KB.component('text-editor', function (containerElement, options) {
    var textarea, viewModeElement, writeModeElement, previewElement, selectionStart, selectionEnd;

    this.render = function() {
        writeModeElement = buildWriteMode();
        viewModeElement = buildViewMode();

        containerElement.appendChild(KB.dom('div')
            .attr('class', 'text-editor')
            .add(viewModeElement)
            .add(writeModeElement)
            .build());

        if (options.autofocus) {
            textarea.focus();
        }
    };

    function buildViewMode() {
        var toolbarElement = KB.dom('div')
            .attr('class', 'text-editor-toolbar')
            .for('a', [
                {href: '#', html: '<i class="fa fa-pencil-square-o fa-fw"></i> ' + options.labelWrite, click: function() { toggleViewMode(); }}
            ])
            .build();

        previewElement = KB.dom('div')
            .attr('class', 'text-editor-preview-area markdown')
            .build();

        return KB.dom('div')
            .attr('class', 'text-editor-view-mode')
            .add(toolbarElement)
            .add(previewElement)
            .hide()
            .build();
    }

    function buildWriteMode() {
        var toolbarElement = KB.dom('div')
            .attr('class', 'text-editor-toolbar')
            .for('a', [
                {href: '#', html: '<i class="fa fa-eye fa-fw"></i> ' + options.labelPreview, click: function() { toggleViewMode(); }},
                {href: '#', html: '<i class="fa fa-bold fa-fw"></i>', click: function() { insertEnclosedTag('**'); }},
                {href: '#', html: '<i class="fa fa-italic fa-fw"></i>', click: function() { insertEnclosedTag('_'); }},
                {href: '#', html: '<i class="fa fa-strikethrough fa-fw"></i>', click: function() { insertEnclosedTag('~~'); }},
                {href: '#', html: '<i class="fa fa-quote-right fa-fw"></i>', click: function() { insertPrependTag('> '); }},
                {href: '#', html: '<i class="fa fa-list-ul fa-fw"></i>', click: function() { insertPrependTag('* '); }},
                {href: '#', html: '<i class="fa fa-code fa-fw"></i>', click: function() { insertBlockTag('```'); }}
            ])
            .build();

        textarea = KB.dom('textarea')
            .attr('name', options.name)
            .attr('tabindex', options.tabindex || '-1')
            .attr('required', options.required || false)
            .text(options.text) // Order is important for IE11
            .attr('placeholder', options.placeholder || null)
            .build();

        if (options.mentionUrl) {
            KB.getComponent('suggest-menu', textarea, {triggers: {'@': options.mentionUrl}}).render();
        }

        return KB.dom('div')
            .attr('class', 'text-editor-write-mode')
            .add(toolbarElement)
            .add(textarea)
            .build();
    }

    function toggleViewMode() {
        KB.dom(previewElement).html(marked(textarea.value, {sanitize: true}));
        KB.dom(viewModeElement).toggle();
        KB.dom(writeModeElement).toggle();
    }

    function getSelectedText() {
        return textarea.value.substring(textarea.selectionStart, textarea.selectionEnd);
    }

    function replaceTextRange(s, start, end, substitute) {
        return s.substring(0, start) + substitute + s.substring(end);
    }

    function insertEnclosedTag(tag) {
        var selectedText = getSelectedText();

        insertText(tag + selectedText + tag);
        setCursorBeforeClosingTag(tag);
    }

    function insertBlockTag(tag) {
        var selectedText = getSelectedText();

        insertText('\n' + tag + '\n' + selectedText + '\n' + tag);
        setCursorBeforeClosingTag(tag, 2);
    }

    function insertPrependTag(tag) {
        var selectedText = getSelectedText();

        if (selectedText.indexOf('\n') === -1) {
            insertText('\n' + tag + selectedText);
        } else {
            var lines = selectedText.split('\n');

            for (var i = 0; i < lines.length; i++) {
                if (lines[i].indexOf(tag) === -1) {
                    lines[i] = tag + lines[i];
                }
            }

            insertText(lines.join('\n'));
        }
    }

    function insertText(replacedText) {
        var result = false;

        selectionStart = textarea.selectionStart;
        selectionEnd = textarea.selectionEnd;
        textarea.focus();

        if (document.queryCommandSupported('insertText')) {
            result = document.execCommand('insertText', false, replacedText);
        }

        if (! result) {
            try {
                document.execCommand('ms-beginUndoUnit');
            } catch (error) {}

            textarea.value = replaceTextRange(textarea.value, textarea.selectionStart, textarea.selectionEnd, replacedText);

            try {
                document.execCommand('ms-endUndoUnit');
            } catch (error) {}
        }
    }

    function setCursorBeforeClosingTag(tag, offset) {
        offset = offset || 0;
        var position = selectionEnd + tag.length + offset;
        textarea.setSelectionRange(position, position);
    }
});