Fix Planetiler tmp-file format detection, add build progress and delete

Root cause of "planetiler exited with status 1: ... Unsupported format
tmp" (and likely the earlier unexplained "pmtiles exited with status
1"): Planetiler/go-pmtiles pick their output archive format from the
file extension, and the atomic-rename tmp files were named
"offline.pmtiles.tmp"/"terrain.pmtiles.tmp" — ".tmp" as the extension,
not ".pmtiles". Renamed to "offline.tmp.pmtiles"/"terrain.tmp.pmtiles".

Also, since build-status only ever said "running since X" with no way
to tell what it was actually doing:
- GET .../build-status now includes a `step` string ("fetching PL
  (3/4) — done: SK, CZ — pending: HU", "tiling with planetiler", ...)
  while a build is in progress.
- DELETE /api/offline-tiles / /api/terrain-tiles clear a built file,
  its sidecar meta, and (for offline) the whole per-country download
  cache — a manual "reclaim space" / "start over" action the region
  picker's Apply never did on its own. DELETE
  /api/offline-tiles/cache/:code clears just one country's cached
  extract. All three are 409 while that kind's build is running, and
  surfaced as a small "Delete" button on each row in the Offline data
  panel.

.gitignore

@@ -12,6 +12,10 @@
 # see docs/development.adoc)
 /data/*.pmtiles
 
+# Per-country .osm.pbf cache for offline.pmtiles rebuilds (also large,
+# also local-only — see PmtilesBuilder.cached_extract)
+/data/geofabrik_cache/
+
 # Offline Wikipedia ZIM for kiwix-serve (also large, also local-only —
 # same story, see docs/development.adoc)
 /data/kiwix/*

app.rb

@@ -277,6 +277,33 @@ module Maptool
       json PmtilesBuilder.offline_status
     end
 
+    # Deletes offline.pmtiles plus its whole per-country download cache —
+    # a manual "reclaim the space"/"start over" action, distinct from
+    # unticking countries in the region picker (which only changes what a
+    # future build covers, doesn't free anything already on disk).
+    delete "/api/offline-tiles" do
+      require_login!
+      begin
+        PmtilesBuilder.delete_offline_data(DATA_DIR)
+      rescue PmtilesBuilder::BuildError => e
+        halt 409, json(error: e.message)
+      end
+      json ok: true
+    end
+
+    # Deletes one country's cached Geofabrik extract only — e.g. to force a
+    # clean re-download of just that one, or reclaim space for a country
+    # that's no longer selected (the cache otherwise keeps it indefinitely).
+    delete "/api/offline-tiles/cache/:code" do
+      require_login!
+      begin
+        PmtilesBuilder.delete_cached_extract(DATA_DIR, params[:code])
+      rescue PmtilesBuilder::BuildError => e
+        halt 409, json(error: e.message)
+      end
+      json ok: true
+    end
+
     # Same optional-local-file story as offline.pmtiles above — see
     # docs/development.adoc for how to generate one, until then hillshade
     # just stays unavailable while the offline basemap is active.
@@ -309,6 +336,17 @@ module Maptool
       json PmtilesBuilder.terrain_status
     end
 
+    # Same reasoning as DELETE /api/offline-tiles above.
+    delete "/api/terrain-tiles" do
+      require_login!
+      begin
+        PmtilesBuilder.delete_terrain_data(DATA_DIR)
+      rescue PmtilesBuilder::BuildError => e
+        halt 409, json(error: e.message)
+      end
+      json ok: true
+    end
+
     # Pinged once per page load (public/js/map.js) — url is a same-origin
     # path (not kiwix-serve's own address, which the browser can't reach
     # directly behind the reverse proxy in front of this app), proxied by

docs/development.adoc

@@ -94,15 +94,20 @@ Ticking countries and clicking "Apply changes" saves the selection
 (`data/offline_regions.json`, an array of ISO A2 codes) and rebuilds
 both files to cover it.
 
-There's no standalone per-country file to individually delete —
+There's no standalone per-country *built* file — `offline.pmtiles`/
-`offline.pmtiles`/`terrain.pmtiles` are always one combined extract for
+`terrain.pmtiles` are always one combined extract for the *whole
-the *whole current selection*. "Remove a country" and "refresh a
+current selection*. "Remove a country" is just "change the selection,
-country" are both just "change the selection, then Apply" (unticking a
+then Apply" (unticking a country and applying rebuilds without it).
-country and applying rebuilds without it; nothing to separately
+terrain.pmtiles re-extracts its selection from scratch on
-delete). Every Apply re-extracts the entire selection from scratch, not
+every Apply — fine given that extraction is byte-range requests
-just what changed — fine given extraction is fast (byte-range requests
+against a remote archive, not full downloads. offline.pmtiles, by
-against remote archives, not per-tile fetches), but worth revisiting if
+contrast, downloads a whole country's `.osm.pbf` from Geofabrik (can be
-someone selects half of Europe at once and finds it slow.
+multi-GB), so it keeps a per-country cache under
+`data/geofabrik_cache/` instead of re-fetching on every Apply — a
+country already cached is only re-downloaded if Geofabrik's own
+`Last-Modified` for it has moved on since (checked with a cheap `HEAD`,
+see `PmtilesBuilder.cached_extract`), so growing or shrinking the
+selection only touches whatever's actually new to it.
 
