// Copyright 2021 The Chromium OS 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 MISSIVE_STORAGE_STORAGE_QUEUE_H_
#define MISSIVE_STORAGE_STORAGE_QUEUE_H_

#include <list>
#include <map>
#include <memory>
#include <string>
#include <vector>

#include <base/callback.h>
#include <base/containers/flat_set.h>
#include <base/files/file.h>
#include <base/files/file_enumerator.h>
#include <base/files/file_path.h>
#include <base/memory/ref_counted.h>
#include <base/memory/scoped_refptr.h>
#include <base/optional.h>
#include <base/sequenced_task_runner.h>
#include <base/strings/string_piece.h>
#include <base/threading/thread.h>
#include <base/threading/thread_task_runner_handle.h>
#include <base/timer/timer.h>

#include "missive/encryption/encryption_module_interface.h"
#include "missive/proto/record.pb.h"
#include "missive/storage/storage_configuration.h"
#include "missive/storage/storage_uploader_interface.h"
#include "missive/util/status.h"
#include "missive/util/statusor.h"

namespace reporting {

// Storage queue represents single queue of data to be collected and stored
// persistently. It allows to add whole data records as necessary,
// flush previously collected records and confirm records up to certain
// sequencing id to be eliminated.
class StorageQueue : public base::RefCountedThreadSafe<StorageQueue> {
 public:
  // Callback type for UploadeInterface provider for this queue.
  using AsyncStartUploaderCb = base::RepeatingCallback<void(
      UploaderInterface::UploaderInterfaceResultCb)>;

  // Creates StorageQueue instance with the specified options, and returns it
  // with the |completion_cb| callback. |async_start_upload_cb| is a factory
  // callback that instantiates UploaderInterface every time the queue starts
  // uploading records - periodically or immediately after Write (and in the
  // near future - upon explicit Flush request).
  static void Create(
      const QueueOptions& options,
      AsyncStartUploaderCb async_start_upload_cb,
      scoped_refptr<EncryptionModuleInterface> encryption_module,
      base::OnceCallback<void(StatusOr<scoped_refptr<StorageQueue>>)>
          completion_cb);

  // Wraps and serializes Record (taking ownership of it), encrypts and writes
  // the resulting blob into the StorageQueue (the last file of it) with the
  // next sequencing id assigned. The write is a non-blocking operation -
  // caller can "fire and forget" it (|completion_cb| allows to verify that
  // record has been successfully enqueued). If file is going to become too
  // large, it is closed and new file is created.
  // Helper methods: AssignLastFile, WriteHeaderAndBlock, OpenNewWriteableFile,
  // WriteMetadata, DeleteOutdatedMetadata.
  void Write(Record record, base::OnceCallback<void(Status)> completion_cb);

  // Confirms acceptance of the records up to |sequencing_id| (inclusively).
  // All records with sequencing ids <= this one can be removed from
  // the StorageQueue, and can no longer be uploaded.
  // If |force| is false (which is used in most cases), |sequencing_id| is
  // only accepted if no higher ids were confirmed before; otherwise it is
  // accepted unconditionally.
  // Helper methods: RemoveConfirmedData.
  void Confirm(base::Optional<int64_t> sequencing_id,
               bool force,
               base::OnceCallback<void(Status)> completion_cb);

  // Initiates upload of collected records. Called periodically by timer, based
  // on upload_period of the queue, and can also be called explicitly - for
  // a queue with an infinite or very large upload period. Multiple |Flush|
  // calls can safely run in parallel.
  // Starts by calling |async_start_upload_cb_| that instantiates
  // |UploaderInterface uploader|. Then repeatedly reads EncryptedRecord(s) one
  // by one from the StorageQueue starting from |first_sequencing_id_|, handing
  // each one over to |uploader|->ProcessRecord (keeping ownership of the
  // buffer) and resuming after result callback returns 'true'. Only files that
  // have been closed are included in reading; |Upload| makes sure to close the
  // last writeable file and create a new one before starting to send records to
  // the |uploader|. If some records are not available or corrupt,
  // |uploader|->ProcessGap is called. If the monotonic order of sequencing is
  // broken, INTERNAL error Status is reported. |Upload| can be stopped after
  // any record by returning 'false' to |processed_cb| callback - in that case
  // |Upload| will behave as if the end of data has been reached. While one or
  // more |Upload|s are active, files can be added to the StorageQueue but
  // cannot be deleted. If processing of the record takes significant time,
  // |uploader| implementation should be offset to another thread to avoid
  // locking StorageQueue. Helper methods: SwitchLastFileIfNotEmpty,
  // CollectFilesForUpload.
  void Flush();

  // Test only: makes specified records fail on reading.
  void TestInjectBlockReadErrors(std::initializer_list<int64_t> sequencing_ids);

