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package io.deephaven.engine.table.impl.updateby.em;

import io.deephaven.api.updateby.OperationControl;
import io.deephaven.chunk.CharChunk;
import io.deephaven.chunk.Chunk;
import io.deephaven.chunk.LongChunk;
import io.deephaven.chunk.attributes.Values;
import io.deephaven.engine.rowset.RowSequence;
import io.deephaven.engine.table.ColumnSource;
import io.deephaven.engine.table.impl.MatchPair;
import io.deephaven.engine.table.impl.updateby.UpdateByOperator;
import io.deephaven.engine.table.impl.util.RowRedirection;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import static io.deephaven.util.QueryConstants.*;

public class CharEMOperator extends BasePrimitiveEMOperator {
    public final ColumnSource valueSource;
    // region extra-fields
    // endregion extra-fields

    protected class Context extends BasePrimitiveEMOperator.Context {
        public CharChunk charValueChunk;

        protected Context(final int affectedChunkSize, final int influencerChunkSize) {
            super(affectedChunkSize);
        }

        @Override
        public void setValueChunks(@NotNull final Chunk[] valueChunks) {
            charValueChunk = valueChunks[0].asCharChunk();
        }

        @Override
        public void accumulateCumulative(@NotNull RowSequence inputKeys,
                                         Chunk[] valueChunkArr,
                                         LongChunk tsChunk,
                                         int len) {
            setValueChunks(valueChunkArr);

            // chunk processing
            if (timestampColumnName == null) {
                // compute with ticks
                for (int ii = 0; ii < len; ii++) {
                    // read the value from the values chunk
                    final char input = charValueChunk.get(ii);

                    if (input == NULL_CHAR) {
                        handleBadData(this, true, false);
                    } else {
                        if (curVal == NULL_DOUBLE) {
                            curVal = input;
                        } else {
                            curVal = aggFunction.apply(curVal, input, opAlpha, opOneMinusAlpha);
                        }
                    }
                    outputValues.set(ii, curVal);
                }
            } else {
                // compute with time
                for (int ii = 0; ii < len; ii++) {
                    // read the value from the values chunk
                    final char input = charValueChunk.get(ii);
                    final long timestamp = tsChunk.get(ii);
                    //noinspection ConstantConditions
                    final boolean isNull = input == NULL_CHAR;
                    final boolean isNullTime = timestamp == NULL_LONG;
                    if (isNull) {
                        handleBadData(this, true, false);
                    } else if (isNullTime) {
                        // no change to curVal and lastStamp
                    } else if (curVal == NULL_DOUBLE) {
                        curVal = input;
                        lastStamp = timestamp;
                    } else {
                        final long dt = timestamp - lastStamp;
                        if (dt != lastDt) {
                            // Alpha is dynamic based on time, but only recalculated when needed
                            alpha = Math.exp(-dt / reverseWindowScaleUnits);
                            oneMinusAlpha = 1.0 - alpha;
                            lastDt = dt;
                        }
                        curVal = aggFunction.apply(curVal, input, alpha, oneMinusAlpha);
                        lastStamp = timestamp;
                    }
                    outputValues.set(ii, curVal);
                }
            }

            // chunk output to column
            writeToOutputColumn(inputKeys);
        }

        @Override
        public boolean isValueValid(long atKey) {
            return valueSource.getChar(atKey) != NULL_CHAR;
        }

        @Override
        public void push(int pos, int count) {
            throw new IllegalStateException("EMAOperator#push() is not used");
        }
    }

    /**
     * An operator that computes an EMA from a char column using an exponential decay function.
     *
     * @param pair                the {@link MatchPair} that defines the input/output for this operation
     * @param affectingColumns    the names of the columns that affect this ema
     * @param rowRedirection      the {@link RowRedirection} to use for dense output sources
     * @param control             defines how to handle {@code null} input values.
     * @param timestampColumnName the name of the column containing timestamps for time-based calcuations
     * @param windowScaleUnits      the smoothing window for the EMA. If no {@code timestampColumnName} is provided, this is measured in ticks, otherwise it is measured in nanoseconds
     * @param valueSource         a reference to the input column source for this operation
     */
    public CharEMOperator(@NotNull final MatchPair pair,
                          @NotNull final String[] affectingColumns,
                          @Nullable final RowRedirection rowRedirection,
                          @NotNull final OperationControl control,
                          @Nullable final String timestampColumnName,
                          final double windowScaleUnits,
                          final ColumnSource valueSource,
                          @NotNull final EmFunction aggFunction
                          // region extra-constructor-args
                          // endregion extra-constructor-args
    ) {
        super(pair, affectingColumns, rowRedirection, control, timestampColumnName, windowScaleUnits, aggFunction);
        this.valueSource = valueSource;
        // region constructor
        // endregion constructor
    }

    @NotNull
    @Override
    public UpdateByOperator.Context makeUpdateContext(final int affectedChunkSize, final int influencerChunkSize) {
        return new Context(affectedChunkSize, influencerChunkSize);
    }
}