Add ls command to tvm (#37)

* Add ls command to tvm

This allows you to list the locally-downloaded versions of Terraform in
the tvm repo/cache.

astro/tvm/cli/tvm/cmd/install.go

@@ -20,11 +20,10 @@ import (
 	"fmt"
 	"log"
 
+	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
 
 	"github.com/uber/astro/astro/tvm"
-
-	"github.com/spf13/cobra"
 )
 
 // defaultInstallPath is the path that the Terraform binary will be

astro/tvm/cli/tvm/cmd/list.go

@@ -0,0 +1,95 @@
+/*
+ *  Copyright (c) 2019 Uber Technologies, Inc.
+ *
+ *     Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"sort"
+
+	version "github.com/burl/go-version"
+	"github.com/spf13/cobra"
+
+	"github.com/uber/astro/astro/tvm"
+)
+
+var listCmd = &cobra.Command{
+	Use:   "ls",
+	Short: "List locally downloaded versions of Terraform",
+	Run: func(cmd *cobra.Command, args []string) {
+		tvm, err := tvm.NewVersionRepoForCurrentSystem(repoPath)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		// Get list of downloaded versions and path to binaries
+		versionsPaths, err := tvm.List()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		// Extract just the version strings
+		versions := []string{}
+		for v := range versionsPaths {
+			versions = append(versions, v)
+		}
+
+		// Get the path to the current Terraform binary, according to $PATH
+		terraformPath, _ := exec.LookPath("terraform")
+
+		// Get path that Terraform binary links to
+		terraformLinkPath, _ := os.Readlink(terraformPath)
+
+		// List the versions
+		for _, v := range sortedVersions(versions) {
+			s := v.String()
+			print(s)
+
+			// If the current Terraform binary is linked to a particular
+			// path from tvm, then it's active and has been installed by tvm
+			if versionsPaths[s] == terraformLinkPath {
+				fmt.Printf(" (current, installed at: %s)", terraformPath)
+			}
+
+			println()
+		}
+	},
+}
+
+// sortedVersions takes a list of version strings and returns them sorted in
+// reverse order.
+func sortedVersions(versions []string) (sortedVersions version.Collection) {
+	for _, v := range versions {
+		semver, err := version.NewVersion(v)
+		if err != nil {
+			log.Println(err)
+			continue
+		}
+
+		sortedVersions = append(sortedVersions, semver)
+	}
+
+	sort.Sort(sort.Reverse(sortedVersions))
+
+	return
+}
+
+func init() {
+	rootCmd.AddCommand(listCmd)
+}

astro/tvm/versionrepo.go

@@ -25,6 +25,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"regexp"
 	"runtime"
 	"sync"
 
@@ -40,6 +41,10 @@ const terraformBinaryFile = "terraform"
 // files from the Hashicorp website.
 var terraformZipFileDownloadURL = "https://releases.hashicorp.com/terraform/%s/terraform_%s_%s_%s.zip"
 
+// versionDirectoryFormat is a regexp that matches Terraform semver,
+// e.g. "1.2.30"
+var versionDirectoryFormat = regexp.MustCompile(`\d+\.\d+\.\d+`)
+
 // VersionRepo is a directory on the filesystem that keeps
 // Terraform binaries.
 type VersionRepo struct {
@@ -191,6 +196,32 @@ func (r *VersionRepo) Link(version string, targetPath string, overwrite bool) er
 	return os.Symlink(terraformPath, targetPath)
 }
 
+// List returns all locally downloaded Terraform versions and their paths.
+func (r *VersionRepo) List() (map[string]string, error) {
+	dirs := map[string]string{}
+
+	repoBaseDir := r.dir("")
+	f, err := os.Open(repoBaseDir)
+	defer f.Close()
+	if err != nil {
+		return nil, err
+	}
+
+	files, err := f.Readdir(-1)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, file := range files {
+		terraformVersion := file.Name()
+		if file.IsDir() && versionDirectoryFormat.MatchString(terraformVersion) {
+			dirs[terraformVersion] = r.terraformPath(terraformVersion)
+		}
+	}
+
+	return dirs, nil
+}
+
 // terraformPath returns the path to the Terraform binary file with the
 // specified version.
 func (r *VersionRepo) terraformPath(version string) string {