 This wraps exactly the manual workflows documented above
 (`lib/maptool/pmtiles_builder.rb`). offline.pmtiles downloads each
@@ -128,7 +133,21 @@ the current selection, `POST` to change it, then `POST
 /api/offline-tiles/build` / `/api/terrain-tiles/build`, polled via the
 matching `*/build-status` route) — only one of each kind at a time;
 starting a second while one's running gets a 409, as does starting
-either with nothing selected yet.
+either with nothing selected yet. While running, `build-status` also
+includes a `step` string (e.g. `"fetching PL (3/4) — done: SK, CZ —
+pending: HU"`, or `"tiling with planetiler"`) — see
+`PmtilesBuilder.run_job`'s `report_step`.
+
+`DELETE /api/offline-tiles` removes offline.pmtiles, its sidecar meta,
+and the whole per-country download cache (`data/geofabrik_cache/`) —
+`DELETE /api/terrain-tiles` does the same for terrain.pmtiles. Both are
+a manual "reclaim the space" / "start over" action (409 while that
+kind's build is running), separate from the region picker's Apply,
+which only changes what a *future* build covers and never frees
+anything already on disk. `DELETE
+/api/offline-tiles/cache/:code` removes just one country's cached
+extract, e.g. to force a clean re-download of it without touching the
+rest of the cache.
 
 Each successful build also writes a small sidecar (`offline.pmtiles.
 meta.json` — each source country's code/Geofabrik slug/Last-Modified;

lib/maptool/pmtiles_builder.rb

@@ -179,17 +179,21 @@ module Maptool
     # finishes — raises BuildError (the caller turns this into an error
     # response) if nothing's selected yet, or one's already running.
     #
-    # download_extract exists as an injectable seam so tests can exercise
+    # download_extract/fetch_last_modified exist as injectable seams so
-    # the rest of this (scratch dir, osmium/planetiler invocation, atomic
+    # tests can exercise the rest of this (scratch dir, osmium/planetiler
-    # rename) without a real network call — same reasoning test_helper.rb
+    # invocation, atomic rename, the per-country cache below) without a
-    # already gives for keeping /api/plugins route tests off the real
+    # real network call — same reasoning test_helper.rb already gives for
-    # Overpass API.
+    # keeping /api/plugins route tests off the real Overpass API.
-    def self.build_offline(data_dir:, download_extract: method(:download_extract))
+    def self.build_offline(data_dir:, download_extract: method(:download_extract), fetch_last_modified: method(:fetch_geofabrik_last_modified))
       codes = selected_regions(data_dir)
       raise BuildError, "select at least one region first" if codes.empty?
 
       begin_run!(OFFLINE_MUTEX, OFFLINE_STATUS)
-      Thread.new { run_job(OFFLINE_MUTEX, OFFLINE_STATUS) { extract_offline(codes, data_dir, download_extract) } }
+      Thread.new do
+        run_job(OFFLINE_MUTEX, OFFLINE_STATUS) do |report_step|
+          extract_offline(codes, data_dir, download_extract, fetch_last_modified, report_step)
+        end
+      end
     end
 
     # fetch_manifest: same injectable-seam reasoning as download_extract
@@ -199,7 +203,11 @@ module Maptool
       raise BuildError, "select at least one region first" if codes.empty?
 
       begin_run!(TERRAIN_MUTEX, TERRAIN_STATUS)
-      Thread.new { run_job(TERRAIN_MUTEX, TERRAIN_STATUS) { build_terrain_pmtiles(codes, data_dir, fetch_manifest) } }
+      Thread.new do
+        run_job(TERRAIN_MUTEX, TERRAIN_STATUS) do |report_step|
+          build_terrain_pmtiles(codes, data_dir, fetch_manifest, report_step)
+        end
+      end
     end
 
     def self.begin_run!(mutex, status)
@@ -210,11 +218,19 @@ module Maptool
     end
     private_class_method :begin_run!
 
