class Multiselect extends HTMLDivElement {
    constructor() {
        super();
        this.initialized = false;
        this.toSearch = '';
        this.highlighted = 0;
    }

    connectedCallback() {
        if (!this.initialized) {
            for (const child of this.children) {
                switch (child.nodeName) {
                    case 'SELECT':
                        this.select = child;
                        break;
                    case 'LABEL':
                        this.label = child;
                        break;
                }
            }
            if (this.label && this.select) {
                this.init();
            }
        }
    }

    init() {
        this.initialized = true;

        this.select.style.display = 'none';
        for (const option of this.select.options) {
            option.dataset.numerusSearch = Multiselect.normalize(option.textContent);
        }

        this.tags = document.createElement('div');
        this.append(this.tags);
        this.tags.classList.add('tags');
        this.tags.addEventListener('click', () => this.toggle());

        this.search = document.createElement('input');
        this.tags.append(this.search);
        this.search.id = this.select.id;
        this.select.removeAttribute('id');
        this.select.setAttribute('aria-hidden', 'true');
        this.search.setAttribute('spellcheck', 'false');
        this.search.setAttribute('autocomplete', 'false');
        this.search.setAttribute('role', 'combobox');
        this.search.addEventListener('input', (e) => {
            this.open();
            this.filter(e.target.value);
        });
        this.search.addEventListener('keydown', (e) => {
            switch (e.code) {
                case "Enter":
                    e.preventDefault();
                    this.selectHighlighted();
                    break;
                case "ArrowDown":
                    if (e.altKey) {
                        this.open();
                    } else {
                        e.preventDefault();
                        this.highlightNext();
                    }
                    break;
                case "ArrowUp":
                    if (e.altKey) {
                        this.close();
                    } else {
                        e.preventDefault();
                        this.highlightPrev();
                    }
                    break;
                case "Backspace":
                    if (e.target.value === '') {
                        this.deselectLast();
                    }
                    break;
                case "Escape":
                    this.close();
                    break;
            }
        });

        // Must come after the search input
        this.tags.append(this.label);

        this.options = document.createElement('ul');
        this.append(this.options);
        this.options.id = this.search.id + '-options-' + Array.from(crypto.getRandomValues(new Uint8Array(4))).map(n => n.toString(16)).join('');
        this.search.setAttribute('aria-controls', this.options.id);
        this.options.classList.add('options');
        this.options.setAttribute('role', 'listbox');
        this.close();

        window.addEventListener('focusin', (e) => {
            if (this.contains(e.target)) return;
            this.close();
        });

        document.addEventListener('click', (e) => {
            if (this.contains(e.target)) return;
            if (!e.target.isConnected) return;
            this.close();
        });

        this.rebuild();
    }

    rebuildOptions() {
        this.options.innerHTML = '';
        let highlight = true;
        for (const option of this.select.options) {
            if (!this.isOptionSelectable(option)) {
                continue;
            }
            const li = document.createElement('li');
            this.options.append(li);
            li.id = this.options.id + '-' + option.index;
            li.dataset.index = option.index;
            li.textContent = option.textContent;
            li.addEventListener('click', () => this.selectOption(option, true));
            if (highlight && (option.index >= this.highlighted)) {
                highlight = false;
                this.highlight(null, li);
            }
        }
        if (highlight) {
            this.highlight(null, this.options.querySelector('li:last-child'));
        }
    }

    highlightNext() {
        const current = this.currentHighlighted();
        if (!current) {
            return;
        }
        this.highlight(current, current.nextElementSibling);
    }

    highlightPrev() {
        const current = this.currentHighlighted();
        if (!current) {
            return;
        }
        this.highlight(current, current.previousElementSibling);
    }

    highlight(current, upcoming) {
        if (!upcoming) {
            return;
        }
        if (current) {
            current.classList.remove('highlight');
        }
        upcoming.classList.remove('highlight');
        this.search.setAttribute('aria-activedescendant', upcoming.id);
        this.highlighted = upcoming.dataset.index;
        upcoming.classList.add('highlight');
    }

    currentHighlighted() {
        return document.getElementById(this.search.getAttribute('aria-activedescendant'));
    }

    isOptionSelectable(option) {
        if (!option) {
            return false;
        }
        if (option.selected) {
            return false;
        }
        return this.toSearch === '' || option.dataset.numerusSearch.includes(this.toSearch);
    }

    selectOption(option, selected) {
        if (!option) {
            return;
        }
        option.selected = selected;
        this.toSearch = this.search.value = '';
        this.rebuild();
    }

    selectHighlighted() {
        if (!this.isOpen()) {
            return;
        }
        const option = this.select.options[this.highlighted];
        if (this.isOptionSelectable(option)) {
            this.selectOption(option, true);
        }
    }

    deselectLast() {
        const options = this.select.options;
        for (let i = options.length - 1; i >= 0; i--) {
            const option = options[i];
            if (option.selected) {
                this.selectOption(option, false);
                break;
            }
        }
    }

    rebuild() {
        this.rebuildTags();
        this.rebuildOptions();
    }

    rebuildTags() {
        this.tags.querySelectorAll('.tag').forEach((tag) => tag.remove());
        let empty = true;
        for (const option of this.select.options) {
            if (!option.selected) {
                continue;
            }
            empty = false;
            const tag = document.createElement('div');
            this.tags.insertBefore(tag, this.search);
            tag.classList.add('tag');
            tag.dataset.numerusSearch = option.dataset.numerusSearch;

            const span = document.createElement('span');
            tag.append(span);
            span.textContent = option.textContent;

            const button = document.createElement('button');
            tag.append(button);
            button.type = 'button';
            button.textContent = '×';
            button.addEventListener('click', (e) => {
                e.stopPropagation();
                this.selectOption(option, false)
            });
        }
        if (empty) {
            this.search.setAttribute('placeholder', this.label.textContent);
        } else {
            this.search.removeAttribute('placeholder');
        }
    }

    close() {
        this.options.style.display = 'none';
        this.search.setAttribute('aria-expanded', 'false');
    }

    open() {
        this.options.removeAttribute('style');
        this.search.setAttribute('aria-expanded', 'true');
    }

    toggle() {
        if (this.isOpen()) {
            this.close();
        } else {
            this.open();
        }
    }

    isOpen() {
        return !this.options.hasAttribute('style');
    }

    filter(search) {
        this.toSearch = Multiselect.normalize(search);
        this.rebuildOptions()
    }

    static normalize(s) {
        return s.normalize('NFD').replace(/\p{Diacritic}/gu, '').toLowerCase().trim();
    }
}

customElements.define('numerus-multiselect', Multiselect, {extends: 'div'});