import { Prng, mulberry32 } from "../lib/prng";
import { BEACH, ICECAP } from "./data";
import { ALL_ISLANDS, BIG_ISLANDS, LobeGenerator } from "./generators";

export class IslandGrid {
  data: number[];
  rng: Prng;

  generators: LobeGenerator[] = [];

  done = false;

  constructor(public width: number, public height: number, seed: number) {
    this.data = Array(width * height).fill(0);
    this.rng = mulberry32(seed);

    this.generators.push(this.choose(BIG_ISLANDS)(this, this.data.length >> 1));
    this.generators.push(
      this.choose(ALL_ISLANDS)(
        this,
        this.xy(
          (width >> 1) + (this.rng() % 48) - 24,
          (height >> 1) + (this.rng() % 48) - 24
        )
      )
    );
    this.generators.push(
      this.choose(ALL_ISLANDS)(
        this,
        this.xy(
          (width >> 1) + (this.rng() % 48) - 24,
          (height >> 1) + (this.rng() % 48) - 24
        )
      )
    );
  }

  public xy(x: number, y: number): number {
    return (
      (((x % this.width) + this.width) % this.width) +
      this.width * (((y % this.height) + this.height) % this.height)
    );
  }

  public floodSearch(
    startPos: number,
    shouldExpand: (tile: number) => boolean
  ): number[] {
    const len = this.data.length;
    const width = this.width;
    const seen = new Uint8Array(len);

    const hitPositions: number[] = [];

    function enqueue(pos: number) {
      if (!seen[pos]) {
        hitPositions.push(pos);
        seen[pos] = 1;
      }
    }

    enqueue(startPos);

    for (let i = 0; i < hitPositions.length; i++) {
      const pos = hitPositions[i];
      if (shouldExpand(this.data[pos])) {
        enqueue((pos - width) % len);
        enqueue((pos - 1) % len);
        enqueue((pos + 1) % len);
        enqueue((pos + width) % len);
      }
    }

    return hitPositions;
  }

  public drop(pos: number): void {
    const lowerNeighbors: number[] = [];

    const check = (adjPos: number) => {
      if (this.data[adjPos] < this.data[pos]) {
        lowerNeighbors.push(adjPos);
      }
    };

    // try to roll in cardinal directions

    check((pos - this.width) % this.data.length);
    check((pos - 1) % this.data.length);
    check((pos + 1) % this.data.length);
    check((pos + this.width) % this.data.length);

    if (lowerNeighbors.length > 0) {
      const downhill = lowerNeighbors[this.rng() % lowerNeighbors.length];
      return this.drop(downhill);
    }

    // try to roll in diagonal directions

    check((pos - this.width - 1) % this.data.length);
    check((pos - this.width + 1) % this.data.length);
    check((pos + this.width - 1) % this.data.length);
    check((pos + this.width + 1) % this.data.length);

    if (lowerNeighbors.length > 0) {
      const downhill = lowerNeighbors[this.rng() % lowerNeighbors.length];
      return this.drop(downhill);
    }

    // flat, increase elevation
    const newValue = ++this.data[pos];
    if (newValue == ICECAP) {
      this.done = true;
    }
  }

  public choose<T>(list: T[]) {
    if (list.length == 0) {
      throw new Error("Picking from empty list");
    }
    return list[this.rng() % list.length];
  }

  public dropWithin(tiles: number[]) {
    if (tiles.length > 0) {
      this.drop(this.choose(tiles));
    }
  }

  public step() {
    this.done = this.generators
      .map((generator) => generator())
      .every((done) => done);
  }
}