handle_filter(struct strbuf *line)
{
        static int filter = 0;

        /* filter tells us which part we left off on */
        switch (filter) {
        case 0:
                if (!handle_commit_msg(line))
                        break;
                filter++;
        case 1:
                handle_patch(line);
                break;
        }
}

static void handle_body(void)
{
        int len = 0;
        struct strbuf prev = STRBUF_INIT;

        /* Skip up to the first boundary */
        if (*content_top) {
                if (!find_boundary())
                        goto handle_body_out;
        }

        do {
                strbuf_setlen(&line, line.len + len);

                /* process any boundary lines */
                if (*content_top && is_multipart_boundary(&line)) {
                        /* flush any leftover */
                        if (prev.len) {
                                handle_filter(&prev);
                                strbuf_reset(&prev);
                        }
                        if (!handle_boundary())
                                goto handle_body_out;
                }

                /* Unwrap transfer encoding */
                decode_transfer_encoding(&line);

                switch (transfer_encoding) {
                case TE_BASE64:
                case TE_QP:
                {
                        struct strbuf **lines, **it, *sb;

                        /* Prepend any previous partial lines */
                        strbuf_insert(&line, 0, prev.buf, prev.len);
                        strbuf_reset(&prev);

                        /* binary data most likely doesn't have newlines */
                        if (message_type != TYPE_TEXT) {
                                handle_filter(&line);
                                break;
                        }
                        /*
                         * This is a decoded line that may contain
                         * multiple new lines.  Pass only one chunk
                         * at a time to handle_filter()
                         */
                        lines = strbuf_split(&line, '\n');
                        for (it = lines; (sb = *it); it++) {
                                if (*(it + 1) == NULL) /* The last line */
                                        if (sb->buf[sb->len - 1] != '\n') {
                                                /* Partial line, save it for later. */
                                                strbuf_addbuf(&prev, sb);
                                                break;
                                        }
                                handle_filter(sb);
                        }
                        /*
                         * The partial chunk is saved in "prev" and will be
                         * appended by the next iteration of read_line_with_nul().
                         */
                        strbuf_list_free(lines);
                        break;
                }
                default:
                        handle_filter(&line);
                }

                strbuf_reset(&line);
                if (strbuf_avail(&line) < 100)
                        strbuf_grow(&line, 100);
        } while ((len = read_line_with_nul(line.buf, strbuf_avail(&line), fin)));

handle_body_out:
        strbuf_release(&prev);
}

static void output_header_lines(FILE *fout, const char *hdr, const struct strbuf *data)
{
        const char *sp = data->buf;
        while (1) {
                char *ep = strchr(sp, '\n');
                int len;
                if (!ep)
                        len = strlen(sp);
                else
                        len = ep - sp;
                fprintf(fout, "%s: %.*s\n", hdr, len, sp);
                if (!ep)
                        break;
                sp = ep + 1;
        }
}

static void handle_info(void)
{
        struct strbuf *hdr;
        int i;

        for (i = 0; header[i]; i++) {
                /* only print inbody headers if we output a patch file */
                if (patch_lines && s_hdr_data[i])
                        hdr = s_hdr_data[i];
                else if (p_hdr_data[i])
                        hdr = p_hdr_data[i];
                else
                        continue;

                if (!memcmp(header[i], "Subject", 7)) {
                        if (!keep_subject) {
                                cleanup_subject(hdr);
                                cleanup_space(hdr);
                        }
                        output_header_lines(fout, "Subject", hdr);
                } else if (!memcmp(header[i], "From", 4)) {
                        handle_from(hdr);
                        fprintf(fout, "Author: %s\n", name.buf);
                        fprintf(fout, "Email: %s\n", email.buf);
                } else {
                        cleanup_space(hdr);
                        fprintf(fout, "%s: %s\n", header[i], hdr->buf);
                }
        }
        fprintf(fout, "\n");
}

static int mailinfo(FILE *in, FILE *out, int ks, const char *encoding,
                    const char *msg, const char *patch)
{
        int peek;
        keep_subject = ks;
        metainfo_charset = encoding;
        fin = in;
        fout = out;

        cmitmsg = fopen(msg, "w");
        if (!cmitmsg) {
                perror(msg);
                return -1;
        }
        patchfile = fopen(patch, "w");
        if (!patchfile) {
                perror(patch);
                fclose(cmitmsg);
                return -1;
        }

        p_hdr_data = xcalloc(MAX_HDR_PARSED, sizeof(*p_hdr_data));
        s_hdr_data = xcalloc(MAX_HDR_PARSED, sizeof(*s_hdr_data));

        do {
                peek = fgetc(in);
        } while (isspace(peek));
        ungetc(peek, in);

        /* process the email header */
        while (read_one_header_line(&line, fin))
                check_header(&line, p_hdr_data, 1);

        handle_body();
        handle_info();

        return 0;
}

static const char mailinfo_usage[] =
        "git mailinfo [-k] [-u | --encoding=<encoding> | -n] msg patch <mail >info";

int cmd_mailinfo(int argc, const char **argv, const char *prefix)
{
        const char *def_charset;

        /* NEEDSWORK: might want to do the optional .git/ directory
         * discovery
         */
        git_config(git_default_config, NULL);

        def_charset = (git_commit_encoding ? git_commit_encoding : "utf-8");
        metainfo_charset = def_charset;

        while (1 < argc && argv[1][0] == '-') {
                if (!strcmp(argv[1], "-k"))
                        keep_subject = 1;
                else if (!strcmp(argv[1], "-u"))
                        metainfo_charset = def_charset;
                else if (!strcmp(argv[1], "-n"))
                        metainfo_charset = NULL;
                else if (!prefixcmp(argv[1], "--encoding="))
                        metainfo_charset = argv[1] + 11;
                else
                        usage(mailinfo_usage);
                argc--; argv++;
        }

        if (argc != 3)
                usage(mailinfo_usage);

        return !!mailinfo(stdin, stdout, keep_subject, metainfo_charset, argv[1], argv[2]);
}