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/*
 * Copyright 2013, 2014 Deutsche Nationalbibliothek
 *
 * 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 org.metafacture.formeta.parser;

import org.metafacture.formeta.Formeta;
import org.metafacture.framework.FormatException;

/**
 * FSA (which additionally keeps track of its nesting level) for parsing records
 * and literals/entities on a structural level. The initial parser state is
 * {@code ITEM_NAME}. The parser has no final state
 * as the sequence of records or literals/entities is theoretically unlimited.
 */
enum StructureParserState {

    ITEM_NAME {
        protected StructureParserState delimiterReached(final char ch, final StructureParserContext ctx) {
            final StructureParserState newState;
            switch (ch) {
                case Formeta.GROUP_START:
                    ctx.startGroup();
                    newState = ITEM_NAME;
                    break;
                case Formeta.NAME_VALUE_SEPARATOR:
                    ctx.startLiteral();
                    newState =  LITERAL_VALUE;
                    break;
                case Formeta.ITEM_SEPARATOR:
                    if (!ctx.isTextEmpty()) {
                        throw new FormatException(getUnexpectedCharMsg(NAME_DELIMITER_EXPECTED, ch));
                    }
                    newState = ITEM_NAME;
                    break;
                case Formeta.GROUP_END:
                    if (!ctx.isTextEmpty() || !ctx.isNested()) {
                        throw new FormatException(getUnexpectedCharMsg(NAME_DELIMITER_EXPECTED, ch));
                    }
                    ctx.endGroup();
                    newState = ITEM_NAME;
                    break;
                default:
                    throw new FormatException(getUnexpectedCharMsg(NAME_DELIMITER_EXPECTED, ch));
            }
            return newState;
        }

        public void endOfInput(final StructureParserContext ctx) {
            ctx.processEOIWithTextParser();
            if (!ctx.isTextEmpty() || ctx.isNested()) {
                throw new FormatException(UNEXPECTED_EOI);
            }
        }
    },
    LITERAL_VALUE {
        protected StructureParserState delimiterReached(final char ch, final StructureParserContext ctx) {
            final StructureParserState newState;
            switch (ch) {
                case Formeta.ITEM_SEPARATOR:
                    ctx.endLiteral();
                    newState = ITEM_NAME;
                    break;
                case Formeta.GROUP_END:
                    if (!ctx.isNested()) {
                        throw new FormatException(getUnexpectedCharMsg(ITEM_SEPARATOR_EXPECTED, ch));
                    }
                    ctx.endLiteral();
                    ctx.endGroup();
                    newState = ITEM_NAME;
                    break;
                default:
                    throw new FormatException(getUnexpectedCharMsg(VALUE_DELIMITER_EXPECTED, ch));
            }
            return newState;
        }

        public void endOfInput(final StructureParserContext ctx) {
            ctx.processEOIWithTextParser();
            if (ctx.isNested()) {
                throw new FormatException(UNEXPECTED_EOI);
            }
            ctx.endLiteral();
        }
    };

    private static final String NAME_DELIMITER_EXPECTED = "'{' or ':'";
    private static final String ITEM_SEPARATOR_EXPECTED = "','";
    private static final String VALUE_DELIMITER_EXPECTED = "'}' or ','";
    private static final String UNEXPECTED_EOI = "Unexpected end of input";

    public StructureParserState processChar(final char ch, final StructureParserContext ctx) {
        if (ctx.processCharWithTextParser(ch)) {
            return delimiterReached(ch, ctx);
        }
        return this;
    }

    public abstract void endOfInput(StructureParserContext ctx);

    protected abstract StructureParserState delimiterReached(char ch, StructureParserContext ctx);

    private static String getUnexpectedCharMsg(final String expected, final char actual) {
        return expected + " expected but got '" + actual + "'";
    }

}