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package org.apache.cayenne.access.flush.operation;

import java.util.function.BiFunction;

/**
 * BiFunction that merges two {@link DbRowOp} changing same object.
 *
 * @since 4.2
 */
public class DbRowOpMerger implements DbRowOpVisitor, BiFunction {

    private DbRowOp dbRow;

    @Override
    public DbRowOp apply(DbRowOp oldValue, DbRowOp newValue) {
        this.dbRow = oldValue;
        return newValue.accept(this);
    }

    @Override
    public DbRowOp visitInsert(InsertDbRowOp other) {
        if(dbRow instanceof DeleteDbRowOp) {
            return new DeleteInsertDbRowOp((DeleteDbRowOp)dbRow, other);
        }
        return mergeValues((DbRowOpWithValues) dbRow, other);
    }

    @Override
    public DbRowOp visitUpdate(UpdateDbRowOp other) {
        // delete beats update ...
        if(dbRow instanceof DeleteDbRowOp) {
            return dbRow;
        }
        return mergeValues((DbRowOpWithValues) dbRow, other);
    }

    @Override
    public DbRowOp visitDelete(DeleteDbRowOp other) {
        if(dbRow.getChangeId() == other.getChangeId()) {
            return other;
        }
        // clash of Insert/Delete with equal ObjectId
        if(dbRow instanceof InsertDbRowOp) {
            return new DeleteInsertDbRowOp(other, (InsertDbRowOp)dbRow);
        }
        return other;
    }

    private DbRowOp mergeValues(DbRowOpWithValues left, DbRowOpWithValues right) {
        if(right.getChangeId() == right.getObject().getObjectId()) {
            right.getValues().merge(left.getValues());
            return right;
        } else {
            left.getValues().merge(right.getValues());
            return left;
        }
    }
}