/* reduce.c - 把 fuzz 找到的失败输入最小化到最短复现样例
 *
 * 判定 (oracle): 同一段输入, "一次性喂" 与 "逐字节喂" 的渲染结果不一致.
 * 用法:  build/reduce build/md_fail.bin
 */
#include "markdown.h"
#include "util.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* 注意: md_feed 只接受 NUL 结尾的字符串, 而最小化过程中的缓冲区
 * 是"长度受限"的, 所以必须先做一份带结尾符的副本.  */
static char *render(const char *src, size_t len, size_t chunk) {
    char *text = xmalloc(len + 1);
    memcpy(text, src, len);
    text[len] = '\0';

    char *buf = NULL;
    size_t size = 0;
    FILE *f = open_memstream(&buf, &size);
    if (!f) {
        free(text);
        return NULL;
    }
    MdRenderer *r = md_new(1);
    md_set_out(r, f);
    if (chunk == 0) {
        md_feed(r, text);
    } else {
        for (size_t i = 0; i < len; i += chunk) {
            size_t n = len - i < chunk ? len - i : chunk;
            char *t = xstrndup(text + i, n);
            md_feed(r, t);
            free(t);
        }
    }
    md_finish(r);
    md_free(r);
    fclose(f);
    free(text);
    return buf;
}

/* 只要"一次性"与"逐字节"不一致就算失败 */
static int fails(const char *src, size_t len) {
    if (len == 0)
        return 0;
    /* md_feed 以 NUL 结尾, 输入里不能有 NUL */
    for (size_t i = 0; i < len; i++)
        if (src[i] == '\0')
            return 0;
    char *a = render(src, len, 0);
    char *b = render(src, len, 1);
    int bad = (a && b && strcmp(a, b) != 0);
    if (bad) {
        /* 确认真的不是"空输出 vs 空输出"这种假阳性 */
        if (strcmp(a, b) == 0)
            bad = 0;
    }
    free(a);
    free(b);
    return bad;
}

static void show(const char *label, const char *buf, size_t len) {
    printf("%s (%zu 字节): ", label, len);
    for (size_t i = 0; i < len; i++) {
        unsigned char c = (unsigned char)buf[i];
        if (c == '\n')
            printf("\\n");
        else if (c == '\t')
            printf("\\t");
        else if (c == 0x1b)
            printf("<ESC>");
        else if (c >= 0x20 && c < 0x7f)
            putchar(c);
        else
            printf("\\x%02x", c);
    }
    putchar('\n');
}

int main(int argc, char **argv) {
    if (argc < 2) {
        fputs("用法: reduce <失败输入文件>\n", stderr);
        return 2;
    }
    size_t len = 0;
    char *buf = read_entire_file(argv[1], &len);
    if (!buf) {
        perror("读取失败");
        return 2;
    }
    if (!fails(buf, len)) {
        puts("该输入当前不复现失败");
        free(buf);
        return 1;
    }

    puts("== 原始失败输入 ==");
    show("  ", buf, len);
    {
        char *a = render(buf, len, 0), *b = render(buf, len, 1);
        show("  一次性", a, strlen(a));
        show("  逐字节", b, strlen(b));
        free(a);
        free(b);
    }

    /* 贪心块删除 */
    size_t gran = len / 2;
    while (gran >= 1) {
        size_t i = 0;
        while (i + gran <= len) {
            char *save = xmalloc(gran);
            memcpy(save, buf + i, gran);
            memmove(buf + i, buf + i + gran, len - i - gran);
            if (fails(buf, len - gran)) {
                len -= gran;
            } else {
                memmove(buf + i + gran, buf + i, len - i - gran);
                memcpy(buf + i, save, gran);
                i += gran;
            }
            free(save);
        }
        if (gran == 1)
            break;
        gran /= 2;
    }

    printf("\n== 最小复现样例 (%zu 字节) ==\n", len);
    show("  ", buf, len);
    {
        char *a = render(buf, len, 0), *b = render(buf, len, 1);
        show("  一次性", a, strlen(a));
        show("  逐字节", b, strlen(b));
        free(a);
        free(b);
    }
    free(buf);
    return 0;
}