pub fn from_schema<S: Schema + ?Sized>() -> Result<Self, Error> {

        let mut schematic = Self {

            name: S::schema_name(),

            contained_collections: HashMap::new(),

            collections_by_type_id: HashMap::new(),

            collection_encryption_keys: HashMap::new(),

            collection_id_generators: HashMap::new(),

            views: HashMap::new(),

            views_by_name: HashMap::new(),

            views_by_collection: HashMap::new(),

            eager_views_by_collection: HashMap::new(),

        };

        S::define_collections(&mut schematic)?;

        Ok(schematic)

    }

    pub fn define_collection<C: Collection + 'static>(&mut self) -> Result<(), Error> {

        let name = C::collection_name();

        match self.contained_collections.entry(name.clone()) {

            hash_map::Entry::Vacant(entry) => {

                self.collections_by_type_id

                    .insert(TypeId::of::<C>(), name.clone());

                if let Some(key) = C::encryption_key() {

                    self.collection_encryption_keys.insert(name.clone(), key);

                }

                self.collection_id_generators

                    .insert(name, Box::<KeyIdGenerator<C>>::default());

                entry.insert(KeyDescription::for_key::<C::PrimaryKey>());

                C::define_views(self)

    }

    pub fn define_view<V: MapReduce + ViewSchema<View = V> + SerializedView + Clone + 'static>(

        &mut self,

        view: V,

    ) -> Result<(), Error> {

        self.define_view_with_schema(view.clone(), view)

    }

    pub fn define_view_with_schema<

        V: SerializedView + 'static,

        S: MapReduce + ViewSchema<View = V> + 'static,

    >(

        &mut self,

        view: V,

        schema: S,

    ) -> Result<(), Error> {

        let instance = ViewInstance { view, schema };

        let name = instance.view_name();

        if self.views_by_name.contains_key(&name) {

        }

        let collection = instance.collection();

        let eager = instance.update_policy().is_eager();

        self.views.insert(TypeId::of::<V>(), Box::new(instance));

        self.views_by_name.insert(name, TypeId::of::<V>());

        if eager {

            let unique_views = self

                .eager_views_by_collection

                .entry(collection.clone())

                .or_insert_with(Vec::new);

            unique_views.push(TypeId::of::<V>());

        }

        let views = self

            .views_by_collection

            .entry(collection)

            .or_insert_with(Vec::new);

        views.push(TypeId::of::<V>());

        Ok(())

    }

    pub fn collection_primary_key_description<'a>(

        &'a self,

        collection: &CollectionName,

    ) -> Option<&'a KeyDescription> {

        self.contained_collections.get(collection)

    }

    pub fn next_id_for_collection(

        &self,

        collection: &CollectionName,

        id: Option<DocumentId>,

    ) -> Result<DocumentId, Error> {

        let generator = self

            .collection_id_generators

            .get(collection)

            .ok_or(Error::CollectionNotFound)?;

        generator.next_id(id)

    }

    pub fn view_by_name(&self, name: &ViewName) -> Result<&'_ dyn view::Serialized, Error> {

        self.views_by_name

            .get(name)

            .and_then(|type_id| self.views.get(type_id))

            .map(AsRef::as_ref)

            .ok_or(Error::ViewNotFound)

    }

    pub fn view<V: View + 'static>(&self) -> Result<&'_ dyn view::Serialized, Error> {

        self.views

            .get(&TypeId::of::<V>())

            .map(AsRef::as_ref)

            .ok_or(Error::ViewNotFound)

    }

    pub fn views(&self) -> impl Iterator<Item = &'_ dyn view::Serialized> {

        self.views.values().map(AsRef::as_ref)

    }

    pub fn views_in_collection(

        &self,

        collection: &CollectionName,

    ) -> impl Iterator<Item = &'_ dyn view::Serialized> {

        self.views_by_collection

            .get(collection)

            .into_iter()

            .flat_map(|view_ids| {

                view_ids

                    .iter()

                    .filter_map(|id| self.views.get(id).map(AsRef::as_ref))

            })

    }

    pub fn eager_views_in_collection(

        &self,

        collection: &CollectionName,

    ) -> impl Iterator<Item = &'_ dyn view::Serialized> {

        self.eager_views_by_collection

            .get(collection)

            .into_iter()

            .flat_map(|view_ids| {

                view_ids

                    .iter()

                    .filter_map(|id| self.views.get(id).map(AsRef::as_ref))

            })

    }

    pub fn encryption_key_for_collection(&self, collection: &CollectionName) -> Option<&KeyId> {

        self.collection_encryption_keys.get(collection)

    }

    pub fn collections(&self) -> impl Iterator<Item = &CollectionName> {

        self.contained_collections.keys()

    }

    fn collection(&self) -> CollectionName {

        <<V as View>::Collection as Collection>::collection_name()

    }

    fn key_description(&self) -> KeyDescription {

        KeyDescription::for_key::<<V as View>::Key>()

    }

    fn update_policy(&self) -> ViewUpdatePolicy {

        self.schema.update_policy()

    }

    fn version(&self) -> u64 {

        self.schema.version()

    }

    fn view_name(&self) -> ViewName {

        self.view.view_name()

    }

    fn map(&self, document: &BorrowedDocument<'_>) -> Result<Vec<map::Serialized>, view::Error> {

        let mappings = self.schema.map(document)?;

        mappings

            .iter()

            .map(map::Map::serialized::<V>)

            .collect::<Result<_, _>>()

            .map_err(view::Error::key_serialization)

    }

    fn reduce(&self, mappings: &[(&[u8], &[u8])], rereduce: bool) -> Result<Vec<u8>, view::Error> {

        let mappings = mappings

            .iter()

            .map(|(key, value)| {

                match <S::MappedKey<'_> as Key>::from_ord_bytes(ByteSource::Borrowed(key)) {

                    Ok(key) => {

                        let value = V::deserialize(value)?;

                        Ok(MappedValue::new(key, value))

            })

            .collect::<Result<Vec<_>, view::Error>>()?;

        let reduced_value = self.schema.reduce(&mappings, rereduce)?;

        V::serialize(&reduced_value).map_err(view::Error::from)

    }

#[derive_where(Default, Debug)]

    fn next_id(&self, id: Option<DocumentId>) -> Result<DocumentId, Error> {

        let key = id.map(|id| id.deserialize::<C::PrimaryKey>()).transpose()?;

        let key = if let Some(key) = key {

            key

            <C::PrimaryKey as Key<'_>>::first_value()

                .map_err(|err| Error::DocumentPush(C::collection_name(), err))?

        let next_value = key

            .next_value()

            .map_err(|err| Error::DocumentPush(C::collection_name(), err))?;

        DocumentId::new(&next_value)

    }

#[test]

fn schema_tests() -> anyhow::Result<()> {

    let schema = Schematic::from_schema::<Basic>()?;

    assert_eq!(schema.collections_by_type_id.len(), 1);

    assert_eq!(

        schema.collections_by_type_id[&TypeId::of::<Basic>()],

        Basic::collection_name()

    );

    assert_eq!(schema.views.len(), 6);

    assert_eq!(

        schema.views[&TypeId::of::<BasicCount>()].view_name(),

        View::view_name(&BasicCount)

    );

    Ok(())

}