/*
 * https://github.com/kraaden/autocomplete
 * Copyright (c) 2016 Denys Krasnoshchok
 * MIT License
 */

export const enum EventTrigger {
    Keyboard = 0,
    Focus = 1
}

export interface AutocompleteItem {
    label?: string;
    group?: string;
}

export interface AutocompleteSettings<T extends AutocompleteItem> {
    /**
     * Autocomplete will be attached to this element.
     */
    input: HTMLInputElement | HTMLTextAreaElement;

    /**
     * Provide your own container for the widget.
     * If not specified, a new DIV element will be created.
     */
    container?: HTMLDivElement;

    /**
     * This method allows you to override the default rendering function for items.
     * It must return a DIV element or undefined to skip rendering.
     */
    render?: (item: T, currentValue: string, index: number) => HTMLDivElement | undefined;

    /**
     * This method allows you to override the default rendering function for item groups.
     * It must return a DIV element or undefined to skip rendering.
     */
    renderGroup?: (name: string, currentValue: string) => HTMLDivElement | undefined;

    /**
     * If specified, the autocomplete DOM element will have this class assigned to it.
     */
    className?: string;

    /**
     * Specify the minimum text length required to show autocomplete.
     */
    minLength?: number;

    /**
     * The message that will be showed when there are no suggestions that match the entered value.
     */
    emptyMsg?: string;

    /**
     * This method will be called when user choose an item in autocomplete. The selected item will be passed as the first parameter.
     */
    onSelect: (item: T, input: HTMLInputElement | HTMLTextAreaElement) => void;

    /**
     * Show autocomplete on focus event. Focus event will ignore the `minLength` property and will always call `fetch`.
     */
    showOnFocus?: boolean;

    /**
     * This method will be called to prepare suggestions and then pass them to autocomplete.
     * @param {string} text - text in the input field
     * @param {(items: T[] | false) => void} update - a callback function that must be called after suggestions are prepared
     * @param {EventTrigger} trigger - type of the event that triggered the fetch
     * @param {number} cursorPos - position of the cursor in the input field
     */
    fetch: (text: string, update: (items: T[] | false) => void, trigger: EventTrigger, cursorPos: number) => void;

    /**
     * Enforces that the fetch function will only be called once within the specified time frame (in milliseconds) and
     * delays execution. This prevents flooding your server with AJAX requests.
     */
    debounceWaitMs?: number;

    /**
     * Callback for additional autocomplete customization
     * @param {HTMLInputElement | HTMLTextAreaElement} input - input box associated with autocomplete
     * @param {ClientRect | DOMRect} inputRect - size of the input box and its position relative to the viewport
     * @param {HTMLDivElement} container - container with suggestions
     * @param {number} maxHeight - max height that can be used by autocomplete
     */
    customize?: (input: HTMLInputElement | HTMLTextAreaElement, inputRect: ClientRect | DOMRect, container: HTMLDivElement, maxHeight: number) => void;

    /**
     * Prevents automatic form submit when ENTER is pressed
     */
    preventSubmit?: boolean;

    /**
     * Prevents the first item in the list from being selected automatically. This option allows you
     * to submit a custom text by pressing ENTER even when autocomplete is displayed.
     */
    disableAutoSelect?: boolean;

    /**
     * Keys that will be ignored and not trigger the fetch callback.
     */
    keysToIgnore?: Keys[];
}

export interface AutocompleteResult {
    destroy: () => void;
}

export const enum Keys {
    Enter = 13,
    Esc = 27,
    Up = 38,
    Down = 40,
    Left = 37,
    Right = 39,
    Shift = 16,
    Ctrl = 17,
    Alt = 18,
    CapsLock = 20,
    WindowsKey = 91,
    Tab = 9,
    F1 = 112,
    F12 = 123
}

export default function autocomplete<T extends AutocompleteItem>(settings: AutocompleteSettings<T>): AutocompleteResult {

