/* 文件：slice-image.ts — 预览页面切图功能：将渲染完的 HTML 页面转为长图，再按比例裁剪为多张 PNG 图片。 */

import { toPng } from 'html-to-image';
import { Notice, TFile } from 'obsidian';
import { NMPSettings } from './settings';
import * as fs from 'fs';
import * as path from 'path';

/**
 * 解析横竖比例字符串（如 "3:4"）为数值
 */
function parseAspectRatio(ratio: string): { width: number; height: number } {
    const parts = ratio.split(':').map(p => parseFloat(p.trim()));
    if (parts.length === 2 && parts[0] > 0 && parts[1] > 0) {
        return { width: parts[0], height: parts[1] };
    }
    // 默认 3:4
    return { width: 3, height: 4 };
}

/**
 * 从 frontmatter 获取 slug，若不存在则使用文件名（去除扩展名）
 */
function getSlugFromFile(file: TFile, app: any): string {
    const cache = app.metadataCache.getFileCache(file);
    if (cache?.frontmatter?.slug) {
        return String(cache.frontmatter.slug).trim();
    }
    return file.basename;
}

/**
 * 确保目录存在
 */
function ensureDir(dirPath: string) {
    if (!fs.existsSync(dirPath)) {
        fs.mkdirSync(dirPath, { recursive: true });
    }
}

/**
 * 将 base64 dataURL 转为 Buffer
 */
function dataURLToBuffer(dataURL: string): Buffer {
    const base64 = dataURL.split(',')[1];
    return Buffer.from(base64, 'base64');
}

/**
 * 切图主函数
 * @param articleElement 预览文章的 HTML 元素（#article-section）
 * @param file 当前文件
 * @param app Obsidian App 实例
 */
export async function sliceArticleImage(articleElement: HTMLElement, file: TFile, app: any) {
    const settings = NMPSettings.getInstance();
    const { sliceImageSavePath, sliceImageWidth, sliceImageAspectRatio } = settings;

    // 解析比例
    const ratio = parseAspectRatio(sliceImageAspectRatio);
    const sliceHeight = Math.round((sliceImageWidth * ratio.height) / ratio.width);

    // 获取 slug
    const slug = getSlugFromFile(file, app);

    new Notice(`开始切图：${slug}，宽度=${sliceImageWidth}，比例=${sliceImageAspectRatio}`);

    try {
        // 1. 保存原始样式
        const originalWidth = articleElement.style.width;
        const originalMaxWidth = articleElement.style.maxWidth;
        const originalMinWidth = articleElement.style.minWidth;
        
        // 2. 临时设置为目标宽度进行渲染
        articleElement.style.width = `${sliceImageWidth}px`;
        articleElement.style.maxWidth = `${sliceImageWidth}px`;
        articleElement.style.minWidth = `${sliceImageWidth}px`;
        
        // 等待样式生效和重排
        await new Promise(resolve => setTimeout(resolve, 100));
        
        new Notice(`设置渲染宽度: ${sliceImageWidth}px`);

        // 3. 生成长图 - 使用实际渲染宽度
        new Notice('正在生成长图...');
        const longImageDataURL = await toPng(articleElement, {
            width: sliceImageWidth,
            pixelRatio: 1,
            cacheBust: true,
        });

        // 4. 恢复原始样式
        articleElement.style.width = originalWidth;
        articleElement.style.maxWidth = originalMaxWidth;
        articleElement.style.minWidth = originalMinWidth;

        // 5. 创建临时 Image 对象以获取长图实际高度
        const img = new Image();
        await new Promise<void>((resolve, reject) => {
            img.onload = () => resolve();
            img.onerror = reject;
            img.src = longImageDataURL;
        });

        const fullHeight = img.height;
        const fullWidth = img.width;

        new Notice(`长图生成完成：${fullWidth}x${fullHeight}px`);

        // 3. 保存完整长图
        ensureDir(sliceImageSavePath);
        const longImagePath = path.join(sliceImageSavePath, `${slug}.png`);
        const longImageBuffer = dataURLToBuffer(longImageDataURL);
        fs.writeFileSync(longImagePath, new Uint8Array(longImageBuffer));
        new Notice(`长图已保存：${longImagePath}`);

        // 4. 计算需要切多少片
        const sliceCount = Math.ceil(fullHeight / sliceHeight);
        new Notice(`开始切图：共 ${sliceCount} 张，每张 ${sliceImageWidth}x${sliceHeight}px`);

        // 5. 使用 Canvas 裁剪
        const canvas = document.createElement('canvas');
        canvas.width = sliceImageWidth;
        canvas.height = sliceHeight;
        const ctx = canvas.getContext('2d');

        if (!ctx) {
            throw new Error('无法创建 Canvas 上下文');
        }

        for (let i = 0; i < sliceCount; i++) {
            const yOffset = i * sliceHeight;
            const actualHeight = Math.min(sliceHeight, fullHeight - yOffset);

            // 清空画布（处理最后一张可能不足高度的情况，用白色填充）
            ctx.fillStyle = '#ffffff';
            ctx.fillRect(0, 0, sliceImageWidth, sliceHeight);

            // 绘制裁剪区域
            ctx.drawImage(
                img,
                0, yOffset, fullWidth, actualHeight,  // 源区域
                0, 0, sliceImageWidth, actualHeight   // 目标区域
            );

            // 导出为 PNG
            const sliceDataURL = canvas.toDataURL('image/png');
            const sliceBuffer = dataURLToBuffer(sliceDataURL);
            const sliceFilename = `${slug}_${i + 1}.png`;
            const slicePath = path.join(sliceImageSavePath, sliceFilename);
            fs.writeFileSync(slicePath, new Uint8Array(sliceBuffer));

            new Notice(`已保存：${sliceFilename}`);
        }

        new Notice(`✅ 切图完成！共 ${sliceCount} 张图片，保存在：${sliceImageSavePath}`);
    } catch (error) {
        console.error('切图失败:', error);
        new Notice(`❌ 切图失败：${error.message}`);
    }
}