<?php
/**
 * DataTables PHP libraries.
 *
 * PHP libraries for DataTables and DataTables Editor, utilising PHP 5.3+.
 *
 *  @author    SpryMedia
 *  @copyright 2012-2014 SpryMedia ( http://sprymedia.co.uk )
 *  @license   http://editor.datatables.net/license DataTables Editor
 *  @link      http://editor.datatables.net
 */

namespace DataTables\Editor;
if (!defined('DATATABLES')) exit();

use DataTables\Editor\ValidateOptions;

/**
 * Validation methods for DataTables Editor fields.
 *
 * These methods will typically be applied through the {@see Field::validator()}
 * method and thus the arguments to be passed will be automatically resolved
 * by Editor.
 *
 * The validation methods in this class all take three parameters:
 *
 * 1. Data to be validated
 * 2. Full data from the form (this can be used with a custom validation method
 *    for dependent validation).
 * 3. Validation configuration options.
 *
 * When using the `Validate` class functions with the {@see Field::validator()}
 * method, the second parameter passed into {@see Field::validator()} is given
 * to the validation functions here as the third parameter. The first and
 * second parameters are automatically resolved by the {@see Field} class.
 *
 * The validation configuration options is an array of options that can be used
 * to customise the validation - for example defining a date format for date
 * validation. Each validation method has the option of defining its own
 * validation options, but all validation methods provide four common options:
 *
 * * `{boolean} optional` - Require the field to be submitted (`false`) or not
 *   (`true` - default). When set to `true` the field does not need to be
 *   included in the list of parameters sent by the client - if set to `false`
 *   then it must be included. This option can be be particularly used in Editor
 *   as Editor will not set a value for fields which have not been submitted -
 *   giving the ability to submit just a partial list of options.
 * * `{boolean} empty` - Allow a field to be empty, i.e. a zero length string -
 *   `''` (`true` - default) or require it to be non-zero length (`false`).
 * * `{boolean} required` - Short-cut for `optional=false` and `empty=false`.
 *   Note that if this option is set the `optional` and `empty` parameters are
 *   automatically set and cannot be overridden by passing in different values.
 * * `{string} message` - Error message shown should validation fail. This
 *   provides complete control over the message shown to the end user, including
 *   internationalisation (i.e. to provide a translation that is not in the
 *   English language).
 *
 *  @example
 *    ```
 *      // Ensure that a non-empty value is given for a field
 *      Field::inst( 'engine' )->validator( Validate::required() )
 *    ```
 *
 *  @example
 *    ```
 *      // Don't require a field to be submitted, but if it is submitted, it
 *      // must be non-empty
 *      Field::inst( 'reg_date' )->validator( Validate::notEmpty() )
 *    ```
 *
 *  @example
 *    ```
 *      // Date validation
 *      Field::inst( 'reg_date' )->validator( Validate::dateFormat( 'D, d M y' ) )
 *    ```
 *
 *  @example
 *    ```
 *      // Date validation with a custom error message
 *      Field::inst( 'reg_date' )->validator( Validate::dateFormat( 'D, d M y',
 *          ValidateOptions::inst()
 *              ->message( 'Invalid date' )
 *      ) )
 *    ```
 *
 *  @example
 *    ```
 *      // Require a non-empty e-mail address
 *      Field::inst( 'reg_date' )->validator( Validate::email( ValidateOptions::inst()
 *        ->empty( false )
 *      ) )
 *    ```
 *
 *  @example
 *    ```
 *      // Custom validation - closure
 *      Field::inst( 'engine' )->validator( function($val, $data, $opts) {
 *         if ( ! preg_match( '/^1/', $val ) ) {
 *           return "Value <b>must</b> start with a 1";
 *         }
 *         return true;
 *      } )
 *    ```
 */
class Validate {
	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Internal functions
	 */

