// License: see LICENSE file at root directory of `master` branch

//! # Zeros

use alloc::{
    string::String,
    vec::Vec,
};

use core::{
    convert::TryFrom,
    fmt::{self, Display, Formatter},
    hash::{Hash, Hasher},
};

#[cfg(test)]
use {
    alloc::string::ToString,
    core::mem,
};

use crate::Error;

/// # 128 bits (16 bytes)
pub type Z128 = [u8; Z128_LEN];

/// # 224 bits (28 bytes)
pub type Z224 = [u8; Z224_LEN];

/// # 256 bits (32 bytes)
pub type Z256 = [u8; Z256_LEN];

/// # 384 bits (48 bytes)
pub type Z384 = [u8; Z384_LEN];

/// # 512 bits (64 bytes)
pub type Z512 = [u8; Z512_LEN];

const Z128_LEN: usize = 128 / 8;
const Z224_LEN: usize = 224 / 8;
const Z256_LEN: usize = 256 / 8;
const Z384_LEN: usize = 384 / 8;
const Z512_LEN: usize = 512 / 8;

#[test]
fn test_type_lengths() {
    assert_eq!(Z128_LEN, mem::size_of::<Z128>());
    assert_eq!(Z224_LEN, mem::size_of::<Z224>());
    assert_eq!(Z256_LEN, mem::size_of::<Z256>());
    assert_eq!(Z384_LEN, mem::size_of::<Z384>());
    assert_eq!(Z512_LEN, mem::size_of::<Z512>());
}

/// # A slice of hexadecimal strings of all [`u8`][r::u8] values
///
/// This slice is used by [`bytes_to_hex()`][::bytes_to_hex()]. Each string consists of 2 characters.
///
/// ## Examples
///
/// ```
/// use zeros::HEX_STRS;
///
/// assert_eq!(HEX_STRS.len(), 256);
/// assert_eq!(HEX_STRS[0], "00");
/// assert_eq!(HEX_STRS[usize::from(u8::max_value())], "ff");
/// ```
///
/// [::bytes_to_hex()]: fn.bytes_to_hex.html
/// [r::u8]: https://doc.rust-lang.org/std/primitive.u8.html
pub const HEX_STRS: &[&str] = &[
    "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "0a", "0b", "0c", "0d", "0e", "0f", "10", "11", "12", "13", "14", "15", "16",
    "17", "18", "19", "1a", "1b", "1c", "1d", "1e", "1f", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "2a", "2b", "2c", "2d",
    "2e", "2f", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "3a", "3b", "3c", "3d", "3e", "3f", "40", "41", "42", "43", "44",
    "45", "46", "47", "48", "49", "4a", "4b", "4c", "4d", "4e", "4f", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "5a", "5b",
    "5c", "5d", "5e", "5f", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "6a", "6b", "6c", "6d", "6e", "6f", "70", "71", "72",
    "73", "74", "75", "76", "77", "78", "79", "7a", "7b", "7c", "7d", "7e", "7f", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89",
    "8a", "8b", "8c", "8d", "8e", "8f", "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "9a", "9b", "9c", "9d", "9e", "9f", "a0",
    "a1", "a2", "a3", "a4", "a5", "a6", "a7", "a8", "a9", "aa", "ab", "ac", "ad", "ae", "af", "b0", "b1", "b2", "b3", "b4", "b5", "b6", "b7",
    "b8", "b9", "ba", "bb", "bc", "bd", "be", "bf", "c0", "c1", "c2", "c3", "c4", "c5", "c6", "c7", "c8", "c9", "ca", "cb", "cc", "cd", "ce",
    "cf", "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7", "d8", "d9", "da", "db", "dc", "dd", "de", "df", "e0", "e1", "e2", "e3", "e4", "e5",
    "e6", "e7", "e8", "e9", "ea", "eb", "ec", "ed", "ee", "ef", "f0", "f1", "f2", "f3", "f4", "f5", "f6", "f7", "f8", "f9", "fa", "fb", "fc",
    "fd", "fe", "ff",
];

#[test]
fn test_hex_strs() {
    assert!(HEX_STRS.len() > usize::from(u8::max_value()));
    for i in 0..HEX_STRS.len() {
        assert_eq!(format!("{:02x}", i), HEX_STRS[i]);
    }
}

