private static RTree ParseSingleSubtree(RevgexStringReader inp, GroupSet groups)
{
var buffer = "";
while (true)
{
switch (inp.Peek())
{
case -1:
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: REmpty.Instance);
case '(':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: ParseAnyGroup(inp, groups));
case ')':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: throw Error(inp, "Unexpected right parenthesis."));
case '*':
case '+':
case '{':
case '?':
if (buffer.Length > 0)
{
if (buffer.Length == 1)
{
return(new RFixedString(buffer, LookupQuantifier(inp)));
}
inp.UnreadEscaped();
return(new RFixedString(buffer.Substring(0, buffer.Length - 1), LookupQuantifier(inp)));
}
throw Error(inp, $"Unexpected character {inp.Peek()}.");
case '\\':
if (TryParseSimpleEscapeSequence(inp, out var ch))
{
buffer += ch;
continue;
}
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: ParseEscapeSequence(inp, groups));
case '$':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: ParseValueReference(inp, groups));
case '.':
if (buffer.Length > 0)
{
return(new RFixedString(buffer, QuantifierOne.Instance));
}
else
{
inp.Read();
return(RChar.Dot(LookupQuantifier(inp)));
}
case '[':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: ParseCharSet(inp));
case '|':
return(buffer.Length > 0
? new RFixedString(buffer, QuantifierOne.Instance)
: REmpty.Instance);
default:
buffer += inp.Read();
continue;
}
}
}
private static RTree ParseEscapeSequence(RevgexStringReader inp, GroupSet groups)
{
inp.Read(); // '\'
var c = inp.Peek();
if (c >= '0' && c <= '9')
{
var groupId = inp.Read() - '0';
c = inp.Peek();
if (c >= '0' && c <= '9')
{
groupId = groupId * 10 + (inp.Read() - '0');
}
if (groupId == 0)
{
throw Error(inp, "Backreference to the entire patternt (zero-th group) is not allowed.");
}
if (groups.Get(groupId) == null)
{
throw Error(inp, "Invalid group backreference.");
}
return(new RGroupRef(groupId, LookupQuantifier(inp)));
}
switch (c)
{
case -1:
throw Error(inp, "Incomplete escape sequence.");
case ':':
var groupName = ParseGroupName(inp);
if (groups.Get(groupName) == null)
{
throw Error(inp, "Invalid named group backreference.");
}
return(new RNamedGroupRef(groupName, LookupQuantifier(inp)));
case '(':
inp.Read();
var groupId = 0;
c = inp.Peek();
do
{
if (c < '0' || c > '9')
{
throw Error(inp, "Invalid group backreference.");
}
groupId = groupId * 10 + (inp.Read() - '0');
} while ((c = inp.Peek()) != ')');
inp.Read(); // ')'
if (groups.Get(groupId) == null)
{
throw Error(inp, "Invalid group backreference.");
}
return(new RGroupRef(groupId, LookupQuantifier(inp)));
case 'w':
inp.Read();
return(RChar.w(LookupQuantifier(inp)));
case 'W':
inp.Read();
return(RChar.W(LookupQuantifier(inp)));
case 's':
inp.Read();
return(RChar.s(LookupQuantifier(inp)));
case 'S':
inp.Read();
return(RChar.S(LookupQuantifier(inp)));
case 'd':
inp.Read();
return(RChar.d(LookupQuantifier(inp)));
case 'D':
inp.Read();
return(RChar.D(LookupQuantifier(inp)));
default:
return(new RFixedString(inp.Read().ToString(), LookupQuantifier(inp)));
}
}