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/* Copyright 2018 Mozilla Foundation
 *
 * 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::{BinaryReader, FromReader, OperatorsReader, Result};

/// Represents an initialization expression.
#[derive(Debug, Copy, Clone)]
pub struct ConstExpr<'a> {
    offset: usize,
    data: &'a [u8],
}

impl<'a> ConstExpr<'a> {
    /// Constructs a new `ConstExpr` from the given data and offset.
    pub fn new(data: &[u8], offset: usize) -> ConstExpr {
        ConstExpr { offset, data }
    }

    /// Gets a binary reader for the initialization expression.
    pub fn get_binary_reader(&self) -> BinaryReader<'a> {
        BinaryReader::new_with_offset(self.data, self.offset)
    }

    /// Gets an operators reader for the initialization expression.
    pub fn get_operators_reader(&self) -> OperatorsReader<'a> {
        OperatorsReader::new(self.get_binary_reader())
    }
}

impl<'a> FromReader<'a> for ConstExpr<'a> {
    fn from_reader(reader: &mut BinaryReader<'a>) -> Result<Self> {
        // FIXME(#188) ideally shouldn't need to skip here
        let reader = reader.skip(|r| r.skip_const_expr())?;
        Ok(ConstExpr::new(
            reader.remaining_buffer(),
            reader.original_position(),
        ))
    }
}