	/**
	 * "Magic" method to automatically apply the required check to any of the
	 * static methods simply by adding '_required' or '_empty' to the end of the
	 * method's name, depending on if you need the field to be submitted or not.
	 *
	 * This is retained for backwards compatibility, but the validation options
	 * are now the recommended way of indicating that a field is required.
	 *
	 * @internal
	 * @param string $name Function name
	 * @param array $arguments Function arguments
	 * @return mixed|string
	 */
	public static function __callStatic( $name, $arguments ) {
		if ( preg_match( '/_required$/', $name ) ) {
			if ( $arguments[0] === null || $arguments[0] === '' ) {
				return 'This field is required';
			}

			return call_user_func_array( 
				__NAMESPACE__.'\Validate::'.str_replace( '_required', '', $name ),
				$arguments
			);
		}
	}


	/**
	 * Extend the options from the user function and the validation function
	 * with core defaults.
	 *
	 *  @internal
	 */
	public static function _extend( $userOpts, $prop, $fnOpts ) {
		$cfg = array(
			'message'  => 'Input not valid',
			'required' => false,
			'empty'    => true,
			'optional' => true
		);

		if ( ! is_array( $userOpts ) ) {
			if ( $prop ) {
				$cfg[ $prop ] = $userOpts;
			}

			// Not an array, but the non-array case has been handled above, so
			// just an empty array
			$userOpts = array();
		}

		// Merge into a single array - first array gets priority if there is a
		// key clash, so user first, then function commands and finally the
		// global options 
		$cfg = $userOpts + $fnOpts + $cfg;

		return $cfg;
	}


	/**
	 * Perform common validation using the configuration parameters
	 *
	 *  @internal
	 */
	public static function _common( $val, $opts ) {
		$optional = $opts->optional();
		$empty    = $opts->allowEmpty();

		// Error state tests
		if ( ! $optional && $val === null  ) {
			// Value must be given
			return false;
		}
		else if ( $empty === false && $val === '' ) {
			// Value must not be empty
			return false;
		}
		
		// Validation passed states
		if ( $optional && $val === null ) {
			return true;
		}
		else if ( $empty === true && $val === '' ) {
			return true;
		}

		// Have the specific validation function perform its tests
		return null;
	}

	/**
	 * Convert the old style validation parameters into ValidateOptions
	 *
	 *  @internal
	 */
	public static function _commonLegacy( $cfg ) {
		$opts = new ValidateOptions();

		if ( is_array( $cfg ) ) {
			// `required` is a legacy shortcut for optional=false, empty=false
			if ( isset( $cfg['required'] ) ) {
				$opts->optional( false );
				$opts->allowEmpty( false );
			}

			if ( isset( $cfg['empty'] ) ) {
				$opts->allowEmpty( $cfg['empty'] );
			}

			if ( isset( $cfg['message'] ) ) {
				$opts->message( $cfg['message'] );
			}

			if ( isset( $cfg['optional'] ) ) {
				$opts->optional( $cfg['optional'] );
			}
		}

		return $opts;
	}


	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Basic validation
	 */

	/**
	 * No validation - all inputs are valid.
	 *  @return callable Validation function
	 */
	public static function none() {
		return function ( $val, $data, $field, $host ) {
			return true;
		};
	}


	/**
	 * Basic validation - this is used to perform the validation provided by the
	 * validation options only. If the validation options pass (e.g. `required`,
	 * `empty` and `optional`) then the validation will pass regardless of the
	 * actual value.
	 *
	 * Note that there are two helper short-cut methods that provide the same
	 * function as this method, but are slightly shorter:
	 *
	 * ```
	 * // Required:
	 * Validate::required()
	 *
	 * // is the same as
	 * Validate::basic( $val, $data, array(
	 *   "required" => true
	 * );
	 * ```
	 *
	 * ```
	 * // Optional, but not empty if given:
	 * Validate::notEmpty()
	 *
	 * // is the same as
	 * Validate::basic( $val, $data, array(
	 *   "empty" => false
	 * );
	 * ```
	 *
	 * @param string $val The value to check for validity
	 * @param string[] $data The full data set submitted
	 * @param array $opts Validation options. No additional options are
	 *    available or required for this validation method.
	 * @param array $host Host information
	 * @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	static function basic( $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );

