(function() {
    'use strict';

    // set listener for event from main window
    window.onmessage = function(e) {
        var html = '';

        if (e.data.html) {
            // display html mail body
            html = e.data.html;
        } else if (e.data.text) {
            // diplay text mail body by with colored conversation nodes
            html = renderNodes(parseConversation(e.data.text));
        }

        // sanitize HTML content: https://github.com/cure53/DOMPurify
        html = window.DOMPurify.sanitize(html);
        // make links open in a new window
        html = html.replace(/<a /g, '<a target="_blank" ');

        // remove sources where necessary
        if (e.data.removeImages) {
            html = html.replace(/(<img[^>]+\b)src=['"][^'">]+['"]/ig, function(match, prefix) {
                return prefix;
            });
        }

        document.body.innerHTML = html;
    };

    /**
     * Parse email body and generate conversation nodes
     * @param  {Object} email The email object
     * @return {Node}       The root node of the conversion
     */
    function parseConversation(textBody) {
        var nodes;

        function parseLines(body) {
            var lines = [];
            body.split('\n').forEach(parseLine);

            function parseLine(line) {
                var regex = /^>*/;
                var result = regex.exec(line);

                lines.push({
                    text: line.replace(regex, '').trim(),
                    level: (result && result.length > 0) ? result[0].length : 0
                });
            }

            return lines;
        }

        function buildTextNodes(lines) {
            var i, j, root, currentLevel, currentNode, levelDelta;

            root = new Node();
            currentLevel = 0;
            currentNode = root;

            // iterate over text lines
            for (i = 0; i < lines.length; i++) {
                levelDelta = lines[i].level - currentLevel;

                if (levelDelta === 0) {
                    // we are at the desired node ... no traversal required
                } else if (levelDelta > 0) {
                    // traverse to child node(s)
                    for (j = 0; j < levelDelta; j++) {
                        var newChild = new Node(currentNode);
                        // create new child node
                        currentNode.children.push(newChild);
                        // go to last child node
                        currentNode = newChild;
                        // increase current level by one
                        currentLevel++;
                    }
                } else {
                    // traverse to parent(s)
                    for (j = levelDelta; j < 0; j++) {
                        currentNode = currentNode.parent;
                        currentLevel--;
                    }
                }

                // add text to the current node
                currentNode.addLine(lines[i].text);
            }

            return root;
        }

        function Node(parent) {
            this.parent = parent;
            this.children = [];
        }
        Node.prototype.addLine = function(lineText) {
            var c, l;

            c = this.children;
            l = c.length;

            // append text node to children if last child is not a text node
            if (l < 1 || typeof c[l - 1] !== 'string') {
                c[l] = '';
                l = c.length;
            }

            // append line to last child (add newline between lines)
            c[l - 1] += lineText + '\n';
        };

        function removeParentReference(node) {
            if (!node.children) {
                // this is a text leaf ... terminate recursion
                return;
            }

            // remove parent node to prevent infinite loop in JSON stringify
            delete node.parent;

            for (var i = 0; i < node.children.length; i++) {
                if (typeof node.children[i] === 'string') {
                    // remove trailing newline in string
                    node.children[i] = node.children[i].replace(/\n$/, '');
                } else {
                    // I used recursion ...
                    removeParentReference(node.children[i]);
                }
            }
        }

        nodes = buildTextNodes(parseLines(textBody.replace(/ >/g, '>')));
        removeParentReference(nodes);

        return nodes;
    }

    /**
     * Render the conversation nodes as markup. This is not injected directly into the DOM, but rather send to a sandboxed iframe to be rendered
     * @param  {Node} root The conversation root node
     * @return {Strin}      The conversation as markup
     */
    function renderNodes(root) {
        var body = '';

        function render(node) {
            var i, html = '';
            if (!node.children) {
                // this is a text leaf
                var lines = node.split('\n');
                for (i = 0; i < lines.length; i++) {
                    // replace all urls with anchors
                    lines[i] = lines[i].replace(/(https?:\/\/[^\s]+)/g, createArchor);
                    // wrap line into an element for easier styling
                    html += '<div class="line';
                    if (isLineEmpty(lines[i])) {
                        html += ' empty-line';
                    }
                    html += '"><span>' + lines[i] + '</span><br></div>';
                }
                return html;
            }

            for (i = 0; i < node.children.length; i++) {
                html += '<div class="prev-message">' + render(node.children[i]) + '</div>';
            }

            return html;
        }

        function createArchor(url) {
            return '<a href="' + url + '">' + url + '</a>';
        }

        function isLineEmpty(line) {
            return line.replace(/>/g, '').trim().length === 0;
        }

        for (var j = 0; j < root.children.length; j++) {
            // start by rendering the root nodes children
            body += render(root.children[j]);
        }

        return '<div class="view-read-body">' + body + '</div>';
    }

})();