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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// 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
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// 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 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)
}