//! An array of specified length `N` of u8 values from 0 to `B`-1
//!
//! See [`ArrayOfBase`]

use crate::ArrayOfHex;
use crate::Error;

#[cfg(feature = "serde")]
use serde::{
    ser::{Serialize, Serializer},
    Deserialize,
};

/// An array of specified length `N` of u8 values from 0 to `B`-1
///
/// # Example - Success
/// ```
/// # use array_of_base::ArrayOfBase;
/// // GIVEN
/// let array = [0, 1, 2, 3, 4, 0, 1, 2, 3, 4];
///
/// // WHEN
/// let actual = ArrayOfBase::<10, 5>::try_new(array);
///
/// // THEN
/// assert!(actual.is_ok())
/// ```
///
/// # Example - Error
///
/// ```
/// # use array_of_base::ArrayOfBase;
/// // GIVEN
/// let array = [16];
///
/// // WHEN
/// let actual = ArrayOfBase::<1, 16>::try_new(array);
///
/// // THEN
/// assert!(actual.is_err())
/// ```
// #[wasm_bindgen::prelude::wasm_bindgen]
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub struct ArrayOfBase<const N: usize, const B: u8> {
    value: [u8; N],
}

impl<const N: usize, const B: u8> ArrayOfBase<N, B> {
    /// Create from Array of u8 numbers of the same size
    ///
    /// See [`ArrayOfBase`] for Example
    ///
    /// # Errors
    ///
    /// Will error if:
    ///
    /// - Invalid value in supplied array [`Error::InvalidValue`]
    ///
    /// # Example
    ///
    /// ```
    /// # use array_of_base::{Error, ArrayOfBase};
    /// // GIVEN
    /// let valid_array     = [0u8, 1, 2, 3, 0];
    /// let invalid_array   = [0u8, 1, 2, 3, 4];
    ///
    /// // WHEN
    /// # let actual: Vec<Result<[u8; 5], Error>> =
    /// #     [valid_array, invalid_array]
    /// #         .into_iter()
    /// #         .map(|v| {
    /// ArrayOfBase::<5, 4>::try_new(v).map(|b| b.unwrap())
    /// // Ran on each
    /// #         })
    /// #         .collect();
    ///
    /// // THEN
    /// assert_eq!(
    ///     actual,
    ///     vec![
    ///         Ok([0u8, 1, 2, 3, 0]),      // valid_array
    ///         Err(Error::InvalidValue),   // invalid_array
    ///     ]
    /// );
    /// ```
    pub fn try_new(v: [u8; N]) -> Result<Self, Error> {
        if v.iter().copied().all(Self::valid_number) {
            Ok(Self { value: v })
        } else {
            Err(Error::InvalidValue)
        }
    }

    /// Create from Vec of u8 numbers
    ///
    /// # Errors
    ///
    /// Will error if:
    ///
    /// - Too many elements in the supplied vector [`Error::Oversized`]
    /// - Too few, but not 0, elements in the supplied vector [`Error::Undersized`]
    /// - Empty vector supplied [`Error::Empty`]
    /// - Invalid value in supplied array [`Error::InvalidValue`]
    ///
    /// # Example
    ///
    /// ```
    /// # use array_of_base::{Error, ArrayOfBase};
    /// // GIVEN
    /// let valid_vec: Vec<u8>      = vec![0, 0, 1, 2, 3];
    /// let undersized_vec: Vec<u8> = vec![1];
    /// let empty_vec: Vec<u8>      = Vec::new();
    /// let oversized_vec: Vec<u8>  = vec![1, 2, 3, 1, 2, 3];
    ///
    /// // WHEN
    /// # let actual: Vec<Result<[u8; 5], Error>> =
    /// #     [valid_vec, undersized_vec, empty_vec, oversized_vec]
    /// #         .iter()
    /// #         .map(|v| {
    /// ArrayOfBase::<5, 4>::try_from_vec_exact(v).map(|b| b.unwrap())
    /// // Ran on each
    /// #         })
    /// #         .collect();
    ///
    /// // THEN
    /// assert_eq!(
    ///     actual,
    ///     vec![
    ///         Ok([0u8, 0, 1, 2, 3]),  // valid_vec
    ///         Err(Error::Undersized), // undersized_vec
    ///         Err(Error::Empty),      // empty_vec
    ///         Err(Error::Oversized),  // oversized_vec
    ///     ]
    /// );
    /// ```
    pub fn try_from_vec_exact(v: &[u8]) -> Result<Self, Error> {
        use std::cmp::Ordering::{Equal, Greater, Less};
        match v.len().cmp(&N) {
            Greater => Err(Error::Oversized),
            Less if v.is_empty() => Err(Error::Empty),
            Less => Err(Error::Undersized),
            Equal => Self::try_new(v.try_into().expect(
                "1666898415 - Unreachable: Correct length already verified",
            )),
        }
    }

