use std::{
    collections::HashSet,
    path::{Path, PathBuf},
    sync::mpsc::Sender,
};

use once_cell::sync::Lazy;
use pasetors::{keys::SymmetricKey, version4::V4};

use crate::{error::AppError, services::UserConfirmationMessage};

static REQUIRED_ENV_VARS: Lazy<HashSet<String>> = Lazy::new(|| {
    HashSet::<String>::from_iter(
        ["TOKEN_KEY", "DATABASE_URL", "ASSETS_DIR"]
            .into_iter()
            .map(ToString::to_string),
    )
});

#[derive(Clone)]
pub struct Environment {
    token_key: SymmetricKey<V4>,
    database_url: String,
    email_sender: Sender<UserConfirmationMessage>,
    assets_dir: PathBuf,
}

impl Environment {
    pub fn init(email_sender: Sender<UserConfirmationMessage>) -> Result<Self, AppError> {
        let mut builder = EnvironmentObjectBuilder::new(email_sender);
        dotenvy::dotenv_iter()
            .expect("Missing .env file")
            .filter_map(|item| item.ok())
            .filter(|(key, _)| REQUIRED_ENV_VARS.contains(key))
            .for_each(|(key, value)| match key.as_str() {
                "TOKEN_KEY" => builder.with_token_key(value),
                "DATABASE_URL" => builder.with_database_url(value),
                "ASSETS_DIR" => builder.with_assets_dir(value),
                _ => {}
            });

        if let Some(missing_vars) = builder.uninitialized_variables() {
            Err(AppError::missing_environment_variables(missing_vars))
        } else {
            Ok(Environment::from(builder))
        }
    }

    pub fn token_key(&self) -> &SymmetricKey<V4> {
        &self.token_key
    }

    pub fn db_connection_uri(&self) -> &str {
        self.database_url.as_str()
    }

    pub fn assets_dir(&self) -> &Path {
        self.assets_dir.as_path()
    }

    pub fn email_sender(&self) -> &Sender<UserConfirmationMessage> {
        &self.email_sender
    }
}

impl From<EnvironmentObjectBuilder> for Environment {
    fn from(builder: EnvironmentObjectBuilder) -> Self {
        let EnvironmentObjectBuilder {
            token_key,
            database_url,
            email_sender,
            assets_dir,
        } = builder;

        Self {
            token_key: token_key.unwrap(),
            database_url: database_url.unwrap(),
            email_sender: email_sender.unwrap(),
            assets_dir: assets_dir.unwrap(),
        }
    }
}

#[derive(Default)]
pub struct EnvironmentObjectBuilder {
    pub token_key: Option<SymmetricKey<V4>>,
    pub database_url: Option<String>,
    pub email_sender: Option<Sender<UserConfirmationMessage>>,
    pub assets_dir: Option<PathBuf>,
}

impl EnvironmentObjectBuilder {
    pub fn new(email_sender: Sender<UserConfirmationMessage>) -> Self {
        Self {
            email_sender: Some(email_sender),
            ..Default::default()
        }
    }

    pub fn uninitialized_variables(&self) -> Option<Vec<&'static str>> {
        let mut missing_vars = Vec::with_capacity(3);
        if self.token_key.is_none() {
            missing_vars.push("TOKEN_KEY");
        }

        if self.database_url.is_none() {
            missing_vars.push("DATABASE_URL");
        }

        if self.assets_dir.is_none() {
            missing_vars.push("ASSETS_DIR");
        }

        if missing_vars.is_empty() {
            None
        } else {
            Some(missing_vars)
        }
    }

    pub fn with_token_key(&mut self, key: String) {
        match SymmetricKey::<V4>::try_from(key.as_str()).map_err(|_| AppError::token_key()) {
            Ok(key) => self.token_key = Some(key),
            Err(err) => panic!("{err}"),
        };
    }

    pub fn with_database_url(&mut self, url: String) {
        self.database_url = Some(url);
    }

    pub fn with_assets_dir(&mut self, assets_dir_path: String) {
        let assets_dir = PathBuf::from(assets_dir_path);
        if !assets_dir.try_exists().unwrap_or_default() {
            panic!(
                "The 'ASSETS_DIR' environment variable points to a directory that doesn't exist."
            );
        }

        if assets_dir.is_file() {
            panic!("The 'ASSETS_DIR' environment variable must be set to a directory, not a file.");
        }

        self.assets_dir = Some(assets_dir);
    }
}