+    # Yields a report_step proc the build can call with a short
+    # human-readable description of what it's doing right now ("downloading
+    # SK (1/2)", "tiling with planetiler", ...) — surfaced as status[:step]
+    # so GET .../build-status can show progress beyond just "running since
+    # X" (see docs/development.adoc).
     def self.run_job(mutex, status)
-      yield
+      report_step = ->(text) { mutex.synchronize { status[:step] = text } }
+      yield report_step
       mutex.synchronize { status.merge!(state: "done", finished_at: Time.now.utc.iso8601).delete(:message) }
     rescue => e
       mutex.synchronize { status.merge!(state: "error", finished_at: Time.now.utc.iso8601, message: e.message) }
+    ensure
+      mutex.synchronize { status.delete(:step) }
     end
     private_class_method :run_job
 
@@ -228,25 +244,30 @@ module Maptool
     # tiles.openfreemap.org's Liberty style already expects, so
     # public/js/map.js's offlineStyle() can reuse ONLINE_STYLE_PATCH
     # unchanged instead of a separate protomaps-themes-base palette.
-    def self.extract_offline(codes, data_dir, download_extract)
+    def self.extract_offline(codes, data_dir, download_extract, fetch_last_modified, report_step)
       scratch_dir = Dir.mktmpdir("maptool-offline")
-      sources = codes.map do |code|
+      sources = codes.each_with_index.map do |code, i|
         slug = GEOFABRIK_SLUGS.fetch(code) { raise BuildError, "no Geofabrik source known for region #{code}" }
-        dest = File.join(scratch_dir, "#{code}.osm.pbf")
+        report_step.call(progress_step("fetching #{code}", codes, i))
-        last_modified = download_extract.call(geofabrik_url(slug), dest)
+        cached_extract(code, slug, data_dir, download_extract, fetch_last_modified)
-        { "code" => code, "slug" => slug, "last_modified" => last_modified, "path" => dest }
       end
 
       osm_path =
         if sources.size == 1
           sources.first["path"]
         else
+          report_step.call("merging with osmium")
           merged_path = File.join(scratch_dir, "merged.osm.pbf")
           run_osmium!("merge", *sources.map { |s| s["path"] }, "-o", merged_path)
           merged_path
         end
 
-      tmp_path = File.join(data_dir, "offline.pmtiles.tmp")
+      report_step.call("tiling with planetiler")
+      # .tmp.pmtiles, not .pmtiles.tmp — Planetiler picks its output archive
+      # format (pmtiles vs mbtiles) from the file extension, so a ".tmp"
+      # suffix made it fail with "Unsupported format tmp" instead of
+      # actually tiling anything.
+      tmp_path = File.join(data_dir, "offline.tmp.pmtiles")
       run_planetiler!("--osm-path=#{osm_path}", "--output=#{tmp_path}")
       File.rename(tmp_path, File.join(data_dir, "offline.pmtiles"))
       File.write(offline_meta_path(data_dir), JSON.generate(sources: sources.map { |s| s.slice("code", "slug", "last_modified") }))
@@ -256,11 +277,60 @@ module Maptool
     end
     private_class_method :extract_offline
 
+    # Renders a report_step string like "fetching PL (3/4) — done: SK, CZ —
+    # pending: HU" — so GET .../build-status shows not just "it's running"
+    # but which of the current build's sources is in flight and which are
+    # already behind/ahead of it.
+    def self.progress_step(action, labels, index)
+      done = labels[0...index]
+      pending = labels[(index + 1)..] || []
+      parts = ["#{action} (#{index + 1}/#{labels.size})"]
+      parts << "done: #{done.join(", ")}" unless done.empty?
+      parts << "pending: #{pending.join(", ")}" unless pending.empty?
+      parts.join(" — ")
+    end
+    private_class_method :progress_step
+
     def self.geofabrik_url(slug)
       "https://download.geofabrik.de/#{slug}-latest.osm.pbf"
     end
     private_class_method :geofabrik_url
 
+    # Per-country .osm.pbf cache, kept across builds under data_dir (not
+    # scratch_dir, which is wiped every run) — changing the region
+    # selection re-downloads only the countries that are new to it, and
+    # re-running the same selection re-downloads nothing unless Geofabrik's
+    # own Last-Modified for that country moved on. A stamp file next to
+    # each cached extract records the Last-Modified it was fetched with;
+    # a HEAD check (cheap) decides whether the multi-GB GET (not cheap) is
+    # skippable.
+    def self.cached_extract(code, slug, data_dir, download_extract, fetch_last_modified)
+      cache_dir = geofabrik_cache_dir(data_dir)
+      FileUtils.mkdir_p(cache_dir)
+      path = File.join(cache_dir, "#{code}.osm.pbf")
+      stamp_path = "#{path}.last_modified"
+      url = geofabrik_url(slug)
+
+      if File.exist?(path) && File.exist?(stamp_path)
+        current = begin
+          fetch_last_modified.call(url)
+        rescue BuildError
+          nil
+        end
+        return { "code" => code, "slug" => slug, "last_modified" => current, "path" => path } if current && current == File.read(stamp_path)
+      end
+
+      last_modified = download_extract.call(url, path)
+      File.write(stamp_path, last_modified.to_s)
+      { "code" => code, "slug" => slug, "last_modified" => last_modified, "path" => path }
+    end
+    private_class_method :cached_extract
+
+    def self.geofabrik_cache_dir(data_dir)
+      File.join(data_dir, "geofabrik_cache")
+    end
+    private_class_method :geofabrik_cache_dir
+
     # Real network implementation of the download_extract seam above —
     # streams the extract to dest (some of these are multi-GB — Net::HTTP's
     # plain #get buffers the whole response body in memory first, which
@@ -345,6 +415,31 @@ module Maptool
     end
     private_class_method :offline_meta_path
 
