// file      : build/lexer -*- C++ -*-
// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
// license   : MIT; see accompanying LICENSE file

#ifndef BUILD_LEXER
#define BUILD_LEXER

#include <stack>
#include <string>
#include <iosfwd>
#include <cstddef> // size_t
#include <cstdint> // uint64_t
#include <cassert>
#include <exception>

#include <butl/char-scanner>

#include <build/types>
#include <build/utility>

#include <build/token>
#include <build/diagnostics>

namespace build
{
  // Context-dependent lexing mode. In the value mode we don't treat
  // certain characters (e.g., +, =) as special so that we can use
  // them in the variable values, e.g., 'foo = g++'. In contrast, in
  // the variable mode, we restrict certain character (e.g., /) from
  // appearing in the name. The pairs mode is just like value except
  // that we split names separated by the pair character. The eval
  // mode is used in the evaluation context.
  //
  // The alternnative modes must be set manually. The value and pairs
  // modes are automatically reset after the end of the line. The
  // variable mode is reset after the name token. And the eval mode
  // is reset after the closing ')'.
  //
  // Quoted is an internal mode and should not be set explicitly.
  //
  enum class lexer_mode {normal, variable, value, pairs, eval, quoted};

  class lexer: protected butl::char_scanner
  {
  public:
    lexer (std::istream& is,
           const std::string& name,
           void (*processor) (token&, const lexer&) = nullptr)
        : char_scanner (is), fail (name), processor_ (processor), sep_ (false)
    {
      mode_.push (lexer_mode::normal);
    }

    const std::string&
    name () const {return fail.name_;}

    // Note: sets mode for the next token. If mode is pairs, then
    // the second argument specifies the separator character.
    //
    void
    mode (lexer_mode m, char pair_separator = '=')
    {
      mode_.push (m);
      pair_separator_ = pair_separator;
    }

    // Expire the current mode early.
    //
    void
    expire_mode () {mode_.pop ();}

    lexer_mode
    mode () const {return mode_.top ();}

    char
    pair_separator () const {return pair_separator_;}

    // Scanner.
    //
    token
    next ();

    // Peek at the first character of the next token. Return the character
    // or 0 if the next token will be eos. Also return an indicator of
    // whether the next token will be separated.
    //
    pair<char, bool>
    peek_char ();

  private:
    token
    next_impl ();

    token
    next_eval ();

    token
    next_quoted ();

    token
    name (bool separated);

    // Return true if we have seen any spaces. Skipped empty lines
    // don't count. In other words, we are only interested in spaces
    // that are on the same line as the following non-space character.
    //
    bool
    skip_spaces ();

    xchar
    escape ();

    // Diagnostics.
    //
  private:
    struct fail_mark_base: build::fail_mark_base<failed>
    {
      fail_mark_base (const std::string& n): name_ (n) {}

      location_prologue
      operator() (const xchar&) const;

      std::string name_;
    };
    typedef diag_mark<fail_mark_base> fail_mark;

  private:
    fail_mark fail;

    void (*processor_) (token&, const lexer&);

    std::stack<lexer_mode> mode_;
    char pair_separator_;
    bool sep_; // True if we skipped spaces in peek().
  };
}

#endif // BUILD_LEXER