import { strictEqual, ok } from "node:assert";
import { describe, it } from "node:test";
import { apply, isLeaf, isStem, isFork } from "../src/tree.js";
import { reduce } from "../src/cli.js";

describe("tree — basic types", () => {
  it("Leaf is empty array", () => {
    ok(isLeaf([]));
    ok(!isStem([]));
    ok(!isFork([]));
  });

  it("Stem is single-element array", () => {
    ok(isStem([[]]));
    ok(!isLeaf([[]]));
  });

  it("Fork is two-element array", () => {
    ok(isFork([[], []]));
    ok(!isLeaf([[], []]));
  });
});

describe("tree — apply rules", () => {
  // Leaf = [], Stem = [child], Fork = [right, left]

  it("apply(Leaf, b) = Stem(b)", () => {
    const b = []; // Leaf
    const result = apply([], b);
    ok(isStem(result), "Stem(b) should be a Stem");
    strictEqual(result[0], b);
  });

  it("apply(Stem(a), b) = Fork(a, b)", () => {
    const a = []; // Leaf
    const b = []; // Leaf
    const result = apply([a], b);
    ok(isFork(result), "Fork(a, b) should be a Fork");
    // Fork = [right, left] = [b, a]
    strictEqual(result[0], b);
    strictEqual(result[1], a);
  });

  it("apply(Fork(Leaf, a), _) = a", () => {
    // Fork(Leaf, a) = [a, Leaf]
    const a = []; // Leaf
    const result = apply([a, []], []);
    strictEqual(result, a);
    ok(isLeaf(result));
  });
});

describe("tree — reduction", () => {
  it("reduces Leaf to Leaf", () => {
    const result = reduce([], 100);
    ok(isLeaf(result));
  });

  it("reduces Stem Leaf to Stem Leaf", () => {
    const result = reduce([[]], 100);
    ok(isStem(result));
    ok(isLeaf(result[0]));
  });

  it("reduces Fork Leaf Leaf to Fork Leaf Leaf", () => {
    const result = reduce([[], []], 100);
    ok(isFork(result));
    ok(isLeaf(result[0]));
    ok(isLeaf(result[1]));
  });

  it("S combinator applied to Leaf reduces", () => {
    // S = t (t (t t)) t = Fork (Fork (Fork Leaf Leaf) Leaf) Leaf
    // In array form: [[[], []], [], []]
    const s = [[], [[[], []], []]];
    const leaf = [];
    const result = reduce([s, leaf], 100);
    ok(Array.isArray(result), "S Leaf should reduce to an array");
  });
});