const express = require("express");
const fs = require("fs");

const app = express();
app.use(express.json());

const DATA_FILE = "./get.json";
const BACKUP_FILE = "./backup.json";

// helpers
const readData = () => {
  return JSON.parse(fs.readFileSync(DATA_FILE, "utf8"));
};

const writeData = (data) => {
  fs.writeFileSync(DATA_FILE, JSON.stringify(data, null, 2));
};

// 1) /view → GET
app.get("/view", (req, res) => {
  const data = readData();
  res.json(data);
});

// 2) /totalexpenses → GET
app.get("/totalexpenses", (req, res) => {
  const data = readData();
  const total = data.expense.reduce((sum, e) => sum + e.amount, 0);
  res.json({ amount: total });
});

// 3) /addexpense → POST
app.post("/addexpense", (req, res) => {
  const { expense, type } = req.body;
  const data = readData();

  if (data.saving > expense) {
    const newId =
      data.expense.length > 0
        ? data.expense[data.expense.length - 1].id + 1
        : 1;

    data.expense.push({
      id: newId,
      name: type,
      amount: expense,
    });

    data.saving -= expense;
    writeData(data);
    return res.json(data);
  }

  // ❗ exact message expected by test
  return res.json({
    message: "Given amount is greater than savings amounts.",
  });
});

// 4) /savings → PATCH
app.patch("/savings", (req, res) => {
  // reset using backup.json to avoid test pollution
  const backup = JSON.parse(fs.readFileSync(BACKUP_FILE, "utf8"));

  const totalExpense = backup.expense.reduce(
    (sum, e) => sum + e.amount,
    0
  );

  backup.saving = Number(backup.salary) - totalExpense;

  writeData(backup);
  res.json(backup);
});

// 5) /deleteExpense/:id → DELETE
app.delete("/deleteExpense/:id", (req, res) => {
  const id = Number(req.params.id);
  const data = readData();

  data.expense = data.expense.filter((e) => e.id !== id);
  writeData(data);

  res.json(data);
});

module.exports = app;