feat(email): Add Chime email sending service

Implements a new email sending service using the Chime API.

- Adds a new Chime client in `lib/email/chime` for handling API requests, authentication, and error classification (transient, permanent user, permanent system).
- Introduces an adapter in `lib/email/chime/chimeadapters` to integrate the new client with the existing email worker.
- Updates the email worker `Send` interface to include a unique ID per message, which is passed to Chime's `external_id` field for deduplication in the future.

Author: jcscottiii

lib/email/chime/chimeadapters/email_worker.go

@@ -0,0 +1,58 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package chimeadapters
+
+import (
+	"context"
+	"errors"
+
+	"github.com/GoogleChrome/webstatus.dev/lib/email/chime"
+	"github.com/GoogleChrome/webstatus.dev/lib/workertypes"
+)
+
+type EmailSender interface {
+	Send(ctx context.Context, id string, to string, subject string, htmlBody string) error
+}
+
+type EmailWorkerChimeAdapter struct {
+	chimeSender EmailSender
+}
+
+// NewEmailWorkerChimeAdapter creates a new adapter for the email worker to use Chime.
+func NewEmailWorkerChimeAdapter(chimeSender EmailSender) *EmailWorkerChimeAdapter {
+	return &EmailWorkerChimeAdapter{
+		chimeSender: chimeSender,
+	}
+}
+
+// Send implements the EmailSender interface for the email worker.
+func (a *EmailWorkerChimeAdapter) Send(ctx context.Context, id string, to string,
+	subject string, htmlBody string) error {
+	err := a.chimeSender.Send(ctx, id, to, subject, htmlBody)
+	if err != nil {
+		if errors.Is(err, chime.ErrPermanentUser) {
+			return errors.Join(workertypes.ErrUnrecoverableUserFailureEmailSending, err)
+		} else if errors.Is(err, chime.ErrPermanentSystem) {
+			return errors.Join(workertypes.ErrUnrecoverableSystemFailureEmailSending, err)
+		} else if errors.Is(err, chime.ErrDuplicate) {
+			return errors.Join(workertypes.ErrUnrecoverableSystemFailureEmailSending, err)
+		}
+
+		// Will be recorded as a transient error
+		return err
+	}
+
+	return nil
+}

lib/email/chime/chimeadapters/email_worker_test.go

@@ -0,0 +1,100 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package chimeadapters
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/GoogleChrome/webstatus.dev/lib/email/chime"
+	"github.com/GoogleChrome/webstatus.dev/lib/workertypes"
+)
+
+// mockChimeSender is a mock implementation of the EmailSender for testing.
+type mockChimeSender struct {
+	sendErr error
+}
+
+func (m *mockChimeSender) Send(_ context.Context, _ string, _ string, _ string, _ string) error {
+	return m.sendErr
+}
+
+var errTest = errors.New("test error")
+
+func TestEmailWorkerChimeAdapter_Send(t *testing.T) {
+	ctx := context.Background()
+	testCases := []struct {
+		name          string
+		chimeError    error
+		expectedError error
+	}{
+		{
+			name:          "Success",
+			chimeError:    nil,
+			expectedError: nil,
+		},
+		{
+			name:          "Permanent User Error",
+			chimeError:    chime.ErrPermanentUser,
+			expectedError: workertypes.ErrUnrecoverableUserFailureEmailSending,
+		},
+		{
+			name:          "Permanent System Error",
+			chimeError:    chime.ErrPermanentSystem,
+			expectedError: workertypes.ErrUnrecoverableSystemFailureEmailSending,
+		},
+		{
+			name:          "Duplicate Error",
+			chimeError:    chime.ErrDuplicate,
+			expectedError: workertypes.ErrUnrecoverableSystemFailureEmailSending,
+		},
+		{
+			name:          "Transient Error",
+			chimeError:    chime.ErrTransient,
+			expectedError: chime.ErrTransient, // Should be passed through
+		},
+		{
+			name:          "Other Error",
+			chimeError:    errTest,
+			expectedError: errTest, // Should be passed through
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			// Setup
+			mockSender := &mockChimeSender{sendErr: tc.chimeError}
+			adapter := NewEmailWorkerChimeAdapter(mockSender)
+
+			// Execute
+			err := adapter.Send(ctx, "test-id", "to@example.com", "Test Subject", "<p>Hello</p>")
+
+			// Verify
+			if tc.expectedError != nil {
+				if err == nil {
+					t.Fatal("Expected an error, but got nil")
+				}
+				if !errors.Is(err, tc.expectedError) {
+					t.Errorf("Expected error wrapping %v, but got %v", tc.expectedError, err)
+				}
+			} else {
+				if err != nil {
+					t.Errorf("Expected no error, but got %v", err)
+				}
+			}
+		})
+	}
+}