//! Implements a trie on T9 numpads
//!
//! # T9:
//! 1:     2:abc  3:def
//! 4:ghi  5:jkl  6:mno
//! 7:pqrs 8:tuv  9:wxyz

use std::{
    collections::VecDeque,
    ops::{Index, IndexMut},
};

#[derive(Debug, Default)]
pub struct Trie9 {
    pub link: Option<Box<[Trie9; 8]>>,
    pub leaf: Vec<String>,
}

impl Trie9 {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn insert(&mut self, string: &str) -> bool {
        let Some(trie) = self.at_mut(string.chars()) else {
            return false;
        };

        trie.leaf.push(string.into());
        true
    }

    pub fn get(&self, index: T9) -> Option<&Trie9> {
        self.link.as_ref()?.get(index as usize)
    }

    pub fn get_mut(&mut self, index: T9) -> Option<&mut Trie9> {
        self.link.as_mut()?.get_mut(index as usize)
    }

    pub fn get_or_insert(&mut self, index: T9) -> &mut Trie9 {
        self.link
            .get_or_insert_default()
            .get_mut(index as usize)
            .expect("link exists at all T9 indices")
    }

    pub fn at<Iter, T>(&self, code: Iter) -> Option<&Self>
    where
        Iter: IntoIterator<Item = T>,
        T: TryInto<T9>,
    {
        let mut code = code.into_iter();
        match code.next() {
            None => Some(self),
            Some(link) => self.get(link.try_into().ok()?)?.at(code),
        }
    }

    pub fn at_mut<Iter, T>(&mut self, code: Iter) -> Option<&mut Self>
    where
        Iter: IntoIterator<Item = T>,
        T: TryInto<T9>,
    {
        let mut code = code.into_iter();
        match code.next() {
            None => Some(self),
            Some(link) => self.get_or_insert(link.try_into().ok()?).at_mut(code),
        }
    }

    pub fn iter<'t>(&'t self) -> Trie9Iter<'t> {
        Trie9Iter::new(self)
    }
}

#[derive(Clone, Debug)]
pub struct Trie9Iter<'t9> {
    queue: VecDeque<&'t9 Trie9>,
    items: std::slice::Iter<'t9, String>,
}

impl<'t> Trie9Iter<'t> {
    pub fn new(trie: &'t Trie9) -> Self {
        Self { queue: VecDeque::from([trie]), items: Default::default() }
    }
}

impl<'t> Iterator for Trie9Iter<'t> {
    type Item = &'t str;

    fn next(&mut self) -> Option<Self::Item> {
        let Self { queue, items } = self;

        if let Some(item) = items.next() {
            return Some(item.as_str());
        }

        let Trie9 { link, leaf } = queue.pop_front()?;
        *items = leaf.iter();
        queue.extend(link.iter().flat_map(|v| v.iter()));

        self.next()
    }
}

impl<'t> IntoIterator for &'t Trie9 {
    type IntoIter = Trie9Iter<'t>;
    type Item = &'t str;

    fn into_iter(self) -> Self::IntoIter {
        Self::IntoIter::new(self)
    }
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum T9 {
    T2,
    T3,
    T4,
    T5,
    T6,
    T7,
    T8,
    T9,
}

impl From<T9> for u8 {
    fn from(value: T9) -> Self {
        value as u8 + 2
    }
}

impl From<T9> for char {
    fn from(value: T9) -> Self {
        match value {
            T9::T2 => '2',
            T9::T3 => '3',
            T9::T4 => '4',
            T9::T5 => '5',
            T9::T6 => '6',
            T9::T7 => '7',
            T9::T8 => '8',
            T9::T9 => '9',
        }
    }
}

impl TryFrom<char> for T9 {
    type Error = char;
    fn try_from(value: char) -> Result<Self, Self::Error> {
        Ok(match value {
            '2' | 'A'..='C' | 'a'..='c' | 'À'..='Æ' | 'à'..='æ' | 'Ç' | 'ç' => Self::T2,
            '3' | 'D'..='F' | 'd'..='f' | 'È'..='Ë' | 'è'..='ë' => Self::T3,
            '4' | 'G'..='I' | 'g'..='i' | 'Ì'..='Ï' | 'ì'..='ï' => Self::T4,
            '5' | 'J'..='L' | 'j'..='l' | '1' => Self::T5,
            '6' | 'M'..='O' | 'm'..='o' | 'Ò'..='Ø' | 'ò'..='ø' | '0' => Self::T6,
            '7' | 'P'..='S' | 'p'..='s' => Self::T7,
            '8' | 'T'..='V' | 't'..='v' | 'Ù'..='Ü' | 'ù'..='ü' => Self::T8,
            '9' | 'W'..='Z' | 'w'..='z' => Self::T9,
            _ => Err(value)?,
        })
    }
}

impl Index<T9> for Trie9 {
    type Output = Trie9;
    fn index(&self, index: T9) -> &Self::Output {
        let Some(link) = self.get(index) else {
            panic!("No Trie9 at index {index:?}");
        };
        link
    }
}

impl IndexMut<T9> for Trie9 {
    fn index_mut(&mut self, index: T9) -> &mut Self::Output {
        self.get_or_insert(index)
    }
}