# Email Template Editor

## Overview

The Email Template Editor provides a powerful interface for creating and modifying email templates with live preview, variable insertion, and test send functionality. It supports split-pane editing for HTML and plain text versions, visual variable insertion, and real-time rendering with sample data.

**Key Features:**

- **Split-Pane Editor** — Side-by-side HTML and text editing
- **Variable Insertion Buttons** — Click to insert {{VARIABLES}} at cursor position
- **Live Preview Rendering** — See rendered HTML with sample data in real-time
- **Test Send Functionality** — Send test emails with custom sample data
- **Auto-Save Drafts** — Prevent data loss with automatic draft saving
- **Version Creation** — Every save creates a new version with change notes
- **Responsive Layout** — Desktop-optimized (mobile warning for small screens)
- **Keyboard Shortcuts** — Ctrl+S to save, Ctrl+P to preview, Esc to close

**Access Control:**
- **Role Required:** SUPER_ADMIN only
- **Route:** `/app/email-templates/:id/edit`
- **Layout:** Full-screen (no AppLayout sidebar)

---

## Architecture

```mermaid
flowchart TB
    subgraph "Editor UI Components"
        Editor[EmailTemplateEditorPage]
        Toolbar[Editor Toolbar]
        HtmlEditor[HTML Editor Pane]
        TextEditor[Text Editor Pane]
        VarPanel[Variable Insertion Panel]
        Preview[Live Preview Pane]
        TestForm[Test Send Form]
    end

    subgraph "State Management"
        State[Component State]
        Draft[LocalStorage Draft]
        AutoSave[Auto-Save Timer]
    end

    subgraph "API Layer"
        GetTemplate[GET /api/email-templates/:id]
        UpdateTemplate[PUT /api/email-templates/:id]
        TestSend[POST /api/email-templates/:id/test]
    end

    subgraph "Backend Processing"
        Template[(EmailTemplate)]
        Variables[(EmailTemplateVariable)]
        Handlebars[Handlebars Compiler]
        EmailService[Email Service]
        TestLog[(EmailTemplateTestLog)]
    end

    Editor --> Toolbar
    Editor --> HtmlEditor
    Editor --> TextEditor
    Editor --> VarPanel
    Editor --> Preview
    Editor --> TestForm

    Editor --> State
    State --> Draft
    State --> AutoSave

    Editor -->|Load| GetTemplate
    GetTemplate --> Template
    GetTemplate --> Variables

    VarPanel -->|Insert| HtmlEditor
    VarPanel -->|Insert| TextEditor

    HtmlEditor -->|Debounce 300ms| Preview
    TextEditor --> State

    Preview --> Handlebars
    Handlebars -->|Render HTML| Preview

    Toolbar -->|Save Click| UpdateTemplate
    UpdateTemplate --> Template
    UpdateTemplate -->|Create Version| Versions[(EmailTemplateVersion)]

    TestForm --> TestSend
    TestSend --> EmailService
    EmailService -->|Send| SMTP[Nodemailer]
    SMTP --> TestLog

    AutoSave --> Draft

    style Editor fill:#4a90e2,color:#fff
    style Template fill:#50c878,color:#fff
    style Preview fill:#ffb347,color:#333
```

**Data Flow:**

1. **Load Template** — Fetch template + variables via GET API
2. **Restore Draft** — Load from localStorage if exists (unsaved changes)
3. **Edit Content** — Type in HTML/text editors, updates component state
4. **Insert Variable** — Click variable button → inserts `{{VAR}}` at cursor
5. **Preview Update** — Debounced (300ms) Handlebars compilation + iframe render
6. **Test Send** — Enter recipient + sample data → POST to test endpoint → email sent
7. **Save Template** — Click save → PUT API → create version → clear draft → redirect
8. **Auto-Save Draft** — Blur event → save to localStorage (not database)

---

## Editor Components

### Toolbar

**Location:** Top bar (sticky)

**Elements:**
- **Template Name** — Read-only display (left)
- **Save Button** — Saves changes and creates version (right)
- **Preview Toggle** — Show/hide live preview pane (right)
- **Test Send Button** — Opens test send modal (right)
- **Back Button** — Returns to EmailTemplatesPage (left)

**Actions:**
```typescript
const handleSave = async () => {
  setSaving(true);
  try {
    await api.put(`/api/email-templates/${id}`, {
      subjectLine,
      htmlContent,
      textContent,
      changeNotes,
    });

    message.success('Template saved successfully');
    localStorage.removeItem(`email-template-draft-${id}`);
    navigate('/app/email-templates');
  } catch (error) {
    message.error('Failed to save template');
  } finally {
    setSaving(false);
  }
};
```

---

### HTML Editor Pane

**Location:** Left side (50% width) or full width when preview hidden

**Features:**
- **Textarea or Monaco Editor** — Syntax highlighting (Monaco upgrade path)
- **Line Numbers** — Visual line number gutter
- **Auto-Resize** — Grows to fit content (max 80vh)
- **Tab Support** — Tab key inserts 2 spaces (not focus change)