/// # Formats a byte slice as a hexadecimal string, in lower-case
///
/// This function uses [`HEX_STRS`][::HEX_STRS], which (at the time) was faster than `format!("{:02x}", ...)`.
///
/// ## Examples
///
/// ```
/// assert_eq!(zeros::bytes_to_hex(     &[202, 254]), "cafe");
/// assert_eq!(zeros::bytes_to_hex(&[192, 255, 238]), "c0ffee");
/// ```
///
/// [::HEX_STRS]: constant.HEX_STRS.html
pub fn bytes_to_hex<B>(bytes: B) -> String where B: AsRef<[u8]> {
    let bytes = bytes.as_ref();

    let mut result = String::with_capacity(bytes.len().saturating_mul(2));
    for b in bytes {
        result.push_str(HEX_STRS[usize::from(*b)]);
    }

    result
}

const DEC_STRS: &[&str] = &[
    "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24",
    "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47",
    "48", "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "70",
    "71", "72", "73", "74", "75", "76", "77", "78", "79", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "90", "91", "92", "93",
    "94", "95", "96", "97", "98", "99", "100", "101", "102", "103", "104", "105", "106", "107", "108", "109", "110", "111", "112", "113", "114",
    "115", "116", "117", "118", "119", "120", "121", "122", "123", "124", "125", "126", "127", "128", "129", "130", "131", "132", "133", "134",
    "135", "136", "137", "138", "139", "140", "141", "142", "143", "144", "145", "146", "147", "148", "149", "150", "151", "152", "153", "154",
    "155", "156", "157", "158", "159", "160", "161", "162", "163", "164", "165", "166", "167", "168", "169", "170", "171", "172", "173", "174",
    "175", "176", "177", "178", "179", "180", "181", "182", "183", "184", "185", "186", "187", "188", "189", "190", "191", "192", "193", "194",
    "195", "196", "197", "198", "199", "200", "201", "202", "203", "204", "205", "206", "207", "208", "209", "210", "211", "212", "213", "214",
    "215", "216", "217", "218", "219", "220", "221", "222", "223", "224", "225", "226", "227", "228", "229", "230", "231", "232", "233", "234",
    "235", "236", "237", "238", "239", "240", "241", "242", "243", "244", "245", "246", "247", "248", "249", "250", "251", "252", "253", "254",
    "255",
];

#[test]
fn test_dec_strs() {
    assert!(DEC_STRS.len() > usize::from(u8::max_value()));
    for i in 0..DEC_STRS.len() {
        assert_eq!(i.to_string(), DEC_STRS[i]);
    }
}

/// # Zeros
///
/// ## Features
///
/// - Can be converted from some common hash slices such as `[u8; 16]`, `[u8; 64]`...
///
/// - Implemented [`Display`][r::Display], which prints hex string of the hash, in lower-case.
///
/// - Implemented [`Eq`][r::Eq] and [`Hash`][r::Hash] traits, so you can use it in [`HashSet`][r::HashSet], [`HashMap`][r::HashMap]...
///
/// - [`Debug`][r::Debug] implementation:
///
///     + `{:#?}` prints bytes in _hexadecimal_ format.
///     + `{:?}` prints bytes in _decimal_ format.
///
/// ## Hexadecimal format (in lower case)
///
/// Examples:
///
/// ```
/// use zeros::Zeros;
///
/// let zeros = Zeros::from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]);
/// assert_eq!(zeros.to_string(), "000102030405060708090a0b0c0d0e0f");
/// ```
///
/// [r::Eq]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
/// [r::HashMap]: https://doc.rust-lang.org/std/collections/struct.HashMap.html
/// [r::HashSet]: https://doc.rust-lang.org/std/collections/struct.HashSet.html
/// [r::Debug]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
/// [r::Display]: https://doc.rust-lang.org/std/fmt/trait.Display.html
/// [r::Hash]: https://doc.rust-lang.org/std/hash/trait.Hash.html
#[derive(Clone)]
pub enum Zeros {

    /// # 128 bits (16 bytes)
    Z128(Z128),

    /// # 224 bits (28 bytes)
    Z224(Z224),

    /// # 256 bits (32 bytes)
    Z256(Z256),

    /// # 384 bits (48 bytes)
    Z384(Z384),

    /// # 512 bits (64 bytes)
    Z512(Z512),

}

impl Zeros {

    /// # Makes new [`Z128`][::Z128] variant with all bytes set to `0`
    ///
    /// [::Z128]: #variant.Z128
    pub const fn new_128() -> Self {
        Zeros::Z128([0; Z128_LEN])
    }

    /// # Makes new [`Z224`][::Z224] variant with all bytes set to `0`
    ///
    /// [::Z224]: #variant.Z224
    pub const fn new_224() -> Self {
        Zeros::Z224([0; Z224_LEN])
    }

    /// # Makes new [`Z256`][::Z256] variant with all bytes set to `0`
    ///
    /// [::Z256]: #variant.Z256
    pub const fn new_256() -> Self {
        Zeros::Z256([0; Z256_LEN])
    }

