// The grid: objects on tiles. `x` grows right, `y` grows down, and any number of
// objects may share a tile.

export type ObjectId = number;

/** A level in the course's level format (`course/schema/level.schema.json`). */
export interface LevelDef {
  width: number;
  height: number;
  objects: LevelObject[];
  /** Module 10, read only by SpellGrid: minions in play, each on its tile. */
  cards?: LevelCard[];
  /** Module 10, read only by SpellGrid: the cards in player 0's hand. */
  hand?: string[];
}

/** A minion card on the grid (Module 10). */
export interface LevelCard {
  card: string;
  x: number;
  y: number;
}

export interface LevelObject {
  kind: string;
  x: number;
  y: number;
}

/**
 * What an object is: a thing named by a noun (kind `"<noun>"`, the noun in lower case),
 * or a piece of text carrying one word (kind `"text:<WORD>"`).
 */
export type Kind = { type: "thing"; noun: string } | { type: "text"; word: string };

const TEXT_PREFIX = "text:";

export const Kind = {
  parse(kind: string): Kind {
    return kind.startsWith(TEXT_PREFIX)
      ? { type: "text", word: kind.slice(TEXT_PREFIX.length).toUpperCase() }
      : { type: "thing", noun: kind.toUpperCase() };
  },
  /** The kind as it is placed: `"<noun>"` in lower case, or `"text:<WORD>"`. */
  format(kind: Kind): string {
    return kind.type === "text" ? TEXT_PREFIX + kind.word : kind.noun.toLowerCase();
  },
};

export interface Obj {
  id: ObjectId;
  kind: Kind;
  x: number;
  y: number;
}

/** What `Board.restore` puts back (Module 9, undo): every object, oldest first, and the id counter. */
export interface BoardState {
  objects: Obj[];
  nextId: ObjectId;
}

export class Board {
  private readonly objectsById = new Map<ObjectId, Obj>();
  private nextId = 0;

  constructor(
    readonly width: number,
    readonly height: number,
  ) {}

  inBounds(x: number, y: number): boolean {
    return x >= 0 && x < this.width && y >= 0 && y < this.height;
  }

  /** Add an object; ids start at 1 and are never reused. Throws off the board. */
  place(kind: Kind, x: number, y: number): ObjectId {
    if (!this.inBounds(x, y)) throw new Error(`(${x}, ${y}) is outside the ${this.width}x${this.height} level`);
    const id = ++this.nextId;
    this.objectsById.set(id, { id, kind, x, y });
    return id;
  }

  /**
   * An id that no object will ever have (Module 10): SpellGrid gives one to each
   * card that isn't on the grid, so cards and objects share one id space.
   */
  reserveId(): ObjectId {
    return ++this.nextId;
  }

  /** The object `id`. Throws if there is none. */
  get(id: ObjectId): Obj {
    const o = this.objectsById.get(id);
    if (o === undefined) throw new Error(`no object ${id}`);
    return o;
  }

  /** The object `id`, or `undefined` once it has been removed. Throws on an id this board never issued. */
  find(id: ObjectId): Obj | undefined {
    if (!(id >= 1 && id <= this.nextId)) throw new Error(`no object ${id}`);
    return this.objectsById.get(id);
  }

  /** Take object `id` off the board for good. */
  remove(id: ObjectId): void {
    this.objectsById.delete(id);
  }

  /** Move object `id` by `[dx, dy]`. Throws if it would leave the board. */
  shift(id: ObjectId, [dx, dy]: readonly [number, number]): void {
    const o = this.get(id);
    const [x, y] = [o.x + dx, o.y + dy];
    if (!this.inBounds(x, y)) throw new Error(`(${x}, ${y}) is outside the ${this.width}x${this.height} level`);
    o.x = x;
    o.y = y;
  }

  /** Make object `id` a `kind`, where it stands. Throws if there is no such object. */
  setKind(id: ObjectId, kind: Kind): void {
    this.get(id).kind = kind;
  }

  /** The objects on tile (x, y), oldest first. */
  at(x: number, y: number): Obj[] {
    return this.objects().filter((o) => o.x === x && o.y === y);
  }

  /** Every object, oldest first. */
  objects(): Obj[] {
    return [...this.objectsById.values()];
  }

  /** A copy of everything the board holds (Module 9, undo). */
  snapshot(): BoardState {
    return { objects: this.objects().map((o) => ({ ...o })), nextId: this.nextId };
  }

  /** Put the board back as `state` recorded it: the same objects, ids, ages and id counter. */
  restore(state: BoardState): void {
    this.objectsById.clear();
    for (const o of state.objects) this.objectsById.set(o.id, { ...o });
    this.nextId = state.nextId;
  }
}