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Library for use in Java components of Vespa. Shared code which do not fit anywhere else.
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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.tensor.functions;

import com.yahoo.tensor.Tensor;
import com.yahoo.tensor.TensorType;
import com.yahoo.tensor.TypeResolver;
import com.yahoo.tensor.evaluation.EvaluationContext;
import com.yahoo.tensor.evaluation.Name;
import com.yahoo.tensor.evaluation.TypeContext;

import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;

/**
 * The cell_cast tensor function creates a new tensor with the specified cell value type.
 *
 * @author lesters
 */
public class CellCast extends PrimitiveTensorFunction {

    private final TensorFunction argument;
    private final TensorType.Value valueType;

    public CellCast(TensorFunction argument, TensorType.Value valueType) {
        Objects.requireNonNull(argument, "The argument tensor cannot be null");
        Objects.requireNonNull(valueType, "The value type cannot be null");
        this.argument = argument;
        this.valueType = valueType;
    }

    @Override
    public List> arguments() { return List.of(argument); }

    @Override
    public TensorFunction withArguments(List> arguments) {
        if ( arguments.size() != 1)
            throw new IllegalArgumentException("CellCast must have 1 argument, got " + arguments.size());
        return new CellCast<>(arguments.get(0), valueType);
    }

    @Override
    public PrimitiveTensorFunction toPrimitive() {
        return new CellCast<>(argument.toPrimitive(), valueType);
    }

    @Override
    public TensorType type(TypeContext context) {
        return TypeResolver.cell_cast(argument.type(context), valueType);
    }

    @Override
    public Tensor evaluate(EvaluationContext context) {
        Tensor tensor = argument.evaluate(context);
        if (tensor.type().valueType() == valueType) {
            return tensor;
        }
        TensorType type = TypeResolver.cell_cast(tensor.type(), valueType);
        return cast(tensor, type);
    }

    private Tensor cast(Tensor tensor, TensorType type) {
        TensorType.Value fromValueType = tensor.type().valueType();
        switch (fromValueType) {
            case DOUBLE:
                return castFromDouble(tensor, type);
            case FLOAT:
            case BFLOAT16:
            case INT8:
                    return castFromSomeFloat(tensor, type);
            default:
                throw new IllegalStateException("Unexpected value type " + fromValueType);
        }
    }

    private Tensor castFromDouble(Tensor tensor, TensorType type) {
        Tensor.Builder builder = Tensor.Builder.of(type);
        var restrict = selectRestrict(type.valueType());
        for (Iterator i = tensor.cellIterator(); i.hasNext(); ) {
            Tensor.Cell cell = i.next();
            builder.cell(cell.getKey(), restrict.apply((float)cell.getDoubleValue()));
        }
        return builder.build();
    }

    private Tensor castFromSomeFloat(Tensor tensor, TensorType type) {
        Tensor.Builder builder = Tensor.Builder.of(type);
        var restrict = selectRestrict(type.valueType());
        for (Iterator i = tensor.cellIterator(); i.hasNext(); ) {
            Tensor.Cell cell = i.next();
            builder.cell(cell.getKey(), restrict.apply(cell.getFloatValue()));
        }
        return builder.build();
    }

    static private Function selectRestrict(TensorType.Value toValueType) {
        return switch (toValueType) {
            case BFLOAT16 -> val -> Float.intBitsToFloat(Float.floatToRawIntBits(val) & ~0xffff);
            case INT8 -> val -> (float) val.byteValue();
            default -> val -> val;
        };
    }

    @Override
    public String toString(ToStringContext context) {
        return "cell_cast(" + argument.toString(context) + ", " + valueType + ")";
    }

    @Override
    public int hashCode() { return Objects.hash("cellcast", argument, valueType); }

}