package server

import (
	"encoding/binary"
	"errors"
	"fmt"
	"git.xdrm.io/schastsp/pkg/scha"
	"git.xdrm.io/schastsp/pkg/timeid"
	"git.xdrm.io/schastsp/pkg/xor"
	"os"
)

/* (1) Store hash into file
*
* @return err<error>			Error or NIL if not
*
---------------------------------------------------------*/
func (s T) store() error {

	/* (1) Try to open file for writing */
	file, err := os.OpenFile(s.conf, os.O_RDWR|os.O_CREATE, 0755)
	if err != nil { return err }

	/* (2) Defer close */
	defer file.Close()

	/* (3) Write hash into file */
	err = binary.Write(file, binary.BigEndian, s.hash)
	if err != nil { return err }

	return nil

}

/* (2) Fetch hash from file
*
* @return err<error>			Error or NIL if not
*
---------------------------------------------------------*/
func (s *T) fetch() error {

	/* (1) Try to open file for reading */
	file, err := os.Open(s.conf)
	if err != nil { return err }

	/* (2) Defer close */
	defer file.Close()

	/* (3) Try to fetch hash from file */
	fetchedHash := make([]byte, scha.HSIZE)
	err = binary.Read(file, binary.BigEndian, fetchedHash)
	if err != nil { return err }

	/* (4) Fail if wrong size */
	if uint16(len(fetchedHash)) != scha.HSIZE {
		return errors.New("Invalid hash size in file")
	}

	/* (5) Copy fetched hash into real one */
	copy(s.hash, fetchedHash)

	return nil

}

/* (3) Request management
*
* @x1<[]byte>						First request component
* @x2<[]byte>						Second request component
*
* @return code<byte>				Error code
*									0 -> authenticated
*									1 -> request error -> may resynchronise
*									2 -> Unknown error (check in returned 'err')
* @return err<error>				Error or NIL if not
*
---------------------------------------------------------*/
func (s *T) manageRequest(x1 []byte, x2 []byte) (byte, error) {

	if DEBUG { fmt.Printf("  stored hash is      H = %x\n", s.hash) }

	/* (1) Extract meta data
	---------------------------------------------------------*/
	/* (1) Get xor between x1 and x2 */
	x := xor.ByteArray(x1, x2)

	/* (2) Extract migration code */
	mcode := uint8(x[1]) % 3
	if DEBUG { fmt.Printf("  extracted code is   o = %d\n", mcode) }

	/* (3) Fail if no migration but different hashes */
	if mcode == 0 && string(x1[2:]) != string(x2[2:]) {
		return 1, nil
	}


	/* (2) TimeID management
	---------------------------------------------------------*/
	/* (1) Extract time mod */
	timeMod := uint32(x[0]) % 2
	if DEBUG { fmt.Printf("  extracted time mod  m = %d\n", timeMod) }

	/* (2) Try to guess time id */
	timeID := timeid.Guess(s.ctx.Window(), timeMod)
	timeIDBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(timeIDBytes, timeID)

	/* (3) Hash guessed time id */
	hashedTimeID, err := scha.Hash(timeIDBytes, 1)
	if err != nil { return 2, err }


	/* (3) Extract hashes
	---------------------------------------------------------*/
	/* (1) Extract hash from x0 */
	h0 := xor.ByteArray(x1, hashedTimeID)
	if DEBUG { fmt.Printf("  supposing hash is  h0 = %x\n", h0) }

	/* (2) Extract next hash from x1 */
	h1 := xor.ByteArray(x2, hashedTimeID)
	if DEBUG { fmt.Printf("  supposing next is  h1 = %x\n", h1) }

	/* (3) Only remove timeMod if migration code = 0 */
	if mcode == 0 {
		h1[0] = xor.Byte(h1[0], byte(timeMod))
	}


	/* (4) Hash h0 to compare with stored hash 's.hash'
	---------------------------------------------------------*/
	/* (1) Hash 1 time to check if matches */
	hashedH0, err := scha.Hash(h0, 1)
	if err != nil { return 2, err }

	/* (2) If migration code = 2 (Rescue mode) -> hash MIN times */
	if mcode == 2 {
		hashedH0, err = scha.Hash(h0, s.ctx.MinDepth())
		if err != nil { return 2, err }

		if DEBUG {
			fmt.Printf("  hashed is      h(min) = %x\n", hashedH0)
		}
	} else if DEBUG {
		fmt.Printf("  hashed is       h(h0) = %x\n", hashedH0)
	}

	/* (3) Fail if does not match */
	if string(hashedH0) != string(s.hash) {
		return 1, nil
	}


	/* (5) Store next hash
	---------------------------------------------------------*/
	copy(s.hash, h1)
	s.store()

	return 0, nil

}

/* (4) Generate resynchronisation response
*
* @y1<[]byte>						First response component to write into
* @y2<[]byte>						Second response component to write into
*
* @return err<error>				Error or nil if not
*
---------------------------------------------------------*/
func (s *T) generateResynchronisationResponse(y1 []byte, y2 []byte) error {

	/* (1) Get current time id */
	timeID, timeMod := timeid.Generate(s.ctx.Window())

	/* (3) Hash the time id */
	timeIDBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(timeIDBytes, timeID)

	hashedTimeID, err := scha.Hash(timeIDBytes, 1)
	if err != nil { return err }

	/* (4) Process y1 = H ^ h(timeId) */
	copy(y1, xor.ByteArray(s.hash, hashedTimeID))

	/* (5) Process y2 = H ^ h(timeId) ^ timeMod = y1 ^ timeMod */
	copy(y2, xor.ByteArray(s.hash, hashedTimeID))
	y2[0] = xor.Byte(y2[0], byte(timeMod))

	if DEBUG {
		fmt.Printf("=== y1 ===\n")
		fmt.Printf("  hash is             H = %x\n", s.hash)
		fmt.Printf("  time id is          t = %x[%d]\n", timeID, timeID)
		fmt.Printf("  				   h(t) = %x\n", hashedTimeID)
		fmt.Printf("  y1 is          H+h(t) = %x\n", y1)
		fmt.Printf("  check y1+h(t) eq H    = %x\n", xor.ByteArray(y1, hashedTimeID))
		fmt.Printf("  check y1+H    eq h(t) = %x\n", xor.ByteArray(y1, s.hash))

		fmt.Printf("=== y2 ===\n")
		fmt.Printf("  time mod is        m = %x[%d]\n", timeMod, timeMod)
		fmt.Printf("  y2 is           y1+m = %x\n", y2)
	}

	return nil

}