rust-web/src/store.rs

/// Store is responsible for manageing the in-memory hashmap of questions by providing initialization read/write functions,
/// and file I/O operations to persist these questions
/// TODO - Results returning errors should use specified types, not strings
use self::{
    answer::{Answer, AnswerDTO},
    question::{Question, QuestionDTO},
};
use crate::*;

const QUESTIONS_DB_PATH: &str = "./questions.json";
const ANSWERS_DB_PATH: &str = "./answers.json";

#[derive(Debug)]
pub struct Store {
    answers_file: File,
    questions_file: File,
    answers: HashMap<u8, Answer>,
    questions: HashMap<u8, Question>,
}

impl Store {
    // Upon initialization, we need to read a questions.json ans anwers.json if they exist and populate our hashmaps from them.
    // Otherwise we create both files.
    // JSON formatting and I/O errors possible here are semi-handled with a message, but ultimetly we will panic in those cases
    // TODO - make this less copy/paste like
    pub fn new() -> Self {
        let questions_file: File = File::create_new(QUESTIONS_DB_PATH)
            .or_else(|e| {
                if e.kind() == ErrorKind::AlreadyExists {
                    File::options()
                        .read(true)
                        .write(true)
                        .open(QUESTIONS_DB_PATH)
                } else {
                    Err(e)
                }
            })
            .unwrap();
        let questions_json = std::io::read_to_string(&questions_file)
            .expect("could not get json from questions file");
        // perhaps there is a more efficient/clever way aside from reading the json to a vector and mapping the vector to a hashmap.
        let questions_vec: Vec<QuestionDTO> =
            serde_json::from_str(&questions_json).expect("can't read questions.json");
        let questions: HashMap<u8, Question> = questions_vec
            .into_iter()
            .map(|question_dto: QuestionDTO| question_dto.to_entity())
            .collect();

        let answers_file: File = File::create_new(ANSWERS_DB_PATH)
            .or_else(|e| {
                if e.kind() == ErrorKind::AlreadyExists {
                    File::options().read(true).write(true).open(ANSWERS_DB_PATH)
                } else {
                    Err(e)
                }
            })
            .unwrap();
        let answers_json =
            std::io::read_to_string(&answers_file).expect("could not get json from answers file");
        let answers_vec: Vec<AnswerDTO> =
            serde_json::from_str(&answers_json).expect("can't read answers.json");
        let answers: HashMap<u8, Answer> = answers_vec
            .into_iter()
            .map(|answer_dto: AnswerDTO| answer_dto.to_entity())
            .collect();

        Store {
            questions,
            answers,
            answers_file,
            questions_file,
        }
    }

    // Take the content of the questions hashmap, convert it to a vector of question DTOs and overwrite the file with these contents
    // Not the most efficient approach if we are just adding or deleting a single question, but it does the job at our current scale
    // TODO - pretty print before writing
    fn write_questions_file(&mut self) {
        let questions: &HashMap<u8, Question> = &self.questions;
        let questions_vec: Vec<QuestionDTO> = questions
            .iter()
            .map(|q: (&u8, &Question)| q.1.to_dto(*q.0))
            .collect();
        let json: String = serde_json::to_string(&questions_vec).unwrap();
        let mut f: &File = &self.questions_file;
        match f
            .rewind()
            .and(f.write_all(json.as_bytes()))
            .and(f.sync_all())
            .and(f.set_len(f.stream_position().unwrap()))
        {
            Ok(()) => (),
            _ => panic!("Could not write file"),
        }
    }

    // Take the content of the answers hashmap, convert it to a vector of answer DTOs and overwrite the file with these contents
    fn write_answers_file(&mut self) {
        let answers: &HashMap<u8, Answer> = &self.answers;
        let answers_vec: Vec<AnswerDTO> = answers
            .iter()
            .map(|q: (&u8, &Answer)| q.1.to_dto(*q.0))
            .collect();
        let json: String = serde_json::to_string(&answers_vec).unwrap();
        let mut f: &File = &self.answers_file;
        match f
            .rewind()
            .and(f.write_all(json.as_bytes()))
            .and(f.sync_all())
            .and(f.set_len(f.stream_position().unwrap()))
        {
            Ok(()) => (),
            _ => panic!("Could not write file"),
        }
    }

    pub fn add_question(&mut self, id: u8, question: Question) -> Result<Question, String> {
        if self.questions.contains_key(&id) {
            return Err(format!("Question with id {} already exists", id));
        }
        match self.questions.insert(id, question.clone()) {
            None => {
                self.write_questions_file();
                Ok(question)
            } //Looks backwards, but insert must return none since key cannot already exist
            _ => Err("Server Error".to_string()),
        }
    }
    pub fn remove_question(&mut self, id: u8) -> Result<Question, String> {
        match self.questions.remove(&id) {
            Some(question) => {
                self.write_questions_file();
                Ok(question)
            }
            None => Err(format!("Question with id {} does not exist", id)),
        }
    }
    pub fn fetch_one_question(&self, id: u8) -> Result<Question, String> {
        match self.questions.get(&id) {
            Some(question) => Ok(question.clone()),
            None => Err(format!("Question with id {} does not exists", id)),
        }
    }
    //by nature of the hashmap, pagination does not follow id order
    pub fn fetch_many_questions(&self, start: usize, size: usize) -> Vec<QuestionDTO> {
        self.questions
            .iter()
            .map(|q| q.1.to_dto(*q.0))
            .skip(start)
            .take(size)
            .collect()
    }
    pub fn update_question(&mut self, id: u8, question: Question) -> Result<Question, String> {
        if !self.questions.contains_key(&id) {
            return Err(format!("Question with id {} does not exists", id));
        }
        match self.questions.insert(id, question) {
            Some(question) => {
                self.write_questions_file();
                Ok(question)
            }
            None => Err("Server Error".to_string()),
        }
    }

    pub fn add_answer(&mut self, id: u8, answer: Answer) -> Result<Answer, String> {
        if self.answers.contains_key(&id) {
            return Err(format!("Answer with id {} already exists", id));
        }
        match self.answers.insert(id, answer.clone()) {
            None => {
                self.write_answers_file();
                Ok(answer)
            }
            _ => Err("Server Error".to_string()),
        }
    }
}