2D6-Dungeon/src/rules/dungeon.ts

import type { ContentPack } from "@/types/content";
import type { DungeonLevelState, RoomExitState, RoomState } from "@/types/state";

import { createLevelShell, generateLevel1StartRoom, generateRoomFromTable } from "./rooms";
import type { DiceRoller } from "./dice";

type CardinalDirection = "north" | "east" | "south" | "west";

export type InitializeLevelOptions = {
  content: ContentPack;
  level?: number;
  startRoomId?: string;
};

export type ExpandFromExitOptions = {
  content: ContentPack;
  levelState: DungeonLevelState;
  fromRoomId: string;
  exitDirection: CardinalDirection;
  roomTableCode: string;
  roomId?: string;
  roller?: DiceRoller;
};

export type ExpansionResult = {
  levelState: DungeonLevelState;
  createdRoom: RoomState;
  fromRoom: RoomState;
};

const DIRECTION_VECTORS: Record<CardinalDirection, { x: number; y: number }> = {
  north: { x: 0, y: -1 },
  east: { x: 1, y: 0 },
  south: { x: 0, y: 1 },
  west: { x: -1, y: 0 },
};

const OPPOSITE_DIRECTION: Record<CardinalDirection, CardinalDirection> = {
  north: "south",
  east: "west",
  south: "north",
  west: "east",
};

function cloneRoom(room: RoomState): RoomState {
  return {
    ...room,
    position: { ...room.position },
    dimensions: { ...room.dimensions },
    exits: room.exits.map((exit) => ({ ...exit })),
    discovery: { ...room.discovery },
    encounter: room.encounter
      ? {
          ...room.encounter,
          creatureIds: [...room.encounter.creatureIds],
          creatureNames: room.encounter.creatureNames
            ? [...room.encounter.creatureNames]
            : undefined,
        }
      : undefined,
    objects: room.objects.map((object) => ({
      ...object,
      effects: object.effects ? [...object.effects] : undefined,
    })),
    notes: [...room.notes],
    flags: [...room.flags],
  };
}

function cloneLevel(levelState: DungeonLevelState): DungeonLevelState {
  return {
    ...levelState,
    rooms: Object.fromEntries(
      Object.entries(levelState.rooms).map(([roomId, room]) => [roomId, cloneRoom(room)]),
    ),
    discoveredRoomOrder: [...levelState.discoveredRoomOrder],
  };
}

function findExit(room: RoomState, direction: CardinalDirection): RoomExitState {
  const exit = room.exits.find((candidate) => candidate.direction === direction);

  if (!exit) {
    throw new Error(`Room ${room.id} does not have an exit facing ${direction}.`);
  }

  return exit;
}

function computeNextPosition(room: RoomState, direction: CardinalDirection) {
  const offset = DIRECTION_VECTORS[direction];

  return {
    x: room.position.x + offset.x,
    y: room.position.y + offset.y,
  };
}

function connectRooms(
  fromRoom: RoomState,
  toRoom: RoomState,
  direction: CardinalDirection,
) {
  const fromExit = findExit(fromRoom, direction);
  fromExit.leadsToRoomId = toRoom.id;
  fromExit.discovered = true;

  const oppositeDirection = OPPOSITE_DIRECTION[direction];
  const returnExit =
    toRoom.exits.find((candidate) => candidate.direction === oppositeDirection) ?? toRoom.exits[0];

  if (!returnExit) {
    throw new Error(`Generated room ${toRoom.id} does not have an available return exit.`);
  }

  returnExit.direction = oppositeDirection;
  returnExit.leadsToRoomId = fromRoom.id;
  returnExit.discovered = true;
}

function getNextRoomId(levelState: DungeonLevelState, roomClass: string) {
  const sequence = levelState.discoveredRoomOrder.length + 1;
  return `room.level${levelState.level}.${roomClass}.${String(sequence).padStart(3, "0")}`;
}

function assertCoordinateAvailable(levelState: DungeonLevelState, position: { x: number; y: number }) {
  const occupiedRoom = Object.values(levelState.rooms).find(
    (room) => room.position.x === position.x && room.position.y === position.y,
  );

  if (occupiedRoom) {
    throw new Error(
      `Cannot place a new room at (${position.x}, ${position.y}); ${occupiedRoom.id} already occupies that position.`,
    );
  }
}

export function initializeDungeonLevel(
  options: InitializeLevelOptions,
): DungeonLevelState {
  const level = options.level ?? 1;

  if (level !== 1) {
    throw new Error("Only Level 1 initialization is currently implemented.");
  }

  const levelState = createLevelShell(level);
  const startResult = generateLevel1StartRoom(
    options.content,
    options.startRoomId ?? `room.level${level}.start`,
  );

  levelState.rooms[startResult.room.id] = startResult.room;
  levelState.discoveredRoomOrder.push(startResult.room.id);

  return levelState;
}

export function getUnresolvedExits(levelState: DungeonLevelState) {
  return levelState.discoveredRoomOrder.flatMap((roomId) => {
    const room = levelState.rooms[roomId];

    return room.exits
      .filter((exit) => !exit.leadsToRoomId && exit.traversable)
      .map((exit) => ({
        roomId,
        exitId: exit.id,
        direction: exit.direction,
        exitType: exit.exitType,
      }));
  });
}

export function expandLevelFromExit(
  options: ExpandFromExitOptions,
): ExpansionResult {
  const levelState = cloneLevel(options.levelState);
  const fromRoom = levelState.rooms[options.fromRoomId];

  if (!fromRoom) {
    throw new Error(`Unknown source room id: ${options.fromRoomId}`);
  }

  const sourceExit = findExit(fromRoom, options.exitDirection);

  if (sourceExit.leadsToRoomId) {
    throw new Error(`Exit ${sourceExit.id} is already connected to ${sourceExit.leadsToRoomId}.`);
  }

  if (!sourceExit.traversable) {
    throw new Error(`Exit ${sourceExit.id} is not traversable.`);
  }

  const position = computeNextPosition(fromRoom, options.exitDirection);
  assertCoordinateAvailable(levelState, position);

  const provisionalRoomId =
    options.roomId ?? getNextRoomId(levelState, options.roomTableCode === "L1SR" ? "small" : "room");
  const result = generateRoomFromTable({
    content: options.content,
    roomId: provisionalRoomId,
    level: levelState.level,
    roomTableCode: options.roomTableCode,
    position,
    roller: options.roller,
  });

  connectRooms(fromRoom, result.room, options.exitDirection);

  levelState.rooms[fromRoom.id] = fromRoom;
  levelState.rooms[result.room.id] = result.room;
  levelState.discoveredRoomOrder.push(result.room.id);

  return {
    levelState,
    createdRoom: result.room,
    fromRoom,
  };
}