package client

import (
	"encoding/binary"
	"fmt"
	"git.xdrm.io/schastsp/client/keyset"
	"git.xdrm.io/schastsp/util/scha"
	"git.xdrm.io/schastsp/util/timeid"
	"git.xdrm.io/schastsp/util/xor"
)

/* (1) Updates 'key' and 'sync' with files
*
---------------------------------------------------------*/
func (c *T) updateConfig() {

	var err error

	/* (1) Restore if both are NIL
	---------------------------------------------------------*/
	if c.key == nil && c.sync == nil {

		/* (1) Create default key */
		c.key, err = keyset.Create(c.ctx)

		/* (2) Fetch key */
		err = c.fkey.Fetch(c.key)

		/* (3) On error -> set key to NIL */
		if err != nil { c.key = nil }

		/* (4) Create default sync */
		c.sync, err = keyset.Create(c.ctx)

		/* (5) Fetch sync */
		err = c.fsync.Fetch(c.sync)

		/* (6) On error -> set sync to NIL */
		if err != nil { c.sync = nil }

		/* (7) Exit if all keysets have been fetched */
		if c.key != nil && c.sync != nil {
			return
		}

	}


	/* (2) If cannot fetch -> create new keysets
	---------------------------------------------------------*/
	if c.key == nil {
		c.key, _ = keyset.Create(c.ctx)
	}

	if c.sync == nil {
		c.sync, _ = keyset.Create(c.ctx)
	}


	/* (3) Store current value
	---------------------------------------------------------*/
	/* (1) Store key */
	err = c.fkey.Store(c.key)
	if err != nil { panic("Cannot store key") }

	/* (2) Store sync */
	err = c.fsync.Store(c.sync)
	if err != nil { panic("Cannot store sync") }

}

/* (2) Migrate current key
*
---------------------------------------------------------*/
func (c *T) migrateKey() {

	var err error

	/* (1) Copy sync into key */
	c.key = c.sync

	/* (2) Regenerate sync */
	c.sync, err = keyset.Create(c.ctx)
	if err != nil { panic(err) }

	/* (3) Store keysets to files */
	c.updateConfig()

}

/* (3) Generate a new 'sync' keyset respecting mod constraints (timeid + migration)
*
---------------------------------------------------------*/
func (c *T) generateKeyWithConstraints() {

	/* Get current hash */
	keyHash, err := c.key.CurrentHash()
	if err != nil { panic(err) }

	/* Search key one is respects contraints */
	for true {

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

		/* (2) Convert timeId to byte array */
		timeIDBytes := make([]byte, 4)
		binary.BigEndian.PutUint32(timeIDBytes, timeID)

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


		/* (2) Generate a new sync
		---------------------------------------------------------*/
		newKey, _ := keyset.Create(c.ctx)


		/* (3) Check constraints
		---------------------------------------------------------*/
		/* (1) Get next hash */
		syncHash, err := newKey.CurrentHash()
		if err != nil { continue }

		/* (2) Get x1 */
		x1 := make([]byte, scha.HSIZE)
		copy(x1, xor.ByteArray(keyHash, hashedTimeID))

		/* (3) Get x2 */
		x2 := make([]byte, scha.HSIZE)
		copy(x2, xor.ByteArray(syncHash, hashedTimeID))

		/* (4) Get x1 xor x2 */
		x := make([]byte, scha.HSIZE)
		copy(x, xor.ByteArray(x1, x2))

		if DEBUG {
			fmt.Printf("+ x1 : '%x'\n", x1)
			fmt.Printf("+ x2 : '%x'\n", x2)
		}

		/* (2) Get time mod difference (first byte) */
		timeConstraintValue := x[0]%2 == byte(timeMod)

		if DEBUG { fmt.Printf("    %.2x ^ %.2x = %.2x[%d] %% 2 = %d == %d ? %t\n", x1[0], x2[0], x[0], x[0], x[0]%2, timeMod, timeConstraintValue) }

		/* (4) Retry if invalid time constraint */
		if !timeConstraintValue { continue }

		/* (5) Get migration mod difference (second byte) */
		migrationConstraintValue := x[1]%3 == byte(c.key.MigrationCode())

		if DEBUG { fmt.Printf("    %.2x ^ %.2x = %.2x[%d] %% 3 = %d == %d ? %t\n", x1[1], x2[1], x[1], x[1], x[1]%3, c.key.MigrationCode(), migrationConstraintValue) }

		/* (6) Retry if invalid time constraint */
		if !migrationConstraintValue { continue }

		/* (7) Store new sync */
		c.sync = newKey

		/* (8) Store keysets to files */
		c.updateConfig()

		break

	}

}

/* (4) Generate the client request
*
* @x1<[]byte>						Byte array to write into
* @x2<[]byte>						Byte array to write into
*
* @return err<error>				The error or NIL if not
*
---------------------------------------------------------*/
func (c *T) generateRequest(x1 []byte, x2 []byte) error {

