Cache parsed GPX/FIT GeoJSON to fix large POI-export loads

A several-thousand-waypoint park4night area export re-parses the
whole file with REXML on every toggle — ~2.4s for a 5k-waypoint/3.6MB
sample, so tens of seconds for a 50k-waypoint one, likely the actual
cause behind a "Could not load" report on a 41.5MB export. MapLibre
already clusters the waypoint layer client-side, so the bottleneck was
never rendering — cache the GeoJSON conversion alongside the source
file (invalidated by mtime) instead of a bigger bbox/tiling rework.

app.rb

@@ -193,18 +193,17 @@ module Maptool
 
     get "/api/gpx/file/*" do
       begin
-        path = GPX_STORE.resolve_file(params[:splat].first)
+        body = GPX_STORE.geojson(params[:splat].first)
       rescue GpxStore::InvalidPath
         halt 400
-      end
-      halt 404 unless File.file?(path)
-
-      begin
-        geojson = path.downcase.end_with?(".fit") ? Fit.to_geojson(path) : Gpx.to_geojson(path)
-        json geojson
+      rescue Errno::ENOENT
+        halt 404
       rescue Gpx::ParseError, Fit::ParseError
         halt 422, json(error: "could not parse file")
       end
+
+      content_type :json
+      body
     end
 
     post "/api/gpx/folder" do

docs/architecture.adoc

@@ -251,7 +251,12 @@ Rendering:: Checking a file fetches `GET /api/gpx/file/<path>`, routed
 by extension to `Maptool::Gpx` or `Maptool::Fit`
 (`lib/maptool/gpx.rb`/`fit.rb`) for parsing, and both convert to the
 same GeoJSON `FeatureCollection` shape so the frontend doesn't need to
-know which format it got. `Gpx` parses the GPX with REXML: `<wpt>`
+know which format it got. `GpxStore#geojson` caches that conversion
+alongside the source file (`<path>.geojson`, invalidated by mtime) —
+REXML parsing a several-thousand-waypoint POI export (a park4night
+area export, say) can take tens of seconds, and without a cache that
+cost repeats on every single toggle rather than just the first one
+after a save. `Gpx` parses the GPX with REXML: `<wpt>`
 waypoints become `Point` features (with `name`, `desc` and `time`
 carried through as properties), each `<trk>` becomes one
 `MultiLineString` feature (one line per `<trkseg>`), and each `<rte>`

lib/maptool/gpx_store.rb

@@ -1,4 +1,5 @@
 require "fileutils"
+require "json"
 require_relative "gpx"
 require_relative "fit"
 
@@ -58,6 +59,7 @@ module Maptool
       raise Errno::ENOENT, path unless File.file?(path)
 
       File.delete(path)
+      File.delete(geojson_cache_path(path)) if File.file?(geojson_cache_path(path))
     end
 
     def delete_folder(relative_path)
@@ -79,10 +81,30 @@ module Maptool
       dest_dir = resolve_dir(to_folder.to_s)
       FileUtils.mkdir_p(dest_dir)
       name = unique_filename(dest_dir, File.basename(source))
-      FileUtils.mv(source, File.join(dest_dir, name))
+      dest = File.join(dest_dir, name)
+      FileUtils.mv(source, dest)
+      FileUtils.mv(geojson_cache_path(source), geojson_cache_path(dest)) if File.file?(geojson_cache_path(source))
       to_folder.to_s.empty? ? name : "#{to_folder}/#{name}"
     end
 
+    # The GeoJSON conversion (Gpx.to_geojson/Fit.to_geojson) re-parses the
+    # whole file with REXML every call — fine for a small track, but a
+    # several-thousand-waypoint POI export (e.g. a park4night area export)
+    # can take tens of seconds, every single time the file is toggled
+    # visible. Cached alongside the source file and invalidated by mtime,
+    # so only the first read after a save (or edit) pays that cost.
+    def geojson(relative_path)
+      path = resolve_file(relative_path)
+      raise Errno::ENOENT, path unless File.file?(path)
+
+      cache = geojson_cache_path(path)
+      if !File.file?(cache) || File.mtime(cache) < File.mtime(path)
+        data = path.downcase.end_with?(".fit") ? Fit.to_geojson(path) : Gpx.to_geojson(path)
+        File.write(cache, JSON.generate(data))
+      end
+      File.read(cache)
+    end
+
     private
 
     def resolve_dir(folder)
@@ -96,6 +118,10 @@ module Maptool
       path == @root || path.start_with?(@root + File::SEPARATOR)
     end
 
+    def geojson_cache_path(path)
+      "#{path}.geojson"
+    end
+
     TRACK_EXTENSIONS = %w[.gpx .fit].freeze
 
     def safe_filename(filename)

test/test_gpx_store.rb

@@ -67,4 +67,59 @@ class GpxStoreTest < Minitest::Test
     assert_equal "archive/ride-1.gpx", new_path
     assert_empty @store.tree["children"].reject { |c| c["name"] == "archive" }
   end
+
+  def test_geojson_is_cached_alongside_the_source_file
+    path = @store.save(folder: "", filename: "ride.gpx", io: StringIO.new(sample_gpx))
+    cache_path = @store.resolve_file(path) + ".geojson"
+    refute File.file?(cache_path)
+
+    first = @store.geojson(path)
+    assert File.file?(cache_path)
+
+    # Corrupt the cache directly to prove the second call reused it instead
+    # of re-parsing the (still-valid) source file.
+    File.write(cache_path, first.sub("waypoint", "cached-waypoint"))
+    assert_includes @store.geojson(path), "cached-waypoint"
+  end
+
+  def test_geojson_cache_is_invalidated_when_the_file_is_resaved
+    path = @store.save(folder: "", filename: "ride.gpx", io: StringIO.new(sample_gpx))
+    @store.geojson(path)
+
+    File.write(@store.resolve_file(path), sample_gpx.sub("Waypoint", "Renamed"))
+    FileUtils.touch(@store.resolve_file(path), mtime: Time.now + 1)
+
+    assert_includes @store.geojson(path), "Renamed"
+  end
+
+  def test_delete_file_removes_the_geojson_cache_too
+    path = @store.save(folder: "", filename: "ride.gpx", io: StringIO.new(sample_gpx))
+    @store.geojson(path)
+    cache_path = @store.resolve_file(path) + ".geojson"
+
+    @store.delete_file(path)
+
+    refute File.file?(cache_path)
+  end
+
+  def test_move_relocates_the_geojson_cache_too
+    path = @store.save(folder: "", filename: "ride.gpx", io: StringIO.new(sample_gpx))
+    @store.geojson(path)
+
+    new_path = @store.move(from: path, to_folder: "archive")
+
+    assert File.file?(@store.resolve_file(new_path) + ".geojson")
+  end
+
+  def test_geojson_raises_enoent_for_a_missing_file
+    assert_raises(Errno::ENOENT) { @store.geojson("nope.gpx") }
+  end
+
+  private
+
+  def sample_gpx
+    <<~GPX
+      <gpx><wpt lat="48.1" lon="17.1"><name>Waypoint</name></wpt></gpx>
+    GPX
+  end
 end