pub struct FibIter {
    f0: u32,
    f1: u32,
}

impl FibIter {
    pub fn new() -> FibIter {
        FibIter { f0: 1, f1: 1, }
    }

    pub fn next(&mut self) -> u32 {
        let f0 = self.f0;
        // 1 2 |-> 2 3
        self.f0 = self.f1;
        self.f1 += f0;
        f0
    }

    pub fn rev(self) -> RevFibIter {
        RevFibIter { f0: self.f1 - self.f0, f1: self.f0 }
    }

    fn inc(&mut self) -> Option<usize> {
        Option::Some(self.next() as usize)
    }
}

struct Split {
    start: usize,
    end:   usize,
    count: u32,
    fib:   Option<FibIter>,
    rfib:  Option<RevFibIter>,
    n:         u32,
    symmetric: bool,
}

impl Split {
    fn new(n: u32, symmetric: bool) -> Split {
        let mut fib = FibIter::new();
        Split { start: 0, end: fib.inc().unwrap(), count: 0, fib: Option::Some(fib), rfib: Option::None, n: n, symmetric: symmetric }
    }

    fn inc(&mut self) {
        if self.symmetric && self.n == self.count {
            self.rfib = Option::Some(self.fib.take().unwrap().rev());
        }

        self.start  = self.end;
        self.end   += match self.fib {
            Some(_) => self. fib.as_mut().unwrap().inc().unwrap(),
            None    => self.rfib.as_mut().unwrap().inc().unwrap()
        };
        self.count += 1;
    }
}

fn _fib_split(text: &str, n: u32, panic: bool, symmetric: bool) -> (Vec<String>, &str) {
    let mut out: Vec<String> = Vec::new();

    let mut sp = Split::new(n, symmetric);
    //                            ( panic -> sp.count < n)
    while sp.end <= text.len() && (!panic || sp.count < n) {
        out.push(text[sp.start..sp.end].to_string());
        sp.inc();
    }

    if panic && sp.count < n {
        panic!("Split into {} our of {} words!", sp.count, n);
    }

    (out, &text[sp.start..])
}

pub fn fib_split(text: &str) -> Vec<String> {
    let (mut init, last) = _fib_split(text, 0, false, false);
    init.push(last.to_string());
    init
}

pub fn fib_split_n(text: &str, n: u32) -> (Vec<String>, &str) {
    _fib_split(text, n, true, false)
}

pub struct RevFibIter {
    f0: u32,
    f1: u32,
}

impl RevFibIter {
    pub fn next(&mut self) -> Option<u32> {
        if self.f1 == 1 {
            return Option::None;
        }

        // 2 3 |-> 1 2
        let f0 = self.f0;
        self.f0 = self.f1 - self.f0;
        self.f1 = f0;

        Option::Some(self.f1)
    }

    fn inc(&mut self) -> Option<usize> {
        let val = self.next();
        match val {
            Option::Some(_) => Option::Some(val.unwrap() as usize),
            Option::None    => Option::None,
        }
    }
}

pub fn fib_split_n_symmetric(text: &str, n: u32) -> (Vec<String>, &str) {
    _fib_split(text, n, true, true)
}

use std::panic::catch_unwind;

#[test]
fn fib_iter() {
    let mut fib_iter = FibIter::new();

    assert_eq!(fib_iter.next(), 1);
    assert_eq!(fib_iter.next(), 1);
    assert_eq!(fib_iter.next(), 2);
    assert_eq!(fib_iter.next(), 3);
    assert_eq!(fib_iter.next(), 5);
    assert_eq!(fib_iter.next(), 8);
    assert_eq!(fib_iter.next(), 13);
}

#[test]
fn rev_fib_iter() {
    let mut fib_iter = FibIter::new();
    for _ in 0..7 {
        fib_iter.next();
    }

    let mut rev_fib_iter = fib_iter.rev();

    assert_eq!(rev_fib_iter.next(), Some(13));
    assert_eq!(rev_fib_iter.next(), Some(8));
    assert_eq!(rev_fib_iter.next(), Some(5));
    assert_eq!(rev_fib_iter.next(), Some(3));
    assert_eq!(rev_fib_iter.next(), Some(2));
    assert_eq!(rev_fib_iter.next(), Some(1));
    assert_eq!(rev_fib_iter.next(), Some(1));
    assert_eq!(rev_fib_iter.next(), None);
    assert_eq!(rev_fib_iter.next(), None);
}

#[test]
fn rev_fib_iter_empty() {
    let fib_iter = FibIter::new();
    let mut rev_fib_iter = fib_iter.rev();
    assert_eq!(rev_fib_iter.next(), None);
}

#[test]
fn fib_split_empty() {
    let words = fib_split("");
    assert!(words == Vec::<&str>::new() || words == &[""]);
}

