// Copyright 2020 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef SRC_WRITER_TEXT_GENERATOR_H_
#define SRC_WRITER_TEXT_GENERATOR_H_

#include <sstream>
#include <string>
#include <utility>

#include "src/diagnostic/diagnostic.h"

namespace tint {
namespace writer {

/// Helper methods for generators which are creating text output
class TextGenerator {
 public:
  /// Constructor
  TextGenerator();
  ~TextGenerator();

  /// Increment the emitter indent level
  void increment_indent() { indent_ += 2; }
  /// Decrement the emiter indent level
  void decrement_indent() {
    if (indent_ < 2) {
      indent_ = 0;
      return;
    }
    indent_ -= 2;
  }

  /// Writes the current indent to the output stream
  void make_indent();

  /// Writes the current indent to `out`
  /// @param out the stream to write the indent to
  void make_indent(std::ostream& out) const;

  /// @returns the result data
  std::string result() const { return out_.str(); }

  /// @returns the list of diagnostics raised by the generator.
  const diag::List& Diagnostics() const { return diagnostics_; }

  /// @returns the error
  std::string error() const { return diagnostics_.str(); }

 protected:
  /// LineWriter is a helper that acts as a string buffer, who's content is
  /// emitted to the TextGenerator as a single line on destruction.
  struct LineWriter {
   public:
    /// Constructor
    /// @param generator the TextGenerator that the LineWriter will append its
    /// content to on destruction
    explicit LineWriter(TextGenerator* generator);
    /// Move constructor
    /// @param rhs the LineWriter to move
    LineWriter(LineWriter&& rhs);
    /// Destructor
    ~LineWriter();

    /// @returns the ostringstream
    operator std::ostream &() { return os; }

    /// @param rhs the value to write to the line
    /// @returns the ostream so calls can be chained
    template <typename T>
    std::ostream& operator<<(T&& rhs) {
      return os << std::forward<T>(rhs);
    }

   private:
    LineWriter(const LineWriter&) = delete;
    LineWriter& operator=(const LineWriter&) = delete;

    std::ostringstream os;
    TextGenerator* gen;
  };

  /// Helper for writing a '(' on construction and a ')' destruction.
  struct ScopedParen {
    /// Constructor
    /// @param stream the std::ostream that will be written to
    explicit ScopedParen(std::ostream& stream);
    /// Destructor
    ~ScopedParen();

   private:
    ScopedParen(ScopedParen&& rhs) = delete;
    ScopedParen(const ScopedParen&) = delete;
    ScopedParen& operator=(const ScopedParen&) = delete;
    std::ostream& s;
  };

  /// Helper for incrementing indentation on construction and decrementing
  /// indentation on destruction.
  struct ScopedIndent {
    /// Constructor
    /// @param generator the TextGenerator that the ScopedIndent will indent
    explicit ScopedIndent(TextGenerator* generator);
    /// Destructor
    ~ScopedIndent();

   private:
    ScopedIndent(ScopedIndent&& rhs) = delete;
    ScopedIndent(const ScopedIndent&) = delete;
    ScopedIndent& operator=(const ScopedIndent&) = delete;
    TextGenerator* gen;
  };

  /// @returns a new LineWriter, used for buffering and writing a line to out_
  LineWriter line() { return LineWriter(this); }

  /// The text output stream
  std::ostringstream out_;
  /// Diagnostics generated by the generator
  diag::List diagnostics_;

 private:
  size_t indent_ = 0;
};

}  // namespace writer
}  // namespace tint

#endif  // SRC_WRITER_TEXT_GENERATOR_H_