#pragma once

#include "graph.hpp"

/**
@file task.hpp
@brief task include file
*/

namespace tf {

// ----------------------------------------------------------------------------
// Task Types
// ----------------------------------------------------------------------------

/**
@enum TaskType

@brief enumeration of all task types
*/
enum class TaskType : int {
  /** @brief placeholder task type */
  PLACEHOLDER = 0,
  /** @brief static task type */
  STATIC,
  /** @brief dynamic (subflow) task type */
  SUBFLOW,
  /** @brief condition task type */
  CONDITION,
  /** @brief module task type */
  MODULE,
  /** @brief asynchronous task type */
  ASYNC,
  /** @brief undefined task type (for internal use only) */
  UNDEFINED
};

/**
@private
@brief array of all task types (used for iterating task types)
*/
inline constexpr std::array<TaskType, 6> TASK_TYPES = {
  TaskType::PLACEHOLDER,
  TaskType::STATIC,
  TaskType::SUBFLOW,
  TaskType::CONDITION,
  TaskType::MODULE,
  TaskType::ASYNC,
};

/**
@brief convert a task type to a human-readable string

The name of each task type is the litte-case string of its characters.

@code{.cpp}
TaskType::PLACEHOLDER     ->  "placeholder"
TaskType::STATIC          ->  "static"
TaskType::SUBFLOW         ->  "subflow"
TaskType::CONDITION       ->  "condition"
TaskType::MODULE          ->  "module"
TaskType::ASYNC           ->  "async"
@endcode
*/
inline const char* to_string(TaskType type) {

  const char* val;

  switch(type) {
    case TaskType::PLACEHOLDER:      val = "placeholder";     break;
    case TaskType::STATIC:           val = "static";          break;
    case TaskType::SUBFLOW:          val = "subflow";         break;
    case TaskType::CONDITION:        val = "condition";       break;
    case TaskType::MODULE:           val = "module";          break;
    case TaskType::ASYNC:            val = "async";           break;
    default:                         val = "undefined";       break;
  }

  return val;
}

// ----------------------------------------------------------------------------
// Task Traits
// ----------------------------------------------------------------------------

/**
@brief determines if a callable is a dynamic task

A dynamic task is a callable object constructible from std::function<void(Subflow&)>.
*/
template <typename C>
constexpr bool is_subflow_task_v = 
  std::is_invocable_r_v<void, C, Subflow&> &&
  !std::is_invocable_r_v<void, C, Runtime&>;

/**
@brief determines if a callable is a condition task

A condition task is a callable object constructible from std::function<int()>
or std::function<int(tf::Runtime&)>.
*/
template <typename C>
constexpr bool is_condition_task_v = 
  (std::is_invocable_r_v<int, C> || std::is_invocable_r_v<int, C, Runtime&>) &&
  !is_subflow_task_v<C>;

/**
@brief determines if a callable is a multi-condition task

A multi-condition task is a callable object constructible from
std::function<tf::SmallVector<int>()> or
std::function<tf::SmallVector<int>(tf::Runtime&)>.
*/
template <typename C>
constexpr bool is_multi_condition_task_v =
  (std::is_invocable_r_v<SmallVector<int>, C> ||
  std::is_invocable_r_v<SmallVector<int>, C, Runtime&>) &&
  !is_subflow_task_v<C>;

/**
@brief determines if a callable is a static task

A static task is a callable object constructible from std::function<void()>
or std::function<void(tf::Runtime&)>.
*/
template <typename C>
constexpr bool is_static_task_v =
  (std::is_invocable_r_v<void, C> || std::is_invocable_r_v<void, C, Runtime&>) &&
  !is_condition_task_v<C> &&
  !is_multi_condition_task_v<C> &&
  !is_subflow_task_v<C>;

// ----------------------------------------------------------------------------
// Task
// ----------------------------------------------------------------------------

/**
@class Task

@brief class to create a task handle over a node in a taskflow graph

A task is a wrapper over a node in a taskflow graph.
It provides a set of methods for users to access and modify the attributes of
the associated node in the taskflow graph.
A task is very lightweight object (i.e., only storing a node pointer) that
can be trivially copied around,
and it does not own the lifetime of the associated node.
*/
class Task {

  friend class FlowBuilder;
  friend class Runtime;
  friend class Taskflow;
  friend class TaskView;
  friend class Executor;

  public:

