import {parse as acornParse} from 'acorn';
import {LRUCache} from 'lru-cache';

import Sandbox from '@/astride/sandbox.js';
import TickingPromise from '@/util/ticking-promise.js';

function parse(code, options = {}) {
  return acornParse(code, {
    ecmaVersion: 'latest',
    sourceType: 'module',
    ...options,
  })
}

const Populated = Symbol.for('sandbox.populated');

export const cache = new LRUCache({
  max: 128,
});

export default class Script {

  constructor(sandbox) {
    this.sandbox = sandbox;
    this.promise = null;
  }

  get context() {
    return this.sandbox.context;
  }

  static createContext(locals = {}) {
    if (locals[Populated]) {
      return locals;
    }
    return {
      [Populated]: true,
      ...locals,
    };
  }

  // async evaluate(callback) {
  //   this.sandbox.reset();
  //   let {done, value} = this.sandbox.next();
  //   if (value instanceof Promise) {
  //     await value;
  //   }
  //   while (!done) {
  //     ({done, value} = this.sandbox.next());
  //     if (value instanceof Promise) {
  //       // eslint-disable-next-line no-await-in-loop
  //       await value;
  //     }
  //   }
  //   if (value instanceof Promise) {
  //     value.then(callback);
  //   }
  //   else {
  //     callback(value);
  //   }
  // }

  static async fromCode(code, context = {}) {
    let ast;
    if (cache.has(code)) {
      ast = cache.get(code);
    }
    else {
      cache.set(code, ast = await this.parse(code));
    }
    return new this(
      new Sandbox(ast, this.createContext(context)),
    );
  }

  static async parse(code) {
    return parse(
      code,
      {
        allowReturnOutsideFunction: true,
      },
    );
  }

  reset() {
    this.promise = null;
    this.sandbox.compile();
  }

  tick(elapsed, resolve, reject) {
    if (this.promise) {
      if (this.promise instanceof TickingPromise) {
        this.promise.tick(elapsed);
      }
      return;
    }
    while (true) {
      this.sandbox.context.elapsed = elapsed;
      const {done, value} = this.sandbox.step();
      if (value) {
        const {value: result} = value;
        if (result instanceof Promise) {
          this.promise = result;
          result
            .catch(reject)
            .then(() => {
              if (done) {
                resolve();
              }
            })
            .finally(() => {
              this.promise = null;
            });
          break;
        }
      }
      if (done) {
        resolve();
        break;
      }
    }
  }

  tickingPromise() {
    return new TickingPromise(
      () => {},
      (elapsed, resolve, reject) => {
        this.tick(elapsed, resolve, reject);
      },
    );
  }

  static tickingPromise(code, context = {}) {
    let tickingPromise;
    return new TickingPromise(
      (resolve) => {
        this.fromCode(code, context)
          .then((script) => {
            tickingPromise = script.tickingPromise();
            resolve(tickingPromise);
          })
      },
      (elapsed) => {
        tickingPromise?.tick?.(elapsed);
      },
    );
  }

};