"""Stitch chunk MP3s into one audiobook and verify it.

All chunks share edge-tts codec parameters (24 kHz MP3), so a stream-copy
concat (-c copy) is lossless and fast. Verification uses astats RMS at
several timestamps to catch dead/silent sections early.
"""
import json
import os
import subprocess
import sys


def stitch(audio_dir: str, out_path: str, verify: bool = True) -> dict:
    files = sorted(f for f in os.listdir(audio_dir) if f.endswith(".mp3"))
    if not files:
        raise SystemExit(f"no mp3 files in {audio_dir}")

    # the list file sits NEXT TO the chunks; the concat demuxer resolves
    # names relative to the list file's directory and does NOT understand
    # JSON-style double quotes (it treats them as part of the filename)
    listfile = os.path.join(audio_dir, "_concat_list.txt")
    with open(listfile, "w") as f:
        for fn in files:
            f.write(f"file '{fn}'\n")

    raw = out_path + ".raw.mp3"
    if os.path.exists(raw):
        os.remove(raw)
    subprocess.run(
        ["ffmpeg", "-y", "-f", "concat", "-safe", "0", "-i", listfile, "-c", "copy", raw],
        check=True,
    )
    os.replace(raw, out_path)
    os.remove(listfile)

    info = {"out": out_path, "chunks": len(files)}

    if verify:
        r = subprocess.run(
            ["ffprobe", "-v", "error", "-show_entries", "format=duration",
             "-of", "default=nw=1:nk=1", out_path],
            capture_output=True, text=True, check=True,
        )
        dur = float(r.stdout.strip())
        info["duration_s"] = dur
        info["size_mb"] = round(os.path.getsize(out_path) / 1e6, 1)
        # spot-check RMS at a few positions
        checks = []
        for frac in (0.05, 0.3, 0.6, 0.9):
            t = dur * frac
            a = subprocess.run(
                ["ffmpeg", "-hide_banner", "-ss", f"{t:.1f}", "-t", "4", "-i", out_path,
                 "-af", "astats=metadata=1", "-f", "null", "-"],
                capture_output=True, text=True,
            )
            rms = None
            for line in a.stderr.splitlines():
                if "RMS level dB:" in line:
                    try:
                        rms = float(line.split("RMS level dB:")[1].strip())
                    except ValueError:
                        pass
                    break
            checks.append((round(frac, 2), t and round(t), rms))
        info["rms_checks"] = checks
        silent = [c for c in checks if c[2] is not None and c[2] < -50]
        info["silent_sections"] = len(silent)
    return info


def main(audio_dir, out_path):
    info = stitch(audio_dir, out_path)
    print(json.dumps(info, indent=1))
    if info.get("silent_sections"):
        print("WARNING: silent sections detected; check the RMS checks above")
        sys.exit(1)


if __name__ == "__main__":
    main(sys.argv[1], sys.argv[2])