use std::cmp;
use std::io::prelude::*;
use std::io::SeekFrom;
use std::io;

use fs::FatFileSystem;

#[allow(dead_code)]
pub struct FatFile {
    first_sector: u32,
    size: u32,
    offset: u32,
}

impl FatFile {
    pub fn new(first_sector: u32, size: u32) -> FatFile {
        FatFile { first_sector, size, offset: 0 }
    }
}

impl<T: Read+Seek> FatFileSystem<T> {
    
    pub fn file_from_cluster(&mut self, cluster: u32, size: u32) -> FatFile {
        FatFile {
            first_sector: self.sector_from_cluster(cluster),
            size: size,
            offset: 0,
        }
    }
    
    pub fn read(&mut self, file: &mut FatFile, buf: &mut [u8]) -> io::Result<usize> {
        let offset = self.offset_from_sector(file.first_sector) + file.offset as u64;
        let mut read_size = cmp::min((file.size - file.offset) as usize, buf.len());
        // FIXME: allow only one cluster for now
        read_size = cmp::min(read_size, (self.get_cluster_size() - file.offset) as usize);
        self.rdr.seek(SeekFrom::Start(offset))?;
        let size = self.rdr.read(&mut buf[..read_size])?;
        file.offset += size as u32;
        Ok(size)
    }
}