+    # Deletes offline.pmtiles, its sidecar meta, and the whole per-country
+    # download cache (data/geofabrik_cache/) — "start over" for the offline
+    # basemap. The current selection (data/offline_regions.json) is left
+    # alone, so a following build just re-downloads it fresh.
+    def self.delete_offline_data(data_dir)
+      OFFLINE_MUTEX.synchronize { raise BuildError, "a build is already running" if OFFLINE_STATUS[:state] == "running" }
+
+      File.delete(File.join(data_dir, "offline.pmtiles")) if File.exist?(File.join(data_dir, "offline.pmtiles"))
+      File.delete(offline_meta_path(data_dir)) if File.exist?(offline_meta_path(data_dir))
+      cache_dir = geofabrik_cache_dir(data_dir)
+      FileUtils.remove_entry(cache_dir) if Dir.exist?(cache_dir)
+    end
+
+    # Deletes just one country's cached .osm.pbf (and its Last-Modified
+    # stamp) — e.g. to force a fresh download without touching the others,
+    # or to reclaim space for a country no longer selected.
+    def self.delete_cached_extract(data_dir, code)
+      OFFLINE_MUTEX.synchronize { raise BuildError, "a build is already running" if OFFLINE_STATUS[:state] == "running" }
+
+      cache_dir = geofabrik_cache_dir(data_dir)
+      path = File.join(cache_dir, "#{code}.osm.pbf")
+      File.delete(path) if File.exist?(path)
+      File.delete("#{path}.last_modified") if File.exist?("#{path}.last_modified")
+    end
+
     # --- terrain.pmtiles ---
 
     # planet.pmtiles (z0-12, always) plus whichever regional chunks
@@ -361,7 +456,8 @@ module Maptool
     # border tiles (extraction copies whole tiles, it doesn't clip vector
     # content to the polygon) — so this always does one extract per
     # *source archive*, never one per country.
-    def self.build_terrain_pmtiles(codes, data_dir, fetch_manifest)
+    def self.build_terrain_pmtiles(codes, data_dir, fetch_manifest, report_step)
+      report_step.call("fetching mapterhorn manifest")
       items = fetch_manifest.call
       planet = items.find { |item| item["name"] == MAPTERHORN_PLANET_NAME }
       raise BuildError, "mapterhorn manifest is missing #{MAPTERHORN_PLANET_NAME}" unless planet
@@ -374,8 +470,14 @@ module Maptool
 
       chunks = items.select { |item| item["name"] != MAPTERHORN_PLANET_NAME && bbox_intersects?(item, south, west, north, east) }
 
-      tmp_path = File.join(data_dir, "terrain.pmtiles.tmp")
+      # .tmp.pmtiles, not .pmtiles.tmp — same reasoning as offline.pmtiles'
-      extracts = [planet, *chunks].each_with_index.map do |item, i|
+      # own tmp_path above, in case go-pmtiles also derives format from
+      # the extension for its "merge" output.
+      tmp_path = File.join(data_dir, "terrain.tmp.pmtiles")
+      sources = [planet, *chunks]
+      labels = sources.map { |item| item["name"] }
+      extracts = sources.each_with_index.map do |item, i|
+        report_step.call(progress_step("extracting #{item["name"]}", labels, i))
         extract_path = File.join(scratch_dir, "extract-#{i}.pmtiles")
         run_pmtiles!("extract", item["url"], extract_path, "--region=#{region_path}", "--maxzoom=#{TERRAIN_MAX_ZOOM}")
         extract_path
@@ -384,6 +486,7 @@ module Maptool
       if extracts.size == 1
         File.rename(extracts.first, tmp_path)
       else
+        report_step.call("merging with pmtiles")
         run_pmtiles!("merge", *extracts, tmp_path)
       end
       File.rename(tmp_path, File.join(data_dir, "terrain.pmtiles"))
@@ -446,6 +549,17 @@ module Maptool
     end
     private_class_method :terrain_meta_path
 
