"""Image + video handling. Stills load directly; videos are sampled into frames
(ffmpeg) at the cadence FC sends — so a video becomes a bag of per-frame
instances, each with a timestamp."""
import io
import logging
import os
import signal
import subprocess
import tempfile
import time

from PIL import Image, ImageFile

from .throttle import PidReadMeter

log = logging.getLogger("fc_agent.media")

# Load slightly-truncated images (a few missing trailing bytes) instead of
# raising — matches the server embedder. These are common in scraped libraries
# and would otherwise fail the job 3× then error (operator-flagged 2026-06-30).
ImageFile.LOAD_TRUNCATED_IMAGES = True

# Disable PIL's decompression-bomb guard: this is a TRUSTED local library, not an
# untrusted upload surface, so a legitimately huge image (high-res scans/prints,
# 90M+ pixels) must load. The default 89M-pixel limit only WARNS, but PIL raises
# DecompressionBombError at 2× (~179M px) — which would fail those jobs outright
# (operator-flagged 2026-06-30, images of 90–95M px).
Image.MAX_IMAGE_PIXELS = None


def is_video(mime: str) -> bool:
    return bool(mime) and (mime.startswith("video/") or mime in {"image/gif"})


def _dhash(img: Image.Image, size: int = 8) -> int:
    """Difference hash: compare adjacent pixels of a (size+1 × size) grayscale
    thumbnail → a `size*size`-bit fingerprint. Cheap (64 comparisons on a 72-px
    thumbnail) and robust to scaling/compression noise — near-identical frames
    hash within a few bits, a real scene change moves many."""
    small = img.convert("L").resize((size + 1, size))
    px = list(small.getdata())
    bits = 0
    for row in range(size):
        base = row * (size + 1)
        for col in range(size):
            bits = (bits << 1) | int(px[base + col] > px[base + col + 1])
    return bits


def dedupe_frames(
    frames: list[tuple[float, Image.Image]], min_distance: int
) -> list[tuple[float, Image.Image]]:
    """Drop visually near-duplicate frames. A near-static video sampled into many
    frames re-runs the WHOLE detect→CCIP→SigLIP chain on ~identical frames — the
    dominant video load. Greedy perceptual-hash dedup: keep a frame only if its
    dHash differs from every already-kept frame by >= min_distance bits (Hamming),
    so a static run collapses to one frame while genuinely distinct scenes all
    survive. Order + timestamps preserved. CPU-only (64-bit int XORs), so it runs
    in the decode stage and spares the GPU the skipped frames entirely.

    min_distance is the coarseness dial: higher keeps more frames (safer for brief
    localized changes an 8×8 hash can miss), 0 disables. The first frame is always
    kept (nothing to compare against)."""
    if min_distance <= 0 or len(frames) <= 1:
        return frames
    kept: list[tuple[float, Image.Image]] = []
    hashes: list[int] = []
    for t, frame in frames:
        h = _dhash(frame)
        if all(bin(h ^ k).count("1") >= min_distance for k in hashes):
            hashes.append(h)
            kept.append((t, frame))
    return kept


def to_rgb(img: Image.Image) -> Image.Image:
    """RGB, flattening any transparency onto white first. A naive convert('RGB')
    on a palette-with-transparency image (common for character PNGs on a clear
    background) lets PIL guess the transparent pixels — usually black artifacts
    that bleed into the crop + the embedding (and the "should be converted to
    RGBA" warning). Compositing over white gives a clean, consistent background."""
    if img.mode in ("RGBA", "LA", "PA") or (
        img.mode == "P" and "transparency" in img.info
    ):
        img = img.convert("RGBA")
        bg = Image.new("RGBA", img.size, (255, 255, 255, 255))
        return Image.alpha_composite(bg, img).convert("RGB")
    return img.convert("RGB")


def load_image(data: bytes) -> Image.Image:
    return to_rgb(Image.open(io.BytesIO(data)))


# ffmpeg reconnect flags — resume a dropped HTTP transfer (a slow/contended media
# store can cut a long stream) instead of failing the whole job. Relies only on
# HTTP + Range, which every FC deployment serves → environment-agnostic.
_RECONNECT = [
    "-reconnect", "1", "-reconnect_streamed", "1",
    "-reconnect_on_network_error", "1", "-reconnect_delay_max", "5",
]


def _collect_frames(
    tmp: str, interval: float, cap: int
) -> list[tuple[float, Image.Image]]:
    out: list[tuple[float, Image.Image]] = []
    names = sorted(n for n in os.listdir(tmp) if n.startswith("f_"))
    for i, name in enumerate(names[:cap]):
        with Image.open(os.path.join(tmp, name)) as im:
            out.append((round(i * interval, 2), to_rgb(im)))
    return out


def _terminate(proc: subprocess.Popen) -> None:
    """Stop an ffmpeg cleanly, then hard-kill if it ignores SIGTERM."""
    try:
        # A bandwidth-paused (SIGSTOPped) process can't receive SIGTERM until it
        # resumes — always CONT first so termination is prompt, not queued.
        proc.send_signal(signal.SIGCONT)
    except OSError:
        pass
    proc.terminate()
    try:
        proc.wait(timeout=2)
    except subprocess.TimeoutExpired:
        proc.kill()
        try:
            proc.wait(timeout=2)
        except subprocess.TimeoutExpired:
            pass


