feat(alert): Add group-specific to email list (#264)

* feat(alert): Add group-specific to email list

Add group-specific to list for email alert

https://github.com/TwiN/gatus/issues/96

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* docs: update

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* Update README.md

* Update README.md

* Update README.md

* chore: update

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* Update README.md

README.md

@@ -377,7 +377,7 @@ endpoints:
 
 #### Configuring Email alerts
 | Parameter                          | Description                                                                                | Default       |
-|:-------------------------------|:-------------------------------------------------------------------------------------------|:----------------------|
+|:---------------------------------- |:------------------------------------------------------------------------------------------ |:------------- |
 | `alerting.email`                   | Configuration for alerts of type `email`                                                   | `{}`          |
 | `alerting.email.from`              | Email used to send the alert                                                               | Required `""` |
 | `alerting.email.username`          | Username of the SMTP server used to send the alert. If empty, uses `alerting.email.from`.  | `""`          |
@@ -386,6 +386,9 @@ endpoints:
 | `alerting.email.port`              | Port the mail server is listening to (e.g. `587`)                                          | Required `0`  |
 | `alerting.email.to`                | Email(s) to send the alerts to                                                             | Required `""` |
 | `alerting.email.default-alert`     | Default alert configuration. <br />See [Setting a default alert](#setting-a-default-alert) | N/A           |
+| `alerting.email.overrides`         | List of overrides that may be prioritized over the default configuration                   | `[]`          |
+| `alerting.email.overrides[].group` | Endpoint group for which the configuration will be overridden by this configuration        | `""`          |
+| `alerting.email.overrides[].to`    | Email(s) to send the alerts to                                                             | `""`          |
 
 ```yaml
 alerting:
@@ -396,6 +399,11 @@ alerting:
     host: "mail.example.com"
     port: 587
     to: "recipient1@example.com,recipient2@example.com"
+    # You can also add group-specific to keys, which will 
+    # override the to key above for the specified groups
+    overrides:
+      - group: "core"
+        to: "recipient3@example.com,recipient4@example.com"
 
 endpoints:
   - name: website
@@ -410,6 +418,19 @@ endpoints:
         enabled: true
         description: "healthcheck failed"
         send-on-resolved: true
+
+  - name: back-end
+    group: core
+    url: "https://example.org/"
+    interval: 5m
+    conditions:
+      - "[STATUS] == 200"
+      - "[CERTIFICATE_EXPIRATION] > 48h"
+    alerts:
+      - type: email
+        enabled: true
+        description: "healthcheck failed"
+        send-on-resolved: true
 ```
 
 **NOTE:** Some mail servers are painfully slow.

alerting/provider/email/email.go

@@ -21,10 +21,29 @@ 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"`
+	To    string `yaml:"to"`
 }
 
 // IsValid returns whether the provider's configuration is valid
 func (provider *AlertProvider) IsValid() bool {
+	registeredGroups := make(map[string]bool)
+	if provider.Overrides != nil {
+		for _, override := range provider.Overrides {
+			if isAlreadyRegistered := registeredGroups[override.Group]; isAlreadyRegistered || override.Group == "" || len(override.To) == 0 {
+				return false
+			}
+			registeredGroups[override.Group] = true
+		}
+	}
+
 	return len(provider.From) > 0 && len(provider.Password) > 0 && len(provider.Host) > 0 && len(provider.To) > 0 && provider.Port > 0 && provider.Port < math.MaxUint16
 }
 
@@ -39,7 +58,7 @@ func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert,
 	subject, body := provider.buildMessageSubjectAndBody(endpoint, alert, result, resolved)
 	m := gomail.NewMessage()
 	m.SetHeader("From", provider.From)
-	m.SetHeader("To", strings.Split(provider.To, ",")...)
+	m.SetHeader("To", strings.Split(provider.getToForGroup(endpoint.Group), ",")...)
 	m.SetHeader("Subject", subject)
 	m.SetBody("text/plain", body)
 	d := gomail.NewDialer(provider.Host, provider.Port, username, provider.Password)
@@ -72,6 +91,18 @@ func (provider *AlertProvider) buildMessageSubjectAndBody(endpoint *core.Endpoin
 	return subject, message + description + "\n\nCondition results:\n" + results
 }
 
