feat(alerting): Add HomeAssistant support (#1125)

* Base homeassistant alerting setup

* Update homeassistant alert documenation

* sort alert.TypeHomeAssistant to comply alphabetic policy

* Validate homeassistant as a provider interfaces implementation on compile

---------

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

alerting/provider/homeassistant/homeassistant_test.go

@@ -0,0 +1,158 @@
+package homeassistant
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/TwiN/gatus/v5/alerting/alert"
+	"github.com/TwiN/gatus/v5/client"
+	"github.com/TwiN/gatus/v5/config/endpoint"
+	"github.com/TwiN/gatus/v5/test"
+)
+
+func TestAlertProvider_Validate(t *testing.T) {
+	invalidProvider := AlertProvider{DefaultConfig: Config{URL: "", Token: ""}}
+	if err := invalidProvider.Validate(); err == nil {
+		t.Error("provider shouldn't have been valid")
+	}
+	invalidProviderNoToken := AlertProvider{DefaultConfig: Config{URL: "http://homeassistant:8123", Token: ""}}
+	if err := invalidProviderNoToken.Validate(); err == nil {
+		t.Error("provider shouldn't have been valid")
+	}
+	validProvider := AlertProvider{DefaultConfig: Config{URL: "http://homeassistant:8123", Token: "token"}}
+	if err := validProvider.Validate(); err != nil {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_ValidateWithOverride(t *testing.T) {
+	providerWithInvalidOverrideGroup := AlertProvider{
+		Overrides: []Override{
+			{
+				Config: Config{URL: "http://homeassistant:8123", Token: "token"},
+				Group:  "",
+			},
+		},
+	}
+	if err := providerWithInvalidOverrideGroup.Validate(); err == nil {
+		t.Error("provider Group shouldn't have been valid")
+	}
+	providerWithValidOverride := AlertProvider{
+		DefaultConfig: Config{URL: "http://homeassistant:8123", Token: "token"},
+		Overrides: []Override{
+			{
+				Config: Config{URL: "http://homeassistant:8123", Token: "token"},
+				Group:  "group",
+			},
+		},
+	}
+	if err := providerWithValidOverride.Validate(); err != nil {
+		t.Error("provider should've been valid")
+	}
+}
+
+func TestAlertProvider_Send(t *testing.T) {
+	defer client.InjectHTTPClient(nil)
+	firstDescription := "description-1"
+	secondDescription := "description-2"
+	scenarios := []struct {
+		Name             string
+		Provider         AlertProvider
+		Alert            alert.Alert
+		Resolved         bool
+		MockRoundTripper test.MockRoundTripper
+		ExpectedError    bool
+	}{
+		{
+			Name:     "triggered",
+			Provider: AlertProvider{DefaultConfig: Config{URL: "http://homeassistant:8123", Token: "token"}},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+		{
+			Name:     "triggered-error",
+			Provider: AlertProvider{DefaultConfig: Config{URL: "http://homeassistant:8123", Token: "token"}},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusInternalServerError, Body: http.NoBody}
+			}),
+			ExpectedError: true,
+		},
+		{
+			Name:     "resolved",
+			Provider: AlertProvider{DefaultConfig: Config{URL: "http://homeassistant:8123", Token: "token"}},
+			Alert:    alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: true,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.Name, func(t *testing.T) {
+			client.InjectHTTPClient(&http.Client{Transport: scenario.MockRoundTripper})
+			err := scenario.Provider.Send(
+				&endpoint.Endpoint{Name: "endpoint-name"},
+				&scenario.Alert,
+				&endpoint.Result{
+					ConditionResults: []*endpoint.ConditionResult{
+						{Condition: "SUCCESSFUL_CONDITION", Success: true},
+						{Condition: "FAILING_CONDITION", Success: false},
+					},
+				},
+				scenario.Resolved,
+			)
+			if scenario.ExpectedError && err == nil {
+				t.Error("expected error, got none")
+			}
+			if !scenario.ExpectedError && err != nil {
+				t.Error("expected no error, got", err.Error())
+			}
+		})
+	}
+}
+
+func TestAlertProvider_buildRequestBody(t *testing.T) {
+	description := "test-description"
+	provider := AlertProvider{DefaultConfig: Config{URL: "http://homeassistant:8123", Token: "token"}}
+	body := provider.buildRequestBody(
+		&endpoint.Endpoint{Name: "endpoint-name"},
+		&alert.Alert{Description: &description, SuccessThreshold: 5, FailureThreshold: 3},
+		&endpoint.Result{
+			ConditionResults: []*endpoint.ConditionResult{
+				{Condition: "SUCCESSFUL_CONDITION", Success: true},
+				{Condition: "FAILING_CONDITION", Success: false},
+			},
+		},
+		false,
+	)
+	var decodedBody Body
+	if err := json.Unmarshal(body, &decodedBody); err != nil {
+		t.Error("expected body to be valid JSON, got error:", err.Error())
+	}
+	if decodedBody.EventType != "gatus_alert" {
+		t.Errorf("expected event_type to be gatus_alert, got %s", decodedBody.EventType)
+	}
+	if decodedBody.EventData.Status != "triggered" {
+		t.Errorf("expected status to be triggered, got %s", decodedBody.EventData.Status)
+	}
+	if decodedBody.EventData.Description != description {
+		t.Errorf("expected description to be %s, got %s", description, decodedBody.EventData.Description)
+	}
+	if len(decodedBody.EventData.Conditions) != 2 {
+		t.Errorf("expected 2 conditions, got %d", len(decodedBody.EventData.Conditions))
+	}
+	if !decodedBody.EventData.Conditions[0].Success {
+		t.Error("expected first condition to be successful")
+	}
+	if decodedBody.EventData.Conditions[1].Success {
+		t.Error("expected second condition to be unsuccessful")
+	}
+}