DocumentSnapshotMapper.java

package durdinapps.rxfirebase2;

import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.QuerySnapshot;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;

import io.reactivex.functions.Function;
import io.reactivex.functions.Predicate;

public abstract class DocumentSnapshotMapper<T, U> implements Function<T, U> {

    private DocumentSnapshotMapper() {
    }

    public static <U> DocumentSnapshotMapper<DocumentSnapshot, U> of(Class<U> clazz) {
        return new TypedDocumentSnapshotMapper<U>(clazz);
    }

    public static <U> DocumentSnapshotMapper<QuerySnapshot, List<U>> listOf(Class<U> clazz) {
        return new TypedListQuerySnapshotMapper<>(clazz);
    }

    public static <U> DocumentSnapshotMapper<QuerySnapshot, List<U>> listOf(Class<U> clazz, Function<DocumentSnapshot, U> mapper) {
        return new TypedListQuerySnapshotMapper<>(clazz, mapper);
    }

    public static <U> TypedMapQuerySnapshotMapper<U> mapOf(Class<U> clazz) {
        return new TypedMapQuerySnapshotMapper<>(clazz);
    }

    private static <U> U getDataSnapshotTypedValue(DocumentSnapshot documentSnapshot, Class<U> clazz) {
        return documentSnapshot.toObject(clazz);
    }

    private static class TypedDocumentSnapshotMapper<U> extends DocumentSnapshotMapper<DocumentSnapshot, U> {

        private final Class<U> clazz;

        public TypedDocumentSnapshotMapper(final Class<U> clazz) {
            this.clazz = clazz;
        }

        @Override
        public U apply(final DocumentSnapshot documentSnapshot) {
            return getDataSnapshotTypedValue(documentSnapshot, clazz);
        }
    }

    private static class TypedListQuerySnapshotMapper<U> extends DocumentSnapshotMapper<QuerySnapshot, List<U>> {

        private final Class<U> clazz;
        private final Function<DocumentSnapshot, U> mapper;

        TypedListQuerySnapshotMapper(final Class<U> clazz) {
            this(clazz, null);
        }

        TypedListQuerySnapshotMapper(final Class<U> clazz, Function<DocumentSnapshot, U> mapper) {
            this.clazz = clazz;
            this.mapper = mapper;
        }

        @Override
        public List<U> apply(final QuerySnapshot querySnapshot) throws Exception {
            List<U> items = new ArrayList<>();
            for (DocumentSnapshot documentSnapshot : querySnapshot) {
                items.add(mapper != null
                    ? mapper.apply(documentSnapshot)
                    : getDataSnapshotTypedValue(documentSnapshot, clazz));
            }
            return items;
        }
    }


    private static class TypedMapQuerySnapshotMapper<U> extends DocumentSnapshotMapper<QuerySnapshot, LinkedHashMap<String, U>> {

        private final Class<U> clazz;

        TypedMapQuerySnapshotMapper(final Class<U> clazz) {
            this.clazz = clazz;
        }

        @Override
        public LinkedHashMap<String, U> apply(final QuerySnapshot querySnapshot) {
            LinkedHashMap<String, U> items = new LinkedHashMap<>();
            for (DocumentSnapshot documentSnapshot : querySnapshot) {
                items.put(documentSnapshot.getId(), getDataSnapshotTypedValue(documentSnapshot, clazz));
            }
            return items;
        }
    }

    static final Predicate<QuerySnapshot> QUERY_EXISTENCE_PREDICATE = querySnapshot -> !querySnapshot.isEmpty();

    static final Predicate<DocumentSnapshot> DOCUMENT_EXISTENCE_PREDICATE = DocumentSnapshot::exists;
}