const vscode = require("vscode");

const AT_RULES = new Set([
	"each",
	"for",
	"from",
	"through",
	"include",
	"responsive",
	"media",
	"supports",
	"concentric",
	"view-transition",
	"predict",
	"measure",
	"property",
	"mixin",
	"stcss",
	"import",
	"charset",
	"document",
	"font-face",
	"keyframes",
	"layer",
	"namespace",
	"page",
	"scope",
	"starting-style",
	"container",
]);

const STATE_WORDS = new Set([
	"active",
	"clicked",
	"focus",
	"hover",
	"open",
	"closed",
	"selected",
	"loading",
	"visible",
	"hidden",
]);

const AT_RULE_DOCS = new Map([
	["mixin", "Declare a reusable STCSS mixin: `@mixin name($param) { … }`"],
	["include", "Expand a mixin: `@include name(10%);`"],
	["each", "Repeat rules over values: `@each $item in a b c { … }`"],
	["for", "Count a range: `@for $i from 1 through 5 { … }`"],
	["responsive", "Wrap rules in a named breakpoint from the config."],
	["media", "Standard `@media` query wrapper."],
	["supports", "Standard `@supports` feature wrapper."],
	["concentric", "Emit concentric nested radii: `@concentric 0.75rem { … }`"],
	["view-transition", "Emit `view-transition-name` on the attached rule."],
	[
		"predict",
		"Declare which properties transition when prediction prefill changes (emits a smooth transition rule).",
	],
	[
		"measure",
		'Mark the attached rule (or listed selectors / `@anchor`s) as a prediction target. Prerender measures the elements and writes geometry. Bare `@anchor` arguments compile to `[data-muddle-anchor="anchor"]`.',
	],
]);

const REFERENCE_DOC =
	'Reads pre-computed geometry recorded from a `@sample` anchor: compiles to `var(--muddle-relate-…)`.\n\nMetrics: `left`, `top`, `width`, `height`. `@anchor` compiles to `[data-muddle-anchor="anchor"]`.';

const RELATE_DOC =
	"Legacy relation value of an anchor (deprecated in favour of `$refer[metric](@anchor)`).";

const CSS_PROPERTIES = [
	"background",
	"background-color",
	"background-image",
	"border",
	"border-color",
	"border-radius",
	"border-width",
	"bottom",
	"box-shadow",
	"box-sizing",
	"color",
	"cursor",
	"display",
	"flex",
	"flex-basis",
	"flex-direction",
	"flex-shrink",
	"flex-wrap",
	"font-family",
	"font-size",
	"font-weight",
	"gap",
	"grid-area",
	"height",
	"inset",
	"justify-content",
	"left",
	"letter-spacing",
	"line-height",
	"margin",
	"max-height",
	"max-width",
	"min-height",
	"min-width",
	"opacity",
	"overflow",
	"padding",
	"pointer-events",
	"position",
	"right",
	"text-decoration",
	"text-transform",
	"top",
	"transform",
	"transition",
	"vertical-align",
	"visibility",
	"white-space",
	"width",
	"z-index",
];

const HTML_ATTRIBUTES = [
	"alt",
	"aria-controls",
	"aria-current",
	"aria-description",
	"aria-expanded",
	"aria-hidden",
	"aria-label",
	"aria-live",
	"autocomplete",
	"class",
	"content",
	"href",
	"id",
	"placeholder",
	"rel",
	"role",
	"src",
	"style",
	"tabindex",
	"target",
	"title",
	"type",
];

const INDEX = {
	anchors: new Map(), // name -> [{ uri, line, kind }]
	variables: new Map(), // $name -> [{ uri, line }]
	spugFiles: [],
	styleFiles: [],
};

let indexToken = 0;

function relativeToWorkspace(uri) {
	const folder = vscode.workspace.getWorkspaceFolder(uri);
	if (!folder) return uri.fsPath.split(/[\\/]/).pop();
	return uri.fsPath.slice(folder.uri.fsPath.length + 1);
}

function debounce(callback, wait) {
	let timer;
	return (...args) => {
		clearTimeout(timer);
		timer = setTimeout(() => callback(...args), wait);
	};
}

async function readText(uri) {
	try {
		const bytes = await vscode.workspace.fs.readFile(uri);
		return new TextDecoder().decode(bytes);
	} catch {
		return "";
	}
}

