use super::*;
use ethereum_types::{H256, U128, U256};

macro_rules! impl_decodable_for_uint {
    ($type: ident, $bit_size: expr) => {
        impl Decode for $type {
            fn is_ssz_fixed_len() -> bool {
                true
            }

            fn ssz_fixed_len() -> usize {
                $bit_size / 8
            }

            fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
                let len = bytes.len();
                let expected = <Self as Decode>::ssz_fixed_len();

                if len != expected {
                    Err(DecodeError::InvalidByteLength { len, expected })
                } else {
                    let mut array: [u8; $bit_size / 8] = std::default::Default::default();
                    array.clone_from_slice(bytes);

                    Ok(Self::from_le_bytes(array))
                }
            }
        }
    };
}

impl_decodable_for_uint!(u8, 8);
impl_decodable_for_uint!(u16, 16);
impl_decodable_for_uint!(u32, 32);
impl_decodable_for_uint!(u64, 64);
impl_decodable_for_uint!(usize, 64);

impl Decode for bool {
    fn is_ssz_fixed_len() -> bool {
        true
    }

    fn ssz_fixed_len() -> usize {
        1
    }

    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
        let len = bytes.len();
        let expected = <Self as Decode>::ssz_fixed_len();

        if len != expected {
            Err(DecodeError::InvalidByteLength { len, expected })
        } else {
            match bytes[0] {
                0b0000_0000 => Ok(false),
                0b0000_0001 => Ok(true),
                _ => Err(DecodeError::BytesInvalid(
                    format!("Out-of-range for boolean: {}", bytes[0]).to_string(),
                )),
            }
        }
    }
}

/// The SSZ union type.
impl<T: Decode> Decode for Option<T> {
    fn is_ssz_fixed_len() -> bool {
        false
    }

    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
        if bytes.len() < BYTES_PER_LENGTH_OFFSET {
            return Err(DecodeError::InvalidByteLength {
                len: bytes.len(),
                expected: BYTES_PER_LENGTH_OFFSET,
            });
        }

        let (index_bytes, value_bytes) = bytes.split_at(BYTES_PER_LENGTH_OFFSET);

        let index = read_union_index(index_bytes)?;
        if index == 0 {
            Ok(None)
        } else if index == 1 {
            Ok(Some(T::from_ssz_bytes(value_bytes)?))
        } else {
            Err(DecodeError::BytesInvalid(format!(
                "{} is not a valid union index for Option<T>",
                index
            )))
        }
    }
}

impl Decode for H256 {
    fn is_ssz_fixed_len() -> bool {
        true
    }

    fn ssz_fixed_len() -> usize {
        32
    }

    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
        let len = bytes.len();
        let expected = <Self as Decode>::ssz_fixed_len();

        if len != expected {
            Err(DecodeError::InvalidByteLength { len, expected })
        } else {
            Ok(H256::from_slice(bytes))
        }
    }
}

impl Decode for U256 {
    fn is_ssz_fixed_len() -> bool {
        true
    }

    fn ssz_fixed_len() -> usize {
        32
    }

    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
        let len = bytes.len();
        let expected = <Self as Decode>::ssz_fixed_len();

        if len != expected {
            Err(DecodeError::InvalidByteLength { len, expected })
        } else {
            Ok(U256::from_little_endian(bytes))
        }
    }
}

impl Decode for U128 {
    fn is_ssz_fixed_len() -> bool {
        true
    }

    fn ssz_fixed_len() -> usize {
        16
    }

    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
        let len = bytes.len();
        let expected = <Self as Decode>::ssz_fixed_len();

        if len != expected {
            Err(DecodeError::InvalidByteLength { len, expected })
        } else {
            Ok(U128::from_little_endian(bytes))
        }
    }
}

macro_rules! impl_decodable_for_u8_array {
    ($len: expr) => {
        impl Decode for [u8; $len] {
            fn is_ssz_fixed_len() -> bool {
                true
            }

            fn ssz_fixed_len() -> usize {
                $len
            }

            fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
                let len = bytes.len();
                let expected = <Self as Decode>::ssz_fixed_len();

                if len != expected {
                    Err(DecodeError::InvalidByteLength { len, expected })
                } else {
                    let mut array: [u8; $len] = [0; $len];
                    array.copy_from_slice(&bytes[..]);

                    Ok(array)
                }
            }
        }
    };
}

impl_decodable_for_u8_array!(4);
impl_decodable_for_u8_array!(32);

impl<T: Decode> Decode for Vec<T> {
    fn is_ssz_fixed_len() -> bool {
        false
    }

    fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, DecodeError> {
        if bytes.is_empty() {
            Ok(vec![])
        } else if T::is_ssz_fixed_len() {
            bytes
                .chunks(T::ssz_fixed_len())
                .map(|chunk| T::from_ssz_bytes(chunk))
                .collect()
        } else {
            decode_list_of_variable_length_items(bytes)
        }
    }
}