    /// Create from non-empty Vec of u8 numbers, pad `0`s to the left
    ///
    /// # Errors
    ///
    /// Will error if:
    ///
    /// - Too many elements in the supplied vector [`Error::Oversized`]
    /// - Empty vector supplied [`Error::Empty`]
    /// - Invalid value in supplied array [`Error::InvalidValue`]
    ///
    /// # Example
    ///
    /// ```
    /// # use array_of_base::{Error, ArrayOfBase};
    /// // GIVEN
    /// let valid_vec: Vec<u8>      = vec![1, 2, 3];
    /// let empty_vec: Vec<u8>      = Vec::new();
    /// let oversized_vec: Vec<u8>  = vec![1, 2, 3, 1, 2, 3];
    ///
    /// // WHEN
    /// # let actual: Vec<Result<[u8; 5], Error>> =
    /// #     [valid_vec, empty_vec, oversized_vec]
    /// #         .iter()
    /// #         .map(|v| {
    /// ArrayOfBase::<5, 4>::try_from_vec_pad(v).map(|b| b.unwrap())
    /// // Ran on each
    /// #         })
    /// #         .collect();
    ///
    /// // THEN
    /// assert_eq!(
    ///     actual,
    ///     vec![
    ///         Ok([0u8, 0, 1, 2, 3]),  // valid_vec
    ///         Err(Error::Empty),      // empty_vec
    ///         Err(Error::Oversized),  // oversized_vec
    ///     ]
    /// );
    /// ```
    pub fn try_from_vec_pad(v: &[u8]) -> Result<Self, Error> {
        use std::cmp::Ordering::{Greater, Less};
        match v.len().cmp(&N) {
            Greater => Err(Error::Oversized),
            Less if v.is_empty() => Err(Error::Empty),
            _ => Self::try_new(Self::pad_array(v)),
        }
    }

    /// Return the contained verified array
    ///
    /// # Example
    ///
    /// ```
    /// # use array_of_base::ArrayOfBase;
    /// // GIVEN
    /// # let valid_u8_array = [1, 2, 3];
    /// # let mut verified = ArrayOfBase::<3, 10>::default();
    /// verified = ArrayOfBase::try_new(valid_u8_array).unwrap();
    ///
    /// // WHEN
    /// let actual = verified.unwrap();
    ///
    /// // THEN
    /// assert_eq!(actual, valid_u8_array)
    /// ```
    #[must_use]
    pub fn unwrap(self) -> [u8; N] {
        self.value
    }

    /// Borrow the contained verified array
    ///
    /// # Example
    ///
    /// ```
    /// # use array_of_base::ArrayOfBase;
    /// // GIVEN
    /// # const VALID_U8_ARRAY: [u8; 3] = [1, 2, 3];
    /// # let mut verified = ArrayOfBase::<3, 10>::default();
    /// verified = ArrayOfBase::try_new(VALID_U8_ARRAY).unwrap();
    ///
    /// // WHEN
    /// let actual = verified.borrow_u8_array();
    ///
    /// // THEN
    /// assert_eq!(actual, &VALID_U8_ARRAY)
    /// ```
    #[must_use]
    pub fn borrow_u8_array(&self) -> &[u8; N] {
        &self.value
    }

    fn valid_number(u8: u8) -> bool {
        u8 < B
    }

    /// Prepend to array 0 values until `N` size reached
    ///
    /// # Panics
    ///
    /// Will Panic if an array that exceeds the desired length is passed
    ///
    /// # Example
    ///
    /// ```
    /// # use array_of_base::ArrayOfBase;
    /// // GIVEN
    /// let x = [1, 2, 3];
    ///
    /// // WHEN
    /// let actual = ArrayOfBase::<5, 10>::pad_array(&x);
    ///
    /// // THEN
    /// assert_eq!(actual, [0u8, 0, 1, 2, 3]);
    /// ```
    #[must_use]
    pub fn pad_array(v: &[u8]) -> [u8; N] {
        assert!(v.len() <= N);
        let mut vec = v.to_vec();
        while vec.len() < N {
            vec.insert(0, 0);
        }
        vec.try_into().expect("1666979421 - Unreachable")
    }

