/**
 * msghandler - Cross-Platform Bi-Directional Data Bridge
 * Browser-Compatible Implementation (Client-Side Rendering)
 * 
 * This module provides functionality for sending and receiving data across network boundaries
 * with support for both direct payload transport and URL-based transport for larger payloads.
 * 
 * Supported payload types: "text", "dictionary", "jsontable", "image", "audio", "video", "binary"
 * Note: Browser version does NOT support Apache Arrow IPC (arrowtable) due to browser compatibility constraints.
 * Use "jsontable" for tabular data in browser applications.
 * 
 * Browser requirements:
 * - Modern browser with ES module support (or use module bundler)
 * - Web Crypto API for UUID generation
 * - Fetch API for HTTP requests
 * 
 * Browser-compatible version uses:
 * - Web Crypto API for UUID generation
 * - Uint8Array instead of Buffer
 * - fetch API for file server communication
 * 
 * @module msghandlerCSR
 */

// Use native fetch available in browsers

// ---------------------------------------------- Constants ---------------------------------------------- //

/**
 * Default size threshold for switching from direct to link transport (0.5MB)
 */
const DEFAULT_SIZE_THRESHOLD = 500_000;

/**
 * Default broker URL
 */
const DEFAULT_BROKER_URL = 'localhost:4222';

/**
 * Default HTTP file server URL for link transport
 */
const DEFAULT_FILESERVER_URL = 'http://localhost:8080';

// ---------------------------------------------- Utility Functions ---------------------------------------------- //

/**
 * Convert Uint8Array to Base64 string
 * @param {Uint8Array} data - Data to encode
 * @returns {string} Base64 encoded string
 */
function bufferToBase64(data) {
    const bytes = new Uint8Array(data);
    const binary = String.fromCharCode(...bytes);
    return btoa(binary);
}

/**
 * Convert Base64 string to Uint8Array
 * @param {string} base64 - Base64 encoded string
 * @returns {Uint8Array} Decoded binary data
 */
function base64ToBuffer(base64) {
    const binary = atob(base64);
    const len = binary.length;
    const bytes = new Uint8Array(len);
    for (let i = 0; i < len; i++) {
        bytes[i] = binary.charCodeAt(i);
    }
    return bytes;
}

/**
 * Generate UUID v4 using Web Crypto API
 * @returns {string} UUID string
 */
function uuidv4() {
    const array = new Uint8Array(16);
    crypto.getRandomValues(array);
    array[6] = (array[6] & 0x0f) | 0x40;
    array[8] = (array[8] & 0x3f) | 0x80;
    return Array.from(array, (val) => val.toString(16).padStart(2, '0').toUpperCase()).join('');
}

/**
 * Log a trace message with correlation ID and timestamp
 * @param {string} correlationId - Correlation ID for tracing
 * @param {string} message - Message content to log
 */
function logTrace(correlationId, message) {
    const timestamp = new Date().toISOString();
    console.log(`[${timestamp}] [Correlation: ${correlationId}] ${message}`);
}

// ---------------------------------------------- Serialization Functions ---------------------------------------------- //

