/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.hcatalog.mapreduce;

import java.io.IOException;
import java.util.Map;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hive.serde2.Deserializer;
import org.apache.hadoop.hive.serde2.SerDeException;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.hcatalog.common.HCatConstants;
import org.apache.hcatalog.common.HCatUtil;
import org.apache.hcatalog.data.DefaultHCatRecord;
import org.apache.hcatalog.data.HCatRecord;
import org.apache.hcatalog.data.LazyHCatRecord;
import org.apache.hcatalog.data.schema.HCatSchema;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/** The HCat wrapper for the underlying RecordReader,
 * this ensures that the initialize on
 * the underlying record reader is done with the underlying split,
 * not with HCatSplit.
 */
class HCatRecordReader extends RecordReader<WritableComparable, HCatRecord> {

    private static final Logger LOG = LoggerFactory.getLogger(HCatRecordReader.class);

    private InputErrorTracker errorTracker;

    WritableComparable currentKey;
    Writable currentValue;
    HCatRecord currentHCatRecord;

    /** The underlying record reader to delegate to. */
    private org.apache.hadoop.mapred.RecordReader<WritableComparable, Writable> baseRecordReader;

    /** The storage handler used */
    private final HCatStorageHandler storageHandler;

    private Deserializer deserializer;

    private Map<String, String> valuesNotInDataCols;

    private HCatSchema outputSchema = null;
    private HCatSchema dataSchema = null;

    /**
     * Instantiates a new hcat record reader.
     */
    public HCatRecordReader(HCatStorageHandler storageHandler,
                            Map<String, String> valuesNotInDataCols) {
        this.storageHandler = storageHandler;
        this.valuesNotInDataCols = valuesNotInDataCols;
    }

    /* (non-Javadoc)
     * @see org.apache.hadoop.mapreduce.RecordReader#initialize(
     * org.apache.hadoop.mapreduce.InputSplit,
     * org.apache.hadoop.mapreduce.TaskAttemptContext)
     */
    @Override
    public void initialize(org.apache.hadoop.mapreduce.InputSplit split,
                           TaskAttemptContext taskContext) throws IOException, InterruptedException {

        HCatSplit hcatSplit = InternalUtil.castToHCatSplit(split);

        baseRecordReader = createBaseRecordReader(hcatSplit, storageHandler, taskContext);
        createDeserializer(hcatSplit, storageHandler, taskContext);

        // Pull the output schema out of the TaskAttemptContext
        outputSchema = (HCatSchema) HCatUtil.deserialize(
            taskContext.getConfiguration().get(HCatConstants.HCAT_KEY_OUTPUT_SCHEMA));

        if (outputSchema == null) {
            outputSchema = hcatSplit.getTableSchema();
        }

        // Pull the table schema out of the Split info
        // TODO This should be passed in the TaskAttemptContext instead
        dataSchema = hcatSplit.getDataSchema();

        errorTracker = new InputErrorTracker(taskContext.getConfiguration());
    }

    private org.apache.hadoop.mapred.RecordReader createBaseRecordReader(HCatSplit hcatSplit,
                                                                         HCatStorageHandler storageHandler, TaskAttemptContext taskContext) throws IOException {

        JobConf jobConf = HCatUtil.getJobConfFromContext(taskContext);
        HCatUtil.copyJobPropertiesToJobConf(hcatSplit.getPartitionInfo().getJobProperties(), jobConf);
        org.apache.hadoop.mapred.InputFormat inputFormat =
            HCatInputFormat.getMapRedInputFormat(jobConf, storageHandler.getInputFormatClass());
        return inputFormat.getRecordReader(hcatSplit.getBaseSplit(), jobConf,
            InternalUtil.createReporter(taskContext));
    }

    private void createDeserializer(HCatSplit hcatSplit, HCatStorageHandler storageHandler,
                                    TaskAttemptContext taskContext) throws IOException {

        deserializer = ReflectionUtils.newInstance(storageHandler.getSerDeClass(),
            taskContext.getConfiguration());

        try {
            InternalUtil.initializeDeserializer(deserializer, storageHandler.getConf(),
                hcatSplit.getPartitionInfo().getTableInfo(),
                hcatSplit.getPartitionInfo().getPartitionSchema());
        } catch (SerDeException e) {
            throw new IOException("Failed initializing deserializer "
                + storageHandler.getSerDeClass().getName(), e);
        }
    }

    /* (non-Javadoc)
    * @see org.apache.hadoop.mapreduce.RecordReader#getCurrentKey()
    */
    @Override
    public WritableComparable getCurrentKey()
        throws IOException, InterruptedException {
        return currentKey;
    }

