import express from "express";
import { readFile, writeFile, exists } from "fs/promises";

const router = express.Router();

interface Task {
  id: string;
  title: string;
  completed: boolean;
}

const getTasks: () => Promise<Task[]> = async () => {
  if (!(await exists("tasks.json"))) {
    await writeFile("tasks.json", JSON.stringify([]));
  }
  const file = await readFile("tasks.json", "utf-8");
  if (file.length === 0) {
    return [];
  }
  return JSON.parse(file);
};

const updateTask = async (task: Task): Promise<void> => {
  const tasks = await getTasks();
  const index = tasks.findIndex((t) => t.id === task.id);
  if (index !== -1) {
    tasks[index] = task;
  } else {
    tasks.push(task);
  }
  await writeFile("tasks.json", JSON.stringify(tasks));
};

const removeTask = async (id: string): Promise<void> => {
  const tasks = await getTasks();
  const index = tasks.findIndex((t) => t.id === id);
  if (index !== -1) {
    tasks.splice(index, 1);
    await writeFile("tasks.json", JSON.stringify(tasks));
  }
};

router.use(express.json());

router.get("/", async (_req, res) => {
  res.json(await getTasks());
});

router.post("/", async (req, res) => {
  if (!(typeof req.body.title === "string")) {
    res.status(400).send("Invalid title");
    return;
  }
  const newTask = {
    id: Math.random().toString(16).substring(2, 8),
    title: req.body.title,
    completed: false,
  };
  await updateTask(newTask);
  res.json(newTask).status(201);
});

router.get("/:id", async (req, res) => {
  const task = (await getTasks()).find((t) => t.id === req.params.id);
  if (!task) {
    res.status(404).send("Task not found");
  } else {
    res.json(task);
  }
});

router.put("/:id", async (req, res) => {
  const task = (await getTasks()).find((t) => t.id === req.params.id);
  if (!task) {
    res.status(404).send("Task not found");
  } else {
    const missing = [];
    if (req.body.title === undefined) missing.push("title");
    if (req.body.completed === undefined) missing.push("completed");
    if (missing.length > 0) {
      res
        .status(400)
        .send(
          `Missing field${missing.length > 1 ? "s" : ""}: ${missing.join(", ")}`,
        );
    }
    const badTypes = [];
    if (!(typeof req.body.title === "string")) badTypes.push("title");
    if (!(typeof req.body.completed === "boolean")) badTypes.push("completed");
    if (badTypes.length > 0) {
      res
        .status(400)
        .send(
          `Invalid type${badTypes.length > 1 ? "s" : ""}: ${badTypes.join(", ")}`,
        );
      return;
    }
    task.title = req.body.title ?? task.title;
    task.completed = req.body.completed ?? task.completed;
    await updateTask(task);
    res.json(task);
  }
});

router.patch("/:id", async (req, res) => {
  const task = (await getTasks()).find((t) => t.id === req.params.id);
  if (!task) {
    res.status(404).send("Task not found");
  } else {
    const badTypes = [];
    if (
      Object.keys(req.body).includes("title") &&
      !(typeof req.body.title === "string")
    )
      badTypes.push("title");
    if (
      Object.keys(req.body).includes("completed") &&
      !(typeof req.body.completed === "boolean")
    )
      badTypes.push("completed");
    if (badTypes.length > 0) {
      res
        .status(400)
        .send(
          `Invalid type${badTypes.length > 1 ? "s" : ""}: ${badTypes.join(", ")}`,
        );
      return;
    }
    task.title = req.body.title ?? task.title;
    task.completed = req.body.completed ?? task.completed;
    await updateTask(task);
    res.json(task);
  }
});

router.delete("/:id", async (req, res) => {
  const task = (await getTasks()).find((t) => t.id === req.params.id);
  if (!task) {
    res.status(404).send("Task not found");
  } else {
    await removeTask(task.id);
    res.status(204).send();
  }
});

export default router;