package tusd

import (
	"io"
)

type MetaData map[string]string

type FileInfo struct {
	ID string
	// Total file size in bytes specified in the NewUpload call
	Size int64
	// Offset in bytes (zero-based)
	Offset   int64
	MetaData MetaData
	// Indicates that this is a partial upload which will later be used to form
	// a final upload by concatenation. Partial uploads should not be processed
	// when they are finished since they are only incomplete chunks of files.
	IsPartial bool
	// Indicates that this is a final upload
	IsFinal bool
	// If the upload is a final one (see IsFinal) this will be a non-empty
	// ordered slice containing the ids of the uploads of which the final upload
	// will consist after concatenation.
	PartialUploads []string
    // Indicates that a write operation is currently pending for this file.
    // This field is not needed to implement the tus specification.
    // Implementations of tusd.DataStore may use this to prevent write
    // collisions or race conditions.
    Locked bool
}

type DataStore interface {
	// Create a new upload using the size as the file's length. The method must
	// return an unique id which is used to identify the upload. If no backend
	// (e.g. Riak) specifes the id you may want to use the uid package to
	// generate one. The properties Size and MetaData will be filled.
	NewUpload(info FileInfo) (id string, err error)
	// Write the chunk read from src into the file specified by the id at the
	// given offset. The handler will take care of validating the offset and
	// limiting the size of the src to not overflow the file's size. It may
	// return an os.ErrNotExist which will be interpretet as a 404 Not Found.
	// It will also lock resources while they are written to ensure only one
	// write happens per time.
	// The function call must return the number of bytes written.
	WriteChunk(id string, offset int64, src io.Reader) (int64, error)
	// Read the fileinformation used to validate the offset and respond to HEAD
	// requests. It may return an os.ErrNotExist which will be interpretet as a
	// 404 Not Found.
	GetInfo(id string) (FileInfo, error)
	// Get an io.Reader to allow downloading the file. This feature is not
	// part of the official tus specification. If this additional function
	// should not be enabled any call to GetReader should return
	// tusd.ErrNotImplemented. The length of the resource is determined by
	// retrieving the offset using GetInfo.
	// If the returned reader also implements the io.Closer interface, the
	// Close() method will be invoked once everything has been read.
	GetReader(id string) (io.Reader, error)
	// Terminate an upload so any further requests to the resource, both reading
	// and writing, must return os.ErrNotExist or similar.
	Terminate(id string) error
	// Lock the upload file for writing. This feature is not part of the
	// official TUS specification. Handlers should call this prior to writing
	// chunks or terminating files. Returns true if the file lock has been
	// acquired.
	LockFile(id string) (bool, error)
	// Unlock the upload file for writing. This feature is not part of the
	// official TUS specification. Handlers should defer calls to this after
	// acquiring a lock.
	UnlockFile(id string) error
}