<?php

namespace Wikimedia\Assert;

/**
 * Assert provides functions for assorting preconditions (such as parameter types) and
 * postconditions. It is intended as a safer alternative to PHP's assert() function.
 *
 * Note that assertions evaluate expressions and add function calls, so using assertions
 * may have a negative impact on performance when used in performance hotspots. The idea
 * if this class is to have a neat tool for assertions if and when they are needed.
 * It is not recommended to place assertions all over the code indiscriminately.
 *
 * For more information, see the the README file.
 *
 * @since 0.1.0
 *
 * @license MIT
 * @author Daniel Kinzler
 * @author Thiemo Kreuz
 * @copyright Wikimedia Deutschland e.V.
 */
class Assert {

	/**
	 * Checks a precondition, that is, throws a PreconditionException if $condition is false.
	 * For checking call parameters, use Assert::parameter() instead.
	 *
	 * This is provided for completeness, most preconditions should be covered by
	 * Assert::parameter() and related assertions.
	 *
	 * @see parameter()
	 *
	 * @note This is intended mostly for checking preconditions in constructors and setters,
	 * or before using parameters in complex computations.
	 * Checking preconditions in every function call is not recommended, since it may have a
	 * negative impact on performance.
	 *
	 * @since 0.1.0
	 *
	 * @param bool $condition
	 * @param string $description The message to include in the exception if the condition fails.
	 *
	 * @throws PreconditionException if $condition is not true.
	 * @phan-assert-true-condition $condition
	 */
	public static function precondition( $condition, $description ): void {
		if ( !$condition ) {
			throw new PreconditionException( "Precondition failed: $description" );
		}
	}

	/**
	 * Checks a parameter, that is, throws a ParameterAssertionException if $condition is false.
	 * This is similar to Assert::precondition().
	 *
	 * @note This is intended for checking parameters in constructors and setters.
	 * Checking parameters in every function call is not recommended, since it may have a
	 * negative impact on performance.
	 *
	 * @since 0.1.0
	 *
	 * @param bool $condition
	 * @param string $name The name of the parameter that was checked.
	 * @param string $description The message to include in the exception if the condition fails.
	 *
	 * @throws ParameterAssertionException if $condition is not true.
	 * @phan-assert-true-condition $condition
	 */
	public static function parameter( $condition, $name, $description ): void {
		if ( !$condition ) {
			throw new ParameterAssertionException( $name, $description );
		}
	}

	/**
	 * Checks an parameter's type, that is, throws a InvalidArgumentException if $value is
	 * not of $type. This is really a special case of Assert::precondition().
	 *
	 * @note This is intended for checking parameters in constructors and setters.
	 * Checking parameters in every function call is not recommended, since it may have a
	 * negative impact on performance.
	 *
	 * @note If possible, type hints should be used instead of calling this function.
	 * It is intended for cases where type hints to not work, e.g. for checking union types.
	 *
	 * @since 0.1.0
	 *
	 * @param string|string[] $types The parameter's expected type. Can be the name of a native type
	 *        or a class or interface, or a list of such names.
	 *        For compatibility with versions before 0.4.0, multiple types can also be given separated
	 *        by pipe characters ("|").
	 * @param mixed $value The parameter's actual value.
	 * @param string $name The name of the parameter that was checked.
	 *
	 * @throws ParameterTypeException if $value is not of type (or, for objects, is not an
	 *         instance of) $type.
	 *
	 */
	public static function parameterType( $types, $value, $name ): void {
		if ( is_string( $types ) ) {
			$types = explode( '|', $types );
		}
		if ( !self::hasType( $value, $types ) ) {
			throw new ParameterTypeException( $name, implode( '|', $types ) );
		}
	}

	/**
	 * @since 0.3.0
	 *
	 * @param string $type Either "integer" or "string". Mixing "integer|string" is not supported
	 *  because this is PHP's default anyway. It is of no value to check this.
	 * @param array $value The parameter's actual value. If this is not an array, a
	 *  ParameterTypeException is raised.
	 * @param string $name The name of the parameter that was checked.
	 *
	 * @throws ParameterTypeException if one of the keys in the array $value is not of type $type.
	 */
	public static function parameterKeyType( $type, $value, $name ): void {
		self::parameterType( 'array', $value, $name );

		if ( $type !== 'integer' && $type !== 'string' ) {
			throw new ParameterAssertionException( 'type', 'must be "integer" or "string"' );
		}

		foreach ( $value as $key => $element ) {
			if ( gettype( $key ) !== $type ) {
				throw new ParameterKeyTypeException( $name, $type );
			}
		}
	}

