Support of '_completion' command (#45)

README.md

@@ -916,6 +916,7 @@ Development in progress
 
 #### Features
 
+* Support of `_completion` command (shell completion helper) ([#45](https://github.com/scaleway/scaleway-cli/issues/45))
 * Returing more resource fields on `scw inspect` ([#50](https://github.com/scaleway/scaleway-cli/issues/50))
 * Show public ip address in PORTS field in `scw ps` ([#54](https://github.com/scaleway/scaleway-cli/issues/54))
 * Support of `inspect --format` option

cli.go

@@ -233,6 +233,7 @@ func (c *Command) GetBootscript(needle string) string {
 var commands = []*Command{
 	cmdAttach,
 	cmdCommit,
+	cmdCompletion,
 	cmdCp,
 	cmdCreate,
 	cmdEvents,

completion.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"sort"
+	"strings"
+)
+
+var cmdCompletion = &Command{
+	Exec:        runCompletion,
+	UsageLine:   "_completion [OPTIONS] CATEGORY",
+	Description: "Completion helper",
+	Help:        "Completion helper.",
+	Hidden:      true,
+	Examples: `
+    $ scw _completion servers-all
+    $ scw _completion images-all
+    $ scw _completion snapshots-all
+    $ scw _completion volumes-all
+    $ scw _completion bootscripts-all
+`,
+}
+
+func init() {
+	cmdCompletion.Flag.BoolVar(&completionHelp, []string{"h", "-help"}, false, "Print usage")
+}
+
+// Flags
+var completionHelp bool // -h, --help flag
+
+func runCompletion(cmd *Command, args []string) {
+	if completionHelp {
+		cmd.PrintUsage()
+	}
+	if len(args) != 1 {
+		cmd.PrintShortUsage()
+	}
+
+	category := args[0]
+
+	elements := []string{}
+
+	switch category {
+	case "servers-all":
+		for identifier, name := range cmd.API.Cache.Servers {
+			elements = append(elements, identifier, wordify(name))
+		}
+	case "images-all":
+		for identifier, name := range cmd.API.Cache.Images {
+			elements = append(elements, identifier, wordify(name))
+		}
+	case "volumes-all":
+		for identifier, name := range cmd.API.Cache.Volumes {
+			elements = append(elements, identifier, wordify(name))
+		}
+	case "snapshots-all":
+		for identifier, name := range cmd.API.Cache.Snapshots {
+			elements = append(elements, identifier, wordify(name))
+		}
+	case "bootscripts-all":
+		for identifier, name := range cmd.API.Cache.Bootscripts {
+			elements = append(elements, identifier, wordify(name))
+		}
+	default:
+		log.Fatalf("Unhandled category of completion: %s", category)
+	}
+
+	sort.Strings(elements)
+	fmt.Println(strings.Join(RemoveDuplicates(elements), "\n"))
+}