**Implementation:**
```typescript
const [htmlContent, setHtmlContent] = useState('');
const htmlEditorRef = useRef<HTMLTextAreaElement>(null);

const handleHtmlChange = (e: React.ChangeEvent<HTMLTextAreaElement>) => {
  setHtmlContent(e.target.value);
  debouncedPreview(e.target.value, sampleData);
};

const handleKeyDown = (e: React.KeyboardEvent<HTMLTextAreaElement>) => {
  // Tab key support
  if (e.key === 'Tab') {
    e.preventDefault();
    const textarea = e.currentTarget;
    const start = textarea.selectionStart;
    const end = textarea.selectionEnd;

    setHtmlContent(
      htmlContent.substring(0, start) + '  ' + htmlContent.substring(end)
    );

    setTimeout(() => {
      textarea.selectionStart = textarea.selectionEnd = start + 2;
    }, 0);
  }
};
```

---

### Text Editor Pane

**Location:** Left side (50% width) or full width when preview hidden

**Features:**
- **Plain Text Editing** — No syntax highlighting needed
- **Auto-Resize** — Matches HTML editor height
- **Variable Insertion** — Same insertion panel as HTML editor

**Implementation:**
```typescript
const [textContent, setTextContent] = useState('');
const textEditorRef = useRef<HTMLTextAreaElement>(null);

const handleTextChange = (e: React.ChangeEvent<HTMLTextAreaElement>) => {
  setTextContent(e.target.value);
};
```

---

### Variable Insertion Panel

**Location:** Right sidebar (collapsible)

**Features:**
- **Variable List** — All template variables with labels
- **Insert Buttons** — Click to insert `{{VAR}}` at cursor
- **Required Badge** — Red badge for required variables
- **Conditional Badge** — Blue badge for conditional variables
- **Sample Value Display** — Shows example value below each variable
- **Search/Filter** — Filter variables by name (if many variables)

**Implementation:**
```typescript
const handleInsertVariable = (variableKey: string, editorType: 'html' | 'text') => {
  const textarea = editorType === 'html' ? htmlEditorRef.current : textEditorRef.current;
  if (!textarea) return;

  const start = textarea.selectionStart;
  const end = textarea.selectionEnd;
  const content = editorType === 'html' ? htmlContent : textContent;

  const before = content.substring(0, start);
  const after = content.substring(end);
  const newContent = before + `{{${variableKey}}}` + after;

  if (editorType === 'html') {
    setHtmlContent(newContent);
  } else {
    setTextContent(newContent);
  }

  // Move cursor after inserted variable
  setTimeout(() => {
    const newPos = start + variableKey.length + 4; // 4 = {{ + }}
    textarea.selectionStart = newPos;
    textarea.selectionEnd = newPos;
    textarea.focus();
  }, 0);
};
```

**Variable List UI:**
```typescript
<Space direction="vertical" style={{ width: '100%' }}>
  {variables
    .sort((a, b) => a.sortOrder - b.sortOrder)
    .map((variable) => (
      <Card key={variable.id} size="small">
        <Space direction="vertical" size={0} style={{ width: '100%' }}>
          <Space>
            <Text strong>{variable.label}</Text>
            {variable.isRequired && <Tag color="red">Required</Tag>}
            {variable.isConditional && <Tag color="blue">Conditional</Tag>}
          </Space>

          <Text type="secondary" style={{ fontSize: 12 }}>
            {variable.description}
          </Text>

          {variable.sampleValue && (
            <Text code style={{ fontSize: 11 }}>
              Example: {variable.sampleValue}
            </Text>
          )}

          <Space size="small">
            <Button
              size="small"
              onClick={() => handleInsertVariable(variable.key, 'html')}
            >
              Insert to HTML
            </Button>
            <Button
              size="small"
              onClick={() => handleInsertVariable(variable.key, 'text')}
            >
              Insert to Text
            </Button>
          </Space>
        </Space>
      </Card>
    ))}
</Space>
```

---

### Live Preview Pane

**Location:** Right side (50% width) when enabled

**Features:**
- **Iframe Rendering** — Isolated HTML preview
- **Sample Data Form** — Edit sample variable values
- **Desktop/Mobile Toggle** — Preview in different viewport sizes
- **Debounced Updates** — Renders 300ms after typing stops
- **Error Display** — Shows Handlebars compilation errors

**Implementation:**
```typescript
import Handlebars from 'handlebars';

const [previewHtml, setPreviewHtml] = useState('');
const [sampleData, setSampleData] = useState<Record<string, unknown>>({});
const previewRef = useRef<HTMLIFrameElement>(null);

const renderPreview = useCallback((html: string, data: Record<string, unknown>) => {
  try {
    const compiled = Handlebars.compile(html);
    const rendered = compiled(data);

    // Inject into iframe
    if (previewRef.current?.contentDocument) {
      const doc = previewRef.current.contentDocument;
      doc.open();
      doc.write(`
        <!DOCTYPE html>
        <html>
          <head>
            <meta charset="UTF-8">
            <meta name="viewport" content="width=device-width, initial-scale=1.0">
            <style>
              body { font-family: Arial, sans-serif; padding: 20px; }
            </style>
          </head>
          <body>${rendered}</body>
        </html>
      `);
      doc.close();
    }

    setPreviewHtml(rendered);
  } catch (error) {
    console.error('Preview render error:', error);
    setPreviewError(error.message);
  }
}, []);

const debouncedPreview = useMemo(
  () => debounce(renderPreview, 300),
  [renderPreview]
);

// Update preview when HTML or sample data changes
useEffect(() => {
  debouncedPreview(htmlContent, sampleData);
}, [htmlContent, sampleData, debouncedPreview]);
```

