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[mediawiki.git] / resources / src / jquery / jquery.byteLimit.js

/**
 * @class jQuery.plugin.byteLimit
 */
( function ( $ ) {

        /**
         * Utility function to trim down a string, based on byteLimit
         * and given a safe start position. It supports insertion anywhere
         * in the string, so "foo" to "fobaro" if limit is 4 will result in
         * "fobo", not "foba". Basically emulating the native maxlength by
         * reconstructing where the insertion occurred.
         *
         * @static
         * @param {string} safeVal Known value that was previously returned by this
         * function, if none, pass empty string.
         * @param {string} newVal New value that may have to be trimmed down.
         * @param {number} byteLimit Number of bytes the value may be in size.
         * @param {Function} [fn] See jQuery#byteLimit.
         * @return {Object}
         * @return {string} return.newVal
         * @return {boolean} return.trimmed
         */
        $.trimByteLength = function ( safeVal, newVal, byteLimit, fn ) {
                var startMatches, endMatches, matchesLen, inpParts,
                        oldVal = safeVal;

                // Run the hook if one was provided, but only on the length
                // assessment. The value itself is not to be affected by the hook.
                if ( $.byteLength( fn ? fn( newVal ) : newVal ) <= byteLimit ) {
                        // Limit was not reached, just remember the new value
                        // and let the user continue.
                        return {
                                newVal: newVal,
                                trimmed: false
                        };
                }

                // Current input is longer than the active limit.
                // Figure out what was added and limit the addition.
                startMatches = 0;
                endMatches = 0;

                // It is important that we keep the search within the range of
                // the shortest string's length.
                // Imagine a user adds text that matches the end of the old value
                // (e.g. "foo" -> "foofoo"). startMatches would be 3, but without
                // limiting both searches to the shortest length, endMatches would
                // also be 3.
                matchesLen = Math.min( newVal.length, oldVal.length );

                // Count same characters from the left, first.
                // (if "foo" -> "foofoo", assume addition was at the end).
                while (
                        startMatches < matchesLen &&
                        oldVal.charAt( startMatches ) === newVal.charAt( startMatches )
                ) {
                        startMatches += 1;
                }

                while (
                        endMatches < ( matchesLen - startMatches ) &&
                        oldVal.charAt( oldVal.length - 1 - endMatches ) === newVal.charAt( newVal.length - 1 - endMatches )
                ) {
                        endMatches += 1;
                }

                inpParts = [
                        // Same start
                        newVal.slice( 0, startMatches ),
                        // Inserted content
                        newVal.slice( startMatches, newVal.length - endMatches ),
                        // Same end
                        newVal.slice( newVal.length - endMatches )
                ];

                // Chop off characters from the end of the "inserted content" string
                // until the limit is statisfied.
                if ( fn ) {
                        // stop, when there is nothing to slice - bug 41450
                        while ( $.byteLength( fn( inpParts.join( '' ) ) ) > byteLimit && inpParts[ 1 ].length > 0 ) {
                                inpParts[ 1 ] = inpParts[ 1 ].slice( 0, -1 );
                        }
                } else {
                        while ( $.byteLength( inpParts.join( '' ) ) > byteLimit ) {
                                inpParts[ 1 ] = inpParts[ 1 ].slice( 0, -1 );
                        }
                }

                return {
                        newVal: inpParts.join( '' ),
                        // For pathological fn() that always returns a value longer than the limit, we might have
                        // ended up not trimming - check for this case to avoid infinite loops
                        trimmed: newVal !== inpParts.join( '' )
                };
        };

        var eventKeys = [
                'keyup.byteLimit',
                'keydown.byteLimit',
                'change.byteLimit',
                'mouseup.byteLimit',
                'cut.byteLimit',
                'paste.byteLimit',
                'focus.byteLimit',
                'blur.byteLimit'
        ].join( ' ' );

        /**
         * Enforces a byte limit on an input field, so that UTF-8 entries are counted as well,
         * when, for example, a database field has a byte limit rather than a character limit.
         * Plugin rationale: Browser has native maxlength for number of characters, this plugin
         * exists to limit number of bytes instead.
         *
         * Can be called with a custom limit (to use that limit instead of the maxlength attribute
         * value), a filter function (in case the limit should apply to something other than the
         * exact input value), or both. Order of parameters is important!
         *
         * @param {number} [limit] Limit to enforce, fallsback to maxLength-attribute,
         *  called with fetched value as argument.
         * @param {Function} [fn] Function to call on the string before assessing the length.
         * @return {jQuery}
         * @chainable
         */
        $.fn.byteLimit = function ( limit, fn ) {
                // If the first argument is the function,
                // set fn to the first argument's value and ignore the second argument.
                if ( $.isFunction( limit ) ) {
                        fn = limit;
                        limit = undefined;
                // Either way, verify it is a function so we don't have to call
                // isFunction again after this.
                } else if ( !fn || !$.isFunction( fn ) ) {
                        fn = undefined;
                }

