use std::env;

const ENV_VAR_PREFIX: &str = "LOCALITY_";

#[derive(Debug)]
pub enum Error {
    MissingEnvironmentVariable(String),
}

impl std::fmt::Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::MissingEnvironmentVariable(v) => {
                write!(f, "The environment variable \"{}\" must be set.", v)
            }
        }
    }
}

impl std::error::Error for Error {}

pub struct Config {
    pub database_url: String,
    pub static_file_path: String,
    pub hmac_secret: Vec<u8>,
}

fn get_config_string(variable: &str) -> Result<String, Error> {
    let full_var = format!("{ENV_VAR_PREFIX}{variable}");
    env::var(&full_var).map_err(|_| Error::MissingEnvironmentVariable(full_var))
}

pub fn get_config() -> Result<Config, Error> {
    Ok(Config {
        database_url: get_config_string("DATABASE_URL")?,
        static_file_path: get_config_string("STATIC_FILE_PATH")?,
        hmac_secret: get_config_string("HMAC_SECRET")?.into_bytes(),
    })
}