/* rdimg.c — stb_image 封装（实现见 rdimg.h）。 */
#include "rdimg.h"
#include "stb_image.h"
#include <stdlib.h>
#include <string.h>

int rdimg_probe_wh(const uint8_t *data, size_t size, int *w, int *h)
{
    if (!data || !w || !h) return -1;
    int x = 0, y = 0, c = 0;
    if (!stbi_info_from_memory(data, (int)size, &x, &y, &c)) return -1;
    *w = x; *h = y;
    return 0;
}

/* 双线性采样单通道：src 步长 sw，取 (fx,fy) 浮点邻近 4 像素加权。 */
static int bilin(const uint8_t *s, int sw, int sh, double fx, double fy, int ch)
{
    int x0 = (int)fx, y0 = (int)fy;
    double dx = fx - x0, dy = fy - y0;
    int x1 = x0 + 1 < sw ? x0 + 1 : x0;
    int y1 = y0 + 1 < sh ? y0 + 1 : y0;
    double top = s[y0 * sw * ch + x0 * ch] * (1 - dx) + s[y0 * sw * ch + x1 * ch] * dx;
    double bot = s[y1 * sw * ch + x0 * ch] * (1 - dx) + s[y1 * sw * ch + x1 * ch] * dx;
    return (int)(top * (1 - dy) + bot * dy);
}

int rdimg_decode_scale(const uint8_t *data, size_t size, int max_w, int max_h,
                       uint16_t **out565, int *ow, int *oh)
{
    if (!data || !out565) return -1;
    *out565 = NULL; *ow = *oh = 0;
    int w = 0, h = 0, ch = 0;
    /* 请求 RGB（3 通道）便于统一处理 */
    stbi_uc *px = stbi_load_from_memory(data, (int)size, &w, &h, &ch, 3);
    if (!px || w <= 0 || h <= 0) return -1;

    /* 缩放：长边超 max 才缩（不放大） */
    double scale = 1.0;
    if (w > max_w && max_w > 0) scale = (double)max_w / w;
    if (h > max_h && max_h > 0) { double s2 = (double)max_h / h; if (s2 < scale) scale = s2; }
    int dw = (int)(w * scale), dh = (int)(h * scale);
    if (dw < 1) dw = 1;
    if (dh < 1) dh = 1;

    uint16_t *dst = (uint16_t *)malloc((size_t)dw * (size_t)dh * 2);
    if (!dst) { stbi_image_free(px); return -6; }
    if (scale == 1.0) {
        /* 原尺寸直接转 565 */
        for (int yy = 0; yy < dh; yy++) {
            const stbi_uc *s = px + (size_t)yy * w * 3;
            uint16_t *d = dst + (size_t)yy * dw;
            for (int xx = 0; xx < dw; xx++) {
                int r = s[xx*3], g = s[xx*3+1], b = s[xx*3+2];
                d[xx] = (uint16_t)(((r >> 3) << 11) | ((g >> 2) << 5) | (b >> 3));
            }
        }
    } else {
        for (int yy = 0; yy < dh; yy++) {
            double fy = (double)yy / scale;
            uint16_t *d = dst + (size_t)yy * dw;
            for (int xx = 0; xx < dw; xx++) {
                double fx = (double)xx / scale;
                int r = bilin(px, w, h, fx, fy, 3);
                int g = bilin((const uint8_t*)px + 1, w, h, fx, fy, 3);
                int b = bilin((const uint8_t*)px + 2, w, h, fx, fy, 3);
                d[xx] = (uint16_t)(((r >> 3) << 11) | ((g >> 2) << 5) | (b >> 3));
            }
        }
    }
    stbi_image_free(px);
    *out565 = dst; *ow = dw; *oh = dh;
    return 0;
}