/**
 * Client-side partial state reassembly and tracking (JavaScript version)
 */

class PartialSnakeData {
    constructor(playerId, playerIdHash) {
        this.playerId = playerId;
        this.playerIdHash = playerIdHash;
        this.body = [];
        this.direction = [1, 0];
        this.alive = true;
        this.stuck = false;
        this.colorIndex = 0;
        this.playerName = '';
        this.inputBuffer = [];
        // For segmented snakes
        this.segments = {};
        this.totalSegments = 1;
        this.isSegmented = false;
    }
}

class PartialStateTracker {
    constructor() {
        this.currentUpdateId = null;
        this.receivedSnakes = {};  // playerIdHash -> PartialSnakeData
        this.foodPositions = [];
        this.gameRunning = false;
        this.playerNameCache = {};  // playerIdHash -> playerName
    }

    /**
     * Process a partial update packet
     * Returns true if ready to apply update
     */
    processPacket(updateId, payload) {
        // Check if new update
        if (updateId !== this.currentUpdateId) {
            // New tick - reset received snakes
            this.currentUpdateId = updateId;
            this.receivedSnakes = {};
        }

        // Decode packet
        let fields;
        try {
            fields = BinaryCodec.decodePayload(payload);
        } catch (e) {
            console.error('Error decoding payload:', e);
            return false;
        }

        // Track current snake being processed
        let currentSnakeHash = null;

        // Process fields
        for (const [fieldId, fieldType, fieldData] of fields) {
            if (fieldId === FieldID.UPDATE_ID) {
                // Already have it
            }
            else if (fieldId === FieldID.GAME_RUNNING) {
                this.gameRunning = fieldData[0] !== 0;
            }
            else if (fieldId === FieldID.FOOD_POSITIONS) {
                // Decode packed positions
                if (fieldData.length > 0) {
                    const count = fieldData[0];
                    const positions = BinaryCodec.decodePackedPositions(fieldData.slice(1), count);
                    this.foodPositions = positions;
                }
            }
            else if (fieldId === FieldID.SNAKE_COUNT) {
                // Just informational
            }
            else if (fieldId === FieldID.PLAYER_ID_HASH) {
                // Start of snake data
                const dv = new DataView(fieldData.buffer, fieldData.byteOffset, fieldData.byteLength);
                const playerHash = dv.getUint32(0, false);  // Big endian
                currentSnakeHash = playerHash;

                if (!(playerHash in this.receivedSnakes)) {
                    this.receivedSnakes[playerHash] = new PartialSnakeData(
                        String(playerHash),  // Will be replaced by actual ID later
                        playerHash
                    );
                }
            }
            else if (fieldId === FieldID.BODY_POSITIONS && currentSnakeHash !== null) {
                // Complete body (delta encoded)
                // Estimate count from data length
                const count = Math.floor(fieldData.length / 2) + 1;
                const body = BinaryCodec.decodeDeltaPositions(fieldData, count);
                this.receivedSnakes[currentSnakeHash].body = body;
            }
            else if (fieldId === FieldID.BODY_SEGMENT && currentSnakeHash !== null) {
                // Partial body segment
                this.receivedSnakes[currentSnakeHash].isSegmented = true;
            }
            else if (fieldId === FieldID.SEGMENT_INFO && currentSnakeHash !== null) {
                // Segment index and total
                if (fieldData.length >= 2) {
                    const segIdx = fieldData[0];
                    const totalSegs = fieldData[1];
                    const snake = this.receivedSnakes[currentSnakeHash];
                    snake.totalSegments = totalSegs;
                }
            }
            else if (fieldId === FieldID.DIRECTION && currentSnakeHash !== null) {
                // Direction + flags (9 bits: dir(2) + alive(1) + stuck(1) + color(5))
                if (fieldData.length >= 2) {
                    const dv = new DataView(fieldData.buffer, fieldData.byteOffset, fieldData.byteLength);
                    const flags = dv.getUint16(0, false);  // Big endian

                    const dirBits = (flags >> 7) & 0x03;
                    const alive = (flags >> 6) & 0x01;
                    const stuck = (flags >> 5) & 0x01;
                    const colorIndex = flags & 0x1F;

                    // Map direction bits to tuple
                    const directionMap = {
                        0: [1, 0],   // Right
                        1: [-1, 0],  // Left
                        2: [0, 1],   // Down
                        3: [0, -1]   // Up
                    };

                    const snake = this.receivedSnakes[currentSnakeHash];
                    snake.direction = directionMap[dirBits] || [1, 0];
                    snake.alive = alive === 1;
                    snake.stuck = stuck === 1;
                    snake.colorIndex = colorIndex;
                }
            }
            else if (fieldId === FieldID.PLAYER_NAME && currentSnakeHash !== null) {
                // Player name (string_16)
                const [name, _] = BinaryCodec.decodeString16(fieldData);
                this.receivedSnakes[currentSnakeHash].playerName = name;
                this.playerNameCache[currentSnakeHash] = name;
            }
            else if (fieldId === FieldID.INPUT_BUFFER && currentSnakeHash !== null) {
                // Input buffer (3x 2-bit directions)
                if (fieldData.length >= 1) {
                    const bufBits = fieldData[0];

                    const directionMap = {
                        0: [1, 0],   // Right
                        1: [-1, 0],  // Left
                        2: [0, 1],   // Down
                        3: [0, -1]   // Up
                    };

                    const inputBuffer = [];
                    for (let i = 0; i < 3; i++) {
                        const dirVal = (bufBits >> (4 - i * 2)) & 0x03;
                        inputBuffer.push(directionMap[dirVal] || [1, 0]);
                    }

                    this.receivedSnakes[currentSnakeHash].inputBuffer = inputBuffer;
                }
            }
        }

        // Always return true to trigger update (best effort)
        return true;
    }

    /**
     * Get current assembled game state
     */
    getGameState(previousState = null) {
        // Create snake objects
        const snakes = [];

        for (const [playerHash, snakeData] of Object.entries(this.receivedSnakes)) {
            // Get player name from cache if not in current data
            let playerName = snakeData.playerName;
            if (!playerName && playerHash in this.playerNameCache) {
                playerName = this.playerNameCache[playerHash];
            }

            const snake = {
                player_id: snakeData.playerId,
                body: snakeData.body,
                direction: snakeData.direction,
                alive: snakeData.alive,
                stuck: snakeData.stuck,
                color_index: snakeData.colorIndex,
                player_name: playerName,
                input_buffer: snakeData.inputBuffer
            };
            snakes.push(snake);
        }

        // If we have previous state, merge in missing snakes
        if (previousState && previousState.snakes) {
            const currentHashes = new Set(Object.keys(this.receivedSnakes).map(Number));

            for (const prevSnake of previousState.snakes) {
                const prevHash = BinaryCodec.playerIdHash(prevSnake.player_id);
                if (!currentHashes.has(prevHash)) {
                    // Keep previous snake data (packet was lost)
                    snakes.push(prevSnake);
                }
            }
        }

        // Create food
        const food = this.foodPositions.map(pos => ({ position: pos }));

        return {
            snakes: snakes,
            food: food,
            game_running: this.gameRunning
        };
    }

    /**
     * Reset tracker for new game
     */
    reset() {
        this.currentUpdateId = null;
        this.receivedSnakes = {};
        this.foodPositions = [];
        this.gameRunning = false;
        // Keep name cache across resets
    }
}