    /// Reduce the size of the array to the specified value
    ///
    /// # Panics
    ///
    /// If the specified size `L` is larger than the current array size `N` the
    /// function will panic
    ///
    /// # Example
    /// ```
    /// # use array_of_base::ArrayOfBase;
    /// // GIVEN
    /// let long_array =
    ///     ArrayOfBase::<5, 4>::try_new([0u8, 1, 2, 3, 0]).unwrap();
    ///
    /// // WHEN
    /// let actual: ArrayOfBase<3, 4> = long_array.trim();
    ///
    /// // THEN
    /// assert_eq!(actual.borrow_u8_array(), &[0u8, 1, 2]);
    /// ```
    #[must_use]
    pub fn trim<const L: usize>(&self) -> ArrayOfBase<L, B> {
        assert!(L <= N);

        ArrayOfBase {
            value: array_from_iter_unchecked(self.value.into_iter().take(L)),
        }
    }
}

impl<const N: usize, const B: u8> Default for ArrayOfBase<N, B> {
    fn default() -> Self {
        Self { value: [0u8; N] }
    }
}

impl<const N: usize> std::fmt::Display for ArrayOfBase<N, 16> {
    /// Output the contents of [`ArrayOfHex`] as a hexadecimal string
    ///
    /// # Restrictions
    ///
    /// This function only works if:
    ///
    /// - The base `B` of the [`ArrayOfBase`] is `16` or [`ArrayOfHex`] is used
    ///
    /// # Example
    /// ```
    /// # use array_of_base::ArrayOfHex;
    /// # const ALL_HEX_VALUES: fn() -> ArrayOfHex<16> = || {
    /// #     ArrayOfHex::try_new(core::array::from_fn(|i| i as u8)).unwrap()
    /// # };
    /// #
    /// // GIVEN
    /// let value: ArrayOfHex<16> = ALL_HEX_VALUES();
    ///
    /// // WHEN
    /// let actual: String = value.to_string();
    ///
    /// // THEN
    /// assert_eq!(actual, "0123456789abcdef");
    /// ```
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        for v in self.borrow_u8_array().iter() {
            match v {
                10 => write!(f, "a")?,
                11 => write!(f, "b")?,
                12 => write!(f, "c")?,
                13 => write!(f, "d")?,
                14 => write!(f, "e")?,
                15 => write!(f, "f")?,
                v => write!(f, "{v}")?,
            }
        }
        Ok(())
    }
}

#[cfg(feature = "serde")]
impl<const N: usize> Serialize for ArrayOfBase<N, 16> {
    /// Allow using [`ArrayOfHex`] in structs that derive [`serde::Serialize`]
    ///
    /// # Restrictions
    ///
    /// This function only works if:
    ///
    /// - The crate feature `serde` is activated
    /// - The base `B` of the [`ArrayOfBase`] is `16` or [`ArrayOfHex`] is used
    ///
    /// # Example
    ///
    /// ```
    /// # use array_of_base::{ArrayOfHex};
    /// #
    /// # #[derive(serde::Serialize)]
    /// # struct DummyStruct {
    /// #     hex_value: ArrayOfHex<5>,
    /// # }
    /// #
    /// // GIVEN
    /// let example_struct = DummyStruct {
    ///     hex_value: ArrayOfHex::try_new([10u8, 1, 11, 2, 12])
    ///         .unwrap()
    ///         .into(),
    /// };
    ///
    /// // WHEN
    /// let string = serde_json::to_string(&example_struct);
    ///
    /// // THEN
    /// assert_eq!(string.unwrap(), r#"{"hex_value":"a1b2c"}"#);
    /// ```
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_str(&self.to_string())
    }
}

impl<const N: usize> std::str::FromStr for ArrayOfBase<N, 16> {
    type Err = String;

    /// Parse a hexadecimal string into [`ArrayOfHex`]
    ///
    /// # Restrictions
    ///
    /// This function only works if:
    ///
    /// - The base `B` of the [`ArrayOfBase`] is `16` or [`ArrayOfHex`] is used
    ///
    /// # Example
    /// ```
    /// # use array_of_base::ArrayOfHex;
    /// # const ALL_HEX_VALUES: fn() -> ArrayOfHex<16> = || {
    /// #     ArrayOfHex::try_new(core::array::from_fn(|i| i as u8)).unwrap()
    /// # };
    /// #
    /// // GIVEN
    /// let string = "0123456789AbCdEf";
    ///
    /// // WHEN
    /// let actual = string.parse::<ArrayOfHex<16>>();
    ///
    /// // THEN
    /// assert_eq!(
    ///     actual.ok().unwrap().borrow_u8_array(),
    ///     ALL_HEX_VALUES().borrow_u8_array()
    /// );
    /// ```
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s.len() != N {
            return Err(format!(
                "1669744337 - String does not match expected length of {N}"
            ));
        }

