import { Injectable, NotFoundException } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';
import { Character } from '../characters/entities/character.entity';
import { calculateDangerRating, DangerRating } from '../hunting/danger-rating';
import { LocationMonster } from '../monsters/entities/location-monster.entity';
import { TravelService } from '../travel/travel.service';
import { WorldDiscoveryService } from './discovery/world-discovery.service';
import { LocationConnection } from './entities/location-connection.entity';
import { LocationDefinition } from './entities/location-definition.entity';
import {
  EncounterPreviewDto,
  LocalLocationPointOfInterestDto,
  LocalLocationPrimaryActionDto,
  LocationInteractionResultDto,
  LocationType,
  RewardPreviewDto,
  toPointOfInterestDto,
} from './local-location.types';
import { locationInteractionUnavailable } from './world.errors';

export interface LocationSummary {
  id: string;
  key: string;
  name: string;
}

export interface CurrentLocationConnection {
  targetLocation: LocationSummary;
  travelDurationSeconds: number;
  danger: 'LOW' | 'HIGH';
}

export interface CurrentLocationResponse {
  id: string;
  key: string;
  name: string;
  description: string;
  regionKey: string;
  minRecommendedLevel: number;
  maxRecommendedLevel: number;
  dangerLevel: number;
  isSafe: boolean;
  huntingEnabled: boolean;
  artworkPath: string;
  regionName: string;
  regionTierLabel: string;
  locationType: LocationType;
  localDescription: string;
  localArtworkPath: string;
  /** `null` where nothing hostile can be met — the view reads that as safe. */
  dangerRating: DangerRating | null;
  recommendationLabel: string;
  pointsOfInterest: LocalLocationPointOfInterestDto[];
  primaryActions: LocalLocationPrimaryActionDto[];
  encounterPreview: EncounterPreviewDto[];
  rewardPreview: RewardPreviewDto[];
  connections: CurrentLocationConnection[];
  possibleMonsters: string[];
}

@Injectable()
export class WorldService {
  constructor(
    private readonly travelService: TravelService,
    @InjectRepository(Character)
    private readonly characters: Repository<Character>,
    @InjectRepository(LocationConnection)
    private readonly connections: Repository<LocationConnection>,
    @InjectRepository(LocationMonster)
    private readonly locationMonsters: Repository<LocationMonster>,
    private readonly worldDiscovery: WorldDiscoveryService,
  ) {}

  async getCurrentLocation(
    characterId: string,
  ): Promise<CurrentLocationResponse> {
    const character = await this.loadCharacterAtCurrentLocation(characterId);

    const connections = await this.connections.find({
      where: { fromLocationId: character.currentLocationId, enabled: true },
      relations: { toLocation: true },
    });
    const location = character.currentLocation;

    const pool = location.huntingEnabled
      ? await this.getEncounterPool(location.id)
      : [];

    // Loaded once per request rather than per connection: `isRouteOpen` is
    // synchronous, so a location with several gated exits costs one query
    // here instead of one per gated connection.
    const discoveredLocationIds =
      await this.worldDiscovery.getDiscoveredLocationIds(characterId);
    const visibleConnections = connections.filter(
      (connection) =>
        connection.enabled &&
        this.worldDiscovery.isRouteOpen(discoveredLocationIds, connection),
    );

    return {
      id: location.id,
      key: location.key,
      name: location.name,
      description: location.description,
      regionKey: location.regionKey,
      minRecommendedLevel: location.minRecommendedLevel,
      maxRecommendedLevel: location.maxRecommendedLevel,
      dangerLevel: location.dangerLevel,
      isSafe: location.isSafe,
      huntingEnabled: location.huntingEnabled,
      artworkPath: location.artworkPath,
      regionName: location.regionName,
      regionTierLabel: location.regionTierLabel,
      locationType: location.locationType,
      localDescription: location.localDescription,
      localArtworkPath: location.localArtworkPath,
      dangerRating: this.toLocalDangerRating(character, pool),
      recommendationLabel: this.toRecommendationLabel(location),
      pointsOfInterest:
        location.localPointsOfInterest.map(toPointOfInterestDto),
      primaryActions: location.localPrimaryActions,
      encounterPreview: pool.map((entry) => ({
        key: entry.monster.key,
        name: entry.monster.name,
        level: entry.monster.level,
        iconPath: entry.monster.iconPath,
      })),
      rewardPreview: location.localRewardPreview,
      connections: visibleConnections.map((connection) => ({
        targetLocation: {
          id: connection.toLocation.id,
          key: connection.toLocation.key,
          name: connection.toLocation.name,
        },
        travelDurationSeconds: connection.travelDurationSeconds,
        danger: this.toDangerRating(connection.ambushChance),
      })),
      possibleMonsters: pool.map((entry) => entry.monster.name),
    };
  }