    // just an alias to minimize JS file size
    const doc = document;

    const container: HTMLDivElement = settings.container || doc.createElement("div");
    container.id = container.id || "autocomplete-" + uid();
    const containerStyle = container.style;
    const debounceWaitMs = settings.debounceWaitMs || 0;
    const preventSubmit = settings.preventSubmit || false;
    const disableAutoSelect = settings.disableAutoSelect || false;

    let items: T[] = [];
    let inputValue = "";
    let minLen = 2;
    const showOnFocus = settings.showOnFocus;
    let selected: T | undefined;
    let keypressCounter = 0;
    let debounceTimer: number | undefined;

    if (settings.minLength !== undefined) {
        minLen = settings.minLength;
    }

    if (!settings.input) {
        throw new Error("input undefined");
    }

    const input: HTMLInputElement | HTMLTextAreaElement = settings.input;

    container.className = "autocomplete " + (settings.className || "");
    container.setAttribute("role", "listbox");

    input.setAttribute("role", "combobox");
    input.setAttribute("aria-expanded", "false");
    input.setAttribute("aria-autocomplete", "list");
    input.setAttribute("aria-controls", container.id);
    input.setAttribute("aria-owns", container.id);
    input.setAttribute("aria-activedescendant", "");
    input.setAttribute("aria-haspopup", "listbox");

    // IOS implementation for fixed positioning has many bugs, so we will use absolute positioning
    containerStyle.position = "absolute";

    /**
     * Generate a unique ID
     */
    function uid(): string {
        return Date.now().toString(36) + Math.random().toString(36).substring(2);
    }

    /**
     * Detach the container from DOM
     */
    function detach(): void {
        const parent = container.parentNode;
        if (parent) {
            parent.removeChild(container);
        }
    }

    /**
     * Clear debouncing timer if assigned
     */
    function clearDebounceTimer(): void {
        if (debounceTimer) {
            window.clearTimeout(debounceTimer);
        }
    }

    /**
     * Attach the container to DOM
     */
    function attach(): void {
        if (!container.parentNode) {
            doc.body.appendChild(container);
        }
    }

    /**
     * Check if container for autocomplete is displayed
     */
    function containerDisplayed(): boolean {
        return !!container.parentNode;
    }

    /**
     * Clear autocomplete state and hide container
     */
    function clear(): void {
        // prevent the update call if there are pending AJAX requests
        keypressCounter++;

        items = [];
        inputValue = "";
        selected = undefined;
        input.setAttribute("aria-activedescendant", "");
        input.setAttribute("aria-expanded", "false");
        detach();
    }

    /**
     * Update autocomplete position
     */
    function updatePosition(): void {
        if (!containerDisplayed()) {
            return;
        }

        input.setAttribute("aria-expanded", "true");

        containerStyle.height = "auto";
        containerStyle.width = input.offsetWidth + "px";

        let maxHeight = 0;
        let inputRect: ClientRect | DOMRect | undefined;

        function calc() {
            const docEl = doc.documentElement as HTMLElement;
            const clientTop = docEl.clientTop || doc.body.clientTop || 0;
            const clientLeft = docEl.clientLeft || doc.body.clientLeft || 0;
            const scrollTop = window.pageYOffset || docEl.scrollTop;
            const scrollLeft = window.pageXOffset || docEl.scrollLeft;

            inputRect = input.getBoundingClientRect();

            const top = inputRect.top + input.offsetHeight + scrollTop - clientTop;
            const left = inputRect.left + scrollLeft - clientLeft;

            containerStyle.top = top + "px";
            containerStyle.left = left + "px";

            maxHeight = window.innerHeight - (inputRect.top + input.offsetHeight);

            if (maxHeight < 0) {
                maxHeight = 0;
            }

            containerStyle.top = top + "px";
            containerStyle.bottom = "";
            containerStyle.left = left + "px";
            containerStyle.maxHeight = maxHeight + "px";
        }

        // the calc method must be called twice, otherwise the calculation may be wrong on resize event (chrome browser)
        calc();
        calc();

        if (settings.customize && inputRect) {
            settings.customize(input, inputRect, container, maxHeight);
        }
    }

    /**
     * Redraw the autocomplete div element with suggestions
     */
    function update(): void {

        // delete all children from autocomplete DOM container
        while (container.firstChild) {
            container.removeChild(container.firstChild);
        }

        input.setAttribute("aria-activedescendant", "");

        // function for rendering autocomplete suggestions
        let render = function (item: T, _: string, __: number): HTMLDivElement | undefined {
            const itemElement = doc.createElement("div");
            itemElement.textContent = item.label || "";
            return itemElement;
        };
        if (settings.render) {
            render = settings.render;
        }

