import { describe, expect, it } from "vitest";
import { OpStack } from "./history.js";

describe("OpStack (T-167/T-170)", () => {
  it("push/undo/redo walk a linear history", () => {
    const s = new OpStack(0, 10);
    s.push(1);
    s.push(2);
    expect(s.present).toBe(2);
    expect(s.canUndo()).toBe(true);
    expect(s.canRedo()).toBe(false);
    expect(s.undo()).toBe(1);
    expect(s.undo()).toBe(0);
    expect(s.canUndo()).toBe(false);
    expect(s.undo()).toBe(0); // no-op at the floor
    expect(s.redo()).toBe(1);
    expect(s.redo()).toBe(2);
    expect(s.redo()).toBe(2); // no-op at the ceiling
  });

  it("push after undo clears the redo branch", () => {
    const s = new OpStack("a", 10);
    s.push("b");
    s.push("c");
    s.undo(); // back to b
    s.push("d"); // new branch
    expect(s.present).toBe("d");
    expect(s.canRedo()).toBe(false); // "c" branch discarded
    expect(s.undo()).toBe("b");
    expect(s.undo()).toBe("a");
  });

  it("is bounded: evicts oldest, reports truncation", () => {
    const s = new OpStack(0, 3);
    for (let i = 1; i <= 10; i++) s.push(i);
    expect(s.present).toBe(10);
    expect(s.depth).toBe(3); // only the last 3 past states kept (7,8,9)
    expect(s.truncated).toBe(true);
    // can undo back to 7 but not further
    expect(s.undo()).toBe(9);
    expect(s.undo()).toBe(8);
    expect(s.undo()).toBe(7);
    expect(s.canUndo()).toBe(false);
  });

  it("no-op push (same reference) is ignored", () => {
    const obj = { v: 1 };
    const s = new OpStack(obj, 10);
    s.push(obj); // same ref
    expect(s.canUndo()).toBe(false);
    expect(s.present).toBe(obj);
  });

  it("rejects capacity < 1", () => {
    expect(() => new OpStack(0, 0)).toThrow();
  });

  it("reset replaces the present with NO undo step (seed/restore)", () => {
    const s = new OpStack("a", 10);
    s.push("b");
    s.push("c");
    expect(s.canUndo()).toBe(true);
    s.reset("x"); // e.g. the server document arrived / a version was restored
    expect(s.present).toBe("x");
    expect(s.canUndo()).toBe(false);
    expect(s.canRedo()).toBe(false);
    // edits after the reset are undoable to the reset state
    s.push("y");
    s.undo();
    expect(s.present).toBe("x");
    expect(s.canUndo()).toBe(false);
  });
});