Scape/SPECS.md

Scape Templates — Product Specification

Project Name

Scape Templates

Project Description

A lightweight, standalone PHP template engine designed for simplicity, security, and performance. Scape is built as an Output Engine first, focusing on marrying pre-processed data with design rather than performing additional business logic or data manipulation.

Project Purpose

To provide a modern, framework-agnostic alternative for template rendering that maintains a strict separation of concerns. Scape enforces a "logic-light" philosophy to ensure templates remain readable and focused purely on presentation.

Project Installation Instructions

Scape can be installed via Composer:

composer require getphred/scape

Project Features

1. File Handling & Configuration

• Template Extensions:
  • All templates, layouts, and partials must use the .scape.php extension.
• Filter Extensions:
  • Custom filters must use the standard .php extension.
  • All custom filters must implement the Scape\Interfaces\FilterInterface to ensure they provide the necessary transformation methods.
• Directory Configuration: Template locations are managed via environment variables:
  • SCAPE_TEMPLATES_DIR: Main directory for application templates.
  • SCAPE_LAYOUTS_DIR: Directory for base layouts and parent templates.
  • SCAPE_PARTIALS_DIR: Directory for reusable snippets/partials.
  • SCAPE_FILTERS_DIR: Directory for user-defined filters.
• Dot Notation Pathing: All internal paths (extends, includes) use dot notation (e.g., sidebar.login_form) relative to their respective directories, omitting the file extension.

2. Syntax & White-space

• All opening and closing tags are white-space independent (e.g., {{var}} is equivalent to {{ var }}).
• Variable Interpolation:
  • {{ var }}: Automatically HTML-escaped output (uses ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5).
  • {{{ var }}}: Raw, unescaped output.
  • Data Access:
    • Use dot-notation for accessing class properties/attributes (e.g., user.name).
    • Use bracket notation for accessing array elements (e.g., items['title'] or users[0]).

3. Logic & Control Flow

• Syntax: Uses {( ... )} for logic tags.
• White-space Management: Logic tags {( ... )} and block/inheritance tags {[ ... ]} automatically consume one trailing newline immediately following their closing )} or ]} to prevent unintended vertical spacing in the rendered output.
• "Logic-Light" Constraints:
  • No generic programming or complex expressions.
  • No if statements or conditional branching (by design).
  • No manual variable assignment within templates.
• Loops:
  • Only bounded iteration is supported: foreach.
  • Grammar:
    • {( foreach item in collection )} ... {( endforeach )}
    • {( foreach key, item in collection )} ... {( endforeach )}
  • Every loop provides access to two local integer variables:
    • index: The current iteration index, 0-indexed (0, 1, 2...).
    • pos: The current human-readable position, 1-indexed (1, 2, 3...).
  • Positional Rendering: Special tags are available within loops to handle presentation based on position:
    • {( first )} ... {( endfirst )}: Renders only on the first iteration.
    • {( inner )} ... {( endinner )}: Renders on all iterations except the first and last.
    • {( last )} ... {( endlast )}: Renders only on the last iteration.

4. Inheritance & Reusability

• Syntax: Uses {[ ... ]} for block and inheritance tags.
• Layouts & Inheritance:
  • Templates can extend layouts from SCAPE_LAYOUTS_DIR using {[ extends 'path' ]}.
  • The extends tag must be the very first thing in a template.
• Blocks:
  • Placeholder: Layouts define placeholders using {[ block 'name' ]} ... {[ endblock ]}.
  • Override: Child templates provide content for these placeholders by defining a block with the same name.
  • Parent Content: Within an override block, the child can render the layout's default content using the {[ parent ]} tag.
  • Default Content: If a child template does not provide a block, the content within the layout's block tags is rendered as a default.
  • Nested Blocks: Blocks can be nested within other blocks.
• Partials:
  • Reusable snippets from SCAPE_PARTIALS_DIR can be included using {[ include 'path' ]}.
  • Encapsulation: Partials are siloed by default and do not inherit the parent template's variables.
  • Passing Data:
    • Data can be passed as an array: {[ include 'path' with data_source ]}.
    • The data_source can be a local variable, a nested array element (items['meta']), a class attribute (user.profile), or an inline array declaration (e.g., ['user' => user, 'id' => 1]).
    • The array keys from the source are expanded into individual local variables within the partial.
    • The full parent context can be passed explicitly: {[ include 'path' with context ]}.
  • Nesting: Partials can include other partials. To prevent infinite recursion, the engine enforces a maximum nesting depth (default: 20).

