package source

import (
	"crypto/md5"
	"fmt"
	"time"
)

type (
	// ChangeSet represents a set of changes from a source
	ChangeSet struct {
		Data      []byte    // binary data
		Checksum  string    // md5 sum
		Format    string    // type of the data
		Source    string    // name of the data source
		Timestamp time.Time // time stamp
	}

	// Watcher is the data source change monitor
	Watcher interface {
		Next() (*ChangeSet, error) // Method returns the changed data set when the data source changes
		Stop() error               // Method stops the data source change monitor
	}

	// Source is configure the data source from which the data loader retrieves the raw binary data.
	Source interface {
		Read() (*ChangeSet, error) // read from source, to change set
		Watch() (Watcher, error)   // watch the source change
		String() string            // return the name of the data source
	}
)

// Sum returns the md5 checksum of the ChangeSet data
func (c *ChangeSet) Sum() string {
	h := md5.New()
	h.Write(c.Data)
	return fmt.Sprintf("%x", h.Sum(nil))
}