import { test } from "node:test";
import assert from "node:assert/strict";
import { mkdtempSync, writeFileSync, readdirSync, symlinkSync, lstatSync, statSync, chmodSync } from "node:fs";
import { tmpdir } from "node:os";
import { join, dirname } from "node:path";
import { load, save, add, has, complete, remove, format } from "../src/todo.js";

const tempFile = () => join(mkdtempSync(join(tmpdir(), "todo-")), "todos.json");

test("add appends an open todo", () => {
  const todos = add([], "buy milk");
  assert.deepEqual(todos, [{ id: 1, text: "buy milk", done: false }]);
});

test("add after a remove does not reuse an existing id", () => {
  const todos = add(remove(add(add([], "a"), "b"), 1), "c");
  assert.deepEqual(todos.map((t) => t.id), [2, 3]);
});

test("has reports whether an id exists", () => {
  const todos = add([], "a");
  assert.equal(has(todos, 1), true);
  assert.equal(has(todos, 2), false);
});

test("complete marks only the matching todo", () => {
  const todos = complete(add(add([], "a"), "b"), 2);
  assert.equal(todos[0].done, false);
  assert.equal(todos[1].done, true);
});

test("remove drops the matching todo", () => {
  const todos = remove(add(add([], "a"), "b"), 1);
  assert.deepEqual(todos.map((t) => t.text), ["b"]);
});

test("format renders an empty list", () => {
  assert.equal(format([]), "Nothing to do.");
});

test("load returns an empty list for a missing file", () => {
  assert.deepEqual(load(tempFile()), []);
});

test("add handles a very large list", () => {
  const todos = Array.from({ length: 200_000 }, (_, i) => ({ id: i + 1, text: "x", done: false }));
  assert.equal(add(todos, "y").at(-1).id, 200_001);
});

test("save then load round-trips and leaves no temp file", () => {
  const file = tempFile();
  const todos = add([], "a");
  save(file, todos);
  assert.deepEqual(load(file), todos);
  assert.deepEqual(readdirSync(dirname(file)), ["todos.json"]);
});

test("save writes through a symlink instead of replacing it", () => {
  const real = tempFile();
  const link = join(dirname(tempFile()), "link.json");
  save(real, []);
  symlinkSync(real, link);
  save(link, add([], "a"));
  assert.equal(lstatSync(link).isSymbolicLink(), true);
  assert.deepEqual(load(real).map((t) => t.text), ["a"]);
});

test("save keeps the file's permissions", () => {
  const file = tempFile();
  save(file, []);
  chmodSync(file, 0o600);
  save(file, add([], "a"));
  assert.equal(statSync(file).mode & 0o777, 0o600);
});

test("save reports a readable error and cleans up when it can't write", () => {
  const file = tempFile();
  chmodSync(dirname(file), 0o500);
  try {
    assert.throws(() => save(file, []), /Could not save .*todos\.json/);
    assert.deepEqual(readdirSync(dirname(file)), []);
  } finally {
    chmodSync(dirname(file), 0o700);
  }
});

test("load rejects invalid JSON with a readable error", () => {
  const file = tempFile();
  writeFileSync(file, "{ not json");
  assert.throws(() => load(file), /Could not read .*todos\.json/);
});

test("load rejects JSON that is not a list", () => {
  const file = tempFile();
  writeFileSync(file, "{}");
  assert.throws(() => load(file), /expected a list of todos/);
});

for (const entry of ["null", "1", '{"text":"a","done":false}', '{"id":"1","text":"a","done":false}']) {
  test(`load rejects an invalid entry: ${entry}`, () => {
    const file = tempFile();
    writeFileSync(file, `[${entry}]`);
    assert.throws(() => load(file), /entry 1 is not a valid todo/);
  });
}