#!/usr/bin/env bash
set -euo pipefail

# trim_mp3_silence_copy.sh
#
# Usage:
#   ./trim_mp3_silence_copy.sh input.mp3 [output.mp3]
#
# Env vars you can override:
#   NOISE_DB   (default: -40dB)  threshold for silencedetect
#   MIN_DUR    (default: 0.5)    minimum silence duration to consider (seconds)

in="${1:-}"
out="${2:-}"

if [[ -z "${in}" ]]; then
  echo "Usage: $0 input.mp3 [output.mp3]" >&2
  exit 1
fi

if [[ ! -f "${in}" ]]; then
  echo "Input file not found: ${in}" >&2
  exit 1
fi

if [[ -z "${out}" ]]; then
  base="${in%.*}"
  out="${base}.trimmed.mp3"
fi

NOISE_DB="${NOISE_DB:--40dB}"
MIN_DUR="${MIN_DUR:-0.5}"

# Get full duration (seconds, as float)
duration="$(ffprobe -v error -show_entries format=duration -of default=nw=1:nk=1 "$in")"

# Run silencedetect and capture lines
sd="$(
  ffmpeg -hide_banner -nostats -i "$in" \
    -af "silencedetect=noise=${NOISE_DB}:d=${MIN_DUR}" \
    -f null - 2>&1 | grep -E 'silence_(start|end):' || true
)"

if [[ -z "$sd" ]]; then
  echo "No silence detected (noise=${NOISE_DB}, d=${MIN_DUR}). Copying original -> ${out}" >&2
  cp -f -- "$in" "$out"
  exit 0
fi

# First silence_end => start of audio
start_keep="$(awk '/silence_end:/ {print $NF; exit}' <<<"$sd")"

# Last silence_start => end of audio (trailing silence start)
end_keep="$(awk '/silence_start:/ {v=$NF} END{if(v!="") print v}' <<<"$sd")"

# Fallbacks / sanity
if [[ -z "${start_keep:-}" ]]; then
  # No leading silence_end found; keep from 0
  start_keep="0"
fi
if [[ -z "${end_keep:-}" ]]; then
  # No trailing silence_start found; keep to full duration
  end_keep="$duration"
fi

# Ensure start < end (handle edge cases)
ok="$(
  awk -v s="$start_keep" -v e="$end_keep" 'BEGIN{ if (s+0 < e+0) print "1"; else print "0"; }'
)"

if [[ "$ok" != "1" ]]; then
  echo "Could not determine a valid trim window." >&2
  echo "Detected start_keep=${start_keep}, end_keep=${end_keep}, duration=${duration}" >&2
  echo "Silencedetect output:" >&2
  echo "$sd" >&2
  exit 2
fi

echo "Input:  $in"
echo "Output: $out"
echo "Keep:   ${start_keep}s -> ${end_keep}s (duration ~ $(awk -v s="$start_keep" -v e="$end_keep" 'BEGIN{printf "%.3f", (e-s)}'))"
echo "Detect: noise=${NOISE_DB}, min_silence=${MIN_DUR}s"

# Stream-copy trim (no re-encode). Use -ss/-to after -i for more accurate seeking while still copying.
ffmpeg -hide_banner -y -i "$in" -ss "$start_keep" -to "$end_keep" -c copy "$out"