Add fluent builder (#3)

src/main/java/org/vaadin/artur/spring/dataprovider/SpringDataProviderBuilder.java

@@ -0,0 +1,81 @@
+package org.vaadin.artur.spring.dataprovider;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BiFunction;
+import java.util.function.ToLongFunction;
+
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.repository.PagingAndSortingRepository;
+
+import com.vaadin.data.provider.ConfigurableFilterDataProvider;
+import com.vaadin.data.provider.DataProvider;
+import com.vaadin.data.provider.Query;
+import com.vaadin.data.provider.QuerySortOrder;
+import com.vaadin.data.provider.SortDirection;
+
+public class SpringDataProviderBuilder<T, F> {
+    private final BiFunction<Pageable, F, Page<T>> queryFunction;
+    private final ToLongFunction<F> lengthFunction;
+    private final List<QuerySortOrder> defaultSortOrders = new ArrayList<>();
+
+    private F defaultFilter = null;
+
+    public SpringDataProviderBuilder(
+            BiFunction<Pageable, F, Page<T>> queryFunction,
+            ToLongFunction<F> lengthFunction) {
+        this.queryFunction = queryFunction;
+        this.lengthFunction = lengthFunction;
+    }
+
+    public SpringDataProviderBuilder<T, F> withDefaultSort(String column,
+            SortDirection direction) {
+        defaultSortOrders.add(new QuerySortOrder(column, direction));
+        return this;
+    }
+
+    public SpringDataProviderBuilder<T, F> withDefaultFilter(F defaultFilter) {
+        this.defaultFilter = defaultFilter;
+        return this;
+    }
+
+    public DataProvider<T, F> build() {
+        return new PageableDataProvider<T, F>() {
+            @Override
+            protected Page<T> fetchFromBackEnd(Query<T, F> query,
+                    Pageable pageable) {
+                return queryFunction.apply(pageable,
+                        query.getFilter().orElse(defaultFilter));
+            }
+
+            @Override
+            protected List<QuerySortOrder> getDefaultSortOrders() {
+                return defaultSortOrders;
+            }
+
+            @Override
+            protected int sizeInBackEnd(Query<T, F> query) {
+                return (int) lengthFunction
+                        .applyAsLong(query.getFilter().orElse(defaultFilter));
+            }
+        };
+    }
+
+    public ConfigurableFilterDataProvider<T, Void, F> buildFilterable() {
+        return build().withConfigurableFilter();
+    }
+
+    public static <T> SpringDataProviderBuilder<T, Void> forRepository(
+            PagingAndSortingRepository<T, ?> repository) {
+        return new SpringDataProviderBuilder<>(
+                (pageable, filter) -> repository.findAll(pageable),
+                filter -> repository.count());
+    }
+
+    public static <T, F> SpringDataProviderBuilder<T, F> forFunctions(
+            BiFunction<Pageable, F, Page<T>> queryFunction,
+            ToLongFunction<F> lengthFunction) {
+        return new SpringDataProviderBuilder<>(queryFunction, lengthFunction);
+    }
+}