foo.diff

diff --git a/control/Controller.php b/control/Controller.php
index 274b567..484c06f 100644
--- a/control/Controller.php
+++ b/control/Controller.php
@@ -502,7 +502,7 @@ class Controller extends RequestHandler implements TemplateGlobalProvider {
 	 */
 	public function redirectBack() {
 		// Don't cache the redirect back ever
-		HTTPCacheControl::singleton()->disableCaching();
+		HTTPCacheControl::singleton()->disableCache(true);
 
 		$url = null;
 
diff --git a/control/Director.php b/control/Director.php
index b98731e..095e700 100644
--- a/control/Director.php
+++ b/control/Director.php
@@ -384,7 +384,7 @@ class Director implements TemplateGlobalProvider {
 					try {
 						$result = $controllerObj->handleRequest($request, $model);
 					} catch(SS_HTTPResponse_Exception $responseException) {
-						HTTPCacheControl::singleton()->disableCaching();
+						HTTPCacheControl::singleton()->disableCache(true);
 						$result = $responseException->getResponse();
 					}
 					if(!is_object($result) || $result instanceof SS_HTTPResponse) return $result;
diff --git a/control/FlushRequestFilter.php b/control/FlushRequestFilter.php
index 64d8de6..5a6e295 100644
--- a/control/FlushRequestFilter.php
+++ b/control/FlushRequestFilter.php
@@ -19,7 +19,7 @@ class FlushRequestFilter implements RequestFilter {
 
 	public function postRequest(SS_HTTPRequest $request, SS_HTTPResponse $response, DataModel $model) {
 		if(array_key_exists('flush', $request->getVars())) {
-			HTTPCacheControl::singleton()->disableCaching();
+			HTTPCacheControl::singleton()->disableCache(true);
 		}
 		return true;
 	}
diff --git a/control/HTTP.php b/control/HTTP.php
index b93df19..5df1481 100644
--- a/control/HTTP.php
+++ b/control/HTTP.php
@@ -341,9 +341,9 @@ class HTTP {
 		$config = Config::inst()->forClass(__CLASS__);
 
 		// if http caching is disabled by config, disable it - used on dev environments due to frequently changing
-		// templates and other data
+		// templates and other data. will be overridden by forced publicCache() or privateCache() calls
 		if ($config->get('disable_http_cache')) {
-			HTTPCacheControl::singleton()->disableCaching();
+			HTTPCacheControl::singleton()->disableCache();
 		}
 
 		// Populate $responseHeaders with all the headers that we want to build
@@ -356,7 +356,7 @@ class HTTP {
 			$requestHeaders = array_change_key_case(apache_request_headers(), CASE_LOWER);
 
 			if (array_key_exists('x-requested-with', $requestHeaders) && strtolower($requestHeaders['x-requested-with']) == 'xmlhttprequest') {
-				HTTPCacheControl::singleton()->disableCaching();
+				HTTPCacheControl::singleton()->disableCache(true);
 			}
 		}
 
@@ -400,11 +400,12 @@ class HTTP {
 			// (http://support.microsoft.com/kb/323308)
 			// Note: this is also fixable by ticking "Do not save encrypted pages to disk" in advanced options.
 			HTTPCacheControl::singleton()
-				->privateCache()
+				->privateCache(true)
 				->removeDirective('no-cache')
 				->removeDirective('no-store');
 		}
 
+		// TODO: These risk overriding nocache / privatecache calls. Perhaps this should only be applied if caching is unspecified or specified as public
 		if (!empty($cacheControlHeaders)) {
 			HTTPCacheControl::singleton()->setDirectivesFromArray($cacheControlHeaders);
 		}
diff --git a/control/HTTPCacheControl.php b/control/HTTPCacheControl.php
index c538a50..dbfd373 100644
--- a/control/HTTPCacheControl.php
+++ b/control/HTTPCacheControl.php
@@ -20,11 +20,33 @@ class HTTPCacheControl extends SS_Object {
 	private $state = array();
 
 	/**
-	 * Whether the cache-control object is locked to further changes
-	 *
-	 * @var bool
+	 * Forcing level of previous setting; higher number wins
+	 * Combination of consts belo
+	 *w
+	 * @var int
 	 */
-	protected $locked = false;
+	protected $forcingLevel = 0;
+
+	/**
+	 * Forcing level forced, optionally combined with one of the below.
+	 */
+	private const LEVEL_FORCED = 10;
+
+	/**
+	 * Forcing level caching disabled. Overrides public/private.
+	 */
+	private const LEVEL_DISABLED = 3;
+
+	/**
+	 * Forcing level private-cached. Overrides public.
+	 */
+	private const LEVEL_PRIVATE = 2;
+
+	/**
+	 * Forcing level public cached. Lowest priority.
+	 */
+	private const LEVEL_PUBLIC = 1;
+
 
 	/**
 	 * A list of allowed cache directives for HTTPResponses
@@ -48,17 +70,6 @@ class HTTPCacheControl extends SS_Object {
 	);
 
 	/**
-	 * Lock the current state of the cache control to prevent further modifications
-	 *
-	 * @return $this
-	 */
-	public function lock()
-	{
-		$this->locked = true;
-		return $this;
-	}
-
-	/**
 	 * Low level method for setting directives include any experimental or custom ones added via config
 	 *
 	 * @param string $directive
@@ -203,35 +214,6 @@ class HTTPCacheControl extends SS_Object {
 	}
 