+    # Deletes terrain.pmtiles and its sidecar meta — same "start over"
+    # reasoning as delete_offline_data above. No download cache to clean up
+    # here: terrain.pmtiles' pmtiles-extract step reads its sources over
+    # HTTP range requests rather than downloading a whole archive first.
+    def self.delete_terrain_data(data_dir)
+      TERRAIN_MUTEX.synchronize { raise BuildError, "a build is already running" if TERRAIN_STATUS[:state] == "running" }
+
+      File.delete(File.join(data_dir, "terrain.pmtiles")) if File.exist?(File.join(data_dir, "terrain.pmtiles"))
+      File.delete(terrain_meta_path(data_dir)) if File.exist?(terrain_meta_path(data_dir))
+    end
+
     # --- shared ---
 
     def self.read_json(path)
@@ -473,25 +587,33 @@ module Maptool
       ENV.fetch("PLANETILER_JAR", "/usr/local/lib/planetiler.jar")
     end
 
+    # Some CLI tools (go-pmtiles included) write their actual error to
+    # stdout rather than stderr — combine both rather than risk raising a
+    # BuildError with nothing useful in it.
+    def self.command_output(stdout, stderr)
+      [stdout, stderr].map(&:strip).reject(&:empty?).join("\n")
+    end
+    private_class_method :command_output
+
     def self.run_pmtiles!(*args)
-      _stdout, stderr, status = Open3.capture3(pmtiles_bin, *args)
+      stdout, stderr, status = Open3.capture3(pmtiles_bin, *args)
-      raise BuildError, "pmtiles exited with status #{status.exitstatus}: #{stderr.strip}" unless status.success?
+      raise BuildError, "pmtiles exited with status #{status.exitstatus}: #{command_output(stdout, stderr)}" unless status.success?
     rescue Errno::ENOENT, Errno::EACCES => e
       raise BuildError, "could not run '#{pmtiles_bin}' (#{e.message}) — is go-pmtiles installed and on PATH? See docs/development.adoc."
     end
     private_class_method :run_pmtiles!
 
     def self.run_osmium!(*args)
-      _stdout, stderr, status = Open3.capture3(osmium_bin, *args)
+      stdout, stderr, status = Open3.capture3(osmium_bin, *args)
-      raise BuildError, "osmium exited with status #{status.exitstatus}: #{stderr.strip}" unless status.success?
+      raise BuildError, "osmium exited with status #{status.exitstatus}: #{command_output(stdout, stderr)}" unless status.success?
     rescue Errno::ENOENT, Errno::EACCES => e
       raise BuildError, "could not run '#{osmium_bin}' (#{e.message}) — is osmium-tool installed and on PATH? See docs/development.adoc."
     end
     private_class_method :run_osmium!
 
     def self.run_planetiler!(*args)
-      _stdout, stderr, status = Open3.capture3(java_bin, "-jar", planetiler_jar, *args)
+      stdout, stderr, status = Open3.capture3(java_bin, "-jar", planetiler_jar, *args)
-      raise BuildError, "planetiler exited with status #{status.exitstatus}: #{stderr.strip}" unless status.success?
+      raise BuildError, "planetiler exited with status #{status.exitstatus}: #{command_output(stdout, stderr)}" unless status.success?
     rescue Errno::ENOENT, Errno::EACCES => e
       raise BuildError, "could not run '#{java_bin} -jar #{planetiler_jar}' (#{e.message}) — is Java and planetiler.jar installed? See docs/development.adoc."
     end

public/css/style.css

@@ -472,6 +472,33 @@ html, body {
   border-top: 1px solid #eee;
 }
 
+.offline-data-panel__row-head {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+}
+
+.offline-data-panel__delete {
+  border: 1px solid #ccc;
+  border-radius: 4px;
+  background: #fff;
+  padding: 2px 8px;
+  font: inherit;
+  font-size: 11px;
+  color: #a33;
+  cursor: pointer;
+}
+
+.offline-data-panel__delete:hover {
+  background: #fdecec;
+}
+
+.offline-data-panel__delete:disabled {
+  opacity: 0.5;
+  cursor: default;
+}
+
 .offline-data-panel__status {
   margin: 6px 0 0;
   color: #666;

public/js/offline_data.js

@@ -17,12 +17,14 @@ function formatElapsed(ms) {
   return minutes > 0 ? `${minutes}m ${seconds}s` : `${seconds}s`;
 }
 
-// "Building…" alone gave no way to tell a slow build from a stuck one —
+// "Building…" alone gave no way to tell a slow build from a stuck one, or
-// elapsed time answers "is it alive" regardless of how long a given
+// which of the current selection's sources it's actually working on right
-// selection takes.
+// now — elapsed time answers "is it alive", status.step (see
+// PmtilesBuilder.run_job) answers "doing what, and what's left".
 function formatRunning(status) {
   const elapsed = status.started_at ? ` (${formatElapsed(Date.now() - new Date(status.started_at).getTime())})` : "";
-  return `Building…${elapsed}`;
+  const step = status.step ? `: ${status.step}` : "";
+  return `Building…${elapsed}${step}`;
 }
 