**Sample Data Form:**
```typescript
const handleSampleDataChange = (variableKey: string, value: unknown) => {
  setSampleData((prev) => ({
    ...prev,
    [variableKey]: value,
  }));
};

// Render form
<Space direction="vertical" style={{ width: '100%', marginBottom: 16 }}>
  <Title level={5}>Sample Data</Title>
  {variables.map((variable) => (
    <Form.Item key={variable.id} label={variable.label}>
      <Input
        value={sampleData[variable.key] as string || ''}
        onChange={(e) => handleSampleDataChange(variable.key, e.target.value)}
        placeholder={variable.sampleValue || ''}
      />
    </Form.Item>
  ))}
</Space>
```

---

### Test Send Form

**Location:** Modal dialog

**Features:**
- **Recipient Email Input** — Where to send test email
- **Sample Data Editor** — JSON editor or form fields
- **Send Button** — Triggers test send API call
- **Success/Failure Notification** — Shows send result
- **Test Log Link** — Link to test send history

**Implementation:**
```typescript
const [testModalVisible, setTestModalVisible] = useState(false);
const [testRecipient, setTestRecipient] = useState('');
const [testData, setTestData] = useState<Record<string, unknown>>({});

const handleTestSend = async () => {
  if (!testRecipient) {
    message.error('Please enter recipient email');
    return;
  }

  setTestSending(true);
  try {
    await api.post(`/api/email-templates/${id}/test`, {
      recipientEmail: testRecipient,
      testData,
    });

    message.success('Test email sent successfully');
    setTestModalVisible(false);
  } catch (error) {
    message.error('Failed to send test email');
  } finally {
    setTestSending(false);
  }
};

// Modal UI
<Modal
  title="Send Test Email"
  visible={testModalVisible}
  onOk={handleTestSend}
  onCancel={() => setTestModalVisible(false)}
  confirmLoading={testSending}
  okText="Send Test"
>
  <Form layout="vertical">
    <Form.Item label="Recipient Email" required>
      <Input
        type="email"
        value={testRecipient}
        onChange={(e) => setTestRecipient(e.target.value)}
        placeholder="your-email@example.com"
      />
    </Form.Item>

    <Form.Item label="Sample Data">
      <Space direction="vertical" style={{ width: '100%' }}>
        {variables.map((variable) => (
          <Input
            key={variable.id}
            addonBefore={variable.label}
            value={testData[variable.key] as string || ''}
            onChange={(e) =>
              setTestData((prev) => ({ ...prev, [variable.key]: e.target.value }))
            }
            placeholder={variable.sampleValue || ''}
          />
        ))}
      </Space>
    </Form.Item>
  </Form>
</Modal>
```

---

## Admin Workflow

### Opening Editor

**From EmailTemplatesPage:**

1. Click template row in table
2. Opens template detail modal
3. Click "Edit" button in modal
4. Opens EmailTemplateEditorPage in same tab

**Direct URL:**
```
/app/email-templates/{id}/edit
```

**Route Definition:**
```typescript
// admin/src/App.tsx

<Route
  path="/app/email-templates/:id/edit"
  element={
    <ProtectedRoute allowedRoles={[SUPER_ADMIN]}>
      <EmailTemplateEditorPage />
    </ProtectedRoute>
  }
/>
```

---

### Editing HTML Content

**Step 1: Load Template**
- Template data fetched via API on component mount
- HTML/text content populated in editors
- Variables loaded in insertion panel

**Step 2: Edit HTML**
- Type HTML with `{{VARIABLES}}` placeholders
- Use variable insertion buttons for convenience
- Preview updates automatically (300ms debounce)

**Step 3: Insert Variables**
- Click variable "Insert to HTML" button
- `{{VARIABLE_KEY}}` inserted at cursor position
- Cursor moves after inserted variable

**Step 4: Preview Changes**
- Live preview pane shows rendered HTML
- Edit sample data to test different values
- Check for formatting issues

**Example Editing Session:**
```html
<!-- Initial HTML -->
<p>Dear {{USER_NAME}},</p>
<p>Thank you for signing up.</p>

<!-- Add shift details -->
<p>Dear {{USER_NAME}},</p>
<p>Thank you for signing up for <strong>{{SHIFT_TITLE}}</strong>.</p>
<ul>
  <li>Date: {{SHIFT_DATE}}</li>
  <li>Time: {{SHIFT_TIME}}</li>
</ul>

<!-- Add conditional phone -->
<p>Dear {{USER_NAME}},</p>
<p>Thank you for signing up for <strong>{{SHIFT_TITLE}}</strong>.</p>
<ul>
  <li>Date: {{SHIFT_DATE}}</li>
  <li>Time: {{SHIFT_TIME}}</li>
</ul>

{{#if HAS_PHONE}}
<p>We'll call you at {{USER_PHONE}} if there are any changes.</p>
{{/if}}
```

---

### Using Variable Insertion

**Keyboard Method:**
1. Type `{{` in HTML editor
2. Type variable name (e.g., `USER_NAME`)
3. Type `}}`

**Button Method:**
1. Place cursor where you want variable
2. Click variable "Insert to HTML" button
3. `{{VARIABLE_KEY}}` inserted at cursor
4. Cursor moves to end of insertion