/**
 * Serialize data according to specified format
 * @param {any} data - Data to serialize
 * @param {string} payloadType - Target format: "text", "dictionary", "jsontable", "image", "audio", "video", "binary"
 * @returns {Uint8Array} Binary representation of the serialized data
 */
async function serializeData(data, payloadType) {
    if (payloadType === 'text') {
        if (typeof data === 'string') {
            return new Uint8Array(new TextEncoder().encode(data));
        } else {
            throw new Error('Text data must be a string');
        }
    } else if (payloadType === 'dictionary') {
        const jsonStr = JSON.stringify(data);
        return new Uint8Array(new TextEncoder().encode(jsonStr));
    } else if (payloadType === 'jsontable') {
        // Serialize array of objects to JSON format
        if (!Array.isArray(data)) {
            throw new Error('JSON table data must be an array');
        }
        const jsonStr = JSON.stringify(data);
        return new Uint8Array(new TextEncoder().encode(jsonStr));
    } else if (payloadType === 'image') {
        if (data instanceof Uint8Array || data instanceof ArrayBuffer || ArrayBuffer.isView(data)) {
            return new Uint8Array(data);
        } else {
            throw new Error('Image data must be Uint8Array, ArrayBuffer, or ArrayBuffer view');
        }
    } else if (payloadType === 'audio') {
        if (data instanceof Uint8Array || data instanceof ArrayBuffer || ArrayBuffer.isView(data)) {
            return new Uint8Array(data);
        } else {
            throw new Error('Audio data must be Uint8Array, ArrayBuffer, or ArrayBuffer view');
        }
    } else if (payloadType === 'video') {
        if (data instanceof Uint8Array || data instanceof ArrayBuffer || ArrayBuffer.isView(data)) {
            return new Uint8Array(data);
        } else {
            throw new Error('Video data must be Uint8Array, ArrayBuffer, or ArrayBuffer view');
        }
    } else if (payloadType === 'binary') {
        if (data instanceof Uint8Array || data instanceof ArrayBuffer || ArrayBuffer.isView(data)) {
            return new Uint8Array(data);
        } else {
            throw new Error('Binary data must be Uint8Array, ArrayBuffer, or ArrayBuffer view');
        }
    } else {
        throw new Error(`Unknown payload_type: ${payloadType}`);
    }
}

/**
 * Deserialize bytes to data based on type
 * @param {Uint8Array|ArrayBuffer} data - Serialized data as bytes
 * @param {string} payloadType - Data type
 * @param {string} correlationId - Correlation ID for logging
 * @returns {any} Deserialized data
 */
async function deserializeData(data, payloadType, correlationId) {
    const buffer = data instanceof Uint8Array ? data : new Uint8Array(data);
    
    logTrace(correlationId, `deserializeData: type=${payloadType}, bufferLength=${buffer.length}`);
    
    // Debug: Show first 20 bytes in hex for binary data
    if (payloadType === 'jsontable' || payloadType === 'image' || payloadType === 'binary') {
        const hexPreview = [];
        for (let i = 0; i < Math.min(20, buffer.length); i++) {
            hexPreview.push(buffer[i].toString(16).padStart(2, '0'));
        }
        logTrace(correlationId, `deserializeData: First 20 bytes (hex): ${hexPreview.join(' ')}`);
    }
    
    if (payloadType === 'text') {
        const result = new TextDecoder().decode(buffer);
        logTrace(correlationId, `deserializeData: text result length=${result.length}`);
        return result;
    } else if (payloadType === 'dictionary') {
        const jsonStr = new TextDecoder().decode(buffer);
        const result = JSON.parse(jsonStr);
        logTrace(correlationId, `deserializeData: dictionary keys=${Object.keys(result).join(', ')}`);
        return result;
    } else if (payloadType === 'jsontable') {
        const jsonStr = new TextDecoder().decode(buffer);
        const result = JSON.parse(jsonStr);
        logTrace(correlationId, `deserializeData: jsontable result length=${Array.isArray(result) ? result.length : 'N/A'}`);
        return result;
    } else if (payloadType === 'image') {
        logTrace(correlationId, `deserializeData: image buffer length=${buffer.length}`);
        return buffer;
    } else if (payloadType === 'audio') {
        logTrace(correlationId, `deserializeData: audio buffer length=${buffer.length}`);
        return buffer;
    } else if (payloadType === 'video') {
        logTrace(correlationId, `deserializeData: video buffer length=${buffer.length}`);
        return buffer;
    } else if (payloadType === 'binary') {
        logTrace(correlationId, `deserializeData: binary buffer length=${buffer.length}`);
        return buffer;
    } else {
        throw new Error(`Unknown payload_type: ${payloadType}`);
    }
}

// ---------------------------------------------- File Server Handlers ---------------------------------------------- //

