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use std::io::{Read, Seek, SeekFrom};

use Result;

/// A type that can read.
pub trait Tape: Read + Seek + Sized {
    /// Read a value.
    #[inline(always)]
    fn take<T: Value>(&mut self) -> Result<T> {
        Value::read(self)
    }

    /// Read a value given a parameter.
    #[inline(always)]
    fn take_given<'l, T: Walue<'l>>(&mut self, parameter: T::Parameter) -> Result<T> {
        Walue::read(self, parameter)
    }

    #[doc(hidden)]
    #[inline]
    fn jump(&mut self, position: u64) -> Result<u64> {
        self.seek(SeekFrom::Start(position))
    }

    #[doc(hidden)]
    #[inline]
    fn peek<T: Value>(&mut self) -> Result<T> {
        self.stay(|tape| Value::read(tape))
    }

    #[doc(hidden)]
    #[inline]
    fn position(&mut self) -> Result<u64> {
        self.seek(SeekFrom::Current(0))
    }

    #[doc(hidden)]
    fn stay<F, T>(&mut self, mut body: F) -> Result<T>
    where
        F: FnMut(&mut Self) -> Result<T>,
    {
        let position = self.position()?;
        let result = body(self);
        self.jump(position)?;
        result
    }

    #[doc(hidden)]
    #[inline(always)]
    fn take_bytes(&mut self, count: usize) -> Result<Vec<u8>> {
        let mut buffer = Vec::with_capacity(count);
        unsafe { buffer.set_len(count) };
        self.read_exact(&mut buffer)?;
        Ok(buffer)
    }
}

/// A type that can be read.
pub trait Value: Sized {
    /// Read a value.
    fn read<T: Tape>(&mut T) -> Result<Self>;
}

/// A type that can be read given a parameter.
pub trait Walue<'l>: Sized {
    /// The parameter type.
    type Parameter;

    /// Read a value.
    fn read<T: Tape>(&mut T, Self::Parameter) -> Result<Self>;
}

impl<T: Read + Seek> Tape for T {}

macro_rules! read(
    ($tape:ident, $size:expr) => (unsafe {
        let mut buffer: [u8; $size] = ::std::mem::uninitialized();
        ::std::io::Read::read_exact($tape, &mut buffer)?;
        ::std::mem::transmute(buffer)
    });
);

macro_rules! value {
    ([$kind:ident; $count:expr], 1) => (
        impl Value for [$kind; $count] {
            fn read<T: Tape>(tape: &mut T) -> Result<Self> {
                Ok(read!(tape, $count))
            }
        }
    );
    ($kind:ident, 1) => (
        impl Value for $kind {
            #[inline]
            fn read<T: Tape>(tape: &mut T) -> Result<Self> {
                Ok(read!(tape, 1))
            }
        }
    );
    ($kind:ident, $size:expr) => (
        impl Value for $kind {
            #[inline]
            fn read<T: Tape>(tape: &mut T) -> Result<Self> {
                Ok($kind::from_be(read!(tape, $size)))
            }
        }
    );
}

value!(i8, 1);
value!(u8, 1);
value!(i16, 2);
value!(u16, 2);
value!(u32, 4);
value!(i64, 8);
value!([u8; 3], 1);
value!([i8; 4], 1);
value!([u8; 4], 1);
value!([u8; 10], 1);

impl<V> Walue<'static> for Vec<V>
where
    V: Value,
{
    type Parameter = usize;

    fn read<T: Tape>(tape: &mut T, count: usize) -> Result<Self> {
        let mut values = Vec::with_capacity(count);
        for _ in 0..count {
            values.push(Value::read(tape)?);
        }
        Ok(values)
    }
}