    /**
    @brief constructs an empty task
    */
    Task() = default;

    /**
    @brief constructs the task with the copy of the other task
    */
    Task(const Task& other);

    /**
    @brief replaces the contents with a copy of the other task
    */
    Task& operator = (const Task&);

    /**
    @brief replaces the contents with a null pointer
    */
    Task& operator = (std::nullptr_t);

    /**
    @brief compares if two tasks are associated with the same graph node
    */
    bool operator == (const Task& rhs) const;

    /**
    @brief compares if two tasks are not associated with the same graph node
    */
    bool operator != (const Task& rhs) const;

    /**
    @brief queries the name of the task
    */
    const std::string& name() const;

    /**
    @brief queries the number of successors of the task
    */
    size_t num_successors() const;

    /**
    @brief queries the number of predecessors of the task
    */
    size_t num_dependents() const;

    /**
    @brief queries the number of strong dependents of the task
    */
    size_t num_strong_dependents() const;

    /**
    @brief queries the number of weak dependents of the task
    */
    size_t num_weak_dependents() const;

    /**
    @brief assigns a name to the task

    @param name a @std_string acceptable string

    @return @c *this
    */
    Task& name(const std::string& name);

    /**
    @brief assigns a callable

    @tparam C callable type

    @param callable callable to construct a task

    @return @c *this
    */
    template <typename C>
    Task& work(C&& callable);

    /**
    @brief creates a module task from a taskflow

    @tparam T object type
    @param object a custom object that defines @c T::graph() method

    @return @c *this
    */
    template <typename T>
    Task& composed_of(T& object);

    /**
    @brief adds precedence links from this to other tasks

    @tparam Ts parameter pack

    @param tasks one or multiple tasks

    @return @c *this
    */
    template <typename... Ts>
    Task& precede(Ts&&... tasks);

    /**
    @brief adds precedence links from other tasks to this

    @tparam Ts parameter pack

    @param tasks one or multiple tasks

    @return @c *this
    */
    template <typename... Ts>
    Task& succeed(Ts&&... tasks);

    /**
    @brief assigns pointer to user data

    @param data pointer to user data

    The following example shows how to attach user data to a task and
    run the task iteratively while changing the data value:

    @code{.cpp}
    tf::Executor executor;
    tf::Taskflow taskflow("attach data to a task");

    int data;

    // create a task and attach it the data
    auto A = taskflow.placeholder();
    A.data(&data).work([A](){
      auto d = *static_cast<int*>(A.data());
      std::cout << "data is " << d << std::endl;
    });

    // run the taskflow iteratively with changing data
    for(data = 0; data<10; data++){
      executor.run(taskflow).wait();
    }
    @endcode

    @return @c *this
    */
    Task& data(void* data);
    
    /**
    @brief resets the task handle to null
    */
    void reset();

    /**
    @brief resets the associated work to a placeholder
    */
    void reset_work();

    /**
    @brief queries if the task handle points to a task node
    */
    bool empty() const;

    /**
    @brief queries if the task has a work assigned
    */
    bool has_work() const;

    /**
    @brief applies an visitor callable to each successor of the task
    */
    template <typename V>
    void for_each_successor(V&& visitor) const;

    /**
    @brief applies an visitor callable to each dependents of the task
    */
    template <typename V>
    void for_each_dependent(V&& visitor) const;

    /**
    @brief obtains a hash value of the underlying node
    */
    size_t hash_value() const;

    /**
    @brief returns the task type
    */
    TaskType type() const;

    /**
    @brief dumps the task through an output stream
    */
    void dump(std::ostream& ostream) const;

    /**
    @brief queries pointer to user data
    */
    void* data() const;


  private:

    Task(Node*);

    Node* _node {nullptr};
};

// Constructor
inline Task::Task(Node* node) : _node {node} {
}

// Constructor
inline Task::Task(const Task& rhs) : _node {rhs._node} {
}

// Function: precede
template <typename... Ts>
Task& Task::precede(Ts&&... tasks) {
  (_node->_precede(tasks._node), ...);
  //_precede(std::forward<Ts>(tasks)...);
  return *this;
}