/**
 * Upload data to plik server in one-shot mode
 * @param {string} fileServerUrl - Base URL of the plik server
 * @param {string} dataname - Name of the file being uploaded
 * @param {Uint8Array} data - Raw byte data of the file content
 * @returns {Promise<{status: number, uploadid: string, fileid: string, url: string}>}
 */
async function plikOneshotUpload(fileServerUrl, dataname, data) {
    const buffer = data instanceof Uint8Array ? data : new Uint8Array(data);
    
    // Get upload id
    const urlGetUploadID = `${fileServerUrl}/upload`;
    const headers = { 'Content-Type': 'application/json' };
    const body = JSON.stringify({ OneShot: true });
    
    const httpResponse = await fetch(urlGetUploadID, {
        method: 'POST',
        headers,
        body
    });
    
    const responseJson = await httpResponse.json();
    const uploadid = responseJson.id;
    const uploadtoken = responseJson.uploadToken;

    // Upload file
    const urlUpload = `${fileServerUrl}/file/${uploadid}`;
    const form = new FormData();
    const blob = new Blob([buffer], { type: 'application/octet-stream' });
    form.append('file', blob, dataname);
    
    const uploadHeaders = {
        'X-UploadToken': uploadtoken
    };

    const uploadResponse = await fetch(urlUpload, {
        method: 'POST',
        headers: uploadHeaders,
        body: form
    });
    
    const uploadJson = await uploadResponse.json();
    const fileid = uploadJson.id;

    const url = `${fileServerUrl}/file/${uploadid}/${fileid}/${dataname}`;

    return {
        status: uploadResponse.status,
        uploadid,
        fileid,
        url
    };
}

/**
 * Fetch data from URL with exponential backoff
 * @param {string} url - URL to fetch from
 * @param {number} maxRetries - Maximum number of retry attempts
 * @param {number} baseDelay - Initial delay in milliseconds
 * @param {number} maxDelay - Maximum delay in milliseconds
 * @param {string} correlationId - Correlation ID for logging
 * @returns {Promise<Uint8Array>} Fetched data as bytes
 */
async function fetchWithBackoff(url, maxRetries, baseDelay, maxDelay, correlationId) {
    let delay = baseDelay;
    
    for (let attempt = 1; attempt <= maxRetries; attempt++) {
        try {
            const response = await fetch(url);
            
            if (response.status === 200) {
                logTrace(correlationId, `Successfully fetched data from ${url} on attempt ${attempt}`);
                const arrayBuffer = await response.arrayBuffer();
                return new Uint8Array(arrayBuffer);
            } else {
                throw new Error(`Failed to fetch: ${response.status}`);
            }
        } catch (e) {
            logTrace(correlationId, `Attempt ${attempt} failed: ${e.constructor.name} - ${e.message}`);
            
            if (attempt < maxRetries) {
                await new Promise(resolve => setTimeout(resolve, delay));
                delay = Math.min(delay * 2, maxDelay);
            }
        }
    }
    
    throw new Error(`Failed to fetch data after ${maxRetries} attempts`);
}

// ---------------------------------------------- Core Functions ---------------------------------------------- //

/**
 * Build message envelope from payloads and metadata
 * @param {string} subject - Subject/topic
 * @param {Array} payloads - Array of payload objects
 * @param {Object} options - Envelope metadata options
 * @returns {Object} Envelope object
 */
function buildEnvelope(subject, payloads, options) {
    return {
        correlation_id: options.correlation_id,
        msg_id: options.msg_id,
        timestamp: new Date().toISOString(),
        send_to: subject,
        msg_purpose: options.msg_purpose,
        sender_name: options.sender_name,
        sender_id: options.sender_id,
        receiver_name: options.receiver_name,
        receiver_id: options.receiver_id,
        reply_to: options.reply_to,
        reply_to_msg_id: options.reply_to_msg_id,
        broker_url: options.broker_url,
        metadata: options.metadata || {},
        payloads: payloads
    };
}

