bitchat-android/app/src/main/java/com/bitchat/android/model/RequestSyncPacket.kt

package com.bitchat.android.model

import com.bitchat.android.sync.SyncDefaults

/**
 * REQUEST_SYNC payload using GCS (Golomb-Coded Set) parameters.
 * TLV (type, length16, value), types:
 *  - 0x01: P (uint8) — Golomb-Rice parameter
 *  - 0x02: M (uint32, big-endian) — hash range (N * 2^P)
 *  - 0x03: data (opaque) — GR bitstream bytes
 */
data class RequestSyncPacket(
    val p: Int,
    val m: Long,
    val data: ByteArray,
    val wantedTypes: List<UByte>? = null,
    val minTimestamp: ULong? = null
) {
    fun encode(): ByteArray {
        val out = ArrayList<Byte>()
        fun putTLV(t: Int, v: ByteArray) {
            out.add(t.toByte())
            val len = v.size
            out.add(((len ushr 8) and 0xFF).toByte())
            out.add((len and 0xFF).toByte())
            out.addAll(v.toList())
        }
        // P
        putTLV(0x01, byteArrayOf(p.toByte()))
        // M (uint32)
        val m32 = m.coerceAtMost(0xffff_ffffL)
        putTLV(
            0x02,
            byteArrayOf(
                ((m32 ushr 24) and 0xFF).toByte(),
                ((m32 ushr 16) and 0xFF).toByte(),
                ((m32 ushr 8) and 0xFF).toByte(),
                (m32 and 0xFF).toByte()
            )
        )
        // data
        putTLV(0x03, data)
        // wantedTypes
        wantedTypes?.let { types ->
            if (types.isNotEmpty()) {
                val typesBytes = types.map { it.toByte() }.toByteArray()
                putTLV(0x04, typesBytes)
            }
        }
        // minTimestamp
        minTimestamp?.let { ts ->
            val tsLong = ts.toLong()
            val tsBytes = byteArrayOf(
                ((tsLong ushr 56) and 0xFF).toByte(),
                ((tsLong ushr 48) and 0xFF).toByte(),
                ((tsLong ushr 40) and 0xFF).toByte(),
                ((tsLong ushr 32) and 0xFF).toByte(),
                ((tsLong ushr 24) and 0xFF).toByte(),
                ((tsLong ushr 16) and 0xFF).toByte(),
                ((tsLong ushr 8) and 0xFF).toByte(),
                (tsLong and 0xFF).toByte()
            )
            putTLV(0x05, tsBytes)
        }
        return out.toByteArray()
    }

    companion object {
        // Receiver-side safety limit (configurable constant)
        const val MAX_ACCEPT_FILTER_BYTES: Int = SyncDefaults.MAX_ACCEPT_FILTER_BYTES

        fun decode(data: ByteArray): RequestSyncPacket? {
            var off = 0
            var p: Int? = null
            var m: Long? = null
            var payload: ByteArray? = null
            var wantedTypes: List<UByte>? = null
            var minTimestamp: ULong? = null

            while (off + 3 <= data.size) {
                val t = (data[off].toInt() and 0xFF); off += 1
                val len = ((data[off].toInt() and 0xFF) shl 8) or (data[off+1].toInt() and 0xFF); off += 2
                if (off + len > data.size) return null
                val v = data.copyOfRange(off, off + len); off += len
                when (t) {
                    0x01 -> if (len == 1) p = (v[0].toInt() and 0xFF)
                    0x02 -> if (len == 4) {
                        val mm = ((v[0].toLong() and 0xFF) shl 24) or
                                 ((v[1].toLong() and 0xFF) shl 16) or
                                 ((v[2].toLong() and 0xFF) shl 8) or
                                 (v[3].toLong() and 0xFF)
                        m = mm
                    }
                    0x03 -> {
                        if (v.size > MAX_ACCEPT_FILTER_BYTES) return null
                        payload = v
                    }
                    0x04 -> {
                        val typesList = mutableListOf<UByte>()
                        for (b in v) {
                            typesList.add(b.toUByte())
                        }
                        wantedTypes = typesList
                    }
                    0x05 -> {
                        if (len == 8) {
                            var tsVal = 0L
                            for (i in 0 until 8) {
                                tsVal = (tsVal shl 8) or (v[i].toLong() and 0xFF)
                            }
                            minTimestamp = tsVal.toULong()
                        }
                    }
                }
            }

            val pp = p ?: return null
            val mm = m ?: return null
            val dd = payload ?: return null
            if (pp < 1 || mm <= 0L) return null
            return RequestSyncPacket(pp, mm, dd, wantedTypes, minTimestamp)
        }
    }
}