Add -json flag to snapshot show|list

Signed-off-by: Joshua Colson <joshua.colson@gmail.com>

cmd/snapshot_list.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"encoding/json"
 	"fmt"
 
 	"github.com/aptly-dev/aptly/deb"
@@ -8,12 +9,23 @@ import (
 )
 
 func aptlySnapshotList(cmd *commander.Command, args []string) error {
-	var err error
 	if len(args) != 0 {
 		cmd.Usage()
 		return commander.ErrCommandError
 	}
 
+	jsonFlag := cmd.Flag.Lookup("json").Value.Get().(bool)
+
+	if jsonFlag {
+		return aptlySnapshotListJson(cmd, args)
+	}
+
+	return aptlySnapshotListTxt(cmd, args)
+}
+
+func aptlySnapshotListTxt(cmd *commander.Command, args []string) error {
+	var err error
+
 	raw := cmd.Flag.Lookup("raw").Value.Get().(bool)
 	sortMethodString := cmd.Flag.Lookup("sort").Value.Get().(string)
 
@@ -46,6 +58,29 @@ func aptlySnapshotList(cmd *commander.Command, args []string) error {
 	return err
 }
 
+func aptlySnapshotListJson(cmd *commander.Command, args []string) error {
+	var err error
+
+	sortMethodString := cmd.Flag.Lookup("sort").Value.Get().(string)
+
+	collection := context.CollectionFactory().SnapshotCollection()
+
+	jsonSnapshots := make([]*deb.Snapshot, collection.Len())
+	i := 0
+	collection.ForEachSorted(sortMethodString, func(snapshot *deb.Snapshot) error {
+		jsonSnapshots[i] = snapshot
+		i++
+		return nil
+	})
+	if output, e := json.MarshalIndent(jsonSnapshots, "", "  "); e == nil {
+		fmt.Println(string(output))
+	} else {
+		err = e
+	}
+
+	return err
+}
+
 func makeCmdSnapshotList() *commander.Command {
 	cmd := &commander.Command{
 		Run:       aptlySnapshotList,
@@ -60,6 +95,7 @@ Example:
 `,
 	}
 
+	cmd.Flag.Bool("json", false, "display list in JSON format")
 	cmd.Flag.Bool("raw", false, "display list in machine-readable format")
 	cmd.Flag.String("sort", "name", "display list in 'name' or creation 'time' order")