Write terraformrc only if it doesn't exist

lib/yle_tf/action/write_terraformrc_defaults.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 require 'fileutils'
+require 'pathname'
+
 require 'yle_tf/logger'
 
 class YleTf
@@ -10,45 +12,58 @@ class WriteTerraformrcDefaults
       RC_PATH = '~/.terraformrc'
 
       # Path of the plugin cache directory
-      DEFAULT_PLUGIN_CACHE_PATH = '$HOME/.terraform.d/plugin-cache'
+      DEFAULT_PLUGIN_CACHE_PATH = '~/.terraform.d/plugin-cache'
 
       def initialize(app)
         @app = app
       end
 
       def call(env)
-        Logger.debug("Writing default configuration to '#{RC_PATH}'")
-        open_rc_file do |rc_file|
-          keys = existing_keys(rc_file)
-
-          configure_checkpoint(rc_file) if !keys.include?('disable_checkpoint')
-          configure_plugin_cache_dir(rc_file) if !keys.include?('plugin_cache_dir')
+        if rc_file.exist?
+          Logger.debug("Terraform configuration file '#{RC_PATH}' already exists")
+          if !existing_keys.include?('plugin_cache_dir')
+            Logger.warn("'plugin_cache_dir' not configured in '#{RC_PATH}'")
+          end
+        else
+          Logger.debug("Writing default configuration to '#{RC_PATH}'")
+          write_default_config
         end
 
         @app.call(env)
       end
 
-      def open_rc_file(&block)
-        File.open(File.expand_path(RC_PATH), 'a+', &block)
+      def rc_file
+        @rc_file ||= Pathname.new(RC_PATH).expand_path
       end
 
-      def existing_keys(rc_file)
-        [].tap do |keys|
-          rc_file.each_line do |line|
+      def existing_keys
+        @existing_keys ||= [].tap do |keys|
+          rc_file.readlines.each do |line|
+            # The matcher is a bit naive, but enough for out use
             keys << Regexp.last_match(1) if line =~ /^(.+?)[ \t]*=/
           end
         end
       end
 
-      def configure_checkpoint(rc_file)
+      def write_default_config
+        rc_file.open('w') do |rc_file|
+          configure_checkpoint(rc_file)
+          configure_plugin_cache_dir(rc_file)
+        end
+      end
+
+      def configure_checkpoint(file)
         Logger.info("Disabling Terraform upgrade and security bulletin checks by '#{RC_PATH}'")
 
-        rc_file.puts('disable_checkpoint = true')
+        file.puts('disable_checkpoint = true')
       end
 
-      def configure_plugin_cache_dir(rc_file)
+      def configure_plugin_cache_dir(file)
         Logger.info("Configuring global Terraform plugin cache by '#{RC_PATH}'")
-        rc_file.puts("plugin_cache_dir   = \"#{DEFAULT_PLUGIN_CACHE_PATH}\"")
+        # Replace `~` with `$HOME` as it is not expanded correctly in all architectures.
+        # Can't use `$HOME` in the constant though, as it won't be expanded by
+        # `expand_path` below. Can't win this game.
+        file.puts("plugin_cache_dir   = \"#{DEFAULT_PLUGIN_CACHE_PATH.sub(/^~/, '$HOME')}\"")
 
         dir = File.expand_path(DEFAULT_PLUGIN_CACHE_PATH)
         return if File.directory?(dir)