import struct
from dataclasses import dataclass
from pathlib import Path

import pytest

from app.fit.rewriter import FitFormatError, convert_fit_device, is_fit_file, read_device_field_values
from tests.fit.builders import compressed_timestamp_data, data, definition, make_fit

FILE_ID_MESG_NUM = 0
DEVICE_INFO_MESG_NUM = 23
RECORD_MESG_NUM = 20
HEADER_SIZE = 14
PRODUCT_NAME_SIZE = 24


@dataclass(frozen=True)
class ComplexFixture:
    fit_bytes: bytes
    metadata_offsets: set[int]
    file_id_manufacturer_offset: int
    file_id_product_offset: int
    file_id_product_name_offset: int
    file_id_product_name_size: int
    creator_manufacturer_offset: int
    creator_product_offset: int
    preserved_ranges: tuple[tuple[int, int], ...]


def _build_complex_fixture() -> ComplexFixture:
    """Builds one synthetic FIT data section covering all of the advanced record
    shapes the parser must handle end-to-end through convert_fit_device():

    1. a normal file_id definition/data pair (local 0);
    2. a device_info definition with a creator record (local 1, device_index=0);
    3. a record definition with one native field and one developer field, plus one
       data record using it (local 2);
    4. a compressed-timestamp data header referring to that same local 2 definition;
    5. a later replacement definition for local message number 2 (redefined as a
       non-creator device_info record, device_index=2), plus a data record using it.

    All byte offsets are derived here from the construction arithmetic itself
    (running length of the accumulated byte stream) -- this function never calls
    into app.fit.rewriter's parser.
    """
    records = bytearray()

    def pos() -> int:
        return HEADER_SIZE + len(records)

    # 1. normal file_id definition/data pair, including the product_name string
    #    field (8) so the string write path -- which zero-fills the whole declared
    #    field, the riskiest byte-preservation behavior in the patcher -- is covered
    #    by the byte-preservation proof and not only by the patching tests.
    records.extend(
        definition(
            0,
            FILE_ID_MESG_NUM,
            [(1, 2, 0x84), (2, 2, 0x84), (8, PRODUCT_NAME_SIZE, 0x07)],
        )
    )

    file_id_data_start = pos()
    original_product_name = b"MyWhoosh Simulator\x00".ljust(PRODUCT_NAME_SIZE, b"\x2A")
    records.extend(data(0, struct.pack("<HH", 255, 999) + original_product_name))
    file_id_manufacturer_offset = file_id_data_start + 1  # +1 for the record header byte
    file_id_product_offset = file_id_manufacturer_offset + 2  # manufacturer is a u16
    file_id_product_name_offset = file_id_product_offset + 2  # product is a u16

    # 2. device_info definition with a creator record (device_index == 0).
    records.extend(definition(1, DEVICE_INFO_MESG_NUM, [(0, 1, 0x02), (2, 2, 0x84), (4, 2, 0x84)]))

    creator_data_start = pos()
    records.extend(data(1, struct.pack("<BHH", 0, 255, 999)))
    creator_manufacturer_offset = creator_data_start + 1 + 1  # header byte + device_index(u8)
    creator_product_offset = creator_manufacturer_offset + 2  # manufacturer is a u16

    # 3. record definition with one native field (power) and one developer field,
    #    plus one data record using it.
    records.extend(definition(2, RECORD_MESG_NUM, [(7, 2, 0x84)], developer_fields=[(0, 4, 0)]))

    record_data_start = pos()
    records.extend(data(2, struct.pack("<H", 1234) + b"\xDE\xAD\xBE\xEF"))
    record_data_end = pos()

    # 4. compressed-timestamp data header referring to the still-active local
    #    definition 2 (the record definition above). Same field layout, so the
    #    payload is a power u16 followed by the 4-byte developer field.
    compressed_start = pos()
    records.extend(compressed_timestamp_data(2, 17, struct.pack("<H", 5678) + b"\xCA\xFE\xBA\xBE"))
    compressed_end = pos()

    # 5. later replacement definition for the same local message number (2): local 2
    #    is redefined as a *non-creator* device_info record (device_index=2), so the
    #    patcher must skip it entirely and its bytes must stay identical.
    records.extend(definition(2, DEVICE_INFO_MESG_NUM, [(0, 1, 0x02), (2, 2, 0x84), (4, 2, 0x84)]))

    sensor_data_start = pos()
    records.extend(data(2, struct.pack("<BHH", 2, 77, 555)))
    sensor_data_end = pos()

    metadata_offsets: set[int] = set()
    metadata_offsets.update(range(file_id_manufacturer_offset, file_id_manufacturer_offset + 2))
    metadata_offsets.update(range(file_id_product_offset, file_id_product_offset + 2))
    metadata_offsets.update(
        range(file_id_product_name_offset, file_id_product_name_offset + PRODUCT_NAME_SIZE)
    )
    metadata_offsets.update(range(creator_manufacturer_offset, creator_manufacturer_offset + 2))
    metadata_offsets.update(range(creator_product_offset, creator_product_offset + 2))

    return ComplexFixture(
        fit_bytes=make_fit(bytes(records)),
        metadata_offsets=metadata_offsets,
        file_id_manufacturer_offset=file_id_manufacturer_offset,
        file_id_product_offset=file_id_product_offset,
        file_id_product_name_offset=file_id_product_name_offset,
        file_id_product_name_size=PRODUCT_NAME_SIZE,
        creator_manufacturer_offset=creator_manufacturer_offset,
        creator_product_offset=creator_product_offset,
        preserved_ranges=(
            (record_data_start, record_data_end),
            (compressed_start, compressed_end),
            (sensor_data_start, sensor_data_end),
        ),
    )


