<?php

namespace Nest\Database;

use Nest\Database\Query\QueryBuilder;
use Nest\Database\Transactions\Transaction;
use Nest\Exceptions\Database\NotCurrentTransactionException;
use Throwable;

/**
 * Class of a database.
 */
abstract class Database
{
	/**
	 * The current transaction, in one is started.
	 * @var Transaction|null
	 */
	private ?Transaction $transaction = null;

	/**
	 * Connect to the database.
	 * @return void
	 */
	public abstract function connect(): void;

	/**
	 * Execute a query.
	 * @param string $statement The query statement.
	 * @param array $bindings The query bindings.
	 * @return object[] Query result as an array of objects.
	 */
	public abstract function execute(string $statement, array $bindings = []): array;

	/**
	 * Get a queries adapter for the current database.
	 * @return DatabaseAdapter A database queries adapter.
	 */
	public abstract function getQueriesAdapter(): DatabaseAdapter;

	/**
	 * Create a new query on the database.
	 * @param ?string $table The table on which to build the new query.
	 * @return QueryBuilder A query builder.
	 */
	public function query(?string $table = null): QueryBuilder
	{
		return new QueryBuilder($this, $table);
	}

	/**
	 * Create a new query on the given table of the database.
	 * @param string $table The table on which to build the new query.
	 * @return QueryBuilder A query builder.
	 */
	public function table(string $table): QueryBuilder
	{
		return $this->query($table);
	}


	/**
	 * Get the current transaction, if there is one.
	 * @return Transaction|null
	 */
	public function getCurrentTransaction(): ?Transaction
	{
		return $this->transaction;
	}

	/**
	 * Called when the state of a transaction changed (inactive -> active or active -> inactive).
	 * @param Transaction $transaction
	 * @return void
	 * @throws NotCurrentTransactionException
	 */
	public function onTransactionStateChanged(Transaction $transaction): void
	{
		if ($transaction->isActive())
		{ // Set the newly active transaction as the current one.

			// Its parent should be the current transaction, if it exists.
			if (!empty($transaction->getParent()) && $transaction->getParent()->getUuid() != $this->transaction->getUuid())
				throw new NotCurrentTransactionException($this->transaction, $transaction->getParent());

			$this->transaction = $transaction;
		}
		else
		{ // The transaction has been terminated, it should be the current one.
			if (!empty($this->transaction) && $this->transaction->getUuid() != $transaction->getUuid())
				throw new NotCurrentTransactionException($this->transaction, $transaction);

			$this->transaction = $transaction->getParent();
		}
	}

	/**
	 * Start a new transaction (in the current one, if there is one).
	 * @return Transaction The new transaction.
	 * @throws NotCurrentTransactionException
	 */
	public function startTransaction(): Transaction
	{
		// Create the transaction as a child of the existing one, if there is one.
		$newTransaction = new Transaction($this, $this->transaction);
		if (!empty($this->transaction))
			// Set the new transaction as child of the current one.
			$this->transaction->setChild($newTransaction);

		$newTransaction->start(); // Start the new transaction.

		return $newTransaction; // Return the new transaction.
	}

	/**
	 * Start a new transaction and execute the function in parameter.
	 * The transaction will be committed / rolled back automatically at the end of the function.
	 * A rollback happen if any exception is thrown in the function.
	 * @param callable(Transaction): mixed $function The function to execute in a transaction.
	 * @return mixed Function result.
	 * @throws Throwable
	 */
	public function transaction(callable $function): mixed
	{
		// Start a new transaction.
		$transaction = $this->startTransaction();

		try
		{ // Trying to run the function in the started transaction.
			$result = $function($transaction);

			// The function finished successfully, commit the transaction.
			$transaction->commit();

			// Return result of the function.
			return $result;
		}
		catch (Throwable $throwable)
		{ // An exception has been thrown, rolling back the transaction and throw it again.
			$transaction->rollback();
			throw $throwable;
		}
	}
}