// Copyright Epic Games, Inc. All Rights Reserved.

"use strict";

import { ZenPage } from "./page.js"
import { marked, Renderer } from "../thirdparty/marked.esm.js"
import { Fetcher } from "../util/fetcher.js"

function slugify(text)
{
	return text.toLowerCase().replace(/[^\w]+/g, "-").replace(/^-|-$/g, "");
}

const renderer = new Renderer();
renderer.heading = function({ text, depth })
{
	const id = slugify(text);
	if (depth === 1)
	{
		return `<h1 id="${id}">${text}<a class="docs-source-link" title="View source"></a><a class="docs-github-link" title="View on GitHub" target="_blank"></a></h1>`;
	}
	if (depth === 2)
	{
		// Close previous <details> section (if any) and open a new one
		return `</details><details class="docs-section" open><summary class="docs-section-title" id="${id}">${text}</summary>`;
	}
	return `<h${depth} id="${id}">${text}</h${depth}>`;
};

////////////////////////////////////////////////////////////////////////////////
export class Page extends ZenPage
{
	generate_crumbs() {}

	async main()
	{
		this.set_title("docs");
		this._parent.inner().classList.add("docs-page");

		const index = await new Fetcher().resource("/dashboard/data/_index.json").json();
		if (!index || index.length === 0)
		{
			this._parent.tag().text("No documentation available.");
			return;
		}

		// Filter input
		const filter_box = document.createElement("input");
		filter_box.type = "text";
		filter_box.className = "docs-filter";
		filter_box.placeholder = "Filter\u2026";
		filter_box.addEventListener("input", () => this._apply_filter(filter_box.value));
		this._parent.inner().appendChild(filter_box);

		// Layout: sidebar + content
		const layout = document.createElement("div");
		layout.className = "docs-layout";
		this._parent.inner().appendChild(layout);

		// Sidebar
		const sidebar = document.createElement("nav");
		sidebar.className = "docs-sidebar";
		layout.appendChild(sidebar);

		this._docs_index = index;
		this._sidebar = sidebar;
		this._selected_link = null;
		this._filter = "";
		this._docs_cache = {};

		for (const entry of index)
		{
			const link = document.createElement("a");
			link.className = "docs-sidebar-link";
			link.textContent = entry.title;
			link.href = "#";
			link.addEventListener("click", (e) => {
				e.preventDefault();
				this._select_doc(entry, link);
			});
			sidebar.appendChild(link);
		}

		// Prefetch all docs in the background for filtering
		Promise.all(index.map(entry =>
			new Fetcher().resource("/dashboard/data/" + entry.path).text()
				.then(md => { this._docs_cache[entry.path] = md.toLowerCase(); })
				.catch(() => {})
		));

		// Content area
		const content = document.createElement("article");
		content.className = "docs-content";
		layout.appendChild(content);
		this._content = content;

		// Intercept clicks on links within rendered doc content
		content.addEventListener("click", (e) => {
			const anchor = e.target.closest("a");
			if (!anchor || anchor.classList.contains("docs-source-link") || anchor.classList.contains("docs-github-link"))
			{
				return;
			}

			const href = anchor.getAttribute("href") || "";

			// Fragment-only link (e.g. #workers) — scroll within current doc
			if (href.startsWith("#"))
			{
				e.preventDefault();
				this._scroll_to_fragment(href.slice(1));
				return;
			}

			// Relative link to another doc (e.g. API.md or specs/CompactBinary.md)
			if (!href.startsWith("http") && href.endsWith(".md"))
			{
				const parts = href.split("#");
				const target_path = parts[0];
				const target_fragment = parts[1] || null;
				const target_entry = this._docs_index.find(d => d.path.toLowerCase() === target_path.toLowerCase());
				if (target_entry)
				{
					e.preventDefault();
					const target_link = this._sidebar.children[this._docs_index.indexOf(target_entry)];
					this._select_doc(target_entry, target_link, target_fragment);
				}
			}
		});

		// Select initial doc from URL param or first entry
		const requested = this.get_param("doc", "");
		const initial = index.find(e => e.path === requested) || index[0];
		const initial_link = sidebar.children[index.indexOf(initial)];
		this._select_doc(initial, initial_link);
	}

	async _select_doc(entry, link, fragment)
	{
		if (this._selected_link)
		{
			this._selected_link.classList.remove("active");
		}
		this._selected_link = link;
		link.classList.add("active");

		this.set_param("doc", entry.path);

		this._content.innerHTML = "<p class=\"docs-loading\">Loading\u2026</p>";

		try
		{
			const md = await new Fetcher().resource("/dashboard/data/" + entry.path).text();
			this._content.innerHTML = marked.parse(md, { renderer });

			const source_link = this._content.querySelector(".docs-source-link");
			if (source_link)
			{
				source_link.href = "/dashboard/data/" + entry.path;
			}

			const github_link = this._content.querySelector(".docs-github-link");
			if (github_link)
			{
				github_link.href = "https://github.com/EpicGames/zen/blob/main/docs/" + entry.path;
			}

			// Render mermaid diagrams
			await this._render_mermaid();

			// Re-apply filter to the newly rendered content
			if (this._filter)
			{
				this._apply_filter_to_content();
			}

			// Scroll to fragment if specified
			const target_fragment = fragment || window.location.hash.slice(1);
			if (target_fragment)
			{
				this._scroll_to_fragment(target_fragment);
			}
			else
			{
				window.scrollTo(0, 0);
			}
		}
		catch (e)
		{
			this._content.innerHTML = "<p class=\"docs-error\">Failed to load document.</p>";
		}
	}

