import {
  RESOLUTION,
  TPS,
} from '@/constants.js';
import Ecs from '@/ecs/ecs.js';
import {decode, encode} from '@/packets/index.js';
import Script from '@/util/script.js';

import createEcs from './create-ecs.js';
import createForest from './create-forest.js';
import createHomestead from './create-homestead.js';
import createHouse from './create-house.js';
import createPlayer from './create-player.js';

import {LRUCache} from 'lru-cache';

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

export default class Engine {

  connectedPlayers = new Map();
  ecses = {};
  frame = 0;
  handle;
  incomingActions = new Map();
  last = Date.now();
  server;

  constructor(Server) {
    this.ecses = {};
    class SilphiusServer extends Server {
      accept(connection, packed) {
        super.accept(connection, decode(packed));
      }
      transmit(connection, packet) {
        super.transmit(connection, encode(packet));
      }
    }
    const engine = this;
    const server = this.server = new SilphiusServer();
    this.Ecs = class EngineEcs extends Ecs {
      get frame() {
        return engine.frame;
      }
      async readAsset(uri) {
        if (!cache.has(uri)) {
          let promise, resolve, reject;
          promise = new Promise((res, rej) => {
            resolve = res;
            reject = rej;
          });
          cache.set(uri, promise);
          server.readAsset(uri)
            .then(resolve)
            .catch(reject);
        }
        return cache.get(uri);
      }
      async readJson(uri) {
        const key = ['$$json', uri].join(':');
        if (!cache.has(key)) {
          let promise, resolve, reject;
          promise = new Promise((res, rej) => {
            resolve = res;
            reject = rej;
          });
          cache.set(key, promise);
          this.readAsset(uri)
            .then((chars) => {
              resolve(chars.byteLength > 0 ? JSON.parse((new TextDecoder()).decode(chars)) : {});
            })
            .catch(reject);
        }
        return cache.get(key);
      }
      async readScript(uri, context) {
        if (!uri) {
          return undefined;
        }
        const code = await this.readAsset(uri);
        if (code.byteLength > 0) {
          return Script.fromCode((new TextDecoder()).decode(code), context);
        }
      }
      async switchEcs(entity, path, updates) {
        for (const [connection, connectedPlayer] of engine.connectedPlayers) {
          if (entity !== connectedPlayer.entity) {
            continue;
          }
          // remove entity link to connection to start queueing actions and pause updates
          delete connectedPlayer.entity;
          // forget previous state
          connectedPlayer.memory.clear();
          // inform client of the upcoming change
          server.send(
            connection,
            {
              type: 'EcsChange',
              payload: {},
            },
          );
          // dump entity state with updates for the transition
          const dumped = {
            ...entity.toJSON(),
            Controlled: entity.Controlled,
            Ecs: {path},
            ...updates,
          };
          // remove from old ECS
          this.destroy(entity.id);
          // load if necessary
          if (!engine.ecses[path]) {
            await engine.loadEcs(path);
          }
          // recreate the entity in the new ECS and again associate it with the connection
          connectedPlayer.entity = engine.ecses[path].get(await engine.ecses[path].create(dumped));
        }
      }
    }
    this.server.addPacketListener('Action', (connection, payload) => {
      if (!this.incomingActions.has(connection)) {
        this.incomingActions.set(connection, []);
      }
      this.incomingActions.get(connection).push(payload);
    });
    this.server.addPacketListener('AdminAction', (connection, payload) => {
      // check...
      if (!this.incomingActions.has(connection)) {
        this.incomingActions.set(connection, []);
      }
      this.incomingActions.get(connection).push(payload);
    });
  }

  acceptActions() {
    for (const [connection, payloads] of this.incomingActions) {
      if (!this.connectedPlayers.get(connection)) {
        continue;
      }
      const {entity} = this.connectedPlayers.get(connection);
      if (!entity) {
        continue;
      }
      const {Controlled, Ecs, Interacts, Inventory, Wielder} = entity;
      for (const payload of payloads) {
        switch (payload.type) {
          case 'paint': {
            const ecs = this.ecses[Ecs.path];
            const {TileLayers} = ecs.get(1);
            const {brush, layer: paintLayer, stamp} = payload.value;
            const layer = TileLayers.layer(paintLayer);
            switch (brush) {
              case 0: {
                layer.stamp(stamp.at, stamp.data)
                break;
              }
            }
            break;
          }
          case 'changeSlot': {
            if (!Controlled.locked) {
              Wielder.activeSlot = payload.value - 1;
            }
            break;
          }
          case 'moveUp':
          case 'moveRight':
          case 'moveDown':
          case 'moveLeft': {
            Controlled[payload.type] = payload.value;
            break;
          }
          case 'swapSlots': {
            if (!Controlled.locked) {
              Inventory.swapSlots(...payload.value);
            }
            break;
          }
          case 'use': {
            if (!Controlled.locked) {
              Wielder.useActiveItem(payload.value);
            }
            break;
          }
          case 'interact': {
            if (!Controlled.locked) {
              if (payload.value) {
                if (Interacts.willInteractWith) {
                  const ecs = this.ecses[Ecs.path];
                  const subject = ecs.get(Interacts.willInteractWith);
                  subject.Interactive.interact(entity);
                }
              }
            }
            break;
          }
        }
      }
      this.incomingActions.set(connection, []);
    }
  }

