// Copyright 2024 The Drasi Authors.
//
// Licensed 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 crate::evaluation::functions::FunctionRegistry;
use crate::in_memory_index::in_memory_result_index::InMemoryResultIndex;
use async_trait::async_trait;
use once_cell::sync::Lazy;
use std::fmt::Formatter;
use std::sync::Arc;

use crate::evaluation::functions::LazyScalarFunction;
use crate::evaluation::variable_value::VariableValue;
use crate::evaluation::{
    ExpressionEvaluationContext, ExpressionEvaluator, FunctionError, FunctionEvaluationError,
};
use drasi_query_ast::ast::{self, Expression};

pub struct Reduce {
    evaluator: Lazy<ExpressionEvaluator>,
}

impl Default for Reduce {
    fn default() -> Self {
        Self::new()
    }
}

impl Reduce {
    pub fn new() -> Self {
        Reduce {
            evaluator: Lazy::new(|| {
                let function_registry = Arc::new(FunctionRegistry::new());
                let ari = Arc::new(InMemoryResultIndex::new());
                ExpressionEvaluator::new(function_registry, ari)
            }),
        }
    }
}

#[async_trait]
impl LazyScalarFunction for Reduce {
    async fn call(
        &self,
        context: &ExpressionEvaluationContext,
        expression: &ast::FunctionExpression,
        args: &Vec<ast::Expression>,
    ) -> Result<VariableValue, FunctionError> {
        if args.len() != 2 {
            return Err(FunctionError {
                function_name: expression.name.to_string(),
                error: FunctionEvaluationError::InvalidArgumentCount,
            });
        }

        let initializer = &args[0];
        let iterator = match &args[1] {
            Expression::IteratorExpression(i) => i,
            _ => {
                return Err(FunctionError {
                    function_name: expression.name.to_string(),
                    error: FunctionEvaluationError::InvalidArgument(1),
                })
            }
        };

        let (accumulator_name, accumulator) = match self
            .evaluator
            .evaluate_assignment(context, initializer)
            .await
        {
            Ok((name, value)) => (name, value),
            Err(e) => {
                return Err(FunctionError {
                    function_name: expression.name.to_string(),
                    error: e,
                })
            }
        };

        let mut query_variables = context.clone_variables(); //Retrieve the query variables from the global context
        query_variables.insert(accumulator_name.to_string().into(), accumulator);

        let context = ExpressionEvaluationContext::new(&query_variables, context.get_clock());
        let result = match self
            .evaluator
            .reduce_iterator_expression(&context, iterator, accumulator_name)
            .await
        {
            Ok(value) => value,
            Err(_e) => {
                return Err(FunctionError {
                    function_name: expression.name.to_string(),
                    error: FunctionEvaluationError::InvalidType {
                        expected: "Valid reduce expression".to_string(),
                    },
                })
            }
        };

        Ok(result)
    }
}

impl std::fmt::Debug for Reduce {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        write!(f, "Reduce")
    }
}
