/*
 * Another stupid program, this one parsing the headers of an
 * email to figure out authorship and subject
 */
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <iconv.h>

static FILE *cmitmsg, *patchfile;

static int keep_subject = 0;
static int metainfo_utf8 = 0;
static char line[1000];
static char date[1000];
static char name[1000];
static char email[1000];
static char subject[1000];

static enum  {
        TE_DONTCARE, TE_QP, TE_BASE64,
} transfer_encoding;
static char charset[256];

static char multipart_boundary[1000];
static int multipart_boundary_len;
static int patch_lines = 0;

static char *sanity_check(char *name, char *email)
{
        int len = strlen(name);
        if (len < 3 || len > 60)
                return email;
        if (strchr(name, '@') || strchr(name, '<') || strchr(name, '>'))
                return email;
        return name;
}

static int handle_from(char *line)
{
        char *at = strchr(line, '@');
        char *dst;

        if (!at)
                return 0;

        /*
         * If we already have one email, don't take any confusing lines
         */
        if (*email && strchr(at+1, '@'))
                return 0;

        /* Pick up the string around '@', possibly delimited with <>
         * pair; that is the email part.  White them out while copying.
         */
        while (at > line) {
                char c = at[-1];
                if (isspace(c))
                        break;
                if (c == '<') {
                        at[-1] = ' ';
                        break;
                }
                at--;
        }
        dst = email;
        for (;;) {
                unsigned char c = *at;
                if (!c || c == '>' || isspace(c)) {
                        if (c == '>')
                                *at = ' ';
                        break;
                }
                *at++ = ' ';
                *dst++ = c;
        }
        *dst++ = 0;

        /* The remainder is name.  It could be "John Doe <john.doe@xz>"
         * or "john.doe@xz (John Doe)", but we have whited out the
         * email part, so trim from both ends, possibly removing
         * the () pair at the end.
         */
        at = line + strlen(line);
        while (at > line) {
                unsigned char c = *--at;
                if (!isspace(c)) {
                        at[(c == ')') ? 0 : 1] = 0;
                        break;
                }
        }

        at = line;
        for (;;) {
                unsigned char c = *at;
                if (!c || !isspace(c)) {
                        if (c == '(')
                                at++;
                        break;
                }
                at++;
        }
        at = sanity_check(at, email);
        strcpy(name, at);
        return 1;
}

static int handle_date(char *line)
{
        strcpy(date, line);
        return 0;
}

static int handle_subject(char *line)
{
        strcpy(subject, line);
        return 0;
}

/* 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, char *attr)
{
        char *ends, *ap = strcasestr(line, name);
        size_t sz;

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

static int handle_subcontent_type(char *line)
{
        /* We do not want to mess with boundary.  Note that we do not
         * handle nested multipart.
         */
        slurp_attr(line, "charset=", charset);
        if (*charset) {
                int i, c;
                for (i = 0; (c = charset[i]) != 0; i++)
                        charset[i] = tolower(c);
        }
        return 0;
}

static int handle_content_type(char *line)
{
        *multipart_boundary = 0;
        if (slurp_attr(line, "boundary=", multipart_boundary + 2)) {
                memcpy(multipart_boundary, "--", 2);
                multipart_boundary_len = strlen(multipart_boundary);
        }
        slurp_attr(line, "charset=", charset);
        return 0;
}

static int handle_content_transfer_encoding(char *line)
{
        if (strcasestr(line, "base64"))
                transfer_encoding = TE_BASE64;
        else if (strcasestr(line, "quoted-printable"))
                transfer_encoding = TE_QP;
        else
                transfer_encoding = TE_DONTCARE;
        return 0;
}

static int is_multipart_boundary(const char *line)
{
        return (!memcmp(line, multipart_boundary, multipart_boundary_len));
}

static int eatspace(char *line)
{
        int len = strlen(line);
        while (len > 0 && isspace(line[len-1]))
                line[--len] = 0;
        return len;
}

