package admin

import (
    "crypto/hmac"
    "crypto/sha256"
    "encoding/binary"
    "encoding/hex"

    "bindbox-game/configs"
)

func unmaskSeed(enc []byte, issueID int64, version int32) []byte {
    key := masterKey()
    if key == nil {
        return enc
    }
    ks := deriveMask(key, issueID, version)
    out := make([]byte, len(enc))
    for i := range enc {
        out[i] = enc[i] ^ ks[i%len(ks)]
    }
    return out
}

func masterKey() []byte {
    s := configs.Get().Random.CommitMasterKey
    if s == "" {
        return nil
    }
    b, err := hex.DecodeString(s)
    if err != nil || len(b) == 0 {
        return nil
    }
    return b
}

func deriveMask(key []byte, issueID int64, version int32) []byte {
    m := hmac.New(sha256.New, key)
    buf := make([]byte, 12)
    binary.BigEndian.PutUint64(buf[:8], uint64(issueID))
    binary.BigEndian.PutUint32(buf[8:12], uint32(version))
    m.Write(buf)
    sum := m.Sum(nil)
    return sum[:32]
}

func encodeMessage(algo string, roundId int64, drawId int64, clientId int64, clientSeed []byte, nonce uint64, itemsRoot []byte, weightsTotal uint64) []byte {
    var buf []byte
    buf = appendUint32String(buf, algo)
    buf = appendUint64(buf, uint64(roundId))
    buf = appendUint64(buf, uint64(drawId))
    buf = appendUint64(buf, uint64(clientId))
    buf = appendUint32Bytes(buf, clientSeed)
    buf = appendUint64(buf, nonce)
    buf = append(buf, itemsRoot...)
    buf = appendUint64(buf, weightsTotal)
    return buf
}

func appendUint32String(b []byte, s string) []byte {
    bs := []byte(s)
    nb := make([]byte, 4)
    binary.BigEndian.PutUint32(nb, uint32(len(bs)))
    b = append(b, nb...)
    b = append(b, bs...)
    return b
}

func appendUint32Bytes(b []byte, bs []byte) []byte {
    nb := make([]byte, 4)
    binary.BigEndian.PutUint32(nb, uint32(len(bs)))
    b = append(b, nb...)
    b = append(b, bs...)
    return b
}

func appendUint64(b []byte, v uint64) []byte {
    nb := make([]byte, 8)
    binary.BigEndian.PutUint64(nb, v)
    b = append(b, nb...)
    return b
}

func hmacSha256(key []byte, msg []byte) []byte {
    m := hmac.New(sha256.New, key)
    m.Write(msg)
    return m.Sum(nil)
}