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

import Sandbox from '@/astride/sandbox.js';
import TickingPromise from '@/util/ticking-promise.js';
import delta from '@/util/delta.js';
import lfo from '@/util/lfo.js';
import * as MathUtil from '@/util/math.js';
import transition from '@/util/transition.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;
  }

  clone() {
    return new this.constructor(this.sandbox.clone());
  }

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

  static contextDefaults() {
    return {
      console,
      delta,
      lfo,
      Math: MathUtil,
      Promise,
      transition,
      wait: (seconds) => (
        new Promise((resolve) => {
          setTimeout(resolve, seconds * 1000);
        })
      ),
    };
  }

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

  evaluate() {
    this.sandbox.reset();
    const {value} = this.sandbox.run();
    return value;
  }

  static async fromCode(code, context = {}) {
    if (!cache.has(code)) {
      cache.set(code, this.parse(code));
    }
    return new this(
      new Sandbox(await cache.get(code), 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 {async, done, value} = this.sandbox.step();
      if (async) {
        this.promise = value;
        value
          .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);
      },
    );
  }

}