		return function ( $val, $data, $field, $host ) use ( $opts ) {
			$common = Validate::_common( $val, $opts );

			return $common === false ?
				$opts->message() :
				true;
		};
	}


	/**
	 * Required field - there must be a value and it must be a non-empty value
	 *
	 * This is a helper short-cut method which is the same as:
	 * 
	 * ```
	 * Validate::basic( $val, $data, array(
	 *   "required" => true
	 * );
	 * ```
	 * 
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param array $opts Validation options. No additional options are
	 *    available or required for this validation method.
	 * @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	static function required( $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		$opts->allowEmpty( false );
		$opts->optional( false );

		return function ( $val, $data, $field, $host ) use ( $opts ) {
			$common = Validate::_common( $val, $opts );

			return $common === false ?
				$opts->message() :
				true;
		};
	}


	/**
	 * Optional field, but if given there must be a non-empty value
	 *
	 * This is a helper short-cut method which is the same as:
	 * 
	 * ```
	 * Validate::basic( $val, $data, array(
	 *   "empty" => false
	 * );
	 * ```
	 *
	 *  @param ValidateOptions $cfg Validation options
	 *  @return callable Validation function
	 */
	static function notEmpty( $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		$opts->allowEmpty( false );

		return function ( $val, $data, $field, $host ) use ( $opts ) {
			$common = Validate::_common( $val, $opts );

			return $common === false ?
				$opts->message() :
				true;
		};
	}


	/**
	 * Validate an input as a boolean value.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param array $opts Validation options. No additional options are
	 *    available or required for this validation method.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function boolean( $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );

		return function ( $val, $data, $field, $host ) use ( $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}
	
			if ( filter_var($val, FILTER_VALIDATE_BOOLEAN, FILTER_NULL_ON_FAILURE) === null ) {
				return $opts->message();
			}
			return true;
		};
	}


	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Number validation methods
	 */

	/**
	 * Check that any input is numeric.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param array $opts Validation options. Additional options:
	 *     * `decimal`: is available to indicate what character should be used
	 *       as the decimal
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function numeric ( $decimal=".", $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );

		return function ( $val, $data, $field, $host ) use ( $opts, $decimal ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}
	
			if ( $decimal !== '.' ) {
				$val = str_replace( $decimal, '.', $val );
			}
	
			return ! is_numeric( $val ) ?
				$opts->message() :
				true;
		};
	}

	/**
	 * Check for a numeric input and that it is greater than a given value.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. Additional options:
	 *     * `min`: indicate the minimum value. If only the default validation
	 *       options are required, this parameter can be given as an integer
	 *       value, which will be used as the minimum value.
	 *     * `decimal`: is available to indicate what character should be used
	 *       as the decimal
	 *    separator (default '.').
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function minNum ( $min, $decimal=".", $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );

		return function ( $val, $data, $field, $host ) use ( $opts, $min, $decimal ) {
			$common = Validate::_common( $val, $opts );
			
			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}
			
			$fn = Validate::numeric( $decimal, $opts );
			$numeric = $fn( $val, $data, $field, $host );

			if ( $numeric !== true ) {
				return $numeric;
			}
	
			if ( $decimal !== '.' ) {
				$val = str_replace( $decimal, '.', $val );
			}
	
			return $val < $min ?
				$opts->message() :
				true;
		};
	}

	/**
	 * Check for a numeric input and that it is less than a given value.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options.
	 *     * `max`: indicate the maximum value. If only the default validation
	 *       options are required, this parameter can be given as an integer
	 *       value, which will be used as the maximum value.
	 *     * `decimal`: is available to indicate what character should be used
	 *       as the decimal
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function maxNum ( $max, $decimal=".", $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );

		return function ( $val, $data, $field, $host ) use ( $opts, $max, $decimal ) {
			$common = Validate::_common( $val, $opts );
			
