#![allow(dead_code, unused_variables)]

use std::fmt;

use serde::{Deserialize, Serialize};

/// A constant to describe the number of bits in one byte.
/// Defined just to improve readability.
const ONE_BYTE_BITS_COUNT: i8 = 8;

/// Struct represents a custom error that should be raised every time
/// a user tries to access or set the bit in the array that is out of this bit array size.
#[derive(Clone, Debug)]
pub struct OutOfRangeError {
    pub bitarray_size: i64,
    pub bitarray_position: i64,
}

impl OutOfRangeError {
    /// Constructor used to initialize a new OutOfRangeError with a given bitarray_size and bitarray_position.
    /// "bitarray_size" - The size in bits of the bitarray where the error was raised.
    /// "bitarray_position" - The wrong position caused an error.
    pub fn new(bitarray_size: i64, bitarray_position: i64) -> Self {
        Self {
            bitarray_size,
            bitarray_position,
        }
    }
}

impl fmt::Display for OutOfRangeError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(
            f,
            "Given position: {} is out of the bitarray size {}.",
            self.bitarray_position, self.bitarray_size
        )
    }
}

/// A structure aimed to bring the bitarray functionality.
/// Structure is described within two fields.
/// "size" - The number of bits that will be allocated during the
///          struct instance initialization.
/// "bit_array" - The vector of 8 bit integer used to represent bits
///               where each 8 bits are packed in every 8 bit integer.
/// ```rust
/// use bitarray_naive::BitArray;
///
/// let bitarray_size: i64 = 9999;
///
/// let mut bitarray: BitArray = BitArray::new(bitarray_size);
///
/// bitarray.set(12, true).unwrap();
///
/// assert_eq!(bitarray.get(12).unwrap(), true);
/// ```
#[derive(Debug, Serialize, Deserialize)]
pub struct BitArray {
    pub size: i64,
    pub bit_array: Vec<u8>,
}

impl BitArray {
    /// Constructor used to initialize a new instance of the bitarray with a given size.
    /// "size" - The number of bits that will be allocated during the
    ///          struct instance initialization.
    pub fn new(size: i64) -> Self {
        // Calculates the number of elements should be allocated in vector per given size
        let _capacity: usize = (size / ONE_BYTE_BITS_COUNT as i64) as usize + 1;

        let mut bit_array: Vec<u8> = Vec::with_capacity(_capacity);

        // Initialize vector with default 0 values. Where each value equal to 8 false bits.
        for _ in 0.._capacity {
            bit_array.push(0);
        }

        Self { size, bit_array }
    }

    /// Calculates the element in bit array vector should be picked per given bit position.
    /// In other words, calculates the index in bitarray vector.
    fn calc_vec_position(position: i64) -> usize {
        (position / ONE_BYTE_BITS_COUNT as i64) as usize
    }

    /// Calculates the bit offset (position) in a given 8 bit integer.
    /// The position should be counted from right to left.
    fn calc_byte_offset(position: i64) -> u8 {
        let _pow: i64 = position % ONE_BYTE_BITS_COUNT as i64;

        2u64.pow(_pow as u32) as u8
    }

    /// Sets either true or false value in bit array at given position.
    pub fn set(&mut self, position: i64, flag: bool) -> Result<(), OutOfRangeError> {
        if position >= self.size {
            Err(OutOfRangeError::new(self.size, position as i64))
        } else {
            let vec_position: usize = Self::calc_vec_position(position);
            let byte_offset: u8 = Self::calc_byte_offset(position);

            if flag {
                self.bit_array[vec_position] |= byte_offset;
            } else {
                self.bit_array[vec_position] &= !byte_offset;
            }

            Ok(())
        }
    }

    /// Gets either true or false value in bit array at given position.
    pub fn get(&self, position: i64) -> Result<bool, OutOfRangeError> {
        if position >= self.size {
            Err(OutOfRangeError::new(self.size, position))
        } else {
            let vec_position: usize = Self::calc_vec_position(position);
            let byte_offset: u8 = Self::calc_byte_offset(position);

            Ok(self.bit_array[vec_position] == (self.bit_array[vec_position] | byte_offset))
        }
    }
}

#[cfg(test)]
mod tests {
    use super::{BitArray, ONE_BYTE_BITS_COUNT};

    #[test]
    fn test_init_bitarray() {
        // Bit array size is a number of bits that will be allocated
        // in a given bitarray.
        // Bit array based on the vector of u8 integers
        // Each u8 integer occupy 8 bits of memory.
        // So the bitarray's vector should be of bitarray_size size / 8 size.
        let bitarray_size: i64 = 10;

        let bitarray: BitArray = BitArray::new(bitarray_size);

        assert_eq!(
            bitarray.bit_array.len(),
            (bitarray_size / ONE_BYTE_BITS_COUNT as i64) as usize + 1
        );
        assert_eq!(bitarray.bit_array.len(), 2);
    }

    #[test]
    fn test_bitarray_set_true() {
        let bitarray_size: i64 = 10;
        let bitarray_position: i64 = 9;

        let mut bitarray: BitArray = BitArray::new(bitarray_size);

        let success: bool = match bitarray.set(bitarray_position, true) {
            Ok(_) => true,
            Err(_) => false,
        };

        assert!(success);
    }

    #[test]
    fn test_bitarray_set_with_error() {
        let bitarray_size: i64 = 10;
        let bitarray_position: i64 = 10;

        let mut bitarray: BitArray = BitArray::new(bitarray_size);

        let success: bool = match bitarray.set(bitarray_position, true) {
            Ok(_) => false,
            Err(err) => {
                err.bitarray_position == 10
                    && err.bitarray_size == 10
                    && format!("{}", err) == "Given position: 10 is out of the bitarray size 10."
            }
        };

        assert!(success);
    }

    #[test]
    fn test_bitarray_get_with_error() {
        let bitarray_size: i64 = 10;
        let bitarray_position: i64 = 10;

        let bitarray: BitArray = BitArray::new(bitarray_size);

        let success: bool = match bitarray.get(bitarray_position) {
            Ok(_) => false,
            Err(err) => {
                err.bitarray_position == 10
                    && err.bitarray_size == 10
                    && format!("{}", err) == "Given position: 10 is out of the bitarray size 10."
            }
        };

        assert!(success);
    }

    #[test]
    fn test_bit_array_get_set() {
        let bitarray_size: i64 = 74845;

        let mut bitarray: BitArray = BitArray::new(bitarray_size);

        for bitarray_position in 0..bitarray_size - 1 {
            assert!(!bitarray.get(bitarray_position).unwrap());
        }

        for bitarray_position in 0..bitarray_size {
            bitarray.set(bitarray_position, true).unwrap();

            assert!(bitarray.get(bitarray_position).unwrap());
        }

        for bitarray_position in 0..bitarray_size - 1 {
            assert!(bitarray.get(bitarray_position).unwrap());
        }

        for bitarray_position in 0..bitarray_size {
            bitarray.set(bitarray_position, false).unwrap();

            assert!(!bitarray.get(bitarray_position).unwrap());
        }

        for bitarray_position in 0..bitarray_size - 1 {
            assert!(!bitarray.get(bitarray_position).unwrap());
        }
    }
}