package server

import (
	"errors"
	"fmt"
	"git.xdrm.io/logauth/schastsp/context"
	"git.xdrm.io/logauth/schastsp/internal/scha"
	"io"
	"os"
	"path/filepath"
)

const DEBUG = false

/* (1) Structure
---------------------------------------------------------*/
type T struct {
	ctx  *context.T // shared context
	hash []byte     // current key
	conf string     // configuration file path
}

/* (2) Constructor
*
* @ctx<context.T>					Shared context
* @savePath<string>					Configuration file path
*
---------------------------------------------------------*/
func New(ctx *context.T, savePath string) (*T, error) {

	inst := new(T)

	/* (1) Store context */
	if ctx == nil {
		return nil, errors.New("Context must not be nil")
	}
	inst.ctx = ctx

	/* (2) Get absolute file path */
	absolutePath, err := filepath.Abs(savePath)
	if err != nil {
		return nil, err
	}

	/* (3) Check file */
	info, err := os.Stat(absolutePath)
	if err != nil {

		// Unknown error
		if !os.IsNotExist(err) {
			return nil, err
		}

		// File does not exist -> try to create file
		_, err2 := os.Create(absolutePath)
		if err2 != nil {
			return nil, err2
		}

		// fail if exists but not regular file
	} else if !info.Mode().IsRegular() {
		return nil, errors.New("Configuration file is not a regular file")
	}

	/* (4) Store file path */
	inst.conf = absolutePath

	/* (5) Try to fetch hash from conf */
	inst.hash = make([]byte, scha.HSIZE)
	err = inst.fetch()
	// if err != nil { return nil, err }

	return inst, nil

}

/* (3) Handle request and send response
*
* @req<io.Reader>					Request reader
* @res<io.Writer>					Response Writer
*
* @return err<error>				Error or NIL if not
*
---------------------------------------------------------*/
func (s *T) HandleRequest(req io.Reader, res io.Writer) error {

	/* (1) Manage request
	---------------------------------------------------------*/
	/* (1) Read x1 */
	x1 := make([]byte, scha.HSIZE)
	read, err := req.Read(x1)
	if err != nil {
		return fmt.Errorf("Reading x1 : %s", err)
	}
	if uint16(read) != scha.HSIZE {
		return fmt.Errorf("Cannot read x1 : %d / %d bytes available", read, scha.HSIZE)
	}

	/* (2) Read x2 */
	x2 := make([]byte, scha.HSIZE)
	read, err = req.Read(x2)
	if err != nil {
		return fmt.Errorf("Reading x2 : %s", err)
	}
	if uint16(read) != scha.HSIZE {
		return fmt.Errorf("Cannot read x2 : %d / %d bytes available", read, scha.HSIZE)
	}

	/* (3) Manage request */
	errCode, err := s.manageRequest(x1, x2)
	if err != nil {
		return err
	}

	/* (4) Valid authentication */
	if errCode == 0 {

		response := []byte{0x00}
		written, err := res.Write(response)
		if written != 1 || err != nil {
			return err
		}

		return nil

	}

	/* (2) If not authenticated -> build resynchronisation response
	---------------------------------------------------------*/
	/* (1) Init y1 + y2 */
	y1 := make([]byte, scha.HSIZE)
	y2 := make([]byte, scha.HSIZE)

	/* (2) Generate response */
	err = s.generateResynchronisationResponse(y1, y2)
	if err != nil {
		return err
	}

	/* (3) Write error code */
	responseCode := []byte{errCode}
	written, err := res.Write(responseCode)
	if err != nil {
		return err
	}
	if written != len(responseCode) {
		return errors.New("Cannot write response code")
	}

	/* (4) Write y1 into response */
	written, err = res.Write(y1)
	if err != nil {
		return err
	}
	if written != len(y1) {
		return errors.New("Cannot write y1")
	}

	/* (5) Write y2 into response */
	written, err = res.Write(y2)
	if err != nil {
		return err
	}
	if written != len(y1) {
		return errors.New("Cannot write y2")
	}

	return nil
}

/* (4) Apply a synchronisation key
*
* @syncKey<[]byte>					Synchronisation key from client
*
* @return err<error>
*
---------------------------------------------------------*/
func (s *T) SynchronisationKey(syncKey []byte) error {

	/* (1) Check size */
	if uint16(len(syncKey)) != scha.HSIZE {
		return fmt.Errorf("Invalid synchronisation key size (%d), expected %d bytes", len(syncKey), scha.HSIZE)
	}

	/* (2) Copy synchronisation key */
	copy(s.hash, syncKey)

	/* (3) Store new config */
	s.store()

	return nil

}