/**
 * Feature Extractor — parses plan.md, spec.md, tasks.md from feature directories
 * into structured ExtractedFeature records.
 *
 * These are already structured markdown generated by maina, so parsing
 * is deterministic (not LLM-dependent).
 */

import { existsSync, readdirSync, readFileSync, statSync } from "node:fs";
import { basename, join } from "node:path";
import type { Result } from "../../db/index";
import type { ExtractedFeature, TaskItem } from "../types";

// ─── Parsing Helpers ─────────────────────────────────────────────────────

function readOptionalFile(path: string): string | null {
	if (!existsSync(path)) return null;
	try {
		return readFileSync(path, "utf-8");
	} catch {
		return null;
	}
}

/**
 * Extract title from plan.md or spec.md heading.
 * Handles:
 *   "# Implementation Plan: Token Refresh"
 *   "# Feature: Token Refresh"
 *   "# Token Refresh"
 */
function extractTitle(content: string): string {
	const firstLine = content.split("\n")[0] ?? "";
	const heading = firstLine.replace(/^#+\s*/, "");

	// Strip common prefixes
	const prefixes = ["Implementation Plan:", "Feature:", "Plan:"];
	for (const prefix of prefixes) {
		if (heading.startsWith(prefix)) {
			return heading.slice(prefix.length).trim();
		}
	}
	return heading.trim();
}

/**
 * Extract tasks from markdown checklist format.
 * Supports: "- [ ] T001: description" and "- [x] T002: description"
 */
function extractTasks(content: string): TaskItem[] {
	const tasks: TaskItem[] = [];
	const lines = content.split("\n");

	for (const line of lines) {
		const match = line.match(/^-\s+\[([ xX])\]\s+(T\d+):\s+(.+)/);
		if (match?.[2]) {
			tasks.push({
				id: match[2],
				description: (match[3] ?? "").trim(),
				completed: match[1] !== " ",
			});
		}
	}

	return tasks;
}

/**
 * Extract acceptance criteria / assertions from spec.md.
 * Looks for checklist items under Acceptance Criteria section.
 */
function extractSpecAssertions(specContent: string): string[] {
	const assertions: string[] = [];
	const lines = specContent.split("\n");
	let inSection = false;

	for (const line of lines) {
		// Detect start of acceptance criteria section
		if (/^##\s+Acceptance Criteria/i.test(line)) {
			inSection = true;
			continue;
		}
		// End of section at next heading
		if (inSection && /^##\s/.test(line)) {
			break;
		}
		if (inSection) {
			const match = line.match(/^-\s+\[[ xX]?\]\s+(.+)/);
			if (match?.[1]) {
				assertions.push(match[1].trim());
			}
		}
	}

	return assertions;
}

/**
 * Extract scope from spec.md. Looks for text under ## Scope section.
 */
function extractScope(specContent: string): string {
	const lines = specContent.split("\n");
	let inSection = false;
	const scopeLines: string[] = [];

	for (const line of lines) {
		if (/^##\s+Scope/i.test(line)) {
			inSection = true;
			continue;
		}
		if (inSection && /^##\s/.test(line)) {
			break;
		}
		if (inSection && line.trim()) {
			scopeLines.push(line.trim());
		}
	}

	return scopeLines.join(" ");
}

// ─── Public API ──────────────────────────────────────────────────────────

export function extractSingleFeature(
	featureDir: string,
): Result<ExtractedFeature> {
	if (!existsSync(featureDir)) {
		return {
			ok: false,
			error: `Feature directory does not exist: ${featureDir}`,
		};
	}

	const id = basename(featureDir);
	const planContent = readOptionalFile(join(featureDir, "plan.md"));
	const specContent = readOptionalFile(join(featureDir, "spec.md"));
	const tasksContent = readOptionalFile(join(featureDir, "tasks.md"));

	// Extract title from plan or spec
	let title = "";
	if (planContent) {
		title = extractTitle(planContent);
	} else if (specContent) {
		title = extractTitle(specContent);
	}

	// Extract tasks from tasks.md or plan.md
	let tasks: TaskItem[] = [];
	if (tasksContent) {
		tasks = extractTasks(tasksContent);
	} else if (planContent) {
		tasks = extractTasks(planContent);
	}

	// Extract spec assertions and scope
	const specAssertions = specContent ? extractSpecAssertions(specContent) : [];
	const scope = specContent ? extractScope(specContent) : "";

	return {
		ok: true,
		value: {
			id,
			title,
			scope,
			specQualityScore: 0,
			specAssertions,
			tasks,
			entitiesModified: [],
			decisionsCreated: [],
			branch: "",
			prNumber: null,
			merged: false,
		},
	};
}

export function extractFeatures(
	featuresDir: string,
): Result<ExtractedFeature[]> {
	if (!existsSync(featuresDir)) {
		return {
			ok: false,
			error: `Features directory does not exist: ${featuresDir}`,
		};
	}

	const entries = readdirSync(featuresDir);
	const features: ExtractedFeature[] = [];

	for (const entry of entries) {
		const entryPath = join(featuresDir, entry);
		try {
			const stat = statSync(entryPath);
			if (!stat.isDirectory()) continue;
		} catch {
			continue;
		}

		const result = extractSingleFeature(entryPath);
		if (result.ok) {
			features.push(result.value);
		}
	}

	return { ok: true, value: features };
}