// Quick primitive expression evaluator
// Operation priorities:
// 0: ()
// 1: + - | ^
// 2: * / % &
// 3: unary+ unary- ~

// Expect to see a ')'
#define PAREN_EXPECT	1
// Eat the closing ')'
#define PAREN_EAT	2

static bool get_expression (const char **s, uint32 *v, int priority = 0, int flags = 0)
{
  uint32 b;
  char *x = get_token (s);

  if (!*x)
  {
    // Got empty token, could be a unary operator or a parenthesis
    switch (peek_char (s))
    {
      case '(':
        (*s)++;
        if (!get_expression (s, v, 0, PAREN_EAT | PAREN_EXPECT))
          return false;
        break;

      case '+':
        (*s)++;
        if (!get_expression (s, v, 3, flags & ~PAREN_EAT))
          return false;
        break;

      case '-':
        (*s)++;
        if (!get_expression (s, v, 3, flags & ~PAREN_EAT))
          return false;
        *v = (uint32)-(int32)*v;
        break;

      case '~':
        (*s)++;
        if (!get_expression (s, v, 3, flags & ~PAREN_EAT))
          return false;
        *v = ~*v;
        break;

      case 0:
      case ',':
        return false;

      default:
        Complain (C_ERROR ("line %d: Unexpected input '%hs'"), line, *s);
        return false;
    }
  }
  else
  {
    if (*x >= '0' && *x <= '9')
    {
      // We got a number
      char *err;
      *v = strtoul (x, &err, 0);
      if (*err)
      {
        Complain (C_ERROR ("line %d: Expected a number, got %hs"), line, x);
        return false;
      }
    }
    // Look through variables
    else if (!GetVar (x, s, v, ScriptVars, ScriptVarsCount)
          && !GetVar (x, s, v, UserVars, UserVarsCount))
    {
      Complain (C_ERROR ("line %d: Unknown variable '%hs' in expression"),
                line, x);
      return false;
    }
  }

  // Peek next char and see if it is a operator
  bool unk_op = false;
  while (!unk_op)
  {
    char op = peek_char (s);
    switch (op)
    {
      case '+':
      case '-':
      case '|':
      case '^':
        if (priority > 1)
          return true;
        (*s)++;
        if (!get_expression (s, &b, 1, flags & ~PAREN_EAT))
          return false;
        switch (op)
        {
          case '+': *v += b; break;
          case '-': *v -= b; break;
          case '|': *v |= b; break;
          case '^': *v ^= b; break;
        }
        break;

      case '*':
      case '/':
      case '%':
      case '&':
        if (priority > 2)
          return true;
        (*s)++;
        if (!get_expression (s, &b, 2, flags & ~PAREN_EAT))
          return false;
        switch (op)
        {
          case '*': *v *= b; break;
          case '/': *v /= b; break;
          case '%': *v %= b; break;
          case '&': *v &= b; break;
        }
        break;

      case ')':
        if (!(flags & PAREN_EXPECT))
        {
          Complain (C_ERROR ("line %d: Unexpected ')'"), line);
          return false;
        }
        if (flags & PAREN_EAT)
          (*s)++;
        return true;

      default:
        unk_op = true;
        break;
    }
  }

  if (flags & PAREN_EXPECT)
  {
    Complain (C_ERROR ("line %d: No closing ')'"), line);
    return false;
  }

  return true;
}