CacheDependency.php

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<?php
class DependencyWrapper {
    private $value;
    private $deps;

    function __construct( $value = false, $deps = array() ) {
        $this->value = $value;

        if ( !is_array( $deps ) ) {
            $deps = array( $deps );
        }

        $this->deps = $deps;
    }

    function isExpired() {
        foreach ( $this->deps as $dep ) {
            if ( $dep->isExpired() ) {
                return true;
            }
        }

        return false;
    }

    function initialiseDeps() {
        foreach ( $this->deps as $dep ) {
            $dep->loadDependencyValues();
        }
    }

    function getValue() {
        return $this->value;
    }

    function storeToCache( $cache, $key, $expiry = 0 ) {
        $this->initialiseDeps();
        $cache->set( $key, $this, $expiry );
    }

    static function getValueFromCache( $cache, $key, $expiry = 0, $callback = false,
        $callbackParams = array(), $deps = array()
    ) {
        $obj = $cache->get( $key );

        if ( is_object( $obj ) && $obj instanceof DependencyWrapper && !$obj->isExpired() ) {
            $value = $obj->value;
        } elseif ( $callback ) {
            $value = call_user_func_array( $callback, $callbackParams );
            # Cache the newly-generated value
            $wrapper = new DependencyWrapper( $value, $deps );
            $wrapper->storeToCache( $cache, $key, $expiry );
        } else {
            $value = null;
        }

        return $value;
    }
}

abstract class CacheDependency {
    abstract function isExpired();

    function loadDependencyValues() {
    }
}

class FileDependency extends CacheDependency {
    private $filename;
    private $timestamp;

    function __construct( $filename, $timestamp = null ) {
        $this->filename = $filename;
        $this->timestamp = $timestamp;
    }

    function __sleep() {
        $this->loadDependencyValues();

        return array( 'filename', 'timestamp' );
    }

    function loadDependencyValues() {
        if ( is_null( $this->timestamp ) ) {
            if ( !file_exists( $this->filename ) ) {
                # Dependency on a non-existent file
                # This is a valid concept!
                $this->timestamp = false;
            } else {
                $this->timestamp = filemtime( $this->filename );
            }
        }
    }

    function isExpired() {
        if ( !file_exists( $this->filename ) ) {
            if ( $this->timestamp === false ) {
                # Still nonexistent
                return false;
            } else {
                # Deleted
                wfDebug( "Dependency triggered: {$this->filename} deleted.\n" );

                return true;
            }
        } else {
            $lastmod = filemtime( $this->filename );
            if ( $lastmod > $this->timestamp ) {
                # Modified or created
                wfDebug( "Dependency triggered: {$this->filename} changed.\n" );

                return true;
            } else {
                # Not modified
                return false;
            }
        }
    }
}

class GlobalDependency extends CacheDependency {
    private $name;
    private $value;

    function __construct( $name ) {
        $this->name = $name;
        $this->value = $GLOBALS[$name];
    }

    function isExpired() {
        if ( !isset( $GLOBALS[$this->name] ) ) {
            return true;
        }

        return $GLOBALS[$this->name] != $this->value;
    }
}

class ConstantDependency extends CacheDependency {
    private $name;
    private $value;

    function __construct( $name ) {
        $this->name = $name;
        $this->value = constant( $name );
    }

    function isExpired() {
        return constant( $this->name ) != $this->value;
    }
}