 // Vendored square-cropped SVGs (public/vendor/flag-icons/, MIT, see
@@ -131,9 +133,10 @@ class RegionPicker {
 // one class covers both rather than writing the same fetch/poll logic
 // twice.
 class DataFileRow {
-  constructor({ label, statusUrl, buildUrl, buildStatusUrl, checkUpdateUrl, formatMeta }) {
+  constructor({ label, statusUrl, deleteUrl, buildUrl, buildStatusUrl, checkUpdateUrl, formatMeta }) {
     this._label = label;
     this._statusUrl = statusUrl;
+    this._deleteUrl = deleteUrl;
     this._buildUrl = buildUrl;
     this._buildStatusUrl = buildStatusUrl;
     this._checkUpdateUrl = checkUpdateUrl;
@@ -144,10 +147,15 @@ class DataFileRow {
     const row = document.createElement("div");
     row.className = "offline-data-panel__row";
     row.innerHTML = `
-      <strong>${this._label}</strong>
+      <div class="offline-data-panel__row-head">
+        <strong>${this._label}</strong>
+        <button type="button" class="offline-data-panel__delete" hidden>Delete</button>
+      </div>
       <p class="offline-data-panel__status">Checking…</p>
     `;
     this._statusEl = row.querySelector(".offline-data-panel__status");
+    this._deleteButton = row.querySelector(".offline-data-panel__delete");
+    this._deleteButton.addEventListener("click", () => this._delete());
     container.appendChild(row);
     this._refreshStatus();
   }
@@ -163,14 +171,39 @@ class DataFileRow {
 
     if (!data.available) {
       this._statusEl.textContent = "Not generated yet.";
+      this._deleteButton.hidden = true;
       return;
     }
 
     const updated = new Date(data.mtime).toLocaleString([], { dateStyle: "short", timeStyle: "short" });
     this._statusEl.textContent = `${formatBytes(data.size)} · updated ${updated}${this._formatMeta(data.meta)}`;
+    this._deleteButton.hidden = !isLoggedIn();
     this._checkUpdate();
   }
 
+  // Deletes the built file (and, for offline.pmtiles, its whole per-country
+  // download cache — see PmtilesBuilder.delete_offline_data) so the row
+  // goes back to "Not generated yet." — a manual way to reclaim space or
+  // force a completely fresh rebuild, since Apply alone never removes
+  // anything already on disk.
+  async _delete() {
+    if (!window.confirm(`Delete ${this._label.toLowerCase()}? This can't be undone.`)) return;
+
+    this._deleteButton.disabled = true;
+    try {
+      const response = await fetch(this._deleteUrl, { method: "DELETE" });
+      const data = await response.json().catch(() => ({}));
+      if (!response.ok) throw new Error(data.error || `could not delete: ${response.status}`);
+    } catch (err) {
+      window.alert(err.message);
+      return;
+    } finally {
+      this._deleteButton.disabled = false;
+    }
+
+    this._refreshStatus();
+  }
+
   // Separate from _refreshStatus's own fetch (and only called once, right
   // after — not polled): this one reaches an external service (Geofabrik
   // or Mapterhorn's manifest, see lib/maptool/pmtiles_builder.rb), so it's
@@ -249,6 +282,7 @@ export class OfflineDataControl {
       new DataFileRow({
         label: "Offline map data",
         statusUrl: "/api/offline-tiles",
+        deleteUrl: "/api/offline-tiles",
         buildUrl: "/api/offline-tiles/build",
         buildStatusUrl: "/api/offline-tiles/build-status",
         checkUpdateUrl: "/api/offline-tiles/check-update",
@@ -257,6 +291,7 @@ export class OfflineDataControl {
       new DataFileRow({
         label: "Offline terrain data",
         statusUrl: "/api/terrain-tiles",
+        deleteUrl: "/api/terrain-tiles",
         buildUrl: "/api/terrain-tiles/build",
         buildStatusUrl: "/api/terrain-tiles/build-status",
         checkUpdateUrl: "/api/terrain-tiles/check-update",

test/test_app.rb

@@ -72,6 +72,9 @@ class AppTest < Minitest::Test
     assert_equal 401, request.post("/api/plugins/test-plugin/run").status
     assert_equal 401, request.post("/api/offline-tiles/build").status
     assert_equal 401, request.post("/api/terrain-tiles/build").status
+    assert_equal 401, request.delete("/api/offline-tiles").status
+    assert_equal 401, request.delete("/api/offline-tiles/cache/SK").status
+    assert_equal 401, request.delete("/api/terrain-tiles").status
   end
 