/// Decodes `bytes` as if it were a list of variable-length items.
///
/// The `ssz::SszDecoder` can also perform this functionality, however it it significantly faster
/// as it is optimized to read same-typed items whilst `ssz::SszDecoder` supports reading items of
/// differing types.
pub fn decode_list_of_variable_length_items<T: Decode>(
    bytes: &[u8],
) -> Result<Vec<T>, DecodeError> {
    let mut next_variable_byte = read_offset(bytes)?;

    // The value of the first offset must not point back into the same bytes that defined
    // it.
    if next_variable_byte < BYTES_PER_LENGTH_OFFSET {
        return Err(DecodeError::OutOfBoundsByte {
            i: next_variable_byte,
        });
    }

    let num_items = next_variable_byte / BYTES_PER_LENGTH_OFFSET;

    // The fixed-length section must be a clean multiple of `BYTES_PER_LENGTH_OFFSET`.
    if next_variable_byte != num_items * BYTES_PER_LENGTH_OFFSET {
        return Err(DecodeError::InvalidByteLength {
            len: next_variable_byte,
            expected: num_items * BYTES_PER_LENGTH_OFFSET,
        });
    }

    let mut values = Vec::with_capacity(num_items);
    for i in 1..=num_items {
        let slice_option = if i == num_items {
            bytes.get(next_variable_byte..)
        } else {
            let offset = read_offset(&bytes[(i * BYTES_PER_LENGTH_OFFSET)..])?;

            let start = next_variable_byte;
            next_variable_byte = offset;

            bytes.get(start..next_variable_byte)
        };

        let slice = slice_option.ok_or_else(|| DecodeError::OutOfBoundsByte {
            i: next_variable_byte,
        })?;

        values.push(T::from_ssz_bytes(slice)?);
    }

    Ok(values)
}

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

    // Note: decoding of valid bytes is generally tested "indirectly" in the `/tests` dir, by
    // encoding then decoding the element.

    #[test]
    fn invalid_u8_array_4() {
        assert_eq!(
            <[u8; 4]>::from_ssz_bytes(&[0; 3]),
            Err(DecodeError::InvalidByteLength {
                len: 3,
                expected: 4
            })
        );

        assert_eq!(
            <[u8; 4]>::from_ssz_bytes(&[0; 5]),
            Err(DecodeError::InvalidByteLength {
                len: 5,
                expected: 4
            })
        );
    }

    #[test]
    fn invalid_bool() {
        assert_eq!(
            bool::from_ssz_bytes(&[0; 2]),
            Err(DecodeError::InvalidByteLength {
                len: 2,
                expected: 1
            })
        );

        assert_eq!(
            bool::from_ssz_bytes(&[]),
            Err(DecodeError::InvalidByteLength {
                len: 0,
                expected: 1
            })
        );

        if let Err(DecodeError::BytesInvalid(_)) = bool::from_ssz_bytes(&[2]) {
            // Success.
        } else {
            panic!("Did not return error on invalid bool val")
        }
    }

    #[test]
    fn invalid_h256() {
        assert_eq!(
            H256::from_ssz_bytes(&[0; 33]),
            Err(DecodeError::InvalidByteLength {
                len: 33,
                expected: 32
            })
        );

        assert_eq!(
            H256::from_ssz_bytes(&[0; 31]),
            Err(DecodeError::InvalidByteLength {
                len: 31,
                expected: 32
            })
        );
    }

    #[test]
    fn first_length_points_backwards() {
        assert_eq!(
            <Vec<Vec<u16>>>::from_ssz_bytes(&[0, 0, 0, 0]),
            Err(DecodeError::OutOfBoundsByte { i: 0 })
        );

        assert_eq!(
            <Vec<Vec<u16>>>::from_ssz_bytes(&[1, 0, 0, 0]),
            Err(DecodeError::OutOfBoundsByte { i: 1 })
        );

        assert_eq!(
            <Vec<Vec<u16>>>::from_ssz_bytes(&[2, 0, 0, 0]),
            Err(DecodeError::OutOfBoundsByte { i: 2 })
        );

        assert_eq!(
            <Vec<Vec<u16>>>::from_ssz_bytes(&[3, 0, 0, 0]),
            Err(DecodeError::OutOfBoundsByte { i: 3 })
        );
    }

