import { readFileSync } from "node:fs";
import { basename } from "node:path";
import { IMPACT_LEVELS, SECTION_MAP } from "./config.js";
import type { CodeExample, ImpactLevel, ParseResult, Rule } from "./types.js";

/**
 * Parse YAML-style frontmatter from markdown content
 */
function parseFrontmatter(content: string): {
	frontmatter: Record<string, string>;
	body: string;
} {
	const frontmatter: Record<string, string> = {};

	if (!content.startsWith("---")) {
		return { frontmatter, body: content };
	}

	const endIndex = content.indexOf("---", 3);
	if (endIndex === -1) {
		return { frontmatter, body: content };
	}

	const frontmatterContent = content.slice(3, endIndex).trim();
	const body = content.slice(endIndex + 3).trim();

	for (const line of frontmatterContent.split("\n")) {
		const colonIndex = line.indexOf(":");
		if (colonIndex === -1) continue;

		const key = line.slice(0, colonIndex).trim();
		let value = line.slice(colonIndex + 1).trim();

		// Strip quotes
		if (
			(value.startsWith('"') && value.endsWith('"')) ||
			(value.startsWith("'") && value.endsWith("'"))
		) {
			value = value.slice(1, -1);
		}

		frontmatter[key] = value;
	}

	return { frontmatter, body };
}

/**
 * Extract section number from filename prefix
 */
function getSectionFromFilename(filename: string): number | null {
	const base = basename(filename, ".md");
	const prefix = base.split("-")[0];
	return SECTION_MAP[prefix] ?? null;
}

/**
 * Extract code examples from markdown body
 */
function extractExamples(body: string): CodeExample[] {
	const examples: CodeExample[] = [];
	const lines = body.split("\n");

	let currentLabel = "";
	let currentDescription = "";
	let inCodeBlock = false;
	let codeBlockLang = "";
	let codeBlockContent: string[] = [];
	let additionalText: string[] = [];

	for (let i = 0; i < lines.length; i++) {
		const line = lines[i];

		// Check for example label: **Label:** or **Label (description):**
		const labelMatch = line.match(
			/^\*\*([^*]+?)(?:\s*\(([^)]+)\))?\s*:\*\*\s*$/,
		);
		if (labelMatch && !inCodeBlock) {
			// Save previous example if exists
			if (currentLabel && codeBlockContent.length > 0) {
				examples.push({
					label: currentLabel,
					description: currentDescription || undefined,
					code: codeBlockContent.join("\n"),
					language: codeBlockLang || undefined,
					additionalText:
						additionalText.length > 0
							? additionalText.join("\n").trim()
							: undefined,
				});
			}

			currentLabel = labelMatch[1].trim();
			currentDescription = labelMatch[2]?.trim() || "";
			codeBlockContent = [];
			codeBlockLang = "";
			additionalText = [];
			continue;
		}

		// Check for code block start
		if (line.startsWith("```") && !inCodeBlock) {
			inCodeBlock = true;
			codeBlockLang = line.slice(3).trim();
			continue;
		}

		// Check for code block end
		if (line.startsWith("```") && inCodeBlock) {
			inCodeBlock = false;
			continue;
		}

		// Collect code block content
		if (inCodeBlock) {
			codeBlockContent.push(line);
			continue;
		}

		// Collect additional text after code block (before next label)
		if (currentLabel && codeBlockContent.length > 0 && line.trim()) {
			// Stop collecting if we hit a heading or reference
			if (line.startsWith("#") || line.startsWith("Reference")) {
				continue;
			}
			additionalText.push(line);
		}
	}

	// Save last example
	if (currentLabel && codeBlockContent.length > 0) {
		examples.push({
			label: currentLabel,
			description: currentDescription || undefined,
			code: codeBlockContent.join("\n"),
			language: codeBlockLang || undefined,
			additionalText:
				additionalText.length > 0
					? additionalText.join("\n").trim()
					: undefined,
		});
	}

	return examples;
}

/**
 * Extract title from first ## heading
 */
function extractTitle(body: string): string | null {
	const match = body.match(/^##\s+(.+)$/m);
	return match ? match[1].trim() : null;
}

/**
 * Extract explanation (content between title and first example)
 */
function extractExplanation(body: string): string {
	const lines = body.split("\n");
	const explanationLines: string[] = [];
	let foundTitle = false;

	for (const line of lines) {
		if (line.startsWith("## ")) {
			foundTitle = true;
			continue;
		}

		if (!foundTitle) continue;

		// Stop at first example label or code block
		if (line.match(/^\*\*[^*]+:\*\*/) || line.startsWith("```")) {
			break;
		}

		explanationLines.push(line);
	}

	return explanationLines.join("\n").trim();
}

/**
 * Extract references from body
 */
function extractReferences(body: string): string[] {
	const references: string[] = [];
	const lines = body.split("\n");

	for (const line of lines) {
		// Match "Reference: [text](url)" or "- [text](url)" after "References:"
		const refMatch = line.match(/Reference:\s*\[([^\]]+)\]\(([^)]+)\)/);
		if (refMatch) {
			references.push(refMatch[2]);
			continue;
		}

		// Match list items under References section
		const listMatch = line.match(/^-\s*\[([^\]]+)\]\(([^)]+)\)/);
		if (listMatch) {
			references.push(listMatch[2]);
		}
	}

	return references;
}

/**
 * Parse a rule file and return structured data
 */
export function parseRuleFile(filePath: string): ParseResult {
	const errors: string[] = [];
	const warnings: string[] = [];

	try {
		const content = readFileSync(filePath, "utf-8");
		const { frontmatter, body } = parseFrontmatter(content);

		// Extract section from filename
		const section = getSectionFromFilename(filePath);
		if (section === null) {
			errors.push(
				`Could not determine section from filename: ${basename(filePath)}`,
			);
			return { success: false, errors, warnings };
		}

		// Get title from frontmatter or body
		const title = frontmatter.title || extractTitle(body);
		if (!title) {
			errors.push("Missing title in frontmatter or body");
			return { success: false, errors, warnings };
		}

		// Get impact level
		const impact = frontmatter.impact as ImpactLevel;
		if (!impact || !IMPACT_LEVELS.includes(impact)) {
			errors.push(
				`Invalid or missing impact level: ${impact}. Must be one of: ${IMPACT_LEVELS.join(", ")}`,
			);
			return { success: false, errors, warnings };
		}

		// Extract other fields
		const explanation = extractExplanation(body);
		const examples = extractExamples(body);

		const tags = frontmatter.tags?.split(",").map((t) => t.trim()) || [];

		// Validation warnings
		if (!explanation || explanation.length < 20) {
			warnings.push("Explanation is very short or missing");
		}

		if (examples.length === 0) {
			warnings.push("No code examples found");
		}

		const rule: Rule = {
			id: "", // Will be assigned during build
			title,
			section,
			impact,
			impactDescription: frontmatter.impactDescription,
			explanation,
			examples,
			references: extractReferences(body),
			tags: tags.length > 0 ? tags : undefined,
		};

		return { success: true, rule, errors, warnings };
	} catch (error) {
		errors.push(`Failed to parse file: ${error}`);
		return { success: false, errors, warnings };
	}
}