package stoken

import (
	"bytes"
	"crypto/ed25519"
	"crypto/rand"
	"encoding/base64"
	"encoding/hex"
	"errors"
	"fmt"
	"github.com/ugorji/go/codec"
	"hash/crc64"
	"strings"
)

const alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"

var b64 = base64.NewEncoding(alphabet).WithPadding(base64.NoPadding)

type linkData struct {
	Signature []byte `codec:"s"`
	Payload   []byte `codec:"p"`
}

type TokenCoder struct {
	valid   bool
	privKey ed25519.PrivateKey
	pubKeys []ed25519.PublicKey
}

func (tc TokenCoder) PublicKey() ed25519.PublicKey {
	if tc.valid {
		pos := len(tc.pubKeys) - 1
		return tc.pubKeys[pos]
	}
	return nil
}

func (tc TokenCoder) Seed() []byte {
	if tc.valid {
		return tc.privKey.Seed()
	}
	return nil
}

func (tc TokenCoder) PublicKeyHex() string {
	return hex.EncodeToString(tc.PublicKey())
}

func (tc TokenCoder) SeedHex() string {
	return hex.EncodeToString(tc.Seed())
}

func NewTokenCoder(seed []byte, pubKeys ...[]byte) (tc TokenCoder, err error) {
	tc.pubKeys = make([]ed25519.PublicKey, len(pubKeys)+1, len(pubKeys)+1)
	if len(seed) == 0 {
		seed = make([]byte, ed25519.SeedSize, ed25519.SeedSize)
		_, err = rand.Read(seed)
		if err != nil {
			return
		}
	}

	if len(seed) != ed25519.SeedSize {
		err = errors.New("Incorrect seed size")
		return
	}

	tc.privKey = ed25519.NewKeyFromSeed(seed)
	tc.pubKeys[len(pubKeys)] = tc.privKey.Public().(ed25519.PublicKey)

	for pos, key := range pubKeys {
		if len(key) != ed25519.PublicKeySize {
			err = errors.New("Incorrect public key size")
			return
		}
		tc.pubKeys[pos] = ed25519.PublicKey(key)
	}
	tc.valid = true
	return
}

func NewTokenCoderHex(seed string, pubKeys ...string) (tc TokenCoder, err error) {
	var rawSeed []byte
	rawPubKeys := make([][]byte, len(pubKeys), len(pubKeys))
	rawSeed, err = hex.DecodeString(seed)
	if err != nil {
		return
	}
	for pos, pubKey := range pubKeys {
		rawPubKeys[pos], err = hex.DecodeString(pubKey)
		if err != nil {
			return
		}
	}
	return NewTokenCoder(rawSeed, rawPubKeys...)
}

func trim(r rune) bool {
	return !strings.ContainsRune(alphabet, r)
}

func (tc TokenCoder) Encode(payload interface{}) (token string, err error) {
	if !tc.valid {
		err = errors.New("Invalid TokenCoder")
		return
	}

	buf := bytes.NewBuffer(nil)
	var handle codec.CborHandle

	enc := codec.NewEncoder(buf, &handle)
	enc.Encode(payload)

	var ld linkData
	ld.Signature = ed25519.Sign(tc.privKey, buf.Bytes())
	ld.Payload = buf.Bytes()
	buf.Reset()
	enc.Encode(ld)
	token = b64.EncodeToString(buf.Bytes())
	return
}

func (tc TokenCoder) Decode(token string, payload interface{}) (sum string, err error) {
	if !tc.valid {
		err = errors.New("Invalid TokenCoder")
		return
	}

	var data []byte
	data, err = b64.DecodeString(strings.TrimFunc(token, trim))
	if err != nil {
		return
	}

	buf := bytes.NewBuffer(nil)
	var handle codec.CborHandle

	buf.Write(data)
	dec := codec.NewDecoder(buf, &handle)

	var ld linkData
	err = dec.Decode(&ld)
	if err != nil {
		return
	}

	ok := false
	for _, key := range tc.pubKeys {
		if ed25519.Verify(key, ld.Payload, ld.Signature) {
			ok = true
			break
		}
	}

	if !ok {
		err = errors.New("Signature validation failed")
		return
	}

	buf.Reset()
	buf.Write(ld.Payload)

	hash := crc64.New(crc64.MakeTable(crc64.ISO))
	hash.Write(ld.Payload)

	sum = hex.EncodeToString(hash.Sum(nil))
	err = dec.Decode(&payload)
	return
}