"""The moving map: what is drawn, and whether the file is really a GIF.

A picture is checked here the way a picture has to be -- by reading the pixels
back -- and the file by taking it apart with a reader written from the GIF
specification rather than from the encoder in the program.  An encoder checked
against itself is not checked.
"""
import struct
import subprocess
from pathlib import Path

import numpy as np
import pytest

from bandsaunter import flightmap as fm
from bandsaunter.flightlog import Fix, Track


# ---------------------------------------------------------------------------
# A GIF reader, built from the specification
# ---------------------------------------------------------------------------

def lzw_decode(data: bytes, code_bits: int) -> bytes:
    """GIF's LZW, the reading side, written from the standard."""
    clear, end = 1 << code_bits, (1 << code_bits) + 1
    table = {i: bytes([i]) for i in range(clear)}
    width = code_bits + 1
    counter = end + 1                 # counts codes read, not entries added
    out = bytearray()
    previous = None
    value = held = at = 0
    while True:
        while held < width and at < len(data):
            value |= data[at] << held
            held += 8
            at += 1
        if held < width:
            break
        code = value & ((1 << width) - 1)
        value >>= width
        held -= width
        if code == clear:
            table = {i: bytes([i]) for i in range(clear)}
            width, counter, previous = code_bits + 1, end + 1, None
            continue
        if code == end:
            break
        # The width goes up as codes are read rather than as the table is
        # filled: the decoder builds its table one code behind the encoder,
        # and counting entries instead would widen the codes one too late.
        read_at = counter
        if counter < 4096:
            counter += 1
            if counter > (1 << width) and width < 12:
                width += 1
        if code in table:
            entry = table[code]
        elif previous is not None:
            entry = previous + previous[:1]
        else:
            raise ValueError(f"code {code} before anything defined it")
        out += entry
        if previous is not None and read_at - 1 < 4096:
            table[read_at - 1] = previous + entry[:1]
        previous = entry
    return bytes(out)


def read_gif(path: Path) -> dict:
    """Take a GIF apart: the screen, the palette and every frame in it."""
    raw = Path(path).read_bytes()
    assert raw[:6] == b"GIF89a", "not a GIF89a"
    width, height, packed, _bg, _aspect = struct.unpack("<HHBBB", raw[6:13])
    at = 13
    table_size = 2 ** ((packed & 0x07) + 1)
    assert packed & 0x80, "no global colour table"
    palette = np.frombuffer(raw[at:at + table_size * 3],
                            dtype=np.uint8).reshape(-1, 3)
    at += table_size * 3

    frames, loops, control = [], False, {}
    while at < len(raw):
        block = raw[at]
        if block == 0x3B:                       # trailer
            break
        if block == 0x21:                       # extension
            label = raw[at + 1]
            at += 2
            body = b""
            while raw[at]:
                size = raw[at]
                body += raw[at + 1:at + 1 + size]
                at += size + 1
            at += 1
            if label == 0xF9:
                control = {"disposal": (body[0] >> 2) & 0x07,
                           "transparent": body[3] if body[0] & 1 else None,
                           "delay": struct.unpack("<H", body[1:3])[0]}
            elif label == 0xFF and body.startswith(b"NETSCAPE2.0"):
                loops = True
            continue
        if block == 0x2C:                       # image descriptor
            left, top, w, h, flags = struct.unpack("<HHHHB", raw[at + 1:at + 10])
            at += 10
            assert not flags & 0x80, "a local colour table was not expected"
            code_bits = raw[at]
            at += 1
            data = b""
            while raw[at]:
                size = raw[at]
                data += raw[at + 1:at + 1 + size]
                at += size + 1
            at += 1
            pixels = np.frombuffer(lzw_decode(data, code_bits),
                                   dtype=np.uint8)
            assert pixels.size == w * h, f"{pixels.size} pixels for {w}x{h}"
            frames.append({"left": left, "top": top, "width": w, "height": h,
                           "pixels": pixels.reshape(h, w), **control})
            continue
        raise ValueError(f"unknown block {block:#x} at {at}")
    return {"width": width, "height": height, "palette": palette,
            "frames": frames, "loops": loops}


def played(gif: dict) -> list[np.ndarray]:
    """Every frame as it appears on the screen, patches laid over each other."""
    canvas = np.zeros((gif["height"], gif["width"]), dtype=np.uint8)
    out = []
    for frame in gif["frames"]:
        patch = frame["pixels"]
        top, left = frame["top"], frame["left"]
        area = canvas[top:top + frame["height"], left:left + frame["width"]]
        if frame.get("transparent") is None:
            area[:, :] = patch
        else:
            keep = patch != frame["transparent"]
            area[keep] = patch[keep]
        out.append(canvas.copy())
    return out


