private static void DoFinal(ref RangeParserContext context)
{
if (!context.IsWhitespace)
{
context.Error("The range expression contains redundant content.");
}
}
private static void DoStart(ref RangeParserContext context)
{
switch (context.Character)
{
case '(':
context.Reset(State.Minimum, Flags.Parenthesis);
break;
case '*':
case '?':
context.Reset(State.MinimumFinal);
break;
case '~':
context.Reset(State.Separator);
break;
default:
if (!context.IsWhitespace)
{
context.Accept(State.Minimum);
}
break;
}
}
private static void DoMaximumFinal(ref RangeParserContext context)
{
switch (context.Character)
{
case ')':
context.Reset(State.Final);
break;
default:
if (!context.IsWhitespace)
{
context.Error($"The invalid character is at {context.Index + 1} character.");
}
break;
}
}
private static void DoSeparator(ref RangeParserContext context)
{
switch (context.Character)
{
case '*':
case '?':
context.Reset(State.MaximumFinal);
break;
default:
if (!context.IsWhitespace)
{
context.Accept(State.Maximum);
}
break;
}
}
private static void DoMaximum(ref RangeParserContext context, out ReadOnlySpan <char> value)
{
switch (context.Character)
{
case '*':
case '?':
context.Reset(State.MaximumFinal, out value);
break;
case ')':
context.Reset(State.Final, out value);
break;
default:
context.Accept(State.Maximum);
value = ReadOnlySpan <char> .Empty;
break;
}
}
public static RangeParserResult Parse <T>(ReadOnlySpan <char> span, int start = 0) where T : struct
{
var minimum = ReadOnlySpan <char> .Empty;
var maximum = ReadOnlySpan <char> .Empty;
var context = new RangeParserContext(span);
for (int i = start; i < span.Length; i++)
{
context.Move(i);
switch (context.State)
{
case State.Error:
return(new RangeParserResult(context.ErrorMessage));
case State.Start:
DoStart(ref context);
break;
case State.Final:
DoFinal(ref context);
break;
case State.Minimum:
DoMinimum(ref context, out minimum);
break;
case State.MinimumFinal:
DoMinimunFinal(ref context);
break;
case State.Maximum:
DoMaximum(ref context, out maximum);
break;
case State.MaximumFinal:
DoMaximumFinal(ref context);
break;
case State.Separator:
DoSeparator(ref context);
break;
}
}
if (context.State != State.Final)
{
//未正常关闭圆括号
if (context.HasFlags(Flags.Parenthesis))
{
return(new RangeParserResult("Missing the closing parenthesis."));
}
//必须移动指针到最后，以便Reset正确计算内容值
context.Move(-1);
switch (context.State)
{
case State.Minimum:
case State.MinimumFinal:
case State.Separator:
context.Reset(out minimum);
break;
default:
context.Reset(out maximum);
break;
}
}
if (maximum.IsEmpty && (context.State == State.Minimum || context.State == State.MinimumFinal))
{
maximum = minimum;
}
return(new RangeParserResult(minimum, maximum));
}