/**
 * Build payload object from serialized data
 * @param {string} dataname - Name of the payload
 * @param {string} payloadType - Type of the payload
 * @param {Uint8Array} payloadBytes - Serialized payload bytes
 * @param {string} transport - Transport type ("direct" or "link")
 * @param {string} data - Data (base64 for direct, URL for link)
 * @returns {Object} Payload object
 */
function buildPayload(dataname, payloadType, payloadBytes, transport, data) {
    // Determine encoding based on payload type (matching Julia implementation)
    let encoding = 'base64';
    if (payloadType === 'jsontable') {
        encoding = 'json';
    }
    
    return {
        id: uuidv4(),
        dataname,
        payload_type: payloadType,
        transport,
        encoding,
        size: payloadBytes.byteLength,
        data,
        metadata: transport === 'direct' ? { payload_bytes: payloadBytes.byteLength } : {}
    };
}

/**
 * Send data with automatic transport selection
 * 
 * This function intelligently routes data delivery based on payload size.
 * If the serialized payload is smaller than size_threshold, it encodes the data as Base64
 * into a "direct" payload. Otherwise, it uploads the data to a fileserver
 * and creates a "link" payload with the URL.
 * 
 * Transport publishing is the caller's responsibility. This function returns the
 * envelope and its JSON string representation.
 * 
 * @param {string} subject - Subject/topic to send the message to
 * @param {Array} data - List of [dataname, data, type] tuples to send
 *          - type: "text", "dictionary", "jsontable", "image", "audio", "video", "binary"
 *          - Note: "arrowtable" is NOT supported in browser (use "jsontable" for tabular data)
 * @param {Object} options - Optional configuration
 * @param {string} [options.broker_url=DEFAULT_BROKER_URL] - Broker URL (for envelope metadata)
 * @param {string} [options.fileserver_url=DEFAULT_FILESERVER_URL] - URL of the HTTP file server
 * @param {Function} [options.fileserver_upload_handler=plikOneshotUpload] - Function to handle fileserver uploads
 * @param {number} [options.size_threshold=DEFAULT_SIZE_THRESHOLD] - Threshold separating direct vs link transport
 * @param {string} [options.correlation_id=uuidv4()] - Correlation ID for tracing
 * @param {string} [options.msg_purpose="chat"] - Purpose of the message
 * @param {string} [options.sender_name="msghandler"] - Name of the sender
 * @param {string} [options.receiver_name=""] - Name of the receiver (empty means broadcast)
 * @param {string} [options.receiver_id=""] - UUID of the receiver (empty means broadcast)
 * @param {string} [options.reply_to=""] - Topic to reply to
 * @param {string} [options.reply_to_msg_id=""] - Message ID this message is replying to
 * @param {string} [options.msg_id=uuidv4()] - Message ID
 * @param {string} [options.sender_id=uuidv4()] - Sender ID
 * @returns {Promise<[Object, string]>} Tuple of [env, env_json_str]
 * 
 * @example
 * // Send a single payload
 * const [env, envJsonStr] = await msghandlerCSR.smartpack(
 *     "/test",
 *     [["dataname1", data1, "dictionary"]]
 * );
 * 
 * // Send multiple payloads (use jsontable instead of arrowtable for browser)
 * const [env, envJsonStr] = await msghandlerCSR.smartpack(
 *     "/test",
 *     [
 *         ["dataname1", data1, "dictionary"],
 *         ["dataname2", tableData, "jsontable"]
 *     ]
 * );
 * 
 * // Publish via your transport (NATS, MQTT, HTTP, etc.)
 * // await myNatsClient.publish("/test", envJsonStr);
 */
async function smartpack(subject, data, options = {}) {
    const {
        broker_url = DEFAULT_BROKER_URL,
        fileserver_url = DEFAULT_FILESERVER_URL,
        fileserver_upload_handler = plikOneshotUpload,
        size_threshold = DEFAULT_SIZE_THRESHOLD,
        correlation_id = uuidv4(),
        msg_purpose = 'chat',
        sender_name = 'msghandler',
        receiver_name = '',
        receiver_id = '',
        reply_to = '',
        reply_to_msg_id = '',
        msg_id = uuidv4(),
        sender_id = uuidv4()
    } = options;

    logTrace(correlation_id, `Starting smartpack for subject: ${subject}`);
    logTrace(correlation_id, `smartpack: data array length=${data.length}`);
    
