<?php

namespace Psr\Http\Message;

use InvalidArgumentException;

/**
 * HTTP messages consist of requests from a client to a server and responses
 * from a server to a client. This interface defines the methods common to
 * each.
 *
 * Messages are considered immutable; all methods that might change state MUST
 * be implemented such that they retain the internal state of the current
 * message and return an instance that contains the changed state.
 *
 * @link http://www.ietf.org/rfc/rfc7230.txt
 * @link http://www.ietf.org/rfc/rfc7231.txt
 */
interface MessageInterface {
	/**
	 * Retrieves the HTTP protocol version as a string.
	 *
	 * The string MUST contain only the HTTP version number (e.g., "1.1", "1.0").
	 *
	 * @return string HTTP protocol version.
	 */
	public function getProtocolVersion();

	/**
	 * Return an instance with the specified HTTP protocol version.
	 *
	 * The version string MUST contain only the HTTP version number (e.g.,
	 * "1.1", "1.0").
	 *
	 * This method MUST be implemented in such a way as to retain the
	 * immutability of the message, and MUST return an instance that has the
	 * new protocol version.
	 *
	 * @param string $version HTTP protocol version
	 *
	 * @return static
	 */
	public function withProtocolVersion( $version );

	/**
	 * Retrieves all message header values.
	 *
	 * The keys represent the header name as it will be sent over the wire, and
	 * each value is an array of strings associated with the header.
	 *
	 *     // Represent the headers as a string
	 *     foreach ($message->getHeaders() as $name => $values) {
	 *         echo $name . ": " . implode(", ", $values);
	 *     }
	 *
	 *     // Emit headers iteratively:
	 *     foreach ($message->getHeaders() as $name => $values) {
	 *         foreach ($values as $value) {
	 *             header(sprintf('%s: %s', $name, $value), false);
	 *         }
	 *     }
	 *
	 * While header names are not case-sensitive, getHeaders() will preserve the
	 * exact case in which headers were originally specified.
	 *
	 * @return string[][] Returns an associative array of the message's headers. Each
	 *     key MUST be a header name, and each value MUST be an array of strings
	 *     for that header.
	 */
	public function getHeaders();

	/**
	 * Checks if a header exists by the given case-insensitive name.
	 *
	 * @param string $name Case-insensitive header field name.
	 *
	 * @return bool Returns true if any header names match the given header
	 *     name using a case-insensitive string comparison. Returns false if
	 *     no matching header name is found in the message.
	 */
	public function hasHeader( $name );

	/**
	 * Retrieves a message header value by the given case-insensitive name.
	 *
	 * This method returns an array of all the header values of the given
	 * case-insensitive header name.
	 *
	 * If the header does not appear in the message, this method MUST return an
	 * empty array.
	 *
	 * @param string $name Case-insensitive header field name.
	 *
	 * @return string[] An array of string values as provided for the given
	 *    header. If the header does not appear in the message, this method MUST
	 *    return an empty array.
	 */
	public function getHeader( $name );

	/**
	 * Retrieves a comma-separated string of the values for a single header.
	 *
	 * This method returns all of the header values of the given
	 * case-insensitive header name as a string concatenated together using
	 * a comma.
	 *
	 * NOTE: Not all header values may be appropriately represented using
	 * comma concatenation. For such headers, use getHeader() instead
	 * and supply your own delimiter when concatenating.
	 *
	 * If the header does not appear in the message, this method MUST return
	 * an empty string.
	 *
	 * @param string $name Case-insensitive header field name.
	 *
	 * @return string A string of values as provided for the given header
	 *    concatenated together using a comma. If the header does not appear in
	 *    the message, this method MUST return an empty string.
	 */
	public function getHeaderLine( $name );

	/**
	 * Return an instance with the provided value replacing the specified header.
	 *
	 * While header names are case-insensitive, the casing of the header will
	 * be preserved by this function, and returned from getHeaders().
	 *
	 * This method MUST be implemented in such a way as to retain the
	 * immutability of the message, and MUST return an instance that has the
	 * new and/or updated header and value.
	 *
	 * @param string $name Case-insensitive header field name.
	 * @param string|string[] $value Header value(s).
	 *
	 * @return static
	 * @throws InvalidArgumentException for invalid header names or values.
	 */
	public function withHeader( $name, $value );

	/**
	 * Return an instance with the specified header appended with the given value.
	 *
	 * Existing values for the specified header will be maintained. The new
	 * value(s) will be appended to the existing list. If the header did not
	 * exist previously, it will be added.
	 *
	 * This method MUST be implemented in such a way as to retain the
	 * immutability of the message, and MUST return an instance that has the
	 * new header and/or value.
	 *
	 * @param string $name Case-insensitive header field name to add.
	 * @param string|string[] $value Header value(s).
	 *
	 * @return static
	 * @throws InvalidArgumentException for invalid header names or values.
	 */
	public function withAddedHeader( $name, $value );

	/**
	 * Return an instance without the specified header.
	 *
	 * Header resolution MUST be done without case-sensitivity.
	 *
	 * This method MUST be implemented in such a way as to retain the
	 * immutability of the message, and MUST return an instance that removes
	 * the named header.
	 *
	 * @param string $name Case-insensitive header field name to remove.
	 *
	 * @return static
	 */
	public function withoutHeader( $name );

	/**
	 * Gets the body of the message.
	 *
	 * @return StreamInterface Returns the body as a stream.
	 */
	public function getBody();

	/**
	 * Return an instance with the specified message body.
	 *
	 * The body MUST be a StreamInterface object.
	 *
	 * This method MUST be implemented in such a way as to retain the
	 * immutability of the message, and MUST return a new instance that has the
	 * new body stream.
	 *
	 * @param StreamInterface $body Body.
	 *
	 * @return static
	 * @throws InvalidArgumentException When the body is not valid.
	 */
	public function withBody( StreamInterface $body );
}
