"""Tests for Apollo protocol utilities — sync words and AGC packets."""

import pytest

from apollo.constants import (
    AGC_CH_DNTM1,
    AGC_CH_INLINK,
    AGC_CH_OUTLINK,
    DEFAULT_SYNC_A,
    DEFAULT_SYNC_B,
    DEFAULT_SYNC_CORE,
)
from apollo.protocol import (
    adc_to_voltage,
    bits_to_sync_word,
    form_io_packet,
    generate_sync_word,
    parse_io_packet,
    parse_sync_word,
    sync_word_to_bits,
    voltage_to_adc,
)


class TestSyncWordGeneration:
    """Test 32-bit PCM frame sync word generation and parsing."""

    def test_roundtrip(self):
        """Generate → parse → verify all fields match."""
        word = generate_sync_word(frame_id=1)
        fields = parse_sync_word(word)
        assert fields["a_bits"] == DEFAULT_SYNC_A
        assert fields["core"] == DEFAULT_SYNC_CORE
        assert fields["b_bits"] == DEFAULT_SYNC_B
        assert fields["frame_id"] == 1

    def test_frame_id_range(self):
        """All valid frame IDs (1-50) should roundtrip."""
        for fid in range(1, 51):
            word = generate_sync_word(frame_id=fid)
            fields = parse_sync_word(word)
            assert fields["frame_id"] == fid

    def test_invalid_frame_id(self):
        with pytest.raises(ValueError):
            generate_sync_word(frame_id=0)
        with pytest.raises(ValueError):
            generate_sync_word(frame_id=51)

    def test_odd_frame_complements_core(self):
        """Odd frames should have complemented core."""
        even = generate_sync_word(frame_id=2, odd=False)
        odd = generate_sync_word(frame_id=1, odd=True)
        even_fields = parse_sync_word(even)
        odd_fields = parse_sync_word(odd)
        # Core should be bitwise complement (15 bits)
        assert (even_fields["core"] ^ odd_fields["core"]) == 0x7FFF

    def test_word_is_32_bits(self):
        word = generate_sync_word(frame_id=25)
        assert 0 <= word < (1 << 32)

    def test_bits_roundtrip(self):
        """word → bits → word should be identity."""
        word = generate_sync_word(frame_id=42)
        bits = sync_word_to_bits(word)
        assert len(bits) == 32
        assert all(b in (0, 1) for b in bits)
        recovered = bits_to_sync_word(bits)
        assert recovered == word

    def test_bits_msb_first(self):
        """Bit 0 in the list should be the MSB of the word."""
        word = generate_sync_word(frame_id=1)
        bits = sync_word_to_bits(word)
        # MSB is bit 31
        assert bits[0] == (word >> 31) & 1


class TestAGCPacketProtocol:
    """Test Virtual AGC socket protocol encode/decode."""

    def test_roundtrip_basic(self):
        """Encode → decode should preserve channel and value."""
        packet = form_io_packet(channel=AGC_CH_OUTLINK, value=12345)
        ch, val, u = parse_io_packet(packet)
        assert ch == AGC_CH_OUTLINK
        assert val == 12345

    def test_roundtrip_all_telecom_channels(self):
        for ch in [AGC_CH_INLINK, AGC_CH_OUTLINK, AGC_CH_DNTM1]:
            for val in [0, 1, 0x3FFF, 0x7FFF]:
                packet = form_io_packet(channel=ch, value=val)
                got_ch, got_val, _ = parse_io_packet(packet)
                assert got_ch == ch, f"Channel mismatch: {got_ch} != {ch}"
                assert got_val == val, f"Value mismatch: {got_val} != {val}"

    def test_packet_length(self):
        packet = form_io_packet(channel=0, value=0)
        assert len(packet) == 4

    def test_signature_bits(self):
        """Verify the 2-bit signatures in each byte."""
        packet = form_io_packet(channel=100, value=5000)
        assert (packet[0] & 0xC0) == 0x00
        assert (packet[1] & 0xC0) == 0x40
        assert (packet[2] & 0xC0) == 0x80
        assert (packet[3] & 0xC0) == 0xC0

    def test_invalid_packet_length(self):
        with pytest.raises(ValueError):
            parse_io_packet(b"\x00\x40\x80")

    def test_invalid_signature(self):
        with pytest.raises(ValueError):
            parse_io_packet(b"\xFF\x40\x80\xC0")

    def test_zero_values(self):
        packet = form_io_packet(channel=0, value=0)
        ch, val, _ = parse_io_packet(packet)
        assert ch == 0
        assert val == 0

    def test_max_values(self):
        packet = form_io_packet(channel=0x1FF, value=0x7FFF)
        ch, val, _ = parse_io_packet(packet)
        assert ch == 0x1FF
        assert val == 0x7FFF


class TestADCConversion:
    """Test A/D converter code ↔ voltage conversion (IMPL_SPEC section 5.3)."""

    def test_zero_code(self):
        """Code 1 = 0V."""
        assert adc_to_voltage(1) == 0.0

    def test_fullscale_code(self):
        """Code 254 = 4.98V."""
        assert abs(adc_to_voltage(254) - 4.98) < 0.001

    def test_overflow_code(self):
        """Code 255 = >5V (clamped to 5.0)."""
        assert adc_to_voltage(255) == 5.0

    def test_midscale(self):
        """Midscale should be roughly 2.5V."""
        mid_code = 128
        voltage = adc_to_voltage(mid_code)
        assert abs(voltage - 2.5) < 0.1  # within 100mV

    def test_voltage_roundtrip(self):
        """voltage_to_adc(adc_to_voltage(code)) ≈ code for valid range."""
        for code in [1, 50, 127, 200, 254]:
            v = adc_to_voltage(code)
            recovered = voltage_to_adc(v)
            assert abs(recovered - code) <= 1, f"Code {code}: {v}V → {recovered}"

    def test_low_level_scaling(self):
        """Low-level inputs use ×125 gain: 0-40 mV → 0-5V internal."""
        # 40 mV at low-level = 40 * 125 = 5000 mV = 5V internal → code 254
        v = adc_to_voltage(254, low_level=True)
        assert abs(v - 0.03984) < 0.001  # 4.98V / 125 ≈ 0.03984V

    def test_step_size(self):
        """Step size should be ~19.7 mV per LSB."""
        v1 = adc_to_voltage(100)
        v2 = adc_to_voltage(101)
        step_mv = (v2 - v1) * 1000
        assert abs(step_mv - 19.7) < 0.1