    // Debug: Log input data structure
    for (let i = 0; i < data.length; i++) {
        const [dataname, payloadData, payloadType] = data[i];
        logTrace(correlation_id, `smartpack: payload[${i}] dataname=${dataname}, type=${payloadType}, data type=${typeof payloadData}, constructor=${payloadData?.constructor?.name}`);
    }

    // Process payloads
    const payloads = [];
    for (const [dataname, payloadData, payloadType] of data) {
        logTrace(correlation_id, `smartpack: Processing payload '${dataname}' type=${payloadType}`);
        logTrace(correlation_id, `smartpack: payloadData type=${typeof payloadData}, constructor=${payloadData?.constructor?.name}`);
        
        const payloadBytes = await serializeData(payloadData, payloadType);
        const payloadSize = payloadBytes.byteLength;

        logTrace(correlation_id, `Serialized payload '${dataname}' (type: ${payloadType}) size: ${payloadSize} bytes`);

        // Debug: Show first 20 bytes of serialized data for table type
        if (payloadType === 'table') {
            const hexPreview = [];
            for (let i = 0; i < Math.min(20, payloadBytes.length); i++) {
                hexPreview.push(payloadBytes[i].toString(16).padStart(2, '0'));
            }
            logTrace(correlation_id, `Serialized table data first 20 bytes (hex): ${hexPreview.join(' ')}`);
        }

        if (payloadSize < size_threshold) {
            // Direct path
            const payloadB64 = bufferToBase64(payloadBytes);
            logTrace(correlation_id, `Using direct transport for ${payloadSize} bytes, base64 length=${payloadB64.length}`);

            const payload = buildPayload(dataname, payloadType, payloadBytes, 'direct', payloadB64);
            payloads.push(payload);
        } else {
            // Link path
            logTrace(correlation_id, `Using link transport, uploading to fileserver`);

            const response = await fileserver_upload_handler(fileserver_url, dataname, payloadBytes);

            if (response.status !== 200) {
                throw new Error(`Failed to upload data to fileserver: ${response.status}`);
            }

            logTrace(correlation_id, `Uploaded to URL: ${response.url}`);

            const payload = buildPayload(dataname, payloadType, payloadBytes, 'link', response.url);
            payloads.push(payload);
        }
    }

    // Build envelope
    const env = buildEnvelope(subject, payloads, {
        correlation_id,
        msg_id,
        msg_purpose,
        sender_name,
        sender_id,
        receiver_name,
        receiver_id,
        reply_to,
        reply_to_msg_id,
        broker_url
    });

    const env_json_str = JSON.stringify(env);

    return [env, env_json_str];
}

/**
 * Receive and process messages
 * 
 * This function processes incoming messages, handling both direct transport
 * (base64 decoded payloads) and link transport (URL-based payloads).
 * It deserializes the data based on the transport type and returns the result.
 * 
 * @param {string|Object} msg - Message payload. Accepts either a JSON string directly,
 *          or an object with a `data` or `payload` property containing the JSON string.
 * @param {Object} options - Optional configuration
 * @param {Function} [options.fileserver_download_handler=fetchWithBackoff] - Function to handle fileserver downloads
 * @param {number} [options.max_retries=5] - Maximum retry attempts for fetching URL
 * @param {number} [options.base_delay=100] - Initial delay for exponential backoff in ms
 * @param {number} [options.max_delay=5000] - Maximum delay for exponential backoff in ms
 * @returns {Promise<Object>} Envelope object with processed payloads
 * 
 * @example
 * // Receive from JSON string directly
 * const env = await msghandlerCSR.smartunpack(jsonString, {
 *     fileserver_download_handler: msghandlerCSR.fetchWithBackoff,
 *     max_retries: 5,
 *     base_delay: 100,
 *     max_delay: 5000
 * });
 * 
 * // Receive from transport message object (e.g., NATS, MQTT)
 * const env = await msghandlerCSR.smartunpack(natsMsg, {
 *     fileserver_download_handler: msghandlerCSR.fetchWithBackoff
 * });
 * // env.payloads is an Array of [dataname, data, type] arrays
 * for (const [dataname, data, type] of env.payloads) {
 *     console.log(`${dataname}: ${data} (type: ${type})`);
 * }
 */
async function smartunpack(msg, options = {}) {
    const {
        fileserver_download_handler = fetchWithBackoff,
        max_retries = 5,
        base_delay = 100,
        max_delay = 5000
    } = options;

    let envJsonObj;

