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

static FILE *cmitmsg, *patchfile;

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

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;

        while (at > line) {
                char c = at[-1];
                if (isspace(c) || c == '<')
                        break;
                at--;
        }
        dst = email;
        for (;;) {
                unsigned char c = *at;
                if (!c || c == '>' || isspace(c))
                        break;
                *at++ = ' ';
                *dst++ = c;
        }
        *dst++ = 0;

        at = line + strlen(line);
        while (at > line) {
                unsigned char c = *--at;
                if (isalnum(c))
                        break;
                *at = 0;
        }

        at = line;
        for (;;) {
                unsigned char c = *at;
                if (!c)
                        break;
                if (isalnum(c))
                        break;
                at++;
        }

        at = sanity_check(at, email);
        
        strcpy(name, at);
        return 1;
}

static void handle_date(char *line)
{
        strcpy(date, line);
}

static void handle_subject(char *line)
{
        strcpy(subject, line);
}

static void check_line(char *line, int len)
{
        if (!memcmp(line, "From:", 5) && isspace(line[5]))
                handle_from(line+6);
        else if (!memcmp(line, "Date:", 5) && isspace(line[5]))
                handle_date(line+6);
        else if (!memcmp(line, "Subject:", 8) && isspace(line[8]))
                handle_subject(line+9);
}

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;
                        }
                }
        }
}

static void handle_rest(void)
{
        FILE *out = cmitmsg;
        char *sub = cleanup_subject(subject);
        cleanup_space(name);
        cleanup_space(date);
        cleanup_space(email);
        cleanup_space(sub);
        printf("Author: %s\nEmail: %s\nSubject: %s\nDate: %s\n\n", name, email, sub, date);

        do {
                if (!memcmp("diff -", line, 6) ||
                    !memcmp("---", line, 3) ||
                    !memcmp("Index: ", line, 7))
                        out = patchfile;

                fputs(line, out);
        } while (fgets(line, sizeof(line), stdin) != NULL);

        if (out == cmitmsg) {
                fprintf(stderr, "No patch found\n");
                exit(1);
        }

        fclose(cmitmsg);
        fclose(patchfile);
}

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

static void handle_body(void)
{
        int has_from = 0;
        int has_date = 0;

        /* First lines of body can have From: and Date: */
        while (fgets(line, sizeof(line), stdin) != NULL) {
                int len = eatspace(line);
                if (!len)
                        continue;
                if (!memcmp("From:", line, 5) && isspace(line[5])) {
                        if (!has_from && handle_from(line+6)) {
                                has_from = 1;
                                continue;
                        }
                }
                if (!memcmp("Date:", line, 5) && isspace(line[5])) {
                        if (!has_date) {
                                handle_date(line+6);
                                has_date = 1;
                                continue;
                        }
                }
                line[len] = '\n';
                handle_rest();
                break;
        }
}

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 void usage(void)
{
        fprintf(stderr, "mailinfo msg-file patch-file < email\n");
        exit(1);
}

static const char mailinfo_usage[] =
"git-mailinfo [-k] msg patch <mail >info";
int main(int argc, char ** argv)
{
        while (1 < argc && argv[1][0] == '-') {
                if (!strcmp(argv[1], "-k"))
                        keep_subject = 1;
                else {
                        fprintf(stderr, "usage: %s\n", mailinfo_usage);
                        exit(1);
                }
                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) {
                        handle_body();
                        break;
                }
                check_line(line, len);
        }
        return 0;
}