/**
 * MCTS Data Parser
 *
 * Parses TGN game files and visit count JSON files to reconstruct
 * move-by-move MCTS statistics.
 */

import { TrigoGame } from "../../../inc/trigo/game";
import type { MCTSMoveData, MCTSMoveStatistic } from "../types/mcts";


/**
 * Parse MCTS data from TGN and visit counts JSON
 *
 * @param tgnContent - TGN game notation string
 * @param visitCountsJson - JSON string containing visit counts array
 * @returns Array of MCTS move data for each move in the game
 * @throws Error if parsing fails or data is invalid
 */
export async function parseMCTSData(
	tgnContent: string,
	visitCountsJson: string
): Promise<MCTSMoveData[]> {
	// 1. Parse TGN to get game
	let game: TrigoGame;
	try {
		game = TrigoGame.fromTGN(tgnContent);
	} catch (error) {
		throw new Error(`Failed to parse TGN file: ${error instanceof Error ? error.message : String(error)}`);
	}

	// 2. Validate board shape (must be 2D)
	const shape = game.getShape();
	if (shape.z !== 1) {
		throw new Error(
			`Only 2D boards (z=1) are supported. This game has shape ${shape.x}×${shape.y}×${shape.z}`
		);
	}

	// 3. Parse visit counts JSON
	let visitCounts: number[][];
	try {
		visitCounts = JSON.parse(visitCountsJson);

		if (!Array.isArray(visitCounts)) {
			throw new Error("Visit counts must be an array");
		}

		if (visitCounts.length === 0) {
			throw new Error("Visit counts array is empty");
		}

		// Validate that each element is an array of numbers
		for (let i = 0; i < visitCounts.length; i++) {
			if (!Array.isArray(visitCounts[i])) {
				throw new Error(`Visit counts at index ${i} is not an array`);
			}
		}
	} catch (error) {
		throw new Error(`Failed to parse visit counts JSON: ${error instanceof Error ? error.message : String(error)}`);
	}

	// 4. Replay game move-by-move and map visit counts to positions
	const result: MCTSMoveData[] = [];
	const replayGame = new TrigoGame(shape, {});
	const stepHistory = game.getHistory();

	// Ensure we have visit counts for each move
	if (visitCounts.length !== stepHistory.length) {
		console.warn(
			`Visit counts length (${visitCounts.length}) doesn't match step history length (${stepHistory.length}). Using minimum.`
		);
	}

	const minLength = Math.min(visitCounts.length, stepHistory.length);

	for (let i = 0; i < minLength; i++) {
		// Get current player
		const currentPlayer = replayGame.getCurrentPlayer() === 1 ? "black" : "white";

		// Get all valid positions at this state
		const validPos = replayGame.validMovePositions();

		// Map visit counts to positions
		const statistics: MCTSMoveStatistic[] = validPos.map((pos, idx) => ({
			position: pos,
			actionKey: `${pos.x},${pos.y},${pos.z}`,
			N: visitCounts[i][idx] || 0,
			pi: 0 // Will be calculated after
		}));

		// Add pass move (typically the last element in visit counts)
		const passN = visitCounts[i][validPos.length] || 0;
		statistics.push({
			position: null,
			actionKey: "pass",
			N: passN,
			pi: 0
		});

		// Calculate total visits
		const totalN = statistics.reduce((sum, stat) => sum + stat.N, 0);

		// Normalize to get search policy π
		if (totalN > 0) {
			statistics.forEach((stat) => {
				stat.pi = stat.N / totalN;
			});
		}

		// Store move data
		result.push({
			moveNumber: i,
			player: currentPlayer,
			gameState: replayGame.clone(),
			statistics
		});

		// Apply move to advance game state
		const step = stepHistory[i];
		if (step.type === 1) { // StepType.PASS
			replayGame.pass();
		} else if (step.position) {
			replayGame.drop(step.position);
		}
	}

	if (result.length === 0) {
		throw new Error("No MCTS data could be parsed");
	}

	console.log(`[MCTS Parser] Successfully parsed ${result.length} moves`);
	return result;
}


/**
 * Validate that visit counts data has the expected structure
 */
export function validateVisitCounts(visitCounts: any): visitCounts is number[][] {
	if (!Array.isArray(visitCounts)) {
		return false;
	}

	for (const counts of visitCounts) {
		if (!Array.isArray(counts)) {
			return false;
		}

		for (const count of counts) {
			if (typeof count !== "number" || !Number.isFinite(count) || count < 0) {
				return false;
			}
		}
	}

	return true;
}


/**
 * Format position for display
 */
export function formatPosition(position: { x: number; y: number; z?: number } | null): string {
	if (!position) {
		return "Pass";
	}

	// Convert to chess-like notation: column letter + row number
	const col = String.fromCharCode(65 + position.x); // A, B, C, ...
	const row = position.y + 1; // 1, 2, 3, ...

	return `${col}${row}`;
}