def _pause(proc: subprocess.Popen, seconds: float, should_stop) -> bool:
    """SIGSTOP ffmpeg for ~`seconds` of bandwidth debt, staying responsive to
    Stop. While paused, the kernel socket buffer fills and TCP flow control
    stalls curator's send side — that's the throttle. SIGCONT is ALWAYS sent
    before returning. False = a Stop arrived mid-pause."""
    try:
        proc.send_signal(signal.SIGSTOP)
    except OSError:
        return True                     # already exited — nothing to pause
    try:
        end = time.monotonic() + seconds
        while (left := end - time.monotonic()) > 0:
            if should_stop and should_stop():
                return False
            time.sleep(min(0.5, left))
        return True
    finally:
        try:
            proc.send_signal(signal.SIGCONT)
        except OSError:
            pass


def sample_frames_from_url(
    url: str, interval_seconds: float, max_frames: int,
    *, headers: str = "", timeout: float = 1200.0, should_stop=None,
    governor=None,
) -> tuple[list[tuple[float, Image.Image]], str | None]:
    """Sample frames by pointing ffmpeg STRAIGHT at the media URL — it Range-reads
    only the video index + up to max_frames worth of content, so the agent never
    downloads the whole file (VR/4K originals run 800MB+ and would buffer ~1GB in
    RAM and get cut off mid-download). Reconnect flags resume a dropped transfer;
    the timeout is the per-video ceiling (a slow/reconnecting stream can otherwise
    run for minutes). `should_stop` is polled while ffmpeg runs so a Stop KILLS the
    subprocess at once — otherwise a downloader stuck in a long decode keeps the
    agent "working" long after Stop. `governor` (the worker's shared TokenBucket)
    meters ffmpeg's network reads from outside via /proc/<pid>/io and SIGSTOPs
    the process into budget, so video streaming honors the same aggregate
    bandwidth cap as still downloads.

    Returns (frames, reason): frames is empty on failure/stop/timeout, and
    `reason` then carries the SPECIFIC cause (ffmpeg's stderr tail / timeout) so
    the caller can put it in the job's error — a bare "no frames" hid a filter
    bug as "unprocessable" for weeks. None reason on success."""
    interval = max(0.5, float(interval_seconds or 4.0))
    cap = max(1, int(max_frames or 64))
    hdr = ["-headers", headers] if headers else []
    # select (NOT the fps filter): always keep the FIRST frame, then one per
    # `interval` seconds of timestamp. fps=1/N emits round(duration/N) frames,
    # which is ZERO for any clip shorter than ~N/2 seconds — a whole class of
    # short animation loops failed as "unprocessable" that way (operator-flagged
    # 2026-07-02: 0.5s/1.75s clips). scale=out_range=full converts limited-range
    # yuv420p to full range so the mjpeg (jpg) encoder accepts it at default
    # strictness instead of erroring on "non full-range YUV".
    vf = (
        f"select='isnan(prev_selected_t)+gte(t-prev_selected_t\\,{interval})',"
        "scale=out_range=full"
    )
    with tempfile.TemporaryDirectory() as tmp:
        pattern = os.path.join(tmp, "f_%05d.jpg")
        cmd = ["ffmpeg", "-nostdin", "-loglevel", "error", *_RECONNECT, *hdr,
               "-i", url, "-vf", vf, "-fps_mode", "vfr",
               "-frames:v", str(cap), "-q:v", "3", pattern]
        # ffmpeg's stderr goes to a file (not a PIPE, which could fill and
        # deadlock; not DEVNULL, which is how a filter bug hid as "unprocessable"
        # for weeks) — on failure its tail is logged so the operator can see WHY.
        errpath = os.path.join(tmp, "stderr.txt")
        try:
            with open(errpath, "wb") as errf:
                proc = subprocess.Popen(
                    cmd, stdin=subprocess.DEVNULL,
                    stdout=subprocess.DEVNULL, stderr=errf,
                )
                meter = PidReadMeter(proc.pid) if governor is not None else None
                # Poll rather than block, so a Stop (or the per-video timeout) can
                # kill a slow/wedged ffmpeg promptly instead of waiting it out.
                start = time.monotonic()
                while True:
                    try:
                        proc.wait(timeout=0.5)
                        break
                    except subprocess.TimeoutExpired:
                        stopped = should_stop and should_stop()
                        if stopped or (time.monotonic() - start > timeout):
                            _terminate(proc)
                            if stopped:
                                return [], "stopped"
                            log.warning("ffmpeg timed out after %.0fs: %s",
                                        timeout, url)
                            return [], f"ffmpeg timed out after {timeout:.0f}s"
                        if meter is not None:
                            read = meter.delta()
                            if read is None:      # /proc gone → stop governing
                                meter = None
                            elif (debt := governor.charge(read)) > 0:
                                # Over budget: pause ffmpeg until the bucket
                                # recovers. Pause time counts toward `timeout`
                                # (it stays the wedge backstop either way).
                                if not _pause(proc, debt, should_stop):
                                    _terminate(proc)
                                    return [], "stopped"
        except (OSError, ValueError) as exc:
            return [], f"ffmpeg not runnable: {exc}"
        frames = _collect_frames(tmp, interval, cap)
        if not frames:
            reason = f"ffmpeg exit {proc.returncode}: {_tail(errpath)}"
            log.warning("ffmpeg produced no frames for %s — %s", url, reason)
            return [], reason
        return frames, None


def _tail(path: str, limit: int = 300) -> str:
    """Last `limit` chars of a (stderr) file, flattened — for failure logs."""
    try:
        with open(path, "rb") as f:
            f.seek(0, os.SEEK_END)
            f.seek(max(0, f.tell() - limit))
            return f.read().decode("utf-8", "replace").replace("\n", " ").strip()
    except OSError:
        return "?"
