import { lstatSync, readdirSync, readFileSync } from "node:fs";
import path from "node:path";
import {
	type FrontmatterMap,
	type MarkdownDocumentError,
	parseFrontmatter,
} from "./markdown.ts";
import { SystemDocumentError } from "./project-root.ts";
import {
	type DocumentType,
	parseDocumentId,
	type SystemConfig,
} from "./system-config.ts";

export {
	discoverProjectRoot,
	requireProjectRoot,
	resolveGovernedPath,
	SystemDocumentError,
} from "./project-root.ts";
export * from "./system-config.ts";

export const PHASE_BYTE_LIMIT = 32 * 1024;
export type ResearchMetadata = Readonly<{
	id: string;
	type: "research";
	title: string;
}>;
export type SpecMetadata = Readonly<{
	id: string;
	type: "spec";
	title: string;
	research?: readonly string[];
}>;
export type PhaseMetadata = Readonly<{
	id: string;
	type: "phase";
	title: string;
	label: string;
}>;
export type PlanMetadata = Readonly<{
	id: string;
	type: "plan";
	title: string;
	spec: string;
	status: "draft" | "approved";
	depends_on?: readonly string[];
}>;
export type IssueMetadata = Readonly<{
	id: string;
	type: "issue";
	title: string;
	specs: readonly string[];
}>;
export type DocumentMetadata =
	| ResearchMetadata
	| SpecMetadata
	| PhaseMetadata
	| PlanMetadata
	| IssueMetadata;
export type Diagnostic = Readonly<{
	code: string;
	path: string;
	message: string;
}>;
export type AuthoredDocument = Readonly<{
	metadata: DocumentMetadata;
	frontmatter: FrontmatterMap;
}>;
export type BundleDocumentSource = Readonly<{ path: string; markdown: string }>;
export type BundleDocumentRecord = Readonly<{
	path: string;
	metadata: DocumentMetadata;
	frontmatter: FrontmatterMap;
}>;
export type BundleDocumentIndex = Readonly<{
	documents: readonly BundleDocumentRecord[];
	diagnostics: readonly Diagnostic[];
}>;
export type BundleDiscovery = Readonly<{
	sources: readonly BundleDocumentSource[];
	diagnostics: readonly Diagnostic[];
}>;

const SLUG = "[a-z0-9]+(?:-[a-z0-9]+)*";
const DIRECTORY_BY_TYPE: Readonly<Record<DocumentType, string>> = {
	spec: "specs",
	phase: "phases",
	plan: "plans",
	issue: "issues",
	research: "research",
};

export function directoryForType(type: DocumentType): string {
	return DIRECTORY_BY_TYPE[type];
}

export function validateDocumentPath(
	documentPath: string,
	metadata: DocumentMetadata,
	prefix: string,
): void {
	const parsed = parseDocumentId(metadata.id, prefix);
	const expectedDirectory = DIRECTORY_BY_TYPE[metadata.type];
	const pattern = new RegExp(`^${metadata.id}-${SLUG}$`);
	const parts = documentPath.split("/");
	if (
		parsed.type !== metadata.type ||
		parts.length !== 4 ||
		parts[0] !== ".system" ||
		parts[1] !== expectedDirectory ||
		!pattern.test(parts[2] ?? "") ||
		parts[3] !== "index.md"
	)
		throw new SystemDocumentError(
			"document.path",
			`Bundle path mismatch for ${metadata.id}: ${documentPath}`,
		);
}

