//! types for working with raw big-endian bytes

/// A trait for font scalars.
///
/// This is an internal trait for encoding and decoding big-endian bytes.
///
/// You do not need to implement this trait directly; it is an implemention
/// detail of the [`BigEndian`] wrapper.
pub trait Scalar {
    /// The raw byte representation of this type.
    type Raw: Copy + AsRef<[u8]>;

    /// Create an instance of this type from raw big-endian bytes
    fn from_raw(raw: Self::Raw) -> Self;
    /// Encode this type as raw big-endian bytes
    fn to_raw(self) -> Self::Raw;
}

/// A trait for types that have a known, constant size.
pub trait FixedSize: Sized {
    /// The raw size of this type, in bytes.
    ///
    /// This is the size required to represent this type in a font file, which
    /// may differ from the size of the native type:
    ///
    /// ```
    /// # use font_types::{FixedSize, Offset24};
    /// assert_eq!(std::mem::size_of::<u16>(), u16::RAW_BYTE_LEN);
    /// assert_eq!(Offset24::RAW_BYTE_LEN, 3);
    /// assert_eq!(std::mem::size_of::<Offset24>(), 4);
    /// ```
    const RAW_BYTE_LEN: usize;
}

/// A trait for types that can be read from raw bytes.
///
/// This is a generalization that gives us a failable read method for all our
/// `Scalar` types, as well as their `BigEndian` representations.
///
/// You should not need to implement this trait; it is provided automatically
/// when you implement [`Scalar`].
pub trait ReadScalar: FixedSize {
    /// Interpret the provided bytes as `Self`, if they are the right length.
    ///
    /// This should use all the provided bytes; bounds checking is performed upstream.
    fn read(bytes: &[u8]) -> Option<Self>;
}

/// A wrapper around raw big-endian bytes for some type.
#[derive(Clone, Copy, PartialEq, Eq)]
#[repr(transparent)]
pub struct BigEndian<T: Scalar>(pub(crate) T::Raw);

impl<T: Scalar> BigEndian<T> {
    /// construct a new `BigEndian<T>` from raw bytes
    pub fn new(raw: T::Raw) -> BigEndian<T> {
        BigEndian(raw)
    }
    /// Read a copy of this type from raw bytes.
    pub fn get(&self) -> T {
        T::from_raw(self.0)
    }

    /// Set the value, overwriting the bytes.
    pub fn set(&mut self, value: T) {
        self.0 = value.to_raw();
    }

    /// Get the raw big-endian bytes.
    pub fn be_bytes(&self) -> &[u8] {
        self.0.as_ref()
    }
}

impl<T: Scalar> From<T> for BigEndian<T> {
    #[inline]
    fn from(val: T) -> Self {
        BigEndian(val.to_raw())
    }
}

impl<T: Scalar + Default> Default for BigEndian<T> {
    fn default() -> Self {
        Self::from(T::default())
    }
}

impl<T: Scalar + Copy + PartialEq> PartialEq<T> for BigEndian<T> {
    fn eq(&self, other: &T) -> bool {
        self.get() == *other
    }
}

// these following impls are an elaborate way to impl ReadScalar for BigEndian<T>
impl<const N: usize> FixedSize for [u8; N] {
    const RAW_BYTE_LEN: usize = N;
}

impl<const N: usize> ReadScalar for [u8; N] {
    #[inline]
    fn read(bytes: &[u8]) -> Option<Self> {
        bytes.try_into().ok()
    }
}

impl<T> ReadScalar for BigEndian<T>
where
    T: Scalar + FixedSize,
    <T as Scalar>::Raw: ReadScalar,
{
    #[inline]
    fn read(bytes: &[u8]) -> Option<Self> {
        T::Raw::read(bytes).map(BigEndian)
    }
}

// and then we can impl ReadScalar for T based on the impl for BigEndian<T>
impl<T> ReadScalar for T
where
    T: Scalar + FixedSize,
    <T as Scalar>::Raw: ReadScalar,
{
    #[inline]
    fn read(bytes: &[u8]) -> Option<Self> {
        BigEndian::<T>::read(bytes).as_ref().map(BigEndian::get)
    }
}

// and impl FixedSized for T based on the impl for the arrays
impl<T> FixedSize for T
where
    T: Scalar,
    <T as Scalar>::Raw: FixedSize,
{
    const RAW_BYTE_LEN: usize = <T as Scalar>::Raw::RAW_BYTE_LEN;
}

// and impl FixedSized for BigEndian<T> based on the impl forr T
impl<T: Scalar + FixedSize> FixedSize for BigEndian<T> {
    const RAW_BYTE_LEN: usize = T::RAW_BYTE_LEN;
}

/// An internal macro for implementing the `RawType` trait.
#[macro_export]
macro_rules! newtype_scalar {
    ($ty:ident, $raw:ty) => {
        impl $crate::raw::Scalar for $ty {
            type Raw = $raw;
            fn to_raw(self) -> $raw {
                self.0.to_raw()
            }

            fn from_raw(raw: $raw) -> Self {
                Self($crate::raw::Scalar::from_raw(raw))
            }
        }
    };
}

macro_rules! int_scalar {
    ($ty:ty, $raw:ty) => {
        impl crate::raw::Scalar for $ty {
            type Raw = $raw;
            fn to_raw(self) -> $raw {
                self.to_be_bytes()
            }

            fn from_raw(raw: $raw) -> $ty {
                Self::from_be_bytes(raw)
            }
        }
    };
}

int_scalar!(u8, [u8; 1]);
int_scalar!(i8, [u8; 1]);
int_scalar!(u16, [u8; 2]);
int_scalar!(i16, [u8; 2]);
int_scalar!(u32, [u8; 4]);
int_scalar!(i32, [u8; 4]);
int_scalar!(i64, [u8; 8]);
int_scalar!(crate::Uint24, [u8; 3]);

impl<T: std::fmt::Debug + Scalar + Copy> std::fmt::Debug for BigEndian<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        self.get().fmt(f)
    }
}

impl<T: std::fmt::Display + Scalar + Copy> std::fmt::Display for BigEndian<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        self.get().fmt(f)
    }
}