**Insertion Logic:**
```typescript
const handleInsertVariable = (variableKey: string, editorType: 'html' | 'text') => {
  const textarea = editorType === 'html' ? htmlEditorRef.current : textEditorRef.current;
  if (!textarea) return;

  const start = textarea.selectionStart;
  const end = textarea.selectionEnd;
  const content = editorType === 'html' ? htmlContent : textContent;

  // Replace selection with variable
  const before = content.substring(0, start);
  const after = content.substring(end);
  const variable = `{{${variableKey}}}`;
  const newContent = before + variable + after;

  // Update state
  if (editorType === 'html') {
    setHtmlContent(newContent);
  } else {
    setTextContent(newContent);
  }

  // Move cursor to end of inserted variable
  setTimeout(() => {
    const newPos = start + variable.length;
    textarea.selectionStart = newPos;
    textarea.selectionEnd = newPos;
    textarea.focus();
  }, 0);
};
```

---

### Live Preview

**Preview Update Flow:**

1. **Type in HTML Editor**
   - `onChange` event fires
   - Updates `htmlContent` state
   - Triggers debounced preview render (300ms)

2. **Debounced Render**
   - Waits 300ms after typing stops
   - Compiles Handlebars template
   - Interpolates with sample data
   - Injects HTML into iframe

3. **Sample Data Changes**
   - Edit sample data form fields
   - Updates `sampleData` state
   - Immediately triggers preview render (no debounce)

**Preview Error Handling:**
```typescript
const renderPreview = (html: string, data: Record<string, unknown>) => {
  try {
    const compiled = Handlebars.compile(html);
    const rendered = compiled(data);

    // Inject into iframe...
    setPreviewError(null);
  } catch (error) {
    // Show error in preview pane
    setPreviewError(error.message);

    if (previewRef.current?.contentDocument) {
      const doc = previewRef.current.contentDocument;
      doc.open();
      doc.write(`
        <div style="color: red; padding: 20px;">
          <h3>Preview Error</h3>
          <pre>${error.message}</pre>
        </div>
      `);
      doc.close();
    }
  }
};
```

---

### Testing Template

**Step 1: Click "Send Test" Button**
- Opens test send modal

**Step 2: Enter Recipient Email**
- Your email address (or test account)
- Validates email format before sending

**Step 3: Edit Sample Data**
- Pre-filled with variable sample values
- Modify to test specific scenarios
- Example: Set `HAS_PHONE` to `false` to test conditional block

**Step 4: Click "Send Test"**
- POST request to `/api/email-templates/:id/test`
- Email sent via SMTP (or MailHog in test mode)
- Success notification displayed

**Step 5: Check Email**
- Open email client (or MailHog at http://localhost:8025)
- Verify rendering, variables, formatting
- Test links, images, layout

**Step 6: Review Test Log**
- Navigate to "Test Logs" tab in template detail modal
- See test send history (recipient, timestamp, success/failure)
- Debug errors if send failed

---

### Saving Changes

**Step 1: Click "Save" Button**
- Toolbar save button (or Ctrl+S keyboard shortcut)

**Step 2: Enter Change Notes**
- Modal prompts for change description
- Used for version history audit trail
- Optional but recommended

**Step 3: Confirm Save**
- PUT request to `/api/email-templates/:id`
- Creates new version automatically
- Clears localStorage draft
- Redirects to EmailTemplatesPage

**Save Implementation:**
```typescript
const [saveModalVisible, setSaveModalVisible] = useState(false);
const [changeNotes, setChangeNotes] = useState('');

const handleSave = async () => {
  setSaving(true);
  try {
    await api.put(`/api/email-templates/${id}`, {
      subjectLine,
      htmlContent,
      textContent,
      changeNotes: changeNotes || undefined,
    });

    message.success('Template saved successfully');

    // Clear draft
    localStorage.removeItem(`email-template-draft-${id}`);

    // Redirect
    navigate('/app/email-templates');
  } catch (error) {
    message.error('Failed to save template');
  } finally {
    setSaving(false);
    setSaveModalVisible(false);
  }
};

// Keyboard shortcut
useEffect(() => {
  const handleKeyDown = (e: KeyboardEvent) => {
    if ((e.ctrlKey || e.metaKey) && e.key === 's') {
      e.preventDefault();
      setSaveModalVisible(true);
    }
  };

  window.addEventListener('keydown', handleKeyDown);
  return () => window.removeEventListener('keydown', handleKeyDown);
}, []);
```

