import { readdir } from "node:fs/promises";

import {
  getBuiltinTemplatesDir,
  getUserTemplatesDir,
  isValidTemplateName,
} from "./load-template.ts";

const TEMPLATE_FILE_EXTENSION = ".md";

export interface TemplateInfo {
  name: string;
  /** 模板来源：用户模板目录或包内内置目录。 */
  source: "user" | "builtin";
}

/** 读取目录中的合法模板名，目录不存在时返回空列表。 */
async function readTemplateNames(dir: string): Promise<string[]> {
  let entries;
  try {
    entries = await readdir(dir, { withFileTypes: true });
  } catch (error) {
    if (error instanceof Error && (error as NodeJS.ErrnoException).code === "ENOENT") {
      return [];
    }
    const detail = error instanceof Error ? error.message : String(error);
    throw new Error(`Failed to read templates directory ${dir}: ${detail}`);
  }

  return entries
    .filter((entry) => entry.isFile() && entry.name.endsWith(TEMPLATE_FILE_EXTENSION))
    .map((entry) => entry.name.slice(0, -TEMPLATE_FILE_EXTENSION.length))
    .filter((name) => isValidTemplateName(name));
}

/** 列出全部可用模板；同名时用户模板覆盖内置模板，用户模板排在内置模板之前，组内按名称排序。 */
export async function listTemplates(): Promise<TemplateInfo[]> {
  const [userNames, builtinNames] = await Promise.all([
    readTemplateNames(getUserTemplatesDir()),
    readTemplateNames(getBuiltinTemplatesDir()),
  ]);

  const templates = new Map<string, TemplateInfo>();
  for (const name of builtinNames) {
    templates.set(name, { name, source: "builtin" });
  }
  for (const name of userNames) {
    templates.set(name, { name, source: "user" });
  }
  return [...templates.values()].sort((a, b) => {
    if (a.source !== b.source) {
      return a.source === "user" ? -1 : 1;
    }
    return a.name.localeCompare(b.name);
  });
}