5. Extensibility

• Filters:
  • Used with variable interpolation to transform data.
  • Piping: Supports chaining multiple filters: {{ var | lower | ucfirst }}.
  • Arguments: Supports passing simple arguments (strings, numbers, or other variables): {{ price | currency('USD') }}.
  • The FilterInterface: All filters must implement Scape\Interfaces\FilterInterface:

    public function transform(mixed $value, array $args = []): mixed;
    

  • Loading: Filters must be pre-loaded at the top of the template.
  • Internal Libraries: Engine-provided filters are loaded using the uses keyword:
    • Syntax: {( uses namespace:library )} (e.g., {( uses filters:string )}).
  • Custom Filters: User-defined filters are loaded from SCAPE_FILTERS_DIR using load_filter.
    • Syntax: {( load_filter('path') )} where path is dot-notated.

6. Security & Error Handling

• Contextual Escaping: Standard {{ }} interpolation ensures XSS protection.
• Missing Assets: If a layout or partial is missing, the engine looks for a user-provided 404.scape.php in SCAPE_TEMPLATES_DIR. If not found, it renders a built-in "Template 404" placeholder.
• Exceptions: The engine throws specific exceptions within the Scape\Exceptions namespace:
  • TemplateNotFoundException: Main template, layout, or partial missing.
  • SyntaxException: Malformed tags or disallowed logic (e.g. if).
  • FilterNotFoundException: Target of uses or load_filter missing.
  • PropertyNotFoundException: (Debug only) Accessing undefined key/property.
  • RecursionLimitException: Partials exceed nesting limit (default 20).
• Variable Access:
  • Debug Mode: Accessing a non-existent object property or array key throws a PropertyNotFoundException.
  • Production Mode: Accessing a non-existent property or key fails silently and renders an empty string.

7. Performance

• AST Caching: The engine caches the parsed Abstract Syntax Tree (AST) of templates to speed up subsequent renders.
• Cache Location: Cache files are stored locally in the project directory under .scape/cache.
• No Compiling: Scape does not compile templates into raw PHP files; it interprets the cached AST directly.
• Cache Modes:
  • Development: Engine checks file modification times (mtime) to invalidate the cache when a template changes.
  • Production: Engine skips mtime checks and serves the cached AST directly for maximum performance.

8. Host Integration (IoC)

• The host Namespace: Scape provides a reserved host namespace that can be used with the uses keyword or as a filter/function prefix.
• Provider Registration: Host frameworks (e.g., Phred) can register custom providers to handle calls in this namespace.
• Use Cases: Used for framework-level features like feature flags (Flagpole), routing, or translations without creating a hard dependency within the engine.
• Default Behavior: If no provider is registered, calls to the host namespace return the input value unchanged or null.

9. Runtime API

• The Scape\Engine Class: The primary entry point for the library.
• Configuration Precedence: Programmatic Config > Environment Variables > Defaults.
• Rendering:
  • Method: public function render(string $template, array $data = []): string
  • The $template argument uses dot notation.
• Mode Control: The engine operating mode (debug vs production) can be set via the SCAPE_MODE environment variable or explicitly during instantiation.

Project Dependencies

• PHP: ^8.2
• PHPUnit: ^10.0 (Development)