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{ writers, coreutils, grib2json, curl, jq, findutils, imagemagick }:
writers.writeDashBin "nomads-cloud" ''
prefix=$(mktemp -d)
grib_path=$prefix.grib
json_path=$prefix.json
pgm_path=$prefix.pgm
png_path="$1"
mkdir -p "$prefix"
date=$(${coreutils}/bin/date +%Y%m%d)
for hour in 18 12 06 00; do
url="https://nomads.ncep.noaa.gov/cgi-bin/filter_gfs_0p25_1hr.pl?file=gfs.t''${hour}z.pgrb2.0p25.anl&lev_entire_atmosphere_%5C%28considered_as_a_single_layer%5C%29=on&var_CWAT=on&leftlon=-180&rightlon=180&toplat=90&bottomlat=-90&dir=%2Fgfs.$date%2F$hour"
${curl}/bin/curl -fsS "$url" > "$grib_path"
if [ "$?" -eq 0 ]; then
break
fi
done
${grib2json}/bin/grib2json --data "$grib_path" > "$json_path"
width=$(${jq}/bin/jq '.[0].header.nx' < "$json_path")
height=$(${jq}/bin/jq '.[0].header.ny' < "$json_path")
# The maximum gray value. Must be bigger than 0 and less than 65536.
maxval=1000
# pgm - Netpbm grayscale image format
# http://netpbm.sourceforge.net/doc/pgm.html
{
echo P2
echo "$width $height"
echo "$maxval"
cat "$json_path" |
${jq}/bin/jq --argjson maxval "$maxval" -c '
((.[0].data[] | sqrt | sqrt) * $maxval | round)
' |
${findutils}/bin/xargs -n "$width"
} > "$pgm_path"
${imagemagick}/bin/convert -roll +50% "$pgm_path" "$png_path"
rm -r "$prefix"
''
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