1 files changed, 109 insertions, 0 deletions
diff --git a/dev/sentry.cr b/dev/sentry.cr
new file mode 100644
index 00000000..86d3261c
--- /dev/null
+++ b/dev/sentry.cr
@@ -0,0 +1,109 @@
+module Sentry
+  FILE_TIMESTAMPS = {} of String => String # {file => timestamp}
+
+  class ProcessRunner
+    getter app_process : (Nil | Process) = nil
+    property process_name : String
+    property should_build = true
+    property files = [] of String
+
+    def initialize(
+                   @process_name : String,
+                   @build_command : String,
+                   @run_command : String,
+                   @build_args : Array(String) = [] of String,
+                   @run_args : Array(String) = [] of String,
+                   files = [] of String,
+                   should_build = true)
+      @files = files
+      @should_build = should_build
+      @should_kill = false
+      @app_built = false
+    end
+
+    private def build_app_process
+      puts "🤖  compiling #{process_name}..."
+      build_args = @build_args
+      if build_args.size > 0
+        Process.run(@build_command, build_args, shell: true, output: Process::Redirect::Inherit, error: Process::Redirect::Inherit)
+      else
+        Process.run(@build_command, shell: true, output: Process::Redirect::Inherit, error: Process::Redirect::Inherit)
+      end
+    end
+
+    private def create_app_process
+      app_process = @app_process
+      if app_process.is_a? Process
+        unless app_process.terminated?
+          puts "🤖  killing #{process_name}..."
+          app_process.kill
+        end
+      end
+
+      puts "🤖  starting #{process_name}..."
+      run_args = @run_args
+      if run_args.size > 0
+        @app_process = Process.new(@run_command, run_args, output: Process::Redirect::Inherit, error: Process::Redirect::Inherit)
+      else
+        @app_process = Process.new(@run_command, output: Process::Redirect::Inherit, error: Process::Redirect::Inherit)
+      end
+    end
+
+    private def get_timestamp(file : String)
+      File.stat(file).mtime.to_s("%Y%m%d%H%M%S")
+    end
+
+    # Compiles and starts the application
+    #
+    def start_app
+      return create_app_process unless @should_build
+      build_result = build_app_process()
+      if build_result && build_result.success?
+        @app_built = true
+        create_app_process()
+      elsif !@app_built # if build fails on first time compiling, then exit
+        puts "🤖  Compile time errors detected. SentryBot shutting down..."
+        exit 1
+      end
+    end
+
+    # Scans all of the `@files`
+    #
+    def scan_files
+      file_changed = false
+      app_process = @app_process
+      files = @files
+      Dir.glob(files) do |file|
+        timestamp = get_timestamp(file)
+        if FILE_TIMESTAMPS[file]? && FILE_TIMESTAMPS[file] != timestamp
+          FILE_TIMESTAMPS[file] = timestamp
+          file_changed = true
+          puts "🤖  #{file}"
+        elsif FILE_TIMESTAMPS[file]?.nil?
+          puts "🤖  watching file: #{file}"
+          FILE_TIMESTAMPS[file] = timestamp
+          file_changed = true if (app_process && !app_process.terminated?)
+        end
+      end
+
+      start_app() if (file_changed || app_process.nil?)
+    end
+
+    def run
+      puts "🤖  Your SentryBot is vigilant. beep-boop..."
+
+      loop do
+        if @should_kill
+          puts "🤖  Powering down your SentryBot..."
+          break
+        end
+        scan_files
+        sleep 1
+      end
+    end
+
+    def kill
+      @should_kill = true
+    end
+  end
+end