// Function: succeed
template <typename... Ts>
Task& Task::succeed(Ts&&... tasks) {
  (tasks._node->_precede(_node), ...);
  //_succeed(std::forward<Ts>(tasks)...);
  return *this;
}

// Function: composed_of
template <typename T>
Task& Task::composed_of(T& object) {
  _node->_handle.emplace<Node::Module>(object);
  return *this;
}

// Operator =
inline Task& Task::operator = (const Task& rhs) {
  _node = rhs._node;
  return *this;
}

// Operator =
inline Task& Task::operator = (std::nullptr_t ptr) {
  _node = ptr;
  return *this;
}

// Operator ==
inline bool Task::operator == (const Task& rhs) const {
  return _node == rhs._node;
}

// Operator !=
inline bool Task::operator != (const Task& rhs) const {
  return _node != rhs._node;
}

// Function: name
inline Task& Task::name(const std::string& name) {
  _node->_name = name;
  return *this;
}

// Procedure: reset
inline void Task::reset() {
  _node = nullptr;
}

// Procedure: reset_work
inline void Task::reset_work() {
  _node->_handle.emplace<std::monostate>();
}

// Function: name
inline const std::string& Task::name() const {
  return _node->_name;
}

// Function: num_dependents
inline size_t Task::num_dependents() const {
  return _node->num_dependents();
}

// Function: num_strong_dependents
inline size_t Task::num_strong_dependents() const {
  return _node->num_strong_dependents();
}

// Function: num_weak_dependents
inline size_t Task::num_weak_dependents() const {
  return _node->num_weak_dependents();
}

// Function: num_successors
inline size_t Task::num_successors() const {
  return _node->num_successors();
}

// Function: empty
inline bool Task::empty() const {
  return _node == nullptr;
}

// Function: has_work
inline bool Task::has_work() const {
  return _node ? _node->_handle.index() != 0 : false;
}

// Function: task_type
inline TaskType Task::type() const {
  switch(_node->_handle.index()) {
    case Node::PLACEHOLDER:     return TaskType::PLACEHOLDER;
    case Node::STATIC:          return TaskType::STATIC;
    case Node::SUBFLOW:         return TaskType::SUBFLOW;
    case Node::CONDITION:       return TaskType::CONDITION;
    case Node::MULTI_CONDITION: return TaskType::CONDITION;
    case Node::MODULE:          return TaskType::MODULE;
    case Node::ASYNC:           return TaskType::ASYNC;
    case Node::DEPENDENT_ASYNC: return TaskType::ASYNC;
    default:                    return TaskType::UNDEFINED;
  }
}

// Function: for_each_successor
template <typename V>
void Task::for_each_successor(V&& visitor) const {
  for(size_t i=0; i<_node->_successors.size(); ++i) {
    visitor(Task(_node->_successors[i]));
  }
}

// Function: for_each_dependent
template <typename V>
void Task::for_each_dependent(V&& visitor) const {
  for(size_t i=0; i<_node->_dependents.size(); ++i) {
    visitor(Task(_node->_dependents[i]));
  }
}

// Function: hash_value
inline size_t Task::hash_value() const {
  return std::hash<Node*>{}(_node);
}

// Procedure: dump
inline void Task::dump(std::ostream& os) const {
  os << "task ";
  if(name().empty()) os << _node;
  else os << name();
  os << " [type=" << to_string(type()) << ']';
}

// Function: work
template <typename C>
Task& Task::work(C&& c) {

  if constexpr(is_static_task_v<C>) {
    _node->_handle.emplace<Node::Static>(std::forward<C>(c));
  }
  else if constexpr(is_subflow_task_v<C>) {
    _node->_handle.emplace<Node::Subflow>(std::forward<C>(c));
  }
  else if constexpr(is_condition_task_v<C>) {
    _node->_handle.emplace<Node::Condition>(std::forward<C>(c));
  }
  else if constexpr(is_multi_condition_task_v<C>) {
    _node->_handle.emplace<Node::MultiCondition>(std::forward<C>(c));
  }
  else {
    static_assert(dependent_false_v<C>, "invalid task callable");
  }
  return *this;
}

