import { parse } from 'csv-parse/browser/esm/sync';
import yaml from 'js-yaml';

/**
 * 全局缓存已加载的 CSV 内容
 */
const csvCache = new Map<string, Record<string, string>[]>();

/**
 * 解析 front matter
 * @param content 包含 front matter 的内容
 * @returns 解析结果，包含 front matter 和剩余内容
 */
function parseFrontMatter(content: string): { frontmatter?: JSONObject; remainingContent: string } {
  // 检查是否以 --- 开头
  if (!content.trim().startsWith('---')) {
    return { remainingContent: content };
  }

  // 分割内容
  const parts = content.split(/(?:^|\n)---\s*\n/);
  
  // 至少需要三个部分：空字符串、front matter、剩余内容
  if (parts.length < 3) {
    return { remainingContent: content };
  }

  try {
    // 解析 YAML front matter
    const frontmatterStr = parts[1].trim();
    const frontmatter = yaml.load(frontmatterStr) as JSONObject;
    
    // 剩余内容是第三部分及之后的所有内容
    const remainingContent = parts.slice(2).join('---\n').trimStart();
    
    return { frontmatter, remainingContent };
  } catch (error) {
    console.warn('Failed to parse front matter:', error);
    return { remainingContent: content };
  }
}

/**
 * 加载 CSV 文件
 * @template T 返回数据的类型，默认为 Record<string, string>
 */
export async function loadCSV<T = Record<string, string>>(path: string): Promise<CSV<T>> {
  if (csvCache.has(path)) {
    return csvCache.get(path)! as CSV<T>;
  }

  const response = await fetch(path);
  const content = await response.text();
  
  // 解析 front matter
  const { frontmatter, remainingContent } = parseFrontMatter(content);
  
  const records = parse(remainingContent, {
    columns: true,
    comment: '#',
    trim: true,
    skipEmptyLines: true
  });

  const result = records as Record<string, string>[];
  // 添加 front matter 到结果中
  const csvResult = result as CSV<T>;
  if (frontmatter) {
    csvResult.frontmatter = frontmatter;
    for(const each of result){
      Object.setPrototypeOf(each, frontmatter);
    }
  }
  
  csvCache.set(path, result);
  return csvResult;
}

type JSONData = JSONArray | JSONObject | string | number | boolean | null;
interface JSONArray extends Array<JSONData> {}
interface JSONObject extends Record<string, JSONData> {}

export type CSV<T> = T[] & {
  frontmatter?: JSONObject;
}

export function processVariables<T extends JSONObject> (body: string, currentRow: T, csv: CSV<T>, filtered?: T[], remix?: boolean): string {
  const rolled = filtered || csv;

  function replaceProp(key: string) {
    const row = remix ?
        rolled[Math.floor(Math.random() * rolled.length)] :
        currentRow;
    const frontMatter = csv.frontmatter;
    if(key in row) return row[key];
    if(frontMatter && key in frontMatter) return frontMatter[key];
    return `{{${key}}}`;
  }

  return body.replace(/\{\{(\w+)\}\}/g, (_, key) => `${replaceProp(key)}`);
}