#define SEEN_FROM 01
#define SEEN_DATE 02
#define SEEN_SUBJECT 04

/* First lines of body can have From:, Date:, and Subject: */
static int handle_inbody_header(int *seen, char *line)
{
        if (!memcmp("From:", line, 5) && isspace(line[5])) {
                if (!(*seen & SEEN_FROM) && handle_from(line+6)) {
                        *seen |= SEEN_FROM;
                        return 1;
                }
        }
        if (!memcmp("Date:", line, 5) && isspace(line[5])) {
                if (!(*seen & SEEN_DATE)) {
                        handle_date(line+6);
                        *seen |= SEEN_DATE;
                        return 1;
                }
        }
        if (!memcmp("Subject:", line, 8) && isspace(line[8])) {
                if (!(*seen & SEEN_SUBJECT)) {
                        handle_subject(line+9);
                        *seen |= SEEN_SUBJECT;
                        return 1;
                }
        }
        if (!memcmp("[PATCH]", line, 7) && isspace(line[7])) {
                if (!(*seen & SEEN_SUBJECT)) {
                        handle_subject(line);
                        *seen |= SEEN_SUBJECT;
                        return 1;
                }
        }
        return 0;
}

static char *cleanup_subject(char *subject)
{
        if (keep_subject)
                return subject;
        for (;;) {
                char *p;
                int len, remove;
                switch (*subject) {
                case 'r': case 'R':
                        if (!memcmp("e:", subject+1, 2)) {
                                subject +=3;
                                continue;
                        }
                        break;
                case ' ': case '\t': case ':':
                        subject++;
                        continue;

                case '[':
                        p = strchr(subject, ']');
                        if (!p) {
                                subject++;
                                continue;
                        }
                        len = strlen(p);
                        remove = p - subject;
                        if (remove <= len *2) {
                                subject = p+1;
                                continue;
                        }       
                        break;
                }
                return subject;
        }
}                       

static void cleanup_space(char *buf)
{
        unsigned char c;
        while ((c = *buf) != 0) {
                buf++;
                if (isspace(c)) {
                        buf[-1] = ' ';
                        c = *buf;
                        while (isspace(c)) {
                                int len = strlen(buf);
                                memmove(buf, buf+1, len);
                                c = *buf;
                        }
                }
        }
}

typedef int (*header_fn_t)(char *);
struct header_def {
        const char *name;
        header_fn_t func;
        int namelen;
};

static void check_header(char *line, int len, struct header_def *header)
{
        int i;

        if (header[0].namelen <= 0) {
                for (i = 0; header[i].name; i++)
                        header[i].namelen = strlen(header[i].name);
        }
        for (i = 0; header[i].name; i++) {
                int len = header[i].namelen;
                if (!strncasecmp(line, header[i].name, len) &&
                    line[len] == ':' && isspace(line[len + 1])) {
                        header[i].func(line + len + 2);
                        break;
                }
        }
}

static void check_subheader_line(char *line, int len)
{
        static struct header_def header[] = {
                { "Content-Type", handle_subcontent_type },
                { "Content-Transfer-Encoding",
                  handle_content_transfer_encoding },
                { NULL },
        };
        check_header(line, len, header);
}
static void check_header_line(char *line, int len)
{
        static struct header_def header[] = {
                { "From", handle_from },
                { "Date", handle_date },
                { "Subject", handle_subject },
                { "Content-Type", handle_content_type },
                { "Content-Transfer-Encoding",
                  handle_content_transfer_encoding },
                { NULL },
        };
        check_header(line, len, header);
}

static int read_one_header_line(char *line, int sz, FILE *in)
{
        int ofs = 0;
        while (ofs < sz) {
                int peek, len;
                if (fgets(line + ofs, sz - ofs, in) == NULL)
                        return ofs;
                len = eatspace(line + ofs);
                if (len == 0)
                        return ofs;
                peek = fgetc(in); ungetc(peek, in);
                if (peek == ' ' || peek == '\t') {
                        /* Yuck, 2822 header "folding" */
                        ofs += len;
                        continue;
                }
                return ofs + len;
        }
        return ofs;
}

static unsigned hexval(int c)
{
        if (c >= '0' && c <= '9')
                return c - '0';
        if (c >= 'a' && c <= 'f')
                return c - 'a' + 10;
        if (c >= 'A' && c <= 'F')
                return c - 'A' + 10;
        return ~0;
}

static int decode_q_segment(char *in, char *ot, char *ep)
{
        int c;
        while ((c = *in++) != 0 && (in <= ep)) {
                if (c == '=') {
                        int d = *in++;
                        if (d == '\n' || !d)
                                break; /* drop trailing newline */
                        *ot++ = ((hexval(d) << 4) | hexval(*in++));
                }
                else
                        *ot++ = c;
        }
        *ot = 0;
        return 0;
}

