Swift-MessageUtils/Sources/MessageUtils/MessageUtils.swift

// The Swift Programming Language
// https://docs.swift.org/swift-book

import Foundation
import Crypto

public func serializeV1(msg: MessageP) -> Data {

    let MESSAGE_CAPACITY: Int = countBytes(msg: msg)

    var serializedData: Data = Data(count: MESSAGE_CAPACITY)

    // Serialize Header

    // UGLY: extrapolate in functions
    serializedData[0] = msg.version
    serializedData[1] = msg.messageType.rawValue
    serializedData[2] = msg.devType.rawValue
    serializedData[3] = msg.RESERVED
    serializedData[4...7] = msg.signType.rawValue.data
    // First 8 bytes

    serializedData[8...15] = msg.timestamp.data
    // 8 Bytes

    serializedData[16...31] = msg.devID.data
    // 16 bytes

    serializedData[32...39] = msg.location.x.data
    // 8 Bytes

    serializedData[40...47] = msg.location.y.data
    // 8 Bytes

    serializedData[48...55] = msg.location.z.data
    // 8 Bytes

    var index = 56

    for field in msg.fields {

        serializedData[index..<(index + 4)] = UInt32(field.key.count).data
        serializedData[(index + 4)..<(index + 8)] = UInt32(field.value.count).data

        index += 8

        serializedData[index..<(index + field.key.count)] = Data(field.key)

        index += field.key.count

        serializedData[index..<(index + field.value.count)] = Data(field.value)

        index += field.value.count
    }

    let paddingBytes = (8 - (index % 8)) % 8

    serializedData[index..<(index + paddingBytes)] = Data(count: paddingBytes)
    index += paddingBytes

    // Add STOP FIELDS
    serializedData[index..<(index + 8)] = UInt64(0).data

    return serializedData
}

public func signMessage(msgData: Data, signType: SignType, key: P521.Signing.PrivateKey) throws -> [UInt8] {
    let signatureBytes = try signatureBytes(signature: signType)

    // UGLY We are hypothesisying that signType is P521
    let signature = try signP521(object: msgData, key: key).map { value in
        return value
    }

    return signature

}


public func verifyMessageSignature(message: SignedMessage, key: P521.Signing.PublicKey) throws -> Bool {
    // UGLY Assuming P521 Signature

    let msgData = serializeV1(msg:  message)
    return try verifySignatureP521(signature: Data(message.signature), object: msgData, key: key)
    
}

public func deserializeV1(serializedData: Data) throws -> SignedMessage {

    // Serialize Header

    // UGLY: extrapolate in functions
    let version: UInt8 = serializedData[0]
    let messageType: MessageType = MessageType(rawValue: serializedData[1])!
    let devType: DeviceType = DeviceType(rawValue: serializedData[2])!
    let RESERVED: UInt8 = serializedData[3]
    let signType: SignType = SignType(rawValue: serializedData[4...7].uint32)!
    // First 8 bytes

    let signBytes = try signatureBytes(signature: signType)

    let timestamp = serializedData[8...15].timestamp
    // 8 Bytes

    let devID = serializedData[16...31].uint128
    // 16 bytes

    let locationX = serializedData[32...39].uint64
    // 8 Bytes

    let locationY = serializedData[40...47].uint64
    // 8 Bytes

    let locationZ = serializedData[48...55].uint64
    // 8 Bytes

    var index = 56

    // Deserializing Fields
    var MORE_FIELDS = true
    var fields: [Field] = []

    while MORE_FIELDS {

        let nextChunk = serializedData[index..<(index + 8)]

        let a = nextChunk.map { value in
            return value
        }

        if nextChunk.uint64 == 0 {
            MORE_FIELDS = false
            continue
        }

        let fieldKeyCount = serializedData[index..<(index + 4)].uint32
        let fieldValueCount = serializedData[(index + 4)..<(index + 8)].uint32

        index += 8

        let key = serializedData[index..<(index + Int(fieldKeyCount))].map { value in
            return value
        }
        index += Int(fieldKeyCount)
        let value = serializedData[index..<(index + Int(fieldValueCount))].map { value in
            return value
        }
        index += Int(fieldValueCount)

        fields.append(Field(key: key, value: value))

    }

    let paddingBytes = (8 - (index % 8)) % 8

    // Skip padding bytes
    index += paddingBytes + 8

    let signature = serializedData[index..<serializedData.count].map { value in
        return value
    }

    // Sanity check signature with signatureType
    if signature.count != signBytes {
        throw DeserializationError.UNMATCHING_SIGNATURE_TYPE
    }

    return SignedMessage(
        version: version,
        messageType: messageType,
        devType: devType,
        RESERVED: RESERVED,
        signType: signType,
        timestamp: timestamp,
        devID: devID,
        location: Location(x: locationX, y: locationY, z: locationZ),
        fields: fields,
        signature: signature
    )
}

public func countBytes(msg: MessageP) -> Int {

    ///
    /// Author: Christian Risi
    ///
    /// This is computed as all the bits for the fixed fields
    ///
    let INITIAL_CAPACITY_BYTES: Int = 56
    let FIELD_HEADER_CAPACITY_BYTES: Int = 8

    var fieldReveservedCapacity: Int = 0

    for field in msg.fields {
        fieldReveservedCapacity += FIELD_HEADER_CAPACITY_BYTES + field.key.count + field.value.count
    }

    fieldReveservedCapacity += (8 - (fieldReveservedCapacity % 8)) % 8 + 8

    return INITIAL_CAPACITY_BYTES + fieldReveservedCapacity

}

public func signatureBytes(signature: SignType) throws -> Int {
    switch signature {

    case .P521:
        return 132

    default:
        throw CommonError.SIGNATURE_NOT_SUPPORTED
    }
}