"""multi-segment-derkachi — ≥3 disjoint blackout windows, NO spoof (FT-P-08).

Generates a blackout-only fixture: ``n_segments`` disjoint all-black
windows distributed across the Derkachi flight, with no paired GPS spoof.
Drives the satellite-reference re-localization positive path; explicitly
NOT the security failsafe path (that's FT-N-04 / NFT-RES-04, owned by the
blackout_spoof injector).

Constraints (AC-5):

* ≥3 disjoint blackout windows.
* Consecutive windows separated by ≥30 s of normal frames.
* Total blackout coverage ≤25 % of the source duration.

Window placement is deterministic-positional (anchored at fixed fractions
of the source duration) rather than random — that keeps the test's
"window N starts at second X" assertion stable. The seed is still
accepted for API symmetry with the other injectors but currently does
not affect the output (documented in the dataclass docstring); future
NFT-RES-04 variants may use it to perturb segment lengths.

Public-boundary discipline: this module does NOT import any
``src/gps_denied_onboard`` symbol.
"""

from __future__ import annotations

import argparse
import csv
import io
import json
import logging
import shutil
import sys
from dataclasses import dataclass
from pathlib import Path

from ._common import tmpfs_root

logger = logging.getLogger(__name__)

# Constraint constants (AC-5 of AZ-408).
_MIN_INTER_SEGMENT_GAP_SECONDS = 30.0
_MAX_TOTAL_BLACKOUT_FRACTION = 0.25
_DEFAULT_SRC_FPS = 30.0
_TILE_W = 256
_TILE_H = 256


@dataclass(frozen=True)
class MultiSegmentPlan:
    """Configuration for the multi-segment-derkachi fixture.

    AZ-408 replaces the AZ-406 scaffold dataclass; the previous shape
    (just ``n_segments`` + ``gap_seconds``) is extended to include the
    inputs the build path needs. ``seed`` is accepted for symmetry but
    is not currently consumed — segment placement is deterministic-positional.
    """

    source_frames_dir: Path
    n_segments: int = 3
    segment_seconds: float = 12.0
    source_fps: float = _DEFAULT_SRC_FPS
    seed: int = 0


@dataclass(frozen=True)
class SegmentWindow:
    start_ms: int
    end_ms: int
    first_frame_idx: int
    last_frame_idx: int


@dataclass(frozen=True)
class MultiSegmentReport:
    out_root: Path
    segments: list[SegmentWindow]
    source_duration_ms: int
    total_blackout_frames: int
    total_blackout_fraction: float


def _plan_segments(plan: MultiSegmentPlan, total_frames: int) -> list[SegmentWindow]:
    """Compute the segment windows that satisfy AC-5.

    Strategy: place ``n_segments`` windows uniformly across the source
    duration, each window starts at ``(i+1) / (n+1)`` of the duration
    (so first window is not at t=0 and last window is not at t=END).
    Then validate the gap constraint + the total-coverage constraint
    and raise if the plan is infeasible (rather than silently truncating).
    """
    if plan.n_segments < 3:
        raise ValueError(f"n_segments must be ≥3 (AC-5); got {plan.n_segments}")
    if plan.segment_seconds <= 0:
        raise ValueError(f"segment_seconds must be > 0; got {plan.segment_seconds}")

    src_duration_s = total_frames / plan.source_fps
    src_duration_ms = int(round(src_duration_s * 1000.0))
    seg_ms = int(round(plan.segment_seconds * 1000.0))

    segments: list[SegmentWindow] = []
    for i in range(plan.n_segments):
        anchor_s = src_duration_s * (i + 1) / (plan.n_segments + 1)
        start_ms = int(round(anchor_s * 1000.0))
        end_ms = min(start_ms + seg_ms, src_duration_ms)
        first_frame = int(round(start_ms / 1000.0 * plan.source_fps))
        last_frame = int(round(end_ms / 1000.0 * plan.source_fps))
        segments.append(
            SegmentWindow(
                start_ms=start_ms,
                end_ms=end_ms,
                first_frame_idx=first_frame,
                last_frame_idx=min(last_frame, total_frames),
            )
        )

    # AC-5 gap check.
    for prev, nxt in zip(segments, segments[1:]):
        gap_ms = nxt.start_ms - prev.end_ms
        if gap_ms < _MIN_INTER_SEGMENT_GAP_SECONDS * 1000:
            raise ValueError(
                f"infeasible plan: gap between segment ending at {prev.end_ms} ms "
                f"and segment starting at {nxt.start_ms} ms is {gap_ms} ms < "
                f"{int(_MIN_INTER_SEGMENT_GAP_SECONDS * 1000)} ms (AC-5). Reduce "
                "segment_seconds or n_segments, or use a longer source."
            )

    # AC-5 coverage check.
    total_blackout_ms = sum(s.end_ms - s.start_ms for s in segments)
    fraction = total_blackout_ms / max(1, src_duration_ms)
    if fraction > _MAX_TOTAL_BLACKOUT_FRACTION:
        raise ValueError(
            f"infeasible plan: total blackout fraction is {fraction:.3f} "
            f"> {_MAX_TOTAL_BLACKOUT_FRACTION:.2f} (AC-5). Reduce "
            "segment_seconds or n_segments."
        )

    return segments


def _black_jpeg_bytes() -> bytes:
    from PIL import Image  # noqa: PLC0415 — heavy import, deferred

    img = Image.new("RGB", (_TILE_W, _TILE_H), color=(0, 0, 0))
    buf = io.BytesIO()
    img.save(
        buf,
        format="JPEG",
        quality=85,
        optimize=False,
        progressive=False,
        subsampling=2,
    )
    return buf.getvalue()


