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 *  http://www.apache.org/licenses/LICENSE-2.0
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 *  distributed under the License is distributed on an "AS IS" BASIS,
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package io.questdb.griffin.engine.functions.eq;

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.PlanSink;
import io.questdb.griffin.SqlExecutionContext;
import io.questdb.griffin.engine.functions.NegatableBooleanFunction;
import io.questdb.griffin.engine.functions.UnaryFunction;
import io.questdb.std.Chars;
import io.questdb.std.IntList;
import io.questdb.std.ObjList;

public class EqStrFunctionFactory implements FunctionFactory {

    @Override
    public String getSignature() {
        return "=(SS)";
    }

    @Override
    public boolean isBoolean() {
        return true;
    }

    @Override
    public Function newInstance(
            int position,
            ObjList args,
            IntList argPositions,
            CairoConfiguration configuration,
            SqlExecutionContext sqlExecutionContext
    ) {
        // there are optimisation opportunities
        // 1. when one of args is constant null comparison can boil down to checking
        //    length of non-constant (must be -1)
        // 2. when one of arguments is constant, save method call and use a field

        final Function a = args.getQuick(0);
        final Function b = args.getQuick(1);

        if (a.isConstant() && !b.isConstant()) {
            return createHalfConstantFunc(a, b);
        }

        if (!a.isConstant() && b.isConstant()) {
            return createHalfConstantFunc(b, a);
        }

        return new Func(a, b);
    }

    private Function createHalfConstantFunc(Function constFunc, Function varFunc) {
        CharSequence constValue = constFunc.getStrA(null);
        if (constValue == null) {
            return new NullCheckFunc(varFunc);
        }
        return new ConstCheckFunc(varFunc, constValue);
    }

    public static class ConstCheckFunc extends NegatableBooleanFunction implements UnaryFunction {
        private final Function arg;
        private final CharSequence constant;

        public ConstCheckFunc(Function arg, CharSequence constant) {
            this.arg = arg;
            this.constant = constant;
        }

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

        @Override
        public boolean getBool(Record rec) {
            return negated != Chars.equalsNc(constant, arg.getStrA(rec));
        }

        @Override
        public void toPlan(PlanSink sink) {
            sink.val(arg);
            if (negated) {
                sink.val('!');
            }
            sink.val("='").val(constant).val('\'');
        }
    }

    private static class Func extends AbstractEqBinaryFunction {
        public Func(Function left, Function right) {
            super(left, right);
        }

        @Override
        public boolean getBool(Record rec) {
            // important to compare A and B strings in case
            // these are columns of the same record
            // records have re-usable character sequences
            final CharSequence a = left.getStrA(rec);
            final CharSequence b = right.getStrB(rec);

            if (a == null) {
                return negated != (b == null);
            }

            return negated != Chars.equalsNc(a, b);
        }

        @Override
        public String getName() {
            if (negated) {
                return "!=";
            } else {
                return "=";
            }
        }
    }

    public static class NullCheckFunc extends NegatableBooleanFunction implements UnaryFunction {
        private final Function arg;

        public NullCheckFunc(Function arg) {
            this.arg = arg;
        }

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

        @Override
        public boolean getBool(Record rec) {
            return negated != (arg.getStrLen(rec) == -1L);
        }

        @Override
        public void toPlan(PlanSink sink) {
            sink.val(arg);
            if (negated) {
                sink.val(" is not null");
            } else {
                sink.val(" is null");
            }
        }
    }
}