        let mut array = [0; N];

        for (i, v) in s.chars().enumerate() {
            array[i] = match v {
                '0' => 0,
                '1' => 1,
                '2' => 2,
                '3' => 3,
                '4' => 4,
                '5' => 5,
                '6' => 6,
                '7' => 7,
                '8' => 8,
                '9' => 9,
                'a' | 'A' => 10,
                'b' | 'B' => 11,
                'c' | 'C' => 12,
                'd' | 'D' => 13,
                'e' | 'E' => 14,
                'f' | 'F' => 15,
                v => {
                    return Err(format!(
                        "1669744576 - Unrecognized char `{v}` at position {i}"
                    ));
                }
            };
        }

        ArrayOfHex::try_new(array).map_err(|_| {
            unreachable!("1669744870 - Input values already validated")
        })
    }
}

#[cfg(feature = "serde")]
impl<'de, const N: usize> Deserialize<'de> for ArrayOfBase<N, 16> {
    /// Allow using [`ArrayOfHex`] in structs that derive [`serde::Deserialize`]
    ///
    /// # Restrictions
    ///
    /// This function only works if:
    ///
    /// - The crate feature `serde` is activated
    /// - The base `B` of the [`ArrayOfBase`] is `16` or [`ArrayOfHex`] is used
    ///
    /// # Example
    ///
    /// ```
    /// # use array_of_base::ArrayOfHex;
    /// #
    /// # #[derive(serde::Deserialize)]
    /// # struct DummyStruct {
    /// #     hex_value: ArrayOfHex<5>,
    /// # }
    /// #
    /// // GIVEN
    /// let example_string = r#"{"hex_value":"A1b2C"}"#;
    ///
    /// // WHEN
    /// let parsed = serde_json::from_str::<DummyStruct>(example_string);
    ///
    /// // THEN
    /// assert_eq!(
    ///     parsed.ok().unwrap().hex_value.borrow_u8_array(),
    ///     &[10u8, 1, 11, 2, 12]
    /// );
    /// ```
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        let s = String::deserialize(deserializer)?;
        std::str::FromStr::from_str(&s).map_err(serde::de::Error::custom)
    }
}

fn array_from_iter_unchecked<const N: usize, I: Iterator<Item = u8>>(
    mut i: I,
) -> [u8; N] {
    std::array::from_fn(|_| i.next().unwrap_or_default())
}

/// Convert u8 into 2 u4 encoded as u8
///
/// # Example
///
#[must_use]
fn u8_to_u4_as_u8(v: u8) -> [u8; 2] {
    [(v & 0xf0) >> 4, v & 0x0f]
}

impl<const N: usize> ArrayOfBase<N, 16> {
    /// Split [`u8`] values into `u4` values, construct into [`ArrayOfHex`]
    ///
    /// # Todo
    ///
    /// TODO: Replace with `from_u8_array(array: [u8; {N / 2}])` when `generic_const_exprs` feature stabilizes
    ///
    /// # Panics
    ///
    /// - If the `I` value is not half `N` the function will panic.
    /// - If `N` is not an even number, the function will panic.
    ///
    /// This will be resolved when `generic_const_exprs` feature stabilizes
    ///
    /// # Example
    ///
    /// ```
    /// # use array_of_base::ArrayOfHex;
    /// // GIVEN
    /// let u8_array = [0u8, 16, 255];
    ///
    /// // WHEN
    /// let actual = ArrayOfHex::<6>::from_u8_array(u8_array);
    /// //                     ^^^^^ - Required until `generic_const_exprs` feature stabilizes
    ///
    /// // THEN
    /// assert_eq!(actual.borrow_u8_array(), &[0u8, 0, 1, 0, 15, 15]);
    /// ```
    pub fn from_u8_array<const I: usize>(array: [u8; I]) -> ArrayOfHex<N> {
        assert!(N == I * 2);
        ArrayOfBase {
            value: array_from_iter_unchecked(
                array.into_iter().flat_map(u8_to_u4_as_u8),
            ),
        }
    }
}

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

    #[test]
    fn test1669773971_u8_to_u4_as_u8() {
        // GIVEN
        let x = 0xab;

        // WHEN
        let actual = u8_to_u4_as_u8(x);

        // THEN
        assert_eq!(actual, [0xa, 0xb]);
    }
}