// file      : libbuild2/script/lexer.cxx -*- C++ -*-
// license   : MIT; see accompanying LICENSE file

#include <libbuild2/script/lexer.hxx>

#include <cstring> // strchr()

using namespace std;

namespace build2
{
  namespace script
  {
    using type = token_type;

    void lexer::
    mode (base_mode m, char ps, optional<const char*> esc)
    {
      bool a (false); // attributes

      const char* s1 (nullptr);
      const char* s2 (nullptr);

      bool s (true); // space
      bool n (true); // newline
      bool q (true); // quotes

      if (!esc)
      {
        assert (!state_.empty ());
        esc = state_.top ().escapes;
      }

      switch (m)
      {
      case lexer_mode::command_expansion:
        {
          // Note that whitespaces are not word separators in this mode.
          //
          s1 = "|&<>";
          s2 = "    ";
          s = false;
          break;
        }
      case lexer_mode::here_line_single:
        {
          // This one is like a single-quoted string except it treats
          // newlines as a separator. We also treat quotes as literals.
          //
          // Note that it might be tempting to enable line continuation
          // escapes. However, we will then have to also enable escaping of
          // the backslash, which makes it a lot less tempting.
          //
          s1 = "\n";
          s2 = " ";
          esc = ""; // Disable escape sequences.
          s = false;
          q = false;
          break;
        }
      case lexer_mode::here_line_double:
        {
          // This one is like a double-quoted string except it treats
          // newlines as a separator. We also treat quotes as literals.
          //
          s1 = "$(\n";
          s2 = "   ";
          s = false;
          q = false;
          break;
        }
      default:
        {
          // Make sure pair separators are only enabled where we expect
          // them.
          //
          // @@ Should we disable pair separators in the eval mode?
          //
          assert (ps == '\0' ||
                  m == lexer_mode::eval ||
                  m == lexer_mode::attribute_value);

          base_lexer::mode (m, ps, esc);
          return;
        }
      }

      assert (ps == '\0');
      state_.push (state {m, a, ps, s, n, q, *esc, s1, s2});
    }

    token lexer::
    next ()
    {
      token r;

      switch (state_.top ().mode)
      {
      case lexer_mode::command_expansion:
      case lexer_mode::here_line_single:
      case lexer_mode::here_line_double:
        r = next_line ();
        break;
      default:
        r = base_lexer::next ();
        break;
      }

      if (r.qtype != quote_type::unquoted)
        ++quoted_;

      return r;
    }

    token lexer::
    next_line ()
    {
      bool sep (skip_spaces ());

      xchar c (get ());
      uint64_t ln (c.line), cn (c.column);

      const state& st (state_.top ());
      lexer_mode m (st.mode);

      auto make_token = [&sep, &m, ln, cn] (type t)
      {
        bool q (m == lexer_mode::here_line_double);

        return token (t, string (), sep,
                      (q ? quote_type::double_ : quote_type::unquoted), q,
                      ln, cn,
                      token_printer);
      };

      if (eos (c))
        return make_token (type::eos);

      // NOTE: remember to update mode() if adding new special characters.

      if (m != lexer_mode::command_expansion)
      {
        switch (c)
        {
        case '\n':
          {
            sep = true; // Treat newline as always separated.
            return make_token (type::newline);
          }
        }
      }

      if (m != lexer_mode::here_line_single)
      {
        switch (c)
        {
          // Variable expansion, function call, and evaluation context.
          //
        case '$': return make_token (type::dollar);
        case '(': return make_token (type::lparen);
        }
      }

      // Command operators.
      //
      if (m == lexer_mode::command_expansion)
      {
        if (optional<token> t = next_cmd_op (c, sep, m))
          return move (*t);
      }

      // Otherwise it is a word.
      //
      unget (c);
      return word (st, sep);
    }

    optional<token> lexer::
    next_cmd_op (const xchar& c, bool sep, lexer_mode m)
    {
      auto make_token = [&sep, &m, &c] (type t, string v = string ())
      {
        bool q (m == lexer_mode::here_line_double);

        return token (t, move (v), sep,
                      (q ? quote_type::double_ : quote_type::unquoted), q,
                      c.line, c.column,
                      token_printer);
      };

      auto make_token_with_modifiers =
        [&make_token, this] (type t,
                             const char* mods,           // To recorgnize.
                             const char* stop = nullptr) // To stop after.
        {
          string v;
          if (mods != nullptr)
          {
            for (xchar p (peek ());
                 (strchr (mods, p) != nullptr &&      // Modifier.
                  strchr (v.c_str (), p) == nullptr); // Not already seen.
                 p = peek ())
            {
              get ();
              v += p;

              if (stop != nullptr && strchr (stop, p) != nullptr)
                break;
            }
          }

          return make_token (t, move (v));
        };

      switch (c)
      {
        // |, ||
        //
      case '|':
        {
          if (peek () == '|')
          {
            get ();
            return make_token (type::log_or);
          }
          else
            return make_token (type::pipe);
        }
        // &, &&
        //
      case '&':
        {
          xchar p (peek ());

          if (p == '&')
          {
            get ();
            return make_token (type::log_and);
          }

          // These modifiers are mutually exclusive so stop after seeing
          // either one.
          //
          return make_token_with_modifiers (type::clean, "!?", "!?");
        }
        // <
        //
      case '<':
        {
          type r (type::in_str);
          xchar p (peek ());

          if (p == '|' || p == '-' || p == '<')
          {
            get ();

            switch (p)
            {
            case '|': return make_token (type::in_pass);
            case '-': return make_token (type::in_null);
            case '<':
              {
                r = type::in_doc;
                p = peek ();

                if (p == '<')
                {
                  get ();
                  r = type::in_file;
                }
                break;
              }
            }
          }

          // Handle modifiers.
          //
          const char* mods (nullptr);
          switch (r)
          {
          case type::in_str:
          case type::in_doc: mods = ":/"; break;
          }

          return make_token_with_modifiers (r, mods);
        }
        // >
        //
      case '>':
        {
          type r (type::out_str);
          xchar p (peek ());

          if (p == '|' || p == '-' || p == '!' || p == '&' ||
              p == '=' || p == '+' || p == '>')
          {
            get ();

            switch (p)
            {
            case '|': return make_token (type::out_pass);
            case '-': return make_token (type::out_null);
            case '!': return make_token (type::out_trace);
            case '&': return make_token (type::out_merge);
            case '=': return make_token (type::out_file_ovr);
            case '+': return make_token (type::out_file_app);
            case '>':
              {
                r = type::out_doc;
                p = peek ();

                if (p == '>')
                {
                  get ();
                  r = type::out_file_cmp;
                }
                break;
              }
            }
          }

          // Handle modifiers.
          //
          const char* mods (nullptr);
          const char* stop (nullptr);
          switch (r)
          {
          case type::out_str:
          case type::out_doc: mods = ":/~"; stop = "~"; break;
          }

          return make_token_with_modifiers (r, mods, stop);
        }
      }

      return nullopt;
    }
  }
}