import React from 'react';
import firebase from 'firebase/app';
import equal from 'deep-equal';

function filterKeys(raw, allowed) {
  if (!raw) {
    return raw;
  }
  let s = new Set(allowed);
  return Object.keys(raw)
    .filter(key => s.has(key))
    .reduce((obj, key) => {
      obj[key] = raw[key];
      return obj;
    }, {});
}

function parseSpec(spec) {
  let {template} = spec;
  let starts = template.split('{')
  starts.shift();
  let propIds = [];
  for (let start of starts) {
    propIds.push(start.split('}')[0]);
  }
  let formatPath = (props) => {
    let vals = props;
    let path = template;
    for (let key of Object.keys(vals)) {
      if (!vals[key] && path.includes(`{${key}}`)) {
        return null;
      }
      path = path.replace(`{${key}}`, vals[key]);
    }
    return path;
  }
  return { propIds, formatPath };
}

export function withDbData(specs) {
  let propToSpecs = {};
  for (let spec of specs) {
    let {propIds} = parseSpec(spec);
    for (let propId of propIds) {
      if (!propToSpecs[propId]) {
        propToSpecs[propId] = [];
      }
      propToSpecs[propId].push(spec);
    }
  }

  return (Child) => {
    let Wrapper = class extends React.PureComponent {
      constructor(props) {
        super(props);
        this.unmounting = false;
        this.offs = {};
        this.state = {};
      }
      subscribeToSpec(spec) {
        let { name, keys } = spec;
        let { propIds, formatPath } = parseSpec(spec);
        let path = formatPath(this.props);
        if (!path) {
          return;
        }
        let ref = firebase.database().ref(path);
        let offFunc = ref.on('value', (snap) => {
          let dat = keys ? filterKeys(snap.val(), keys) : snap.val();
          if (equal(dat, this.state[name])) {
            return;
          }
          this.setState({
            [name]: dat,
          });
        });
        let hasBeenOffed = false;
        let off = () => {
          if (hasBeenOffed) {
            return;
          }
          hasBeenOffed = true;
          if (!this.unmounting) {
            this.setState({
              [name]: null,
            });
          }
          ref.off('value', offFunc);
        };
        for (let propId of propIds) {
          if (!this.offs[propId]) {
            this.offs[propId] = [];
          }
          this.offs[propId].push(off)
        }
      }
      componentDidMount() {
        for (let spec of specs) {
          this.subscribeToSpec(spec)
        }
      }
      componentDidUpdate(prevProps) {
        let resubs = new Set();
        for (let prop of Object.keys(propToSpecs)) {
          if (prevProps[prop] !== this.props[prop]) {
            if (this.offs[prop]) {
              for (let off of this.offs[prop]) {
                off();
              }
            }
            this.offs[prop] = [];
            for (let spec of propToSpecs[prop]) {
              if (resubs.has(spec.name)) {
                continue;
              }
              resubs.add(spec.name);
              this.subscribeToSpec(spec);
            }
          }
        }
      }
      componentWillUnmount() {
        this.unmounting = true;
        for (let offList of Object.values(this.offs)) {
          for (let off of offList) {
            off();
          }
        }
        this.offs = {};
      }
      render() {
        for (let spec of specs) {
          if (spec.await && !this.state[spec.name]) {
            return null;
          }
        }
        let childProps = Object.assign({}, this.props, this.state);
        return (<Child {... childProps} />);
      }
    }
    return Wrapper;
  }
}