use core::num::{NonZeroU16, NonZeroU32, NonZeroU8, NonZeroUsize};

/// Types implementing this trait can be used as keys for all Rodeos
///
/// # Safety
///
/// into/from must be perfectly symmetrical, any key that goes on must be perfectly reproduced with the other
///
/// [`ReadOnlyLasso`]: crate::ReadOnlyLasso
pub unsafe trait Key: Copy + Eq {
    /// Returns the `usize` that represents the current key
    fn into_usize(self) -> usize;

    /// Attempts to create a key from a `usize`, returning `None` if it fails
    fn try_from_usize(int: usize) -> Option<Self>;
}

/// A key type taking up `size_of::<usize>()` bytes of space (generally 4 or 8 bytes)
///
/// Internally is a `NonZeroUsize` to allow for space optimizations when stored inside of an [`Option`]
///
/// [`ReadOnlyLasso`]: crate::ReadOnlyLasso
/// [`Option`]: https://doc.rust-lang.org/std/option/enum.Option.html
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
pub struct LargeSpur {
    key: NonZeroUsize,
}

unsafe impl Key for LargeSpur {
    #[cfg_attr(feature = "inline-more", inline)]
    fn into_usize(self) -> usize {
        self.key.get() - 1
    }

    /// Returns `None` if `int` is greater than `usize::MAX - 1`
    #[cfg_attr(feature = "inline-more", inline)]
    fn try_from_usize(int: usize) -> Option<Self> {
        if int < usize::max_value() {
            // Safety: The integer is less than the max value and then incremented by one, meaning that
            // is is impossible for a zero to inhabit the NonZeroUsize
            unsafe {
                Some(Self {
                    key: NonZeroUsize::new_unchecked(int + 1),
                })
            }
        } else {
            None
        }
    }
}

impl Default for LargeSpur {
    #[cfg_attr(feature = "inline-more", inline)]
    fn default() -> Self {
        Self::try_from_usize(0).unwrap()
    }
}

/// The default key for every Rodeo, uses only 32 bits of space
///
/// Internally is a `NonZeroU32` to allow for space optimizations when stored inside of an [`Option`]
///
/// [`ReadOnlyLasso`]: crate::ReadOnlyLasso
/// [`Option`]: https://doc.rust-lang.org/std/option/enum.Option.html
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
pub struct Spur {
    key: NonZeroU32,
}

unsafe impl Key for Spur {
    #[cfg_attr(feature = "inline-more", inline)]
    fn into_usize(self) -> usize {
        self.key.get() as usize - 1
    }

    /// Returns `None` if `int` is greater than `u32::MAX - 1`
    #[cfg_attr(feature = "inline-more", inline)]
    fn try_from_usize(int: usize) -> Option<Self> {
        if int < u32::max_value() as usize {
            // Safety: The integer is less than the max value and then incremented by one, meaning that
            // is is impossible for a zero to inhabit the NonZeroU32
            unsafe {
                Some(Self {
                    key: NonZeroU32::new_unchecked(int as u32 + 1),
                })
            }
        } else {
            None
        }
    }
}

impl Default for Spur {
    #[cfg_attr(feature = "inline-more", inline)]
    fn default() -> Self {
        Self::try_from_usize(0).unwrap()
    }
}

/// A miniature Key utilizing only 16 bits of space
///
/// Internally is a `NonZeroU16` to allow for space optimizations when stored inside of an [`Option`]
///
/// [`ReadOnlyLasso`]: crate::ReadOnlyLasso
/// [`Option`]: https://doc.rust-lang.org/std/option/enum.Option.html
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
pub struct MiniSpur {
    key: NonZeroU16,
}

unsafe impl Key for MiniSpur {
    #[cfg_attr(feature = "inline-more", inline)]
    fn into_usize(self) -> usize {
        self.key.get() as usize - 1
    }

    /// Returns `None` if `int` is greater than `u16::MAX - 1`
    #[cfg_attr(feature = "inline-more", inline)]
    fn try_from_usize(int: usize) -> Option<Self> {
        if int < u16::max_value() as usize {
            // Safety: The integer is less than the max value and then incremented by one, meaning that
            // is is impossible for a zero to inhabit the NonZeroU16
            unsafe {
                Some(Self {
                    key: NonZeroU16::new_unchecked(int as u16 + 1),
                })
            }
        } else {
            None
        }
    }
}

impl Default for MiniSpur {
    #[cfg_attr(feature = "inline-more", inline)]
    fn default() -> Self {
        Self::try_from_usize(0).unwrap()
    }
}