# ---------------------------------------------------------------------------
# Tracks to draw
# ---------------------------------------------------------------------------

def straight(icao="4CA1FA", callsign="RYR1234", lat=51.0, lon=-1.0,
             heading=90.0, speed=480.0, altitude=35_000, seconds=600.0,
             every=20.0, start=1_000_000.0) -> Track:
    """One aircraft flying a straight line at a steady speed."""
    from bandsaunter.flightlog import move

    fixes = []
    when = 0.0
    while when <= seconds:
        step = speed * when / 3600.0
        here = move(lat, lon, heading, step)
        fixes.append(Fix(at=start + when, latitude=here[0], longitude=here[1],
                         altitude_ft=altitude, ground_speed_kt=speed,
                         track_deg=heading))
        when += every
    return Track(icao=icao, callsign=callsign, fixes=fixes,
                 frames=len(fixes) * 3, first_seen=start,
                 last_seen=start + seconds)


def two_aircraft() -> list[Track]:
    return [straight(),
            straight(icao="A835AF", callsign="UAL1902", lat=51.4, lon=-0.6,
                     heading=250.0, speed=300.0, altitude=9_000)]


# ---------------------------------------------------------------------------
# Colours and geometry
# ---------------------------------------------------------------------------

def test_the_palette_is_a_full_table_with_room_for_transparency():
    assert fm.PALETTE.shape == (256, 3)
    assert fm.TRANSPARENT == 255


def test_altitude_becomes_a_colour_that_climbs_with_it():
    steps = [fm.altitude_step(ft) for ft in (0, 5_000, 20_000, 35_000, 45_000)]
    assert steps == sorted(steps)
    assert steps[0] == 0 and steps[-1] == fm.RAMP_STEPS - 1
    assert fm.altitude_step(90_000) == fm.RAMP_STEPS - 1      # clamped


def test_the_map_holds_every_position_that_was_reported():
    tracks = two_aircraft()
    view = fm.fit(tracks, width=800)
    for track in tracks:
        for fix in track.fixes:
            assert view.inside(fix.latitude, fix.longitude)
            x, y = view.xy(fix.latitude, fix.longitude)
            assert view.left <= x < view.left + view.width
            assert view.top <= y < view.top + view.height


def test_a_mile_across_is_a_mile_up_the_picture():
    """Longitude is squeezed by the cosine, or everything at fifty degrees
    north comes out stretched half as wide again."""
    view = fm.fit(two_aircraft(), width=800)
    per_nm_x = view.width / view.width_nm
    tall_nm = (view.north - view.south) * 60.0
    per_nm_y = view.height / tall_nm
    assert per_nm_x == pytest.approx(per_nm_y, rel=0.02)


def test_one_aircraft_heard_once_still_gets_a_map():
    track = Track(icao="4CA1FA", fixes=[Fix(at=1.0, latitude=51.0,
                                            longitude=-1.0)])
    view = fm.fit([track], width=400)
    assert view is not None and view.north > view.south


def test_nothing_to_draw_draws_nothing(tmp_path):
    assert fm.fit([Track(icao="4CA1FA")]) is None
    assert fm.animate([Track(icao="4CA1FA")], tmp_path / "x.gif") is None


# ---------------------------------------------------------------------------
# What ends up on the picture
# ---------------------------------------------------------------------------

def test_the_background_has_a_grid_a_scale_and_a_title():
    view = fm.fit(two_aircraft(), width=800)
    base = fm.background(view, title="6 AIRCRAFT 2026-09-03")
    assert (base == fm.GRID).sum() > 200          # the graticule and the border
    assert (base == fm.INK).sum() > 40            # the title
    assert (base == fm.DIM).sum() > 40            # scale bar and axis labels
    assert (base == fm.RAMP + fm.RAMP_STEPS - 1).any()   # the key


def test_an_aircraft_is_drawn_where_it_was_at_that_moment():
    tracks = [straight()]
    view = fm.fit(tracks, width=800)
    base = fm.background(view)
    when = tracks[0].first_seen + 300.0
    frame = fm.render_frame(base, view, tracks, when)
    fix = tracks[0].at(when)
    x, y = view.xy(fix.latitude, fix.longitude)
    patch = frame[y - 6:y + 7, x - 6:x + 7]
    assert (patch >= fm.RAMP).any() and (patch < fm.TRAIL).any()


