#include "builtin.h"

static void flush_current_id(int patchlen, unsigned char *id, unsigned char *result)
{
        char name[50];

        if (!patchlen)
                return;

        memcpy(name, sha1_to_hex(id), 41);
        printf("%s %s\n", sha1_to_hex(result), name);
}

static int remove_space(char *line)
{
        char *src = line;
        char *dst = line;
        unsigned char c;

        while ((c = *src++) != '\0') {
                if (!isspace(c))
                        *dst++ = c;
        }
        return dst - line;
}

static int scan_hunk_header(const char *p, int *p_before, int *p_after)
{
        static const char digits[] = "0123456789";
        const char *q, *r;
        int n;

        q = p + 4;
        n = strspn(q, digits);
        if (q[n] == ',') {
                q += n + 1;
                n = strspn(q, digits);
        }
        if (n == 0 || q[n] != ' ' || q[n+1] != '+')
                return 0;

        r = q + n + 2;
        n = strspn(r, digits);
        if (r[n] == ',') {
                r += n + 1;
                n = strspn(r, digits);
        }
        if (n == 0)
                return 0;

        *p_before = atoi(q);
        *p_after = atoi(r);
        return 1;
}

static void flush_one_hunk(unsigned char *result, git_SHA_CTX *ctx)
{
        unsigned char hash[20];
        unsigned short carry = 0;
        int i;

        git_SHA1_Final(hash, ctx);
        git_SHA1_Init(ctx);
        /* 20-byte sum, with carry */
        for (i = 0; i < 20; ++i) {
                carry += result[i] + hash[i];
                result[i] = carry;
                carry >>= 8;
        }
}

static int get_one_patchid(unsigned char *next_sha1, unsigned char *result,
                           struct strbuf *line_buf, int stable)
{
        int patchlen = 0, found_next = 0;
        int before = -1, after = -1;
        git_SHA_CTX ctx;

        git_SHA1_Init(&ctx);
        hashclr(result);

        while (strbuf_getwholeline(line_buf, stdin, '\n') != EOF) {
                char *line = line_buf->buf;
                char *p = line;
                int len;

                if (!memcmp(line, "diff-tree ", 10))
                        p += 10;
                else if (!memcmp(line, "commit ", 7))
                        p += 7;
                else if (!memcmp(line, "From ", 5))
                        p += 5;
                else if (!memcmp(line, "\\ ", 2) && 12 < strlen(line))
                        continue;

                if (!get_sha1_hex(p, next_sha1)) {
                        found_next = 1;
                        break;
                }

                /* Ignore commit comments */
                if (!patchlen && memcmp(line, "diff ", 5))
                        continue;

                /* Parsing diff header?  */
                if (before == -1) {
                        if (!memcmp(line, "index ", 6))
                                continue;
                        else if (!memcmp(line, "--- ", 4))
                                before = after = 1;
                        else if (!isalpha(line[0]))
                                break;
                }

                /* Looking for a valid hunk header?  */
                if (before == 0 && after == 0) {
                        if (!memcmp(line, "@@ -", 4)) {
                                /* Parse next hunk, but ignore line numbers.  */
                                scan_hunk_header(line, &before, &after);
                                continue;
                        }

                        /* Split at the end of the patch.  */
                        if (memcmp(line, "diff ", 5))
                                break;

                        /* Else we're parsing another header.  */
                        if (stable)
                                flush_one_hunk(result, &ctx);
                        before = after = -1;
                }

                /* If we get here, we're inside a hunk.  */
                if (line[0] == '-' || line[0] == ' ')
                        before--;
                if (line[0] == '+' || line[0] == ' ')
                        after--;

                /* Compute the sha without whitespace */
                len = remove_space(line);
                patchlen += len;
                git_SHA1_Update(&ctx, line, len);
        }

        if (!found_next)
                hashclr(next_sha1);

        flush_one_hunk(result, &ctx);

        return patchlen;
}

static void generate_id_list(int stable)
{
        unsigned char sha1[20], n[20], result[20];
        int patchlen;
        struct strbuf line_buf = STRBUF_INIT;

        hashclr(sha1);
        while (!feof(stdin)) {
                patchlen = get_one_patchid(n, result, &line_buf, stable);
                flush_current_id(patchlen, sha1, result);
                hashcpy(sha1, n);
        }
        strbuf_release(&line_buf);
}

static const char patch_id_usage[] = "git patch-id [--stable | --unstable] < patch";

static int git_patch_id_config(const char *var, const char *value, void *cb)
{
        int *stable = cb;

        if (!strcmp(var, "patchid.stable")) {
                *stable = git_config_bool(var, value);
                return 0;
        }

        return git_default_config(var, value, cb);
}

int cmd_patch_id(int argc, const char **argv, const char *prefix)
{
        int stable = -1;

        git_config(git_patch_id_config, &stable);

        /* If nothing is set, default to unstable. */
        if (stable < 0)
                stable = 0;

        if (argc == 2 && !strcmp(argv[1], "--stable"))
                stable = 1;
        else if (argc == 2 && !strcmp(argv[1], "--unstable"))
                stable = 0;
        else if (argc != 1)
                usage(patch_id_usage);

        generate_id_list(stable);
        return 0;
}