	/**
	 * Checks the type of all elements of an parameter, assuming the parameter is an array,
	 * that is, throws a ParameterElementTypeException if any elements in $value are not of $type.
	 *
	 * @note This is intended for checking parameters in constructors and setters.
	 * Checking parameters in every function call is not recommended, since it may have a
	 * negative impact on performance.
	 *
	 * @since 0.1.0
	 *
	 * @param string|string[] $types The elements' expected type. Can be the name of a native type
	 *        or a class or interface. Multiple types can be given in an array (or a string separated
	 *        by a pipe character ("|"), for compatibility with versions before 0.5.0).
	 * @param array $value The parameter's actual value. If this is not an array,
	 *        a ParameterTypeException is raised.
	 * @param string $name The name of the parameter that was checked.
	 *
	 * @throws ParameterTypeException If $value is not an array.
	 * @throws ParameterElementTypeException If an element of $value  is not of type
	 *         (or, for objects, is not an instance of) $type.
	 *
	 */
	public static function parameterElementType( $types, $value, $name ): void {
		self::parameterType( 'array', $value, $name );
		if ( is_string( $types ) ) {
			$types = explode( '|', $types );
		}

		foreach ( $value as $element ) {
			if ( !self::hasType( $element, $types ) ) {
				throw new ParameterElementTypeException( $name, implode( '|', $types ) );
			}
		}
	}

	/**
	 * @since 0.3.0
	 *
	 * @param string $value
	 * @param string $name
	 *
	 * @throws ParameterTypeException if $value is not a non-empty string.
	 * @phan-assert non-empty-string $value
	 */
	public static function nonEmptyString( $value, $name ): void {
		if ( !is_string( $value ) || $value === '' ) {
			throw new ParameterTypeException( $name, 'non-empty string' );
		}
	}

	/**
	 * Checks a postcondition, that is, throws a PostconditionException if $condition is false.
	 * This is very similar Assert::invariant() but is intended for use only after a computation
	 * is complete.
	 *
	 * @note This is intended for double checking in the implementation of complex algorithms.
	 * Note however that it should not be used in performance hotspots, since evaluating
	 * $condition and calling postcondition() costs time.
	 *
	 * @since 0.1.0
	 *
	 * @param bool $condition
	 * @param string $description The message to include in the exception if the condition fails.
	 *
	 * @throws PostconditionException
	 * @phan-assert-true-condition $condition
	 */
	public static function postcondition( $condition, $description ): void {
		if ( !$condition ) {
			throw new PostconditionException( "Postcondition failed: $description" );
		}
	}

	/**
	 * Checks an invariant, that is, throws a InvariantException if $condition is false.
	 * This is very similar Assert::postcondition() but is intended for use throughout the code.
	 *
	 * @note The $condition is expected to be falsifiable.  If you are trying
	 * to indicate that a code path is unreachable, use
	 * `throw new UnreachableException( 'why this code is unreachable' )`
	 * instead of `Assert::invariant( false, '…' )`.  Code checking tools
	 * will complain about the latter.
	 *
	 * @note This is intended for double checking in the implementation of complex algorithms.
	 * Note however that it should not be used in performance hotspots, since evaluating
	 * $condition and calling invariant() costs time.
	 *
	 * @since 0.1.0
	 *
	 * @param bool $condition
	 * @param string $description The message to include in the exception if the condition fails.
	 *
	 * @throws InvariantException
	 * @phan-assert-true-condition $condition
	 */
	public static function invariant( $condition, $description ): void {
		if ( !$condition ) {
			throw new InvariantException( "Invariant failed: $description" );
		}
	}

	/**
	 * @param mixed $value
	 * @param string[] $allowedTypes
	 *
	 * @return bool
	 */
	private static function hasType( $value, array $allowedTypes ): bool {
		// Apply strtolower because gettype returns "NULL" for null values.
		$type = strtolower( gettype( $value ) );

		if ( in_array( $type, $allowedTypes ) ) {
			return true;
		}

		if ( in_array( 'callable', $allowedTypes ) && is_callable( $value ) ) {
			return true;
		}

		if ( is_object( $value ) && self::isInstanceOf( $value, $allowedTypes ) ) {
			return true;
		}

		if ( is_array( $value ) && in_array( 'Traversable', $allowedTypes ) ) {
			return true;
		}

		if ( $value === false && in_array( 'false', $allowedTypes ) ) {
			return true;
		}
		if ( $value === true && in_array( 'true', $allowedTypes ) ) {
			return true;
		}

		return false;
	}

	/**
	 * @param object $value
	 * @param string[] $allowedTypes
	 *
	 * @return bool
	 */
	private static function isInstanceOf( $value, array $allowedTypes ): bool {
		foreach ( $allowedTypes as $type ) {
			if ( $value instanceof $type ) {
				return true;
			}
		}

		return false;
	}

}