function contrast(color) {
	const exploded = color?.match(color.length >= 6 ? /[0-9a-fA-F]{2}/g : /[0-9a-fA-F]/g);
	if(!exploded || exploded?.length < 3) return 'black';
	const [r, g, b] = exploded.map(hex => parseInt(hex.length === 1 ? `${hex}${hex}` : hex, 16));
	const luminance = (0.299 * r + 0.587 * g + 0.114 * b) / 255;
	return luminance > 0.5 ? 'black' : 'white';
}

function shadeColor(hex, amount) {
	function dec2Hex(num) {
		const hex = Math.round(num * 255).toString(16);
		return hex.length === 1 ? '0' + hex : hex;
	}

	function hex2Int(hex) {
		let r = 0, g = 0, b = 0;
		if (hex.length === 4) {
			r = parseInt(hex[1] + hex[1], 16);
			g = parseInt(hex[2] + hex[2], 16);
			b = parseInt(hex[3] + hex[3], 16);
		} else {
			r = parseInt(hex.slice(1, 3), 16);
			g = parseInt(hex.slice(3, 5), 16);
			b = parseInt(hex.slice(5, 7), 16);
		}
		return { r, g, b };
	}

	function hue2rgb(p, q, t) {
		if (t < 0) t += 1;
		if (t > 1) t -= 1;
		if (t < 1 / 6) return p + (q - p) * 6 * t;
		if (t < 1 / 2) return q;
		if (t < 2 / 3) return p + (q - p) * (2 / 3 - t) * 6;
		return p;
	}

	function int2Hex(r, g, b) {
		return '#' + dec2Hex(r) + dec2Hex(g) + dec2Hex(b);
	}

	let { r, g, b } = hex2Int(hex);
	r /= 255; g /= 255; b /= 255;
	const max = Math.max(r, g, b), min = Math.min(r, g, b);
	let h, s, l = (max + min) / 2;

	if (max === min) {
		h = s = 0;
	} else {
		const d = max - min;
		s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
		switch (max) {
			case r: h = (g - b) / d + (g < b ? 6 : 0); break;
			case g: h = (b - r) / d + 2; break;
			case b: h = (r - g) / d + 4; break;
			default: h = 0; break;
		}
		h /= 6;
	}

	l = Math.max(0, Math.min(1, l + amount));
	const q = l < 0.5 ? l * (1 + s) : l + s - l * s;
	const p = 2 * l - q;
	return int2Hex(hue2rgb(p, q, h + 1 / 3), hue2rgb(p, q, h), hue2rgb(p, q, h - 1 / 3));
}

class BtnComponent extends HTMLElement {
	constructor() {
		super();
		this.attachShadow({ mode: 'open' });

		this.shadowRoot.innerHTML = `
            <style>
                :host {
                    --base-color: #ccc;
                    --dark-color: #999;
                    --light-color: #eee;
                    --text-color: #000;
                }

                .btn {
                    display: inline-flex;
                    min-width: 40px;
                    width: 100%;
                    height: 40px;
                    padding: 5px;
                    border-radius: 6px;
                    font-size: 20px;
                    transition: transform 0.1s, background-color 0.2s, border-color 0.2s, box-shadow 0.2s;
                    align-items: center;
                    justify-content: center;
                    user-select: none;
                    cursor: url('/assets/cursor.png'), auto;
                    fill: var(--text-color);
                    color: var(--text-color);
					box-sizing: border-box;
                }

                .btn:not(.disabled) {
                    background: var(--base-color);
                    border: 2px solid var(--dark-color);
                    box-shadow: 0 4px 0 var(--dark-color);
                }

                .btn:not(.disabled):hover {
					transform: translateY(-2px);
					background: var(--light-color);
					border: 2px solid var(--base-color);
					box-shadow: 0 6px 0 var(--base-color);
				}

				.btn:not(.disabled):active {
					transform: translateY(2px);
					background: var(--base-color);
					border: 2px solid var(--dark-color);
					box-shadow: 0 2px 0 var(--dark-color);
				}

				.btn.disabled {
					cursor: no-drop;
					background: var(--dark-color);
					border: 2px solid var(--base-color);
                    box-shadow: 0 4px 0 var(--dark-color);
				}
            </style>
            <div class="btn">
                <slot></slot>
			</div>
        `;

		this.shadowRoot.querySelector('.btn').addEventListener('click', (e) => {
			if(this.hasAttribute('disabled')) {
				e.stopPropagation();
				e.preventDefault();
			}
		});

		this.updateColors();
	}

	static get observedAttributes() {
		return ['color', 'disabled'];
	}

	attributeChangedCallback(name, oldValue, newValue) {
		if(name === 'color') this.updateColors();
		if(name === 'disabled') {
			const disabled = this.hasAttribute('disabled');
			this.shadowRoot.querySelector('.btn').classList[disabled ? 'add' : 'remove']('disabled');
		}
	}

	updateColors() {
		const hex = this.getAttribute('color');
		this.shadowRoot.host.style.setProperty('--base-color', hex);
		this.shadowRoot.host.style.setProperty('--dark-color', shadeColor(hex, -.1));
		this.shadowRoot.host.style.setProperty('--light-color', shadeColor(hex, .1));
		this.shadowRoot.host.style.setProperty('--text-color', contrast(hex));
	}
}

customElements.define('btn-component', BtnComponent);