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// Copyright (C) 2019-2020 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/>.

//! Enforces array access in a compiled Leo program.

use crate::{errors::ExpressionError, program::ConstrainedProgram, value::ConstrainedValue, GroupType};
use leo_typed::{Expression, RangeOrExpression, Span, Type};

use snarkos_models::{
    curves::{Field, PrimeField},
    gadgets::r1cs::ConstraintSystem,
};

impl<F: Field + PrimeField, G: GroupType<F>> ConstrainedProgram<F, G> {
    pub fn enforce_array_access<CS: ConstraintSystem<F>>(
        &mut self,
        cs: &mut CS,
        file_scope: String,
        function_scope: String,
        expected_type: Option<Type>,
        array: Box<Expression>,
        index: RangeOrExpression,
        span: Span,
    ) -> Result<ConstrainedValue<F, G>, ExpressionError> {
        let array = match self.enforce_operand(
            cs,
            file_scope.clone(),
            function_scope.clone(),
            expected_type,
            *array,
            span.clone(),
        )? {
            ConstrainedValue::Array(array) => array,
            value => return Err(ExpressionError::undefined_array(value.to_string(), span)),
        };

        match index {
            RangeOrExpression::Range(from, to) => {
                let from_resolved = match from {
                    Some(from_index) => {
                        self.enforce_index(cs, file_scope.clone(), function_scope.clone(), from_index, span.clone())?
                    }
                    None => 0usize, // Array slice starts at index 0
                };
                let to_resolved = match to {
                    Some(to_index) => {
                        self.enforce_index(cs, file_scope.clone(), function_scope.clone(), to_index, span.clone())?
                    }
                    None => array.len(), // Array slice ends at array length
                };
                Ok(ConstrainedValue::Array(array[from_resolved..to_resolved].to_owned()))
            }
            RangeOrExpression::Expression(index) => {
                let index_resolved = self.enforce_index(cs, file_scope, function_scope, index, span)?;
                Ok(array[index_resolved].to_owned())
            }
        }
    }
}