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use std::mem::size_of;
use std::io::{Read, Write};
use std::fs::File;
use std::slice;

pub trait IOExt : Read + Write {
    fn write_copy<T : Copy>(&mut self, t: &T) -> std::io::Result<()> {
        let buffer = unsafe {
            slice::from_raw_parts(t as *const T as *const u8, size_of::<T>())
        };
        self.write(buffer)?;
        Ok(())
    }

    fn read_copy<T : Copy>(&mut self) ->  std::io::Result<T> {
        let mut t : T = unsafe { std::mem::uninitialized() };
        let mut buffer = unsafe {
            slice::from_raw_parts_mut(&mut t as *mut T as *mut u8, size_of::<T>())
        };
        self.read_exact(buffer)?;
        Ok(t)
    }

    fn write_str(&mut self, s: &str) -> std::io::Result<()> {
        let bytes = s.as_bytes();
        self.write_copy(&s.len())?;
        self.write(bytes)?;
        Ok(())
    }

    fn read_str(&mut self) -> std::io::Result<String> {
        let mut buffer = vec![0u8; self.read_copy::<usize>()?];
        self.read_exact(&mut buffer)?;
        Ok(String::from_utf8(buffer).unwrap())
    }

    fn write_slice<T : Copy>(&mut self, ts : &[T]) -> std::io::Result<()> {
        let size = ts.len();
        let buffer = unsafe {
            slice::from_raw_parts(ts.as_ptr() as *const u8, size * size_of::<T>())
        };
        self.write_copy(&size)?;
        self.write(buffer)?;
        Ok(())
    }

    fn read_slice<T : Copy>(&mut self) -> std::io::Result<Vec<T>> {
        let size = self.read_copy::<usize>()?;
        unsafe {
            let mut ts = vec![std::mem::uninitialized::<T>(); size];
            let mut buffer = slice::from_raw_parts_mut(
                ts.as_mut_ptr() as *mut u8, size * size_of::<T>()
            );
            self.read(buffer)?;
            Ok(ts)
        }
    }
}

impl IOExt for File {}

#[cfg(test)]
mod tests {
    use std::mem::size_of;
    use std::fs::{File, remove_file};
    use std::io::Write;
    use ::IOExt;

    // Why so many 42??? BECAUSE
    const FILE_PATH : &str = "test.txt";
    const A : i32 = -4242;
    const B : f64 = 42.42;
    const C : u8 = 42;
    const D : &str = "42";
    const E : &[f64] = &[2.6125, 5.25, 10.5, 21.0, 42.0];

    #[test]
    fn write_read() {
        println!("Creating the file");
        let mut f = File::create(FILE_PATH).expect("Create file");

        println!("Write started");
        write(&mut f);
        f.flush().expect("Flush the file");
        println!("Write ended");

        let mut f = File::open(FILE_PATH).expect("Reopening the file");

        println!("Read started");
        read(&mut f);
        println!("Read ended");

        remove_file(FILE_PATH).expect("Delete file");
    }

    fn write(f : &mut File) {
        // Write copy test
        f.write_copy(&A).expect("A");
        f.write_copy(&B).expect("B");
        f.write_copy(&C).expect("C");

        // Write str test
        f.write_str(D).expect("D");

        // Write slices test
        f.write_slice(E).expect("E");
    }

    fn read(f : &mut File) {
        // Read copy
        assert_eq!(f.read_copy::<i32>().expect("A"), A);
        assert_eq!(f.read_copy::<f64>().expect("B"), B);
        assert_eq!(f.read_copy::<u8>().expect("C"), C);

        // Read str
        assert_eq!(&f.read_str().expect("D"), D);

        // Read slices
        assert_eq!(f.read_slice::<f64>().expect("E").as_slice(), E);
    }
}