//
// Copyright 2013 Mike Friesen
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
package ca.gobits.bnf.parser;
import java.util.Map;
import ca.gobits.bnf.parser.states.BNFState;
import ca.gobits.bnf.parser.states.BNFStateEmpty;
import ca.gobits.bnf.tokenizer.BNFToken;
public class BNFParserImpl implements BNFParser {
private Map<String, BNFStateDefinition> stateDefinitions;
private BNFStack stack = new BNFStack();
public BNFParserImpl(Map<String, BNFStateDefinition> stateDefinitions) {
this.stateDefinitions = stateDefinitions;
}
@Override
public BNFParseResult parse(BNFToken token) {
stack.clear();
BNFParseResultImpl result = new BNFParseResultImpl();
result.setTop(token);
result.setMaxMatchToken(token);
BNFStateDefinition sd = stateDefinitions.get("@start");
pushToStackOrFirstState(token, sd);
while (!stack.isEmpty()) {
BNFPath sp = stack.peek();
if (sp.isStateEnd()) {
sp = stack.pop();
if (isEmpty(sp.getToken())) {
break;
}
} else if (sp.getToken() == null) {
stack.rewindToNextTokenAndNextSequence();
} else if (sp.isStateDefinition()) {
boolean added = parseStateDefinition(sp.getToken());
if (!added) {
break;
}
} else {
parseState(result);
}
}
result.complete();
return result;
}
private boolean isEmpty(BNFToken token) {
return token == null || token.getStringValue() == null || token.getStringValue().trim().length() == 0;
}
private boolean parseStateDefinition(BNFToken token) {
boolean success = false;
BNFPathStateDefinition sd = (BNFPathStateDefinition) stack.peek();
BNFState state = sd.getNextSequence();
if (state != null) {
success = true;
pushToStack(state, token);
}
return success;
}
private void pushToStack(BNFState state, BNFToken token) {
if (state != null) {
BNFPathState path = new BNFPathState(state, token);
stack.push(path);
}
}
private void pushToStack(BNFToken token, BNFStateDefinition sd) {
BNFPathStateDefinition path = new BNFPathStateDefinition();
path.setToken(token);
path.setStateDefinition(sd);
stack.push(path);
}
private void pushToStackOrFirstState(BNFToken token, BNFStateDefinition sd) {
if (sd.hasSequences()) {
pushToStack(token, sd);
} else {
pushToStack(sd.getFirstState(), token);
}
}
private void parseState(BNFParseResultImpl result) {
BNFPathState sp = (BNFPathState) stack.peek();
BNFState state = sp.getState();
BNFToken token = sp.getToken();
if (!state.isTerminal()) {
BNFStateDefinition sd = stateDefinitions.get(state.getName());
if (sd == null) {
throw new RuntimeException("unknown state " + state.getName());
}
pushToStackOrFirstState(token, sd);
} else if (state.getClass().equals(BNFStateEmpty.class)) {
if (isEmpty(token)) {
result.setSuccess(true);
}
BNFState rewindState = stack.rewindStackEmptyState();
pushToStack(rewindState, token);
} else if (state.match(token)) {
result.setSuccess(true);
token = token.getNextToken();
result.setMaxMatchToken(token);
BNFState rewindState = stack.rewindStackMatchedToken();
pushToStack(rewindState, token);
} else {
result.setSuccess(false);
BNFState nextState = stack.rewindStackUnmatchedToken();
pushToStack(nextState, token);
}
}
}