static int decode_b_segment(char *in, char *ot, char *ep)
{
        /* Decode in..ep, possibly in-place to ot */
        int c, pos = 0, acc = 0;

        while ((c = *in++) != 0 && (in <= ep)) {
                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:
                        *ot++ = (acc | (c >> 4));
                        acc = (c & 15) << 4;
                        break;
                case 2:
                        *ot++ = (acc | (c >> 2));
                        acc = (c & 3) << 6;
                        break;
                case 3:
                        *ot++ = (acc | c);
                        acc = pos = 0;
                        break;
                }
        }
        *ot = 0;
        return 0;
}

static void convert_to_utf8(char *line, char *charset)
{
        if (*charset) {
                char *in, *out;
                size_t insize, outsize, nrc;
                char outbuf[4096]; /* cheat */
                iconv_t conv = iconv_open("utf-8", charset);

                if (conv == (iconv_t) -1) {
                        fprintf(stderr, "cannot convert from %s to utf-8\n",
                                charset);
                        *charset = 0;
                        return;
                }
                in = line;
                insize = strlen(in);
                out = outbuf;
                outsize = sizeof(outbuf);
                nrc = iconv(conv, &in, &insize, &out, &outsize);
                iconv_close(conv);
                if (nrc == (size_t) -1)
                        return;
                *out = 0;
                strcpy(line, outbuf);
        }
}

static void decode_header_bq(char *it)
{
        char *in, *out, *ep, *cp, *sp;
        char outbuf[1000];

        in = it;
        out = outbuf;
        while ((ep = strstr(in, "=?")) != NULL) {
                int sz, encoding;
                char charset_q[256], piecebuf[256];
                if (in != ep) {
                        sz = ep - in;
                        memcpy(out, in, sz);
                        out += sz;
                        in += sz;
                }
                /* E.g.
                 * ep : "=?iso-2022-jp?B?GyR...?= foo"
                 * ep : "=?ISO-8859-1?Q?Foo=FCbar?= baz"
                 */
                ep += 2;
                cp = strchr(ep, '?');
                if (!cp)
                        return; /* no munging */
                for (sp = ep; sp < cp; sp++)
                        charset_q[sp - ep] = tolower(*sp);
                charset_q[cp - ep] = 0;
                encoding = cp[1];
                if (!encoding || cp[2] != '?')
                        return; /* no munging */
                ep = strstr(cp + 3, "?=");
                if (!ep)
                        return; /* no munging */
                switch (tolower(encoding)) {
                default:
                        return; /* no munging */
                case 'b':
                        sz = decode_b_segment(cp + 3, piecebuf, ep);
                        break;
                case 'q':
                        sz = decode_q_segment(cp + 3, piecebuf, ep);
                        break;
                }
                if (sz < 0)
                        return;
                if (metainfo_utf8)
                        convert_to_utf8(piecebuf, charset_q);
                strcpy(out, piecebuf);
                out += strlen(out);
                in = ep + 2;
        }
        strcpy(out, in);
        strcpy(it, outbuf);
}

static void decode_transfer_encoding(char *line)
{
        char *ep;

        switch (transfer_encoding) {
        case TE_QP:
                ep = line + strlen(line);
                decode_q_segment(line, line, ep);
                break;
        case TE_BASE64:
                ep = line + strlen(line);
                decode_b_segment(line, line, ep);
                break;
        case TE_DONTCARE:
                break;
        }
}

static void handle_info(void)
{
        char *sub;
        static int done_info = 0;

        if (done_info)
                return;

        done_info = 1;
        sub = cleanup_subject(subject);
        cleanup_space(name);
        cleanup_space(date);
        cleanup_space(email);
        cleanup_space(sub);

        /* Unwrap inline B and Q encoding, and optionally
         * normalize the meta information to utf8.
         */
        decode_header_bq(name);
        decode_header_bq(date);
        decode_header_bq(email);
        decode_header_bq(sub);
        printf("Author: %s\nEmail: %s\nSubject: %s\nDate: %s\n\n",
               name, email, sub, date);
}

/* We are inside message body and have read line[] already.
 * Spit out the commit log.
 */
static int handle_commit_msg(void)
{
        if (!cmitmsg)
                return 0;
        do {
                if (!memcmp("diff -", line, 6) ||
                    !memcmp("---", line, 3) ||
                    !memcmp("Index: ", line, 7))
                        break;
                if ((multipart_boundary[0] && is_multipart_boundary(line))) {
                        /* We come here when the first part had only
                         * the commit message without any patch.  We
                         * pretend we have not seen this line yet, and
                         * go back to the loop.
                         */
                        return 1;
                }