    // NATS's Javascript lib already return JSON object
    if (msg !== null && typeof msg === 'object') {
        envJsonObj = msg;
    } else {
        throw new Error('Invalid message format: expected JSON string or message object');
    }
 
    logTrace(envJsonObj.correlation_id, 'Processing received message');
    logTrace(envJsonObj.correlation_id, `smartunpack: envelope has ${envJsonObj.payloads.length} payloads`);

    // Process all payloads in the envelope
    const payloadsList = [];
    const numPayloads = envJsonObj.payloads.length;

    logTrace(envJsonObj.correlation_id, `smartunpack: Processing ${numPayloads} payloads`);

    for (let i = 0; i < numPayloads; i++) {
        const payloadObj = envJsonObj.payloads[i];
        const transport = payloadObj.transport;
        const dataname = payloadObj.dataname;
        const payloadType = payloadObj.payload_type;

        logTrace(envJsonObj.correlation_id, `smartunpack: Processing payload ${i + 1}/${numPayloads}: dataname=${dataname}, type=${payloadType}, transport=${transport}`);

        if (transport === 'direct') {
            logTrace(envJsonObj.correlation_id, `Direct transport - decoding payload '${dataname}'`);

            // Extract base64 payload from the payload
            const payloadB64 = payloadObj.data;
            logTrace(envJsonObj.correlation_id, `Direct transport: base64 length=${payloadB64?.length}`);

            // Decode Base64 payload
            const payloadBytes = base64ToBuffer(payloadB64);
            logTrace(envJsonObj.correlation_id, `Direct transport: decoded bytes=${payloadBytes.length}`);

            // Deserialize based on type
            const dataType = payloadObj.payload_type;
            const data = await deserializeData(payloadBytes, dataType, envJsonObj.correlation_id);
            logTrace(envJsonObj.correlation_id, `Direct transport: deserialized data type=${typeof data}, constructor=${data?.constructor?.name}`);

            payloadsList.push([dataname, data, dataType]);
        } else if (transport === 'link') {
            // Extract download URL from the payload
            const url = payloadObj.data;
            logTrace(envJsonObj.correlation_id, `Link transport - fetching '${dataname}' from URL: ${url}`);

            // Fetch with exponential backoff using the download handler
            const downloadedData = await fileserver_download_handler(
                url,
                max_retries,
                base_delay,
                max_delay,
                envJsonObj.correlation_id
            );

            // Deserialize based on type
            const dataType = payloadObj.payload_type;
            const data = await deserializeData(downloadedData, dataType, envJsonObj.correlation_id);

            payloadsList.push([dataname, data, dataType]);
        } else {
            throw new Error(`Unknown transport type for payload '${dataname}': ${transport}`);
        }
    }

    logTrace(envJsonObj.correlation_id, `smartunpack: Successfully processed all ${payloadsList.length} payloads`);
    envJsonObj.payloads = payloadsList;
    return envJsonObj;
}

// ---------------------------------------------- Module Exports ---------------------------------------------- //

const msghandlerCSR = {
    /**
     * Send data with automatic transport selection
     */
    smartpack,

    /**
     * Receive and process messages
     */
    smartunpack,

    /**
     * Upload data to plik server in one-shot mode
     */
    plikOneshotUpload,

    /**
     * Fetch data from URL with exponential backoff
     */
    fetchWithBackoff,

    /**
     * Default constants
     */
    DEFAULT_SIZE_THRESHOLD,
    DEFAULT_BROKER_URL,
    DEFAULT_FILESERVER_URL
};

export default msghandlerCSR;