Finish the API endpoint for cover upload

src/upload.cr

@@ -0,0 +1,60 @@
+require "./util"
+
+class Upload
+  def initialize(@dir : String, @logger : Logger)
+    unless Dir.exists? @dir
+      @logger.info "The uploads directory #{@dir} does not exist. " \
+                   "Attempting to create it"
+      Dir.mkdir_p @dir
+    end
+  end
+
+  # Writes IO to a file with random filename in the uploads directory and
+  #	  returns the full path of created file
+  # e.g., save("image", ".png", <io>)
+  #	  ==> "~/mango/uploads/image/<random string>.png"
+  def save(sub_dir : String, ext : String, io : IO)
+    full_dir = File.join @dir, sub_dir
+    filename = random_str + ext
+    file_path = File.join full_dir, filename
+
+    unless Dir.exists? full_dir
+      @logger.debug "creating directory #{full_dir}"
+      Dir.mkdir_p full_dir
+    end
+
+    File.open file_path, "w" do |f|
+      IO.copy io, f
+    end
+
+    file_path
+  end
+
+  # Converts path to a file in the uploads directory to the URL path for
+  #   accessing the file.
+  def path_to_url(path : String)
+    dir_mathed = false
+    ary = [] of String
+    # We fill it with parts until it equals to @upload_dir
+    dir_ary = [] of String
+
+    Path.new(path).each_part do |part|
+      if dir_mathed
+        ary << part
+      else
+        dir_ary << part
+        if File.same? @dir, File.join dir_ary
+          dir_mathed = true
+        end
+      end
+    end
+
+    if ary.empty?
+      @logger.warn "File #{path} is not in the upload directory #{@dir}"
+      return
+    end
+
+    ary.unshift UPLOAD_URL_PREFIX
+    File.join(ary).to_s
+  end
+end