"""Prepare the licensed daytime riverside ambience used by exploration."""

from __future__ import annotations

import argparse
import os
from pathlib import Path
import shutil
import subprocess


SOURCE_URL = (
    "https://pixabay.com/sound-effects/"
    "nature-stream-water-with-birds-459511/"
)
TARGET_DURATION_SECONDS = 32
SOURCE_OFFSET_SECONDS = 7
LOOP_CROSSFADE_SECONDS = 2


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser()
    parser.add_argument("--input", required=True, type=Path)
    parser.add_argument("--output", required=True, type=Path)
    return parser.parse_args()


def main() -> None:
    args = parse_args()
    source_path = args.input.resolve()
    output_path = args.output.resolve()
    if not source_path.is_file():
        raise FileNotFoundError(source_path)

    ffmpeg = os.environ.get("FFMPEG_PATH") or shutil.which("ffmpeg")
    if not ffmpeg:
        raise RuntimeError("ffmpeg is required to build the ambience track.")

    output_path.parent.mkdir(parents=True, exist_ok=True)
    loop_end = SOURCE_OFFSET_SECONDS + TARGET_DURATION_SECONDS
    head_end = SOURCE_OFFSET_SECONDS + LOOP_CROSSFADE_SECONDS
    body_start = head_end
    tail_start = loop_end
    tail_end = loop_end + LOOP_CROSSFADE_SECONDS
    filter_graph = (
        "[0:a]asplit=3[tailSource][headSource][bodySource];"
        f"[tailSource]atrim=start={tail_start}:end={tail_end},"
        f"asetpts=PTS-STARTPTS,afade=t=out:st=0:"
        f"d={LOOP_CROSSFADE_SECONDS}[tail];"
        f"[headSource]atrim=start={SOURCE_OFFSET_SECONDS}:end={head_end},"
        f"asetpts=PTS-STARTPTS,afade=t=in:st=0:"
        f"d={LOOP_CROSSFADE_SECONDS}[head];"
        "[tail][head]amix=inputs=2:normalize=0:duration=first[seam];"
        f"[bodySource]atrim=start={body_start}:end={loop_end},"
        "asetpts=PTS-STARTPTS[body];"
        "[seam][body]concat=n=2:v=0:a=1,"
        "loudnorm=I=-24:TP=-3:LRA=7[out]"
    )
    command = [
        ffmpeg,
        "-hide_banner",
        "-loglevel",
        "error",
        "-y",
        "-i",
        str(source_path),
        "-filter_complex",
        filter_graph,
        "-map",
        "[out]",
        "-ar",
        "44100",
        "-ac",
        "2",
        "-codec:a",
        "libmp3lame",
        "-b:a",
        "128k",
        "-metadata",
        "title=Riverside Village Day Ambience",
        "-metadata",
        "artist=loswin23",
        "-metadata",
        (
            "comment=Derived from Stream Water with Birds; "
            f"Pixabay Content License; {SOURCE_URL}"
        ),
        str(output_path),
    ]
    subprocess.run(command, check=True)

    if output_path.stat().st_size <= 0:
        raise RuntimeError(f"Empty ambience output: {output_path}")
    print(
        f"Built {output_path} ({TARGET_DURATION_SECONDS}s target, "
        f"{output_path.stat().st_size} bytes)."
    )


if __name__ == "__main__":
    main()