const requiredStringField = (fields: FrontmatterMap, key: string): string => {
	const value = fields.get(key);
	if (typeof value !== "string" || value.trim() === "")
		throw new SystemDocumentError(
			"metadata.value",
			`${key} must be a non-empty string`,
		);
	return value;
};
const optionalUniqueStrings = (
	fields: FrontmatterMap,
	key: string,
): readonly string[] | undefined => {
	const value = fields.get(key);
	if (value === undefined) return undefined;
	if (!Array.isArray(value) || value.some((item) => typeof item !== "string"))
		throw new SystemDocumentError(
			"metadata.value",
			`${key} must be a string array`,
		);
	if (new Set(value).size !== value.length)
		throw new SystemDocumentError(
			"metadata.duplicate",
			`${key} must contain unique values`,
		);
	return value as readonly string[];
};
const requiredUniqueStrings = (
	fields: FrontmatterMap,
	key: string,
): readonly string[] => {
	const value = optionalUniqueStrings(fields, key);
	if (!value)
		throw new SystemDocumentError(
			"metadata.value",
			`${key} must be a string array`,
		);
	return value;
};
const statusField = <T extends string>(
	fields: FrontmatterMap,
	allowed: readonly T[],
	message: string,
): T => {
	const status = requiredStringField(fields, "status");
	if (!allowed.includes(status as T))
		throw new SystemDocumentError("metadata.status", message);
	return status as T;
};
const projectMetadata = (
	fields: FrontmatterMap,
	prefix: string,
): DocumentMetadata => {
	const id = requiredStringField(fields, "id");
	const type = requiredStringField(fields, "type");
	const title = requiredStringField(fields, "title");
	const own = parseDocumentId(id, prefix);
	if (own.type !== type)
		throw new SystemDocumentError(
			"metadata.identity",
			`Metadata ID/type mismatch: ${id} / ${type}`,
		);
	const reference = (key: string, expected: DocumentType) => {
		const value = requiredStringField(fields, key);
		const parsed = parseDocumentId(value, prefix);
		if (parsed.type !== expected)
			throw new SystemDocumentError(
				"metadata.reference-type",
				`${key} must reference ${expected}: ${value}`,
			);
		return value;
	};
	const dependencies = (expected: "plan") => {
		const values = optionalUniqueStrings(fields, "depends_on");
		if (!values) return undefined;
		for (const value of values) {
			const parsed = parseDocumentId(value, prefix);
			if (parsed.type !== expected)
				throw new SystemDocumentError(
					"metadata.reference-type",
					`depends_on must reference ${expected}: ${value}`,
				);
		}
		return values;
	};
	switch (type) {
		case "research":
			return { id, type, title };
		case "spec": {
			const research = optionalUniqueStrings(fields, "research");
			if (research) for (const item of research) parseDocumentId(item, prefix);
			return research ? { id, type, title, research } : { id, type, title };
		}
		case "phase": {
			const label = requiredStringField(fields, "label");
			if (!/^[A-Za-z0-9._-]{1,12}$/.test(label))
				throw new SystemDocumentError(
					"metadata.phase-label",
					"Phase label must contain 1-12 ASCII letters, digits, dots, underscores, or hyphens",
				);
			return { id, type, title, label };
		}
		case "plan": {
			const depends_on = dependencies("plan");
			return {
				id,
				type,
				title,
				spec: reference("spec", "spec"),
				status: statusField(
					fields,
					["draft", "approved"],
					"Plan status must be draft or approved",
				),
				...(depends_on ? { depends_on } : {}),
			};
		}
		case "issue":
			return {
				id,
				type,
				title,
				specs: requiredUniqueStrings(fields, "specs"),
			};
		default:
			throw new SystemDocumentError(
				"metadata.type",
				`Unsupported metadata type: ${type}`,
			);
	}
};

export function parseAuthoredDocument(
	source: string,
	prefix: string,
): AuthoredDocument {
	const frontmatter = parseFrontmatter(source);
	const metadata = projectMetadata(frontmatter, prefix);
	if (
		metadata.type === "phase" &&
		Buffer.byteLength(source, "utf8") > PHASE_BYTE_LIMIT
	)
		throw new SystemDocumentError(
			"document.phase-size",
			`Phase exceeds the ${PHASE_BYTE_LIMIT}-byte limit`,
		);
	return { metadata, frontmatter };
}

export type CurrentPhaseDocument = Readonly<{
	path: string;
	metadata: PhaseMetadata;
	markdown: string;
}>;

