Add a pre-deploy hook

Useful for checking the status of CI before deploying. Doing this at
this point in the deployment maximises the parallelisation of building
and running CI.

lib/mrsk/cli/base.rb

@@ -133,15 +133,39 @@ module Mrsk::Cli
         end
       end
 
-      def run_hook(hook, **details)
+      def run_hook(hook, **extra_details)
         if !options[:skip_hooks] && MRSK.hook.hook_exists?(hook)
+          details = { hosts: MRSK.hosts.join(","), command: command, subcommand: subcommand }
+
           say "Running the #{hook} hook...", :magenta
           run_locally do
-            MRSK.with_verbosity(:debug) { execute *MRSK.hook.run(hook, **details, hosts: MRSK.hosts.join(",")) }
+            MRSK.with_verbosity(:debug) { execute *MRSK.hook.run(hook, **details, **extra_details) }
           rescue SSHKit::Command::Failed
             raise HookError.new("Hook `#{hook}` failed")
           end
         end
       end
-  end
+
+      def command
+        @mrsk_command ||= begin
+          invocation_class, invocation_commands = *first_invocation
+          if invocation_class == Mrsk::Cli::Main
+            invocation_commands[0]
+          else
+            Mrsk::Cli::Main.subcommand_classes.find { |command, clazz| clazz == invocation_class }[0]
+          end
+        end
+      end
+
+      def subcommand
+        @mrsk_subcommand ||= begin
+          invocation_class, invocation_commands = *first_invocation
+          invocation_commands[0] if invocation_class != Mrsk::Cli::Main
+        end
+      end
+
+      def first_invocation
+        instance_variable_get("@_invocations").first
+      end
+    end
 end

lib/mrsk/cli/main.rb

@@ -28,6 +28,8 @@ class Mrsk::Cli::Main < Mrsk::Cli::Base
           invoke "mrsk:cli:build:deliver", [], invoke_options
         end
 
+        run_hook "pre-deploy"
+
         say "Ensure Traefik is running...", :magenta
         invoke "mrsk:cli:traefik:boot", [], invoke_options
 
@@ -62,6 +64,8 @@ class Mrsk::Cli::Main < Mrsk::Cli::Base
           invoke "mrsk:cli:build:deliver", [], invoke_options
         end
 
+        run_hook "pre-deploy"
+
         say "Ensure app can pass healthcheck...", :magenta
         invoke "mrsk:cli:healthcheck:perform", [], invoke_options
 
@@ -86,6 +90,8 @@ class Mrsk::Cli::Main < Mrsk::Cli::Base
         old_version = nil
 
         if container_available?(version)
+          run_hook "pre-deploy"
+
           invoke "mrsk:cli:app:boot", [], invoke_options.merge(version: version)
           rolled_back = true
         else

lib/mrsk/cli/templates/sample_hooks/pre-deploy.sample

@@ -0,0 +1,82 @@
+#!/bin/sh
+
+# A sample pre-deploy hook
+#
+# Checks the Github status of the build, waiting for a pending build to complete for up to 720 seconds.
+#
+# Fails unless the combined status is "success"
+#
+# These environment variables are available:
+# MRSK_RECORDED_AT
+# MRSK_PERFORMER
+# MRSK_VERSION
+# MRSK_HOSTS
+# MRSK_COMMAND
+# MRSK_SUBCOMMAND
+# MRSK_ROLE (if set)
+# MRSK_DESTINATION (if set)
+
+#!/usr/bin/env ruby
+
+# Only check the build status for production deployments
+if ENV["MRSK_COMMAND"] == "rollback" || ENV["MRSK_DESTINATION"] != "production"
+  exit 0
+end
+
+require "bundler/inline"
+
+# true = install gems so this is fast on repeat invocations
+gemfile(true, quiet: true) do
+  source "https://rubygems.org"
+
+  gem "octokit"
+  gem "faraday-retry"
+end
+
+MAX_ATTEMPTS = 72
+ATTEMPTS_GAP = 10
+
+def exit_with_error(message)
+  $stderr.puts message
+  exit 1
+end
+
+def first_status_url(combined_status, state)
+  first_status = combined_status[:statuses].find { |status| status[:state] == state }
+  first_status && first_status[:target_url]
+end
+
+remote_url = `git config --get remote.origin.url`.strip.delete_prefix("https://github.com/")
+git_sha = `git rev-parse HEAD`.strip
+
+repository = Octokit::Repository.from_url(remote_url)
+github_client = Octokit::Client.new(access_token: ENV["GITHUB_TOKEN"])
+attempts = 0
+
+begin
+  loop do
+    combined_status = github_client.combined_status(remote_url, git_sha)
+    state = combined_status[:state]
+    first_status_url = first_status_url(combined_status, state)
+
+    case state
+    when "success"
+      puts "Build passed, see #{first_status_url}"
+      exit 0
+    when "failure"
+      exit_with_error "Build failed, see #{first_status_url}"
+    when "pending"
+      attempts += 1
+    end
+
+    puts "Waiting #{ATTEMPTS_GAP} more seconds for build to complete#{", see #{first_status_url}" if first_status_url}..."
+
+    if attempts == MAX_ATTEMPTS
+      exit_with_error "Build status is still pending, gave up after #{MAX_ATTEMPTS * ATTEMPTS_GAP} seconds"
+    end
+
+    sleep(ATTEMPTS_GAP)
+  end
+rescue Octokit::NotFound
+  exit_with_error "Build status could not be found"
+end