	/* (1) Migrate if validated migration
	---------------------------------------------------------*/
	if c.key.MigrationCode() == 3 {
		c.migrateKey()
	}

	/* (2) Decrement
	---------------------------------------------------------*/
	/* (1) Decrement hash */
	remainingHashes := c.key.Decrement()
	c.updateConfig()

	if DEBUG {
		fmt.Printf("Remaining %x[%d] hashes\n", remainingHashes, remainingHashes)
		fmt.Printf("Migration code is %d\n", c.key.MigrationCode())
	}

	/* (3) New sync hash if key consumed
	---------------------------------------------------------*/
	if c.key.MigrationCode() > 0 {

		/* (1) Generate sync with constraints */
		c.generateKeyWithConstraints()

		/* (2) Notify key needs renewal */
		c.key.MigrationCode(2)

		/* (3) Store config */
		c.updateConfig()
	}

	/* (4) Get useful hashes
	---------------------------------------------------------*/
	/* (1) Store current hash */
	h0, err := c.key.CurrentHash()
	if err != nil { return err }

	/* (2) Copy into next hash (same value) */
	h1 := make([]byte, scha.HSIZE)

	// 1. If migration code = 0 -> use same hash
	copy(h1, h0)

	// 2. Else -> use 'sync'
	if c.key.MigrationCode() > 0 {
		h1, err = c.sync.CurrentHash()
		if err != nil { return err }
	}

	/* (5) Manage time id
	---------------------------------------------------------*/
	/* (1) Get current time id */
	timeID, timeMod := timeid.Generate(c.ctx.Window())

	/* (2) Convert time id to byte array */
	timeIDBytes := make([]byte, 4)
	binary.BigEndian.PutUint32(timeIDBytes, timeID)

	/* (2) Get digest of time id */
	hashedTimeID, err := scha.Hash(timeIDBytes, 1)

	/* (6) Calculate x1 and x2
	---------------------------------------------------------*/
	/* (1) Calculate x1 = h ^ h(timeId) */
	copy(x1, xor.ByteArray(h0, hashedTimeID))

	if DEBUG {
		fmt.Printf("\n=== x1 ===\n")
		fmt.Printf("  hash is            h0 = %x\n", h0)
		fmt.Printf("  time id is          n = %x[%d]\n", timeIDBytes, timeID)
		fmt.Printf("                   h(t) = %x\n", hashedTimeID)
		fmt.Printf("  x1 is         h0+h(t) = %X\n", x1)
		fmt.Printf("  check x1+h(t) eq h0   = %x\n", xor.ByteArray(x1, hashedTimeID))
		fmt.Printf("  check x1+h0   eq h(t) = %x\n", xor.ByteArray(x1, h0))
	}

	/* (2) Calculate x2 = h ^ h(timeId) ^ timeMod */
	copy(x2, xor.ByteArray(h1, hashedTimeID))

	// only add time mod if code = 0
	if c.key.MigrationCode() == 0 {
		x2[0] = xor.Byte(x2[0], byte(timeMod))
	}

	if DEBUG {
		fmt.Printf("\n=== x2 ===\n")
		fmt.Printf("  next is            h1 = %x\n", h1)
		fmt.Printf("  time mod is         m = %x[%d]\n", timeMod, timeMod)
		fmt.Printf("                   h(t) = %x\n", hashedTimeID)
		if c.key.MigrationCode() == 0 {
			fmt.Printf("  x2 is       h1+h(t)+m = %X\n", x2)
			fmt.Printf("  check x2+x1 %% 2 eq m  = %d (%t)\n", uint8(xor.ByteArray(x1, x2)[0]%2), xor.ByteArray(x1, x2)[0]%2 == byte(timeMod))
		} else {
			fmt.Printf("  x2 is       h1+h(t)   = %X\n", x2)
			fmt.Printf("  check x2+x1 %% 2 eq m  = %d (%t)\n", uint8(xor.ByteArray(x1, x2)[0]%2), xor.ByteArray(x1, x2)[0]%2 == byte(timeMod))
		}
		fmt.Printf("  check x2+x1 %% 3 eq o  = %d (%t)\n", uint8(xor.ByteArray(x1, x2)[1]%3), uint8(xor.ByteArray(x1, x2)[1]%3) == c.key.MigrationCode())
	}

	return nil
}

/* (5) Rescue management
*
* @Y1<[]byte>						First rescue parameter
* @Y2<[]byte>						Second rescue parameter
*
* @return err<error>				The error or NIL if not
*
---------------------------------------------------------*/
func (c *T) rescue(y1 []byte, y2 []byte) error {

	/* (1) Extract time mod */
	timeMod := uint32(xor.ByteArray(y1, y2)[0] % 2)

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

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

	/* (4) Get the received hash */
	receivedHash := xor.ByteArray(y1, hashedTimeID)

	/* (5) Try to rescue the key */
	err = c.key.Rescue(receivedHash)
	if err != nil { return err }

	/* (6) Store updated key */
	c.updateConfig()

	return nil

}