namespace CryptoFile
open System.IO

type internal Metadata (d: (string * string) list) =
    new (stream : Stream, size: int) =
        let binaryReader = new BinaryReader (stream)
        new Metadata ([])

    member this.WriteTo (stream : Stream) =
        let memoryStream = new MemoryStream () // To know the serialized meta-data size before writtent them to 'stream'.
        let memoryWriter = new BinaryWriter (memoryStream)
        List.iter (fun (key : string, value : string) -> memoryWriter.Write key; memoryWriter.Write value) d
        (new BinaryWriter (stream)).Write (int memoryStream.Length)
        memoryStream.CopyTo (stream)

module API =
    module internal MetaData =
        let filename = "filename"
        let creationTimeKey = "file-creation-time"

    let generatKeysPair : Key * Key = Crypto.generateRSAKeysPair

    // Encrypt a given file
    let encryptFile (inputFilePath : string) (outputFilePath : string) (signaturePrivKey: Key) (cryptPubKey : Key)  =
        let keyAES, keyMAC, iv = Crypto.rand 32, Crypto.rand 32, Crypto.rand 16
        let fileInfo = new FileInfo (inputFilePath)
        use inputStream = new FileStream (inputFilePath, FileMode.Open, FileAccess.Read)
        use outputStream = new FileStream (outputFilePath, FileMode.Create, FileAccess.Write)
        let writer = new BinaryWriter (outputStream)

        writer.Seek (32 + 256, SeekOrigin.Current) |> ignore // Skips mac and signature. They will be written later.

        Crypto.encryptRSA cryptPubKey (Array.append keyAES <| Array.append keyMAC iv) |> writer.Write

        let (hmacStream, hmac) = Crypto.HMACStream keyMAC outputStream
        use cryptoStream = Crypto.encryptAES keyAES iv hmacStream
        let cryptoWriter = new BinaryWriter (cryptoStream)

        // Write the file metadata.
        let metaData = new Metadata ([MetaData.filename, fileInfo.Name
                                      MetaData.creationTimeKey, fileInfo.CreationTimeUtc.Ticks.ToString ()])
        metaData.WriteTo cryptoStream

        // Write the content of the file.
        inputStream.CopyTo cryptoStream
        cryptoStream.FlushFinalBlock ()

        // Write the HMAC at the begining of the file.
        outputStream.Position <- 0L
        writer.Write hmac.Hash

        // Write the signature.
        Crypto.signRSA signaturePrivKey hmac.Hash |> writer.Write
        ()

    let decryptFile (sourceFilePath : string) (targetDirPath : string) (signaturePubKey: Key) (decryptPrivKey : Key) =
        ()