const cache = require('./data-cache');
// 页面各自记录版本，三级页面修改不会被某一个上层页面“消费”掉。
function withDataCache(definition, loaders) {
  const actions = Array.from(new Set([].concat(...Object.keys(loaders).map(name => loaders[name]))));
  Object.keys(loaders).forEach(name => {
    const load = definition[name];
    if (!load) return;
    definition[name] = function(...args) {
      if (!this._dataLoads) this._dataLoads = {};
      const dependencies = loaders[name];
      const signature = cache.signature(dependencies);
      const previous = this._dataLoads[name];
      const key = JSON.stringify(args);
      if (previous && previous.pending && (previous.signature !== signature || previous.key !== key)) {
        return previous.pending.then(() => this[name](...args));
      }
      const ttl = Math.min(...dependencies.map(action => cache.policies[action] || cache.TTL));
      if (previous && previous.signature === signature && previous.key === key) {
        if (previous.pending) return previous.pending;
        if (Date.now() - previous.time < ttl && !this.data.loadError && !this.data.homeError && !this.data.statsError && !this.data.bindingError && !this.data.commentsError) return Promise.resolve();
      }
      const record = { signature, key, time: 0 };
      this._dataLoads[name] = record;
      record.pending = Promise.resolve().then(() => load.apply(this, args)).then(result => {
        if (!this.data.loadError && !this.data.homeError && !this.data.statsError && !this.data.bindingError && !this.data.commentsError) {
          record.time = Date.now();
          if (name !== 'loadComments') this._hasCachedData = true;
        }
        record.pending = null;
        return result;
      }, error => { record.pending = null; throw error; });
      return record.pending;
    };
  });
  ['onPullDownRefresh', 'onRefresh'].forEach(name => {
    const refresh = definition[name];
    if (refresh) definition[name] = function(...args) {
      cache.invalidate(actions);
      return refresh.apply(this, args);
    };
  });
  return definition;
}
module.exports = { withDataCache };