    /* (non-Javadoc)
     * @see org.apache.hadoop.mapreduce.RecordReader#getCurrentValue()
     */
    @Override
    public HCatRecord getCurrentValue() throws IOException, InterruptedException {
        return currentHCatRecord;
    }

    /* (non-Javadoc)
     * @see org.apache.hadoop.mapreduce.RecordReader#getProgress()
     */
    @Override
    public float getProgress() {
        try {
            return baseRecordReader.getProgress();
        } catch (IOException e) {
            LOG.warn("Exception in HCatRecord reader", e);
        }
        return 0.0f; // errored
    }

    /**
     * Check if the wrapped RecordReader has another record, and if so convert it into an
     * HCatRecord. We both check for records and convert here so a configurable percent of
     * bad records can be tolerated.
     *
     * @return if there is a next record
     * @throws IOException on error
     * @throws InterruptedException on error
     */
    @Override
    public boolean nextKeyValue() throws IOException, InterruptedException {
        if (currentKey == null) {
            currentKey = baseRecordReader.createKey();
            currentValue = baseRecordReader.createValue();
        }

        while (baseRecordReader.next(currentKey, currentValue)) {
            HCatRecord r = null;
            Throwable t = null;

            errorTracker.incRecords();

            try {
                Object o = deserializer.deserialize(currentValue);
                r = new LazyHCatRecord(o, deserializer.getObjectInspector());
            } catch (Throwable throwable) {
                t = throwable;
            }

            if (r == null) {
                errorTracker.incErrors(t);
                continue;
            }

            DefaultHCatRecord dr = new DefaultHCatRecord(outputSchema.size());
            int i = 0;
            for (String fieldName : outputSchema.getFieldNames()) {
                if (dataSchema.getPosition(fieldName) != null) {
                    dr.set(i, r.get(fieldName, dataSchema));
                } else {
                    dr.set(i, valuesNotInDataCols.get(fieldName));
                }
                i++;
            }

            currentHCatRecord = dr;
            return true;
        }

        return false;
    }

    /* (non-Javadoc)
    * @see org.apache.hadoop.mapreduce.RecordReader#close()
    */
    @Override
    public void close() throws IOException {
        baseRecordReader.close();
    }

    /**
     * Tracks number of of errors in input and throws a Runtime exception
     * if the rate of errors crosses a limit.
     * <br/>
     * The intention is to skip over very rare file corruption or incorrect
     * input, but catch programmer errors (incorrect format, or incorrect
     * deserializers etc).
     *
     * This class was largely copied from Elephant-Bird (thanks @rangadi!)
     * https://github.com/kevinweil/elephant-bird/blob/master/core/src/main/java/com/twitter/elephantbird/mapreduce/input/LzoRecordReader.java
     */
    static class InputErrorTracker {
        long numRecords;
        long numErrors;

        double errorThreshold; // max fraction of errors allowed
        long minErrors; // throw error only after this many errors

        InputErrorTracker(Configuration conf) {
            errorThreshold = conf.getFloat(HCatConstants.HCAT_INPUT_BAD_RECORD_THRESHOLD_KEY,
                HCatConstants.HCAT_INPUT_BAD_RECORD_THRESHOLD_DEFAULT);
            minErrors = conf.getLong(HCatConstants.HCAT_INPUT_BAD_RECORD_MIN_KEY,
                HCatConstants.HCAT_INPUT_BAD_RECORD_MIN_DEFAULT);
            numRecords = 0;
            numErrors = 0;
        }

        void incRecords() {
            numRecords++;
        }

        void incErrors(Throwable cause) {
            numErrors++;
            if (numErrors > numRecords) {
                // incorrect use of this class
                throw new RuntimeException("Forgot to invoke incRecords()?");
            }

            if (cause == null) {
                cause = new Exception("Unknown error");
            }

            if (errorThreshold <= 0) { // no errors are tolerated
                throw new RuntimeException("error while reading input records", cause);
            }

            LOG.warn("Error while reading an input record ("
                + numErrors + " out of " + numRecords + " so far ): ", cause);

            double errRate = numErrors / (double) numRecords;

            // will always excuse the first error. We can decide if single
            // error crosses threshold inside close() if we want to.
            if (numErrors >= minErrors && errRate > errorThreshold) {
                LOG.error(numErrors + " out of " + numRecords
                    + " crosses configured threshold (" + errorThreshold + ")");
                throw new RuntimeException("error rate while reading input records crossed threshold", cause);
            }
        }
    }
}