    /// # Makes new [`Z384`][::Z384] variant with all bytes set to `0`
    ///
    /// [::Z384]: #variant.Z384
    pub const fn new_384() -> Self {
        Zeros::Z384([0; Z384_LEN])
    }

    /// # Makes new [`Z512`][::Z512] variant with all bytes set to `0`
    ///
    /// [::Z512]: #variant.Z512
    pub const fn new_512() -> Self {
        Zeros::Z512([0; Z512_LEN])
    }

    /// # Gets number of bytes
    pub fn len(&self) -> usize {
        match self {
            Zeros::Z128(bytes) => bytes.len(),
            Zeros::Z224(bytes) => bytes.len(),
            Zeros::Z256(bytes) => bytes.len(),
            Zeros::Z384(bytes) => bytes.len(),
            Zeros::Z512(bytes) => bytes.len(),
        }
    }

    /// # Checks if this instance is same class as one other
    ///
    /// ## Examples
    ///
    /// ```
    /// use zeros::Zeros;
    ///
    /// assert!(Zeros::from([0; 16]).same_class(&Zeros::from([0; 32])) == false);
    /// assert!(Zeros::from([6; 48]).same_class(&Zeros::from([9; 48])));
    /// ```
    pub fn same_class(&self, other: &Self) -> bool {
        match (self, other) {
            (Zeros::Z128(_), Zeros::Z128(_)) => true,
            (Zeros::Z224(_), Zeros::Z224(_)) => true,
            (Zeros::Z256(_), Zeros::Z256(_)) => true,
            (Zeros::Z384(_), Zeros::Z384(_)) => true,
            (Zeros::Z512(_), Zeros::Z512(_)) => true,
            _ => false,
        }
    }

    /// # Makes a new vector and copies the original slice's content into it
    pub fn to_vec(&self) -> Vec<u8> {
        match self {
            Zeros::Z128(bytes) => bytes.to_vec(),
            Zeros::Z224(bytes) => bytes.to_vec(),
            Zeros::Z256(bytes) => bytes.to_vec(),
            Zeros::Z384(bytes) => bytes.to_vec(),
            Zeros::Z512(bytes) => bytes.to_vec(),
        }
    }

}

/// # Compares slices
fn cmp_slices(a: &[u8], b: &[u8]) -> bool {
    if a.len() != b.len() {
        return false;
    }
    for i in 0..a.len() {
        if a[i] != b[i] {
            return false;
        }
    }
    true
}

impl Eq for Zeros {}

impl PartialEq for Zeros {

    fn eq(&self, other: &Self) -> bool {
        match (self, other) {
            (Zeros::Z128(a), Zeros::Z128(b)) => cmp_slices(a, b),
            (Zeros::Z224(a), Zeros::Z224(b)) => cmp_slices(a, b),
            (Zeros::Z256(a), Zeros::Z256(b)) => cmp_slices(a, b),
            (Zeros::Z384(a), Zeros::Z384(b)) => cmp_slices(a, b),
            (Zeros::Z512(a), Zeros::Z512(b)) => cmp_slices(a, b),
            _ => false,
        }
    }

}

impl PartialEq<[u8]> for Zeros {

    fn eq(&self, other: &[u8]) -> bool {
        match self {
            Zeros::Z128(bytes) => bytes.eq(other),
            Zeros::Z224(bytes) => bytes.eq(other),
            Zeros::Z256(bytes) => bytes.eq(other),
            Zeros::Z384(bytes) => bytes.eq(other),
            Zeros::Z512(bytes) => bytes.eq(other),
        }
    }

}

impl PartialEq<Zeros> for [u8] {

    fn eq(&self, other: &Zeros) -> bool {
        match other {
            Zeros::Z128(bytes) => bytes.eq(self),
            Zeros::Z224(bytes) => bytes.eq(self),
            Zeros::Z256(bytes) => bytes.eq(self),
            Zeros::Z384(bytes) => bytes.eq(self),
            Zeros::Z512(bytes) => bytes.eq(self),
        }
    }

}

impl Hash for Zeros {

    fn hash<H>(&self, h: &mut H) where H: Hasher {
        match self {
            Zeros::Z128(bytes) => bytes.hash(h),
            Zeros::Z224(bytes) => bytes.hash(h),
            Zeros::Z256(bytes) => bytes.hash(h),
            Zeros::Z384(bytes) => bytes.hash(h),
            Zeros::Z512(bytes) => bytes.hash(h),
        };
    }

