Gzip compression

open System
open System.IO
open System.IO.Compression
open System.Text

type CompressionValue = {
    Value: string
    Size: int 
}

type CompressionResult = {
    Original: CompressionValue
    Result: CompressionValue
    Level: CompressionLevel
    Kind: string 
}
with 
    member this.Difference = 
        this.Original.Size - this.Result.Size
    member this.Percent = 
        Math.Abs(decimal this.Difference / decimal this.Original.Size)

let ToGzipAsync (level:CompressionLevel) (value:string) =
    task {
        let bytes = Encoding.Unicode.GetBytes(value)
        use input = new MemoryStream(bytes)
        use output = new MemoryStream()
        use stream = new GZipStream(output, level)
        do! input.CopyToAsync(stream)
        let result = output.ToArray()
        return {
            Original = { Value = value; Size = bytes.Length }
            Result = { Value = Convert.ToBase64String(result); Size = result.Length }
            Level = CompressionLevel.Fastest
            Kind = "GZip"
        }
    }

let FromGzipAsync (value:string) =
    task {
        let bytes = Convert.FromBase64String(value)
        use input = new MemoryStream(bytes)
        use output = new MemoryStream()
        use stream = new GZipStream(input, CompressionMode.Decompress)
        do! stream.CopyToAsync(output)
        do! stream.FlushAsync()
        return Encoding.Unicode.GetString(output.ToArray())
    }

let compress fileName level =
    task {
        let! text =
            Path.Combine(__SOURCE_DIRECTORY__, "resources", fileName)  
            |> File.ReadAllTextAsync
        return! ToGzipAsync level text
    }

let run () =
    let output =
        compress "comedy-of-errors.txt" CompressionLevel.Fastest
        |> Async.AwaitTask
        |> Async.RunSynchronously
    printfn "Original size: %A" (output.Original.Size.ToString("N0"))
    printfn "Compressed size: %A" (output.Result.Size.ToString("N0"))
    printfn "Difference: %A" (output.Difference.ToString("N0"))
    printfn "%% Reduction: %s" (output.Percent.ToString("P"))

run ()