  // Access queue options.
  const QueueOptions& options() const { return options_; }

  StorageQueue(const StorageQueue& other) = delete;
  StorageQueue& operator=(const StorageQueue& other) = delete;

 protected:
  virtual ~StorageQueue();

 private:
  friend class base::RefCountedThreadSafe<StorageQueue>;

  // Private data structures for Read and Write (need access to the private
  // StorageQueue fields).
  class WriteContext;
  class ReadContext;
  class ConfirmContext;

  // Private envelope class for single file in a StorageQueue.
  class SingleFile : public base::RefCountedThreadSafe<SingleFile> {
   public:
    // Factory method creates a SingleFile object for existing
    // or new file (of zero size). In case of any error (e.g. insufficient disk
    // space) returns status.
    static StatusOr<scoped_refptr<SingleFile>> Create(
        const base::FilePath& filename, int64_t size);

    Status Open(bool read_only);  // No-op if already opened.
    void Close();                 // No-op if not opened.

    Status Delete();

    // Attempts to read |size| bytes from position |pos| and returns
    // reference to the data that were actually read (no more than |size|).
    // End of file is indicated by empty data.
    // |max_buffer_size| specifies the largest allowed buffer, which
    // must accommodate the largest possible data block plus header and
    // overhead.
    StatusOr<base::StringPiece> Read(uint32_t pos,
                                     uint32_t size,
                                     size_t max_buffer_size);

    // Appends data to the file.
    StatusOr<uint32_t> Append(base::StringPiece data);

    bool is_opened() const { return handle_.get() != nullptr; }
    bool is_readonly() const {
      DCHECK(is_opened());
      return is_readonly_.value();
    }
    uint64_t size() const { return size_; }
    std::string name() const { return filename_.MaybeAsASCII(); }

   protected:
    virtual ~SingleFile();

   private:
    friend class base::RefCountedThreadSafe<SingleFile>;

    // Private constructor, called by factory method only.
    SingleFile(const base::FilePath& filename, int64_t size);

    // Flag (valid for opened file only): true if file was opened for reading
    // only, false otherwise.
    base::Optional<bool> is_readonly_;

    const base::FilePath filename_;  // relative to the StorageQueue directory
    uint64_t size_ = 0;  // tracked internally rather than by filesystem

    std::unique_ptr<base::File> handle_;  // Set only when opened/created.

    // When reading the file, this is the buffer and data positions.
    // If the data is read sequentially, buffered portions are reused
    // improving performance. When the sequential order is broken (e.g.
    // we start reading the same file in parallel from different position),
    // the buffer is reset.
    size_t data_start_ = 0;
    size_t data_end_ = 0;
    uint64_t file_position_ = 0;
    size_t buffer_size_ = 0;
    std::unique_ptr<char[]> buffer_;
  };

  // Private constructor, to be called by Create factory method only.
  StorageQueue(const QueueOptions& options,
               AsyncStartUploaderCb async_start_upload_cb,
               scoped_refptr<EncryptionModuleInterface> encryption_module);

  // Initializes the object by enumerating files in the assigned directory
  // and determines the sequencing information of the last record.
  // Must be called once and only once after construction.
  // Returns OK or error status, if anything failed to initialize.
  // Called once, during initialization.
  // Helper methods: EnumerateDataFiles, ScanLastFile, RestoreMetadata.
  Status Init();

  // Attaches last record digest to the given record (does not exist at a
  // generation start). Calculates the given record digest and stores it
  // as the last one for the next record.
  void UpdateRecordDigest(WrappedRecord* wrapped_record);

  // Helper method for Init(): process single data file.
  // Return sequencing_id from <prefix>.<sequencing_id> file name, or Status
  // in case there is any error.
  StatusOr<int64_t> AddDataFile(
      const base::FilePath& full_name,
      const base::FileEnumerator::FileInfo& file_info);

  // Helper method for Init(): enumerates all data files in the directory.
  // Valid file names are <prefix>.<sequencing_id>, any other names are ignored.
  // Adds used data files to the set.
  Status EnumerateDataFiles(base::flat_set<base::FilePath>* used_files_set);

  // Helper method for Init(): scans the last file in StorageQueue, if there are
  // files at all, and learns the latest sequencing id. Otherwise (if there
  // are no files) sets it to 0.
  Status ScanLastFile();

  // Helper method for Write(): increments sequencing id and assigns last
  // file to place record in. |size| parameter indicates the size of data that
  // comprise the record expected to be appended; if appending the record will
  // make the file too large, the current last file will be closed, and a new
  // file will be created and assigned to be the last one.
  StatusOr<scoped_refptr<SingleFile>> AssignLastFile(size_t size);

  // Helper method for Write() and Read(): creates and opens a new empty
  // writeable file, adding it to |files_|.
  StatusOr<scoped_refptr<SingleFile>> OpenNewWriteableFile();

