iceberg/spec/schema/

visitor.rs

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// to you 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
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use super::*;

/// A post order schema visitor.
///
/// For order of methods called, please refer to [`visit_schema`].
pub trait SchemaVisitor {
    /// Return type of this visitor.
    type T;

    /// Called before struct field.
    fn before_struct_field(&mut self, _field: &NestedFieldRef) -> Result<()> {
        Ok(())
    }
    /// Called after struct field.
    fn after_struct_field(&mut self, _field: &NestedFieldRef) -> Result<()> {
        Ok(())
    }
    /// Called before list field.
    fn before_list_element(&mut self, _field: &NestedFieldRef) -> Result<()> {
        Ok(())
    }
    /// Called after list field.
    fn after_list_element(&mut self, _field: &NestedFieldRef) -> Result<()> {
        Ok(())
    }
    /// Called before map key field.
    fn before_map_key(&mut self, _field: &NestedFieldRef) -> Result<()> {
        Ok(())
    }
    /// Called after map key field.
    fn after_map_key(&mut self, _field: &NestedFieldRef) -> Result<()> {
        Ok(())
    }
    /// Called before map value field.
    fn before_map_value(&mut self, _field: &NestedFieldRef) -> Result<()> {
        Ok(())
    }
    /// Called after map value field.
    fn after_map_value(&mut self, _field: &NestedFieldRef) -> Result<()> {
        Ok(())
    }

    /// Called after schema's type visited.
    fn schema(&mut self, schema: &Schema, value: Self::T) -> Result<Self::T>;
    /// Called after struct's field type visited.
    fn field(&mut self, field: &NestedFieldRef, value: Self::T) -> Result<Self::T>;
    /// Called after struct's fields visited.
    fn r#struct(&mut self, r#struct: &StructType, results: Vec<Self::T>) -> Result<Self::T>;
    /// Called after list fields visited.
    fn list(&mut self, list: &ListType, value: Self::T) -> Result<Self::T>;
    /// Called after map's key and value fields visited.
    fn map(&mut self, map: &MapType, key_value: Self::T, value: Self::T) -> Result<Self::T>;
    /// Called when see a primitive type.
    fn primitive(&mut self, p: &PrimitiveType) -> Result<Self::T>;
}

/// Visiting a type in post order.
pub(crate) fn visit_type<V: SchemaVisitor>(r#type: &Type, visitor: &mut V) -> Result<V::T> {
    match r#type {
        Type::Primitive(p) => visitor.primitive(p),
        Type::List(list) => {
            visitor.before_list_element(&list.element_field)?;
            let value = visit_type(&list.element_field.field_type, visitor)?;
            visitor.after_list_element(&list.element_field)?;
            visitor.list(list, value)
        }
        Type::Map(map) => {
            let key_result = {
                visitor.before_map_key(&map.key_field)?;
                let ret = visit_type(&map.key_field.field_type, visitor)?;
                visitor.after_map_key(&map.key_field)?;
                ret
            };

            let value_result = {
                visitor.before_map_value(&map.value_field)?;
                let ret = visit_type(&map.value_field.field_type, visitor)?;
                visitor.after_map_value(&map.value_field)?;
                ret
            };

            visitor.map(map, key_result, value_result)
        }
        Type::Struct(s) => visit_struct(s, visitor),
    }
}

/// Visit struct type in post order.
pub fn visit_struct<V: SchemaVisitor>(s: &StructType, visitor: &mut V) -> Result<V::T> {
    let mut results = Vec::with_capacity(s.fields().len());
    for field in s.fields() {
        visitor.before_struct_field(field)?;
        let result = visit_type(&field.field_type, visitor)?;
        visitor.after_struct_field(field)?;
        let result = visitor.field(field, result)?;
        results.push(result);
    }

    visitor.r#struct(s, results)
}

/// Visit schema in post order.
pub fn visit_schema<V: SchemaVisitor>(schema: &Schema, visitor: &mut V) -> Result<V::T> {
    let result = visit_struct(&schema.r#struct, visitor)?;
    visitor.schema(schema, result)
}

/// A post order schema visitor with partner.
///
/// For order of methods called, please refer to [`visit_schema_with_partner`].
pub trait SchemaWithPartnerVisitor<P> {
    /// Return type of this visitor.
    type T;

    /// Called before struct field.
    fn before_struct_field(&mut self, _field: &NestedFieldRef, _partner: &P) -> Result<()> {
        Ok(())
    }
    /// Called after struct field.
    fn after_struct_field(&mut self, _field: &NestedFieldRef, _partner: &P) -> Result<()> {
        Ok(())
    }
    /// Called before list field.
    fn before_list_element(&mut self, _field: &NestedFieldRef, _partner: &P) -> Result<()> {
        Ok(())
    }
    /// Called after list field.
    fn after_list_element(&mut self, _field: &NestedFieldRef, _partner: &P) -> Result<()> {
        Ok(())
    }
    /// Called before map key field.
    fn before_map_key(&mut self, _field: &NestedFieldRef, _partner: &P) -> Result<()> {
        Ok(())
    }
    /// Called after map key field.
    fn after_map_key(&mut self, _field: &NestedFieldRef, _partner: &P) -> Result<()> {
        Ok(())
    }
    /// Called before map value field.
    fn before_map_value(&mut self, _field: &NestedFieldRef, _partner: &P) -> Result<()> {
        Ok(())
    }
    /// Called after map value field.
    fn after_map_value(&mut self, _field: &NestedFieldRef, _partner: &P) -> Result<()> {
        Ok(())
    }

