import path from 'node:path';
import assert from 'node:assert';
import type { Context, EggCore } from '@eggjs/core';
import { ViewManager, type ViewManagerConfig, type RenderOptions } from './view_manager.js';

const RENDER = Symbol.for('contextView#render');
const RENDER_STRING = Symbol.for('contextView#renderString');
const GET_VIEW_ENGINE = Symbol.for('contextView#getViewEngine');
const SET_LOCALS = Symbol.for('contextView#setLocals');

/**
 * View instance for each request.
 *
 * It will find the view engine, and render it.
 * The view engine should be registered in {@link ViewManager}.
 */
export class ContextView {
  protected ctx: Context;
  protected app: EggCore;
  protected viewManager: ViewManager;
  protected config: ViewManagerConfig;

  constructor(ctx: Context) {
    this.ctx = ctx;
    this.app = this.ctx.app;
    this.viewManager = this.app.view;
    this.config = this.app.view.config;
  }

  /**
   * Render a file by view engine
   * @param {String} name - the file path based on root
   * @param {Object} [locals] - data used by template
   * @param {Object} [options] - view options, you can use `options.viewEngine` to specify view engine
   * @return {Promise<String>} result - return a promise with a render result
   */
  async render(name: string, locals?: Record<string, any>, options?: RenderOptions): Promise<string> {
    return await this[RENDER](name, locals, options);
  }

  /**
   * Render a template string by view engine
   * @param {String} tpl - template string
   * @param {Object} [locals] - data used by template
   * @param {Object} [options] - view options, you can use `options.viewEngine` to specify view engine
   * @return {Promise<String>} result - return a promise with a render result
   */
  async renderString(tpl: string, locals?: Record<string, any>, options?: RenderOptions): Promise<string> {
    return await this[RENDER_STRING](tpl, locals, options);
  }

  // ext -> viewEngineName -> viewEngine
  async [RENDER](name: string, locals?: Record<string, any>, options: RenderOptions = {}) {
    // retrieve fullpath matching name from `config.root`
    const filename = await this.viewManager.resolve(name);
    options.name = name;
    options.root = filename.replace(path.normalize(name), '').replace(/[\/\\]$/, '');
    options.locals = locals;

    // get the name of view engine,
    // if viewEngine is specified in options, don't match extension
    let viewEngineName = options.viewEngine;
    if (!viewEngineName) {
      const ext = path.extname(filename);
      viewEngineName = this.viewManager.extMap.get(ext);
    }
    // use the default view engine that is configured if no matching above
    if (!viewEngineName) {
      viewEngineName = this.config.defaultViewEngine;
    }
    assert(viewEngineName, `Can't find viewEngine for ${filename}`);

    // get view engine and render
    const viewEngine = this[GET_VIEW_ENGINE](viewEngineName);
    return await viewEngine.render(filename, this[SET_LOCALS](locals), options);
  }

  async [RENDER_STRING](tpl: string, locals?: Record<string, any>, options?: RenderOptions) {
    let viewEngineName = options && options.viewEngine;
    if (!viewEngineName) {
      viewEngineName = this.config.defaultViewEngine;
    }
    assert(viewEngineName, 'Can\'t find viewEngine');

    // get view engine and render
    const viewEngine = this[GET_VIEW_ENGINE](viewEngineName);
    return await viewEngine.renderString(tpl, this[SET_LOCALS](locals), options);
  }

  [GET_VIEW_ENGINE](name: string) {
    // get view engine
    const ViewEngine = this.viewManager.get(name);
    assert(ViewEngine, `Can't find ViewEngine "${name}"`);

    // use view engine to render
    const engine = new ViewEngine(this.ctx);
    return engine;
  }

  /**
   * set locals for view, inject `locals.ctx`, `locals.request`, `locals.helper`
   * @private
   */
  [SET_LOCALS](locals?: Record<string, any>) {
    return Object.assign({
      ctx: this.ctx,
      request: this.ctx.request,
      helper: this.ctx.helper,
    }, this.ctx.locals, locals);
  }
}