use std::collections::HashMap;

#[derive(Clone)]
pub struct Databases {
    db_map: HashMap<String, String>,
}

impl Databases {
    pub fn new() -> Self {
        Self {
            db_map: HashMap::new(),
        }
    }

    fn add_database(&mut self, name: &str, id: &str) -> Option<String> {
        if self.db_map.contains_key(name) {
            None
        } else {
            self.db_map.insert(name.to_string(), id.to_string());
            Some(id.to_string())
        }
    }

    fn get_database(&self, name: &str) -> Option<String> {
        self.db_map.get(name).cloned()
    }

    fn show(&self) -> Vec<String> {
        let mut names: Vec<String> = self.db_map.clone().into_keys().collect();
        names.sort();
        names
    }
}

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

    #[test]
    fn add_entry() {
        let name = "fred";
        let id = "123456";
        let mut dbs = Databases::new();
        let output = dbs.add_database(name, id);
        assert_eq!(output, Some(id.to_string()));
        let output = dbs.get_database(name);
        assert_eq!(output, Some(id.to_string()));
    }

    #[test]
    fn entry_cannot_be_over_written() {
        let name = "barney";
        let id = "abcde";
        let mut dbs = Databases::new();
        dbs.add_database(name, id);
        let output = dbs.add_database(name, "09876");
        assert_eq!(output, None);
        let output = dbs.get_database(name);
        assert_eq!(output, Some(id.to_string()));
    }

    #[test]
    fn get_bad_database() {
        let dbs = Databases::new();
        let output = dbs.get_database("missing");
        assert_eq!(output, None);
    }

    #[test]
    fn list_databases() {
        let mut dbs = Databases::new();
        dbs.add_database("zebra", "a");
        dbs.add_database("alpha", "a");
        dbs.add_database("charlie", "a");
        dbs.add_database("wilma", "a");
        dbs.add_database("frank", "a");
        let expected = ["alpha", "charlie", "frank", "wilma", "zebra"];
        let output = dbs.show();
        assert_eq!(output, expected);
    }
}