#[test]
fn fib_split_ascii() {
    let words = fib_split("abcd123456");
    assert_eq!(words, &["a", "b", "cd", "123", "456"]);
}

#[test]
fn fib_split_cyrillic() {
    let words = fib_split("манджа с грозде");
    assert_eq!(words, &["м", "а", "нд", "жа ", "с гро", "зде"]);
}

#[test]
fn fib_split_n_zero() {
    let (words, rest) = fib_split_n("", 0);
    assert_eq!(words, Vec::<&str>::new());
    assert_eq!(rest, "");

    let (words, rest) = fib_split_n("abcdгрозде", 0);
    assert_eq!(words, Vec::<&str>::new());
    assert_eq!(rest, "abcdгрозде");
}

#[test]
fn fib_split_n_ascii() {
    let (words, rest) = fib_split_n("abcd_123", 1);
    assert_eq!(words, &["a"]);
    assert_eq!(rest, "bcd_123");

    let (words, rest) = fib_split_n("abcd_123", 4);
    assert_eq!(words, &["a", "b", "cd", "_12"]);
    assert_eq!(rest, "3");
}

#[test]
fn fib_split_n_ascii_exact() {
    let (words, rest) = fib_split_n("abcd_12_3456", 5);
    assert_eq!(words, &["a", "b", "cd", "_12", "_3456"]);
    assert_eq!(rest, "");
}

#[test]
fn fib_split_n_ascii_panic() {
    assert!(catch_unwind(|| fib_split_n("", 1)).is_err());
    assert!(catch_unwind(|| fib_split_n("abcd_123", 5)).is_err());
}

#[test]
fn fib_split_n_cyrillic() {
    let (words, rest) = fib_split_n("манджа_with_грозде", 1);
    assert_eq!(words, &["м"]);
    assert_eq!(rest, "анджа_with_грозде");

    let (words, rest) = fib_split_n("манджа_with_грозде", 5);
    assert_eq!(words, &["м", "а", "нд", "жа_", "with_"]);
    assert_eq!(rest, "грозде");
}

#[test]
fn fib_split_n_cyrillic_exact() {
    let (words, rest) = fib_split_n("манджа_with_", 5);
    assert_eq!(words, &["м", "а", "нд", "жа_", "with_"]);
    assert_eq!(rest, "");
}

#[test]
fn fib_split_n_cyrillic_panic() {
    assert!(catch_unwind(|| fib_split_n("манджа_with_грозде", 6)).is_err());
}

#[test]
fn fib_split_n_symmetric_zero() {
    let (words, rest) = fib_split_n_symmetric("", 0);
    assert_eq!(words, Vec::<&str>::new());
    assert_eq!(rest, "");

    let (words, rest) = fib_split_n_symmetric("abcdгрозде", 0);
    assert_eq!(words, Vec::<&str>::new());
    assert_eq!(rest, "abcdгрозде");
}

#[test]
fn fib_split_n_symmetric_ascii() {
    let (words, rest) = fib_split_n_symmetric("abcd1234", 1);
    assert_eq!(words, &["a", "b"]);
    assert_eq!(rest, "cd1234");

    let (words, rest) = fib_split_n_symmetric("abcd1234", 2);
    assert_eq!(words, &["a", "b", "c", "d"]);
    assert_eq!(rest, "1234");
}

#[test]
fn fib_split_n_symmetric_ascii_exact() {
    let (words, rest) = fib_split_n_symmetric("abcd1234", 3);
    assert_eq!(words, &["a", "b", "cd", "12", "3", "4"]);
    assert_eq!(rest, "");
}

#[test]
fn fib_split_n_symmetric_ascii_panic() {
    assert!(catch_unwind(|| fib_split_n_symmetric("", 1)).is_err());
    assert!(catch_unwind(|| fib_split_n_symmetric("abcd_1234", 4)).is_err());
}

#[test]
fn fib_split_n_symmetric_cyrillic() {
    let (words, rest) = fib_split_n_symmetric("манджа_with_грозде", 1);
    assert_eq!(words, &["м", "а"]);
    assert_eq!(rest, "нджа_with_грозде");

    let (words, rest) = fib_split_n_symmetric("манджа_with_грозде", 4);
    assert_eq!(words, &["м", "а", "нд", "жа_", "wit", "h_", "г", "р"]);
    assert_eq!(rest, "озде");
}

#[test]
fn fib_split_n_symmetric_cyrillic_exact() {
    let (words, rest) = fib_split_n_symmetric("манджа_with_гр", 4);
    assert_eq!(words, &["м", "а", "нд", "жа_", "wit", "h_", "г", "р"]);
    assert_eq!(rest, "");
}

#[test]
fn fib_split_n_symmetric_cyrillic_panic() {
    assert!(catch_unwind(|| fib_split_n_symmetric("манджа_with_грозде", 5)).is_err());
}