use itertools::Itertools;

#[derive(PartialEq, Debug)]
pub enum ElementSubstring {
    Element(String),
    NonElement(String),
}

fn elementsubstringvec_length(elword: &Vec<ElementSubstring>) -> usize {
    let mut size = 0;
    for substring in elword {
        match substring {
            ElementSubstring::Element(s) => {
                for _char in s.chars() {
                    size += 1;
                }
            }
            ElementSubstring::NonElement(s) => {
                for _char in s.chars() {
                    size += 1;
                }
            }
        }
    }
    size
}

const SINGLE_CHAR_ELEMENTS: &'static [&'static str] = &[
    "B", "C", "F", "H", "I", "N", "O", "P", "K", "S", "W", "U", "V", "Y",
];
const DOUBLE_CHAR_ELEMENTS: &'static [&'static str] = &[
    "Ac", "Al", "Am", "Sb", "Ar", "As", "At", "Ba", "Bk", "Be", "Bi", "Bh", "Br", "Cd", "Cs", "Ca",
    "Cf", "Ce", "Cl", "Cr", "Co", "Cn", "Cu", "Cm", "Ds", "Db", "Dy", "Es", "Er", "Eu", "Fm", "Fl",
    "Fr", "Gd", "Ga", "Ge", "Au", "Hf", "Hs", "He", "Ho", "In", "Ir", "Fe", "Kr", "La", "Lr", "Pb",
    "Li", "Lv", "Lu", "Mg", "Mn", "Mt", "Md", "Hg", "Mo", "Mc", "Nd", "Ne", "Np", "Ni", "Nh", "Nb",
    "No", "Og", "Os", "Pd", "Pt", "Pu", "Po", "Pr", "Pm", "Pa", "Ra", "Rn", "Re", "Rh", "Rg", "Rb",
    "Ru", "Rf", "Sm", "Sc", "Sg", "Se", "Si", "Ag", "Na", "Sr", "Ta", "Tc", "Te", "Ts", "Tb", "Tl",
    "Th", "Tm", "Sn", "Ti", "Xe", "Yb", "Zn", "Zr",
];

pub fn partial_elname(word: &str) -> Vec<ElementSubstring> {
    let mut elword = vec![];
    let word = word.to_lowercase();
    let mut substring: String = String::new();
    let mut skip_next_loop = false;
    for (prev, next) in word.chars().tuple_windows() {
        if skip_next_loop {
            skip_next_loop = false;
            continue;
        }
        let potential_el: String = prev.to_string().to_uppercase() + &next.to_string();
        let mut found_match = false;
        for element in DOUBLE_CHAR_ELEMENTS {
            if element == &potential_el {
                if substring.len() > 0 {
                    elword.push(ElementSubstring::NonElement(substring.clone()));
                    substring = String::new();
                }
                elword.push(ElementSubstring::Element(element.to_string()));
                skip_next_loop = true;
                found_match = true;
                break;
            }
        }
        if found_match {
            continue;
        }

        for element in SINGLE_CHAR_ELEMENTS {
            if element.to_lowercase().chars().next().unwrap() == prev {
                if substring.len() > 0 {
                    elword.push(ElementSubstring::NonElement(substring.clone()));
                    substring = String::new();
                }
                elword.push(ElementSubstring::Element(element.to_string()));
                found_match = true;
                break;
            }
        }
        if found_match {
            continue;
        }
        substring.push(prev);
    }
    // This gets triggered when either:
    //  - the last window is 2 valid Elements as in "CrISP", or
    //  - the second to last window is a 2 letter Element (and would be skipped) as in "BaN"
    if elementsubstringvec_length(&elword) <= word.chars().count() - 1 {
        let last_char = word.chars().last().unwrap();
        let mut found_match = false;
        for element in SINGLE_CHAR_ELEMENTS {
            if element.to_lowercase().chars().next().unwrap() == last_char {
                if substring.len() > 0 {
                    elword.push(ElementSubstring::NonElement(substring.clone()));
                    substring = String::new();
                }
                elword.push(ElementSubstring::Element(element.to_string()));
                found_match = true;
                break;
            }
        }
        if !found_match {
            substring.push(last_char);
        }
    }
    if substring.len() > 0 {
        elword.push(ElementSubstring::NonElement(substring.clone()));
    }
    elword
}