def build(plan: MultiSegmentPlan, out_root: Path) -> MultiSegmentReport:
    """Generate the multi-segment-derkachi fixture under ``out_root``."""
    if out_root.exists():
        shutil.rmtree(out_root)
    (out_root / "frames").mkdir(parents=True)

    src_dir = plan.source_frames_dir
    if not src_dir.is_dir():
        raise FileNotFoundError(f"source frames directory not found: {src_dir}")
    frames = sorted(src_dir.glob("AD*.jpg"))
    if not frames:
        raise FileNotFoundError(f"no AD*.jpg frames under {src_dir}")

    total_frames = len(frames)
    src_duration_ms = int(round(total_frames / plan.source_fps * 1000.0))
    segments = _plan_segments(plan, total_frames)

    black_jpeg = _black_jpeg_bytes()
    manifest_rows: list[dict] = []
    blackout_set: set[int] = set()
    for seg_idx, seg in enumerate(segments):
        for f in range(seg.first_frame_idx, min(seg.last_frame_idx, total_frames)):
            blackout_set.add(f)
            manifest_rows.append(
                {
                    "frame_idx": f,
                    "src_jpeg_path": frames[f].name,
                    "segment_idx": seg_idx,
                    "segment_start_ms": seg.start_ms,
                    "segment_end_ms": seg.end_ms,
                }
            )

    for frame_idx, frame_path in enumerate(frames):
        out_path = out_root / "frames" / frame_path.name
        if frame_idx in blackout_set:
            out_path.write_bytes(black_jpeg)
        else:
            shutil.copy2(frame_path, out_path)

    _write_schedule(out_root, segments)
    _write_manifest(out_root, manifest_rows)

    total_blackout = sum(s.last_frame_idx - s.first_frame_idx for s in segments)
    fraction = (sum(s.end_ms - s.start_ms for s in segments)) / max(1, src_duration_ms)
    report = MultiSegmentReport(
        out_root=out_root,
        segments=segments,
        source_duration_ms=src_duration_ms,
        total_blackout_frames=total_blackout,
        total_blackout_fraction=fraction,
    )
    _write_summary(out_root, report)
    return report


def _write_schedule(out_root: Path, segments: list[SegmentWindow]) -> None:
    payload = {
        "segments": [
            {
                "start_ms": s.start_ms,
                "end_ms": s.end_ms,
                "first_frame_idx": s.first_frame_idx,
                "last_frame_idx": s.last_frame_idx,
            }
            for s in segments
        ]
    }
    (out_root / "schedule.json").write_text(
        json.dumps(payload, sort_keys=True, indent=2) + "\n"
    )


def _write_manifest(out_root: Path, rows: list[dict]) -> None:
    manifest = out_root / "manifest.csv"
    with manifest.open("w", newline="") as fp:
        writer = csv.DictWriter(
            fp,
            fieldnames=["frame_idx", "src_jpeg_path", "segment_idx", "segment_start_ms", "segment_end_ms"],
            lineterminator="\n",
        )
        writer.writeheader()
        for row in sorted(rows, key=lambda r: (r["segment_idx"], r["frame_idx"])):
            writer.writerow(row)


def _write_summary(out_root: Path, report: MultiSegmentReport) -> None:
    payload = {
        "scenario": "multi-segment-derkachi",
        "n_segments": len(report.segments),
        "source_duration_ms": report.source_duration_ms,
        "total_blackout_frames": report.total_blackout_frames,
        "total_blackout_fraction": round(report.total_blackout_fraction, 6),
        "segments": [
            {"start_ms": s.start_ms, "end_ms": s.end_ms} for s in report.segments
        ],
    }
    (out_root / "summary.json").write_text(
        json.dumps(payload, sort_keys=True, indent=2) + "\n"
    )


def main(argv: list[str] | None = None) -> int:
    parser = argparse.ArgumentParser(description="Multi-segment blackout (FT-P-08)")
    parser.add_argument("--source-frames", type=Path, required=True)
    parser.add_argument("--n-segments", type=int, default=3)
    parser.add_argument("--segment-seconds", type=float, default=12.0)
    parser.add_argument("--source-fps", type=float, default=_DEFAULT_SRC_FPS)
    parser.add_argument("--seed", type=int, default=0)
    parser.add_argument(
        "--out-root",
        type=Path,
        default=None,
        help="Output dir. If omitted, /tmp/<run_id>/multi-segment/.",
    )
    parser.add_argument("--run-id", default="local")
    parser.add_argument("--quiet", action="store_true")
    args = parser.parse_args(argv)

    logging.basicConfig(
        level=logging.WARNING if args.quiet else logging.INFO,
        format="%(asctime)s %(levelname)s %(name)s %(message)s",
    )

    out_root = args.out_root or tmpfs_root(args.run_id, "multi-segment")
    plan = MultiSegmentPlan(
        source_frames_dir=args.source_frames,
        n_segments=args.n_segments,
        segment_seconds=args.segment_seconds,
        source_fps=args.source_fps,
        seed=args.seed,
    )
    report = build(plan, out_root)
    summary = {
        "scenario": "multi-segment-derkachi",
        "out_root": str(report.out_root),
        "n_segments": len(report.segments),
        "source_duration_ms": report.source_duration_ms,
        "total_blackout_frames": report.total_blackout_frames,
        "total_blackout_fraction": round(report.total_blackout_fraction, 6),
    }
    json.dump(summary, sys.stdout, sort_keys=True, indent=2)
    sys.stdout.write("\n")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())