// This file is part of ICU4X. For terms of use, please see the file

// called LICENSE at the top level of the ICU4X source tree

// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

use crate::ule::*;

// Safety (based on the safety checklist on the ULE trait):

//  1. [T; N] does not include any uninitialized or padding bytes since T is ULE

//  2. [T; N] is aligned to 1 byte since T is ULE

//  3. The impl of validate_bytes() returns an error if any byte is not valid.

//  4. The impl of validate_bytes() returns an error if there are leftover bytes.

//  5. The other ULE methods use the default impl.

//  6. [T; N] byte equality is semantic equality since T is ULE

unsafe impl<T: ULE, const N: usize> ULE for [T; N] {

    #[inline]

    fn validate_bytes(bytes: &[u8]) -> Result<(), UleError> {

        if N == 0 {

            // ZSTs shouldn't be ULE

            return Err(UleError::length::<Self>(bytes.len()));

        }

        if bytes.len() % size_of::<Self>() != 0 {

            return Err(UleError::length::<Self>(bytes.len()));

        }

        // a slice of multiple Selfs is equivalent to just a larger slice of Ts

        T::validate_bytes(bytes)

    }

}

impl<T: AsULE, const N: usize> AsULE for [T; N] {

    type ULE = [T::ULE; N];

    #[inline]

    fn to_unaligned(self) -> Self::ULE {

        self.map(T::to_unaligned)

    }

    #[inline]

    fn from_unaligned(unaligned: Self::ULE) -> Self {

        unaligned.map(T::from_unaligned)

    }

}

unsafe impl<T: EqULE, const N: usize> EqULE for [T; N] {}

// Safety (based on the safety checklist on the VarULE trait):

//  1. str does not include any uninitialized or padding bytes.

//  2. str is aligned to 1 byte.

//  3. The impl of `validate_bytes()` returns an error if any byte is not valid.

//  4. The impl of `validate_bytes()` returns an error if the slice cannot be used in its entirety

//  5. The impl of `from_bytes_unchecked()` returns a reference to the same data.

//  6. `parse_bytes()` is equivalent to `validate_bytes()` followed by `from_bytes_unchecked()`

//  7. str byte equality is semantic equality

unsafe impl VarULE for str {

    #[inline]

    fn validate_bytes(bytes: &[u8]) -> Result<(), UleError> {

        core::str::from_utf8(bytes).map_err(|_| UleError::parse::<Self>())?;

        Ok(())

    }

    #[inline]

    fn parse_bytes(bytes: &[u8]) -> Result<&Self, UleError> {

        core::str::from_utf8(bytes).map_err(|_| UleError::parse::<Self>())

    }

    /// Invariant: must be safe to call when called on a slice that previously

    /// succeeded with `parse_bytes`

    #[inline]

    unsafe fn from_bytes_unchecked(bytes: &[u8]) -> &Self {

        core::str::from_utf8_unchecked(bytes)

    }

Unexecuted instantiation: <str as zerovec::ule::VarULE>::from_bytes_unchecked

Unexecuted instantiation: <str as zerovec::ule::VarULE>::from_bytes_unchecked

}

/// Note: [`VarULE`] is well-defined for all `[T] where T: ULE`, but [`ZeroSlice`] is more ergonomic

/// when `T` is a low-level ULE type. For example:

///

/// ```no_run

/// # use zerovec::ZeroSlice;

/// # use zerovec::VarZeroVec;

/// # use zerovec::ule::AsULE;

/// // OK: [u8] is a useful type

/// let _: VarZeroVec<[u8]> = unimplemented!();

///

/// // Technically works, but [u32::ULE] is not very useful

/// let _: VarZeroVec<[<u32 as AsULE>::ULE]> = unimplemented!();

///

/// // Better: ZeroSlice<u32>

/// let _: VarZeroVec<ZeroSlice<u32>> = unimplemented!();

/// ```

///

/// [`ZeroSlice`]: crate::ZeroSlice

// Safety (based on the safety checklist on the VarULE trait):

//  1. [T] does not include any uninitialized or padding bytes (achieved by being a slice of a ULE type)

//  2. [T] is aligned to 1 byte (achieved by being a slice of a ULE type)

//  3. The impl of `validate_bytes()` returns an error if any byte is not valid.

//  4. The impl of `validate_bytes()` returns an error if the slice cannot be used in its entirety

//  5. The impl of `from_bytes_unchecked()` returns a reference to the same data.

//  6. All other methods are defaulted

//  7. `[T]` byte equality is semantic equality (achieved by being a slice of a ULE type)

unsafe impl<T> VarULE for [T]

where

    T: ULE,

{

    #[inline]

    fn validate_bytes(slice: &[u8]) -> Result<(), UleError> {

        T::validate_bytes(slice)

    }

    #[inline]

    unsafe fn from_bytes_unchecked(bytes: &[u8]) -> &Self {

        T::slice_from_bytes_unchecked(bytes)

    }

Unexecuted instantiation: <[u8] as zerovec::ule::VarULE>::from_bytes_unchecked

Unexecuted instantiation: <[_] as zerovec::ule::VarULE>::from_bytes_unchecked

}

#[cfg(test)]

mod tests {

    use super::*;

    use crate::ZeroSlice;

    #[test]

    fn test_array_ule_validate() {

        let bytes: &[u8] = &[1, 2, 3, 4, 5, 6];

        assert!(<[u8; 2] as ULE>::validate_bytes(bytes).is_ok());

        assert!(<[u8; 3] as ULE>::validate_bytes(bytes).is_ok());

        assert!(<[u8; 6] as ULE>::validate_bytes(bytes).is_ok());

        // Length not a multiple of array size

        assert!(<[u8; 4] as ULE>::validate_bytes(bytes).is_err());

        assert!(<[u8; 5] as ULE>::validate_bytes(bytes).is_err());

        assert!(<[u8; 7] as ULE>::validate_bytes(bytes).is_err());

        // Multi-byte element types (CharULE is 3 bytes, [CharULE; 2] is 6 bytes)

        let chars_6b: &[u8] = &[0x61, 0x00, 0x00, 0x62, 0x00, 0x00]; // 'a', 'b'

        assert!(<[CharULE; 2] as ULE>::validate_bytes(chars_6b).is_ok());

        let chars_9b: &[u8] = &[0x61, 0x00, 0x00, 0x62, 0x00, 0x00, 0x63, 0x00, 0x00]; // 'a', 'b', 'c' (9 bytes: multiple of CharULE (3), but not [CharULE; 2] (6))

        assert!(<[CharULE; 2] as ULE>::validate_bytes(chars_9b).is_err());

        // ZeroSlice::parse_bytes

        assert!(ZeroSlice::<[u8; 3]>::parse_bytes(bytes).is_ok());

        assert!(ZeroSlice::<[u8; 4]>::parse_bytes(bytes).is_err());

        // Zero-length arrays unconditionally error

        assert!(<[u8; 0] as ULE>::validate_bytes(&[]).is_err());

        assert!(<[u8; 0] as ULE>::validate_bytes(bytes).is_err());

        assert!(ZeroSlice::<[u8; 0]>::parse_bytes(&[]).is_err());

        assert!(ZeroSlice::<[u8; 0]>::parse_bytes(bytes).is_err());

    }

}