def test_the_aircraft_moves_between_frames_and_leaves_a_trail():
    tracks = [straight()]
    view = fm.fit(tracks, width=800)
    base = fm.background(view)
    early = fm.render_frame(base, view, tracks, tracks[0].first_seen + 60)
    late = fm.render_frame(base, view, tracks, tracks[0].first_seen + 540)
    assert not np.array_equal(early, late)
    trail_early = (early >= fm.TRAIL) & (early < fm.TRANSPARENT)
    trail_late = (late >= fm.TRAIL) & (late < fm.TRANSPARENT)
    assert trail_late.sum() > trail_early.sum()


def test_an_aircraft_is_not_drawn_before_it_was_ever_heard():
    tracks = [straight()]
    view = fm.fit(tracks, width=800)
    base = fm.background(view)
    frame = fm.render_frame(base, view, tracks, tracks[0].first_seen - 10)
    assert np.array_equal(frame, base)


def test_an_aircraft_long_gone_is_not_drawn_at_a_guessed_position():
    tracks = [straight()]
    view = fm.fit(tracks, width=800)
    base = fm.background(view)
    frame = fm.render_frame(base, view, tracks,
                            tracks[0].last_seen + 900, stale=300)
    assert np.array_equal(frame, base)


def test_the_clock_and_the_count_are_drawn_over_the_map():
    tracks = two_aircraft()
    view = fm.fit(tracks, width=800)
    base = fm.background(view)
    frame = fm.render_frame(base, view, tracks, tracks[0].first_seen + 60,
                            clock="19:45:02")
    assert (frame == fm.PANEL).any()
    assert (frame == fm.INK).sum() > (base == fm.INK).sum()


# ---------------------------------------------------------------------------
# The file
# ---------------------------------------------------------------------------

def test_the_lzw_stream_reads_back_as_what_went_in():
    for body in (b"\x00" * 300, bytes(range(256)) * 3,
                 bytes([7, 7, 7, 8, 9, 7, 7, 8]) * 40):
        assert lzw_decode(fm._lzw(body, 8), 8) == body


def test_a_long_stream_survives_the_table_filling_up():
    rng = np.random.default_rng(4)
    body = rng.integers(0, 60, size=200_000, dtype=np.uint8).tobytes()
    assert lzw_decode(fm._lzw(body, 8), 8) == body


def test_the_animation_is_a_gif_that_loops(tmp_path):
    out = fm.animate(two_aircraft(), tmp_path / "flights.gif", fps=10,
                     seconds=4, width=480)
    assert out is not None and out.path.exists()
    gif = read_gif(out.path)
    assert gif["loops"], "a map that plays once and stops"
    assert len(gif["frames"]) == out.frames
    assert (gif["width"], gif["height"]) == (out.width, out.height)
    assert gif["frames"][0]["delay"] == 10        # hundredths, so 10 a second


def test_only_what_changed_is_written_after_the_first_frame(tmp_path):
    out = fm.animate(two_aircraft(), tmp_path / "flights.gif", fps=8,
                     seconds=4, width=480)
    gif = read_gif(out.path)
    first = gif["frames"][0]
    assert (first["width"], first["height"]) == (out.width, out.height)
    later = gif["frames"][1:]
    assert later, "one frame is not an animation"
    assert all(f["width"] * f["height"] < out.width * out.height for f in later)
    assert all(f["transparent"] is not None for f in later)


def test_the_frames_played_back_show_the_aircraft_moving(tmp_path):
    tracks = [straight()]
    out = fm.animate(tracks, tmp_path / "one.gif", fps=8, seconds=4, width=480)
    screens = played(read_gif(out.path))
    assert len(screens) == out.frames

    def where(frame):
        lit = np.argwhere((frame >= fm.RAMP) & (frame < fm.TRAIL))
        return lit.mean(axis=0)

    start, end = where(screens[1]), where(screens[-1])
    assert abs(end[1] - start[1]) > 20        # it went east across the picture
    for frame in screens:
        assert frame.shape == (out.height, out.width)


def test_the_animation_says_how_much_flying_it_covers(tmp_path):
    tracks = two_aircraft()
    out = fm.animate(tracks, tmp_path / "flights.gif", fps=10, seconds=5,
                     width=400)
    assert out.covers == pytest.approx(600.0, abs=1.0)
    played_for = out.frames / out.fps
    assert played_for == pytest.approx(5.0, rel=0.3)
    assert out.speed == pytest.approx(out.covers / played_for, rel=0.05)
    assert "aircraft" in out.summary()


def test_asking_for_a_speed_gives_that_speed(tmp_path):
    out = fm.animate(two_aircraft(), tmp_path / "flights.gif", fps=10,
                     speed=60.0, width=400)
    assert out.speed == pytest.approx(60.0, rel=0.1)
    assert out.frames == pytest.approx(600 / 60 * 10, abs=2)