        // function to render autocomplete groups
        let renderGroup = function (groupName: string, _: string): HTMLDivElement | undefined {
            const groupDiv = doc.createElement("div");
            groupDiv.textContent = groupName;
            return groupDiv;
        };
        if (settings.renderGroup) {
            renderGroup = settings.renderGroup;
        }

        const fragment = doc.createDocumentFragment();
        let prevGroup = "#9?$";

        items.forEach(function (item: T, index: number): void {
            if (item.group && item.group !== prevGroup) {
                prevGroup = item.group;
                const groupDiv = renderGroup(item.group, inputValue);
                if (groupDiv) {
                    groupDiv.className += " group";
                    fragment.appendChild(groupDiv);
                }
            }
            const div = render(item, inputValue, index);
            if (div) {
                div.id = `${container.id}_${index}`;
                div.setAttribute("role", "option");
                div.addEventListener("click", function (ev: MouseEvent): void {
                    settings.onSelect(item, input);
                    clear();
                    ev.preventDefault();
                    ev.stopPropagation();
                });
                if (item === selected) {
                    div.className += " selected";
                    div.setAttribute("aria-selected", "true");
                    input.setAttribute("aria-activedescendant", div.id);
                }
                fragment.appendChild(div);
            }
        });
        container.appendChild(fragment);
        if (items.length < 1) {
            if (settings.emptyMsg) {
                const empty = doc.createElement("div");
                empty.id = `${container.id}_${uid()}`;
                empty.className = "empty";
                empty.textContent = settings.emptyMsg;
                container.appendChild(empty);
                input.setAttribute("aria-activedescendant", empty.id);
            } else {
                clear();
                return;
            }
        }

        attach();
        updatePosition();

        updateScroll();
    }

    function updateIfDisplayed(): void {
        if (containerDisplayed()) {
            update();
        }
    }

    function resizeEventHandler(): void {
        updateIfDisplayed();
    }

    function scrollEventHandler(e: Event): void {
        if (e.target !== container) {
            updateIfDisplayed();
        } else {
            e.preventDefault();
        }
    }

    function keyupEventHandler(ev: KeyboardEvent): void {
        const keyCode = ev.which || ev.keyCode || 0;

        const ignore = settings.keysToIgnore || [Keys.Up, Keys.Enter, Keys.Esc, Keys.Right, Keys.Left, Keys.Shift, Keys.Ctrl, Keys.Alt, Keys.CapsLock, Keys.WindowsKey, Keys.Tab];
        for (const key of ignore) {
            if (keyCode === key) {
                return;
            }
        }

        if (keyCode >= Keys.F1 && keyCode <= Keys.F12 && !settings.keysToIgnore) {
            return;
        }

        // the down key is used to open autocomplete
        if (keyCode === Keys.Down && containerDisplayed()) {
            return;
        }

        startFetch(EventTrigger.Keyboard);
    }

    /**
     * Automatically move scroll bar if selected item is not visible
     */
    function updateScroll(): void {
        const elements = container.getElementsByClassName("selected");
        if (elements.length > 0) {
            let element = elements[0] as HTMLDivElement;

            // make group visible
            const previous = element.previousElementSibling as HTMLDivElement;
            if (previous && previous.className.indexOf("group") !== -1 && !previous.previousElementSibling) {
                element = previous;
            }

            if (element.offsetTop < container.scrollTop) {
                container.scrollTop = element.offsetTop;
            } else {
                const selectBottom = element.offsetTop + element.offsetHeight;
                const containerBottom = container.scrollTop + container.offsetHeight;
                if (selectBottom > containerBottom) {
                    container.scrollTop += selectBottom - containerBottom;
                }
            }
        }
    }

    /**
     * Select the previous item in suggestions
     */
    function selectPrev(): void {
        if (items.length < 1) {
            selected = undefined;
        } else {
            if (selected === items[0]) {
                selected = items[items.length - 1];
            } else {
                for (let i = items.length - 1; i > 0; i--) {
                    if (selected === items[i] || i === 1) {
                        selected = items[i - 1];
                        break;
                    }
                }
            }
        }
    }