			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}
			
			$fn = Validate::numeric( $decimal, $opts );
			$numeric = $fn( $val, $data, $field, $host );

			if ( $numeric !== true ) {
				return $numeric;
			}
	
			if ( $decimal !== '.' ) {
				$val = str_replace( $decimal, '.', $val );
			}
	
			return $val > $max ?
				$opts->message() :
				true;
		};
	}


	/**
	 * Check for a numeric input and that it is both greater and smaller than
	 * given numbers.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. Additional options:
	 *     * `min`: indicate the minimum value.
	 *     * `max`: indicate the maximum value.
	 *     * `decimal`: is available to indicate what character should be used
	 *       as the decimal
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function minMaxNum ( $min, $max, $decimal='.', $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $opts, $min, $max, $decimal ) {
			$common = Validate::_common( $val, $opts );
			
			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}
			
			$fn = Validate::numeric( $decimal, $opts );
			$numeric = $fn( $val, $data, $field, $host );

			if ( $numeric !== true ) {
				return $numeric;
			}

			$fn = Validate::minNum( $min, $decimal, $opts );
			$numeric = $fn( $val, $data, $field, $host );

			if ( $numeric !== true ) {
				return $numeric;
			}
			
			$fn = Validate::maxNum( $max, $decimal, $opts );
			$numeric = $fn( $val, $data, $field, $host );

			if ( $numeric !== true ) {
				return $numeric;
			}

			return true;
		};
	}


	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * String validation methods
	 */

	/**
	 * Validate an input as an e-mail address.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param array $opts Validation options. No additional options are
	 *    available or required for this validation method.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function email( $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			return filter_var($val, FILTER_VALIDATE_EMAIL) !== false ?
				true :
				$opts->message();
		};
	}


	/**
	 * Validate a string has a minimum length.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. The additional option of
	 *    `min` is available for this method to indicate the minimum string
	 *    length. If only the default validation options are required, this
	 *    parameter can be given as an integer value, which will be used as the
	 *    minimum string length.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function minLen( $min, $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $min, $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			$strlen = is_callable('mb_strlen') ?
				'mb_strlen' :
				'strlen';

			return $strlen( $val ) < $min ?
				$opts->message() :
				true;
		};
	}


	/**
	 * Validate a string does not exceed a maximum length.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. The additional option of
	 *    `max` is available for this method to indicate the maximum string
	 *    length. If only the default validation options are required, this
	 *    parameter can be given as an integer value, which will be used as the
	 *    maximum string length.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function maxLen( $max, $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $max, $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			$strlen = is_callable('mb_strlen') ?
				'mb_strlen' :
				'strlen';

			return $strlen( $val ) > $max ?
				$opts->message() :
				true;
		};
	}

	/**
	 * Require a string with a certain minimum or maximum number of characters.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. The additional options of
	 *    `min` and `max` are available for this method to indicate the minimum
	 *    and maximum string lengths, respectively.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function minMaxLen( $min, $max, $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $opts, $min, $max ) {
			$common = Validate::_common( $val, $opts );
			
			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}
			
			$fn = Validate::minLen( $min, $opts );
			$res = $fn( $val, $data, $field, $host );

			if ( $res !== true ) {
				return $res;
			}
			
			$fn = Validate::maxLen( $max, $opts );
			$res = $fn( $val, $data, $field, $host );

			if ( $res !== true ) {
				return $res;
			}

			return true;
		};
	}


	/**
	 * Validate as an IP address.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param array $opts Validation options. No additional options are
	 *    available or required for this validation method.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function ip( $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			return filter_var($val, FILTER_VALIDATE_IP) !== false ?
				true :
				$opts->message();
		};
	}


	/**
	 * Validate as an URL address.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param array $opts Validation options. No additional options are
	 *    available or required for this validation method.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function url( $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			return filter_var($val, FILTER_VALIDATE_URL) !== false ?
				true :
				$opts->message();
		};
	}


