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// Copyright 2026 Shota FUJI
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.
//
// SPDX-License-Identifier: MPL-2.0

import css from "./x-preview.css";

const SCALE_MIN = 0.1;
const SCALE_MAX = 5.0;

export class XPreview extends HTMLElement {
	#slot = document.createElement("slot");
	#gesturePlane = document.createElement("div");

	#size = null;
	#resizeObserver = new ResizeObserver((entries) => {
		for (const entry of entries) {
			this.#size = entry.contentRect;
			return;
		}
	});

	#dx = 0;
	#dy = 0;
	#scale = 1.0;

	#isRenderScheduled = false;

	constructor() {
		super();

		const shadow = this.attachShadow({
			mode: "open",
		});

		const style = document.createElement("style");
		style.textContent = css;
		shadow.appendChild(style);

		shadow.appendChild(this.#slot);

		this.#gesturePlane.classList.add("gesture-plane");
		shadow.appendChild(this.#gesturePlane);

		const reset = document.createElement("button");
		reset.textContent = "Reset Viewport";
		reset.classList.add("reset");
		reset.classList.add("hidden");
		reset.addEventListener("click", (event) => {
			this.#dx = 0;
			this.#dy = 0;
			this.#scale = 1.0;

			this.#render();
		});
		shadow.appendChild(reset);
	}

	connectedCallback() {
		this.#gesturePlane.addEventListener("wheel", this.#onWheel);

		this.#render();

		this.#resizeObserver.observe(this.#gesturePlane);
	}

	disconnectedCallback() {
		this.#gesturePlane.removeEventListener("wheel", this.#onWheel);
		this.#resizeObserver.disconnect();
	}

	#onWheel = (event) => {
		event.preventDefault();

		if (event.ctrlKey || event.metaKey) {
			let { deltaY } = event;
			// Workaround shitty design.
			switch (event.deltaMode) {
				// DOM_DELTA_LINE
				case 1:
					deltaY *= 15;
					break;
				// DOM_DELTA_PAGE
				case 2:
					deltaY *= 100;
					break;
			}

			const previous = this.#scale;
			this.#scale = Math.max(SCALE_MIN, Math.min(SCALE_MAX, this.#scale * (1 - deltaY / 100)));

			const ox = event.offsetX - this.#size.width * 0.5;
			const oy = event.offsetY - this.#size.height * 0.5;

			this.#dx += ox / this.#scale - ox / previous;
			this.#dy += oy / this.#scale - oy / previous;
		} else {
			this.#dx -= event.deltaX / this.#scale;
			this.#dy -= event.deltaY / this.#scale;
		}

		this.#render();
	};

	#render() {
		if (this.#isRenderScheduled) {
			return;
		}

		this.#isRenderScheduled = true;

		requestAnimationFrame(() => {
			if (!this.isConnected) {
				return;
			}

			for (const element of this.#slot.assignedElements()) {
				element.style.transform = `scale(${this.#scale}) translate(${this.#dx}px, ${this.#dy}px)`;
			}

			this.#isRenderScheduled = false;
		});
	}
}