export function readCurrentPhase(
	root: string,
	config: SystemConfig,
): CurrentPhaseDocument | undefined {
	if (!config.currentPhase) return undefined;
	const directory = path.join(root, ".system/phases");
	let matches: string[];
	try {
		matches = readdirSync(directory).filter((name) =>
			name.startsWith(`${config.currentPhase}-`),
		);
	} catch {
		throw new SystemDocumentError(
			"config.current-phase",
			`Current phase does not exist: ${config.currentPhase}`,
		);
	}
	if (matches.length !== 1)
		throw new SystemDocumentError(
			"config.current-phase",
			matches.length === 0
				? `Current phase does not exist: ${config.currentPhase}`
				: `Current phase is ambiguous: ${config.currentPhase}`,
		);
	const relative = `.system/phases/${matches[0]}/index.md`;
	const bundle = path.join(directory, matches[0] as string);
	const target = path.join(bundle, "index.md");
	const targetStats = lstatSync(target, { throwIfNoEntry: false });
	if (
		lstatSync(bundle, { throwIfNoEntry: false })?.isSymbolicLink() ||
		!targetStats?.isFile() ||
		targetStats.isSymbolicLink()
	)
		throw new SystemDocumentError(
			"config.current-phase",
			`Current phase is not a regular document: ${config.currentPhase}`,
		);
	if (targetStats.size > PHASE_BYTE_LIMIT)
		throw new SystemDocumentError(
			"document.phase-size",
			`Current phase exceeds the ${PHASE_BYTE_LIMIT}-byte limit`,
		);
	const markdown = readFileSync(target, "utf8");
	const authored = parseAuthoredDocument(markdown, config.prefix);
	validateDocumentPath(relative, authored.metadata, config.prefix);
	if (
		authored.metadata.type !== "phase" ||
		authored.metadata.id !== config.currentPhase
	)
		throw new SystemDocumentError(
			"config.current-phase",
			`Current phase document does not match ${config.currentPhase}`,
		);
	return { path: relative, metadata: authored.metadata, markdown };
}

const diagnostic = (
	code: string,
	diagnosticPath: string,
	message: string,
): Diagnostic => ({ code, path: diagnosticPath, message });
const compareDiagnostics = (left: Diagnostic, right: Diagnostic) =>
	left.path.localeCompare(right.path) ||
	left.code.localeCompare(right.code) ||
	left.message.localeCompare(right.message);
const scanBundleAssets = (
	absolute: string,
	relative: string,
	findings: Diagnostic[],
): void => {
	for (const entry of readdirSync(absolute, { withFileTypes: true }).sort(
		(left, right) => left.name.localeCompare(right.name),
	)) {
		if (relative.split("/").length === 3 && entry.name === "index.md") continue;
		const childAbsolute = path.join(absolute, entry.name);
		const childRelative = `${relative}/${entry.name}`;
		const stats = lstatSync(childAbsolute, { throwIfNoEntry: false });
		if (!stats) continue;
		if (stats.isSymbolicLink())
			findings.push(
				diagnostic(
					"bundle.symbolic-link",
					childRelative,
					`Bundle path is a symbolic link: ${childRelative}`,
				),
			);
		else if (stats.isDirectory())
			scanBundleAssets(childAbsolute, childRelative, findings);
	}
};

