// Copyright (c) 2006-2008 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.

// See net/disk_cache/disk_cache.h for the public interface.

#ifndef NET_DISK_CACHE_STORAGE_BLOCK_H__
#define NET_DISK_CACHE_STORAGE_BLOCK_H__
#include "cache_addr.h"
#include "cache_mapped_file.h"
namespace disk_cache {

class EntryImpl;

// This class encapsulates common behavior of a single "block" of data that is
// stored on a block-file. It implements the FileBlock interface, so it can be
// serialized directly to the backing file.
// This object provides a memory buffer for the related data, and it can be used
// to actually share that memory with another instance of the class.
//
// The following example shows how to share storage with another object:
//    StorageBlock<TypeA> a(file, address);
//    StorageBlock<TypeB> b(file, address);
//    a.Load();
//    DoSomething(a.Data());
//    b.SetData(a.Data());
//    ModifySomething(b.Data());
//    // Data modified on the previous call will be saved by b's destructor.
//    b.set_modified();
template<typename T>
class StorageBlock : public FileBlock {
    public:
        StorageBlock(MappedFile* file, Addr address);
        virtual ~StorageBlock();

        // FileBlock interface.
        virtual void* buffer() const;
        virtual size_t size() const;
        virtual int offset() const;

        // Allows the overide of dummy values passed on the constructor.
        bool LazyInit(MappedFile* file, Addr address);

        // Sets the internal storage to share the memory provided by other instance.
        void SetData(T* other);

        // Deletes the data, even if it was modified and not saved. This object must
        // own the memory buffer (it cannot be shared).
        void Discard();

        // Stops sharing the data with another object.
        void StopSharingData();

        // Sets the object to lazily save the in-memory data on destruction.
        void set_modified();

        // Gets a pointer to the internal storage (allocates storage if needed).
        T* Data();

        // Returns true if there is data associated with this object.
        bool HasData() const;

        // Returns true if this object owns the data buffer, false if it is shared.
        bool own_data() const;

        const Addr address() const;

        // Loads and store the data.
        bool Load();
        bool Store();

    private:
        void AllocateData();
        void DeleteData();

        T* data_;
        MappedFile* file_;
        Addr address_;
        bool modified_;
        bool own_data_;  // Is data_ owned by this object or shared with someone else.
        bool extended_;  // Used to store an entry of more than one block.

        DISALLOW_EVIL_CONSTRUCTORS(StorageBlock);
};

typedef StorageBlock<EntryStore> CacheEntryBlock;
typedef StorageBlock<RankingsNode> CacheRankingsBlock;

}  // namespace disk_cache

#endif  // NET_DISK_CACHE_STORAGE_BLOCK_H__
