#!/bin/sh
# Keeps the instance's own map tiles current (Halkyon Train's ADR 0030, D50): the
# newest of Protomaps' daily builds of the planet, cut to MAP_REGION (`west,south,
# east,north` in degrees; by default Europe's, the box BRouter's segments cover) at
# zooms 0 to 15, into /tiles/europe.pmtiles; again every MAP_REFRESH_DAYS days (30)
# where a newer build has come; after a round where the builds' list or the cut
# failed, again in an hour, the wait doubling up to a day while rounds keep failing.
# The cut is written into /tiles/next/ and moved over
# the old one, so the server never reads half a file; until it is done, the old one
# serves. Both at once take twice a cut's room.
set -eu

builds=https://build-metadata.protomaps.dev/builds.json
region=${MAP_REGION:--25,35,45,75}
days=${MAP_REFRESH_DAYS:-30}
cd /tiles

refresh() {
  complete=0
  if ! mkdir -p next; then
    echo "/tiles/next can't be made; the tiles stay as they are." >&2
    return 0
  fi
  build=$(curl -fsS "$builds" | grep -o '"key": *"[0-9]\{8\}\.pmtiles"' |
    grep -o '[0-9]\{8\}\.pmtiles' | sort | tail -n 1) || build=
  if [ -z "$build" ]; then
    echo "Protomaps' builds didn't come; the tiles stay as they are." >&2
    return 0
  fi
  if [ -e europe.build ] && [ "$(cat europe.build)" = "$build" ]; then
    echo "The tiles are $build's, the newest."
    complete=1
    return 0
  fi
  rm -f next/europe.pmtiles
  if pmtiles extract "https://build.protomaps.com/$build" next/europe.pmtiles \
    --bbox="$region" --maxzoom=15 --download-threads=4; then
    mv next/europe.pmtiles europe.pmtiles
    echo "$build" >europe.build
    echo "The tiles are $build's now, $(du -h europe.pmtiles | cut -f1)."
    complete=1
  else
    rm -f next/europe.pmtiles
    echo "The cut of $build failed; the tiles stay as they are." >&2
  fi
}

# Seconds to wait after the $1th incomplete round in a row: $2, doubling up to $3.
backoff() {
  pause=$2 n=1
  while [ "$n" -lt "$1" ] && [ "$pause" -lt "$3" ]; do
    pause=$((pause * 2)) n=$((n + 1))
  done
  if [ "$pause" -gt "$3" ]; then pause=$3; fi
  echo "$pause"
}

failures=0
while :; do
  refresh
  if [ "$complete" -eq 1 ]; then
    failures=0
    sleep $((days * 86400))
  else
    failures=$((failures + 1))
    pause=$(backoff "$failures" 3600 86400)
    echo "The round wasn't complete; trying again in $((pause / 60)) minutes." >&2
    sleep "$pause"
  fi
done