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/*
 * Copyright 2017-2020 the original author or authors.
 *
 * 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
 *
 *      https://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 io.r2dbc.postgresql.codec;

import io.netty.buffer.ByteBuf;
import io.r2dbc.postgresql.client.Parameter;
import io.r2dbc.postgresql.message.Format;
import io.r2dbc.postgresql.type.PostgresqlObjectId;
import io.r2dbc.postgresql.util.Assert;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.util.annotation.Nullable;

import java.util.function.Supplier;

import static io.r2dbc.postgresql.client.Parameter.NULL_VALUE;

/**
 * Abstract codec class that provides a basis for all concrete
 * implementations of a {@link Codec} for well-known {@link PostgresqlObjectId}.
 *
 * @param  the type that is handled by this {@link Codec}.
 */
abstract class AbstractCodec implements Codec {

    private final Class type;

    /**
     * Creates a new {@link AbstractCodec}.
     *
     * @param type the type handled by this codec
     */
    AbstractCodec(Class type) {
        this.type = Assert.requireNonNull(type, "type must not be null");
    }

    @Override
    public boolean canDecode(int dataType, Format format, Class type) {
        Assert.requireNonNull(format, "format must not be null");
        Assert.requireNonNull(type, "type must not be null");

        return PostgresqlObjectId.isValid(dataType) && (type == Object.class || isTypeAssignable(type)) &&
            doCanDecode(PostgresqlObjectId.valueOf(dataType), format);
    }

    @Override
    public boolean canEncode(Object value) {
        Assert.requireNonNull(value, "value must not be null");

        return this.type.isInstance(value);
    }

    @Override
    public final boolean canEncodeNull(Class type) {
        Assert.requireNonNull(type, "type must not be null");

        return this.type.isAssignableFrom(type);
    }

    @Nullable
    @Override
    public final T decode(@Nullable ByteBuf buffer, int dataType, Format format, Class type) {
        if (buffer == null) {
            return null;
        }

        return doDecode(buffer, PostgresqlObjectId.valueOf(dataType), format, type);
    }

    @Override
    @SuppressWarnings("unchecked")
    public final Parameter encode(Object value) {
        Assert.requireNonNull(value, "value must not be null");

        return doEncode((T) value);
    }

    @Override
    public Class type() {
        return this.type;
    }

    /**
     * Create a {@link Parameter}.
     *
     * @param type   the well-known {@link PostgresqlObjectId type OID}
     * @param format the format to use
     * @param value  {@link Publisher} emitting {@link ByteBuf buffers}. Make sure to use deferred buffer creation instead of {@link Mono#just(Object)} and {@link Flux#just(Object)} to avoid memory
     *               leaks
     * @return the encoded  {@link Parameter}
     */
    static Parameter create(PostgresqlObjectId type, Format format, Publisher value) {
        return new Parameter(format, type.getObjectId(), value);
    }

    /**
     * Create a {@link Parameter}.
     *
     * @param type           the well-known {@link PostgresqlObjectId type OID}
     * @param format         the format to use
     * @param bufferSupplier {@link Supplier} supplying the encoded {@link ByteBuf buffer}
     * @return the encoded  {@link Parameter}
     */
    static Parameter create(PostgresqlObjectId type, Format format, Supplier bufferSupplier) {
        return new Parameter(format, type.getObjectId(), Mono.fromSupplier(bufferSupplier));
    }

    /**
     * Encode a {@code null} value.
     *
     * @param type   the well-known {@link PostgresqlObjectId type OID}
     * @param format the data type {@link Format}, text or binary
     * @return the encoded {@code null} value.
     */
    static Parameter createNull(PostgresqlObjectId type, Format format) {
        return create(type, format, NULL_VALUE);
    }

    /**
     * Determine whether this {@link Codec} is capable of decoding column values based on the given {@link Format} and {@link PostgresqlObjectId}.
     *
     * @param type   the well-known {@link PostgresqlObjectId type OID}
     * @param format the data type {@link Format}, text or binary
     * @return {@code true} if this codec is able to decode values of {@link Format} and {@link PostgresqlObjectId}.
     */
    abstract boolean doCanDecode(PostgresqlObjectId type, Format format);

    /**
     * Decode the {@link ByteBuf data} into the {@link Class value type}.
     *
     * @param buffer   the data buffer
     * @param dataType the well-known {@link PostgresqlObjectId type OID}
     * @param format   data type format
     * @param type     the desired value type.
     * @return the decoded value. Can be {@code null} if the column value is {@code null}.
     */
    abstract T doDecode(ByteBuf buffer, PostgresqlObjectId dataType, Format format, Class type);

    /**
     * @param value the  {@code value}.
     * @return the encoded value.
     */
    abstract Parameter doEncode(T value);

    boolean isTypeAssignable(Class type) {
        Assert.requireNonNull(type, "type must not be null");

        return type.isAssignableFrom(this.type);
    }

}