/*

* Copyright (C) 2019 The Dagger Authors.

*

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

package dagger.example.atm;

import java.math.BigDecimal;

import java.util.HashMap;

import java.util.Map;

import javax.inject.Inject;

import javax.inject.Singleton;

/** A database that stores all of its data in memory. */

@Singleton

final class InMemoryDatabase implements Database {

private final Map<String, Account> accounts = new HashMap<>();

@Inject

InMemoryDatabase() {}

@Override

public Account getAccount(String username) {

return accounts.computeIfAbsent(username, InMemoryAccount::new);

}

private static final class InMemoryAccount implements Account {

private final String username;

private BigDecimal balance = BigDecimal.ZERO;

InMemoryAccount(String username) {

this.username = username;

}

@Override

public String username() {

return username;

}

@Override

public void deposit(BigDecimal amount) {

checkNonNegative(amount, "deposit");

balance = balance.add(amount);

}

@Override

public void withdraw(BigDecimal amount) {

checkNonNegative(amount, "withdraw");

balance = balance.subtract(amount);

}

private void checkNonNegative(BigDecimal amount, String action) {

if (amount.signum() == -1) {

throw new IllegalArgumentException(

String.format("Cannot %s negative amounts: %s", action, amount));

}

}

@Override

public BigDecimal balance() {

return balance;

}

}

}