feat(alerting): Add overrides for Mattermost (#292)

* add override support for mattermost

* add documentation for override Mattermost webhooks

* Apply suggestions from code review

Co-authored-by: TwiN <twin@linux.com>

* fix formatting

Co-authored-by: Michael Engelhardt <me@mindcrime.dev>
Co-authored-by: TwiN <twin@linux.com>

README.md

@@ -488,11 +488,14 @@ endpoints:
 
 #### Configuring Mattermost alerts
 | Parameter                                     | Description                                                                                 | Default       |
-|:------------------------------------|:--------------------------------------------------------------------------------------------|:--------------|
+|:----------------------------------------------|:--------------------------------------------------------------------------------------------|:--------------|
 | `alerting.mattermost`                         | Configuration for alerts of type `mattermost`                                               | `{}`          |
 | `alerting.mattermost.webhook-url`             | Mattermost Webhook URL                                                                      | Required `""` |
 | `alerting.mattermost.client`                  | Client configuration. <br />See [Client configuration](#client-configuration).              | `{}`          |
 | `alerting.mattermost.default-alert`           | Default alert configuration. <br />See [Setting a default alert](#setting-a-default-alert). | N/A           |
+| `alerting.mattermost.overrides`               | List of overrides that may be prioritized over the default configuration                    | `[]`          |
+| `alerting.mattermost.overrides[].group`       | Endpoint group for which the configuration will be overridden by this configuration         | `""`          |
+| `alerting.mattermist.overrides[].webhook-url` | Mattermost Webhook URL                                                                      | `""`          |
 
 ```yaml
 alerting:

alerting/provider/mattermost/mattermost.go

@@ -20,6 +20,15 @@ type AlertProvider struct {
 
 	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
 	DefaultAlert *alert.Alert `yaml:"default-alert,omitempty"`
+
+	// Overrides is a list of Override that may be prioritized over the default configuration
+	Overrides []Override `yaml:"overrides,omitempty"`
+}
+
+// Override is a case under which the default integration is overridden
+type Override struct {
+	Group      string `yaml:"group"`
+	WebhookURL string `yaml:"webhook-url"`
 }
 
 // IsValid returns whether the provider's configuration is valid
@@ -27,13 +36,22 @@ func (provider *AlertProvider) IsValid() bool {
 	if provider.ClientConfig == nil {
 		provider.ClientConfig = client.GetDefaultConfig()
 	}
+	if provider.Overrides != nil {
+		registeredGroups := make(map[string]bool)
+		for _, override := range provider.Overrides {
+			if isAlreadyRegistered := registeredGroups[override.Group]; isAlreadyRegistered || override.Group == "" || len(override.WebhookURL) == 0 {
+				return false
+			}
+			registeredGroups[override.Group] = true
+		}
+	}
 	return len(provider.WebhookURL) > 0
 }
 
 // Send an alert using the provider
 func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
 	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
-	request, err := http.NewRequest(http.MethodPost, provider.WebhookURL, buffer)
+	request, err := http.NewRequest(http.MethodPost, provider.getWebhookURLForGroup(endpoint.Group), buffer)
 	if err != nil {
 		return err
 	}
@@ -101,6 +119,19 @@ func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *
 }`, message, message, description, color, endpoint.URL, results)
 }
 
+
+// getWebhookURLForGroup returns the appropriate Webhook URL integration to for a given group
+func (provider *AlertProvider) getWebhookURLForGroup(group string) string {
+	if provider.Overrides != nil {
+		for _, override := range provider.Overrides {
+			if group == override.Group {
+				return override.WebhookURL
+			}
+		}
+	}
+	return provider.WebhookURL
+}
+
 // GetDefaultAlert returns the provider's default alert configuration
 func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
 	return provider.DefaultAlert

alerting/provider/mattermost/mattermost_test.go

@@ -22,6 +22,47 @@ func TestAlertProvider_IsValid(t *testing.T) {
 	}
 }
 
+func TestAlertProvider_IsValidWithOverride(t *testing.T) {
+	providerWithInvalidOverrideGroup := AlertProvider{
+		Overrides: []Override{
+			{
+				WebhookURL: "http://example.com",
+				Group:      "",
+			},
+		},
+	}
+
+	if providerWithInvalidOverrideGroup.IsValid() {
+		t.Error("provider Group shouldn't have been valid")
+	}
+
+	providerWithInvalidOverrideWebHookUrl := AlertProvider{
+		Overrides: []Override{
+			{
+
+				WebhookURL: "",
+				Group:      "group",
+			},
+		},
+	}
+	if providerWithInvalidOverrideWebHookUrl.IsValid() {
+		t.Error("provider WebHookURL shoudn't have been valid")
+	}
+
+	providerWithValidOverride := AlertProvider{
+		WebhookURL: "http://example.com",
+		Overrides: []Override{
+			{
+				WebhookURL: "http://example.com",
+				Group:      "group",
+			},
+		},
+	}
+	if !providerWithValidOverride.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
 func TestAlertProvider_Send(t *testing.T) {
 	defer client.InjectHTTPClient(nil)
 	firstDescription := "description-1"
@@ -156,3 +197,66 @@ func TestAlertProvider_GetDefaultAlert(t *testing.T) {
 		t.Error("expected default alert to be nil")
 	}
 }
+
+func TestAlertProvider_getWebhookURLForGroup(t *testing.T) {
+	tests := []struct {
+		Name           string
+		Provider       AlertProvider
+		InputGroup     string
+		ExpectedOutput string
+	}{
+		{
+			Name: "provider-no-override-specify-no-group-should-default",
+			Provider: AlertProvider{
+				WebhookURL: "http://example.com",
+				Overrides:  nil,
+			},
+			InputGroup:     "",
+			ExpectedOutput: "http://example.com",
+		},
+		{
+			Name: "provider-no-override-specify-group-should-default",
+			Provider: AlertProvider{
+				WebhookURL: "http://example.com",
+				Overrides:  nil,
+			},
+			InputGroup:     "group",
+			ExpectedOutput: "http://example.com",
+		},
+		{
+			Name: "provider-with-override-specify-no-group-should-default",
+			Provider: AlertProvider{
+				WebhookURL: "http://example.com",
+				Overrides: []Override{
+					{
+						Group:      "group",
+						WebhookURL: "http://example01.com",
+					},
+				},
+			},
+			InputGroup:     "",
+			ExpectedOutput: "http://example.com",
+		},
+		{
+			Name: "provider-with-override-specify-group-should-override",
+			Provider: AlertProvider{
+				WebhookURL: "http://example.com",
+				Overrides: []Override{
+					{
+						Group:      "group",
+						WebhookURL: "http://example01.com",
+					},
+				},
+			},
+			InputGroup:     "group",
+			ExpectedOutput: "http://example01.com",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.Name, func(t *testing.T) {
+			if got := tt.Provider.getWebhookURLForGroup(tt.InputGroup); got != tt.ExpectedOutput {
+				t.Errorf("AlertProvider.getToForGroup() = %v, want %v", got, tt.ExpectedOutput)
+			}
+		})
+	}
+}