---

## Code Examples

### EmailTemplateEditorPage Component

**Full Component Structure:**

```typescript
// admin/src/pages/EmailTemplateEditorPage.tsx

import React, { useState, useEffect, useRef, useCallback, useMemo } from 'react';
import { useParams, useNavigate } from 'react-router-dom';
import { Button, Input, Space, Card, Tag, Typography, Modal, Form, message } from 'antd';
import { SaveOutlined, SendOutlined, ArrowLeftOutlined, EyeOutlined } from '@ant-design/icons';
import Handlebars from 'handlebars';
import { debounce } from 'lodash';
import { api } from '@/lib/api';
import type { EmailTemplate, EmailTemplateVariable } from '@/types/api';

const { Title, Text } = Typography;
const { TextArea } = Input;

export default function EmailTemplateEditorPage() {
  const { id } = useParams<{ id: string }>();
  const navigate = useNavigate();

  // State
  const [loading, setLoading] = useState(true);
  const [saving, setSaving] = useState(false);
  const [template, setTemplate] = useState<EmailTemplate | null>(null);
  const [variables, setVariables] = useState<EmailTemplateVariable[]>([]);

  const [subjectLine, setSubjectLine] = useState('');
  const [htmlContent, setHtmlContent] = useState('');
  const [textContent, setTextContent] = useState('');

  const [showPreview, setShowPreview] = useState(true);
  const [sampleData, setSampleData] = useState<Record<string, unknown>>({});
  const [previewError, setPreviewError] = useState<string | null>(null);

  const [testModalVisible, setTestModalVisible] = useState(false);
  const [testRecipient, setTestRecipient] = useState('');
  const [testSending, setTestSending] = useState(false);

  const [saveModalVisible, setSaveModalVisible] = useState(false);
  const [changeNotes, setChangeNotes] = useState('');

  // Refs
  const htmlEditorRef = useRef<HTMLTextAreaElement>(null);
  const textEditorRef = useRef<HTMLTextAreaElement>(null);
  const previewRef = useRef<HTMLIFrameElement>(null);

  // Load template
  useEffect(() => {
    const loadTemplate = async () => {
      try {
        const response = await api.get(`/api/email-templates/${id}`);
        const { template: tmpl, variables: vars } = response.data;

        setTemplate(tmpl);
        setVariables(vars);

        setSubjectLine(tmpl.subjectLine);
        setHtmlContent(tmpl.htmlContent);
        setTextContent(tmpl.textContent);

        // Initialize sample data from variable sample values
        const initialSampleData: Record<string, unknown> = {};
        vars.forEach((v: EmailTemplateVariable) => {
          if (v.sampleValue) {
            initialSampleData[v.key] = v.sampleValue;
          }
        });
        setSampleData(initialSampleData);

        // Restore draft if exists
        const draft = localStorage.getItem(`email-template-draft-${id}`);
        if (draft) {
          const { subjectLine: draftSubject, htmlContent: draftHtml, textContent: draftText } = JSON.parse(draft);
          setSubjectLine(draftSubject);
          setHtmlContent(draftHtml);
          setTextContent(draftText);
          message.info('Restored unsaved changes from draft');
        }

        setLoading(false);
      } catch (error) {
        message.error('Failed to load template');
        navigate('/app/email-templates');
      }
    };

    loadTemplate();
  }, [id, navigate]);

  // Auto-save draft to localStorage
  useEffect(() => {
    if (!loading && template) {
      const draft = {
        subjectLine,
        htmlContent,
        textContent,
      };
      localStorage.setItem(`email-template-draft-${id}`, JSON.stringify(draft));
    }
  }, [subjectLine, htmlContent, textContent, loading, template, id]);

  // Preview rendering
  const renderPreview = useCallback((html: string, data: Record<string, unknown>) => {
    try {
      const compiled = Handlebars.compile(html);
      const rendered = compiled(data);

      if (previewRef.current?.contentDocument) {
        const doc = previewRef.current.contentDocument;
        doc.open();
        doc.write(`
          <!DOCTYPE html>
          <html>
            <head>
              <meta charset="UTF-8">
              <meta name="viewport" content="width=device-width, initial-scale=1.0">
              <style>
                body {
                  font-family: Arial, sans-serif;
                  padding: 20px;
                  line-height: 1.6;
                }
              </style>
            </head>
            <body>${rendered}</body>
          </html>
        `);
        doc.close();
      }

      setPreviewError(null);
    } catch (error: any) {
      setPreviewError(error.message);

      if (previewRef.current?.contentDocument) {
        const doc = previewRef.current.contentDocument;
        doc.open();
        doc.write(`
          <div style="color: red; padding: 20px;">
            <h3>Preview Error</h3>
            <pre>${error.message}</pre>
          </div>
        `);
        doc.close();
      }
    }
  }, []);

  // Debounced preview
  const debouncedPreview = useMemo(
    () => debounce(renderPreview, 300),
    [renderPreview]
  );

  // Update preview when HTML or sample data changes
  useEffect(() => {
    if (showPreview) {
      debouncedPreview(htmlContent, sampleData);
    }
  }, [htmlContent, sampleData, showPreview, debouncedPreview]);

  // Variable insertion
  const handleInsertVariable = (variableKey: string, editorType: 'html' | 'text') => {
    const textarea = editorType === 'html' ? htmlEditorRef.current : textEditorRef.current;
    if (!textarea) return;

    const start = textarea.selectionStart;
    const end = textarea.selectionEnd;
    const content = editorType === 'html' ? htmlContent : textContent;

    const before = content.substring(0, start);
    const after = content.substring(end);
    const variable = `{{${variableKey}}}`;
    const newContent = before + variable + after;

    if (editorType === 'html') {
      setHtmlContent(newContent);
    } else {
      setTextContent(newContent);
    }

    setTimeout(() => {
      const newPos = start + variable.length;
      textarea.selectionStart = newPos;
      textarea.selectionEnd = newPos;
      textarea.focus();
    }, 0);
  };

  // Save template
  const handleSave = async () => {
    setSaving(true);
    try {
      await api.put(`/api/email-templates/${id}`, {
        subjectLine,
        htmlContent,
        textContent,
        changeNotes: changeNotes || undefined,
      });

      message.success('Template saved successfully');
      localStorage.removeItem(`email-template-draft-${id}`);
      navigate('/app/email-templates');
    } catch (error) {
      message.error('Failed to save template');
    } finally {
      setSaving(false);
      setSaveModalVisible(false);
    }
  };

  // Test send
  const handleTestSend = async () => {
    if (!testRecipient) {
      message.error('Please enter recipient email');
      return;
    }

    setTestSending(true);
    try {
      await api.post(`/api/email-templates/${id}/test`, {
        recipientEmail: testRecipient,
        testData: sampleData,
      });

      message.success('Test email sent successfully');
      setTestModalVisible(false);
    } catch (error) {
      message.error('Failed to send test email');
    } finally {
      setTestSending(false);
    }
  };

  // Keyboard shortcuts
  useEffect(() => {
    const handleKeyDown = (e: KeyboardEvent) => {
