//===--- StringExtras.h - String Utilities ----------------------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file provides utilities for working with English words and
// camelCase names.
//
//===----------------------------------------------------------------------===//
#ifndef SWIFT_BASIC_STRINGEXTRAS_HPP
#define SWIFT_BASIC_STRINGEXTRAS_HPP

#include "swift/Basic/LLVM.h"
#include "llvm/ADT/StringRef.h"
#include <iterator>

namespace swift {
  /// Describes the kind of preposition a word is.
  enum PrepositionKind {
    PK_None = 0,
    PK_Directional,
    PK_Nondirectional
  };

  /// Determine what kind of preposition the given word is, if any,
  /// ignoring case.
  PrepositionKind getPrepositionKind(StringRef word);

  namespace camel_case {
    class WordIterator;

    /// A bidirectional iterator that walks through the words in a camelCase
    /// string.
    ///
    /// Note that this iterator is not technically conforming bidirectional 
    /// iterator, because it's reference type is not a true reference. But it 
    /// quacks like a duck.
    class WordIterator {
      StringRef String;
      unsigned Position;
      mutable unsigned NextPosition : 31;
      mutable unsigned NextPositionValid : 1;
      mutable unsigned PrevPosition : 31;
      mutable unsigned PrevPositionValid : 1;

      void computeNextPosition() const;
      void computePrevPosition() const;

      /// Proxy used for the arrow operator of the word iterator.
      class ArrowProxy {
        StringRef String;

      public:
        explicit ArrowProxy(StringRef string) : String(string) { }

        const StringRef *operator->() const {
          return &String;
        }
      };

    public:
      typedef StringRef value_type;
      typedef StringRef reference;
      typedef ArrowProxy pointer;
      typedef int difference_type;
      typedef std::bidirectional_iterator_tag iterator_category;

      WordIterator(StringRef string, unsigned position)
        : String(string), Position(position) 
      {
        NextPositionValid = false;
        PrevPositionValid = false;
      }

      StringRef operator*() const {
        if (!NextPositionValid)
          computeNextPosition();

        return String.slice(Position, NextPosition);
      }

      ArrowProxy operator->() const {
        return ArrowProxy(**this);
      }

      WordIterator &operator++() {
        if (!NextPositionValid)
          computeNextPosition();

        // Save the previous position.
        PrevPosition = Position;
        PrevPositionValid = true;

        // Move to the next position.
        Position = NextPosition;
        
        // We don't know what lies ahead.
        NextPositionValid = false;
        return *this;
      }

      WordIterator operator++(int) {
        WordIterator tmp(*this);
        ++(*this);
        return tmp;
      }

      WordIterator &operator--() {
        if (!PrevPositionValid)
          computePrevPosition();

        // Save the next position.
        NextPosition = Position;
        NextPositionValid = true;

        // Move to the previous position.
        Position = PrevPosition;

        // We don't know what lies behind.
        PrevPositionValid = false;

        return *this;
      }

      WordIterator operator--(int) {
        WordIterator tmp(*this);
        --(*this);
        return tmp;
      }

      friend bool operator==(const WordIterator &x, const WordIterator &y) {
        assert(x.String.data() == y.String.data() && 
               x.String.size() == y.String.size() &&
               "comparing word iterators from different strings");
        return x.Position == y.Position;
      }

      friend bool operator!=(const WordIterator &x, const WordIterator &y) {
        return !(x == y);
      }
    };

    /// Find the first camelCase word in the given string.
    StringRef getFirstWord(StringRef string);

    /// Find the last camelCase word in the given string.
    StringRef getLastWord(StringRef string);

    /// A wrapper that treats a string as a container of camelCase words.
    class Words {
      StringRef String;

    public:
      typedef WordIterator iterator;
      typedef WordIterator const_iterator;
      typedef std::reverse_iterator<WordIterator> reverse_iterator;
      typedef std::reverse_iterator<WordIterator> const_reverse_iterator;
      
      explicit Words(StringRef string) : String(string) { }

      bool empty() const { return String.empty(); }

      iterator begin() const { return WordIterator(String, 0); }
      iterator end() const { return WordIterator(String, String.size()); }

      reverse_iterator rbegin() const { return reverse_iterator(end()); }
      reverse_iterator rend() const { return reverse_iterator(begin()); }
    };

    /// Retrieve the camelCase words in the given string.
    inline Words getWords(StringRef string) { return Words(string); }

    /// Find the last preposition in the given camelCase string.
    ///
    /// \returns a pair containing the starting index of the last
    /// preposition as well as the kind of preposition found.
    std::pair<unsigned, PrepositionKind> findLastPreposition(StringRef string);
  } // end namespace camel_case
}

#endif // LLVM_SWIFT_BASIC_STRINGEXTRAS_HPP