/* 扁平 JSON 解析 + 定长写入器。契约与「刻意不支持」的清单在 cmd_json.h。 */
#include "cmd_json.h"

#include <stdio.h>
#include <string.h>

static const char *ws(const char *p)
{
    while (*p == ' ' || *p == '\t' || *p == '\r' || *p == '\n') {
        p++;
    }
    return p;
}

/* 读一个 `"..."`，写进 out（容量 cap，含结尾 0）。返回引号之后的位置，失败 NULL。
   只收可打印 ASCII 之外不做任何解释：反斜杠与控制字符一律失败。 */
static const char *str(const char *p, char *out, size_t cap)
{
    if (*p != '"') {
        return NULL;
    }
    p++;
    size_t n = 0;
    while (*p != '"') {
        const unsigned char c = (unsigned char)*p;
        if (c == '\0' || c == '\\' || c < 0x20) {
            return NULL;
        }
        if (n + 1 >= cap) {
            return NULL; /* 太长：截断会把 "set_voltage_x" 读成别的东西 */
        }
        out[n++] = (char)c;
        p++;
    }
    out[n] = '\0';
    return p + 1;
}

static const char *num(const char *p, int64_t *v)
{
    bool neg = false;
    if (*p == '-') {
        neg = true;
        p++;
    }
    if (*p < '0' || *p > '9') {
        return NULL;
    }
    if (*p == '0' && p[1] >= '0' && p[1] <= '9') {
        return NULL; /* 前导零：JSON 本身就不许，也防 "010" 被当成八进制理解 */
    }
    int64_t acc = 0;
    int     digits = 0;
    while (*p >= '0' && *p <= '9') {
        if (++digits > 18) {
            return NULL;
        }
        acc = acc * 10 + (*p - '0');
        p++;
    }
    if (*p == '.' || *p == 'e' || *p == 'E') {
        return NULL; /* 浮点：见头文件 */
    }
    *v = neg ? -acc : acc;
    return p;
}

static bool word(const char **pp, const char *w)
{
    const size_t n = strlen(w);
    if (strncmp(*pp, w, n) != 0) {
        return false;
    }
    *pp += n;
    return true;
}

static const cj_field_t *find(const cj_obj_t *o, const char *key)
{
    for (int i = 0; i < o->n; i++) {
        if (strcmp(o->f[i].key, key) == 0) {
            return &o->f[i];
        }
    }
    return NULL;
}

bool cj_parse(const char *line, cj_obj_t *o)
{
    memset(o, 0, sizeof(*o));
    if (line == NULL) {
        return false;
    }
    const char *p = ws(line);
    if (*p++ != '{') {
        return false;
    }
    p = ws(p);
    if (*p == '}') {
        p++;
    } else {
        for (;;) {
            if (o->n >= CMD_JSON_MAX_FIELDS) {
                return false;
            }
            cj_field_t *f = &o->f[o->n];
            p = str(p, f->key, sizeof(f->key));
            if (p == NULL || f->key[0] == '\0' || find(o, f->key) != NULL) {
                return false; /* 解析失败 / 空键 / 重复键 */
            }
            p = ws(p);
            if (*p++ != ':') {
                return false;
            }
            p = ws(p);
            if (*p == '"') {
                f->type = CJ_STR;
                p = str(p, f->s, sizeof(f->s));
            } else if (word(&p, "true")) {
                f->type = CJ_BOOL;
                f->i = 1;
            } else if (word(&p, "false")) {
                f->type = CJ_BOOL;
                f->i = 0;
            } else {
                f->type = CJ_INT;
                p = num(p, &f->i);
            }
            if (p == NULL) {
                return false;
            }
            o->n++;
            p = ws(p);
            if (*p == ',') {
                p = ws(p + 1);
                continue;
            }
            if (*p == '}') {
                p++;
                break;
            }
            return false;
        }
    }
    return *ws(p) == '\0'; /* 右括号之后只许有空白：两条命令粘在一行里是分帧的 bug */
}

int cj_get_int(const cj_obj_t *o, const char *key, int64_t *v)
{
    const cj_field_t *f = find(o, key);
    if (f == NULL) {
        return 0;
    }
    if (f->type != CJ_INT) {
        return -1;
    }
    *v = f->i;
    return 1;
}

int cj_get_str(const cj_obj_t *o, const char *key, const char **s)
{
    const cj_field_t *f = find(o, key);
    if (f == NULL) {
        return 0;
    }
    if (f->type != CJ_STR) {
        return -1;
    }
    *s = f->s;
    return 1;
}

int cj_get_bool(const cj_obj_t *o, const char *key, bool *v)
{
    const cj_field_t *f = find(o, key);
    if (f == NULL) {
        return 0;
    }
    if (f->type != CJ_BOOL) {
        return -1; /* `"on":1` 不是布尔。收 1 的话 `"on":2` 该算什么就说不清了 */
    }
    *v = f->i != 0;
    return 1;
}

void cj_w_init(cj_writer_t *w, char *buf, size_t cap)
{
    w->buf = buf;
    w->cap = cap;
    w->pos = 0;
    w->overflow = (buf == NULL || cap == 0);
    if (!w->overflow) {
        buf[0] = '\0';
    }
}

void cj_w(cj_writer_t *w, const char *fmt, ...)
{
    if (w->overflow) {
        return;
    }
    va_list ap;
    va_start(ap, fmt);
    const int n = vsnprintf(w->buf + w->pos, w->cap - w->pos, fmt, ap);
    va_end(ap);
    if (n < 0 || (size_t)n >= w->cap - w->pos) {
        w->overflow = true;
        w->buf[w->pos] = '\0'; /* 把写了一半的那段撤掉 */
        return;
    }
    w->pos += (size_t)n;
}