use futures::future::join_all;
use itertools::Itertools as _;
use p256::ecdsa::VerifyingKey;
use sqlx::SqlitePool;
use web_push::{
    ContentEncoding, PartialVapidSignatureBuilder, SubscriptionInfo, WebPushClient, WebPushError,
    WebPushMessage, WebPushMessageBuilder,
};

use super::repo::Provider as _;
use crate::{
    db,
    error::failed::{ErrorExt as _, Failed, ResultExt as _},
    login::Login,
    token::extract::Identity,
    vapid::repo::Provider as _,
};

pub struct Push<P> {
    db: SqlitePool,
    webpush: P,
}

impl<P> Push<P> {
    pub const fn new(db: SqlitePool, webpush: P) -> Self {
        Self { db, webpush }
    }

    pub async fn subscribe(
        &self,
        subscriber: &Identity,
        subscription: &SubscriptionInfo,
        vapid: &VerifyingKey,
    ) -> Result<(), SubscribeError> {
        let mut tx = self.db.begin().await.fail(db::failed::BEGIN)?;

        let current = tx
            .vapid()
            .current()
            .await
            .fail("Failed to load current VAPID key")?;
        if vapid != &current.key {
            return Err(SubscribeError::StaleVapidKey(current.key));
        }

        match tx.push().create(&subscriber.token, subscription).await {
            Ok(()) => (),
            Err(err) => {
                if let Some(err) = err.as_database_error()
                    && err.is_unique_violation()
                {
                    let current = tx
                        .push()
                        .by_endpoint(&subscriber.login, &subscription.endpoint)
                        .await
                        .fail("Failed to load existing subscriptions for endpoint")?;
                    // If we already have a subscription for this endpoint, with _different_
                    // parameters, then this is a client error. They shouldn't reuse endpoint URLs,
                    // per the various RFCs.
                    //
                    // However, if we have a subscription for this endpoint with the same parameters
                    // then we accept it and silently do nothing. This may happen if, for example,
                    // the subscribe request is retried due to a network interruption where it's
                    // not clear whether the original request succeeded.
                    if &current != subscription {
                        return Err(SubscribeError::Duplicate);
                    }
                } else {
                    return Err(err.fail("Failed to create push subscription"));
                }
            }
        }

        tx.commit().await.fail(db::failed::COMMIT)?;

        Ok(())
    }
}

impl<P> Push<P>
where
    P: WebPushClient,
{
    fn prepare_ping(
        signer: &PartialVapidSignatureBuilder,
        subscription: &SubscriptionInfo,
    ) -> Result<WebPushMessage, PushError> {
        let signature = signer
            .clone()
            .add_sub_info(subscription)
            .build()
            .fail("Failed to build VAPID signature")?;

        let payload = "ping".as_bytes();

        let mut message = WebPushMessageBuilder::new(subscription);
        message.set_payload(ContentEncoding::Aes128Gcm, payload);
        message.set_vapid_signature(signature);
        let message = message.build().fail("Failed to build push message")?;

        Ok(message)
    }

    pub async fn ping(&self, recipient: &Login) -> Result<(), PushError> {
        let mut tx = self.db.begin().await.fail(db::failed::BEGIN)?;

        let signer = tx
            .vapid()
            .signer()
            .await
            .fail("Failed to load current VAPID signer")?;
        let subscriptions = tx.push().by_login(recipient).await.fail_with(|| {
            format!(
                "Failed to find push subscriptions for login: {}",
                recipient.id
            )
        })?;

        let pings: Vec<_> = subscriptions
            .into_iter()
            .map(|sub| Self::prepare_ping(&signer, &sub).map(|message| (sub, message)))
            .try_collect()?;

        let deliveries = pings
            .into_iter()
            .map(async |(sub, message)| (sub, self.webpush.send(message).await));

        let failures: Vec<_> = join_all(deliveries)
            .await
            .into_iter()
            .filter_map(|(sub, result)| result.err().map(|err| (sub, err)))
            .collect();

        if !failures.is_empty() {
            for (sub, err) in &failures {
                match err {
                    // I _think_ this is the complete set of permanent failures. See
                    // <https://docs.rs/web-push/latest/web_push/enum.WebPushError.html> for a complete
                    // list.
                    WebPushError::Unauthorized(_)
                    | WebPushError::InvalidUri
                    | WebPushError::EndpointNotValid(_)
                    | WebPushError::EndpointNotFound(_)
                    | WebPushError::InvalidCryptoKeys
                    | WebPushError::MissingCryptoKeys => {
                        tx.push()
                            .unsubscribe(sub)
                            .await
                            .fail("Failed to unsubscribe after permanent push message rejection")?;
                    }
                    _ => (),
                }
            }

            return Err(PushError::Delivery(
                failures.into_iter().map(|(_, err)| err).collect(),
            ));
        }

        tx.commit().await.fail(db::failed::COMMIT)?;

        Ok(())
    }
}

#[derive(Debug, thiserror::Error)]
pub enum SubscribeError {
    #[error("subscription created with stale VAPID key")]
    StaleVapidKey(VerifyingKey),
    #[error("subscription already exists for endpoint")]
    // The endpoint URL is not included in the error, as it is a bearer credential in its own right
    // and we want to limit its proliferation. The only intended recipient of this message is the
    // client, which already knows the endpoint anyways and doesn't need us to tell them.
    Duplicate,
    #[error(transparent)]
    Failed(#[from] Failed),
}

#[derive(Debug, thiserror::Error)]
pub enum PushError {
    #[error("push message delivery failures: {0:?}")]
    Delivery(Vec<WebPushError>),
    #[error(transparent)]
    Failed(#[from] Failed),
}