/*
 * 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 com.facebook.presto.rcfile.binary;

import com.facebook.presto.common.block.Block;
import com.facebook.presto.common.block.BlockBuilder;
import com.facebook.presto.common.type.Type;
import com.google.common.collect.ImmutableList;
import io.airlift.slice.Slice;
import io.airlift.slice.SliceOutput;

import java.util.List;

public class StructEncoding
        extends BlockEncoding
{
    private final List<BinaryColumnEncoding> structFields;

    public StructEncoding(Type type, List<BinaryColumnEncoding> structFields)
    {
        super(type);
        this.structFields = ImmutableList.copyOf(structFields);
    }

    @Override
    public void encodeValue(Block block, int position, SliceOutput output)
    {
        Block row = block.getBlock(position);

        // write values
        for (int batchStart = 0; batchStart < row.getPositionCount(); batchStart += 8) {
            int batchEnd = Math.min(batchStart + 8, structFields.size());

            int nullByte = 0;
            for (int fieldId = batchStart; fieldId < batchEnd; fieldId++) {
                if (!row.isNull(fieldId)) {
                    nullByte |= (1 << (fieldId % 8));
                }
            }
            output.writeByte(nullByte);
            for (int fieldId = batchStart; fieldId < batchEnd; fieldId++) {
                if (!row.isNull(fieldId)) {
                    BinaryColumnEncoding field = structFields.get(fieldId);
                    field.encodeValueInto(row, fieldId, output);
                }
            }
        }
    }

    @Override
    public void decodeValueInto(BlockBuilder builder, Slice slice, int offset, int length)
    {
        int fieldId = 0;
        int nullByte = 0;
        int elementOffset = offset;
        BlockBuilder rowBuilder = builder.beginBlockEntry();
        while (fieldId < structFields.size() && elementOffset < offset + length) {
            BinaryColumnEncoding field = structFields.get(fieldId);

            // null byte prefixes every 8 fields
            if ((fieldId % 8) == 0) {
                nullByte = slice.getByte(elementOffset);
                elementOffset++;
            }

            // read field
            if ((nullByte & (1 << (fieldId % 8))) != 0) {
                int valueOffset = field.getValueOffset(slice, elementOffset);
                int valueLength = field.getValueLength(slice, elementOffset);

                field.decodeValueInto(rowBuilder, slice, elementOffset + valueOffset, valueLength);

                elementOffset = elementOffset + valueOffset + valueLength;
            }
            else {
                rowBuilder.appendNull();
            }
            fieldId++;
        }

        // Some times a struct does not have all fields written
        // so we fill with nulls
        while (fieldId < structFields.size()) {
            rowBuilder.appendNull();
            fieldId++;
        }

        builder.closeEntry();
    }
}
