#include "builtin.h"

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

        if (!patchlen)
                return;

        memcpy(name, oid_to_hex(id), GIT_SHA1_HEXSZ + 1);
        printf("%s %s\n", oid_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(struct object_id *result, git_SHA_CTX *ctx)
{
        unsigned char hash[GIT_SHA1_RAWSZ];
        unsigned short carry = 0;
        int i;

        git_SHA1_Final(hash, ctx);
        git_SHA1_Init(ctx);
        /* 20-byte sum, with carry */
        for (i = 0; i < GIT_SHA1_RAWSZ; ++i) {
                carry += result->hash[i] + hash[i];
                result->hash[i] = carry;
                carry >>= 8;
        }
}

static int get_one_patchid(struct object_id *next_oid, struct object_id *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);
        oidclr(result);

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

                if (!skip_prefix(line, "diff-tree ", &p) &&
                    !skip_prefix(line, "commit ", &p) &&
                    !skip_prefix(line, "From ", &p) &&
                    starts_with(line, "\\ ") && 12 < strlen(line))
                        continue;

                if (!get_oid_hex(p, next_oid)) {
                        found_next = 1;
                        break;
                }

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

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

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

                        /* Split at the end of the patch.  */
                        if (!starts_with(line, "diff "))
                                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)
                oidclr(next_oid);

        flush_one_hunk(result, &ctx);

        return patchlen;
}

static void generate_id_list(int stable)
{
        struct object_id oid, n, result;
        int patchlen;
        struct strbuf line_buf = STRBUF_INIT;

        oidclr(&oid);
        while (!feof(stdin)) {
                patchlen = get_one_patchid(&n, &result, &line_buf, stable);
                flush_current_id(patchlen, &oid, &result);
                oidcpy(&oid, &n);
        }
        strbuf_release(&line_buf);
}

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

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;
}