Add ensure command

Author: bitfield

Diff for: README.md

@@ -165,6 +165,21 @@ uptimerobot new -c 0102759,2053888 https://www.example.com/ "Example.com website
 New monitor created with ID 780689019
 ```
 
+## Ensuring a monitor exists
+
+Sometimes you want to create a new monitor only if a monitor doesn't already exist for the same URL. This is especially useful in automation.
+
+To do this, run `uptimerobot ensure URL NAME`:
+
+```
+uptimerobot ensure https://www.example.com/ "Example.com website"
+Monitor ID 780689018
+```
+
+If a monitor already existed for the same URL, its ID will be returned. Otherwise, a new monitor will be created, and its ID returned.
+
+You can use the `-c` flag to add alert contacts, just as for the `uptimerobot new` command.
+
 ## Using the Go library
 
 If the command-line client doesn't do quite what you need, or if you want to use UptimeRobot API access in your own programs, import the library using:

Diff for: cmd/ensure.go

@@ -0,0 +1,33 @@
+package cmd
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/bitfield/uptimerobot/pkg"
+	"github.com/spf13/cobra"
+)
+
+var ensureCmd = &cobra.Command{
+	Use:   "ensure",
+	Short: "add a new monitor if not present",
+	Long:  `Create a new monitor with the specified URL and friendly name, if the monitor does not already exist`,
+	Args:  cobra.ExactArgs(2),
+	Run: func(cmd *cobra.Command, args []string) {
+		m := uptimerobot.Monitor{
+			URL:           args[0],
+			FriendlyName:  args[1],
+			Type:          uptimerobot.MonitorType("HTTP"),
+			AlertContacts: contacts,
+		}
+		result, err := client.EnsureMonitor(m)
+		if err != nil {
+			log.Fatal(err)
+		}
+		fmt.Printf("Monitor ID %d\n", result.ID)
+	},
+}
+
+func init() {
+	RootCmd.AddCommand(ensureCmd)
+}

Diff for: pkg/uptimerobot.go

@@ -196,6 +196,26 @@ func (c *Client) NewMonitor(m Monitor) (Monitor, error) {
 	return r.Monitor, nil
 }
 
+// EnsureMonitor takes a Monitor and creates a new UptimeRobot monitor with the
+// specified details, if a monitor for the same URL does not already exist. It
+// returns a Monitor with the ID field set to the ID of the newly created
+// monitor or the existing monitor if it already existed, or an error if the
+// operation failed.
+func (c *Client) EnsureMonitor(m Monitor) (Monitor, error) {
+	monitors, err := c.GetMonitorsBySearch(m.URL)
+	if err != nil {
+		return Monitor{}, err
+	}
+	if len(monitors) == 0 {
+		new, err := c.NewMonitor(m)
+		if err != nil {
+			return Monitor{}, err
+		}
+		return new, nil
+	}
+	return monitors[0], nil
+}
+
 // DeleteMonitor takes a Monitor with the ID field set, and deletes the
 // corresponding monitor. It returns a Monitor with the ID field set to the ID
 // of the deleted monitor, or an error if the operation failed.

Diff for: pkg/uptimerobot_test.go

@@ -217,6 +217,26 @@ func TestNewMonitor(t *testing.T) {
 	}
 }
 
+func TestEnsureMonitor(t *testing.T) {
+	c := New("dummy")
+	mockClient := MockHTTPClient{
+		DoFunc: fakeGetMonitorsBySearchHandler,
+	}
+	c.http = &mockClient
+	want := Monitor{
+		FriendlyName: "My Web Page",
+		URL:          "http://mywebpage.com",
+		Type:         MonitorType("HTTP"),
+	}
+	got, err := c.EnsureMonitor(want)
+	if err != nil {
+		t.Error(err)
+	}
+	if got.ID != 777712827 {
+		t.Errorf("EnsureMonitor() => ID %d, want 777712827", got.ID)
+	}
+}
+
 func TestDeleteMonitor(t *testing.T) {
 	c := New("dummy")
 	mockClient := MockHTTPClient{