                /* Unwrap transfer encoding and optionally
                 * normalize the log message to UTF-8.
                 */
                decode_transfer_encoding(line);
                if (metainfo_utf8)
                        convert_to_utf8(line, charset);
                fputs(line, cmitmsg);
        } while (fgets(line, sizeof(line), stdin) != NULL);
        fclose(cmitmsg);
        cmitmsg = NULL;
        return 0;
}

/* We have done the commit message and have the first
 * line of the patch in line[].
 */
static void handle_patch(void)
{
        do {
                if (multipart_boundary[0] && is_multipart_boundary(line))
                        break;
                /* Only unwrap transfer encoding but otherwise do not
                 * do anything.  We do *NOT* want UTF-8 conversion
                 * here; we are dealing with the user payload.
                 */
                decode_transfer_encoding(line);
                fputs(line, patchfile);
                patch_lines++;
        } while (fgets(line, sizeof(line), stdin) != NULL);
}

/* multipart boundary and transfer encoding are set up for us, and we
 * are at the end of the sub header.  do equivalent of handle_body up
 * to the next boundary without closing patchfile --- we will expect
 * that the first part to contain commit message and a patch, and
 * handle other parts as pure patches.
 */
static int handle_multipart_one_part(void)
{
        int seen = 0;
        int n = 0;
        int len;

        while (fgets(line, sizeof(line), stdin) != NULL) {
        again:
                len = eatspace(line);
                n++;
                if (!len)
                        continue;
                if (is_multipart_boundary(line))
                        break;
                if (0 <= seen && handle_inbody_header(&seen, line))
                        continue;
                seen = -1; /* no more inbody headers */
                line[len] = '\n';
                handle_info();
                if (handle_commit_msg())
                        goto again;
                handle_patch();
                break;
        }
        if (n == 0)
                return -1;
        return 0;
}

static void handle_multipart_body(void)
{
        int part_num = 0;

        /* Skip up to the first boundary */
        while (fgets(line, sizeof(line), stdin) != NULL)
                if (is_multipart_boundary(line)) {
                        part_num = 1;
                        break;
                }
        if (!part_num)
                return;
        /* We are on boundary line.  Start slurping the subhead. */
        while (1) {
                int len = read_one_header_line(line, sizeof(line), stdin);
                if (!len) {
                        if (handle_multipart_one_part() < 0)
                                return;
                }
                else
                        check_subheader_line(line, len);
        }
        fclose(patchfile);
        if (!patch_lines) {
                fprintf(stderr, "No patch found\n");
                exit(1);
        }
}

/* Non multipart message */
static void handle_body(void)
{
        int seen = 0;

        while (fgets(line, sizeof(line), stdin) != NULL) {
                int len = eatspace(line);
                if (!len)
                        continue;
                if (0 <= seen && handle_inbody_header(&seen, line))
                        continue;
                seen = -1; /* no more inbody headers */
                line[len] = '\n';
                handle_info();
                handle_commit_msg();
                handle_patch();
                break;
        }
        fclose(patchfile);
        if (!patch_lines) {
                fprintf(stderr, "No patch found\n");
                exit(1);
        }
}

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

static void usage(void) {
        fprintf(stderr, "%s\n", mailinfo_usage);
        exit(1);
}

int main(int argc, char **argv)
{
        while (1 < argc && argv[1][0] == '-') {
                if (!strcmp(argv[1], "-k"))
                        keep_subject = 1;
                else if (!strcmp(argv[1], "-u"))
                        metainfo_utf8 = 1;
                else
                        usage();
                argc--; argv++;
        }

        if (argc != 3)
                usage();
        cmitmsg = fopen(argv[1], "w");
        if (!cmitmsg) {
                perror(argv[1]);
                exit(1);
        }
        patchfile = fopen(argv[2], "w");
        if (!patchfile) {
                perror(argv[2]);
                exit(1);
        }
        while (1) {
                int len = read_one_header_line(line, sizeof(line), stdin);
                if (!len) {
                        if (multipart_boundary[0])
                                handle_multipart_body();
                        else
                                handle_body();
                        break;
                }
                check_header_line(line, len);
        }
        return 0;
}