    /// Called after schema's type visited.
    fn schema(&mut self, schema: &Schema, partner: &P, value: Self::T) -> Result<Self::T>;
    /// Called after struct's field type visited.
    fn field(&mut self, field: &NestedFieldRef, partner: &P, value: Self::T) -> Result<Self::T>;
    /// Called after struct's fields visited.
    fn r#struct(
        &mut self,
        r#struct: &StructType,
        partner: &P,
        results: Vec<Self::T>,
    ) -> Result<Self::T>;
    /// Called after list fields visited.
    fn list(&mut self, list: &ListType, partner: &P, value: Self::T) -> Result<Self::T>;
    /// Called after map's key and value fields visited.
    fn map(
        &mut self,
        map: &MapType,
        partner: &P,
        key_value: Self::T,
        value: Self::T,
    ) -> Result<Self::T>;
    /// Called when see a primitive type.
    fn primitive(&mut self, p: &PrimitiveType, partner: &P) -> Result<Self::T>;
}

/// Accessor used to get child partner from parent partner.
pub trait PartnerAccessor<P> {
    /// Get the struct partner from schema partner.
    fn struct_partner<'a>(&self, schema_partner: &'a P) -> Result<&'a P>;
    /// Get the field partner from struct partner.
    fn field_partner<'a>(&self, struct_partner: &'a P, field: &NestedField) -> Result<&'a P>;
    /// Get the list element partner from list partner.
    fn list_element_partner<'a>(&self, list_partner: &'a P) -> Result<&'a P>;
    /// Get the map key partner from map partner.
    fn map_key_partner<'a>(&self, map_partner: &'a P) -> Result<&'a P>;
    /// Get the map value partner from map partner.
    fn map_value_partner<'a>(&self, map_partner: &'a P) -> Result<&'a P>;
}

/// Visiting a type in post order.
pub(crate) fn visit_type_with_partner<P, V: SchemaWithPartnerVisitor<P>, A: PartnerAccessor<P>>(
    r#type: &Type,
    partner: &P,
    visitor: &mut V,
    accessor: &A,
) -> Result<V::T> {
    match r#type {
        Type::Primitive(p) => visitor.primitive(p, partner),
        Type::List(list) => {
            let list_element_partner = accessor.list_element_partner(partner)?;
            visitor.before_list_element(&list.element_field, list_element_partner)?;
            let element_results = visit_type_with_partner(
                &list.element_field.field_type,
                list_element_partner,
                visitor,
                accessor,
            )?;
            visitor.after_list_element(&list.element_field, list_element_partner)?;
            visitor.list(list, partner, element_results)
        }
        Type::Map(map) => {
            let key_partner = accessor.map_key_partner(partner)?;
            visitor.before_map_key(&map.key_field, key_partner)?;
            let key_result =
                visit_type_with_partner(&map.key_field.field_type, key_partner, visitor, accessor)?;
            visitor.after_map_key(&map.key_field, key_partner)?;

            let value_partner = accessor.map_value_partner(partner)?;
            visitor.before_map_value(&map.value_field, value_partner)?;
            let value_result = visit_type_with_partner(
                &map.value_field.field_type,
                value_partner,
                visitor,
                accessor,
            )?;
            visitor.after_map_value(&map.value_field, value_partner)?;

            visitor.map(map, partner, key_result, value_result)
        }
        Type::Struct(s) => visit_struct_with_partner(s, partner, visitor, accessor),
    }
}

/// Visit struct type in post order.
pub fn visit_struct_with_partner<P, V: SchemaWithPartnerVisitor<P>, A: PartnerAccessor<P>>(
    s: &StructType,
    partner: &P,
    visitor: &mut V,
    accessor: &A,
) -> Result<V::T> {
    let mut results = Vec::with_capacity(s.fields().len());
    for field in s.fields() {
        let field_partner = accessor.field_partner(partner, field)?;
        visitor.before_struct_field(field, field_partner)?;
        let result = visit_type_with_partner(&field.field_type, field_partner, visitor, accessor)?;
        visitor.after_struct_field(field, field_partner)?;
        let result = visitor.field(field, field_partner, result)?;
        results.push(result);
    }

    visitor.r#struct(s, partner, results)
}

/// Visit schema in post order.
pub fn visit_schema_with_partner<P, V: SchemaWithPartnerVisitor<P>, A: PartnerAccessor<P>>(
    schema: &Schema,
    partner: &P,
    visitor: &mut V,
    accessor: &A,
) -> Result<V::T> {
    let result = visit_struct_with_partner(
        &schema.r#struct,
        accessor.struct_partner(partner)?,
        visitor,
        accessor,
    )?;
    visitor.schema(schema, partner, result)
}