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// check-if-email-exists
// Copyright (C) 2018-2021 Amaury Martiny

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.

// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

use crate::syntax::SyntaxDetails;
use crate::util::ser_with_display::ser_with_display;
use async_std_resolver::{config, lookup::MxLookup, resolver, ResolveError};
use serde::{ser::SerializeMap, Serialize, Serializer};
use std::io::Error;

/// Details about the MX lookup.
#[derive(Debug)]
pub struct MxDetails {
	/// MX lookup of this DNS.
	pub lookup: Result<MxLookup, ResolveError>,
}

impl Default for MxDetails {
	fn default() -> Self {
		MxDetails {
			lookup: Err(ResolveError::from("Skipped")),
		}
	}
}

impl From<MxLookup> for MxDetails {
	fn from(lookup: MxLookup) -> Self {
		MxDetails { lookup: Ok(lookup) }
	}
}

impl Serialize for MxDetails {
	fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
	where
		S: Serializer,
	{
		let records = self
			.lookup
			.as_ref()
			.map(|lookup| {
				lookup
					.iter()
					.map(|host| host.exchange().to_string())
					.collect::<Vec<_>>()
			})
			.unwrap_or_else(|_| vec![]); // In case of a resolve error, we don't serialize the error.

		let mut map = serializer.serialize_map(Some(2))?;
		map.serialize_entry("accepts_mail", &!records.is_empty())?;
		map.serialize_entry("records", &records)?;
		map.end()
	}
}

/// Errors that can happen on MX lookups.
#[derive(Debug, Serialize)]
#[serde(tag = "type", content = "message")]
pub enum MxError {
	/// Error with IO.
	#[serde(serialize_with = "ser_with_display")]
	IoError(Error),
	/// Error while resolving MX lookups.
	#[serde(serialize_with = "ser_with_display")]
	ResolveError(ResolveError),
}

impl From<ResolveError> for MxError {
	fn from(error: ResolveError) -> Self {
		MxError::ResolveError(error)
	}
}

/// Make a MX lookup.
pub async fn check_mx(syntax: &SyntaxDetails) -> Result<MxDetails, MxError> {
	// Construct a new Resolver with default configuration options
	let resolver = resolver(
		config::ResolverConfig::default(),
		config::ResolverOpts::default(),
	)
	.await?;

	// Lookup the MX records associated with a name.
	// The final dot forces this to be an FQDN, otherwise the search rules as specified
	// in `ResolverOpts` will take effect. FQDN's are generally cheaper queries.
	match resolver.mx_lookup(syntax.domain.as_ref()).await {
		Ok(lookup) => Ok(MxDetails::from(lookup)),
		Err(err) => Ok(MxDetails { lookup: Err(err) }),
	}
}