 	/**
-	 * Indicates that the response may be cached by any cache. (eg: CDNs, Proxies, Web browsers)
-	 *
-	 * Also removes `public` as this is a contradictory directive
-	 *
-	 * @return $this
-	 */
-	public function setPublic()
-	{
-		$this->setDirective('public');
-		$this->removeDirective('private');
-		return $this;
-	}
-
-	/**
-	 * Indicates that the response is intended for a single user and must not be stored by a shared cache.
-	 * A private cache may store the response.
-	 *
-	 * Also removes `private` as this is a contradictory directive
-	 *
-	 * @return $this
-	 */
-	public function setPrivate()
-	{
-		$this->setDirective('private');
-		$this->removeDirective('public');
-		return $this;
-	}
-
-	/**
 	 * Specifies the maximum amount of time (seconds) a resource will be considered fresh.
 	 * This directive is relative to the time of the request.
 	 *
@@ -282,44 +264,68 @@ class HTTPCacheControl extends SS_Object {
 	 * Removes all state and replaces it with `no-cache, no-store, must-revalidate`. Although `no-store` is sufficient
 	 * the others are added under recommendation from Mozilla (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control#Examples)
 	 *
+	 * This will take precendence over unforced privateCache / publicCache calls
+	 *
+	 * @param bool $force Force the cache to private even if it's forced private or public
 	 * @return $this
 	 */
-	public function disableCaching()
+	public function disableCache($force = false)
 	{
+		// Only exeucute this if its forcing level is high enough
+		$forcingLevel = self::LEVEL_DISABLED + ($force ? self::LEVEL_FORCED : 0);
+		$this->forcingLevel = $forcingLevel;
+
 		$this->state = array(
 			'no-cache' => null,
 			'no-store' => null,
 			'must-revalidate' => null,
 		);
-		$this->lock();
 		return $this;
 	}
 
 	/**
-	 * Helper function to set the current cache to private
+	 * Indicates that the response is intended for a single user and must not be stored by a shared cache.
+	 * A private cache may store the response.
+	 *
+	 * Also removes `private` as this is a contradictory directive
 	 *
+	 * @param bool $force Force the cache to private even if it's forced public
 	 * @return $this
 	 */
-	public function privateCache()
+	public function privateCache($force = false)
 	{
-		$this->setPrivate();
+		// Only exeucute this if its forcing level is high enough
+		$forcingLevel = self::LEVEL_PRIVATE + ($force ? self::LEVEL_FORCED : 0);
+		if ($forcingLevel < $this->forcingLevel) {
+			return;
+		}
+		$this->forcingLevel = $forcingLevel;
+
+		// Update the directives
+		$this->setDirective('private');
+		$this->removeDirective('public');
 		return $this;
 	}
 
 	/**
-	 * Helper function to set the current cache to public
+ 	 * Indicates that the response may be cached by any cache. (eg: CDNs, Proxies, Web browsers)
 	 *
-	 * @param bool $force Force the cache to public even if it's private
+	 * Also removes `public` as this is a contradictory directive
 	 *
+	 * @param bool $force Force the cache to public even if it's private, unless it's been forced private
 	 * @return $this
 	 */
 	public function publicCache($force = false)
 	{
-		if ($force || !$this->hasDirective('private')) {
-			$this->setPublic();
-		} else {
-			user_error('Cannot change a private cache to public', E_USER_WARNING);
+		// Only exeucute this if its forcing level is high enough
+		$forcingLevel = self::LEVEL_PUBLIC + ($force ? self::LEVEL_FORCED : 0);
+		if ($forcingLevel < $this->forcingLevel) {
+			return;
 		}
+		$this->forcingLevel = $forcingLevel;
+
+		$this->setDirective('public');
+		$this->removeDirective('private');
 		return $this;
 	}
 
diff --git a/control/VersionedRequestFilter.php b/control/VersionedRequestFilter.php
index aae5951..7c71de1 100644
--- a/control/VersionedRequestFilter.php
+++ b/control/VersionedRequestFilter.php
@@ -46,7 +46,7 @@ class VersionedRequestFilter implements RequestFilter {
 
 	public function postRequest(SS_HTTPRequest $request, SS_HTTPResponse $response, DataModel $model) {
 		if (Versioned::current_stage() !== Versioned::LIVE && !HTTPCacheControl::singleton()->hasDirective('no-store')) {
-			HTTPCacheControl::singleton()->privateCache();
+			HTTPCacheControl::singleton()->privateCache(true);
 		}
 		return true;
 	}
diff --git a/forms/Form.php b/forms/Form.php
index b07a029..d2f7c00 100644
--- a/forms/Form.php
+++ b/forms/Form.php
@@ -855,7 +855,7 @@ class Form extends RequestHandler {
 
 		// If we need to disable cache, do it
 		if ($needsCacheDisabled) {
-			HTTPCacheControl::singleton()->disableCaching();
+			HTTPCacheControl::singleton()->disableCache(true);
 		}
 
 		$attrs = $this->getAttributes();
diff --git a/security/Security.php b/security/Security.php
index 5fd36c7..15a9058 100644
--- a/security/Security.php
+++ b/security/Security.php
@@ -240,7 +240,7 @@ class Security extends Controller implements TemplateGlobalProvider {
 
 		if(!$controller) $controller = Controller::curr();
 
-		HTTPCacheControl::singleton()->disableCaching();
+		HTTPCacheControl::singleton()->disableCache(true);
 
 		if(Director::is_ajax()) {
 			$response = ($controller) ? $controller->getResponse() : new SS_HTTPResponse();