/// A miniature Key utilizing only 8 bits of space
///
/// Internally is a `NonZeroU8` to allow for space optimizations when stored inside of an [`Option`]
///
/// [`ReadOnlyLasso`]: crate::ReadOnlyLasso
/// [`Option`]: https://doc.rust-lang.org/std/option/enum.Option.html
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
pub struct MicroSpur {
    key: NonZeroU8,
}

unsafe impl Key for MicroSpur {
    #[cfg_attr(feature = "inline-more", inline)]
    fn into_usize(self) -> usize {
        self.key.get() as usize - 1
    }

    /// Returns `None` if `int` is greater than `u8::MAX - 1`
    #[cfg_attr(feature = "inline-more", inline)]
    fn try_from_usize(int: usize) -> Option<Self> {
        if int < u8::max_value() as usize {
            // Safety: The integer is less than the max value and then incremented by one, meaning that
            // is is impossible for a zero to inhabit the NonZeroU8
            unsafe {
                Some(Self {
                    key: NonZeroU8::new_unchecked(int as u8 + 1),
                })
            }
        } else {
            None
        }
    }
}

impl Default for MicroSpur {
    #[cfg_attr(feature = "inline-more", inline)]
    fn default() -> Self {
        Self::try_from_usize(0).unwrap()
    }
}

macro_rules! impl_serde {
    ($($key:ident => $ty:ident),* $(,)?) => {
        #[cfg(feature = "serialize")]
        mod __serde {
            use super::{$($key),*};
            use serde::{
                de::{Deserialize, Deserializer},
                ser::{Serialize, Serializer},
            };
            use core::num::{$($ty),*};

            $(
                impl Serialize for $key {
                    #[cfg_attr(feature = "inline-more", inline)]
                    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
                    where
                        S: Serializer,
                    {
                        self.key.serialize(serializer)
                    }
                }

                impl<'de> Deserialize<'de> for $key {
                    #[cfg_attr(feature = "inline-more", inline)]
                    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
                    where
                        D: Deserializer<'de>,
                    {
                        let key = <$ty>::deserialize(deserializer)?;
                        Ok(Self { key })
                    }
                }
            )*
        }
    };
}

// Implement `Serialize` and `Deserialize` when the `serde` feature is enabled
impl_serde! {
    Spur => NonZeroU32,
    MiniSpur => NonZeroU16,
    MicroSpur => NonZeroU8,
    LargeSpur => NonZeroUsize,
}

macro_rules! impl_deepsize {
    ($($type:ident),* $(,)?) => {
        #[cfg(feature = "deepsize")]
        mod __deepsize {
            use super::{$($type),*};
            #[cfg(test)]
            use super::Key;
            use deepsize::{DeepSizeOf, Context};
            use core::mem;

            $(
                impl DeepSizeOf for $type {
                    fn deep_size_of_children(&self, _context: &mut Context) -> usize {
                        0
                    }

                    fn deep_size_of(&self) -> usize {
                        mem::size_of::<$type>()
                    }
                }
            )*

            #[test]
            fn deepsize_implementations() {
                $(
                    assert_eq!(
                        mem::size_of::<$type>(),
                        $type::try_from_usize(0).unwrap().deep_size_of(),
                    );
                )*
            }
        }
    };
}

// Implement `DeepSizeOf` when the `deepsize` feature is enabled
impl_deepsize! {
    Spur,
    MiniSpur,
    MicroSpur,
    LargeSpur,
}

macro_rules! impl_abomonation {
    ($($type:ident),* $(,)?) => {
        #[cfg(all(feature = "abomonation", not(feature = "no-std")))]
        mod __abomonation {
            use super::{$($type),*};
            #[cfg(test)]
            use super::Key;
            use abomonation::Abomonation;
            use std::io::{self, Write};

            $(
                impl Abomonation for $type {
                    unsafe fn entomb<W: Write>(&self, write: &mut W) -> io::Result<()> {
                        self.key.entomb(write)
                    }

                    unsafe fn exhume<'a, 'b>(&'a mut self, bytes: &'b mut [u8]) -> Option<&'b mut [u8]> {
                        self.key.exhume(bytes)
                    }

                    fn extent(&self) -> usize {
                        self.key.extent()
                    }
                }
            )*

