Ruby planner (without Rails) (#164)

## Summary

Simple first pass at a Ruby planner. Runs `app.rb` inside the container.

## How was it tested?
`devbox shell` and `devbox build`

Author: ipince

go.mod

@@ -5,6 +5,7 @@ go 1.19
 require (
 	cuelang.org/go v0.4.3
 	github.com/bmatcuk/doublestar/v4 v4.2.0
+	github.com/creekorful/mvnparser v1.5.0
 	github.com/denisbrodbeck/machineid v1.0.1
 	github.com/fatih/color v1.13.0
 	github.com/google/go-cmp v0.4.0
@@ -25,7 +26,6 @@ require golang.org/x/net v0.0.0-20200226121028-0de0cce0169b // indirect
 require (
 	github.com/bmizerany/assert v0.0.0-20160611221934-b7ed37b82869 // indirect
 	github.com/cockroachdb/apd/v2 v2.0.1 // indirect
-	github.com/creekorful/mvnparser v1.5.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/google/uuid v1.2.0 // indirect
 	github.com/inconshreveable/mousetrap v1.0.0 // indirect

planner/languages/ruby/ruby_planner.go

@@ -4,22 +4,78 @@
 package ruby
 
 import (
+	"bufio"
+	"os"
+	"path/filepath"
+	"regexp"
+
 	"go.jetpack.io/devbox/planner/plansdk"
+	"golang.org/x/mod/semver"
 )
 
 type Planner struct{}
 
 // Implements interface Planner (compile-time check)
 var _ plansdk.Planner = (*Planner)(nil)
 
+var nixPackages = map[string]string{
+	"3.1": "ruby_3_1",
+	"3.0": "ruby_3_0",
+	"2.7": "ruby",
+}
+
+const defaultPkg = "ruby_3_1"
+
 func (p *Planner) Name() string {
 	return "ruby.Planner"
 }
 
 func (p *Planner) IsRelevant(srcDir string) bool {
-	return false
+	return plansdk.FileExists(filepath.Join(srcDir, "Gemfile"))
 }
 
 func (p *Planner) GetPlan(srcDir string) *plansdk.Plan {
-	return &plansdk.Plan{}
+	v := parseRubyVersion(filepath.Join(srcDir, "Gemfile"))
+	pkg, ok := nixPackages[semver.MajorMinor(v)]
+	if !ok {
+		pkg = defaultPkg
+	}
+	return &plansdk.Plan{
+		DevPackages: []string{
+			pkg,
+		},
+		RuntimePackages: []string{
+			pkg,
+		},
+		InstallStage: &plansdk.Stage{
+			InputFiles: plansdk.AllFiles(),
+			Command:    "bundle config set --local deployment 'true' && bundle install",
+		},
+		StartStage: &plansdk.Stage{
+			InputFiles: plansdk.AllFiles(),
+			Command:    "bundle exec ruby app.rb",
+		},
+	}
+}
+
+var rubyVersionRegex = regexp.MustCompile(`ruby\s+"(<|>|<=|>=|~>|=|)\s*([\d|\\.]+)"`)
+
+func parseRubyVersion(gemfile string) string {
+	f, err := os.Open(gemfile)
+	if err != nil {
+		return ""
+	}
+	s := bufio.NewScanner(f)
+	for s.Scan() {
+		line := s.Text()
+		matches := rubyVersionRegex.FindStringSubmatch(line)
+		if matches != nil {
+			// TODO: return and use comparator as well.
+			return matches[2]
+		}
+	}
+	if err := s.Err(); err != nil {
+		return ""
+	}
+	return "" // not found
 }

testdata/ruby/ruby-3.1/Gemfile

@@ -0,0 +1,5 @@
+source "https://rubygems.org"
+
+ruby "~> 3.1.0"
+
+gem "colorize", "~> 0.8.1"

testdata/ruby/ruby-3.1/Gemfile.lock

@@ -0,0 +1,17 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    colorize (0.8.1)
+
+PLATFORMS
+  x86_64-darwin-17
+  x86_64-linux
+
+DEPENDENCIES
+  colorize (~> 0.8.1)
+
+RUBY VERSION
+   ruby 3.1.2p20
+
+BUNDLED WITH
+   2.3.7

testdata/ruby/ruby-3.1/app.rb

@@ -0,0 +1,4 @@
+require 'colorize'
+
+puts "Hello world in red!".colorize(:red)
+

testdata/ruby/ruby-3.1/devbox.json

@@ -0,0 +1,7 @@
+{
+  "packages": [
+  ],
+  "shell": {
+    "init_hook": null
+  }
+}