const express = require("express");
const { DateTime } = require("luxon");
const Todo = require("../models/Todo");

const router = express.Router();

// Korea Standard Time zone
const KST_TIMEZONE = "Asia/Seoul";

// Get day range in Korea Standard Time (Asia/Seoul)
const getDayRange = () => {
  // Get current time in KST
  const nowKst = DateTime.now().setZone(KST_TIMEZONE);

  // Start of day in KST (00:00:00.000)
  const startOfDayKst = nowKst.startOf("day");

  // End of day in KST (23:59:59.999)
  const endOfDayKst = nowKst.endOf("day");

  // Convert to JavaScript Date objects (UTC) for MongoDB query
  const start = startOfDayKst.toJSDate();
  const end = endOfDayKst.toJSDate();

  return { start, end };
};

router.get("/", async (req, res) => {
  try {
    const todos = await Todo.find().sort({ dueDate: 1, createdAt: -1 });
    res.json(todos);
  } catch (error) {
    res.status(500).json({ message: "Failed to fetch todos" });
  }
});

router.get("/today", async (req, res) => {
  try {
    const { start, end } = getDayRange();
    // Show todos that are:
    // 1. Due today (between start and end of today) - both completed and incomplete
    // 2. Due in the future (not yet due) - only incomplete
    // 3. Have no due date set - both completed and incomplete (always show)
    // Filter out: overdue todos (due date before today)
    const todos = await Todo.find({
      $or: [
        // Today's todos (completed or not) - show with strikethrough if completed
        { dueDate: { $gte: start, $lte: end } },
        // Future todos - only incomplete
        { dueDate: { $gt: end }, completed: false },
        // No due date - always show (completed or not)
        { dueDate: { $exists: false } },
        { dueDate: null }
      ]
    }).sort({
      completed: 1,  // Incomplete first
      dueDate: 1,
      createdAt: -1,
    });
    res.json(todos);
  } catch (error) {
    res.status(500).json({ message: "Failed to fetch today todos" });
  }
});

// Normalize dueDate to noon KST to avoid timezone boundary issues
const normalizeDueDate = (dueDate) => {
  if (!dueDate) return null;
  // Parse the date and set it to noon KST
  const date = DateTime.fromISO(dueDate, { zone: KST_TIMEZONE });
  // Set to noon (12:00) of that day in KST
  return date.set({ hour: 12, minute: 0, second: 0, millisecond: 0 }).toJSDate();
};

router.post("/", async (req, res) => {
  try {
    const todoData = { ...req.body };
    if (todoData.dueDate) {
      todoData.dueDate = normalizeDueDate(todoData.dueDate);
    }
    const todo = await Todo.create(todoData);
    res.status(201).json(todo);
  } catch (error) {
    res.status(400).json({ message: "Failed to create todo" });
  }
});

router.get("/:id", async (req, res) => {
  try {
    const todo = await Todo.findById(req.params.id);
    if (!todo) {
      return res.status(404).json({ message: "Todo not found" });
    }
    res.json(todo);
  } catch (error) {
    res.status(400).json({ message: "Failed to fetch todo" });
  }
});

router.put("/:id", async (req, res) => {
  try {
    const updateData = { ...req.body };
    if (updateData.dueDate) {
      updateData.dueDate = normalizeDueDate(updateData.dueDate);
    }
    const todo = await Todo.findByIdAndUpdate(req.params.id, updateData, { new: true });
    if (!todo) {
      return res.status(404).json({ message: "Todo not found" });
    }
    res.json(todo);
  } catch (error) {
    res.status(400).json({ message: "Failed to update todo" });
  }
});

router.delete("/:id", async (req, res) => {
  try {
    const todo = await Todo.findByIdAndDelete(req.params.id);
    if (!todo) {
      return res.status(404).json({ message: "Todo not found" });
    }
    res.json({ ok: true });
  } catch (error) {
    res.status(400).json({ message: "Failed to delete todo" });
  }
});

module.exports = router;