export function discoverDocumentBundles(root: string): BundleDiscovery {
	const sources: BundleDocumentSource[] = [];
	const diagnostics: Diagnostic[] = [];
	const systemRoot = path.join(root, ".system");
	if (lstatSync(systemRoot, { throwIfNoEntry: false })?.isSymbolicLink())
		return {
			sources,
			diagnostics: [
				diagnostic(
					"bundle.symbolic-link",
					".system",
					"Bundle path is a symbolic link: .system",
				),
			],
		};
	for (const directory of Object.values(DIRECTORY_BY_TYPE)) {
		const relativeDirectory = `.system/${directory}`;
		const absoluteDirectory = path.join(root, relativeDirectory);
		const directoryStats = lstatSync(absoluteDirectory, {
			throwIfNoEntry: false,
		});
		if (!directoryStats) continue;
		if (directoryStats.isSymbolicLink()) {
			diagnostics.push(
				diagnostic(
					"bundle.symbolic-link",
					relativeDirectory,
					`Bundle path is a symbolic link: ${relativeDirectory}`,
				),
			);
			continue;
		}
		if (!directoryStats.isDirectory()) {
			diagnostics.push(
				diagnostic(
					"bundle.expected-directory",
					relativeDirectory,
					`Expected a document collection directory: ${relativeDirectory}`,
				),
			);
			continue;
		}
		for (const entry of readdirSync(absoluteDirectory, {
			withFileTypes: true,
		}).sort((left, right) => left.name.localeCompare(right.name))) {
			const bundleRelative = `${relativeDirectory}/${entry.name}`;
			const bundleAbsolute = path.join(absoluteDirectory, entry.name);
			const bundleStats = lstatSync(bundleAbsolute, { throwIfNoEntry: false });
			if (bundleStats?.isSymbolicLink()) {
				diagnostics.push(
					diagnostic(
						"bundle.symbolic-link",
						bundleRelative,
						`Bundle path is a symbolic link: ${bundleRelative}`,
					),
				);
				continue;
			}
			if (!bundleStats?.isDirectory()) {
				diagnostics.push(
					diagnostic(
						"bundle.expected-directory",
						bundleRelative,
						`Expected a document bundle directory: ${bundleRelative}`,
					),
				);
				continue;
			}
			const indexRelative = `${bundleRelative}/index.md`;
			const indexAbsolute = path.join(bundleAbsolute, "index.md");
			const indexStats = lstatSync(indexAbsolute, { throwIfNoEntry: false });
			if (!indexStats)
				diagnostics.push(
					diagnostic(
						"bundle.missing-index",
						bundleRelative,
						`Bundle is missing index.md: ${bundleRelative}`,
					),
				);
			else if (indexStats.isSymbolicLink())
				diagnostics.push(
					diagnostic(
						"bundle.symbolic-link",
						indexRelative,
						`Bundle path is a symbolic link: ${indexRelative}`,
					),
				);
			else if (!indexStats.isFile())
				diagnostics.push(
					diagnostic(
						"bundle.expected-file",
						indexRelative,
						`Expected a regular index.md: ${indexRelative}`,
					),
				);
			else
				sources.push({
					path: indexRelative,
					markdown: readFileSync(indexAbsolute, "utf8"),
				});
			scanBundleAssets(bundleAbsolute, bundleRelative, diagnostics);
		}
	}
	return {
		sources: sources.sort((left, right) => left.path.localeCompare(right.path)),
		diagnostics: diagnostics.sort(compareDiagnostics),
	};
}

export const references = (
	metadata: DocumentMetadata,
): readonly (readonly [string, DocumentType])[] => {
	switch (metadata.type) {
		case "spec":
			return (metadata.research ?? []).map((id) => [id, "research"] as const);
		case "phase":
			return [];
		case "plan":
			return [
				[metadata.spec, "spec"],
				...(metadata.depends_on ?? []).map((id) => [id, "plan"] as const),
			];
		case "issue":
			return metadata.specs.map((spec) => [spec, "spec"] as const);
		default:
			return [];
	}
};

export const dependencyReferences = (
	metadata: DocumentMetadata,
): readonly string[] =>
	metadata.type === "plan" ? (metadata.depends_on ?? []) : [];
const diagnosticIdentity = (item: Diagnostic) =>
	JSON.stringify([item.path, item.code, item.message]);