	/**
	 * Check if string could contain an XSS attack string
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. The additional options of
	 *    `db` - database connection object, `table` - database table to use and
	 *    `column` - the column to check this value against as value, are also
	 *    available. These options are not required and if not given are
	 *    automatically derived from the Editor and Field instances.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function xss ( $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			return $field->xssSafety( $val ) != $val ?
				$opts->message() :
				true;
		};
	}


	/**
	 * Confirm that the value submitted is in a list of allowable values
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. The additional options of
	 *    `db` - database connection object, `table` - database table to use and
	 *    `column` - the column to check this value against as value, are also
	 *    available. These options are not required and if not given are
	 *    automatically derived from the Editor and Field instances.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function values( $values, $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $values, $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			return in_array($val, $values) ?
				true :
				$opts->message();
		};
	}


	/**
	 * Check if there are any tags in the submitted value
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. The additional options of
	 *    `db` - database connection object, `table` - database table to use and
	 *    `column` - the column to check this value against as value, are also
	 *    available. These options are not required and if not given are
	 *    automatically derived from the Editor and Field instances.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function noTags ( $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			return strip_tags( $val ) != $val ?
				$opts->message() :
				true;
		};
	}


	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Date validation methods
	 */

	/**
	 * Check that a valid date input is given
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param array|string $opts If given as a string, then $opts is the date
	 *    format to check the validity of. If given as an array, then the
	 *    date format is in the 'format' parameter, and the return error
	 *    message in the 'message' parameter.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function dateFormat( $format, $cfg=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $format, $opts ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			$formatCreate = substr($format, 0, 1) !== '!' ?
				'!'.$format :
				$format;

			$date = \DateTime::createFromFormat( $formatCreate, $val );

			return $date && $date->format( $format ) === $val ?
				true :
				$opts->message();
		};
	}


	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Database validation methods
	 */

	/**
	 * Check that the given value is unique in the database
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. The additional options of
	 *    `db` - database connection object, `table` - database table to use and
	 *    `column` - the column to check this value against as value, are also
	 *    available. These options are not required and if not given are
	 *    automatically derived from the Editor and Field instances.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function unique( $cfg=null, $column=null, $table=null, $db=null ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $opts, $column, $table, $db ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			$editor = $host['editor'];

			if ( ! $db ) {
				$db = $host['db'];
			}

			if ( ! $table ) {
				$table = $editor->table(); // Returns an array, but `select` will take an array
			}

			if ( ! $column ) {
				$column = $field->dbField();
			}

			$query = $db
				->query( 'select', $table )
				->get( $column )
				->where( $column, $val );

			// If doing an edit, then we need to also discount the current row,
			// since it is of course already validly unique
			if ( $host['action'] === 'edit' ) {
				$cond = $editor->pkeyToArray( $host['id'], true );
				$query->where( $cond, null, '!=' );
			}

			$res = $query->exec();

			return $res->count() === 0 ?
				true :
				$opts->message(); 
		};
	}

	/**
	 * Check that the given value is a value that is available in a database -
	 * i.e. a join primary key. This will attempt to automatically use the table
	 * name and value column from the field's `options` method (under the
	 * assumption that it will typically be used with a joined field), but the
	 * table and field can also be specified via the options.
	 *
	 *  @param string $val The value to check for validity
	 *  @param string[] $data The full data set submitted
	 *  @param int|array $opts Validation options. The additional options of
	 *    `db` - database connection object, `table` - database table to use and
	 *    `column` - the column to check this value against as value, are also
	 *    available. These options are not required and if not given are
	 *    automatically derived from the Editor and Field instances.
	 *  @param array $host Host information
	 *  @return string|true true if the value is valid, a string with an error
	 *    message otherwise.
	 */
	public static function dbValues( $cfg=null, $column=null, $table=null, $db=null, $values=array() ) {
		$opts = ValidateOptions::select( $cfg );
		
		return function ( $val, $data, $field, $host ) use ( $opts, $column, $table, $db, $values ) {
			$common = Validate::_common( $val, $opts );

			if ( $common !== null ) {
				return $common === false ?
					$opts->message() :
					$common;
			}

			// Allow local values to be defined - for example null
			if ( in_array($val, $values) ) {
				return true;
			}

