A simple markov text generator written in Rust.

markov.rs

use std::collections::HashMap;

use rand::Rng;
use regex::Regex;

const BEGIN: &str = "___BEGIN__";
const END: &str = "___END__";

const STATE_SIZE: usize = 2;

type State = Vec<String>;
type Weight = HashMap<String, i32>;
type Model = HashMap<State, Weight>;

#[derive(Debug, Default)]
pub struct Chain {
    pub model: Model,
    begin_choices: Vec<String>,
    begin_weights: Vec<i32>,
}

impl Chain {
    pub fn accumulate(ns: Vec<i32>) -> Vec<i32> {
        let mut numbers: Vec<i32> = Vec::new();
        let mut total = ns[0];
        for n in ns {
            numbers.push(total);
            total += n;
        }
        numbers
    }

    pub fn compile_next(data: Weight) -> (Vec<String>, Vec<i32>) {
        let words: Vec<String> = data.keys().cloned().collect();
        let cum: Vec<i32> = Self::accumulate(data.values().cloned().collect());
        (words, cum)
    }

    fn bisect_right<T: Ord>(slice: &[T], x: &T) -> usize {
        match slice.binary_search(x) {
            Ok(idx) => idx + 1, // if found, insert to the right
            Err(idx) => idx,    // if not found, Err gives insertion point
        }
    }
}

impl Chain {
    pub fn new(data: Vec<Vec<String>>) -> Self {
        let mut chain = Self::default();
        chain.model = chain.build(data);
        chain.compute();
        chain
    }

    pub fn build(&self, data: Vec<Vec<String>>) -> Model {
        let mut model: Model = HashMap::new();

        for run in data {
            let mut items: Vec<&str> = vec![BEGIN; STATE_SIZE];
            items.extend(run.iter().map(|s| s.as_str()));
            items.push(END);

            for i in 0..run.len() + 1 {
                let state: State = items[i..i + STATE_SIZE]
                    .iter()
                    .map(|s| (*s).to_string())
                    .collect::<Vec<String>>()
                    .try_into()
                    .unwrap();
                let follow: &str = items[i + STATE_SIZE];

                // FIXME: clones
                if !model.contains_key(&state) {
                    model.insert(state.clone(), HashMap::new());
                }

                // FIXME: &str to String
                if !model.get(&state).unwrap().contains_key(follow) {
                    model.get_mut(&state).unwrap().insert(follow.to_string(), 0);
                }

                *model.get_mut(&state).unwrap().get_mut(follow).unwrap() += 1;
            }
        }

        model
    }

    pub fn begin_state(&self) -> State {
        vec![BEGIN.to_string(); STATE_SIZE]
    }

    pub fn compute(&mut self) {
        let begin_state = self.begin_state();
        let (choices, cum) = Self::compile_next(self.model.get(&begin_state).unwrap().clone());
        self.begin_choices = choices;
        self.begin_weights = cum;
    }

    pub fn r#move(&self, state: &State) -> String {
        let (mut choices, mut cumdist) = (self.begin_choices.clone(), self.begin_weights.clone());
        if state != &self.begin_state() {
            // FIXME: This is flawed
            choices.clear();
            cumdist.clear();
            let mut weights: Vec<i32> = Vec::new();
            for (word, weight) in self.model.get(state).unwrap() {
                choices.push(word.clone());
                weights.push(*weight);
            }
            cumdist = Self::accumulate(weights);
        }
        let r: f32 = rand::thread_rng().gen_range(0.0..1.0) * (*cumdist.last().unwrap() as f32);
        let r_i32 = r as i32;
        choices[Self::bisect_right(&cumdist, &r_i32)].clone()
    }

    pub fn r#gen(&self, init_state: Option<State>) -> Vec<String> {
        let mut state = init_state.unwrap_or(self.begin_state());
        let mut result: Vec<String> = Vec::new();
        loop {
            let next_word: String = self.r#move(&state);
            if next_word == END {
                break;
            }
            // FIXME: clones
            result.push(next_word.clone());
            state = state[1..].to_vec();
            state.push(next_word.clone());
        }
        result
    }
}

#[derive(Debug, Default)]
pub struct Text {
    reject: Option<Regex>,
    parsed_sentences: Vec<Vec<String>>,
    rejoined_text: String,
    pub chain: Chain,
}

impl Text {
    pub fn sentence_input(&self, s: &str) -> bool {
        if s.trim().is_empty() {
            return false;
        }
        let decoded = unidecode::unidecode(s);
        if let Some(re) = &self.reject
            && re.is_match(&decoded)
        {
            return false;
        }
        true
    }
}

impl Text {
    pub fn new(data: String) -> Self {
        let mut text = Text::default();
        text.reject = Regex::new(&format!(r"(^')|('$)|\s'|'\s|[\{}(\(\)\[\])]", '"')).ok();
        text.parsed_sentences = text.parse(data);
        text.rejoined_text = text
            .parsed_sentences
            .iter()
            .map(|s| s.join(" "))
            .collect::<Vec<String>>()
            .join(" ");
        text.chain = Chain::new(text.parsed_sentences.clone());

        text
    }

    fn verify(&self, words: &[String], mor: f32, mot: usize) -> bool {
        let overlap_ratio = (mor * words.len() as f32).round() as usize;
        let overlap_max = mot.min(overlap_ratio);
        let overlap_over = overlap_max + 1;
        let gram_count = (words.len().saturating_sub(overlap_max)).max(1);

        for i in 0..gram_count {
            let end = (i + overlap_over).min(words.len());
            let gram = &words[i..end];
            let gram_joined = gram.join(" ");
            if self.rejoined_text.contains(&gram_joined) {
                return false;
            }
        }

        true
    }
    pub fn parse(&self, data: String) -> Vec<Vec<String>> {
        data.split("\n")
            .filter(|s| self.sentence_input(s))
            .map(|s| s.split_whitespace().map(|w| w.to_string()).collect())
            .collect()
    }

    pub fn generate(&self, tries: i32, min_words: i32, max_words: i32) -> String {
        for _ in 0..tries {
            let words: Vec<String> = self.chain.r#gen(None);
            if words.len() > max_words as usize || words.len() < min_words as usize {
                continue;
            }
            if self.verify(&words, 0.7, 15) {
                return words.join(" ");
            }
        }

        String::new()
    }
}