}

macro_rules! impl_from_slices_for_zeros { ($($ty: ty, $code: tt,)+) => {
    $(
        impl From<$ty> for Zeros {

            fn from(slice: $ty) -> Self {
                $code(slice)
            }

        }
    )+
}}

impl_from_slices_for_zeros! {
    Z128, (Zeros::Z128),
    Z224, (Zeros::Z224),
    Z256, (Zeros::Z256),
    Z384, (Zeros::Z384),
    Z512, (Zeros::Z512),
}

impl AsRef<[u8]> for Zeros {

    fn as_ref(&self) -> &[u8] {
        match self {
            Zeros::Z128(bytes) => bytes,
            Zeros::Z224(bytes) => bytes,
            Zeros::Z256(bytes) => bytes,
            Zeros::Z384(bytes) => bytes,
            Zeros::Z512(bytes) => bytes,
        }
    }

}

impl AsMut<[u8]> for Zeros {

    fn as_mut(&mut self) -> &mut [u8] {
        match self {
            Zeros::Z128(bytes) => bytes,
            Zeros::Z224(bytes) => bytes,
            Zeros::Z256(bytes) => bytes,
            Zeros::Z384(bytes) => bytes,
            Zeros::Z512(bytes) => bytes,
        }
    }

}

/// # Formats a [`&Zeros`][::Zeros] into a hexadecimal string, in lower-case
///
/// ## Examples
///
/// ```
/// use zeros::Zeros;
///
/// assert_eq!(
///     Zeros::from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]).to_string(),
///     "000102030405060708090a0b0c0d0e0f",
/// );
/// ```
///
/// [::Zeros]: struct.Zeros.html
impl Display for Zeros {

    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
        f.write_str(&match self {
            Zeros::Z128(bytes) => bytes_to_hex(&bytes[..]),
            Zeros::Z224(bytes) => bytes_to_hex(&bytes[..]),
            Zeros::Z256(bytes) => bytes_to_hex(&bytes[..]),
            Zeros::Z384(bytes) => bytes_to_hex(&bytes[..]),
            Zeros::Z512(bytes) => bytes_to_hex(&bytes[..]),
        })
    }

}

impl fmt::Debug for Zeros {

    fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
        let bytes = match self {
            Zeros::Z128(bytes) => {
                f.write_str("Zeros::Z128([")?;
                &bytes[..]
            }
            Zeros::Z224(bytes) => {
                f.write_str("Zeros::Z224([")?;
                &bytes[..]
            }
            Zeros::Z256(bytes) => {
                f.write_str("Zeros::Z256([")?;
                &bytes[..]
            }
            Zeros::Z384(bytes) => {
                f.write_str("Zeros::Z384([")?;
                &bytes[..]
            }
            Zeros::Z512(bytes) => {
                f.write_str("Zeros::Z512([")?;
                &bytes[..]
            }
        };

        let alternate = f.alternate();
        for (i, b) in bytes.iter().enumerate() {
            if i > 0 {
                f.write_str(", ")?;
            }
            match alternate {
                true => write!(f, "0x{}", HEX_STRS[usize::from(*b)])?,
                false => f.write_str(DEC_STRS[usize::from(*b)])?,
            };
        }

        f.write_str("])")
    }

}

macro_rules! impl_try_from_zeros_for_slices { ($($code: tt, $ty: ty,)+) => {
    $(
        impl TryFrom<Zeros> for $ty {

            type Error = Error;

            fn try_from(zeros: Zeros) -> Result<Self, Self::Error> {
                match zeros {
                    Zeros::$code(slice) => Ok(slice),
                    _ => Err(e!("Not an instance of {:?}", stringify!($code))),
                }
            }

        }
    )+
}}

impl_try_from_zeros_for_slices! {
    Z128, Z128,
    Z224, Z224,
    Z256, Z256,
    Z384, Z384,
    Z512, Z512,
}

macro_rules! copy_slice_to_zeros { ($vec: ident, $size: ident) => {{
    let mut array = [0_u8; $size];
    for (i, b) in $vec.into_iter().enumerate() {
        array[i] = *b;
    }
    Ok(Zeros::from(array))
}}}

impl TryFrom<&[u8]> for Zeros {

    type Error = Error;

    fn try_from(bytes: &[u8]) -> Result<Self, Self::Error> {
        match bytes.len() {
            Z128_LEN => copy_slice_to_zeros!(bytes, Z128_LEN),
            Z224_LEN => copy_slice_to_zeros!(bytes, Z224_LEN),
            Z256_LEN => copy_slice_to_zeros!(bytes, Z256_LEN),
            Z384_LEN => copy_slice_to_zeros!(bytes, Z384_LEN),
            Z512_LEN => copy_slice_to_zeros!(bytes, Z512_LEN),
            other => Err(e!("Slice size is not supported: {}", other)),
        }
    }

}

impl TryFrom<Vec<u8>> for Zeros {

    type Error = Error;

    fn try_from(bytes: Vec<u8>) -> Result<Self, Self::Error> {
        Self::try_from(bytes.as_slice())
    }

}