	_scroll_to_fragment(id)
	{
		if (!id)
		{
			return;
		}
		const target = this._content.querySelector("#" + CSS.escape(id));
		if (target)
		{
			target.scrollIntoView({ behavior: "smooth" });
		}
	}

	_apply_filter(query)
	{
		this._filter = query.toLowerCase().trim();

		// Filter sidebar entries based on cached doc content
		const sidebar_links = this._sidebar.children;
		for (let i = 0; i < this._docs_index.length; i++)
		{
			const entry = this._docs_index[i];
			const link = sidebar_links[i];
			if (!this._filter)
			{
				link.style.display = "";
				continue;
			}

			const cached = this._docs_cache[entry.path];
			const matches = !cached || cached.includes(this._filter) || entry.title.toLowerCase().includes(this._filter);
			link.style.display = matches ? "" : "none";
		}

		this._apply_filter_to_content();
	}

	_apply_filter_to_content()
	{
		// Remove existing highlights
		for (const mark of this._content.querySelectorAll("mark.docs-highlight"))
		{
			const parent = mark.parentNode;
			parent.replaceChild(document.createTextNode(mark.textContent), mark);
			parent.normalize();
		}

		const sections = this._content.querySelectorAll("details.docs-section");

		for (const section of sections)
		{
			if (!this._filter)
			{
				section.style.display = "";
				section.open = true;
				continue;
			}

			const matches = section.textContent.toLowerCase().includes(this._filter);
			section.style.display = matches ? "" : "none";

			if (matches)
			{
				section.open = true;
				this._highlight_element(section);
			}
		}
	}

	_get_mermaid_theme()
	{
		const attr = document.documentElement.getAttribute("data-theme");
		const is_dark = attr
			? attr === "dark"
			: window.matchMedia("(prefers-color-scheme: dark)").matches;
		return is_dark ? "dark" : "default";
	}

	async _load_mermaid()
	{
		if (window.mermaid)
		{
			return window.mermaid;
		}

		return new Promise((resolve, reject) => {
			const script = document.createElement("script");
			script.src = "/dashboard/thirdparty/mermaid.min.js";
			script.onload = () => {
				window.mermaid.initialize({
					startOnLoad: false,
					theme: this._get_mermaid_theme(),
					themeVariables: {
						background: "transparent",
					},
				});
				resolve(window.mermaid);
			};
			script.onerror = reject;
			document.head.appendChild(script);
		});
	}

	async _render_mermaid()
	{
		// marked renders ```mermaid blocks as <code class="language-mermaid"> inside <pre>
		const code_blocks = this._content.querySelectorAll("pre > code.language-mermaid");
		if (code_blocks.length === 0)
		{
			return;
		}

		try
		{
			const mermaid = await this._load_mermaid();

			for (let i = 0; i < code_blocks.length; i++)
			{
				const code = code_blocks[i];
				const pre = code.parentElement;
				const definition = code.textContent;

				const { svg } = await mermaid.render(`mermaid-${Date.now()}-${i}`, definition);

				const container = document.createElement("div");
				container.className = "docs-mermaid";
				container.dataset.definition = definition;
				container.innerHTML = svg;
				pre.replaceWith(container);
			}

			this._watch_theme();
		}
		catch (e)
		{
			// Mermaid failed to load or render — leave code blocks as-is
		}
	}

	_watch_theme()
	{
		if (this._theme_observer)
		{
			return;
		}

		this._theme_observer = new MutationObserver(() => this._rerender_mermaid());
		this._theme_observer.observe(document.documentElement, {
			attributes: true,
			attributeFilter: ["data-theme"],
		});
	}

	async _rerender_mermaid()
	{
		const containers = this._content.querySelectorAll(".docs-mermaid[data-definition]");
		if (containers.length === 0)
		{
			return;
		}

		try
		{
			const mermaid = await this._load_mermaid();
			mermaid.initialize({
				startOnLoad: false,
				theme: this._get_mermaid_theme(),
				themeVariables: {
					background: "transparent",
				},
			});

			for (let i = 0; i < containers.length; i++)
			{
				const container = containers[i];
				const definition = container.dataset.definition;
				const { svg } = await mermaid.render(`mermaid-${Date.now()}-${i}`, definition);
				container.innerHTML = svg;
			}
		}
		catch (e)
		{
			// Mermaid failed to re-render — leave existing SVGs as-is
		}
	}

	_highlight_element(root)
	{
		const filter = this._filter;
		const walker = document.createTreeWalker(root, NodeFilter.SHOW_TEXT);
		const matches = [];

		let node;
		while ((node = walker.nextNode()))
		{
			if (node.parentElement && node.parentElement.closest("pre"))
			{
				continue;
			}

			const text = node.textContent.toLowerCase();
			let pos = 0;
			while ((pos = text.indexOf(filter, pos)) !== -1)
			{
				matches.push({ node, pos, len: filter.length });
				pos += filter.length;
			}
		}

		for (let i = matches.length - 1; i >= 0; i--)
		{
			const { node: text_node, pos, len } = matches[i];
			const after = text_node.splitText(pos);
			after.splitText(len);

			const mark = document.createElement("mark");
			mark.className = "docs-highlight";
			mark.textContent = after.textContent;
			after.parentNode.replaceChild(mark, after);
		}
	}
}