tdb-succinct 0.1.2

use super::integer::{bigint_to_storage, storage_to_bigint_and_sign, NEGATIVE_ZERO};
use bytes::Buf;
use lazy_static::lazy_static;
use regex::Regex;
use rug::Integer;
use thiserror::Error;

#[derive(PartialEq, Debug)]
pub struct Decimal(pub(crate) String);

#[derive(Debug, Error)]
#[error("Invalid format for decimal: `{value}`")]
pub struct DecimalValidationError {
    pub value: String,
}

impl Decimal {
    pub fn new(s: String) -> Result<Self, DecimalValidationError> {
        validate_decimal(&s)?;
        Ok(Decimal(s))
    }
}

pub fn validate_decimal(s: &str) -> Result<(), DecimalValidationError> {
    lazy_static! {
        static ref RE: Regex = Regex::new(r"^-?\d+(\.\d+)?([eE@](-|\+)?\d+)?$").unwrap();
    }
    if RE.is_match(s) {
        Ok(())
    } else {
        Err(DecimalValidationError {
            value: s.to_string(),
        })
    }
}

fn encode_fraction(fraction: Option<&str>) -> Vec<u8> {
    if let Some(f) = fraction {
        if f.is_empty() {
            return vec![0x00]; // a "false zero" so we don't represent it at all.
        }
        let len = f.len();
        let size = len / 2 + usize::from(len % 2 != 0);
        let mut bcd = Vec::with_capacity(size);
        for i in 0..size {
            let last = if i * 2 + 2 > len {
                i * 2 + 1
            } else {
                i * 2 + 2
            };
            let two = &f[2 * i..last];
            let mut this_int = centary_decimal_encode(two);
            this_int <<= 1;
            if i != size - 1 {
                this_int |= 1 // add continuation bit.
            }
            bcd.push(this_int)
        }
        bcd
    } else {
        vec![0x00] // a "false zero" so we don't represent no fraction as a fraction
    }
}

fn centary_decimal_encode(s: &str) -> u8 {
    if s.len() == 1 {
        let i = s.parse::<u8>().unwrap();
        i * 11 + 1
    } else {
        let i = s.parse::<u8>().unwrap();
        let o = i / 10 + 1;
        i + o + 1
    }
}

fn centary_decimal_decode(i: u8) -> String {
    let j = i - 1;
    if j % 11 == 0 {
        let num = j / 11;
        format!("{num:}")
    } else {
        let d = j / 11;
        let num = j - d - 1;
        format!("{num:02}")
    }
}

pub fn decode_fraction<B: Buf>(fraction_buf: &mut B, is_pos: bool) -> String {
    let mut first_byte = fraction_buf.chunk()[0];
    if !is_pos {
        first_byte = !first_byte;
    }
    if first_byte == 0x00 {
        "".to_string()
    } else {
        let mut s = String::new();
        while fraction_buf.has_remaining() {
            let mut byte = fraction_buf.get_u8();
            if !is_pos {
                byte = !byte;
            }
            let num = byte >> 1;
            let res = centary_decimal_decode(num);
            s.push_str(&res);
            if res.len() == 1 || byte & 1 == 0 {
                break;
            }
        }
        s
    }
}

pub fn decimal_to_storage(decimal: &str) -> Vec<u8> {
    lazy_static! {
        static ref STD: Regex = Regex::new(r"^-?\d+(\.\d*)?$").unwrap();
        static ref SCIENTIFIC: Regex = Regex::new(
            r"^(?P<sign>-)?(?P<integer>\d+)(\.(?P<fraction>\d+))?([eE@](?P<exp>(-|\+)?\d+))?$"
        )
        .unwrap();
    }
    if STD.is_match(decimal) {
        let mut parts = decimal.split('.');
        let bigint = parts.next().unwrap_or(decimal);
        let fraction = parts.next();
        let integer_part = bigint.parse::<Integer>().unwrap();
        let is_neg = decimal.starts_with('-');
        integer_and_fraction_to_storage(is_neg, integer_part, fraction)
    } else {
        let captures = SCIENTIFIC.captures(decimal).unwrap(); // prevalidated
        let is_neg = captures.name("sign").is_some();
        let exp: i32 = if let Some(exp_string) = captures.name("exp") {
            exp_string.as_str().parse::<i32>().unwrap()
        } else {
            0_i32
        };
        let integer_str = captures.name("integer").map(|m| m.as_str()).unwrap();
        let fraction_str = captures.name("fraction").map_or_else(|| "", |m| m.as_str());
        let left_pad = if -exp > integer_str.len() as i32 {
            "0.".to_string()
                + &"0".repeat((-exp - integer_str.len() as i32).unsigned_abs() as usize)
        } else {
            "".to_string()
        };
        let right_pad = if exp > fraction_str.len() as i32 {
            "0".repeat((exp - fraction_str.len() as i32) as usize)
        } else {
            "".to_string()
        };
        let left_len = left_pad.len() as i32 + integer_str.len() as i32;
        let combined = left_pad + integer_str + fraction_str + &right_pad;
        let shift = (left_len + exp) as usize;
        let integer_str = &combined[0..shift];
        let sign = if is_neg { -1 } else { 1 };
        let integer_part = sign
            * integer_str
                .parse::<Integer>()
                .unwrap_or_else(|_| Integer::from(0));
        let fraction = &combined[shift..];
        let fraction = if fraction.is_empty() {
            None
        } else {
            Some(fraction)
        };
        integer_and_fraction_to_storage(is_neg, integer_part, fraction)
    }
}

pub fn storage_to_decimal<B: Buf>(bytes: &mut B) -> String {
    let (int, is_pos) = storage_to_bigint_and_sign(bytes);
    let fraction = decode_fraction(bytes, is_pos);
    if fraction.is_empty() {
        format!("{int:}")
    } else {
        let sign = if int == 0 && !is_pos { "-" } else { "" };
        format!("{sign:}{int:}.{fraction:}")
    }
}

pub fn integer_and_fraction_to_storage(
    is_neg: bool,
    integer: Integer,
    fraction: Option<&str>,
) -> Vec<u8> {
    let prefix = bigint_to_storage(integer.clone());
    let mut prefix = if integer == 0 && is_neg {
        vec![NEGATIVE_ZERO] // negative zero
    } else {
        prefix
    };
    let suffix = if is_neg {
        let mut suffix = encode_fraction(fraction);
        for elt in &mut suffix {
            *elt = !(*elt)
        }
        suffix
    } else {
        encode_fraction(fraction)
    };
    prefix.extend(suffix);
    prefix
}