// Checks if the provided child is descendant of the parent (any level)
function is_descendant(parent, child) {
    var node = child.parentNode;
    while (node !== null) {
        console.log(node)
        if (node === parent) return true;
        node = node.parentNode;
    }
    return false;
}

Number.prototype.base26 = (function () {
    return function base26() {
        n = this/*  w ww  .j  a  v  a 2s.  co  m*/
        ret = "";
        while (parseInt(n) > 0) {
            --n;
            ret += String.fromCharCode("A".charCodeAt(0) + (n % 26));
            n /= 26;
        }
        return ret.split("").reverse().join("").toLowerCase();
    };
}());

function isVisible(element) {
    // Element is obviously not visible
    if (element.offsetWidth === 0 || element.offsetHeight === 0) return false;
    let rect = element.getClientRects()[0];
    if (!rect) return false;

    // Get the element clicked in the center of the element rect
    var element_in_position = document.elementFromPoint((rect.left + rect.right) / 2, (rect.top + rect.bottom) / 2);

    // If there's no result, assume not visible
    if (!element_in_position) return false;

    // If the element clicked is the same as provided, the element is clearly visible
    if (element_in_position === element) return true;

    // If the element is not in the position we clicked, check if it's at least a child node
    return is_descendant(element, element_in_position);
}

class KeyHinter {
    constructor() {
        this.number = 0;
        this.nodes = {};

        this.currentSelection = [];
    }

    // Highlight
    highlight() {
        if (this.number !== 0)
            return false

        this.listenKeybinds()

        var _this = this;
        document.querySelectorAll('a, form, input').forEach(function (nodeEl) {
            if (isVisible(nodeEl)) {
                _this.number++;
                _this.nodes[_this.number.base26()] = nodeEl;

                var el = _this.generateLabelFor(nodeEl);

                el.textContent = _this.number.base26();
                el.setAttribute('data-keyhinter-label', _this.number.base26());

                document.body.appendChild(el);
            }
        })
    }

    // Label generation
    generateLabelFor(node) {
        var el = document.createElement('div');
        var nodePosition = node.getBoundingClientRect();
        el.classList.add('keyhinter-label');

        el.style.left = nodePosition.left + 'px';
        el.style.top = nodePosition.top + 'px';

        if (node.nodeName === 'A') {
            el.classList.add('keyhinter-label-anchor');
        } else if (node.nodeName === 'FORM') {
            el.classList.add('keyhinter-label-form');
        } else if (node.nodeName === 'INPUT') {
            el.classList.add('keyhinter-label-input');
        }

        return el;
    }

    doClick(obj) {
        switch (obj.nodeName) {
            case 'INPUT':
                obj.focus();
                break;
            case 'FORM':
                obj.submit();
                break;
            default:
                obj.click();
                break;
        }
    }

    // Keybinds
    listenKeybinds() {
        var _this = this;
        document.onkeydown = function (event) {
            if (event.code === 'Escape') {
                event.preventDefault();
                _this.destroy();
            } else if (event.code.startsWith("Key")) {
                event.preventDefault();
                var letter = event.key;
                _this.currentSelection.push(letter);

                document.querySelectorAll('[data-keyhinter-label]').forEach(function (item) {
                    item.style.visibility = 'hidden';
                })

                var query = document.querySelectorAll('[data-keyhinter-label^="' + _this.currentSelection.join('') + '"]')
                if (query.length === 1) {
                    var node = _this.nodes[_this.currentSelection.join('')];
                    _this.doClick(node);
                    _this.destroy();
                } else {
                    query.forEach(function (item) {
                        item.style.visibility = 'visible'
                    })
                }
            } else {
                console.log("Default:" + event.code + "," + event.key)
            }
        }
    }

    stopListeningKeybinds() {
        document.onkeydown = null;
    }

    // Non-safe methods
    destroy() {
        document.querySelectorAll('.keyhinter-label').forEach(function (node) {
            document.body.removeChild(node);
        })
        this.stopListeningKeybinds();
        keyHinter = new KeyHinter()
    }
}

var keyHinter = new KeyHinter();

chrome.runtime.onMessage.addListener(function (msg, sender, sendResponse) {
    // If the received message has the expected format...
    if (msg.action === 'start_keyhinter') {
        // Call the specified callback, passing
        // the web-page's DOM content as argument
        keyHinter.highlight();
    }
});