import * as fs from "node:fs";
import * as path from "node:path";

const MAX_META_FILE_CHARS = 12_000;
const MAX_META_TOTAL_CHARS = 32_000;

export const META_FILE_ORDER = ["GOAL.md", "LEDGER.md", "STATUS.md", "ROADMAP.md"];

const META_FILE_TEMPLATES: Record<string, string> = {
	"GOAL.md": "# Goal\n\nRecord the user's durable goal, constraints, and completion evidence here.\n",
	"ROADMAP.md": "# Roadmap\n\nTrack milestones, ordering, dependencies, and evidence for completing the goal.\n",
	"LEDGER.md":
		"# Ledger\n\nUse this for durable facts, decisions, evidence, failed approaches, blockers, and useful pointers.\n",
	"STATUS.md":
		"# Status\n\nKeep a brief human-readable summary of material results, remaining work or blockers, and evidence.\n",
};

export interface MetaBootstrap {
	created: string[];
	existing: string[];
}

function orderedMarkdownFiles(metaDir: string): string[] {
	const files = fs
		.readdirSync(metaDir, { withFileTypes: true })
		.filter((entry) => entry.isFile() && entry.name.toLowerCase().endsWith(".md"))
		.map((entry) => entry.name);
	const priority = new Map(META_FILE_ORDER.map((name, index) => [name, index]));
	return files.sort((left, right) => {
		const leftPriority = priority.get(left) ?? META_FILE_ORDER.length;
		const rightPriority = priority.get(right) ?? META_FILE_ORDER.length;
		return leftPriority - rightPriority || left.localeCompare(right);
	});
}

export function metaDirFor(cwd: string): string {
	return path.join(cwd, ".pi", "meta");
}

export function readMetaFiles(cwd: string): Array<{ name: string; content: string }> {
	const metaDir = metaDirFor(cwd);
	try {
		if (!fs.statSync(metaDir).isDirectory()) return [];
	} catch {
		return [];
	}

	const result: Array<{ name: string; content: string }> = [];
	let remaining = MAX_META_TOTAL_CHARS;
	for (const name of orderedMarkdownFiles(metaDir)) {
		if (remaining <= 0) break;
		try {
			const content = fs.readFileSync(path.join(metaDir, name), "utf8");
			const included = content.slice(0, Math.min(MAX_META_FILE_CHARS, remaining));
			result.push({ name, content: included });
			remaining -= included.length;
		} catch {
			// A concurrently changed meta file should not block an agent turn.
		}
	}
	return result;
}

export function bootstrapMetaFiles(cwd: string): MetaBootstrap {
	const metaDir = metaDirFor(cwd);
	fs.mkdirSync(metaDir, { recursive: true });
	const result: MetaBootstrap = { created: [], existing: [] };
	for (const name of META_FILE_ORDER) {
		const filePath = path.join(metaDir, name);
		try {
			fs.writeFileSync(filePath, META_FILE_TEMPLATES[name] ?? "", { encoding: "utf8", flag: "wx" });
			result.created.push(name);
		} catch (error) {
			if ((error as NodeJS.ErrnoException).code !== "EEXIST") throw error;
			result.existing.push(name);
		}
	}
	return result;
}

export function buildOrchestrationPrompt(cwd: string): string {
	const files = readMetaFiles(cwd);
	const metaDir = metaDirFor(cwd);
	const guidance = [
		"## Autonomous execution",
		"",
		"Work head down and autonomously until the user's entire goal is achieved and supported by concrete evidence.",
		`- The fixed durable-memory directory for this session is \`${metaDir}\`. Keep it there even when the implementation or reference repositories live in nested directories.`,
		"- Use the standard files supplied there—`GOAL.md`, `LEDGER.md`, `STATUS.md`, and `ROADMAP.md`—as durable memory when useful.",
		"- `GOAL.md`: the durable target, constraints, and completion evidence. Update it when the user changes the goal or evidence corrects an earlier assumption.",
		"- `LEDGER.md`: durable working memory for yourself: important facts, technical details, decisions, evidence, failed approaches, blockers, and useful pointers.",
		"- `STATUS.md`: a brief plain-language snapshot for the human: material results, what remains or is blocked, and supporting evidence. Summarize rather than copy the ledger.",
		"- `ROADMAP.md`: the strategic milestone map: phases, ordering, dependencies, coverage, and evidence showing which milestones are complete.",
		`- These are standard files, not a limit. Create additional clearly named Markdown files in \`${metaDir}\` when useful for durable note-taking.`,
		"- Until the goal is verifiably achieved, keep taking substantive actions. A summary of progress, a list of remaining work, or the size of the remaining work is not a reason to stop.",
		"- Do not end after a small batch of changes. Continue through the complete remaining queue of known tasks, gaps, unchecked roadmap items, TODOs, placeholders, stubs, failing checks, and unverified behavior.",
		"- Only end when no known work remains. Do not mark an item complete merely to shorten the remaining list; completion requires evidence.",
		"- Do not ask the user for guidance, prioritization, confirmation, or permission when a reasonable autonomous choice is available. Ask only when progress truly requires unavailable user-only information or authority.",
		"- Do not pause for progress reports between actions. Keep using tools and completing work.",
		"- Do not end a work pass to seek assessment, approval, or more direction. Perform all work and verification available to you first.",
		"- Do not silently narrow, downgrade, or relabel the user's goal to match partial progress.",
		"- Maintaining meta files is not progress and must not replace substantive work.",
		"- Updating durable memory or committing a batch is not a stopping point while any known work remains; return immediately to substantive work.",
		"- For broad goals with multiple independent workstreams, actively use subagents early. Give them concrete deliverables and non-overlapping ownership, run independent work in parallel when safe, and continue your own work while they run. Integrate and verify their results; delegation does not transfer responsibility for the full goal.",
		"- Create specialized agents when that materially improves a workstream. Keep `.pi/meta/` out of delegated prompts unless directly needed.",
		"- If repeated approaches stall, reassess the strategy and try a materially different approach.",
		"- Before claiming completion, compare the result with `GOAL.md` and verify it with concrete evidence.",
		"- Before ending your work, synchronize `GOAL.md`, `LEDGER.md`, `STATUS.md`, and `ROADMAP.md` with the actual result, concrete evidence, and any remaining limitations.",
	];
	if (files.length === 0) return guidance.join("\n");

	const memory = files.flatMap(({ name, content }) => ["", `### .pi/meta/${name}`, "", content]);
	return [...guidance, "", "Current durable memory:", ...memory].join("\n");
}