function posFromOffset(text, offset) {
	const before = text.slice(0, offset);
	const newline = before.lastIndexOf("\n");
	return new vscode.Position(
		before.split("\n").length - 1,
		offset - newline - 1,
	);
}

function rangeOf(text, offset, length) {
	return new vscode.Range(
		posFromOffset(text, offset),
		posFromOffset(text, offset + Math.max(length, 1)),
	);
}

function isStcss(document) {
	return document.languageId === "stcss";
}

function rememberAnchor(name, uri, line, kind) {
	const list = INDEX.anchors.get(name) ?? [];
	list.push({ uri, line, kind });
	INDEX.anchors.set(name, list);
}

function indexSpugDocument(uri, text) {
	const lines = text.split("\n");
	const anchorRegex = /@([A-Za-z_][\w-]*)(?:\(([^(){}]*)\))?/g;
	lines.forEach((line, index) => {
		let match;
		anchorRegex.lastIndex = 0;
		while ((match = anchorRegex.exec(line))) {
			if (AT_RULES.has(match[1]) || match[1] === "sample") continue;
			rememberAnchor(match[1], uri, index + 1, "declared in SPUG");
		}
	});
}

function indexStcssDocument(uri, text) {
	const variableRegex = /(\$[\w-]+)\s*:/g;
	let match;
	while ((match = variableRegex.exec(text))) {
		const position = posFromOffset(text, match.index);
		const list = INDEX.variables.get(match[1]) ?? [];
		list.push({ uri, line: position.line + 1 });
		INDEX.variables.set(match[1], list);
	}

	const anchorRegex = /@([A-Za-z_][\w-]*)/g;
	while ((match = anchorRegex.exec(text))) {
		if (AT_RULES.has(match[1])) continue;
		rememberAnchor(
			match[1],
			uri,
			posFromOffset(text, match.index).line + 1,
			"referenced in STCSS",
		);
	}
}

async function indexWorkspace() {
	const token = ++indexToken;
	if (!vscode.workspace.workspaceFolders) return;
	const [spugFiles, styleFiles] = await Promise.all([
		vscode.workspace.findFiles("**/*.spug", "**/node_modules/**"),
		vscode.workspace.findFiles("**/*.stcss", "**/node_modules/**"),
	]);
	if (token !== indexToken) return;
	INDEX.anchors = new Map();
	INDEX.variables = new Map();
	INDEX.spugFiles = spugFiles;
	INDEX.styleFiles = styleFiles;
	await Promise.all([
		...spugFiles.map(async (uri) =>
			indexSpugDocument(uri, await readText(uri)),
		),
		...styleFiles.map(async (uri) =>
			indexStcssDocument(uri, await readText(uri)),
		),
	]);
}

function anchorCompletions() {
	return [...INDEX.anchors.keys()].map((name) => {
		const item = new vscode.CompletionItem(
			`@${name}`,
			vscode.CompletionItemKind.Keyword,
		);
		item.detail = "relation anchor";
		const first = INDEX.anchors.get(name)[0];
		if (first)
			item.documentation = new vscode.MarkdownString(
				`${first.kind}: \`${relativeToWorkspace(first.uri)}:${first.line}\``,
			);
		return item;
	});
}

