<?php namespace Laravel\Database;

abstract class Grammar {

	/**
	 * The keyword identifier for the database system.
	 *
	 * @var string
	 */
	protected $wrapper = '"%s"';

	/**
	 * The database connection instance for the grammar.
	 *
	 * @var Connection
	 */
	protected $connection;

	/**
	 * Create a new database grammar instance.
	 *
	 * @param  Connection  $connection
	 * @return void
	 */
	public function __construct(Connection $connection)
	{
		$this->connection = $connection;
	}

	/**
	 * Wrap a table in keyword identifiers.
	 *
	 * @param  string  $table
	 * @return string
	 */
	public function wrap_table($table)
	{
		// Expressions should be injected into the query as raw strings
		// so we do not want to wrap them in any way. We will just return
		// the string value from the expression to be included.
		if ($table instanceof Expression)
		{
			return $this->wrap($table);
		}

		$prefix = '';

		// Tables may be prefixed with a string. This allows developers to
		// prefix tables by application on the same database which may be
		// required in some brown-field situations.
		if (isset($this->connection->config['prefix']))
		{
			$prefix = $this->connection->config['prefix'];
		}

		return $this->wrap($prefix.$table);
	}

	/**
	 * Wrap a value in keyword identifiers.
	 *
	 * @param  string  $value
	 * @return string
	 */
	public function wrap($value)
	{
		// Expressions should be injected into the query as raw strings
		// so we do not want to wrap them in any way. We will just return
		// the string value from the expression to be included.
		if ($value instanceof Expression)
		{
			return $value->get();
		}

		// If the value being wrapped contains a column alias, we need to
		// wrap it a little differently as each segment must be wrapped
		// and not the entire string.
		if (strpos(strtolower($value), ' as ') !== false)
		{
			$segments = explode(' ', $value);

			return sprintf(
				'%s AS %s',
				$this->wrap($segments[0]),
				$this->wrap($segments[2])
			);
		}

		// Since columns may be prefixed with their corresponding table
		// name so as to not make them ambiguous, we will need to wrap
		// the table and the column in keyword identifiers.
		$segments = explode('.', $value);

		foreach ($segments as $key => $value)
		{
			if ($key == 0 and count($segments) > 1)
			{
				$wrapped[] = $this->wrap_table($value);
			}
			else
			{
				$wrapped[] = $this->wrap_value($value);
			}
		}

		return implode('.', $wrapped);
	}

	/**
	 * Wrap a single string value in keyword identifiers.
	 *
	 * @param  string  $value
	 * @return string
	 */
	protected function wrap_value($value)
	{
		return ($value !== '*') ? sprintf($this->wrapper, $value) : $value;
	}

	/**
	 * Create query parameters from an array of values.
	 *
	 * <code>
	 *		Returns "?, ?, ?", which may be used as PDO place-holders
	 *		$parameters = $grammar->parameterize(array(1, 2, 3));
	 *
	 *		// Returns "?, "Taylor"" since an expression is used
	 *		$parameters = $grammar->parameterize(array(1, DB::raw('Taylor')));
	 * </code>
	 *
	 * @param  array   $values
	 * @return string
	 */
	final public function parameterize($values)
	{
		return implode(', ', array_map(array($this, 'parameter'), $values));
	}

	/**
	 * Get the appropriate query parameter string for a value.
	 *
	 * <code>
	 *		// Returns a "?" PDO place-holder
	 *		$value = $grammar->parameter('Taylor Otwell');
	 *
	 *		// Returns "Taylor Otwell" as the raw value of the expression
	 *		$value = $grammar->parameter(DB::raw('Taylor Otwell'));
	 * </code>
	 *
	 * @param  mixed   $value
	 * @return string
	 */
	final public function parameter($value)
	{
		return ($value instanceof Expression) ? $value->get() : '?';
	}

	/**
	 * Create a comma-delimited list of wrapped column names.
	 *
	 * <code>
	 *		// Returns ""Taylor", "Otwell"" when the identifier is quotes
	 *		$columns = $grammar->columnize(array('Taylor', 'Otwell'));
	 * </code>
	 *
	 * @param  array   $columns
	 * @return string
	 */
	final public function columnize($columns)
	{
		return implode(', ', array_map(array($this, 'wrap'), $columns));
	}

}