pixi-demo/src/game/chase/model.ts

import { shortestPathLength } from "./hexGraph";
import {
  generateChaseRound,
  type ChaseRound,
  type GenerateChaseRoundInput,
} from "./generator";
import { createRng, normalizeSeed, type Rng } from "./rng";
import type { Difficulty, NodeId } from "./types";

type GameStatus = "playing" | "win" | "lose";

type ModelSnapshot = Omit<ChaseRound["snapshot"], "status"> & {
  status: GameStatus;
};

interface ChaseGameState {
  snapshot: ModelSnapshot;
  winCount: number;
  turn: number;
  loseReason?: "caught" | "trapped";
}

interface ChaseGameModelOptions {
  random?: () => number;
}

const GUARD_SHORTEST_RATE: Record<Difficulty, number> = {
  easy: 0.6,
  normal: 0.85,
  hard: 1,
};

function cloneRound(round: ChaseRound): ChaseGameState {
  return {
    snapshot: {
      ...round.snapshot,
      status: "playing",
    },
    winCount: 0,
    turn: 0,
    loseReason: undefined,
  };
}

function cloneSnapshot(snapshot: ModelSnapshot): ModelSnapshot {
  const graph = {
    nodes: Object.fromEntries(
      Object.entries(snapshot.graph.nodes).map(([id, node]) => [
        id,
        { ...node, neighbors: [...node.neighbors] },
      ]),
    ),
    edgeList: snapshot.graph.edgeList.map(([a, b]) => [a, b] as [NodeId, NodeId]),
  };

  return {
    ...snapshot,
    graph,
  };
}

export class ChaseGameModel {
  private state: ChaseGameState;
  private initialSnapshot: ModelSnapshot;
  private readonly randomOverride?: () => number;
  private random: () => number;

  private constructor(state: ChaseGameState, random: () => number, randomOverride?: () => number) {
    this.state = state;
    this.initialSnapshot = cloneSnapshot(state.snapshot);
    this.randomOverride = randomOverride;
    this.random = random;
  }

  static createWithSeed(
    input: GenerateChaseRoundInput,
    options: ChaseGameModelOptions = {},
  ): ChaseGameModel {
    const round = generateChaseRound(input);
    const state = cloneRound(round);
    const rng = options.random ?? createRng(normalizeSeed(state.snapshot.seed));
    return new ChaseGameModel(state, rng, options.random);
  }

  getState(): ChaseGameState {
    return {
      ...this.state,
      snapshot: cloneSnapshot(this.state.snapshot),
    };
  }

  getAvailableMoves(): NodeId[] {
    if (this.state.snapshot.status !== "playing") {
      return [];
    }

    const node = this.state.snapshot.graph.nodes[this.state.snapshot.thiefNodeId];
    if (!node) {
      return [];
    }

    return node.neighbors.filter((id) => id !== this.state.snapshot.guardNodeId);
  }

  moveThief(target: NodeId): ChaseGameState {
    if (this.state.snapshot.status !== "playing") {
      return this.getState();
    }

    const availableMoves = this.getAvailableMoves();
    if (!availableMoves.includes(target)) {
      return this.getState();
    }

    this.state.turn += 1;
    this.state.snapshot.thiefNodeId = target;
    if (this.state.snapshot.thiefNodeId === this.state.snapshot.exitNodeId) {
      this.state.snapshot.status = "win";
      this.state.winCount += 1;
      this.state.loseReason = undefined;
      return this.getState();
    }

    this.moveGuardOneStep();

    if (this.state.snapshot.guardNodeId === this.state.snapshot.thiefNodeId) {
      this.state.snapshot.status = "lose";
      this.state.loseReason = "caught";
      return this.getState();
    }

    if (this.getAvailableMoves().length === 0) {
      this.state.snapshot.status = "lose";
      this.state.loseReason = "trapped";
    }

    return this.getState();
  }

  retryRound(): ChaseGameState {
    const winCount = this.state.winCount;
    this.resetRng(this.initialSnapshot.seed);
    this.state = {
      snapshot: cloneSnapshot(this.initialSnapshot),
      winCount,
      turn: 0,
      loseReason: undefined,
    };
    return this.getState();
  }

  newRound(seed: number | string, difficulty: Difficulty): ChaseGameState {
    const round = generateChaseRound({ seed, difficulty });
    const winCount = this.state.winCount;
    const newState = cloneRound(round);
    this.state = { ...newState, winCount };
    this.initialSnapshot = cloneSnapshot(newState.snapshot);
    this.resetRng(newState.snapshot.seed);
    return this.getState();
  }

  private resetRng(seed: number): void {
    if (this.randomOverride) {
      this.random = this.randomOverride;
      return;
    }
    this.random = createRng(normalizeSeed(seed));
  }

  private moveGuardOneStep(): void {
    const guardNode = this.state.snapshot.graph.nodes[this.state.snapshot.guardNodeId];
    if (!guardNode || guardNode.neighbors.length === 0) {
      return;
    }

    const movesWithDistance = guardNode.neighbors.map((neighborId) => ({
      nodeId: neighborId,
      distance: shortestPathLength(
        this.state.snapshot.graph,
        neighborId,
        this.state.snapshot.thiefNodeId,
      ),
    }));

    const finiteMoves = movesWithDistance.filter((item) => Number.isFinite(item.distance));
    if (finiteMoves.length === 0) {
      return;
    }

    finiteMoves.sort((a, b) => a.distance - b.distance || a.nodeId.localeCompare(b.nodeId));
    const shortestDistance = finiteMoves[0].distance;
    const shortestMoves = finiteMoves.filter((item) => item.distance === shortestDistance);
    const nonShortestMoves = finiteMoves.filter((item) => item.distance !== shortestDistance);

    const shortestRate = GUARD_SHORTEST_RATE[this.state.snapshot.difficulty];
    let nextMove = shortestMoves[0];
    if (shortestRate < 1 && this.random() > shortestRate && nonShortestMoves.length > 0) {
      const idx = Math.floor(this.random() * nonShortestMoves.length);
      nextMove = nonShortestMoves[idx];
    }

    this.state.snapshot.guardNodeId = nextMove.nodeId;
  }
}