From 5db08804b8fb3ecc6f48b19642790782733e0e21 Mon Sep 17 00:00:00 2001
From: Christian Bruckmayer <christian.bruckmayer@shopify.com>
Date: Wed, 4 Nov 2020 18:08:57 +0000
Subject: [PATCH] Implement file cache

First approach to implement a file cache.

https://github.com/Shopify/erb-lint/issues/158

Co-authored-by: Mike Dalessio <mike.dalessio@gmail.com>
---
 lib/erb_lint.rb       |  1 +
 lib/erb_lint/cache.rb | 47 +++++++++++++++++++++++++++++++++++++++++++
 lib/erb_lint/cli.rb   | 37 +++++++++++++++++++++++++++++++---
 3 files changed, 82 insertions(+), 3 deletions(-)
 create mode 100644 lib/erb_lint/cache.rb

diff --git a/lib/erb_lint.rb b/lib/erb_lint.rb
index 2e235e3b..55006cee 100644
--- a/lib/erb_lint.rb
+++ b/lib/erb_lint.rb
@@ -3,6 +3,7 @@
 require 'rubocop'
 
 require 'erb_lint/corrector'
+require 'erb_lint/cache'
 require 'erb_lint/file_loader'
 require 'erb_lint/linter_config'
 require 'erb_lint/linter_registry'
diff --git a/lib/erb_lint/cache.rb b/lib/erb_lint/cache.rb
new file mode 100644
index 00000000..72d16f6f
--- /dev/null
+++ b/lib/erb_lint/cache.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+module ERBLint
+  class Cache
+    CACHE_DIRECTORY = '.erb-lint-cache'
+    private_constant :CACHE_DIRECTORY
+
+    def initialize(config)
+      @config = config.to_hash
+    end
+
+    def [](filename)
+      JSON.parse(File.read(File.join(CACHE_DIRECTORY, checksum(filename))))
+    end
+    
+    def include?(filename)
+      File.exist?(File.join(CACHE_DIRECTORY, checksum(filename)))
+    end
+    
+    def []=(filename, messages)
+      FileUtils.mkdir_p(CACHE_DIRECTORY)
+
+      File.open(File.join(CACHE_DIRECTORY, checksum(filename)), 'wb') do |f|
+        f.write messages.to_json
+      end
+    end
+
+    private
+
+    attr_reader :config
+
+    def checksum(file)
+      digester = Digest::SHA1.new
+      mode = File.stat(file).mode
+
+      digester.update(
+        "#{file}#{mode}#{config.to_s}"
+      )
+      digester.file(file)
+      digester.hexdigest
+    rescue Errno::ENOENT
+      # Spurious files that come and go should not cause a crash, at least not
+      # here.
+      '_'
+    end
+  end
+end
diff --git a/lib/erb_lint/cli.rb b/lib/erb_lint/cli.rb
index 46c204f6..6aba0851 100644
--- a/lib/erb_lint/cli.rb
+++ b/lib/erb_lint/cli.rb
@@ -38,6 +38,7 @@ def run(args = ARGV)
       @files = dupped_args
 
       load_config
+      @cache = Cache.new(config)
 
       if !@files.empty? && lint_files.empty?
         failure!("no files found...\n")
@@ -60,7 +61,7 @@ def run(args = ARGV)
       lint_files.each do |filename|
         runner.clear_offenses
         begin
-          run_with_corrections(runner, filename)
+          puts run_on_file(runner, filename)
         rescue => e
           @stats.exceptions += 1
           puts "Exception occured when processing: #{relative_filename(filename)}"
@@ -101,10 +102,36 @@ def run(args = ARGV)
 
     private
 
+    attr_reader :cache, :config
+
+    def run_on_file(runner, filename)
+      if with_cache? && !autocorrect?
+        run_using_cache(runner, filename)
+      else
+        run_with_corrections(runner, filename)
+      end
+    end
+
+    def run_using_cache(runner, filename)
+      puts cache.include?(filename)
+      if cache.include?(filename) && !autocorrect?
+        result = cache[filename]
+        @stats.found += result.size
+        result
+      else
+        result = run_with_corrections(runner, filename)
+        cache[filename] = result
+      end
+    end
+
     def autocorrect?
       @options[:autocorrect]
     end
 
+    def with_cache?
+      @options[:with_cache]
+    end
+
     def run_with_corrections(runner, filename)
       file_content = File.read(filename, encoding: Encoding::UTF_8)
 
@@ -128,8 +155,8 @@ def run_with_corrections(runner, filename)
       end
 
       @stats.found += runner.offenses.size
-      runner.offenses.each do |offense|
-        puts <<~EOF
+      runner.offenses.map do |offense|
+        <<~EOF
           #{offense.message}#{Rainbow(' (not autocorrected)').red if autocorrect?}
           In file: #{relative_filename(filename)}:#{offense.line_range.begin}
 
@@ -266,6 +293,10 @@ def option_parser
           @options[:enabled_linters] = known_linter_names
         end
 
+        opts.on("--with_cache", "Enable caching") do |config|
+          @options[:with_cache] = config
+        end
+
         opts.on("--enable-linters LINTER[,LINTER,...]", Array,
           "Only use specified linter", "Known linters are: #{known_linter_names.join(', ')}") do |linters|
           linters.each do |linter|