  async connectPlayer(connection, id) {
    const entityJson = await this.loadPlayer(id);
    if (!this.ecses[entityJson.Ecs.path]) {
      await this.loadEcs(entityJson.Ecs.path);
    }
    const ecs = this.ecses[entityJson.Ecs.path];
    const entity = await ecs.create(entityJson);
    this.connectedPlayers.set(
      connection,
      {
        entity: ecs.get(entity),
        id,
        memory: new Set(),
      },
    );
  }

  async disconnectPlayer(connection) {
    const connectedPlayer = this.connectedPlayers.get(connection);
    if (!connectedPlayer) {
      return;
    }
    const {entity, id} = connectedPlayer;
    const ecs = this.ecses[entity.Ecs.path];
    await this.savePlayer(id, entity);
    ecs.destroy(entity.id);
    this.connectedPlayers.delete(connection);
    this.incomingActions.delete(connection);
  }

  async load() {
  }

  async loadEcs(path) {
    this.ecses[path] = await this.Ecs.deserialize(
      createEcs(this.Ecs),
      await this.server.readData(path),
    );
  }

  async loadPlayer(id) {
    let buffer;
    try {
      buffer = await this.server.readData(['players', `${id}`].join('/'))
    }
    catch (error) {
      if ('ENOENT' !== error.code) {
        throw error;
      }
      const homestead = await createHomestead(this.Ecs, id);
      await this.saveEcs(
        ['homesteads', `${id}`].join('/'),
        homestead,
      );
      const house = await createHouse(this.Ecs, id);
      await this.saveEcs(
        ['houses', `${id}`].join('/'),
        house,
      );
      const forest = await createForest(this.Ecs, id);
      await this.saveEcs(
        ['forests', `${id}`].join('/'),
        forest,
      );
      buffer = await createPlayer(id);
      await this.server.writeData(
        ['players', `${id}`].join('/'),
        buffer,
      );
    }
    return JSON.parse((new TextDecoder()).decode(buffer));
  }

  async saveEcs(path, ecs) {
    const view = this.Ecs.serialize(ecs);
    await this.server.writeData(path, view);
  }

  async saveEcses() {
    const promises = []
    for (const i in this.ecses) {
      promises.push(this.saveEcs(i, this.ecses[i]));
    }
    await Promise.all(promises);
  }

  async savePlayer(id, entity) {
    const encoder = new TextEncoder();
    const buffer = encoder.encode(JSON.stringify(entity.toJSON()));
    await this.server.writeData(['players', `${id}`].join('/'), buffer);
  }

  setClean() {
    for (const i in this.ecses) {
      this.ecses[i].setClean();
    }
  }

  start() {
    const loop = async () => {
      this.acceptActions();
      const elapsed = (Date.now() - this.last) / 1000;
      this.last = Date.now();
      this.tick(elapsed);
      this.update(elapsed);
      this.setClean();
      this.frame += 1;
      this.handle = setTimeout(loop, 1000 / TPS);
    };
    loop();
  }

  stop() {
    clearTimeout(this.handle);
    this.handle = undefined;
  }

  tick(elapsed) {
    for (const i in this.ecses) {
      this.ecses[i].tick(elapsed);
    }
  }

  update(elapsed) {
    for (const [connection, {entity}] of this.connectedPlayers) {
      if (!entity) {
        continue;
      }
      this.server.send(
        connection,
        {
          type: 'Tick',
          payload: {
            ecs: this.updateFor(connection),
            elapsed,
            frame: this.frame,
          },
        },
      );
    }
  }

  updateFor(connection) {
    const update = {};
    const {entity, memory} = this.connectedPlayers.get(connection);
    const mainEntityId = entity.id;
    const ecs = this.ecses[entity.Ecs.path];
    // Entities within half a screen offscreen.
    const x0 = entity.Position.x - RESOLUTION.x;
    const y0 = entity.Position.y - RESOLUTION.y;
    const nearby = ecs.system('VisibleAabbs').within({
      x0,
      x1: x0 + (RESOLUTION.x * 2),
      y0,
      y1: y0 + (RESOLUTION.y * 2),
    });
    // Master entity.
    nearby.add(ecs.get(1));
    const lastMemory = new Set(memory.values());
    for (const entity of nearby) {
      const {id} = entity;
      lastMemory.delete(id);
      if (!memory.has(id)) {
        update[id] = entity.toJSON();
        if (mainEntityId === id) {
          update[id].MainEntity = {};
        }
      }
      else if (ecs.diff[id]) {
        update[id] = ecs.diff[id];
      }
      memory.add(id);
    }
    for (const id of lastMemory) {
      memory.delete(id);
      update[id] = false;
    }
    return update;
  }

}