   # --- GPX/FIT upload and the tree ---
@@ -417,6 +420,35 @@ class AppTest < Minitest::Test
     thread&.join
   end
 
+  def test_offline_tiles_delete_is_ok_when_nothing_was_built
+    assert_equal 200, request.delete("/api/offline-tiles", **logged_in_env).status
+  end
+
+  def test_offline_tiles_delete_removes_the_file_and_cache
+    path = File.join(Maptool::App::DATA_DIR, "offline.pmtiles")
+    cache_dir = File.join(Maptool::App::DATA_DIR, "geofabrik_cache")
+    File.write(path, "fake")
+    FileUtils.mkdir_p(cache_dir)
+    File.write(File.join(cache_dir, "SK.osm.pbf"), "fake")
+
+    response = request.delete("/api/offline-tiles", **logged_in_env)
+
+    assert_equal 200, response.status
+    refute_path_exists path
+    refute_path_exists cache_dir
+  end
+
+  def test_offline_tiles_delete_is_409_when_a_build_is_running
+    Maptool::PmtilesBuilder.set_selected_regions(Maptool::App::DATA_DIR, ["SK"])
+    gate = Queue.new
+    thread = Maptool::PmtilesBuilder.build_offline(data_dir: Maptool::App::DATA_DIR, download_extract: ->(_url, _dest) { gate.pop })
+
+    assert_equal 409, request.delete("/api/offline-tiles", **logged_in_env).status
+  ensure
+    gate.push("unused")
+    thread&.join
+  end
+
   # --- LiveTrack webhook ---
 
   def test_livetrack_webhook_requires_the_configured_secret

test/test_pmtiles_builder.rb

@@ -102,8 +102,12 @@ class PmtilesBuilderTest < Minitest::Test
   # download_extract stub: writes a marker file (same "fake" content the
   # pmtiles/osmium/java fixtures use) instead of hitting Geofabrik, and
   # returns a fixed Last-Modified so sidecar-meta assertions are stable.
-  def fake_download(last_modified: "Wed, 10 Sep 2026 08:00:01 GMT")
+  # `calls` (an Array, shared across builds if the caller wants it) records
-    ->(_url, dest) {
+  # every URL actually downloaded, for asserting the per-country cache
+  # skipped (or didn't skip) a re-download.
+  def fake_download(last_modified: "Wed, 10 Sep 2026 08:00:01 GMT", calls: nil)
+    ->(url, dest) {
+      calls << url if calls
       File.write(dest, "fake")
       last_modified
     }
@@ -167,7 +171,7 @@ class PmtilesBuilderTest < Minitest::Test
     thread.join
 
     assert_path_exists File.join(@data_dir, "offline.pmtiles")
-    refute_path_exists File.join(@data_dir, "offline.pmtiles.tmp")
+    refute_path_exists File.join(@data_dir, "offline.tmp.pmtiles")
     assert_equal "done", Maptool::PmtilesBuilder.offline_status[:state]
     assert_equal ["planetiler --osm-path"], log_lines
     assert_equal(
@@ -189,6 +193,151 @@ class PmtilesBuilderTest < Minitest::Test
     assert_equal %w[SK AT], codes
   end
 
