/*=============================================================================
 *
 *
 * XOD-specific list/array implementations
 *
 *
 =============================================================================*/

#ifndef XOD_LIST_H
#define XOD_LIST_H

namespace xod {
namespace detail {

/*
 * Cursors are used internaly by iterators and list views. They are not exposed
 * directly to a list consumer.
 *
 * The base `Cursor` is an interface which provides the bare minimum of methods
 * to facilitate a single iteration pass.
 */
template<typename T> class Cursor {
  public:
    virtual ~Cursor() { }
    virtual bool isValid() const = 0;
    virtual bool value(T* out) const = 0;
    virtual void next() = 0;
};

template<typename T> class NilCursor : public Cursor<T> {
  public:
    virtual bool isValid() const { return false; }
    virtual bool value(T*) const { return false; }
    virtual void next() { }
};

} // namespace detail

/*
 * Iterator is an object used to iterate a list once.
 *
 * Users create new iterators by calling `someList.iterate()`.
 * Iterators are created on stack and are supposed to have a
 * short live, e.g. for a duration of `for` loop or node’s
 * `evaluate` function. Iterators can’t be copied.
 *
 * Implemented as a pimpl pattern wrapper over the cursor.
 * Once created for a cursor, an iterator owns that cursor
 * and will delete the cursor object once destroyed itself.
 */
template<typename T>
class Iterator {
  public:
    static Iterator<T> nil() {
        return Iterator<T>(new detail::NilCursor<T>());
    }

    Iterator(detail::Cursor<T>* cursor)
        : _cursor(cursor)
    { }

    ~Iterator() {
        if (_cursor)
            delete _cursor;
    }

    Iterator(const Iterator& that) = delete;
    Iterator& operator=(const Iterator& that) = delete;

    Iterator(Iterator&& it)
        : _cursor(it._cursor)
    {
        it._cursor = nullptr;
    }

    Iterator& operator=(Iterator&& it) {
        auto tmp = it._cursor;
        it._cursor = _cursor;
        _cursor = tmp;
        return *this;
    }

    operator bool() const { return _cursor->isValid(); }

    bool value(T* out) const {
        return _cursor->value(out);
    }

    T operator*() const {
        T out;
        _cursor->value(&out);
        return out;
    }

    Iterator& operator++() {
        _cursor->next();
        return *this;
    }

  private:
    detail::Cursor<T>* _cursor;
};

/*
 * An interface for a list view. A particular list view provides a new
 * kind of iteration over existing data. This way we can use list slices,
 * list concatenations, list rotations, etc without introducing new data
 * buffers. We just change the way already existing data is iterated.
 *
 * ListView is not exposed to a list user directly, it is used internally
 * by the List class. However, deriving a new ListView is necessary if you
 * make a new list/string processing node.
 */
template<typename T> class ListView {
  public:
    virtual Iterator<T> iterate() const = 0;
};

/*
 * The list as it seen by data consumers. Have a single method `iterate`
 * to create a new iterator.
 *
 * Implemented as pimpl pattern wrapper over a list view. Takes pointer
 * to a list view in constructor and expects the view will be alive for
 * the whole life time of the list.
 */
template<typename T> class List {
  public:
    constexpr List()
        : _view(nullptr)
    { }

    List(const ListView<T>* view)
        : _view(view)
    { }

    Iterator<T> iterate() const {
        return _view ? _view->iterate() : Iterator<T>::nil();
    }

    // pre 0.15.0 backward compatibility
    List* operator->() __attribute__ ((deprecated)) { return this; }
    const List* operator->() const __attribute__ ((deprecated)) { return this; }

  private:
    const ListView<T>* _view;
};

/*
 * A list view over an old good plain C array.
 *
 * Expects the array will be alive for the whole life time of the
 * view.
 */
template<typename T> class PlainListView : public ListView<T> {
  public:
    class Cursor : public detail::Cursor<T> {
      public:
        Cursor(const PlainListView* owner)
            : _owner(owner)
            , _idx(0)
        { }

        bool isValid() const override {
            return _idx < _owner->_len;
        }

        bool value(T* out) const override {
            if (!isValid())
                return false;
            *out = _owner->_data[_idx];
            return true;
        }

        void next() override { ++_idx; }

      private:
        const PlainListView* _owner;
        size_t _idx;
    };

  public:
    PlainListView(const T* data, size_t len)
        : _data(data)
        , _len(len)
    { }

    virtual Iterator<T> iterate() const override {
        return Iterator<T>(new Cursor(this));
    }

  private:
    friend class Cursor;
    const T* _data;
    size_t _len;
};

/*
 * A list view over a null-terminated C-String.
 *
 * Expects the char buffer will be alive for the whole life time of the view.
 * You can use string literals as a buffer, since they are persistent for
 * the program execution time.
 */
class CStringView : public ListView<char> {
  public:
    class Cursor : public detail::Cursor<char> {
      public:
        Cursor(const char* str)
            : _ptr(str)
        { }

        bool isValid() const override {
            return (bool)*_ptr;
        }

        bool value(char* out) const override {
            *out = *_ptr;
            return (bool)*_ptr;
        }

        void next() override { ++_ptr; }

      private:
        const char* _ptr;
    };

  public:
    CStringView(const char* str = nullptr)
        : _str(str)
    { }

    CStringView& operator=(const CStringView& rhs) {
        _str = rhs._str;
        return *this;
    }

    virtual Iterator<char> iterate() const override {
        return _str ? Iterator<char>(new Cursor(_str)) : Iterator<char>::nil();
    }

  private:
    friend class Cursor;
    const char* _str;
};

/*
 * A list view over two other lists (Left and Right) which first iterates the
 * left one, and when exhausted, iterates the right one.
 *
 * Expects both Left and Right to be alive for the whole view life time.
 */
template<typename T> class ConcatListView : public ListView<T> {
  public:
    class Cursor : public detail::Cursor<T> {
      public:
        Cursor(Iterator<T>&& left, Iterator<T>&& right)
            : _left(std::move(left))
            , _right(std::move(right))
        { }

        bool isValid() const override {
            return _left || _right;
        }

        bool value(T* out) const override {
            return _left.value(out) || _right.value(out);
        }

        void next() override {
            _left ? ++_left : ++_right;
        }

      private:
        Iterator<T> _left;
        Iterator<T> _right;
    };

  public:
    ConcatListView() { }

    ConcatListView(List<T> left, List<T> right)
        : _left(left)
        , _right(right)
    { }

    ConcatListView& operator=(const ConcatListView& rhs) {
        _left = rhs._left;
        _right = rhs._right;
        return *this;
    }

    virtual Iterator<T> iterate() const override {
        return Iterator<T>(new Cursor(_left.iterate(), _right.iterate()));
    }

  private:
    friend class Cursor;
    List<T> _left;
    List<T> _right;
};

//----------------------------------------------------------------------------
// Text string helpers
//----------------------------------------------------------------------------

using XString = List<char>;

/*
 * List and list view in a single pack. An utility used to define constant
 * string literals in XOD.
 */
class XStringCString : public XString {
  public:
    XStringCString(const char* str)
        : XString(&_view)
        , _view(str)
    { }

  private:
    CStringView _view;
};

} // namespace xod

#endif