			$editor = $host['editor'];
			$options = $field->options();

			if ( ! $db ) {
				$db = $host['db'];
			}

			if ( ! $table ) {
				$table = $options->table(); // Returns an array, but `select` will take an array
			}

			if ( ! $column ) {
				$column = $options->value();
			}

			if ( ! $table ) {
				throw new \Exception('Table for database value check is not defined for field '.$field->name());
			}

			if ( ! $column ) {
				throw new \Exception('Value column for database value check is not defined for field '.$field->name());
			}

			// Try / catch in case the submitted value can't be represented as the
			// database type (e.g. an empty string as an integer)
			try {
				$count = $db
					->query( 'select', $table )
					->get( $column )
					->where( $column, $val )
					->exec()
					->count();

				return $count === 0 ?
					$opts->message() :
					true;
			}
			catch (\Exception $e) {
				return $opts->message();
			}
		};
	}
	
	
	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	* File validation methods
	*/
	static function fileExtensions ( $extensions, $msg="This file type cannot be uploaded." ) {
		return function ( $file ) use ( $extensions, $msg ) {
			$extn = pathinfo($file['name'], PATHINFO_EXTENSION);

			for ( $i=0, $ien=count($extensions) ; $i<$ien ; $i++ ) {
				if ( strtolower( $extn ) === strtolower( $extensions[$i] ) ) {
					return true;
				}
			}

			return $msg;
		};
	}

	static function fileSize ( $size, $msg="Uploaded file is too large." ) {
		return function ( $file ) use ( $size, $msg ) {
			return $file['size'] > $size ?
				$msg :
				true;
		};
	}


	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	* Mjoin validation methods
	*/
	static function mjoinMinCount ( $count, $msg="Too few items." ) {
		return function ( $editor, $action, $values ) use ( $count, $msg ) {
			if ( $action === 'create' || $action === 'edit' ) {
				return count($values) < $count ?
					$msg :
					true;
			}
			return true;
		};
	}

	static function mjoinMaxCount ( $count, $msg="Too many items." ) {
		return function ( $editor, $action, $values ) use ( $count, $msg ) {
			if ( $action === 'create' || $action === 'edit' ) {
				return count($values) > $count ?
					$msg :
					true;
			}
			return true;
		};
	}


	/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
	 * Internal functions
	 * These legacy methods are for backwards compatibility with the old way of
	 * using the validation methods. They basically do argument swapping.
	 */

	/**
	 * @internal
	 */
	static function noneLegacy( $legacyOpts ) {
		return Validate::none();
	}
	
	/**
	 * @internal
	 */
	static function basicLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array() );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::required( $opts );
	}
	
	/**
	 * @internal
	 */
	static function requiredLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "This field is required."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::required( $opts );
	}
	
	/**
	 * @internal
	 */
	static function notEmptyLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "This field is required."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::notEmpty( $opts );
	}
	
	/**
	 * @internal
	 */
	static function booleanLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "Please enter true or false."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::notEmpty( $opts );
	}
	
	/**
	 * @internal
	 */
	static function numericLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "This input must be given as a number."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return isset( $legacyOpts['decimal'] ) ?
			Validate::numeric( $legacyOpts['decimal'], $opts ) :
			Validate::numeric( '.', $opts );
	}
	
	/**
	 * @internal
	 */
	static function minNumLegacy( $legacyOpts ) {
		$min = is_array($legacyOpts) ? $legacyOpts['min'] : $legacyOpts;
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "Number is too small, must be ".$min." or larger."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return isset( $legacyOpts['decimal'] ) ?
			Validate::minNum( $min, $legacyOpts['decimal'], $opts ) :
			Validate::minNum( $min, '.', $opts );
	}
	
	/**
	 * @internal
	 */
	static function maxNumLegacy( $legacyOpts ) {
		$max = is_array($legacyOpts) ? $legacyOpts['max'] : $legacyOpts;
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "Number is too large, must be ".$max." or smaller."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return isset( $legacyOpts['decimal'] ) ?
			Validate::maxNum( $max, $legacyOpts['decimal'], $opts ) :
			Validate::maxNum( $max, '.', $opts );
	}
	
