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//! Graphic segment definition and associated functions
use super::headers::{reserved_extension_hdr::ReservedExtensionHeader, NitfSegmentHeader};
use memmap2::{Mmap, MmapOptions};
use std::fmt::Display;
use std::io::SeekFrom::Start;
use std::{fs::File, io::Seek, ops::Deref};

#[derive(Debug)]
pub struct ReservedExtension {
    /// Header fields defined in module
    pub meta: ReservedExtensionHeader,
    /// Segment data, must define function interface for access
    pub data: Mmap,
    /// Byte offset of header start
    pub header_offset: u64,
    /// Byte size of header
    pub header_size: u32,
    /// Data byte offset
    pub data_offset: u64,
    /// Data size in bytes
    pub data_size: u64,
}

impl ReservedExtension {
    pub fn initialize(reader: &mut File, header_size: u32, data_size: u64) -> Self {
        let header_offset = reader.stream_position().unwrap();
        let header_size = header_size;
        let data_size = data_size;
        let data_offset = header_offset + header_size as u64;
        let meta = ReservedExtensionHeader::from_reader(reader);
        let mut memmap_opts = MmapOptions::new();
        let data = unsafe {
            memmap_opts
                .offset(data_offset)
                .len(data_size as usize)
                .map(reader.deref())
                .unwrap()
        };
        // Seek to end of data for next segment to be read
        reader.seek(Start(data_offset + data_size)).unwrap();
        Self {
            meta,
            data,
            header_offset,
            header_size,
            data_size,
            data_offset,
        }
    }
}
impl Display for ReservedExtension {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.meta)
    }
}