export function indexBundleDocuments(
	sources: readonly BundleDocumentSource[],
	prefix: string,
): BundleDocumentIndex {
	const documents: BundleDocumentRecord[] = [];
	const graphEligible: BundleDocumentRecord[] = [];
	const diagnostics: Diagnostic[] = [];
	for (const item of [...sources].sort((left, right) =>
		left.path.localeCompare(right.path),
	)) {
		try {
			const parsed = parseAuthoredDocument(item.markdown, prefix);
			let pathValid = true;
			try {
				validateDocumentPath(item.path, parsed.metadata, prefix);
			} catch (error) {
				pathValid = false;
				diagnostics.push(
					diagnostic("document.path", item.path, (error as Error).message),
				);
			}
			const record = {
				path: item.path,
				metadata: parsed.metadata,
				frontmatter: parsed.frontmatter,
			};
			documents.push(record);
			if (pathValid) graphEligible.push(record);
		} catch (error) {
			const value = error as SystemDocumentError | MarkdownDocumentError;
			diagnostics.push(
				diagnostic(
					"document.metadata",
					item.path,
					`${value.code}: ${value.message}`,
				),
			);
		}
	}
	const groups = new Map<string, BundleDocumentRecord[]>();
	for (const document of graphEligible)
		groups.set(document.metadata.id, [
			...(groups.get(document.metadata.id) ?? []),
			document,
		]);
	for (const [id, records] of groups) {
		if (records.length < 2) continue;
		const paths = records.map((record) => record.path).sort();
		for (const record of records)
			diagnostics.push(
				diagnostic(
					"graph.duplicate-id",
					record.path,
					`Duplicate ID ${id}: ${paths.join(", ")}`,
				),
			);
	}
	const unique = new Map(
		[...groups].flatMap(([id, records]) => {
			const [record] = records;
			return records.length === 1 && record ? [[id, record] as const] : [];
		}),
	);
	for (const document of graphEligible) {
		for (const [targetId, expectedType] of references(document.metadata)) {
			const referencedType = parseDocumentId(targetId, prefix).type;
			const target = unique.get(targetId);
			if (referencedType !== expectedType)
				diagnostics.push(
					diagnostic(
						"graph.forbidden-edge",
						document.path,
						`${document.metadata.id} must reference ${expectedType}; ${targetId} is ${referencedType}`,
					),
				);
			else if (!target)
				diagnostics.push(
					diagnostic(
						"graph.dangling-reference",
						document.path,
						`${document.metadata.id} references missing ${targetId}`,
					),
				);
			else if (target.metadata.type !== expectedType)
				diagnostics.push(
					diagnostic(
						"graph.forbidden-edge",
						document.path,
						`${document.metadata.id} must reference ${expectedType}; ${targetId} is ${target.metadata.type}`,
					),
				);
		}
		if (document.metadata.type === "plan") {
			for (const dependencyId of dependencyReferences(document.metadata)) {
				const dependency = unique.get(dependencyId);
				if (
					dependency?.metadata.type === document.metadata.type &&
					dependency.metadata.spec !== document.metadata.spec
				)
					diagnostics.push(
						diagnostic(
							"graph.forbidden-edge",
							document.path,
							`${dependencyId} belongs to ${dependency.metadata.spec}, not ${document.metadata.spec}`,
						),
					);
			}
		}
	}
	const visiting = new Set<string>();
	const visited = new Set<string>();
	const visit = (document: BundleDocumentRecord, stack: readonly string[]) => {
		const id = document.metadata.id;
		if (visited.has(id)) return;
		if (visiting.has(id)) {
			const start = stack.indexOf(id);
			diagnostics.push(
				diagnostic(
					"graph.dependency-cycle",
					document.path,
					`Dependency cycle: ${[...stack.slice(start), id].join(" -> ")}`,
				),
			);
			return;
		}
		visiting.add(id);
		for (const dependencyId of [
			...dependencyReferences(document.metadata),
		].sort()) {
			const dependency = unique.get(dependencyId);
			if (dependency?.metadata.type === document.metadata.type)
				visit(dependency, [...stack, id]);
		}
		visiting.delete(id);
		visited.add(id);
	};
	for (const document of graphEligible)
		if (document.metadata.type === "plan") visit(document, []);
	return { documents, diagnostics: diagnostics.sort(compareDiagnostics) };
}

export function validateBundleCandidate(
	current: readonly BundleDocumentSource[],
	candidate: BundleDocumentSource,
	prefix: string,
): readonly Diagnostic[] {
	const baseline = new Set(
		indexBundleDocuments(current, prefix).diagnostics.map(diagnosticIdentity),
	);
	const next = indexBundleDocuments(
		[...current.filter((source) => source.path !== candidate.path), candidate],
		prefix,
	);
	return next.diagnostics.filter(
		(item) =>
			item.path === candidate.path ||
			(!baseline.has(diagnosticIdentity(item)) &&
				item.code !== "graph.duplicate-id"),
	);
}