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

# Usage: nvenc_compress.sh <video_path> [target_size_mb]

VIDEO="$1"
TARGET_MB="${2:-9}"
TARGET_BYTES=$((TARGET_MB * 1024 * 1024))

if [[ ! -f "$VIDEO" ]]; then
  echo "Error: file not found: $VIDEO"
  exit 1
fi

BASENAME="${VIDEO##*/}"
BASENAME="${BASENAME%.*}"
OUTDIR="$(dirname "$VIDEO")"
OUTFILE="$OUTDIR/${BASENAME}_compressed.mp4"

# nvenc cq range: 0 (best/largest) to 51 (worst/smallest)
# We binary search this range to hit the target file size
LO=0
HI=51
BEST_DIFF=999999999
BEST_CQ=23
MAX_ITERATIONS=20

echo "Target size: ${TARGET_MB}MB (${TARGET_BYTES} bytes)"
echo "Encoding with nvenc (h264_nvenc)..."
echo ""

for ((i=0; i<MAX_ITERATIONS; i++)); do
  CQ=$(( (LO + HI) / 2 ))
  TMPFILE="${OUTFILE}_iter_${i}_cq${CQ}.mp4"

  echo "--- Iteration $((i+1))/$MAX_ITERATIONS ---"
  echo "Trying cq=$CQ (lo=$LO, hi=$HI)"

  ffmpeg -y -i "$VIDEO" -c:v h264_nvenc -cq "$CQ" -c:a copy -preset p7 -f mp4 "$TMPFILE" 2>/dev/null

  if [[ ! -f "$TMPFILE" ]]; then
    echo "Error: ffmpeg failed at cq=$CQ"
    rm -f "$TMPFILE"
    break
  fi

  FILE_SIZE=$(stat -c%s "$TMPFILE" 2>/dev/null || stat -f%z "$TMPFILE" 2>/dev/null)
  DIFF=$(( FILE_SIZE - TARGET_BYTES ))
  ABS_DIFF=${DIFF#-}

  echo "  Size: $(( FILE_SIZE / 1024 / 1024 ))MB (diff: $(( DIFF / 1024 / 1024 ))MB)"

  if (( ABS_DIFF < BEST_DIFF )); then
    BEST_DIFF=$ABS_DIFF
    BEST_CQ=$CQ
    cp "$TMPFILE" "$OUTFILE"
  fi

  rm -f "$TMPFILE"

  # If within 1% of target, we're close enough
  if (( ABS_DIFF < TARGET_BYTES / 100 )); then
    echo ""
    echo "Within tolerance! Stopping."
    break
  fi

  # Binary search direction:
  # Higher cq = smaller file, lower cq = larger file
  if (( FILE_SIZE > TARGET_BYTES )); then
    # File too big, need higher cq (smaller)
    LO=$(( CQ + 1 ))
  else
    # File too small, need lower cq (larger)
    HI=$(( CQ - 1 ))
  fi

  if (( LO > HI )); then
    echo ""
    echo "Range exhausted. Stopping."
    break
  fi
done

echo ""
echo "Done! Best cq=$BEST_CQ, final size: $(( BEST_DIFF / 1024 / 1024 ))MB from target"
echo "Output: $OUTFILE"