function stcssCompletions() {
	const atRules = [...AT_RULE_DOCS.keys()].map((name) => {
		const item = new vscode.CompletionItem(
			`@${name}`,
			vscode.CompletionItemKind.Struct,
		);
		item.detail = "stcss at-rule";
		item.insertText = new vscode.SnippetString(
			name === "concentric" || name === "media"
				? `${name} $1 {\n\t$0\n}`
				: `${name};`,
		);
		item.documentation = new vscode.MarkdownString(AT_RULE_DOCS.get(name));
		return item;
	});
	const metrics = ["left", "top", "width", "height"].map((metric) => {
		const item = new vscode.CompletionItem(
			`$refer[${metric}](@)`,
			vscode.CompletionItemKind.Function,
		);
		item.insertText = new vscode.SnippetString(
			`$refer[${metric}](@\${1:anchor})`,
		);
		item.documentation = new vscode.MarkdownString(REFERENCE_DOC);
		return item;
	});
	const relate = new vscode.CompletionItem(
		"$relate(@)",
		vscode.CompletionItemKind.Function,
	);
	relate.insertText = new vscode.SnippetString("$relate(@${1:anchor})");
	relate.documentation = new vscode.MarkdownString(RELATE_DOC);
	const states = [...STATE_WORDS].map((state) => {
		const item = new vscode.CompletionItem(
			state,
			vscode.CompletionItemKind.EnumMember,
		);
		item.detail = "anchor state";
		return item;
	});
	const properties = CSS_PROPERTIES.map((name) => {
		const item = new vscode.CompletionItem(
			name,
			vscode.CompletionItemKind.Property,
		);
		item.insertText = new vscode.SnippetString(`${name}: $0;`);
		return item;
	});
	const variables = [...INDEX.variables.keys()].map((name) => {
		const item = new vscode.CompletionItem(
			name,
			vscode.CompletionItemKind.Variable,
		);
		item.detail = "stcss variable";
		return item;
	});
	return [
		...atRules,
		...metrics,
		relate,
		...states,
		...properties,
		...variables,
	];
}

function spugCompletions() {
	const keywords = [
		"extends",
		"include",
		"block",
		"append",
		"prepend",
		"mixin",
		"slot",
		"yield",
		"island",
		"component",
		"render",
		"doctype",
	].map((word) => {
		const item = new vscode.CompletionItem(
			word,
			vscode.CompletionItemKind.Keyword,
		);
		return item;
	});
	const javascript = new vscode.CompletionItem(
		"javascript!",
		vscode.CompletionItemKind.Keyword,
	);
	javascript.insertText = new vscode.SnippetString("javascript!\n\t$0\nend");
	const control = [
		"if",
		"else",
		"unless",
		"each",
		"while",
		"case",
		"when",
		"default",
		"props",
	].map(
		(word) =>
			new vscode.CompletionItem(word, vscode.CompletionItemKind.Keyword),
	);
	const attributes = HTML_ATTRIBUTES.map((name) => {
		const item = new vscode.CompletionItem(
			name,
			vscode.CompletionItemKind.Property,
		);
		item.insertText = new vscode.SnippetString(`${name}=$0`);
		return item;
	});
	return [
		...keywords,
		javascript,
		...control,
		...attributes,
		...anchorCompletions(),
	];
}

function stcssHover(document, position) {
	const line = document.lineAt(position.line).text;
	const preceding = line.slice(0, position.character);
	const anchor = /(?:^|[^\w$])@([A-Za-z_][\w-]*)$/.exec(preceding)?.[1];
	if (anchor) return hoverAnchor(anchor);
	const variable = /\$[\w-]+$/.exec(preceding)?.[0];
	if (variable) {
		const hits = INDEX.variables.get(variable) ?? [];
		return new vscode.Hover(
			new vscode.MarkdownString(
				hits.length
					? `**${variable}**: defined in ${hits.map((h) => `${relativeToWorkspace(h.uri)}:${h.line}`).join(", ")}`
					: `**${variable}**`,
			),
		);
	}
	const refer = /(?:\$\w+(?:\[[\w-]+\])?)$/.exec(preceding)?.[0];
	if (refer) {
		if (refer.startsWith("$refer"))
			return new vscode.Hover(new vscode.MarkdownString(REFERENCE_DOC));
		if (refer.startsWith("$relate"))
			return new vscode.Hover(new vscode.MarkdownString(RELATE_DOC));
	}
	return null;
}

function hoverAnchor(name) {
	const hits = INDEX.anchors.get(name) ?? [];
	if (!hits.length) return null;
	const body = hits
		.slice(0, 8)
		.map(
			(hit) => `- ${hit.kind}: \`${relativeToWorkspace(hit.uri)}:${hit.line}\``,
		)
		.join("\n");
	return new vscode.Hover(
		new vscode.MarkdownString(`**@${name}**: relation anchor\n\n${body}`),
	);
}

function spugHover(document, position) {
	const range = document.getWordRangeAtPosition(position, /@?[A-Za-z_][\w-]*/);
	if (!range) return null;
	const word = document.getText(range);
	if (
		word.startsWith("@") ||
		document.getText(
			new vscode.Range(
				range.start.translate({ characterDelta: -1 }),
				range.start,
			),
		) === "@"
	) {
		return hoverAnchor(word.replace(/^@/, ""));
	}
	return null;
}