      if ((e.ctrlKey || e.metaKey) && e.key === 's') {
        e.preventDefault();
        setSaveModalVisible(true);
      }
      if ((e.ctrlKey || e.metaKey) && e.key === 'p') {
        e.preventDefault();
        setShowPreview(!showPreview);
      }
    };

    window.addEventListener('keydown', handleKeyDown);
    return () => window.removeEventListener('keydown', handleKeyDown);
  }, [showPreview]);

  if (loading) {
    return <div style={{ padding: 24 }}>Loading...</div>;
  }

  return (
    <div style={{ height: '100vh', display: 'flex', flexDirection: 'column' }}>
      {/* Toolbar */}
      <div
        style={{
          padding: '12px 24px',
          borderBottom: '1px solid #f0f0f0',
          display: 'flex',
          justifyContent: 'space-between',
          alignItems: 'center',
        }}
      >
        <Space>
          <Button icon={<ArrowLeftOutlined />} onClick={() => navigate('/app/email-templates')}>
            Back
          </Button>
          <Title level={4} style={{ margin: 0 }}>
            {template?.name}
          </Title>
        </Space>

        <Space>
          <Button icon={<EyeOutlined />} onClick={() => setShowPreview(!showPreview)}>
            {showPreview ? 'Hide' : 'Show'} Preview
          </Button>
          <Button icon={<SendOutlined />} onClick={() => setTestModalVisible(true)}>
            Send Test
          </Button>
          <Button type="primary" icon={<SaveOutlined />} onClick={() => setSaveModalVisible(true)}>
            Save
          </Button>
        </Space>
      </div>

      {/* Editor Area */}
      <div style={{ flex: 1, display: 'flex', overflow: 'hidden' }}>
        {/* Left: Editors */}
        <div
          style={{
            flex: showPreview ? 1 : 2,
            padding: 24,
            overflowY: 'auto',
            borderRight: '1px solid #f0f0f0',
          }}
        >
          <Space direction="vertical" style={{ width: '100%' }} size="large">
            {/* Subject Line */}
            <div>
              <Text strong>Subject Line</Text>
              <Input
                value={subjectLine}
                onChange={(e) => setSubjectLine(e.target.value)}
                placeholder="Enter subject line with {{VARIABLES}}"
              />
            </div>

            {/* HTML Editor */}
            <div>
              <Text strong>HTML Content</Text>
              <TextArea
                ref={htmlEditorRef}
                value={htmlContent}
                onChange={(e) => setHtmlContent(e.target.value)}
                placeholder="Enter HTML content with {{VARIABLES}}"
                rows={20}
                style={{ fontFamily: 'monospace', fontSize: 13 }}
              />
            </div>

            {/* Text Editor */}
            <div>
              <Text strong>Plain Text Content</Text>
              <TextArea
                ref={textEditorRef}
                value={textContent}
                onChange={(e) => setTextContent(e.target.value)}
                placeholder="Enter plain text version"
                rows={15}
                style={{ fontFamily: 'monospace', fontSize: 13 }}
              />
            </div>
          </Space>
        </div>

        {/* Right: Preview + Variables */}
        {showPreview && (
          <div style={{ flex: 1, padding: 24, overflowY: 'auto' }}>
            <Space direction="vertical" style={{ width: '100%' }} size="large">
              {/* Variables Panel */}
              <Card title="Variables" size="small">
                <Space direction="vertical" style={{ width: '100%' }} size="small">
                  {variables
                    .sort((a, b) => a.sortOrder - b.sortOrder)
                    .map((variable) => (
                      <Card key={variable.id} size="small" style={{ marginBottom: 8 }}>
                        <Space direction="vertical" size={4} style={{ width: '100%' }}>
                          <Space>
                            <Text strong>{variable.label}</Text>
                            {variable.isRequired && <Tag color="red">Required</Tag>}
                            {variable.isConditional && <Tag color="blue">Conditional</Tag>}
                          </Space>

                          {variable.description && (
                            <Text type="secondary" style={{ fontSize: 12 }}>
                              {variable.description}
                            </Text>
                          )}

                          <Space size="small">
                            <Button size="small" onClick={() => handleInsertVariable(variable.key, 'html')}>
                              Insert to HTML
                            </Button>
                            <Button size="small" onClick={() => handleInsertVariable(variable.key, 'text')}>
                              Insert to Text
                            </Button>
                          </Space>
                        </Space>
                      </Card>
                    ))}
                </Space>
              </Card>

              {/* Preview */}
              <Card title="Live Preview" size="small">
                {previewError && (
                  <div style={{ color: 'red', marginBottom: 12 }}>
                    <Text strong>Error:</Text> {previewError}
                  </div>
                )}

                <iframe
                  ref={previewRef}
                  style={{
                    width: '100%',
                    height: 600,
                    border: '1px solid #d9d9d9',
                    borderRadius: 4,
                  }}
                  title="Email Preview"
                />
              </Card>
            </Space>
          </div>
        )}
      </div>

      {/* Save Modal */}
      <Modal
        title="Save Template"
        visible={saveModalVisible}
        onOk={handleSave}
        onCancel={() => setSaveModalVisible(false)}
        confirmLoading={saving}
        okText="Save"
      >
        <Form layout="vertical">
          <Form.Item label="Change Notes (optional)">
            <TextArea
              value={changeNotes}
              onChange={(e) => setChangeNotes(e.target.value)}
              placeholder="Describe what changed in this version"
              rows={4}
            />
          </Form.Item>
        </Form>
      </Modal>

      {/* Test Send Modal */}
      <Modal
        title="Send Test Email"
        visible={testModalVisible}
        onOk={handleTestSend}
        onCancel={() => setTestModalVisible(false)}
        confirmLoading={testSending}
        okText="Send Test"
      >
        <Form layout="vertical">
          <Form.Item label="Recipient Email" required>
            <Input
              type="email"
              value={testRecipient}
              onChange={(e) => setTestRecipient(e.target.value)}
              placeholder="your-email@example.com"
            />
          </Form.Item>

          <Form.Item label="Sample Data">
            <Text type="secondary" style={{ display: 'block', marginBottom: 8 }}>
              Using sample data from preview. Edit values in the preview panel to change test data.
            </Text>
            <pre style={{ background: '#f5f5f5', padding: 12, borderRadius: 4 }}>
              {JSON.stringify(sampleData, null, 2)}
            </pre>
          </Form.Item>
        </Form>
      </Modal>
    </div>
  );
}
```

