ADR-003 - Template Engine

ADR-003: Template Engine (Smarty)

Architecture Decision Record for XOOPS’s adoption of the Smarty template engine.

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Status

Accepted - Core decision since XOOPS 2.0

Evolving - Migration to Smarty 4/5 planned for XOOPS 4.0

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Context

XOOPS needed a templating solution that would:

1. Separate presentation from business logic
2. Allow theme designers to work without PHP knowledge
3. Support template inheritance and includes
4. Provide caching for performance
5. Enable user-customizable templates
6. Support internationalization

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Decision Diagram

flowchart TB
    subgraph "PHP Layer"
        A[Module Controller]
        B[Template Variables]
    end

    subgraph "Smarty Engine"
        C[Smarty Core]
        D[Template Compiler]
        E[Cache Manager]
    end

    subgraph "Templates"
        F[Module Templates]
        G[Theme Templates]
        H[Block Templates]
    end

    subgraph "Output"
        I[Compiled PHP]
        J[Cached HTML]
        K[Final HTML]
    end

    A --> B
    B --> C
    C --> D
    C --> E
    D --> F
    D --> G
    D --> H
    F --> I
    G --> I
    H --> I
    E --> J
    I --> K
    J --> K

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Decision

We will use Smarty as the template engine because:

1. Separation of Concerns

// PHP (Controller) - Business logic
$items = $itemHandler->getPublishedItems();
$xoopsTpl->assign('items', $items);

// Smarty (View) - Presentation
// templates/items.tpl

{* Smarty template - No PHP logic *}
<{foreach item=item from=$items}>
    <article>
        <h2><{$item.title}></h2>
        <p><{$item.summary}></p>
    </article>
<{/foreach}>

2. XOOPS Delimiters

XOOPS uses <{ and }> instead of standard { }:

{* Standard Smarty *}
{$variable}

{* XOOPS Smarty - Avoids JavaScript conflicts *}
<{$variable}>

3. Template Hierarchy

graph TB
    A[Theme Master Template<br>theme.html] --> B[Module Template<br>module_index.tpl]
    A --> C[Block Templates<br>block_*.tpl]
    B --> D[Partial Templates<br>_header.tpl]
    B --> E[Partial Templates<br>_footer.tpl]

    style A fill:#f9f,stroke:#333
    style B fill:#9ff,stroke:#333
    style C fill:#ff9,stroke:#333

4. Template Storage

• Database: Customized templates stored for revert capability
• File System: Original templates in module directories
• Cache: Compiled templates for performance

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Smarty Configuration

// XOOPS Smarty initialization
$xoopsTpl = new XoopsTpl();

// Custom delimiters
$xoopsTpl->left_delim = '<{';
$xoopsTpl->right_delim = '}>';

// Caching
$xoopsTpl->caching = XOOPS_TEMPLATE_CACHE;
$xoopsTpl->cache_lifetime = 3600;

// Security
$xoopsTpl->security_policy = new Smarty_Security($xoopsTpl);
$xoopsTpl->security_policy->php_functions = [];
$xoopsTpl->security_policy->php_modifiers = ['escape', 'count'];

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Template Features Used

Variables

{* Simple variable *}
<{$title}>

{* Object property *}
<{$item.title}>

{* With modifier *}
<{$content|truncate:200:'...'}>

{* Escaped output *}
<{$userInput|escape:'html'}>

Control Structures

{* Conditional *}
<{if $isAdmin}>
    <a href="admin.php">Admin</a>
<{elseif $isUser}>
    <a href="profile.php">Profile</a>
<{else}>
    <a href="login.php">Login</a>
<{/if}>

{* Loop *}
<{foreach item=item from=$items name=itemloop}>
    <{$smarty.foreach.itemloop.index}>: <{$item.title}>
<{/foreach}>

Includes

{* Include another template *}
<{include file="db:mymodule_header.tpl"}>

{* Include with variables *}
<{include file="db:mymodule_item.tpl" item=$currentItem}>

{* Include from theme *}
<{include file="file:$theme_path/partials/sidebar.tpl"}>

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Consequences

Positive

1. Designer-friendly: HTML-like syntax
2. Caching: Built-in template caching
3. Security: PHP code isolation
4. Flexibility: Modifiers, functions, plugins
5. Customization: Users can modify templates
6. Community: Large Smarty ecosystem

Negative

1. Learning curve: Smarty-specific syntax
2. Overhead: Compilation step required
3. Debugging: Template errors can be cryptic
4. Version issues: Breaking changes between versions

Mitigations

• Learning: Comprehensive documentation
• Performance: Aggressive caching
• Debugging: Debug console, clear error messages
• Versions: Compatibility layer in XOOPS

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Version History

timeline
    title Smarty in XOOPS
    2003 : Smarty 2.x
         : Initial integration
    2013 : Smarty 3.0
         : XOOPS 2.5.5
    2020 : Smarty 3.1
         : XOOPS 2.5.10
    2026 : Smarty 4/5
         : XOOPS 4.0

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Migration: Smarty 3 to 4/5

Breaking Changes

{* Smarty 3 - Deprecated *}
<{php}>echo date('Y');<{/php}>

{* Smarty 4+ - Use modifiers or assign from PHP *}
<{$current_year}>

{* Smarty 3 - {section} deprecated *}
<{section name=i loop=$items}>
    <{$items[i].title}>
<{/section}>

{* Smarty 4+ - Use {foreach} *}
<{foreach $items as $item}>
    <{$item.title}>
<{/foreach}>

Compatibility Layer

XOOPS provides a compatibility layer for smooth transitions:

// XoopsTpl extends Smarty with compatibility methods
class XoopsTpl extends Smarty
{
    public function assign($tpl_var, $value = null)
    {
        // Handles both Smarty 3 and 4 syntax
        return parent::assign($tpl_var, $value);
    }
}

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Alternatives Considered

1. Twig

Pros: Modern, Symfony ecosystem Cons: Different syntax, migration effort Decision: Possible future option for XOOPS 3.x

2. Blade (Laravel)

Pros: Clean syntax, popular Cons: Laravel-specific Decision: Not suitable for standalone use

3. Native PHP Templates

Pros: No learning curve, fast Cons: Security risks, no separation Decision: Rejected for maintainability

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Related Decisions

• ADR-001: Modular Architecture
• ADR-002: Database Abstraction

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References

• Smarty Documentation: https://www.smarty.net/docs/en/
• XOOPS Template System Guide
• MVC Pattern in Web Applications

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#xoops #architecture #adr #smarty #templates #design-decision