+// getToForGroup returns the appropriate email integration to for a given group
+func (provider *AlertProvider) getToForGroup(group string) string {
+	if provider.Overrides != nil {
+		for _, override := range provider.Overrides {
+			if group == override.Group {
+				return override.To
+			}
+		}
+	}
+	return provider.To
+}
+
 // GetDefaultAlert returns the provider's default alert configuration
 func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
 	return provider.DefaultAlert

alerting/provider/email/email_test.go

@@ -7,7 +7,7 @@ import (
 	"github.com/TwiN/gatus/v3/core"
 )
 
-func TestAlertProvider_IsValid(t *testing.T) {
+func TestAlertDefaultProvider_IsValid(t *testing.T) {
 	invalidProvider := AlertProvider{}
 	if invalidProvider.IsValid() {
 		t.Error("provider shouldn't have been valid")
@@ -18,6 +18,47 @@ func TestAlertProvider_IsValid(t *testing.T) {
 	}
 }
 
+func TestAlertProvider_IsValidWithOverride(t *testing.T) {
+	providerWithInvalidOverrideGroup := AlertProvider{
+		Overrides: []Override{
+			{
+				To:    "to@example.com",
+				Group: "",
+			},
+		},
+	}
+	if providerWithInvalidOverrideGroup.IsValid() {
+		t.Error("provider Group shouldn't have been valid")
+	}
+	providerWithInvalidOverrideTo := AlertProvider{
+		Overrides: []Override{
+			{
+				To:    "",
+				Group: "group",
+			},
+		},
+	}
+	if providerWithInvalidOverrideTo.IsValid() {
+		t.Error("provider integration key shouldn't have been valid")
+	}
+	providerWithValidOverride := AlertProvider{
+		From:     "from@example.com",
+		Password: "password",
+		Host:     "smtp.gmail.com",
+		Port:     587,
+		To:       "to@example.com",
+		Overrides: []Override{
+			{
+				To:    "to@example.com",
+				Group: "group",
+			},
+		},
+	}
+	if !providerWithValidOverride.IsValid() {
+		t.Error("provider should've been valid")
+	}
+}
+
 func TestAlertProvider_buildRequestBody(t *testing.T) {
 	firstDescription := "description-1"
 	secondDescription := "description-2"
@@ -77,3 +118,66 @@ func TestAlertProvider_GetDefaultAlert(t *testing.T) {
 		t.Error("expected default alert to be nil")
 	}
 }
+
+func TestAlertProvider_getToForGroup(t *testing.T) {
+	tests := []struct {
+		Name           string
+		Provider       AlertProvider
+		InputGroup     string
+		ExpectedOutput string
+	}{
+		{
+			Name: "provider-no-override-specify-no-group-should-default",
+			Provider: AlertProvider{
+				To:        "to@example.com",
+				Overrides: nil,
+			},
+			InputGroup:     "",
+			ExpectedOutput: "to@example.com",
+		},
+		{
+			Name: "provider-no-override-specify-group-should-default",
+			Provider: AlertProvider{
+				To:        "to@example.com",
+				Overrides: nil,
+			},
+			InputGroup:     "group",
+			ExpectedOutput: "to@example.com",
+		},
+		{
+			Name: "provider-with-override-specify-no-group-should-default",
+			Provider: AlertProvider{
+				To: "to@example.com",
+				Overrides: []Override{
+					{
+						Group: "group",
+						To:    "to01@example.com",
+					},
+				},
+			},
+			InputGroup:     "",
+			ExpectedOutput: "to@example.com",
+		},
+		{
+			Name: "provider-with-override-specify-group-should-override",
+			Provider: AlertProvider{
+				To: "to@example.com",
+				Overrides: []Override{
+					{
+						Group: "group",
+						To:    "to01@example.com",
+					},
+				},
+			},
+			InputGroup:     "group",
+			ExpectedOutput: "to01@example.com",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.Name, func(t *testing.T) {
+			if got := tt.Provider.getToForGroup(tt.InputGroup); got != tt.ExpectedOutput {
+				t.Errorf("AlertProvider.getToForGroup() = %v, want %v", got, tt.ExpectedOutput)
+			}
+		})
+	}
+}