	/**
	 * @internal
	 */
	static function minMaxNumLegacy( $legacyOpts ) {
		$min = $legacyOpts['min'];
		$max = $legacyOpts['max'];
		$cfg = Validate::_extend( $legacyOpts, null, array() );
		$opts = Validate::_commonLegacy( $cfg );

		return isset( $legacyOpts['decimal'] ) ?
			Validate::minMaxNum( $min, $max, $legacyOpts['decimal'], $opts ) :
			Validate::minMaxNum( $min, $max, '.', $opts );
	}
	
	/**
	 * @internal
	 */
	static function emailLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "Please enter a valid e-mail address."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::email( $opts );
	}
	
	/**
	 * @internal
	 */
	static function minLenLegacy( $legacyOpts ) {
		$min = is_array($legacyOpts) ? $legacyOpts['min'] : $legacyOpts;
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "The input is too short. ".$min." characters required."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::minLen( $min, $opts );
	}
	
	/**
	 * @internal
	 */
	static function maxLenLegacy( $legacyOpts ) {
		$max = is_array($legacyOpts) ? $legacyOpts['max'] : $legacyOpts;
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "The input is too long. ".$max." characters maximum."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::maxLen( $max, $opts );
	}
	
	/**
	 * @internal
	 */
	static function minMaxLenLegacy( $legacyOpts ) {
		$min = $legacyOpts['min'];
		$max = $legacyOpts['max'];
		$cfg = Validate::_extend( $legacyOpts, null, array() );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::minMaxLen( $min, $max, $opts );
	}
	
	/**
	 * @internal
	 */
	static function ipLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "Please enter a valid IP address."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::ip( $opts );
	}
	
	/**
	 * @internal
	 */
	static function urlLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "Please enter a valid URL."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::url( $opts );
	}
	
	/**
	 * @internal
	 */
	static function xssLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "This field contains potentially unsafe data."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::xss( $opts );
	}
	
	/**
	 * @internal
	 */
	static function valuesLegacy( $legacyOpts ) {
		$values = isset($legacyOpts['valid']) ? $legacyOpts['valid'] : $legacyOpts;
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "This value is not valid."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::values( $values, $opts );
	}
	
	/**
	 * @internal
	 */
	static function noTagsLegacy( $legacyOpts ) {
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "This field may not contain HTML."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::noTags( $opts );
	}
	
	/**
	 * @internal
	 */
	static function dateFormatLegacy( $legacyOpts ) {
		$format = is_array($legacyOpts) ? $legacyOpts['format'] : $legacyOpts;
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "Date is not in the expected format."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::dateFormat( $format, $opts );
	}
	
	/**
	 * @internal
	 */
	static function uniqueLegacy( $legacyOpts ) {
		$table =  isset( $legacyOpts['table'] )  ? $legacyOpts['table']  : null;
		$column = isset( $legacyOpts['column'] ) ? $legacyOpts['column'] : null;
		$db =     isset( $legacyOpts['db'] )     ? $legacyOpts['db']     : null;
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "This field must have a unique value."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::unique( $opts, $column, $table, $db );
	}
	
	/**
	 * @internal
	 */
	static function dbValuesLegacy( $legacyOpts ) {
		$table =  isset( $legacyOpts['table'] )  ? $legacyOpts['table']  : null;
		$column = isset( $legacyOpts['column'] ) ? $legacyOpts['column'] : null;
		$db =     isset( $legacyOpts['db'] )     ? $legacyOpts['db']     : null;
		$values = isset( $legacyOpts['values'] ) ? $legacyOpts['values'] : array();
		$cfg = Validate::_extend( $legacyOpts, null, array(
			'message' => "This value is not valid."
		) );
		$opts = Validate::_commonLegacy( $cfg );

		return Validate::dbValues( $opts, $column, $table, $db, $values );
	}
}