ios/chrome/browser/snapshots/snapshot_cache.h

// Copyright 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_H_
#define IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_H_

#import <UIKit/UIKit.h>

#include "base/time/time.h"

@protocol SnapshotCacheObserver;

// A singleton providing an in-memory and on-disk cache of tab snapshots.
// A snapshot is a full-screen image of the contents of the page at the current
// scroll offset and zoom level, used to stand in for the WKWebView if it has
// been purged from memory or when quickly switching tabs.
// Persists to disk on a background thread each time a snapshot changes.
@interface SnapshotCache : NSObject

// Track session IDs to not release on low memory and to reload on
// |UIApplicationDidBecomeActiveNotification|.
@property(nonatomic, strong) NSSet* pinnedIDs;

// The scale that should be used for snapshots.
- (CGFloat)snapshotScaleForDevice;

// Retrieve a cached snapshot for the |sessionID| and return it via the callback
// if it exists. The callback is guaranteed to be called synchronously if the
// image is in memory. It will be called asynchronously if the image is on disk
// or with nil if the image is not present at all.
- (void)retrieveImageForSessionID:(NSString*)sessionID
                         callback:(void (^)(UIImage*))callback;

// Request the session's grey snapshot. If the image is already loaded in
// memory, this will immediately call back on |callback|.
- (void)retrieveGreyImageForSessionID:(NSString*)sessionID
                             callback:(void (^)(UIImage*))callback;

- (void)setImage:(UIImage*)img withSessionID:(NSString*)sessionID;

// Removes the image from both the LRU and disk cache, unless it is marked for
// deferred deletion. Images marked for deferred deletion can only be removed by
// calling |-removeMarkedImages|.
- (void)removeImageWithSessionID:(NSString*)sessionID;

// Marks an image for deferred deletion. The image will not be immediately
// deleted when |-removeImageWithSessionID:| is called. Images marked for
// deferred deletion can only be removed by calling |-removeMarkedImages|.
- (void)markImageWithSessionID:(NSString*)sessionID;

// Removes all marked images from both the LRU and disk cache.
- (void)removeMarkedImages;

// Unmarks all images, so they remain in the cache. They are no longer marked
// for deferred deletion.
- (void)unmarkAllImages;

// Purge the cache of snapshots that are older than |date|. The snapshots for
// the sessions given in |liveSessionIds| will be kept. This will be done
// asynchronously on a background thread.
- (void)purgeCacheOlderThan:(const base::Time&)date
                    keeping:(NSSet*)liveSessionIds;
// Hint that the snapshot for |sessionID| will likely be saved to disk when the
// application is backgrounded.  The snapshot is then saved in memory, so it
// does not need to be read off disk.
- (void)willBeSavedGreyWhenBackgrounding:(NSString*)sessionID;

// Create temporary cache of grey images for tablet side swipe.
- (void)createGreyCache:(NSArray*)sessionIDs;
// Release all images in grey cache.
- (void)removeGreyCache;
// Request the session's grey snapshot. If the image is already loaded this will
// immediately call back on |callback|. Otherwise, only use |callback| for the
// most recent caller. The callback is not guaranteed to be called.
- (void)greyImageForSessionID:(NSString*)sessionID
                     callback:(void (^)(UIImage*))callback;

// Write a grey copy of the snapshot for |sessionID| to disk, but if and only if
// a color version of the snapshot already exists in memory or on disk.
- (void)saveGreyInBackgroundForSessionID:(NSString*)sessionID;

// Adds an observer to this snapshot cache.
- (void)addObserver:(id<SnapshotCacheObserver>)observer;

// Removes an observer from this snapshot cache.
- (void)removeObserver:(id<SnapshotCacheObserver>)observer;

// Invoked before the instance is deallocated. Needs to release all reference
// to C++ objects. Object will soon be deallocated.
- (void)shutdown;

@end

// Additionnal methods that should only be used for tests.
@interface SnapshotCache (TestingAdditions)
- (BOOL)hasImageInMemory:(NSString*)sessionID;
- (BOOL)hasGreyImageInMemory:(NSString*)sessionID;
- (NSUInteger)lruCacheMaxSize;
@end

#endif  // IOS_CHROME_BROWSER_SNAPSHOTS_SNAPSHOT_CACHE_H_