// Function: data
inline void* Task::data() const {
  return _node->_data;
}

// Function: data
inline Task& Task::data(void* data) {
  _node->_data = data;
  return *this;
}

// ----------------------------------------------------------------------------
// global ostream
// ----------------------------------------------------------------------------

/**
@brief overload of ostream inserter operator for Task
*/
inline std::ostream& operator << (std::ostream& os, const Task& task) {
  task.dump(os);
  return os;
}

// ----------------------------------------------------------------------------
// Task View
// ----------------------------------------------------------------------------

/**
@class TaskView

@brief class to access task information from the observer interface
*/
class TaskView {

  friend class Executor;

  public:

    /**
    @brief queries the name of the task
    */
    const std::string& name() const;

    /**
    @brief queries the number of successors of the task
    */
    size_t num_successors() const;

    /**
    @brief queries the number of predecessors of the task
    */
    size_t num_dependents() const;

    /**
    @brief queries the number of strong dependents of the task
    */
    size_t num_strong_dependents() const;

    /**
    @brief queries the number of weak dependents of the task
    */
    size_t num_weak_dependents() const;

    /**
    @brief applies an visitor callable to each successor of the task
    */
    template <typename V>
    void for_each_successor(V&& visitor) const;

    /**
    @brief applies an visitor callable to each dependents of the task
    */
    template <typename V>
    void for_each_dependent(V&& visitor) const;

    /**
    @brief queries the task type
    */
    TaskType type() const;

    /**
    @brief obtains a hash value of the underlying node
    */
    size_t hash_value() const;

  private:

    TaskView(const Node&);
    TaskView(const TaskView&) = default;

    const Node& _node;
};

// Constructor
inline TaskView::TaskView(const Node& node) : _node {node} {
}

// Function: name
inline const std::string& TaskView::name() const {
  return _node._name;
}

// Function: num_dependents
inline size_t TaskView::num_dependents() const {
  return _node.num_dependents();
}

// Function: num_strong_dependents
inline size_t TaskView::num_strong_dependents() const {
  return _node.num_strong_dependents();
}

// Function: num_weak_dependents
inline size_t TaskView::num_weak_dependents() const {
  return _node.num_weak_dependents();
}

// Function: num_successors
inline size_t TaskView::num_successors() const {
  return _node.num_successors();
}

// Function: type
inline TaskType TaskView::type() const {
  switch(_node._handle.index()) {
    case Node::PLACEHOLDER:     return TaskType::PLACEHOLDER;
    case Node::STATIC:          return TaskType::STATIC;
    case Node::SUBFLOW:         return TaskType::SUBFLOW;
    case Node::CONDITION:       return TaskType::CONDITION;
    case Node::MULTI_CONDITION: return TaskType::CONDITION;
    case Node::MODULE:          return TaskType::MODULE;
    case Node::ASYNC:           return TaskType::ASYNC;
    case Node::DEPENDENT_ASYNC: return TaskType::ASYNC;
    default:                    return TaskType::UNDEFINED;
  }
}

// Function: hash_value
inline size_t TaskView::hash_value() const {
  return std::hash<const Node*>{}(&_node);
}

// Function: for_each_successor
template <typename V>
void TaskView::for_each_successor(V&& visitor) const {
  for(size_t i=0; i<_node._successors.size(); ++i) {
    visitor(TaskView(*_node._successors[i]));
  }
}

// Function: for_each_dependent
template <typename V>
void TaskView::for_each_dependent(V&& visitor) const {
  for(size_t i=0; i<_node._dependents.size(); ++i) {
    visitor(TaskView(*_node._dependents[i]));
  }
}

}  // end of namespace tf. ----------------------------------------------------

namespace std {

/**
@struct hash

@brief hash specialization for std::hash<tf::Task>
*/
template <>
struct hash<tf::Task> {
  auto operator() (const tf::Task& task) const noexcept {
    return task.hash_value();
  }
};

/**
@struct hash

@brief hash specialization for std::hash<tf::TaskView>
*/
template <>
struct hash<tf::TaskView> {
  auto operator() (const tf::TaskView& task_view) const noexcept {
    return task_view.hash_value();
  }
};

}  // end of namespace std ----------------------------------------------------