function anchorDefinition(name) {
	return (INDEX.anchors.get(name) ?? [])
		.filter((hit) => hit.kind === "declared in SPUG")
		.map(
			(hit) =>
				new vscode.Location(hit.uri, new vscode.Position(hit.line - 1, 0)),
		);
}

function stcssDefinition(document, position) {
	const line = document
		.lineAt(position.line)
		.text.slice(0, position.character + 1);
	const anchor = /@([A-Za-z_][\w-]*)[^\w]?$/.exec(line)?.[1];
	if (anchor) return anchorDefinition(anchor);
	return null;
}

function spugDefinition(document, position) {
	const before = document
		.lineAt(position.line)
		.text.slice(0, position.character + 1);
	const anchor = /@([A-Za-z_][\w-]*)[^\w]?$/.exec(before)?.[1];
	if (anchor) {
		// jump from anchor to its STCSS references
		const refs = (INDEX.anchors.get(anchor) ?? []).filter(
			(hit) => hit.kind === "referenced in STCSS",
		);
		return refs.map(
			(hit) =>
				new vscode.Location(
					hit.uri,
					new vscode.Range(hit.line - 1, 0, hit.line - 1, 200),
				),
		);
	}
	return null;
}

function diagnosticCollection() {
	return vscode.languages.createDiagnosticCollection("muddle");
}

function lintDocument(document, collection) {
	if (document.languageId !== "stcss" && document.languageId !== "spug")
		return [];
	const text = document.getText();
	const issues = [];

	// balanced braces in both languages
	let depth = 0;
	let lastOpen = 0;
	for (let index = 0; index < text.length && issues.length < 40; index += 1) {
		const char = text[index];
		if (char === "{") {
			depth += 1;
			lastOpen = index;
		} else if (char === "}") {
			depth -= 1;
			if (depth < 0) {
				issues.push(
					new vscode.Diagnostic(
						rangeOf(text, index, 1),
						"Unexpected `}`.",
						vscode.DiagnosticSeverity.Error,
					),
				);
				depth = 0;
			}
		}
	}
	if (depth > 0) {
		issues.push(
			new vscode.Diagnostic(
				rangeOf(text, lastOpen, 1),
				"Unclosed `{` block.",
				vscode.DiagnosticSeverity.Error,
			),
		);
	}

	if (document.languageId === "stcss") {
		const anchorRegex = /@([A-Za-z_][\w-]*)/g;
		let match;
		while ((match = anchorRegex.exec(text))) {
			const name = match[1];
			const offset = match.index;
			const previous = text[offset - 1];
			const dynamic = text
				.slice(
					offset,
					text.indexOf("\n", offset) === -1
						? text.length
						: text.indexOf("\n", offset),
				)
				.includes("(");
			if (AT_RULES.has(name) || previous === "$" || dynamic) continue;
			if (!INDEX.anchors.has(name)) {
				issues.push(
					new vscode.Diagnostic(
						rangeOf(text, offset, match[0].length),
						`No SPUG file declares relation anchor \`@${name}\`.`,
						vscode.DiagnosticSeverity.Warning,
					),
				);
			}
		}
	}

	collection.set(document.uri, issues);
	return issues;
}

function lintVisible() {
	for (const editor of vscode.window.visibleTextEditors)
		lintDocument(editor.document, diagnostics);
}

function symbolKindFor(document) {
	return isStcss(document) ? vscode.SymbolKind.Class : vscode.SymbolKind.Module;
}

function symbolsOf(document) {
	const flat = [];
	for (let line = 0; line < document.lineCount; line += 1) {
		const text = document.lineAt(line).text;
		const match = /^(\s*)(@?[A-Za-z][^\n{;]*?|@[\w-]+)\s*\{?\s*$/.exec(text);
		if (!match || !text.trim()) continue;
		if (isStcss(document) && !text.includes("{")) continue;
		if (!isStcss(document) && text.includes("{")) continue;
		const label = match[2].trim() || "root";
		const symbol = new vscode.DocumentSymbol(
			label,
			"",
			symbolKindFor(document),
			new vscode.Range(line, 0, line, text.length),
			new vscode.Range(
				line,
				match[1].length,
				line,
				match[1].length + label.length,
			),
		);
		flat.push({ symbol, indent: match[1].length });
	}
	const roots = [];
	const stack = [];
	for (const entry of flat) {
		while (stack.length && entry.indent <= stack[stack.length - 1].indent)
			stack.pop();
		if (stack.length)
			stack[stack.length - 1].symbol.children.push(entry.symbol);
		else roots.push(entry.symbol);
		stack.push(entry);
	}
	return roots;
}