  // Helper method for Write(): stores a file with metadata to match the
  // incoming new record. Synchronously composes metadata to record, then
  // asynchronously writes it into a file with next sequencing id and then
  // notifies the Write operation that it can now complete. After that it
  // asynchronously deletes all other files with lower sequencing id
  // (multiple Writes can see the same files and attempt to delete them, and
  // that is not an error).
  Status WriteMetadata();

  // Helper method for Init(): locates file with metadata that matches the
  // last sequencing id and loads metadata from it.
  // Adds used metadata file to the set.
  Status RestoreMetadata(base::flat_set<base::FilePath>* used_files_set);

  // Delete all files except those listed in the set.
  void DeleteUnusedFiles(
      const base::flat_set<base::FilePath>& used_files_setused_files_set);

  // Helper method for Write(): deletes meta files up to, but not including
  // |sequencing_id_to_keep|. Any errors are ignored.
  void DeleteOutdatedMetadata(int64_t sequencing_id_to_keep);

  // Helper method for Write(): composes record header and writes it to the
  // file, followed by data.
  Status WriteHeaderAndBlock(base::StringPiece data,
                             scoped_refptr<SingleFile> file);

  // Helper method for Upload: if the last file is not empty (has at least one
  // record), close it and create the new one, so that its records are also
  // included in the reading.
  Status SwitchLastFileIfNotEmpty();

  // Helper method for Upload: collects and sets aside |files| in the
  // StorageQueue that have data for the Upload (all files that have records
  // with sequencing ids equal or higher than |sequencing_id|).
  std::map<int64_t, scoped_refptr<SingleFile>> CollectFilesForUpload(
      int64_t sequencing_id) const;

  // Helper method for Confirm: Moves |first_sequencing_id_| to
  // (|sequencing_id|+1) and removes files that only have records with seq
  // ids below or equal to |sequencing_id| (below |first_sequencing_id_|).
  Status RemoveConfirmedData(int64_t sequencing_id);

  // Helper method to release all file instances held by the queue.
  // Files on the disk remain as they were.
  void ReleaseAllFileInstances();

  // Immutable options, stored at the time of creation.
  const QueueOptions options_;

  // Current generation id, unique per device and queue.
  // Set up once during initialization by reading from the 'gen_id.NNNN' file
  // matching the last sequencing id, or generated anew as a random number if no
  // such file found (files do not match the id).
  int64_t generation_id_ = 0;

  // Digest of the last written record (loaded at queue initialization, absent
  // if the new generation has just started, and no records where stored yet).
  base::Optional<std::string> last_record_digest_;

  // Queue of the write context instances in the order of creation, sequencing
  // ids and record digests. Context is always removed from this queue before
  // being destructed. We use std::list rather than std::queue, because
  // if the write fails, it needs to be removed from the queue regardless of
  // whether it is at the head, tail or middle.
  std::list<WriteContext*> write_contexts_queue_;

  // Next sequencing id to store (not assigned yet).
  int64_t next_sequencing_id_ = 0;

  // First sequencing id store still has (no records with lower
  // sequencing id exist in store).
  int64_t first_sequencing_id_ = 0;

  // First unconfirmed sequencing id (no records with lower
  // sequencing id will be ever uploaded). Set by the first
  // Confirm call.
  // If first_unconfirmed_sequencing_id_ < first_sequencing_id_,
  // [first_unconfirmed_sequencing_id_, first_sequencing_id_) is a gap
  // that cannot be filled in and is uploaded as such.
  base::Optional<int64_t> first_unconfirmed_sequencing_id_;

  // Latest metafile. May be null.
  scoped_refptr<SingleFile> meta_file_;

  // Ordered map of the files by ascending sequencing id.
  std::map<int64_t, scoped_refptr<SingleFile>> files_;

  // Counter of the Read operations. When not 0, none of the files_ can be
  // deleted. Incremented by |ReadContext::OnStart|, decremented by
  // |ReadContext::OnComplete|. Accessed by |RemoveConfirmedData|.
  // All accesses take place on sequenced_task_runner_.
  int32_t active_read_operations_ = 0;

  // Upload timer (active only if options_.upload_period() is not 0).
  base::RepeatingTimer upload_timer_;

  // Upload provider callback.
  const AsyncStartUploaderCb async_start_upload_cb_;

  // Encryption module.
  scoped_refptr<EncryptionModuleInterface> encryption_module_;

  // Test only: records specified to fail on reading.
  base::flat_set<int64_t> test_injected_fail_sequencing_ids_;

  // Sequential task runner for all activities in this StorageQueue.
  scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner_;

  SEQUENCE_CHECKER(storage_queue_sequence_checker_);
};

}  // namespace reporting

#endif  // MISSIVE_STORAGE_STORAGE_QUEUE_H_