require "uuid"
require "openssl"
require "json"
require "base64"

module FileStorage

	extend self

	# 1 MB read buffer, on-disk
	def file_reading_buffer_size
		1_000_000
	end

	# 1 KB message data buffer, on-network
	def message_buffer_size
		1_000
	end

	class Exception < ::Exception
	end

	enum MessageType
		Error
		Authentication
		UploadRequest
		DownloadRequest
		Response
		Responses
		Transfer
	end

	class Chunk
		JSON.mapping({
			# chunk's number
			n: Int32,
			# number of chunks
			on: Int32,
			# digest of the current chunk
			digest: String
		})

		def initialize(@n, @on, data)
			@digest = FileStorage.data_digest data.to_slice
		end
	end

	# For now, upload and download are sequentials.
	# In a future version, we will be able to send
	# arbitrary parts of each file.

	class Token
		JSON.mapping({
			uid: Int32,
			login: String
		})

		def initialize(@uid, @login)
		end
	end

	# Who knows, maybe someday we will be on UDP, too.
	#class SHA256
	#	JSON.mapping({
	#		chunk: Slice(UInt8)
	#	})
	#end


	# A file has a name, a size and tags.
	class FileInfo
		JSON.mapping({
			name: String,
			size: UInt64,
			nb_chunks: Int32,
			# SHA256 file digest
			digest: String,

			# list of SHA256, if we are on UDP
			# chunks: Array(SHA256),
			tags: Array(String)?
		})

		def initialize(file : File, @tags = nil)
			@name = File.basename file.path
			@size = file.size
			@digest = FileStorage.file_digest file
			@nb_chunks = (@size / FileStorage.message_buffer_size).ceil.to_i
		end
	end

	class Message
	end

	alias Request = UploadRequest | DownloadRequest

	class UploadRequest < Message
		JSON.mapping({
			# autogenerated
			mid: String,
			file: FileInfo
		})

		def initialize(@file)
			@mid = UUID.random.to_s
		end
	end


	# WIP
	class DownloadRequest < Message
		JSON.mapping({
			# autogenerated
			mid: String,
			# SHA256 digest of the file, used as ID
			uuid: String?,
			name: String?,
			tags: Array(String)?
		})

		def initialize(@uuid = nil, @name = nil, @tags = nil)
			@mid = UUID.random.to_s
		end
	end

	class Authentication < Message
		JSON.mapping({
			# autogenerated
			mid: String,
			token: Token,
			uploads: Array(UploadRequest),
			downloads: Array(DownloadRequest)
		})

		def initialize(@token, @uploads = Array(UploadRequest).new, @downloads = Array(DownloadRequest).new)
			@mid = UUID.random.to_s
		end
	end

	class Response < Message
		JSON.mapping({
			mid: String,
			response: String,
			reason: String?
		})

		def initialize(@mid, @response, @reason = nil)
		end
	end

	class Error < Message
		JSON.mapping({
			mid: String,
			# a response for each request
			response: String,
			reason: String?
		})

		def initialize(@mid, @response, @reason = nil)
		end
	end

	class Responses < Message
		JSON.mapping({
			mid: String,
			# a response for each request
			responses: Array(Response),
			response: String,
			reason: String?
		})

		def initialize(@mid, @response, @responses, @reason = nil)
		end
	end

	class Transfer < Message
		JSON.mapping({
			# autogenerated
			mid: String,
			# SHA256 digest of the entire file
			filedigest: String,
			# For now, just the counter in a string
			chunk: Chunk,
			# base64 slice
			data: String,
		})

		def initialize(file_info : FileInfo, count, bindata)
			# count: chunk number

			@filedigest = file_info.digest
			@data = Base64.encode bindata
			@chunk = FileStorage::Chunk.new count, file_info.nb_chunks, @data
			@mid = UUID.random.to_s
		end
	end

	# private function
	def data_digest(data : Bytes)

		iodata = IO::Memory.new data, false
		buffer = Bytes.new FileStorage.file_reading_buffer_size

		io = OpenSSL::DigestIO.new(iodata, "SHA256")
		while io.read(buffer) > 0; end

		io.digest.hexstring
	end

	# private function
	def file_digest(file : File)
		# 1M read buffer
		buffer = Bytes.new(1_000_000)

		io = OpenSSL::DigestIO.new(file, "SHA256")
		while io.read(buffer) > 0 ; end

		io.digest.hexstring
	end
end