function foldingOf(document) {
	const ranges = [];
	const stack = [];
	for (let line = 0; line < document.lineCount; line += 1) {
		const text = document.lineAt(line).text;
		if (isStcss(document)) {
			const opens = (text.match(/\{/g) ?? []).length;
			const closes = (text.match(/\}/g) ?? []).length;
			for (let i = 0; i < opens; i += 1) stack.push(line);
			for (let i = 0; i < closes && stack.length; i += 1) {
				const start = stack.pop();
				if (line > start) ranges.push(new vscode.FoldingRange(start, line));
			}
		} else {
			const indent = text.match(/^(\s*)/)[1].length;
			if (!text.trim()) continue;
			while (stack.length && indent <= stack[stack.length - 1].indent) {
				const start = stack.pop();
				if (line - 1 > start)
					ranges.push(new vscode.FoldingRange(start, line - 1));
			}
			stack.push({ indent, line });
		}
	}
	while (stack.length) {
		const start =
			typeof stack[stack.length - 1] === "number"
				? stack.pop()
				: stack.pop().line;
		if (document.lineCount - 1 > start)
			ranges.push(new vscode.FoldingRange(start, document.lineCount - 1));
	}
	return ranges;
}

let diagnostics;

function completionsFor(document, position) {
	const line = document.lineAt(position.line);
	const before = line.text.slice(0, position.character);
	if (line.isEmptyOrWhitespace) return [];
	const prefix = before.trim();
	if (prefix.length === 0 && position.character > 0) return [];
	// completions popped while just typing whitespace mid-line are noise
	if (
		before.length > 0 &&
		/\s$/.test(before) &&
		!/[$@:(\[=,{]\s*$/.test(before)
	)
		return [];
	return isStcss(document) ? stcssCompletions(before) : spugCompletions(before);
}

function activate(context) {
	diagnostics = diagnosticCollection();

	const refresh = debounce(async () => {
		await indexWorkspace();
		lintVisible();
	}, 500);

	Promise.resolve(refresh());

	context.subscriptions.push(
		diagnostics,

		vscode.languages.registerCompletionItemProvider(
			["stcss", "spug"],
			{
				provideCompletionItems(document, position) {
					return completionsFor(document, position);
				},
			},
			"@",
			"$",
			".",
			"-",
			":",
			"=",
		),

		vscode.languages.registerHoverProvider(["stcss", "spug"], {
			provideHover(document, position) {
				const word = document.getWordRangeAtPosition(position, /[@$]?[\w-]+/);
				if (!word) return null;
				try {
					return isStcss(document)
						? stcssHover(document, position)
						: spugHover(document, position);
				} catch {
					return null;
				}
			},
		}),

		vscode.languages.registerDefinitionProvider(["stcss", "spug"], {
			provideDefinition(document, position) {
				try {
					return isStcss(document)
						? stcssDefinition(document, position)
						: spugDefinition(document, position);
				} catch {
					return null;
				}
			},
		}),

		vscode.languages.registerDocumentSymbolProvider(["stcss", "spug"], {
			provideDocumentSymbols(document) {
				return symbolsOf(document);
			},
		}),

		vscode.languages.registerFoldingRangeProvider(["stcss", "spug"], {
			provideFoldingRanges(document) {
				return foldingOf(document);
			},
		}),

		vscode.workspace.onDidOpenTextDocument((document) =>
			lintDocument(document, diagnostics),
		),
		vscode.workspace.onDidChangeTextDocument((event) => {
			lintDocument(event.document, diagnostics);
			refresh();
		}),
		vscode.workspace.onDidSaveTextDocument(refresh),
		vscode.workspace.onDidCreateFiles(refresh),
		vscode.workspace.onDidDeleteFiles(refresh),
	);

	lintVisible();
}

function deactivate() {
	return undefined;
}

module.exports = { activate, deactivate };