from __future__ import annotations

from dataclasses import dataclass
from typing import Iterable


P9_ACK_BIT = 0x80
P9_STROBE_BIT = 0x02


@dataclass(frozen=True)
class P9StrobeEvent:
    edge: str
    ddr: int
    dr: int
    data_bit: int
    bit7_output: bool


class P9Bus:
    """Small model for the ROM's P9 bit-banged serial handshake."""

    def __init__(self, ddr: int = 0x00, dr: int = 0x00, input_bits: Iterable[int] = ()) -> None:
        self.ddr = ddr & 0xFF
        self.dr_latch = dr & 0xFF
        self.input_bits: list[int] = [1 if bit else 0 for bit in input_bits]
        self.default_input_bit = 0
        self.strobe_edges: list[P9StrobeEvent] = []
        self.transmitted_bits: list[int] = []
        self.byte_candidates: list[int] = []

    def write_ddr(self, value: int) -> int:
        self.ddr = value & 0xFF
        return self.ddr

    def write_dr(self, value: int) -> int:
        previous = self.dr_latch
        self.dr_latch = value & 0xFF

        previous_strobe = bool(previous & P9_STROBE_BIT)
        current_strobe = bool(self.dr_latch & P9_STROBE_BIT)
        if previous_strobe != current_strobe:
            edge = "rising" if current_strobe else "falling"
            data_bit = 1 if self.dr_latch & P9_ACK_BIT else 0
            bit7_output = bool(self.ddr & P9_ACK_BIT)
            self.strobe_edges.append(P9StrobeEvent(edge, self.ddr, self.dr_latch, data_bit, bit7_output))
            if edge == "rising" and bit7_output:
                self._record_transmitted_bit(data_bit)

        return self.dr_latch

    def read_ddr(self) -> int:
        return self.ddr

    def read_dr(self) -> int:
        value = self.dr_latch
        if not (self.ddr & P9_ACK_BIT):
            if self.input_bits:
                input_bit = self.input_bits.pop(0)
            else:
                input_bit = self.default_input_bit
            if input_bit:
                value |= P9_ACK_BIT
            else:
                value &= ~P9_ACK_BIT
        return value & 0xFF

    def queue_input_bits(self, bits: Iterable[int]) -> None:
        self.input_bits.extend(1 if bit else 0 for bit in bits)

    def set_default_input_bit(self, bit: int) -> None:
        self.default_input_bit = 1 if bit else 0

    def _record_transmitted_bit(self, bit: int) -> None:
        self.transmitted_bits.append(bit)
        if len(self.transmitted_bits) % 8 == 0:
            byte = 0
            for data_bit in self.transmitted_bits[-8:]:
                byte = (byte << 1) | data_bit
            self.byte_candidates.append(byte)