//! SMTP server implementation for receiving and processing emails.
//!
//! This module handles SMTP connections, email parsing, and forwarding to
//! Telegram.

use crate::{
	Cursor,
	telegram::TelegramTransport,
	utils::{
		Attachment,
		RE_DOMAIN,
		validate,

		INVALID_CREDENTIALS,
		NO_MAILBOX,
		OK
	},
};
use regex::{
	Regex,
	RegexBuilder,
	escape,
};
use stacked_errors::{
	Result,
	StackableErr,
	bail,
};

}

/// `MailServer` Central object with TG api and configuration
#[derive(Clone, Debug)]
pub struct MailServer {
	data: Vec<u8>,
	headers: Option<SomeHeaders>,
	relay: bool,
	tg: Arc<TelegramTransport>,
	fields: HashSet<String>,
	address: Regex,
}

impl MailServer {
	/// Initializes the mail server: sets up the Telegram API client and
	/// Initialize API and read configuration
	pub fn new(settings: config::Config) -> Result<MailServer> {
	/// validates all required configuration values.
	///
	/// # Arguments
	/// * `settings` - Parsed application configuration.
	///
	/// # Errors
	/// Returns an error if required configuration values are missing or invalid.
	/// server fails to start.
	pub fn new (settings: config::Config) -> Result<MailServer> {
		let api_key = settings.get_string("api_key")
			.context("[smtp2tg.toml] missing \"api_key\" parameter.\n")?;
		let mut recipients = HashMap::new();
		for (name, value) in settings.get_table("recipients")
			.expect("[smtp2tg.toml] missing table \"recipients\".\n")
			.context("[smtp2tg.toml] missing table \"recipients\".\n")?
		{
			let value = value.into_int()
				.context("[smtp2tg.toml] \"recipient\" table values should be integers.\n")?;
			recipients.insert(name, value);
			recipients.insert(name.to_lowercase(), value);
		}

		let tg = Arc::new(TelegramTransport::new(api_key, recipients, &settings)?);
		let fields = HashSet::<String>::from_iter(settings.get_array("fields")
			.expect("[smtp2tg.toml] \"fields\" should be an array")
			.iter().map(|x| x.clone().into_string().expect("should be strings")));
			.context("[smtp2tg.toml] \"fields\" should be an array")?
			.iter().map(|x| x.clone().into_string().context("should be strings"))
			.collect::<Result<Vec<String>>>()?);
		let mut domains: HashSet<String> = HashSet::new();
		let extra_domains = settings.get_array("domains").stack()?;
		for domain in extra_domains {
			let domain = domain.to_string().to_lowercase();
			if RE_DOMAIN.is_match(&domain) {
				domains.insert(domain);
			} else {
				panic!("[smtp2tg.toml] can't check of domains in \"domains\": {domain}");
				bail!("[smtp2tg.toml] can't check domains in \"domains\": {domain}");
			}
		}
		if domains.is_empty() {
			bail!("No domains, need at least one: default `localhost` would do.");
		}
		let domains = domains.into_iter().map(|s| escape(&s))
			.collect::<Vec<String>>().join("|");
		let address = Regex::new(&format!("^(?P<user>[a-z0-9][-a-z0-9])(@({domains}))$")).stack()?;
		let address = RegexBuilder::new(&format!("^[a-z0-9][a-z0-9.-]*(@({domains}))?$"))
		let relay = match settings.get_string("unknown")
			.context("[smtp2tg.toml] can't get \"unknown\" policy.\n")?.as_str()
		{
			"relay" => true,
			.case_insensitive(true).build().stack()?;
			"deny" => false,
			_ => {
				bail!("[smtp2tg.toml] \"unknown\" should be either \"relay\" or \"deny\".\n");
			},
		};

		Ok(MailServer {
			data: vec!(),
			headers: None,
			relay,
			tg,
			fields,
			address,
		})
	}

	/// Retrieves the Telegram chat ID for a given email address, checks that
	/// used domain is allowed.
	///
	/// # Arguments
	/// * `name` - Email address or username to look up.
	///
	/// Returns id for provided email address
	pub fn get_id (&self, name_str: &str) -> Result<&ChatPeerId> {
	/// # Returns
	/// * `Result<ChatPeerId>` - Telegram chat ID for the address, or default if
	///   not found.
	pub fn get_id (&self, name: &str) -> Result<&ChatPeerId> {
		// here we need to store String locally to borrow it after
		let mut link = name_str;
		let name: String;
		if let Some(caps) = self.address.captures(link) {
		if self.address.is_match(name) {
			name = caps["name"].to_string();
			link = &name;
		}
			Ok(self.tg.get(name).unwrap_or(&self.tg.default))
		} else {
		match self.tg.get(link) {
			Ok(addr) => Ok(addr),
			bail!("Doesn't look like address from one of our domains.");
			Err(_) => Ok(&self.tg.default),
		}
	}

	/// Attempt to deliver one message
	async fn relay_mail (&self) -> Result<()> {
		if let Some(headers) = &self.headers {
			let mail = mail_parser::MessageParser::new().parse(&self.data)
				.context("Failed to parse mail.")?;

			// Adding all known addresses to recipient list, for anyone else adding default
			// Also if list is empty also adding default
			let mut rcpt: HashSet<&ChatPeerId> = HashSet::new();
			if headers.to.is_empty() && !self.relay {
			if headers.to.is_empty() {
				bail!("Relaying is disabled, and there's no destination address");
			}
			for item in &headers.to {
				rcpt.insert(self.get_id(item)?);
			};
			if rcpt.is_empty() {
				self.tg.debug("No recipient or envelope address.").await?;

		} else {
			bail!("Required headers were not found.");
		}
		Ok(())
	}
}

/// SMTP handler implementation for mailin-embedded.
impl mailin_embedded::Handler for MailServer {
	/// Just deny login auth
	fn auth_login (&mut self, _username: &str, _password: &str) -> Response {
		INVALID_CREDENTIALS
	}

	/// Just deny plain auth
	fn auth_plain (&mut self, _authorization_id: &str, _authentication_id: &str, _password: &str) -> Response {
		INVALID_CREDENTIALS
	}

	/// Verify whether address is deliverable
	fn rcpt (&mut self, to: &str) -> Response {
		if self.relay {
			OK
		} else {
			match self.get_id(to) {
		if self.get_id(to).is_ok() {
				Ok(_) => OK,
				Err(_) => {
					if self.relay {
						OK
					} else {
						NO_MAILBOX
			OK
		} else {
			NO_MAILBOX
					}
				}
			}
		}
	}

	/// Save headers we need
	fn data_start (&mut self, _domain: &str, from: &str, _is8bit: bool, to: &[String]) -> Response {
		self.headers = Some(SomeHeaders{
			from: from.to_string(),