    /**
     * Select the next item in suggestions
     */
    function selectNext(): void {
        if (items.length < 1) {
            selected = undefined;
        }
        if (!selected || selected === items[items.length - 1]) {
            selected = items[0];
            return;
        }
        for (let i = 0; i < (items.length - 1); i++) {
            if (selected === items[i]) {
                selected = items[i + 1];
                break;
            }
        }
    }

    function keydownEventHandler(ev: KeyboardEvent): void {
        const keyCode = ev.which || ev.keyCode || 0;

        if (keyCode === Keys.Up || keyCode === Keys.Down || keyCode === Keys.Esc) {
            const containerIsDisplayed = containerDisplayed();

            if (keyCode === Keys.Esc) {
                clear();
            } else {
                if (!containerIsDisplayed || items.length < 1) {
                    return;
                }
                keyCode === Keys.Up
                    ? selectPrev()
                    : selectNext();
                update();
            }

            ev.preventDefault();
            if (containerIsDisplayed) {
                ev.stopPropagation();
            }

            return;
        }

        if (keyCode === Keys.Enter) {
            if (selected) {
                settings.onSelect(selected, input);
                clear();
            }

            if (preventSubmit) {
                ev.preventDefault();
            }
        }
    }

    function focusEventHandler(): void {
        if (showOnFocus) {
            startFetch(EventTrigger.Focus);
        }
    }

    function startFetch(trigger: EventTrigger) {
        // If multiple keys were pressed, before we get an update from server,
        // this may cause redrawing autocomplete multiple times after the last key was pressed.
        // To avoid this, the number of times keyboard was pressed will be saved and checked before redraw.
        const savedKeypressCounter = ++keypressCounter;

        const inputText = input.value;
        const cursorPos = input.selectionStart || 0;

        if (inputText.length >= minLen || trigger === EventTrigger.Focus) {
            clearDebounceTimer();
            debounceTimer = window.setTimeout(function (): void {
                settings.fetch(inputText, function (elements: T[] | false): void {
                    if (keypressCounter === savedKeypressCounter && elements) {
                        items = elements;
                        inputValue = inputText;
                        selected = (items.length < 1 || disableAutoSelect) ? undefined : items[0];
                        update();
                    }
                }, trigger, cursorPos);
            }, trigger === EventTrigger.Keyboard ? debounceWaitMs : 0);
        } else {
            clear();
        }
    }

    function blurEventHandler(): void {
        // we need to delay clear, because when we click on an item, blur will be called before click and remove items from DOM
        setTimeout(() => {
            if (doc.activeElement !== input) {
                clear();
            }
        }, 200);
    }

    /**
     * Fixes #26: on long clicks focus will be lost and onSelect method will not be called
     */
    container.addEventListener("mousedown", function (evt: Event) {
        evt.stopPropagation();
        evt.preventDefault();
    });

    /**
     * Fixes #30: autocomplete closes when scrollbar is clicked in IE
     * See: https://stackoverflow.com/a/9210267/13172349
     */
    container.addEventListener("focus", () => input.focus());

    /**
     * This function will remove DOM elements and clear event handlers
     */
    function destroy(): void {
        input.removeEventListener("focus", focusEventHandler);
        input.removeEventListener("keydown", keydownEventHandler as EventListenerOrEventListenerObject);
        input.removeEventListener("keyup", keyupEventHandler as EventListenerOrEventListenerObject);
        input.removeEventListener("blur", blurEventHandler);
        window.removeEventListener("resize", resizeEventHandler);
        doc.removeEventListener("scroll", scrollEventHandler, true);
        input.removeAttribute("role");
        input.removeAttribute("aria-expanded");
        input.removeAttribute("aria-autocomplete");
        input.removeAttribute("aria-controls");
        input.removeAttribute("aria-activedescendant");
        input.removeAttribute("aria-owns");
        input.removeAttribute("aria-haspopup");
        clearDebounceTimer();
        clear();
    }

    // setup event handlers
    input.addEventListener("keydown", keydownEventHandler as EventListenerOrEventListenerObject);
    input.addEventListener("keyup", keyupEventHandler as EventListenerOrEventListenerObject);
    input.addEventListener("blur", blurEventHandler);
    input.addEventListener("focus", focusEventHandler);
    window.addEventListener("resize", resizeEventHandler);
    doc.addEventListener("scroll", scrollEventHandler, true);

    return {
        destroy
    };
}