    #[test]
    fn lengths_are_decreasing() {
        assert_eq!(
            <Vec<Vec<u16>>>::from_ssz_bytes(&[12, 0, 0, 0, 14, 0, 0, 0, 12, 0, 0, 0, 1, 0, 1, 0]),
            Err(DecodeError::OutOfBoundsByte { i: 12 })
        );
    }

    #[test]
    fn awkward_fixed_lenth_portion() {
        assert_eq!(
            <Vec<Vec<u16>>>::from_ssz_bytes(&[10, 0, 0, 0, 10, 0, 0, 0, 0, 0]),
            Err(DecodeError::InvalidByteLength {
                len: 10,
                expected: 8
            })
        );
    }

    #[test]
    fn length_out_of_bounds() {
        assert_eq!(
            <Vec<Vec<u16>>>::from_ssz_bytes(&[5, 0, 0, 0]),
            Err(DecodeError::InvalidByteLength {
                len: 5,
                expected: 4
            })
        );
        assert_eq!(
            <Vec<Vec<u16>>>::from_ssz_bytes(&[8, 0, 0, 0, 9, 0, 0, 0]),
            Err(DecodeError::OutOfBoundsByte { i: 9 })
        );
    }

    #[test]
    fn vec_of_vec_of_u16() {
        assert_eq!(
            <Vec<Vec<u16>>>::from_ssz_bytes(&[4, 0, 0, 0]),
            Ok(vec![vec![]])
        );

        assert_eq!(
            <Vec<u16>>::from_ssz_bytes(&[0, 0, 1, 0, 2, 0, 3, 0]),
            Ok(vec![0, 1, 2, 3])
        );
        assert_eq!(<u16>::from_ssz_bytes(&[16, 0]), Ok(16));
        assert_eq!(<u16>::from_ssz_bytes(&[0, 1]), Ok(256));
        assert_eq!(<u16>::from_ssz_bytes(&[255, 255]), Ok(65535));

        assert_eq!(
            <u16>::from_ssz_bytes(&[255]),
            Err(DecodeError::InvalidByteLength {
                len: 1,
                expected: 2
            })
        );

        assert_eq!(
            <u16>::from_ssz_bytes(&[]),
            Err(DecodeError::InvalidByteLength {
                len: 0,
                expected: 2
            })
        );

        assert_eq!(
            <u16>::from_ssz_bytes(&[0, 1, 2]),
            Err(DecodeError::InvalidByteLength {
                len: 3,
                expected: 2
            })
        );
    }

    #[test]
    fn vec_of_u16() {
        assert_eq!(<Vec<u16>>::from_ssz_bytes(&[0, 0, 0, 0]), Ok(vec![0, 0]));
        assert_eq!(
            <Vec<u16>>::from_ssz_bytes(&[0, 0, 1, 0, 2, 0, 3, 0]),
            Ok(vec![0, 1, 2, 3])
        );
        assert_eq!(<u16>::from_ssz_bytes(&[16, 0]), Ok(16));
        assert_eq!(<u16>::from_ssz_bytes(&[0, 1]), Ok(256));
        assert_eq!(<u16>::from_ssz_bytes(&[255, 255]), Ok(65535));

        assert_eq!(
            <u16>::from_ssz_bytes(&[255]),
            Err(DecodeError::InvalidByteLength {
                len: 1,
                expected: 2
            })
        );

        assert_eq!(
            <u16>::from_ssz_bytes(&[]),
            Err(DecodeError::InvalidByteLength {
                len: 0,
                expected: 2
            })
        );

        assert_eq!(
            <u16>::from_ssz_bytes(&[0, 1, 2]),
            Err(DecodeError::InvalidByteLength {
                len: 3,
                expected: 2
            })
        );
    }

    #[test]
    fn u16() {
        assert_eq!(<u16>::from_ssz_bytes(&[0, 0]), Ok(0));
        assert_eq!(<u16>::from_ssz_bytes(&[16, 0]), Ok(16));
        assert_eq!(<u16>::from_ssz_bytes(&[0, 1]), Ok(256));
        assert_eq!(<u16>::from_ssz_bytes(&[255, 255]), Ok(65535));

        assert_eq!(
            <u16>::from_ssz_bytes(&[255]),
            Err(DecodeError::InvalidByteLength {
                len: 1,
                expected: 2
            })
        );

        assert_eq!(
            <u16>::from_ssz_bytes(&[]),
            Err(DecodeError::InvalidByteLength {
                len: 0,
                expected: 2
            })
        );

        assert_eq!(
            <u16>::from_ssz_bytes(&[0, 1, 2]),
            Err(DecodeError::InvalidByteLength {
                len: 3,
                expected: 2
            })
        );
    }
}