Split offline hiking trails per country, add a picker instead of one big file

data/hiking_trails.geojson is now data/hiking_trails/<CODE>.geojson —
one file per country instead of a merge, generated per-source
(PmtilesBuilder.extract_hiking_trails), cached the same way
geofabrik_cache is (skipped once a country's own extract is already
newer than its source .osm.pbf, so growing the selection by one
country only re-extracts that one). GET /api/hiking-trails now lists
available country codes instead of a single file's status.

The Overlays panel's "Hiking trails" item becomes an expandable
per-country checklist once any offline extract exists (same shape as
Radar's own expand), replacing the plain on/off checkbox — nobody
covering a dozen countries' worth of offline map data needs all of
their hiking trails loaded and parsed at once, so each ticked country
fetches its own GeoJSON independently instead.

HikingTrails.extract_merged (server-side multi-country merge, no
longer needed now that the client picks per country) removed again.
Verified the new extract_hiking_trails + caching skip live on brick
against a real cached country PBF.

lib/maptool/hiking_trails.rb

@@ -63,22 +63,6 @@ module Maptool
       end
     end
 
-    # Runs extract() over one .osm.pbf per selected country and combines the
-    # results into a single FeatureCollection — a route relation crossing a
-    # border (an E-path, say) shows up once per country whose extract it
-    # was pulled from, deduplicated here by OSM relation id (properties.id)
-    # rather than left to render as overlapping duplicate lines.
-    # extract: same injectable-seam reasoning as PmtilesBuilder's own
-    # download_extract:/fetch_manifest: — lets a test swap out the real
-    # (osmium-shelling-out) implementation for a canned one.
-    def self.extract_merged(pbf_paths, extract: method(:extract))
-      seen = {}
-      pbf_paths.each do |pbf_path|
-        extract.call(pbf_path)["features"].each { |feature| seen[feature["properties"]["id"]] ||= feature }
-      end
-      { "type" => "FeatureCollection", "features" => seen.values }
-    end
-
     # Pure — no subprocess — so it's cheaply testable against a canned OPL
     # fixture, same "keep the real logic testable without the real tool
     # installed" reasoning OverpassPois.to_geojson already gives for staying

lib/maptool/pmtiles_builder.rb

@@ -299,26 +299,55 @@ module Maptool
     end
     private_class_method :extract_offline
 
-    # Runs over the same per-country .osm.pbf files sources above already
+    # One GeoJSON per country (data/hiking_trails/<CODE>.geojson), not one
+    # merged file — the frontend only ever needs to show a country at a
+    # time the viewer actually picks (see HikingTrailsControl's country
+    # checklist), and a combined multi-country file was needlessly making
+    # every viewer fetch every selected country's trails regardless.
+    #
+    # Runs over the same per-country .osm.pbf files `sources` above already
     # downloaded/cached for offline.pmtiles itself — no separate download.
-    # Best-effort: a hiking-trails extraction problem (a malformed PBF
-    # region, osmium hiccup on one particular file) shouldn't fail the
-    # whole offline.pmtiles build over what's a bonus overlay, not the
-    # core map — logged into the sidecar meta's own "error" field instead,
-    # so it's visible without taking build_offline itself down.
+    # Cached the same way geofabrik_cache is: skipped for a country whose
+    # extract is already newer than its source .osm.pbf, so growing the
+    # region selection by one country only extracts that one, not every
+    # already-covered country all over again.
+    #
+    # Best-effort per country: an extraction problem (a malformed PBF
+    # region, an osmium hiccup) shouldn't fail the whole offline.pmtiles
+    # build, or even the other countries in this same selection, over
+    # what's a bonus overlay, not the core map.
     def self.extract_hiking_trails(sources, data_dir)
-      geojson = HikingTrails.extract_merged(sources.map { |s| s["path"] })
-      tmp_path = "#{hiking_trails_path(data_dir)}.tmp"
-      File.write(tmp_path, JSON.generate(geojson))
-      File.rename(tmp_path, hiking_trails_path(data_dir))
-    rescue HikingTrails::ExtractError => e
-      File.delete(tmp_path) if tmp_path && File.exist?(tmp_path)
-      warn "hiking trails extraction failed, skipping: #{e.message}"
+      FileUtils.mkdir_p(hiking_trails_dir(data_dir))
+      sources.each do |source|
+        out_path = hiking_trails_country_path(data_dir, source["code"])
+        next if File.exist?(out_path) && File.mtime(out_path) >= File.mtime(source["path"])
+
+        tmp_path = "#{out_path}.tmp"
+        begin
+          File.write(tmp_path, JSON.generate(HikingTrails.extract(source["path"])))
+          File.rename(tmp_path, out_path)
+        rescue HikingTrails::ExtractError => e
+          File.delete(tmp_path) if File.exist?(tmp_path)
+          warn "hiking trails extraction failed for #{source["code"]}, skipping: #{e.message}"
+        end
+      end
     end
     private_class_method :extract_hiking_trails
 
-    def self.hiking_trails_path(data_dir)
-      File.join(data_dir, "hiking_trails.geojson")
+    def self.hiking_trails_dir(data_dir)
+      File.join(data_dir, "hiking_trails")
+    end
+
+    def self.hiking_trails_country_path(data_dir, code)
+      File.join(hiking_trails_dir(data_dir), "#{code}.geojson")
+    end
+
+    # Country codes with an already-extracted offline hiking-trails file,
+    # sorted — not necessarily the same as the *current* region selection
+    # (accumulates like geofabrik_cache does; a country deselected after
+    # being built once is left alone rather than swept up here).
+    def self.hiking_trails_countries(data_dir)
+      Dir.glob(File.join(hiking_trails_dir(data_dir), "*.geojson")).map { |path| File.basename(path, ".geojson") }.sort
     end
 
     # Renders a report_step string like "fetching PL (3/4) — done: SK, CZ —
@@ -468,7 +497,7 @@ module Maptool
 
       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))
-      File.delete(hiking_trails_path(data_dir)) if File.exist?(hiking_trails_path(data_dir))
+      FileUtils.remove_entry(hiking_trails_dir(data_dir)) if Dir.exist?(hiking_trails_dir(data_dir))
       cache_dir = geofabrik_cache_dir(data_dir)
       FileUtils.remove_entry(cache_dir) if Dir.exist?(cache_dir)
     end