---

## Troubleshooting

### Problem: Preview not updating

**Symptoms:**
- Type in HTML editor but preview doesn't change
- Preview shows old content

**Causes:**
1. Debounce timer still running (300ms delay)
2. Handlebars compilation error (silent failure)
3. Iframe not re-rendering

**Solutions:**

**Wait for debounce:**
- Wait 300ms after typing stops
- Preview should update automatically

**Check browser console:**
```javascript
// Look for errors
Handlebars.compile error: ...
```

**Force preview update:**
```typescript
// Add button to manually trigger preview
<Button onClick={() => renderPreview(htmlContent, sampleData)}>
  Refresh Preview
</Button>
```

**Check iframe contentDocument:**
```typescript
console.log('Iframe doc:', previewRef.current?.contentDocument);
// Should not be null
```

---

### Problem: Test send fails

**Symptoms:**
- "Failed to send test email" error
- Email not received in inbox or MailHog

**Causes:**
1. SMTP configuration incorrect
2. Email test mode disabled (sending to real SMTP)
3. Recipient email invalid
4. Template has compilation errors

**Solutions:**

**Check SMTP settings:**
```bash
# .env
EMAIL_TEST_MODE=true  # Use MailHog
```

**Verify MailHog running:**
```bash
docker compose ps mailhog
# Should show "Up"
```

**Check test logs:**
```sql
SELECT * FROM email_template_test_logs
WHERE template_id = 'xxx'
ORDER BY created_at DESC
LIMIT 5;

-- Look at error_message column
```

**Test with minimal template:**
```html
<p>Hello {{USER_NAME}}</p>
```

**Validate email address:**
```typescript
import validator from 'validator';

if (!validator.isEmail(testRecipient)) {
  message.error('Invalid email address');
  return;
}
```

---

### Problem: Variable insertion doesn't work

**Symptoms:**
- Click "Insert to HTML" button but nothing happens
- Variable inserted in wrong location

**Causes:**
1. Textarea ref not set
2. Cursor position not captured correctly
3. State update timing issue

**Solutions:**

**Check ref exists:**
```typescript
console.log('HTML ref:', htmlEditorRef.current);
// Should be <textarea> element
```

**Debug cursor position:**
```typescript
const handleInsertVariable = (variableKey: string, editorType: 'html' | 'text') => {
  const textarea = editorType === 'html' ? htmlEditorRef.current : textEditorRef.current;
  console.log('Cursor position:', textarea?.selectionStart, textarea?.selectionEnd);

  // Rest of insertion logic...
};
```

**Manual workaround:**
- Type `{{VARIABLE_KEY}}` manually instead of using button

---

### Problem: Draft not restored on reload

**Symptoms:**
- Unsaved changes lost after browser refresh
- No "Restored draft" message

**Causes:**
1. localStorage not available (private browsing)
2. Draft key mismatch
3. localStorage quota exceeded

**Solutions:**

**Check localStorage:**
```javascript
// Browser console
localStorage.getItem('email-template-draft-cuid123');
// Should return JSON string
```

**Verify draft key:**
```typescript
console.log('Draft key:', `email-template-draft-${id}`);
```

**Clear old drafts:**
```javascript
// Browser console
for (let i = 0; i < localStorage.length; i++) {
  const key = localStorage.key(i);
  if (key?.startsWith('email-template-draft-')) {
    localStorage.removeItem(key);
  }
}
```

---

## Future Enhancements

### Monaco Editor Integration

**Current:** Basic HTML textarea
**Future:** Monaco Editor with syntax highlighting, IntelliSense, error detection

**Benefits:**
- Syntax highlighting for HTML
- Auto-completion for HTML tags and Handlebars syntax
- Error squiggles for invalid HTML
- Multi-cursor editing
- Code folding

**Implementation:**
```typescript
import Editor from '@monaco-editor/react';

<Editor
  height="600px"
  language="html"
  value={htmlContent}
  onChange={(value) => setHtmlContent(value || '')}
  options={{
    minimap: { enabled: false },
    lineNumbers: 'on',
    wordWrap: 'on',
  }}
/>
```

