/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree.
 */

#pragma once

#include <cinttypes>
#include <vector>

#include <folly/Optional.h>

namespace facebook::glean::worklist {

struct Counter {
  struct Value {
    // index of current work item
    uint32_t start;
    // index of first work item not in current work block
    uint32_t end;

    uint32_t size() const {
      return start < end ? end - start : 0;
    }

    bool empty() const {
      return start >= end;
    }

    bool operator==(const Value& other) const {
      return start == other.start && end == other.end;
    }

    bool operator!=(const Value& other) const {
      return !(*this == other);
    }
  };

  /// Returns the next work item to process or none if we are done
  virtual folly::Optional<Value> next() = 0;

  virtual ~Counter() = default;
};

/// A Counter which simply returns all items in the range [index,end[ and
/// then stops.
std::unique_ptr<Counter> serialCounter(size_t index, size_t end);

/// A work-stealing Counter.
std::unique_ptr<Counter> stealingCounter(
    const std::string& path, // path a file initialised via stealingCounterSetup
    size_t worker_index, // index of current worker
    size_t worker_count // total number of workers
);

/// Setup a stealing counter file
void stealingCounterSetup(
    const std::string& path,
    const std::vector<Counter::Value>& values);

} // namespace facebook::glean::worklist