<?php

declare(strict_types=1);

class MySqlDatabase implements DatabaseInterface
{
	private const CHARS_ALLOWED_IN_TABLE_NAMES = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890_-';

	private ?PDO $connection;
	private ?PDOStatement $cursor;

	public function __construct(
		string $hostname = Setting::MYSQL_HOST,
		string $user = Setting::MYSQL_USER,
		string $password = Setting::MYSQL_PASSWORD,
		string $database = Setting::MYSQL_DATABASE
	) {
	    $this->connection = new PDO("mysql:host=$hostname;dbname=$database", $user, $password);
	}

	public function __destruct()
	{
		$this->connection = null;
	}

    /**
     * {@inheritDoc}
     */
	public function Query(string $query, array $params = []): void
	{
		$this->cursor = $this->connection->prepare($query);

		if (!$this->cursor) {
			throw new Exception('Initialization of database cursor failed');
		}

		foreach ($params as $key => $param) {
		    if (is_bool($param)) {
		        $param = (int)$param;
            }

			$this->cursor->bindValue(':' . $key, $param);
		}

		if (!$this->cursor->execute()) {
            throw new Exception($this->cursor->errorInfo()[2]);
        }
	}

    /**
     * {@inheritDoc}
     */
	public function getResult(): array
	{
		$result = [];

		while ($fetch = $this->cursor->fetchObject()) {
			$row = [];

			foreach (get_object_vars($fetch) as $key => $value) {
				$row[$key] = $value;
			}

			$result[] = $row;
		}

		return $result;
	}

    /**
     * Selects data from a table.
     */
    public function Select(
		string $tableName,
		array $fields = [],
		array $conditions = [],
		int $limit = 0,
		array $orderBy = [],
		bool $asc = true,
        int $offset = 0
	): array {
		if (!self::isValidTableName($tableName)) {
			[];
		}

		if (count($fields) === 0) {
			$fieldsExpression = '*';
		} else {
			$fieldsExpression = implode(',', $fields);
		}

		$conditionsExpression = '';
		$conditionPairs = [];

		foreach ($conditions as $field => $value) {
			$conditionPairs[] = sprintf('%s = :%s ', $field, $field);
		}

		if (count($conditions) > 0) {
			$conditionsExpression = 'WHERE ';
			$conditionsExpression .= implode(' AND ', $conditionPairs);
		}

		$orderStatement = '';

		if (count($orderBy) > 0) {
			$orderStatement = 'ORDER BY ' . implode(',', $orderBy);

			if (!$asc) {
				$orderStatement .= ' DESC';
			}
		}

		$limitStatement = '';

		if ($limit > 0) {
			$limitStatement = 'LIMIT ' . $limit;
		}

		$offsetStatement = '';

		if ($offset > 0) {
		    $offsetStatement = 'OFFSET ' . $offset;
        }

		$query = sprintf(
			'SELECT %s FROM %s %s %s %s %s',
			$fieldsExpression,
			$tableName,
			$conditionsExpression,
			$orderStatement,
			$limitStatement,
            $offsetStatement
		);

        try {
            $this->Query($query, $conditions);
        } catch (Throwable $e) {
            return [];
        }

        return $this->getResult();
	}

    /**
     * Deletes rows from a table.
     */
    public function Delete(string $table, array $conditions): void
    {
        if (count($conditions) === 0) {
            $conditionsStatement = '1';
        } else {
            $conditionPairs = [];

            foreach ($conditions as $field => $value) {
                $conditionPairs[] = sprintf('%s=:Condition%s', $field, $field);
                $conditions['Condition' . $field] = $value;
                unset($conditions[$field]);
            }

            $conditionsStatement = implode(' AND ', $conditionPairs);
        }

        $query = sprintf('DELETE FROM %s WHERE %s', $table, $conditionsStatement);

        $this->Query($query, $conditions);
    }

    /**
     * {@inheritDoc}
     */
    public function Insert(string $table, array $fields): ?int
    {
        if (count($fields) === 0) {
           throw new Exception('Row to insert is empty!');
        }

        $fieldNames = implode(',', array_keys($fields));
        $fieldPlaceholder = [];

        foreach ($fields as $name => $value) {
            $fieldPlaceholder[] = ':' . $name;
        }

        $query = sprintf(
            'INSERT INTO %s (%s) VALUES (%s)', $table, $fieldNames, implode(',', $fieldPlaceholder)
        );

        $this->Query($query, $fields);

        $lastInsertedId = $this->GetLastInsertedId();

        if ((int)$lastInsertedId === 0) {
            return null;
        }

        return $lastInsertedId;
    }

    /**
     * {@inheritDoc}
     */
    public function Update(string $table, array $fields, array $conditions): void
    {
        $conditionPairs = [];

        foreach ($conditions as $field => $value) {
            $conditionPairs[] = sprintf('%s=:Condition%s', $field, $field);
            $conditions['Condition' . $field] = $value;
            unset($conditions[$field]);
        }

        $conditionsStatement = implode(' AND ', $conditionPairs);

        $fieldPairs = [];

        foreach ($fields as $field => $value) {
            $fieldPairs[] = sprintf('%s=:%s', $field, $field);
        }

        $fieldsStatement = implode(',', $fieldPairs);

        $query = sprintf('UPDATE %s SET %s WHERE %s', $table, $fieldsStatement, $conditionsStatement);


        $this->Query($query, array_merge($fields, $conditions));
    }

    /**
     * {@inheritDoc}
     */
    public function Count(string $table, array $conditions = []): int
    {
        $result = $this->Select($table, ['count(*)'], $conditions);

        return (int)$result[0]['count(*)'];
    }

    /**
     * {@inheritDoc}
     */
    public function GetLastInsertedId(): int
    {
        $this->Query('SELECT LAST_INSERT_ID() as ID');

        return (int)$this->getResult()[0]['ID'];
    }

    /**
     * Does a check if the given table name contains forbidden chars.
     */
	private static function isValidTableName(string $tableName): bool
	{
		foreach (str_split($tableName) as $char) {
			if (substr_count(self::CHARS_ALLOWED_IN_TABLE_NAMES, $char) === 0) {
				return false;
			}
		}

		return true;
	}
}