"""Stream packet types — wire format for I2P streaming protocol."""

import struct


class Flags:
    """Stream packet flag constants."""
    SYNCHRONIZE = 0x0001
    CLOSE = 0x0002
    RESET = 0x0004
    SIGNATURE_INCLUDED = 0x0008
    SIGNATURE_REQUESTED = 0x0010
    FROM_INCLUDED = 0x0020
    DELAY_REQUESTED = 0x0040
    MAX_PACKET_SIZE_INCLUDED = 0x0080
    PROFILE_INTERACTIVE = 0x0100
    ECHO = 0x0200
    NO_ACK = 0x0400


class StreamPacket:
    """I2P streaming protocol packet.

    Wire format:
      send_id(4) + recv_id(4) + seq_num(4) + ack_through(4) +
      nack_count(1) + nack_list(nack_count*4) + resend_delay(1) +
      flags(2) + option_size(2) + options + payload
    """

    def __init__(self, send_id: int, recv_id: int, seq_num: int,
                 ack_through: int, flags: int, payload: bytes = b"",
                 nacks: list[int] | None = None, resend_delay: int = 0,
                 options: bytes = b""):
        self.send_id = send_id
        self.recv_id = recv_id
        self.seq_num = seq_num
        self.ack_through = ack_through
        self.nacks = nacks or []
        self.resend_delay = resend_delay
        self.flags = flags
        self.options = options
        self.payload = payload

    def to_bytes(self) -> bytes:
        parts = [
            struct.pack("!IIII", self.send_id, self.recv_id,
                        self.seq_num, self.ack_through),
            struct.pack("!B", len(self.nacks)),
        ]
        for nack in self.nacks:
            parts.append(struct.pack("!I", nack))
        parts.append(struct.pack("!BHH", self.resend_delay,
                                 self.flags, len(self.options)))
        parts.append(self.options)
        parts.append(self.payload)
        return b"".join(parts)

    @classmethod
    def from_bytes(cls, data: bytes) -> "StreamPacket":
        send_id, recv_id, seq_num, ack_through = struct.unpack("!IIII", data[:16])
        offset = 16
        nack_count = data[offset]
        offset += 1
        nacks = []
        for _ in range(nack_count):
            nacks.append(struct.unpack("!I", data[offset:offset + 4])[0])
            offset += 4
        resend_delay, flags, option_size = struct.unpack("!BHH", data[offset:offset + 5])
        offset += 5
        options = data[offset:offset + option_size]
        offset += option_size
        payload = data[offset:]
        return cls(send_id, recv_id, seq_num, ack_through, flags,
                   payload, nacks, resend_delay, options)