+  # The actual bug report this covers: hitting "Apply" after tweaking the
+  # region selection used to re-download every selected country's .osm.pbf
+  # from scratch, even ones already fetched by an earlier build.
+  def test_build_offline_skips_redownloading_an_unchanged_cached_country
+    select_regions("SK")
+    calls = []
+    Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: fake_download(calls: calls)).join
+    assert_equal 1, calls.size
+
+    Maptool::PmtilesBuilder.build_offline(
+      data_dir: @data_dir,
+      download_extract: fake_download(calls: calls),
+      fetch_last_modified: ->(_url) { "Wed, 10 Sep 2026 08:00:01 GMT" },
+    ).join
+
+    assert_equal 1, calls.size
+    assert_equal "done", Maptool::PmtilesBuilder.offline_status[:state]
+  end
+
+  def test_build_offline_redownloads_a_country_whose_extract_changed
+    select_regions("SK")
+    calls = []
+    Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: fake_download(calls: calls)).join
+
+    Maptool::PmtilesBuilder.build_offline(
+      data_dir: @data_dir,
+      download_extract: fake_download(calls: calls, last_modified: "Thu, 11 Sep 2026 08:00:01 GMT"),
+      fetch_last_modified: ->(_url) { "Thu, 11 Sep 2026 08:00:01 GMT" },
+    ).join
+
+    assert_equal 2, calls.size
+  end
+
+  # A cache-freshness check that itself fails (Geofabrik unreachable) should
+  # fall back to re-downloading rather than aborting the build.
+  def test_build_offline_redownloads_when_the_cache_check_fails
+    select_regions("SK")
+    calls = []
+    Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: fake_download(calls: calls)).join
+
+    fetch_last_modified = ->(_url) { raise Maptool::PmtilesBuilder::BuildError, "could not reach geofabrik" }
+    Maptool::PmtilesBuilder.build_offline(
+      data_dir: @data_dir,
+      download_extract: fake_download(calls: calls),
+      fetch_last_modified: fetch_last_modified,
+    ).join
+
+    assert_equal 2, calls.size
+    assert_equal "done", Maptool::PmtilesBuilder.offline_status[:state]
+  end
+
+  def test_build_offline_only_downloads_a_newly_added_country
+    select_regions("SK")
+    calls = []
+    Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: fake_download(calls: calls)).join
+
+    select_regions("SK", "AT")
+    Maptool::PmtilesBuilder.build_offline(
+      data_dir: @data_dir,
+      download_extract: fake_download(calls: calls),
+      fetch_last_modified: ->(_url) { "Wed, 10 Sep 2026 08:00:01 GMT" },
+    ).join
+
+    assert_equal 1, calls.count { |url| url.include?("slovakia") }
+    assert_equal 1, calls.count { |url| url.include?("austria") }
+  end
+
+  # offline_status[:step] should say which country is in flight right now
+  # and which of the current build's selection are already done/still
+  # pending — not just "running since X".
+  def test_build_offline_reports_progress_step_while_running
+    select_regions("SK", "AT")
+    started = Queue.new
+    gate = Queue.new
+    download_extract = ->(url, dest) {
+      started.push(url)
+      gate.pop
+      File.write(dest, "fake")
+      "Wed, 10 Sep 2026 08:00:01 GMT"
+    }
+    thread = Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: download_extract)
+
+    started.pop
+    assert_equal "fetching SK (1/2) — pending: AT", Maptool::PmtilesBuilder.offline_status[:step]
+    gate.push(:go)
+
+    started.pop
+    assert_equal "fetching AT (2/2) — done: SK", Maptool::PmtilesBuilder.offline_status[:step]
+    gate.push(:go)
+
+    thread.join
+    assert_nil Maptool::PmtilesBuilder.offline_status[:step]
+  end
+
+  def test_delete_offline_data_removes_the_file_meta_and_cache
+    select_regions("SK")
+    Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: fake_download).join
+    assert_path_exists File.join(@data_dir, "offline.pmtiles")
+    assert_path_exists File.join(@data_dir, "geofabrik_cache", "SK.osm.pbf")
+
+    Maptool::PmtilesBuilder.delete_offline_data(@data_dir)
+
+    refute_path_exists File.join(@data_dir, "offline.pmtiles")
+    refute_path_exists File.join(@data_dir, "geofabrik_cache")
+    assert_nil Maptool::PmtilesBuilder.offline_meta(@data_dir)
+  end
+
+  def test_delete_offline_data_is_a_noop_when_nothing_was_built
+    Maptool::PmtilesBuilder.delete_offline_data(@data_dir) # should not raise
+  end
+
+  def test_delete_offline_data_raises_while_a_build_is_running
+    select_regions("SK")
+    gate = Queue.new
+    thread = Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: ->(_url, _dest) { gate.pop })
+
+    assert_raises(Maptool::PmtilesBuilder::BuildError) { Maptool::PmtilesBuilder.delete_offline_data(@data_dir) }
+  ensure
+    gate.push("unused")
+    thread&.join
+  end
+
+  def test_delete_cached_extract_removes_only_that_country
+    select_regions("SK", "AT")
+    Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: fake_download).join
+
+    Maptool::PmtilesBuilder.delete_cached_extract(@data_dir, "SK")
+
+    refute_path_exists File.join(@data_dir, "geofabrik_cache", "SK.osm.pbf")
+    assert_path_exists File.join(@data_dir, "geofabrik_cache", "AT.osm.pbf")
+  end
+
+  def test_delete_terrain_data_removes_the_file_and_meta
+    select_regions("ES")
+    ENV["PMTILES_BIN"] = @pmtiles_ok
+    thread = Maptool::PmtilesBuilder.build_terrain(data_dir: @data_dir, fetch_manifest: -> { fake_manifest })
+    thread.join
+    assert_path_exists File.join(@data_dir, "terrain.pmtiles")
+
+    Maptool::PmtilesBuilder.delete_terrain_data(@data_dir)
+
+    refute_path_exists File.join(@data_dir, "terrain.pmtiles")
+    assert_nil Maptool::PmtilesBuilder.terrain_meta(@data_dir)
+  end
+
   def test_offline_meta_is_nil_before_any_build
     assert_nil Maptool::PmtilesBuilder.offline_meta(@data_dir)
   end