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 *  Copyright (c) 2014-2019 Appsicle
 *  Copyright (c) 2019-2020 QuestDB
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 *  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
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 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
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package io.questdb.griffin.engine.functions.date;

import io.questdb.cairo.CairoConfiguration;
import io.questdb.cairo.sql.Function;
import io.questdb.cairo.sql.Record;
import io.questdb.griffin.FunctionFactory;
import io.questdb.griffin.engine.functions.BinaryFunction;
import io.questdb.griffin.engine.functions.LongFunction;
import io.questdb.griffin.engine.functions.TernaryFunction;
import io.questdb.griffin.engine.functions.UnaryFunction;
import io.questdb.griffin.engine.functions.constants.TimestampConstant;
import io.questdb.std.Numbers;
import io.questdb.std.ObjList;
import io.questdb.std.microtime.Timestamps;

public class TimestampDiffFunctionFactory implements FunctionFactory {
    private static final ObjList diffFunctions = new ObjList<>();
    private static final int diffFunctionsMax;

    @Override
    public String getSignature() {
        return "datediff(ANN)";
    }

    @Override
    public Function newInstance(ObjList args, int position, CairoConfiguration configuration) {

        final Function perionFunction = args.getQuick(0);
        if (perionFunction.isConstant()) {
            final Function start = args.getQuick(1);
            final Function end = args.getQuick(2);
            final char period = perionFunction.getChar(null);
            if (period < diffFunctionsMax) {
                final LongDiffFunction func = diffFunctions.getQuick(period);
                if (func != null) {
                    if (start.isConstant() && start.getTimestamp(null) != Numbers.LONG_NaN) {
                        return new DiffVarConstFunction(position, args.getQuick(2), start.getLong(null), func);
                    }
                    if (end.isConstant() && end.getTimestamp(null) != Numbers.LONG_NaN) {
                        return new DiffVarConstFunction(position, args.getQuick(1), end.getLong(null), func);
                    }
                    return new DiffVarVarFunction(position, args.getQuick(1), args.getQuick(2), func);
                }
            }
            return new TimestampConstant(position, Numbers.LONG_NaN);
        }
        return new DateDiffFunc(position, args.getQuick(0), args.getQuick(1), args.getQuick(2));
    }

    @FunctionalInterface
    private interface LongDiffFunction {
        long diff(long a, long b);
    }

    private static class DiffVarVarFunction extends LongFunction implements BinaryFunction {
        private final Function left;
        private final Function right;
        private final LongDiffFunction func;

        public DiffVarVarFunction(int position, Function left, Function right, LongDiffFunction func) {
            super(position);
            this.left = left;
            this.right = right;
            this.func = func;
        }

        @Override
        public Function getLeft() {
            return left;
        }

        @Override
        public Function getRight() {
            return right;
        }

        @Override
        public long getLong(Record rec) {
            final long l = left.getTimestamp(rec);
            final long r = right.getTimestamp(rec);
            if (l == Numbers.LONG_NaN || r == Numbers.LONG_NaN) {
                return Numbers.LONG_NaN;
            }
            return func.diff(l, r);
        }
    }

    private static class DiffVarConstFunction extends LongFunction implements UnaryFunction {
        private final Function arg;
        private final long constantTime;
        private final LongDiffFunction func;

        public DiffVarConstFunction(int position, Function left, long right, LongDiffFunction func) {
            super(position);
            this.arg = left;
            this.constantTime = right;
            this.func = func;
        }

        @Override
        public Function getArg() {
            return arg;
        }

        @Override
        public long getLong(Record rec) {
            final long l = arg.getTimestamp(rec);
            if (l == Numbers.LONG_NaN) {
                return Numbers.LONG_NaN;
            }
            return func.diff(l, constantTime);
        }
    }

    private static class DateDiffFunc extends LongFunction implements TernaryFunction {
        final Function left;
        final Function center;
        final Function right;

        public DateDiffFunc(int position, Function left, Function center, Function right) {
            super(position);
            this.left = left;
            this.center = center;
            this.right = right;
        }

        @Override
        public Function getLeft() {
            return left;
        }

        @Override
        public Function getCenter() {
            return center;
        }

        @Override
        public Function getRight() {
            return right;
        }

        @Override
        public long getLong(Record rec) {
            final char l = left.getChar(rec);
            final long c = center.getTimestamp(rec);
            final long r = right.getTimestamp(rec);
            if (c == Numbers.LONG_NaN || r == Numbers.LONG_NaN) {
                return Numbers.LONG_NaN;
            }
            return Timestamps.getPeriodBetween(l, c, r);
        }
    }

    static {
        diffFunctions.extendAndSet('s', Timestamps::getSecondsBetween);
        diffFunctions.extendAndSet('m', Timestamps::getMinutesBetween);
        diffFunctions.extendAndSet('h', Timestamps::getHoursBetween);
        diffFunctions.extendAndSet('d', Timestamps::getDaysBetween);
        diffFunctions.extendAndSet('w', Timestamps::getWeeksBetween);
        diffFunctions.extendAndSet('M', Timestamps::getMonthsBetween);
        diffFunctions.extendAndSet('y', Timestamps::getYearsBetween);
        diffFunctionsMax = diffFunctions.size();
    }
}