nomads-cloud: init

krebs/5pkgs/simple/nomads-cloud/default.nix

@@ -0,0 +1,43 @@
+{ 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' < "$json_path")
+
+  # The maximum gray value.  Must be bigger than 0 and less than 65536.
+  maxval=256
+
+  # pgm - Netpbm grayscale image format
+  # http://netpbm.sourceforge.net/doc/pgm.html
+  {
+    echo P2
+    echo "$width $height"
+    echo "$maxval"
+    cat "$json_path" |
+    ${jq}/bin/jq --argjson maxval "$maxval" -c '
+      .[0].data[] * $maxval | round
+    ' |
+    ${findutils}/bin/xargs -n "$width"
+  } > "$pgm_path"
+
+  ${imagemagick}/bin/convert -roll +50% "$pgm_path" "$png_path"
+
+  rm -r "$prefix"
+''