def test_a_still_picture_is_a_png_of_the_whole_evening(tmp_path):
    from bandsaunter.images import PNG_SIGNATURE

    out = fm.animate(two_aircraft(), tmp_path / "flights.png", width=400)
    assert out.kind == "png"
    assert out.path.read_bytes()[:8] == PNG_SIGNATURE


def test_pillow_agrees_that_it_is_an_animation(tmp_path):
    """Not a dependency; when it happens to be installed it is a second
    opinion from a decoder nobody here wrote."""
    Image = pytest.importorskip("PIL.Image")
    out = fm.animate(two_aircraft(), tmp_path / "flights.gif", fps=10,
                     seconds=3, width=400)
    with Image.open(out.path) as picture:
        assert picture.n_frames == out.frames
        assert picture.size == (out.width, out.height)
        picture.seek(0)
        first = np.array(picture.convert("RGB"))
        picture.seek(picture.n_frames - 1)
        last = np.array(picture.convert("RGB"))
    assert not np.array_equal(first, last)


@pytest.mark.skipif(not fm.ffmpeg_available(), reason="ffmpeg is not installed")
def test_a_video_can_be_written_where_ffmpeg_exists(tmp_path):
    out = fm.animate(two_aircraft(), tmp_path / "flights.mp4", fps=10,
                     seconds=3, width=400)
    assert out.kind == "mp4" and out.path.stat().st_size > 1000
    probe = subprocess.run(["ffprobe", "-v", "error", "-select_streams", "v:0",
                            "-show_entries", "stream=width,height",
                            "-of", "csv=p=0", str(out.path)],
                           capture_output=True, text=True)
    if probe.returncode == 0:
        assert probe.stdout.strip() == f"{out.width},{out.height}"


def test_the_picture_is_an_even_number_of_pixels_across(tmp_path):
    """Video encoders refuse an odd width, and it costs nothing to be even."""
    for width in (401, 402, 555):
        view = fm.fit(two_aircraft(), width=width)
        w, h = fm.canvas_size(view)
        assert w % 2 == 0 and h % 2 == 0


# ---------------------------------------------------------------------------
# Speeds in whatever the user reads
# ---------------------------------------------------------------------------

def _label_text(unit: str, width: int = 700) -> np.ndarray:
    """Draw one aircraft and hand back the pixels its label was written in."""
    tracks = [straight(speed=480.0)]
    view = fm.fit(tracks, width=width)
    base = fm.background(view, unit=unit)
    return fm.render_frame(base, view, tracks, tracks[0].first_seen + 120,
                           unit=unit)


def _has_text(frame: np.ndarray, text: str) -> bool:
    """Whether a string was stamped anywhere in the frame, found by drawing
    it again and looking for the same pattern."""
    from bandsaunter.images import GLYPH_H, draw_text, text_width

    stamp = np.zeros((GLYPH_H, max(1, text_width(text))), dtype=np.uint8)
    draw_text(stamp, 0, 0, text, 1)
    rows, cols = stamp.shape
    wanted = stamp.astype(bool)
    if not wanted.any():
        return False
    for y in range(frame.shape[0] - rows):
        for x in range(frame.shape[1] - cols):
            patch = frame[y:y + rows, x:x + cols]
            if np.all(patch[wanted] != fm.BG) and \
                    np.all(patch[~wanted] == patch[~wanted][0]):
                return True
    return False


@pytest.mark.parametrize("unit,label", [("knots", "KT"), ("mph", "MPH"),
                                        ("kph", "KM/H")])
def test_the_speed_on_the_map_carries_its_unit(unit, label):
    """A bare 480 beside an aircraft is three different speeds depending on
    who is reading it."""
    assert _has_text(_label_text(unit), label)


def test_the_number_beside_it_is_converted():
    assert _has_text(_label_text("knots"), "480KT")
    assert _has_text(_label_text("mph"), "552MPH")
    assert _has_text(_label_text("kph"), "889KM/H")


@pytest.mark.parametrize("unit,label", [("knots", "NM"), ("mph", "MI"),
                                        ("kph", "KM")])
def test_the_scale_bar_uses_the_same_kind_of_mile(unit, label):
    """Miles an hour beside a scale in nautical miles is two different miles
    on one picture."""
    view = fm.fit(two_aircraft(), width=700)
    assert _has_text(fm.background(view, unit=unit), label)


def test_the_animation_takes_the_unit_through_to_the_file(tmp_path):
    out = fm.animate(two_aircraft(), tmp_path / "mph.png", width=500,
                     unit="mph")
    assert out is not None and out.path.is_file()