import { access, mkdir, readFile, writeFile } from "node:fs/promises";
import { dirname, join } from "node:path";
import { withFileMutationQueue } from "@earendil-works/pi-coding-agent";
import { parse, stringify } from "yaml";
import {
	applyTaskOperation,
	createEmptyArtifact,
	filterTasks,
	formatTaskList,
	validateArtifact,
	type Task,
	type TaskArtifact,
	type TaskIdHashGenerator,
	type TaskOperation,
	type TaskOperationResult,
} from "./tasks";

export const TASKS_DIR = ".pi";
export const TASKS_FILE = "telos-tasks.md";

export type ArtifactLoad = {
	artifact: TaskArtifact;
	existed: boolean;
};

export function taskFilePath(cwd: string): string {
	return join(cwd, TASKS_DIR, TASKS_FILE);
}

export function parseArtifactText(text: string): TaskArtifact {
	const match = /^---\r?\n([\s\S]*?)\r?\n---(?:\r?\n|$)/.exec(text);
	if (!match) throw new Error("telos-tasks.md must start with Telos YAML frontmatter delimited by ---");

	let raw: unknown;
	try {
		raw = parse(match[1]);
	} catch (error) {
		throw new Error(`Failed to parse Telos YAML frontmatter: ${error instanceof Error ? error.message : String(error)}`);
	}

	return validateArtifact(raw);
}

export function serializeArtifact(artifact: TaskArtifact): string {
	const validated = validateArtifact(artifact);
	const frontmatter = stringify(validated, { lineWidth: 0 }).trimEnd();
	return `---\n${frontmatter}\n---\n\n${renderMarkdownBody(validated.tasks)}`;
}

export function renderMarkdownBody(tasks: Task[]): string {
	const active = filterTasks(tasks, "active");
	const archived = filterTasks(tasks, "archived");
	const doneCount = tasks.filter((task) => task.status === "done").length;

	const lines: string[] = [
		"# Tasks",
		"",
		"> Generated by Telos. The YAML frontmatter above is the source of truth; this Markdown body is regenerated after successful Telos mutations.",
		"",
		"## Summary",
		"",
		`- Active: ${active.length}`,
		`- Archived: ${archived.length}`,
		`- Done: ${doneCount}`,
		`- Total: ${tasks.length}`,
		"",
		"## Active",
		"",
	];

	appendTaskTable(lines, active, "No active tasks.");
	lines.push("", "## Archived", "");
	appendTaskTable(lines, archived, "No archived tasks.");
	lines.push("");
	return lines.join("\n");
}

export async function loadTaskArtifact(filePath: string): Promise<ArtifactLoad> {
	try {
		await access(filePath);
	} catch {
		return { artifact: createEmptyArtifact(), existed: false };
	}

	const text = await readFile(filePath, "utf8");
	return { artifact: parseArtifactText(text), existed: true };
}

export async function writeTaskArtifact(filePath: string, artifact: TaskArtifact): Promise<void> {
	await mkdir(dirname(filePath), { recursive: true });
	await writeFile(filePath, serializeArtifact(artifact), "utf8");
}

export async function mutateTaskArtifact(
	filePath: string,
	operation: TaskOperation,
	now: () => Date = () => new Date(),
	generateIdHash?: TaskIdHashGenerator,
): Promise<TaskOperationResult> {
	return withFileMutationQueue(filePath, async () => {
		const before = await loadTaskArtifact(filePath);
		const result = applyTaskOperation(before.artifact, operation, now, generateIdHash);

		if (result.artifact.tasks.length < before.artifact.tasks.length) {
			throw new Error("Task operation would remove an existing task record; refusing to write telos-tasks.md");
		}

		if (!result.rejected && isMutatingOperation(operation)) {
			await writeTaskArtifact(filePath, result.artifact);
		}

		return result;
	});
}

export function isMutatingOperation(operation: TaskOperation): boolean {
	return operation.action !== "list" && operation.action !== "show" && operation.action !== "delete";
}

export function formatArtifactList(artifact: TaskArtifact, scope: "active" | "archived" | "all" = "active"): string {
	return formatTaskList(filterTasks(artifact.tasks, scope), scope);
}

function appendTaskTable(lines: string[], tasks: Task[], emptyText: string): void {
	if (tasks.length === 0) {
		lines.push(emptyText);
		return;
	}

	lines.push("| ID | Status | Priority | Depends on | Title | Updated |", "| --- | --- | --- | --- | --- | --- |");
	for (const task of tasks) {
		const dependencies = task.dependencies.length > 0 ? task.dependencies.join(", ") : "—";
		lines.push(
			`| ${escapeTable(task.id)} | ${escapeTable(task.status)} | ${escapeTable(task.priority)} | ${escapeTable(dependencies)} | ${escapeTable(task.title)} | ${escapeTable(task.updated)} |`,
		);
	}
}

function escapeTable(value: string): string {
	return value.replace(/\|/g, "\\|").replace(/\r?\n/g, " ");
}