//! `human-sort` is a collection of utilities to sort and compare strings with numeric symbols
//! in human-friendly order.
//!
//! Utilities built over `iterator` and compare strings `char` by char (except for numerals)
//! until the first difference found.
//!
//! Utilities don't create Strings or another structures with whole data from provided `&str`,
//! so don't require lots of memory.
//!
//! # Examples
//!
//! ```
//! use human_sort::sort;
//!
//! let mut arr = ["file10.txt", "file2.txt", "file1.txt"];
//! sort(&mut arr);
//!
//! assert_eq!(arr, ["file1.txt", "file2.txt", "file10.txt"]);
//! ```
//!
//! ```
//! use std::cmp::Ordering;
//! use human_sort::compare;
//!
//! assert_eq!(compare("item200", "item3"), Ordering::Greater);
//! ```

use std::{cmp::Ordering, iter::Peekable, str::Chars};

/// Sorts [&str] in human order
///
/// # Example
///
/// ```
/// use human_sort::sort;
///
/// let mut arr = ["file10.txt", "file2.txt", "file1.txt"];
/// sort(&mut arr);
///
/// assert_eq!(arr, ["file1.txt", "file2.txt", "file10.txt"]);
/// ```
///
pub fn sort(arr: &mut [&str]) {
    arr.sort_by(|a, b| compare(a, b));
}

/// Compares two string slices case insensitively
///
/// # Example
///
/// ```
/// use std::cmp::Ordering;
/// use human_sort::compare;
///
/// assert_eq!(compare("item200", "item3"), Ordering::Greater);
/// ```
///
pub fn compare(s1: &str, s2: &str) -> Ordering {
    let mut s1_iter = s1.chars().peekable();
    let mut s2_iter = s2.chars().peekable();

    loop {
        let (x, y) = (s1_iter.next(), s2_iter.next());

        if x.is_some() && y.is_some() {
            let (x, y) = (x.unwrap(), y.unwrap());

            if x == y {
                continue;
            } else {
                match (x.is_numeric(), y.is_numeric()) {
                    (false, false) => return x.to_lowercase().cmp(y.to_lowercase()),
                    (true, false) => return Ordering::Greater,
                    (false, true) => return Ordering::Less,
                    (true, true) => {
                        let x_sum = parse_numeric_part(x, &mut s1_iter);
                        let y_sum = parse_numeric_part(y, &mut s2_iter);

                        if x_sum != y_sum {
                            return x_sum.cmp(&y_sum);
                        }
                    }
                }
            };
        } else {
            return s1.len().cmp(&s2.len());
        };
    }
}

fn parse_numeric_part(val: char, iter: &mut Peekable<Chars>) -> u32 {
    let mut sum = val.to_string();

    while iter.peek().is_some() && iter.peek().unwrap().is_numeric() {
        sum.push(iter.next().unwrap());
    }

    sum.parse().unwrap()
}