[readme] Add impression of aws-s3-sync-by-hash process

README.org

@@ -8,6 +8,47 @@ The normal ~aws s3 sync ...~ command only uses the time stamp of files
 to decide what files need to be copied. This utility looks at the md5
 hash of the file contents.
 
+* How does aws-s3-sync-by-hash do it?
 
+The following is a rough, first draft, pseudo-scala, impression of the process.
 
+** constructor
 
+val options = Load command line arguments and AWS security keys.
+
+** def sync(): Promise[Upload]
+
+val uploadPromise = createUploadPromise()
+if options contains delete then createDeletePromise()
+else return uploadPromise
+
+** def createUploadPromise(): Promise[Upload]
+
+readdir(options(root))
+loadS3MetaData
+filterByHash
+uploadFile
+callback(file => uploadedFiles += file)
+
+** def loadS3MetaData: Stream[S3MetaData]
+
+HEAD(bucket, key)
+map (metadata => S3MetaData(localFile, bucket, key, metadata.hash, metadata.lastModified))
+
+** def filterByHash(p: S3MetaData => Boolean): Stream[S3MetaData]
+
+md5File(localFile)
+filter(localHash => options.force || localHash != metadataHash)
+
+** def uploadFile(upload: Upload): IO[Unit]
+
+S3Upload(bucket, key, localFile)
+
+** def createDeletePromise(): Promise[Delete]
+
+S3AllKeys(bucket, key)
+filter(remoteKey => localFileExists(remoteFile).negate)
+
+** def deleteFile(delete: Delete): IO[Unit]
+
+S3Delete(bucket, key, remoteKey)