                // The following is specific to each element in the collection.
                return this.each( function ( i, el ) {
                        var $el, elLimit, prevSafeVal;

                        $el = $( el );

                        // If no limit was passed to byteLimit(), use the maxlength value.
                        // Can't re-use 'limit' variable because it's in the higher scope
                        // that would affect the next each() iteration as well.
                        // Note that we use attribute to read the value instead of property,
                        // because in Chrome the maxLength property by default returns the
                        // highest supported value (no indication that it is being enforced
                        // by choice). We don't want to bind all of this for some ridiculously
                        // high default number, unless it was explicitly set in the HTML.
                        // Also cast to a (primitive) number (most commonly because the maxlength
                        // attribute contains a string, but theoretically the limit parameter
                        // could be something else as well).
                        elLimit = Number( limit === undefined ? $el.attr( 'maxlength' ) : limit );

                        // If there is no (valid) limit passed or found in the property,
                        // skip this. The < 0 check is required for Firefox, which returns
                        // -1  (instead of undefined) for maxLength if it is not set.
                        if ( !elLimit || elLimit < 0 ) {
                                return;
                        }

                        if ( fn ) {
                                // Save function for reference
                                $el.data( 'byteLimit.callback', fn );
                        }

                        // Remove old event handlers (if there are any)
                        $el.off( '.byteLimit' );

                        if ( fn ) {
                                // Disable the native maxLength (if there is any), because it interferes
                                // with the (differently calculated) byte limit.
                                // Aside from being differently calculated (average chars with byteLimit
                                // is lower), we also support a callback which can make it to allow longer
                                // values (e.g. count "Foo" from "User:Foo").
                                // maxLength is a strange property. Removing or setting the property to
                                // undefined directly doesn't work. Instead, it can only be unset internally
                                // by the browser when removing the associated attribute (Firefox/Chrome).
                                // http://code.google.com/p/chromium/issues/detail?id=136004
                                $el.removeAttr( 'maxlength' );

                        } else {
                                // If we don't have a callback the bytelimit can only be lower than the charlimit
                                // (that is, there are no characters less than 1 byte in size). So lets (re-)enforce
                                // the native limit for efficiency when possible (it will make the while-loop below
                                // faster by there being less left to interate over).
                                $el.attr( 'maxlength', elLimit );
                        }

                        // Safe base value, used to determine the path between the previous state
                        // and the state that triggered the event handler below - and enforce the
                        // limit approppiately (e.g. don't chop from the end if text was inserted
                        // at the beginning of the string).
                        prevSafeVal = '';

                        // We need to listen to after the change has already happened because we've
                        // learned that trying to guess the new value and canceling the event
                        // accordingly doesn't work because the new value is not always as simple as:
                        // oldValue + String.fromCharCode( e.which ); because of cut, paste, select-drag
                        // replacements, and custom input methods and what not.
                        // Even though we only trim input after it was changed (never prevent it), we do
                        // listen on events that input text, because there are cases where the text has
                        // changed while text is being entered and keyup/change will not be fired yet
                        // (such as holding down a single key, fires keydown, and after each keydown,
                        // we can trim the previous one).
                        // See http://www.w3.org/TR/DOM-Level-3-Events/#events-keyboard-event-order for
                        // the order and characteristics of the key events.
                        $el.on( eventKeys, function () {
                                var res = $.trimByteLength(
                                        prevSafeVal,
                                        this.value,
                                        elLimit,
                                        fn
                                );

                                // Only set value property if it was trimmed, because whenever the
                                // value property is set, the browser needs to re-initiate the text context,
                                // which moves the cursor at the end the input, moving it away from wherever it was.
                                // This is a side-effect of limiting after the fact.
                                if ( res.trimmed === true ) {
                                        this.value = res.newVal;
                                        // Trigger a 'change' event to let other scripts attached to this node know that the value
                                        // was changed. This will also call ourselves again, but that's okay, it'll be a no-op.
                                        $el.trigger( 'change' );
                                }
                                // Always adjust prevSafeVal to reflect the input value. Not doing this could cause
                                // trimByteLength to compare the new value to an empty string instead of the
                                // old value, resulting in trimming always from the end (bug 40850).
                                prevSafeVal = res.newVal;
                        } );
                } );
        };

        /**
         * @class jQuery
         * @mixins jQuery.plugin.byteLimit
         */
}( jQuery ) );