#!/bin/bash

preview_dir="$(dirname "$0")/../previews"

search_dir="${1}"

check_dependencies() {
	if ! mkdir -p "$preview_dir"; then
		echo "ERROR: Unable to create preview directory"
		exit 1
	elif ! command -v ffmpeg 2>&1 >/dev/null; then
		echo "ERROR: FFmpeg must be installed"
		exit 1
	fi
}

check_input() {
	if [[ ! -e "${search_dir}" ]]; then
		echo "ERROR: Input file '${search_dir}' does not exist"
		exit 2
	fi
}

# Search for videos recursively using the MIME type
find_videos() {
	video_list=$(find "${search_dir}" -type f -exec file -i {} \; | grep -oP '.*(?=: video/)')

	echo "${video_list}" >&2
}

create_previews() {
	while IFS= read -r video; do
		echo "Making preview for ${video}"
		make_preview
	done <<< "${video_list}"
}

get_size() {
	IFS=','
	read -r width height <<< $(ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=p=0 "${video}")

	if (( $width >= $height )); then
		rows=4 cols=5
		scale_format="200:-1"
	else
		rows=5 cols=4
		scale_format="-1:200"
	fi
}

get_num_frames() {
	local num_snapshots=$(( rows * cols ))

	num_frames=$(ffprobe -v error -select_streams v:0 -count_frames -show_entries stream=nb_read_frames -of csv=p=0 "${video}")
	echo "Num frames: $num_frames" >&2

	frames_per_snapshot=$(( num_frames / num_snapshots ))
}

make_preview() {
	get_size
	get_num_frames

	filename="$preview_dir/$(basename "${video}").webp"
	filters="select=not(mod(n\,$frames_per_snapshot)),scale=$scale_format,tile=${rows}x${cols}"

    ffmpeg -nostdin -loglevel panic -i "${video}" -frames 1 -q:v 90 -vf "$filters" "${filename}"
}

check_dependencies
check_input
find_videos
create_previews