---

### Drag-Drop Block Builder

**Current:** Manual HTML editing
**Future:** Visual block builder (like GrapesJS)

**Benefits:**
- No HTML knowledge required
- Pre-built email blocks (header, footer, CTA button)
- Drag-drop interface
- Mobile-responsive by default

**Implementation:**
- Use GrapesJS (same as landing page editor)
- Custom blocks for email-safe components
- Export to HTML for template storage

---

### Email Client Previews

**Current:** Single iframe preview
**Future:** Multi-client previews (Gmail, Outlook, Apple Mail)

**Benefits:**
- Test rendering across email clients
- Catch client-specific CSS issues
- Preview dark mode rendering

**Services:**
- [Litmus](https://www.litmus.com/) API integration
- [Email on Acid](https://www.emailonacid.com/) screenshots
- Self-hosted preview using email client CSS emulation

---

### A/B Testing Support

**Current:** Single template version
**Future:** A/B testing with variant templates

**Features:**
- Create template variants (A, B, C)
- Split traffic across variants
- Track open rates, click rates
- Auto-promote winning variant

**Implementation:**
- EmailTemplateVariant model (templateId, variantName, weight, stats)
- Random variant selection on send
- Tracking pixel in email HTML
- Analytics dashboard

---

## Performance

### Auto-Save Timing

**Current Implementation:**
- Save to localStorage on blur (when focus leaves editor)
- No automatic interval-based saves

**Performance Impact:**
- Negligible (localStorage write is < 1ms)
- No network requests (local only)

**Alternative: Interval-Based Auto-Save:**
```typescript
useEffect(() => {
  const interval = setInterval(() => {
    if (htmlContent || textContent) {
      localStorage.setItem(`email-template-draft-${id}`, JSON.stringify({
        subjectLine,
        htmlContent,
        textContent,
        savedAt: new Date().toISOString(),
      }));
    }
  }, 10000); // Every 10 seconds

  return () => clearInterval(interval);
}, [id, subjectLine, htmlContent, textContent]);
```

---

### Preview Rendering Performance

**Debounce Delay:**
- Current: 300ms
- Too short: Preview updates too frequently (distracting)
- Too long: Preview feels laggy

**Handlebars Compilation:**
- Fast (< 1ms for typical templates)
- May slow down for very large templates (> 100KB)

**Iframe Rendering:**
- Browser-native rendering (very fast)
- No performance concerns

**Optimization for Large Templates:**
```typescript
// Skip preview for very large HTML
const renderPreview = (html: string, data: Record<string, unknown>) => {
  if (html.length > 100000) { // 100KB
    setPreviewError('Template too large for live preview. Use test send instead.');
    return;
  }

  // Normal preview rendering...
};
```

---

## Accessibility

### Keyboard Shortcuts

**Implemented:**
- `Ctrl+S` (or `Cmd+S` on Mac) — Save template
- `Ctrl+P` — Toggle preview pane
- `Esc` — Close modal

**Implementation:**
```typescript
useEffect(() => {
  const handleKeyDown = (e: KeyboardEvent) => {
    // Save
    if ((e.ctrlKey || e.metaKey) && e.key === 's') {
      e.preventDefault();
      setSaveModalVisible(true);
    }

    // Preview toggle
    if ((e.ctrlKey || e.metaKey) && e.key === 'p') {
      e.preventDefault();
      setShowPreview(!showPreview);
    }

    // Close modal
    if (e.key === 'Escape') {
      setSaveModalVisible(false);
      setTestModalVisible(false);
    }
  };

  window.addEventListener('keydown', handleKeyDown);
  return () => window.removeEventListener('keydown', handleKeyDown);
}, [showPreview]);
```

---

### Screen Reader Support

**Form Labels:**
```typescript
<Form.Item label="Recipient Email" required>
  <Input
    type="email"
    aria-label="Test email recipient address"
    aria-required="true"
    value={testRecipient}
    onChange={(e) => setTestRecipient(e.target.value)}
  />
</Form.Item>
```

**Button Descriptions:**
```typescript
<Button
  icon={<SaveOutlined />}
  onClick={() => setSaveModalVisible(true)}
  aria-label="Save template and create new version"
>
  Save
</Button>

<Button
  size="small"
  onClick={() => handleInsertVariable(variable.key, 'html')}
  aria-label={`Insert ${variable.label} variable into HTML editor`}
>
  Insert to HTML
</Button>
```

---

## Related Documentation

### Frontend Documentation

- **[EmailTemplatesPage.tsx](../../frontend/pages/email-templates-page.md)** — Email templates list page
- **[App.tsx](../../frontend/app.md)** — Route definition for editor page

### Backend Documentation

- **[Email Templates Module](../../api/modules/email-templates.md)** — API routes
  - `GET /api/email-templates/:id` — Load template + variables
  - `PUT /api/email-templates/:id` — Update template (creates version)
  - `POST /api/email-templates/:id/test` — Send test email

### Feature Documentation

- **[template-system.md](./template-system.md)** — Email template engine overview
- **[variables.md](./variables.md)** — Template variable system
- **[versioning.md](./versioning.md)** — Template version history

### Related Features

- **[Landing Page Editor](../pages/editor.md)** — Similar GrapesJS editor for pages
- **[Campaign Emails](../influence/campaign-emails.md)** — Uses email templates for advocacy emails