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// Copyright (C) 2019-2024 Aleo Systems Inc.
// This file is part of the Leo library.

// The Leo library is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// The Leo library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with the Leo library. If not, see <https://www.gnu.org/licenses/>.

use crate::DeadCodeEliminator;

use leo_ast::{
    AccessExpression,
    AssociatedFunction,
    Expression,
    ExpressionReconstructor,
    Identifier,
    StructExpression,
    StructVariableInitializer,
};
use leo_span::sym;

impl ExpressionReconstructor for DeadCodeEliminator<'_> {
    type AdditionalOutput = ();

    /// Reconstructs the associated function access expression.
    fn reconstruct_associated_function(&mut self, input: AssociatedFunction) -> (Expression, Self::AdditionalOutput) {
        // If the associated function manipulates a mapping, mark the statement as necessary.
        match (&input.variant.name, input.name.name) {
            (&sym::Mapping, sym::remove) | (&sym::Mapping, sym::set) | (&sym::Future, sym::Await) => {
                self.is_necessary = true;
            }
            _ => {}
        };
        // Reconstruct the access expression.
        let result = (
            Expression::Access(AccessExpression::AssociatedFunction(AssociatedFunction {
                variant: input.variant,
                name: input.name,
                arguments: input.arguments.into_iter().map(|arg| self.reconstruct_expression(arg).0).collect(),
                span: input.span,
                id: input.id,
            })),
            Default::default(),
        );
        // Unset `self.is_necessary`.
        self.is_necessary = false;
        result
    }

    /// Reconstruct the components of the struct init expression.
    /// This is necessary since the reconstructor does not explicitly visit each component of the expression.
    fn reconstruct_struct_init(&mut self, input: StructExpression) -> (Expression, Self::AdditionalOutput) {
        (
            Expression::Struct(StructExpression {
                name: input.name,
                // Reconstruct each of the struct members.
                members: input
                    .members
                    .into_iter()
                    .map(|member| StructVariableInitializer {
                        identifier: member.identifier,
                        expression: match member.expression {
                            Some(expression) => Some(self.reconstruct_expression(expression).0),
                            None => unreachable!("Static single assignment ensures that the expression always exists."),
                        },
                        span: member.span,
                        id: member.id,
                    })
                    .collect(),
                span: input.span,
                id: input.id,
            }),
            Default::default(),
        )
    }

    /// Marks identifiers as used.
    /// This is necessary to determine which statements can be eliminated from the program.
    fn reconstruct_identifier(&mut self, input: Identifier) -> (Expression, Self::AdditionalOutput) {
        // Add the identifier to `self.used_variables`.
        if self.is_necessary {
            self.used_variables.insert(input.name);
        }
        // Return the identifier as is.
        (Expression::Identifier(input), Default::default())
    }
}