  /**
   * Runs a short local interaction (investigate, search, talk) and reveals its
   * authored result.
   *
   * The location is taken from the character, never from the request, so a
   * caller cannot reach a hotspot it has not travelled to. Hotspots that only
   * navigate (HUNT, MAP) carry no result text and are rejected here — the
   * client routes those itself.
   */
  async runLocalInteraction(
    characterId: string,
    interactionKey: string,
  ): Promise<LocationInteractionResultDto> {
    const character = await this.loadCharacterAtCurrentLocation(characterId);

    const poi = character.currentLocation.localPointsOfInterest.find(
      (candidate) => candidate.key === interactionKey,
    );

    if (!poi?.enabled || !poi.resultText) {
      throw locationInteractionUnavailable();
    }

    // A hotspot that reveals a route writes before it speaks. Idempotent by
    // the unique pair, so a second click simply reports nothing new.
    const discoveredLocation = poi.discoversLocationKey
      ? await this.worldDiscovery.discover(
          characterId,
          poi.discoversLocationKey,
        )
      : null;

    return {
      interactionKey: poi.key,
      title: poi.resultTitle ?? poi.title,
      text: poi.resultText,
      ...(poi.resultImg === undefined ? {} : { img: poi.resultImg }),
      discoveredLocation,
    };
  }

  /**
   * Loads the character together with the location it actually stands at.
   *
   * Every local interaction resolves through here, so a request can never name
   * the location it wants to act on (plan §5).
   */
  async loadCharacterAtCurrentLocation(
    characterId: string,
  ): Promise<Character> {
    await this.travelService.completeTravelIfDue(characterId);

    const character = await this.characters.findOne({
      where: { id: characterId },
      relations: { currentLocation: true },
    });
    if (!character) {
      throw new NotFoundException('Character not found.');
    }

    return character;
  }

  private getEncounterPool(locationId: string): Promise<LocationMonster[]> {
    return this.locationMonsters.find({
      where: { locationId, enabled: true },
      relations: { monster: true },
      order: { weight: 'DESC' },
    });
  }

  /**
   * Rates the location by the encounter a traveller can typically expect: the
   * pool's weight-averaged stats, not its single worst entry. A rare elite
   * would otherwise make a beginner road read as lethal.
   */
  private toLocalDangerRating(
    character: Character,
    pool: LocationMonster[],
  ): DangerRating | null {
    const totalWeight = pool.reduce((sum, entry) => sum + entry.weight, 0);
    if (totalWeight === 0) {
      return null;
    }

    const average = (pick: (entry: LocationMonster) => number) =>
      pool.reduce((sum, entry) => sum + entry.weight * pick(entry), 0) /
      totalWeight;

    return calculateDangerRating(
      { attack: character.baseAttack, armor: 0, hp: character.baseHp },
      {
        attack: average((entry) => entry.monster.attack),
        armor: average((entry) => entry.monster.armor),
        hp: average((entry) => entry.monster.maxHp),
      },
    );
  }

  private toRecommendationLabel(location: LocationDefinition): string {
    return location.minRecommendedLevel === location.maxRecommendedLevel
      ? `${location.minRecommendedLevel}`
      : `${location.minRecommendedLevel}–${location.maxRecommendedLevel}`;
  }

  private toDangerRating(ambushChance: string): 'LOW' | 'HIGH' {
    return Number(ambushChance) <= 0.05 ? 'LOW' : 'HIGH';
  }
}