#!/bin/bash

# flac2mp3 (based on flac2opus)
# brontosaurusrex 2015

# Usage examples

# Simple:
# ...........................................
# flac2mp3 *.flac
# parallel --gnu flac2mp3 {} ::: *.flac

# With find:
# ...........................................
# If the symlinks are in question (cp -rs flacs /destination/), you could call this script:
# find . -lname "*.flac" -exec flac2mp3 {} \+
# or with parallel
# find . -lname "*.flac" | parallel --gnu flac2mp3 {}

# Or if the files are to be found
# find . -type f -iname "*.flac" -exec flac2mp3 {} \+
# or with parallel
# find . -type f -iname "*.flac" | parallel --gnu flac2mp3 {}

# note: Using parallel (apt-get install parallel) will give enormous encoding speed boost. 

command -v mediainfo >/dev/null 2>&1 || { echo "I need mediainfo installed." ; exit 1; }
command -v flac      >/dev/null 2>&1 || { echo "I need flac installed." ; exit 1; }
command -v metaflac  >/dev/null 2>&1 || { echo "metaflac not found - I need flac installed." ; exit 1; }
command -v lame      >/dev/null 2>&1 || { echo "I need lame installed." ; exit 1; }

# temp_dir http://mywiki.wooledge.org/BashFAQ/062
   	temp_dir=/tmp/$RANDOM-$$
   	trap '[ -n "$temp_dir" ] && rm -fr "$temp_dir"' EXIT
   	mkdir -m 700 "$temp_dir" || { echo '!! unable to create a tempdir' >&2; temp_dir=; exit 1; }


# functions

# encode, decode flac to tmp wav, lame to mp3 - inject tags, done.

function encode() { # put your encoding settings here
    
             #   ffmpeg_static -hide_banner -loglevel quiet -i "$expanded" -vn -y -codec:a libmp3lame -q:a 3 "$dir/$base.mp3" 
                
	# extract the tags from the flac file
	for tag in TITLE ARTIST ALBUM DATE COMMENT TRACKNUMBER TRACKTOTAL GENRE; do
		eval "$tag=\"`metaflac --show-tag=$tag "$expanded" | sed 's/.*=//'`\""
	done

	# start the conversion and include the extracted tags
	flac -d -f --decode-through-errors "$expanded" -o "$temp_dir/$base.wav"
    
    # encode with lame
    lame -V 3 --tt "$TITLE" --ta "$ARTIST" --tl "$ALBUM" --ty "$DATE" --tc "$COMMENT" --tn "$TRACKNUMBER" --tg "$GENRE" "$temp_dir/$base.wav" "$dir/$base.mp3"
    
    # or you could pipe directly, if you don't care about the pretty lame bitrate graph
    # flac -cd -f --decode-through-errors "$expanded" | lame -V 3 --tt "$TITLE" --ta "$ARTIST" --tl "$ALBUM" --ty "$DATE" --tc "$COMMENT" --tn "$TRACKNUMBER" --tg "$GENRE" - "$dir/$base.mp3"

}

# http://wiki.hydrogenaud.io/index.php?title=Lame#Very_high_quality:_HiFi.2C_home.2C_or_quiet_listening.2C_with_best_file_size


absdiff() { 
                echo -n "$(( (a<b) ? b-a : a-b ))" 
}
# end functions


while [ $# -gt 0 ]; do
  
    expanded=$(readlink -f "$1")
    # echo ".............................."
    echo "$expanded"
    
    base=$(basename "${1}")     # basename, like                file.flac
    base="${base%.*}"           # basename without extension    file
    dir=$(dirname "${1}")       # directory
    

        # Do some checks first
        if [ -f "$dir/$base.mp3" ]
        then # mp3 file in existance, do some duration checking
            echo "    the file exists, checking if source and mp3 durations match"
        
                # mediainfo "--Inform=General;%Duration%"
                
                a=$(mediainfo "--Inform=General;%Duration%" "$expanded")
                b=$(mediainfo "--Inform=General;%Duration%" "$dir/$base.mp3")
                
                if [[ "$a" == "$b" ]]
       
                then
                    echo "    yes, durations match exactly, skipping" # This will probably never happen
                else
                    echo "    no, durations does not match exactly" 
                    
                    # echo "$a" "$b"
                    echo -n "    "
                    absdiff "$a" "$b"
                    echo -n "ms difference"
                        
                        # this 200 is just some value in miliseconds = max difference allowed,
                        # if samplerate is 48 kHz, then it equals to 200x48=9600 samples
                        # 36 ms seems to be the constant in this specific case (unknown reasons)
                        
                        if (( $(absdiff "$a" "$b") < 200 )) 
                        then
                            echo " = still ok (200 ms is max allowed)"
                        else
                            encode
                        fi
                fi
            
            
        else # the mp3 file does not exist yet
            encode
        fi
   
   
       
   
    shift
    

    
done