<template>
  <header>
    <h1>Expense Tracker</h1>
  </header>
  <section>
    <div>Available Funds: {{ data.availableFunds }}</div>
    <div>Total Expenses: {{ data.currentExpenses }}</div>
    <hr />
    <div>Funds left: {{ data.remainingFunds }}</div>
  </section>
  <section>
    <form @submit.prevent="addExpense">
      <div>
        <label for="amount">Amount</label>
        <input id="amount" type="number" v-model="enteredExpense" />
      </div>
      <button>Add Expense</button>
    </form>
  </section>
</template>

<script>
import { ref, reactive, computed, watch } from 'vue';

export default {
  setup() {
    const data = reactive({
      availableFunds: 100,
      currentExpenses: 0,
      enteredExpense: 0
    });

    const enteredExpense = ref(0);

    data.remainingFunds = computed(function() {
      return data.availableFunds - data.currentExpenses;
    });

    function addExpense() {
      data.currentExpenses += enteredExpense.value;
    }

    watch(
      () => data.remainingFunds,
      function(_, newValue) {
        if (newValue < 0) {
          alert('You are broke!');
        }
      }
    );

    return {
      data,
      addExpense,
      enteredExpense
    };
  }
};
</script>

<style>
* {
  box-sizing: border-box;
}
html {
  font-family: sans-serif;
}
body {
  margin: 0;
}
header {
  width: 100%;
  height: 5rem;
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: #30006e;
  color: white;
}
section {
  margin: 2rem auto;
  max-width: 35rem;
  padding: 1rem;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.26);
  border-radius: 12px;
}

form div {
  margin: 1rem 0;
}
input {
  width: 100%;
  padding: 0.15rem;
}
label {
  font-weight: bold;
  margin: 0.5rem 0;
}
button {
  background-color: #30006e;
  border: 1px solid #30006e;
  font: inherit;
  cursor: pointer;
  padding: 0.5rem 1.5rem;
  color: white;
}
button:hover,
button:active {
  background-color: #5819ac;
  border-color: #5819ac;
}
</style>
