assets: Emit source maps

I had to rename deps because there was a name collision where the file was
written to twice once in compile_lib and another time in combine.

This made it much easier to debug some issues.

Makefile

@@ -3,7 +3,7 @@ CONTAINER_COMPOSE ?= $(CONTAINER_ENGINE)-compose
 CONTAINER_ENGINE ?= docker
 
 clean:
-	sudo rm -rfv build/ public/assets/*.js public/assets/*.js.gz public/assets/version.json
+	sudo rm -rfv build/ public/assets/*.js public/assets/*.js.map public/assets/*.js.gz public/assets/version.json
 
 cleandeps:
 	sudo rm -rfv public/assets/deps.js

lib/assets.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'json'
 require 'opal'
 require 'snabberb'
 require 'tempfile'
@@ -97,8 +98,8 @@ def builds(titles = [])
         **game_builds(:all),
       }
     else
-      @_opal ||= compile_lib('opal')
-      @_deps ||= compile_lib('deps', 'assets')
+      @_opal ||= compile_lib('opal', 'opal')
+      @_deps ||= compile_lib('deps_only', 'deps', 'assets')
       @_engine ||= compile('engine', 'lib', 'engine')
       @_app ||= compile('app', 'assets/app', '')
 
@@ -164,6 +165,31 @@ def combine(titles = [])
       @_combined.include?(key) ? next : @_combined.add(key)
 
       source = build['files'].map { |file| File.read(file).to_s }.join("\n")
+      if build['files'].size == 1
+        source = File.read(build['files'][0]).to_s
+        source += "\n//# sourceMappingURL=#{build['path'].delete_prefix('public')}.map\n"
+      else
+        source_map = {
+          'version' => 3,
+          'sections' => [],
+        }
+        current_line = 0
+        source = build['files'].map do |filepath|
+          file_source_map = JSON.parse(File.read(filepath + '.map'))
+          file_source_map['sections'].each do |section|
+            source_map['sections'].append({
+                                            'offset' => { 'line' => current_line + section['offset']['line'], 'column' => 0 },
+                                            'map' => section['map'],
+                                          })
+          end
+
+          file = File.read(filepath).to_s
+          current_line += file.lines.count + 1
+          file
+        end.join("\n")
+        source += "\n//# sourceMappingURL=#{build['path'].delete_prefix('public')}.map\n"
+        File.write(build['path'] + '.map', source_map.to_json)
+      end
       source = compress(key, source) if @compress
       File.write(build['path'], source)
 
@@ -182,13 +208,14 @@ def combine(titles = [])
     [@deps_path, @main_path, *game_paths]
   end
 
-  def compile_lib(name, *append_paths)
+  def compile_lib(output_name, name, *append_paths)
     builder = Opal::Builder.new
     append_paths.each { |ap| builder.append_paths(ap) }
-    path = "#{@out_path}/#{name}.js"
-    if !@cache || !File.exist?(path) || path == @deps_path
+    path = "#{@out_path}/#{output_name}.js"
+    if !@cache || !File.exist?(path)
       time = Time.now
       File.write(path, builder.build(name))
+      File.write("#{path}.map", builder.source_map.map.to_json)
       puts "Compiling #{name} - #{Time.now - time}"
     end
     path
@@ -214,17 +241,30 @@ def compile(name, lib_path, ns = nil, game: nil)
 
       time = Time.now
       File.write(opts[:js_path], compiler.compile)
+      File.write(opts[:js_path] + '.map', compiler.source_map.map.to_json)
       puts "Compiling #{file} - #{Time.now - time}"
     end
 
+    source_map = {
+      'version' => 3,
+      'sections' => [],
+    }
+    current_line = 0
     source = metadata.map do |_file, opts|
-      File.read(opts[:js_path]).to_s
+      file = File.read(opts[:js_path])
+      source_map['sections'].append({
+                                      'offset' => { 'line' => current_line, 'column' => 0 },
+                                      'map' => JSON.parse(File.read(opts[:js_path] + '.map')),
+                                    })
+      current_line += file.lines.count + 1
+      file
     end.join("\n")
 
     opal_load = game ? "engine/game/#{game}" : name
     source += "\nOpal.load('#{opal_load}')"
 
     File.write(output, source)
+    File.write(output + '.map', source_map.to_json)
     output
   end