            #[test]
            fn abomonation_implementations() {
                let mut buf = Vec::new();

                $(
                    unsafe {
                        let base = $type::try_from_usize(0).unwrap();

                        abomonation::encode(&base, &mut buf).unwrap();
                        assert_eq!(base, *abomonation::decode(&mut buf [..]).unwrap().0);
                    }

                    buf.clear();
                )*
            }
        }
    };
}

// Implement `Abomonation` when the `abomonation` feature is enabled
impl_abomonation! {
    Spur,
    MiniSpur,
    MicroSpur,
    LargeSpur,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn large() {
        let zero = LargeSpur::try_from_usize(0).unwrap();
        let max = LargeSpur::try_from_usize(usize::max_value() - 1).unwrap();
        let default = LargeSpur::default();

        assert_eq!(zero.into_usize(), 0);
        assert_eq!(max.into_usize(), usize::max_value() - 1);
        assert_eq!(default.into_usize(), 0);
    }

    #[test]
    fn large_max_returns_none() {
        assert_eq!(None, LargeSpur::try_from_usize(usize::max_value()));
    }

    #[test]
    #[should_panic]
    #[cfg(not(miri))]
    fn large_max_panics() {
        LargeSpur::try_from_usize(usize::max_value()).unwrap();
    }

    #[test]
    fn spur() {
        let zero = Spur::try_from_usize(0).unwrap();
        let max = Spur::try_from_usize(u32::max_value() as usize - 1).unwrap();
        let default = Spur::default();

        assert_eq!(zero.into_usize(), 0);
        assert_eq!(max.into_usize(), u32::max_value() as usize - 1);
        assert_eq!(default.into_usize(), 0);
    }

    #[test]
    fn spur_returns_none() {
        assert_eq!(None, Spur::try_from_usize(u32::max_value() as usize));
    }

    #[test]
    #[should_panic]
    #[cfg(not(miri))]
    fn spur_panics() {
        Spur::try_from_usize(u32::max_value() as usize).unwrap();
    }

    #[test]
    fn mini() {
        let zero = MiniSpur::try_from_usize(0).unwrap();
        let max = MiniSpur::try_from_usize(u16::max_value() as usize - 1).unwrap();
        let default = MiniSpur::default();

        assert_eq!(zero.into_usize(), 0);
        assert_eq!(max.into_usize(), u16::max_value() as usize - 1);
        assert_eq!(default.into_usize(), 0);
    }

    #[test]
    fn mini_returns_none() {
        assert_eq!(None, MiniSpur::try_from_usize(u16::max_value() as usize));
    }

    #[test]
    #[should_panic]
    #[cfg(not(miri))]
    fn mini_panics() {
        MiniSpur::try_from_usize(u16::max_value() as usize).unwrap();
    }

    #[test]
    fn micro() {
        let zero = MicroSpur::try_from_usize(0).unwrap();
        let max = MicroSpur::try_from_usize(u8::max_value() as usize - 1).unwrap();
        let default = MicroSpur::default();

        assert_eq!(zero.into_usize(), 0);
        assert_eq!(max.into_usize(), u8::max_value() as usize - 1);
        assert_eq!(default.into_usize(), 0);
    }

    #[test]
    fn micro_returns_none() {
        assert_eq!(None, MicroSpur::try_from_usize(u8::max_value() as usize));
    }

    #[test]
    #[should_panic]
    #[cfg(not(miri))]
    fn micro_panics() {
        MicroSpur::try_from_usize(u8::max_value() as usize).unwrap();
    }

    #[test]
    #[cfg(feature = "serialize")]
    fn all_serialize() {
        let large = LargeSpur::try_from_usize(0).unwrap();
        let _ = serde_json::to_string(&large).unwrap();

        let normal = Spur::try_from_usize(0).unwrap();
        let _ = serde_json::to_string(&normal).unwrap();

        let mini = MiniSpur::try_from_usize(0).unwrap();
        let _ = serde_json::to_string(&mini).unwrap();

        let micro = MicroSpur::try_from_usize(0).unwrap();
        let _ = serde_json::to_string(&micro).unwrap();
    }
}