#!/bin/bash

if [ "$1" = -f ]
then
    FORCE=y
    shift
fi

if [ $# = 0 ]
then
    TARGET=/dev/stderr
else
    TARGET=$1
fi

die() { printf "%s: Error: %s\n" "$0" "$*" >&2; exit 1; }

measure_write_speed()
{
    MEASURE_PATH=$1/urandom.out
    CACHED_RESULT=$2

    if [ "$FORCE" -o ! -e "$CACHED_RESULT" ]
    then
        mkdir -p "$(dirname "$CACHED_RESULT")"
        sync
        begin=$(date +%s%N)
        count=500
        dd if=/dev/urandom of="$MEASURE_PATH" bs=1M count=$count conv=fdatasync
        end=$(date +%s%N)
        nanosecs=$(( end - begin ))
        millisecs=$(( nanosecs / 1000 / 1000 ))
        bytes=$(( count * 1000 * 1000 ))
        bytes_per_second=$(( 1000 * bytes / millisecs ))
        rm "$MEASURE_PATH"
        printf "Sanity check: megabytes/second = %s\n" \
               "$(( bytes_per_second / 1000 / 1000 ))" >&2
        printf '%s\n' "$bytes_per_second" > "$CACHED_RESULT"
    fi
    cat "$CACHED_RESULT"
}

DIR=~/.mozilla
CONFDIR=$HOME/.config/firestart

if [ -e "$CONFDIR"/conf ]
then
    . "$CONFDIR"/conf
fi

disk_write_speed=$(measure_write_speed "$DIR" "$CONFDIR"/diskspeed.dat)

WRITE_OPS=$(( disk_write_speed / 2 ))
READ_OPS=$WRITE_OPS

[ -e "$DIR" ] || die "does not exist: $DIR"
[ -d "$DIR" ] || die "not a directory: $DIR"

DEV=$(echo $(findmnt --target "$DIR" -o MAJ:MIN -n))
[ "$DEV" ] || die "could not determine backing device for $DIR"

cat > "$TARGET" <<END
[Service]
IOReadIOPSMax = $DEV $READ_OPS
IOWriteIOPSMax = $DEV $WRITE_OPS

END