# Built once at import time so the fixture bytes and the expected-offsets bookkeeping
# can never drift apart from each other.
_FIXTURE = _build_complex_fixture()


@pytest.fixture
def complex_fit_bytes() -> bytes:
    return _FIXTURE.fit_bytes


def find_expected_device_metadata_offsets(before: bytes) -> set[int]:
    """Byte offsets convert_fit_device() is expected to touch, taken from the
    fixture's own construction-time bookkeeping (see _build_complex_fixture above).
    Deliberately does not parse `before` or call any part of app.fit.rewriter, so
    this test cannot become circular (the parser being tested against itself)."""
    del before
    return set(_FIXTURE.metadata_offsets)


def test_only_target_fields_and_crcs_change(tmp_path: Path, complex_fit_bytes: bytes) -> None:
    source = tmp_path / "source.fit"
    output = tmp_path / "output.fit"
    source.write_bytes(complex_fit_bytes)

    convert_fit_device(source, output)

    before = source.read_bytes()
    after = output.read_bytes()
    assert len(before) == len(after)

    changed = {index for index, (a, b) in enumerate(zip(before, after)) if a != b}
    expected_metadata_offsets = set(find_expected_device_metadata_offsets(before))
    crc_offsets = {12, 13, len(before) - 2, len(before) - 1}
    assert changed <= expected_metadata_offsets | crc_offsets


def test_complex_fixture_patches_targets_and_preserves_advanced_records(
    tmp_path: Path, complex_fit_bytes: bytes
) -> None:
    source = tmp_path / "source.fit"
    output = tmp_path / "output.fit"
    source.write_bytes(complex_fit_bytes)

    result = convert_fit_device(source, output)

    assert is_fit_file(output) is True
    assert result.patched_field_count == 5

    after = output.read_bytes()
    assert struct.unpack_from("<H", after, _FIXTURE.file_id_manufacturer_offset)[0] == 1
    assert struct.unpack_from("<H", after, _FIXTURE.file_id_product_offset)[0] == 3570
    assert struct.unpack_from("<H", after, _FIXTURE.creator_manufacturer_offset)[0] == 1
    assert struct.unpack_from("<H", after, _FIXTURE.creator_product_offset)[0] == 3570

    # The record message (developer field), the compressed-timestamp record reusing
    # its definition, and the redefined local-2 sensor device_info record are all
    # untouched by patching -- verify their raw payload bytes are byte-identical.
    for start, end in _FIXTURE.preserved_ranges:
        assert complex_fit_bytes[start:end] == after[start:end]

    values = read_device_field_values(output)
    assert any(
        v.global_message_num == FILE_ID_MESG_NUM and v.field_num == 2 and v.value == 3570 for v in values
    )


def test_product_name_string_write_stays_inside_its_declared_field(
    tmp_path: Path, complex_fit_bytes: bytes
) -> None:
    """The string write path zero-fills the *entire* declared field. Prove that the
    rewrite is confined to the product_name field's own bytes: the target string plus
    a null terminator plus zero padding, with the surrounding record bytes untouched
    (the enclosing preservation test already asserts the global changed-byte set)."""
    source = tmp_path / "source.fit"
    output = tmp_path / "output.fit"
    source.write_bytes(complex_fit_bytes)

    convert_fit_device(source, output)

    start = _FIXTURE.file_id_product_name_offset
    end = start + _FIXTURE.file_id_product_name_size
    after = output.read_bytes()

    expected = b"Edge 1030 Plus\x00".ljust(_FIXTURE.file_id_product_name_size, b"\x00")
    assert after[start:end] == expected
    # The source deliberately padded past its null terminator with 0x2A bytes, so a
    # write that overran (or under-cleared) the field would be visible here.
    assert complex_fit_bytes[start:end] != expected

    values = read_device_field_values(output)
    assert any(
        v.global_message_num == FILE_ID_MESG_NUM
        and v.field_num == 8
        and v.value == "Edge 1030 Plus"
        and v.is_creator
        for v in values
    )


def test_convert_fit_device_supports_12_byte_header(tmp_path: Path) -> None:
    """12-byte headers carry no header CRC field, so conversion must succeed and
    report header_crc=None while still rewriting the file CRC."""
    file_def = definition(0, FILE_ID_MESG_NUM, [(1, 2, 0x84), (2, 2, 0x84)])
    file_data = data(0, struct.pack("<HH", 255, 999))
    source = tmp_path / "source12.fit"
    source.write_bytes(make_fit(file_def + file_data, header_size=12))
    output = tmp_path / "output12.fit"

    result = convert_fit_device(source, output)

    assert result.header_crc is None
    assert result.file_crc is not None
    assert result.patched_field_count == 2
    assert is_fit_file(output) is True
    assert output.read_bytes()[0] == 12

    values = {(v.global_message_num, v.field_num): v.value for v in read_device_field_values(output)}
    assert values[(FILE_ID_MESG_NUM, 1)] == 1
    assert values[(FILE_ID_MESG_NUM, 2)] == 3570


def test_truncated_definition_is_non_recoverable(tmp_path: Path) -> None:
    path = tmp_path / "truncated.fit"
    path.write_bytes(make_fit(bytes([0x40, 0x00, 0x00])))
    assert is_fit_file(path) is False


def test_convert_fit_device_rejects_truncated_definition(tmp_path: Path) -> None:
    source = tmp_path / "truncated.fit"
    source.write_bytes(make_fit(bytes([0x40, 0x00, 0x00])))
    output = tmp_path / "output.fit"

    with pytest.raises(FitFormatError):
        convert_fit_device(source, output)