pub fn complete_elname(word: &str) -> Option<Vec<String>> {
    let mut elword: Vec<String> = vec![];
    let word = word.to_lowercase();
    // The thing feels a bit un-rust-y, but does seem to work!
    let mut skip_next_loop = false;
    for (prev, next) in word.chars().tuple_windows() {
        if skip_next_loop {
            skip_next_loop = false;
            continue;
        }

        let potential_el: String = prev.to_string().to_uppercase() + &next.to_string();

        let mut found_match = false;
        // Can probably short circuit slightly here based on ASCII value or something (if in alphabetical order)
        for element in DOUBLE_CHAR_ELEMENTS {
            if element == &potential_el {
                elword.push(element.to_string());
                skip_next_loop = true;
                found_match = true;
                break;
            }
        }
        if found_match {
            continue;
        }

        for element in SINGLE_CHAR_ELEMENTS {
            if element.to_lowercase().chars().next().unwrap() == prev {
                elword.push(element.to_string());
                found_match = true;
                break;
            }
        }

        if !found_match {
            return None;
        }
    }

    // This gets triggered when either:
    //  - the last window is 2 valid Elements as in "CrISP", or
    //  - the second to last window is a 2 letter Element (and would be skipped) as in "BaN"
    let mut num_chars = 0;
    for els in &elword {
        num_chars += els.chars().count();
    }
    if num_chars == word.chars().count() - 1 {
        let mut found_match = false;
        let last_char = word.chars().last().unwrap();
        for element in SINGLE_CHAR_ELEMENTS {
            if element.to_lowercase().chars().nth(0).unwrap() == last_char {
                elword.push(element.to_string());
                found_match = true;
                break;
            }
        }
        if !found_match {
            return None;
        }
    }

    Some(elword)
}

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

    #[test]
    fn test_complete_elname() {
        assert_eq!(complete_elname("a"), None);
        assert_eq!(complete_elname("bar"), None);
        assert_eq!(complete_elname("zee"), None);
        assert_eq!(complete_elname("ge"), Some(vec!["Ge".to_string()]));
        assert_eq!(
            complete_elname("cras"),
            Some(vec!["Cr".to_string(), "As".to_string()])
        );
        assert_eq!(
            complete_elname("ban"),
            Some(vec!["Ba".to_string(), "N".to_string()])
        );
        assert_eq!(complete_elname("arthur"), None);
        assert_eq!(
            complete_elname("crisp"),
            Some(vec![
                "Cr".to_string(),
                "I".to_string(),
                "S".to_string(),
                "P".to_string()
            ])
        );
        assert_eq!(complete_elname("accepting"), None);
    }

    #[test]
    fn test_partial_elname() {
        type ES = ElementSubstring;
        assert_eq!(partial_elname("a"), vec![ES::NonElement("a".to_string())]);
        assert_eq!(
            partial_elname("bar"),
            vec![
                ES::Element("Ba".to_string()),
                ES::NonElement("r".to_string())
            ]
        );
        assert_eq!(
            partial_elname("zee"),
            vec![ES::NonElement("zee".to_string())]
        );
        assert_eq!(partial_elname("ge"), vec![ES::Element("Ge".to_string())]);
        assert_eq!(
            partial_elname("crisp"),
            vec![
                ES::Element("Cr".to_string()),
                ES::Element("I".to_string()),
                ES::Element("S".to_string()),
                ES::Element("P".to_string())
            ]
        );
        assert_eq!(
            partial_elname("accepting"),
            vec![
                ES::Element("Ac".to_string()),
                ES::Element("Ce".to_string()),
                ES::Element("Pt".to_string()),
                ES::Element("In".to_string()),
                ES::NonElement("g".to_string())
            ]
        );
    }
}