use std::collections::HashSet;
use std::convert::Infallible;
use std::sync::LazyLock;

use crate::api::error::ApiError;
use crate::api::proxy_client::proxy_client;
use crate::state::AppState;
use crate::types::{Did, Nsid};
use crate::util::get_header_str;
use axum::{
    body::Bytes,
    extract::{RawQuery, Request, State},
    handler::Handler,
    http::{HeaderMap, Method},
    response::{IntoResponse, Response},
};
use futures_util::future::Either;
use tower::{Service, util::BoxCloneSyncService};
use tracing::{error, info, warn};

static PROTECTED_METHODS: LazyLock<HashSet<&'static str>> = LazyLock::new(|| {
    [
        "app.bsky.actor.getPreferences",
        "app.bsky.actor.putPreferences",
        "com.atproto.admin.deleteAccount",
        "com.atproto.admin.disableAccountInvites",
        "com.atproto.admin.disableInviteCodes",
        "com.atproto.admin.enableAccountInvites",
        "com.atproto.admin.getAccountInfo",
        "com.atproto.admin.getAccountInfos",
        "com.atproto.admin.getInviteCodes",
        "com.atproto.admin.getSubjectStatus",
        "com.atproto.admin.searchAccounts",
        "com.atproto.admin.sendEmail",
        "com.atproto.admin.updateAccountEmail",
        "com.atproto.admin.updateAccountHandle",
        "com.atproto.admin.updateAccountPassword",
        "com.atproto.admin.updateSubjectStatus",
        "com.atproto.identity.getRecommendedDidCredentials",
        "com.atproto.identity.requestPlcOperationSignature",
        "com.atproto.identity.signPlcOperation",
        "com.atproto.identity.submitPlcOperation",
        "com.atproto.identity.updateHandle",
        "com.atproto.repo.applyWrites",
        "com.atproto.repo.createRecord",
        "com.atproto.repo.deleteRecord",
        "com.atproto.repo.importRepo",
        "com.atproto.repo.putRecord",
        "com.atproto.repo.uploadBlob",
        "com.atproto.server.activateAccount",
        "com.atproto.server.checkAccountStatus",
        "com.atproto.server.confirmEmail",
        "com.atproto.server.confirmSignup",
        "com.atproto.server.createAccount",
        "com.atproto.server.createAppPassword",
        "com.atproto.server.createInviteCode",
        "com.atproto.server.createInviteCodes",
        "com.atproto.server.createSession",
        "com.atproto.server.createTotpSecret",
        "com.atproto.server.deactivateAccount",
        "com.atproto.server.deleteAccount",
        "com.atproto.server.deletePasskey",
        "com.atproto.server.deleteSession",
        "com.atproto.server.describeServer",
        "com.atproto.server.disableTotp",
        "com.atproto.server.enableTotp",
        "com.atproto.server.finishPasskeyRegistration",
        "com.atproto.server.getAccountInviteCodes",
        "com.atproto.server.getServiceAuth",
        "com.atproto.server.getSession",
        "com.atproto.server.getTotpStatus",
        "com.atproto.server.listAppPasswords",
        "com.atproto.server.listPasskeys",
        "com.atproto.server.refreshSession",
        "com.atproto.server.regenerateBackupCodes",
        "com.atproto.server.requestAccountDelete",
        "com.atproto.server.requestEmailConfirmation",
        "com.atproto.server.requestEmailUpdate",
        "com.atproto.server.requestPasswordReset",
        "com.atproto.server.resendMigrationVerification",
        "com.atproto.server.resendVerification",
        "com.atproto.server.reserveSigningKey",
        "com.atproto.server.resetPassword",
        "com.atproto.server.revokeAppPassword",
        "com.atproto.server.startPasskeyRegistration",
        "com.atproto.server.updateEmail",
        "com.atproto.server.updatePasskey",
        "com.atproto.server.verifyMigrationEmail",
        "com.atproto.sync.getBlob",
        "com.atproto.sync.getBlocks",
        "com.atproto.sync.getCheckout",
        "com.atproto.sync.getHead",
        "com.atproto.sync.getLatestCommit",
        "com.atproto.sync.getRecord",
        "com.atproto.sync.getRepo",
        "com.atproto.sync.getRepoStatus",
        "com.atproto.sync.listBlobs",
        "com.atproto.sync.listRepos",
        "com.atproto.sync.notifyOfUpdate",
        "com.atproto.sync.requestCrawl",
        "com.atproto.sync.subscribeRepos",
        "com.atproto.temp.checkSignupQueue",
        "com.atproto.temp.dereferenceScope",
    ]
    .into_iter()
    .collect()
});

fn is_protected_method(method: &str) -> bool {
    PROTECTED_METHODS.contains(method)
}

/// Fetch the `feed` generator record from the AppView and return its `did`.
async fn resolve_feed_generator_did(appview_url: &str, query: Option<&str>) -> Option<Did> {
    #[derive(serde::Deserialize)]
    struct GetFeedQuery {
        feed: String,
    }

    let feed = serde_urlencoded::from_str::<GetFeedQuery>(query?)
        .ok()?
        .feed;
    let at_uri = crate::types::AtUri::new(feed).ok()?;
    let repo = at_uri.did()?;
    let collection = at_uri.collection()?;
    let rkey = at_uri.rkey()?;

    let resp = proxy_client()
        .get(format!("{appview_url}/xrpc/com.atproto.repo.getRecord"))
        .query(&[("repo", repo), ("collection", collection), ("rkey", rkey)])
        .send()
        .await
        .ok()?;
    if !resp.status().is_success() {
        warn!(status = %resp.status(), "getFeed proxy: getRecord for feed generator failed");
        return None;
    }
    let body: serde_json::Value = resp.json().await.ok()?;
    body.get("value")?
        .get("did")?
        .as_str()
        .and_then(|s| Did::new(s).ok())
}

pub struct XrpcProxyLayer {
    state: AppState,
}

impl XrpcProxyLayer {
    pub fn new(state: AppState) -> Self {
        XrpcProxyLayer { state }
    }
}

impl<S> tower_layer::Layer<S> for XrpcProxyLayer {
    type Service = XrpcProxyingService<S>;

    fn layer(&self, inner: S) -> Self::Service {
        XrpcProxyingService {
            inner,
            // TODO(nel): make our own service here instead of boxing a HandlerService
            handler: BoxCloneSyncService::new(proxy_handler.with_state(self.state.clone())),
        }
    }
}

#[derive(Clone)]
pub struct XrpcProxyingService<S> {
    inner: S,
    handler: BoxCloneSyncService<Request, Response, Infallible>,
}

impl<S: Service<Request, Response = Response, Error = Infallible>> Service<Request>
    for XrpcProxyingService<S>
{
    type Response = Response;

    type Error = Infallible;

    type Future = Either<
        <BoxCloneSyncService<Request, Response, Infallible> as Service<Request>>::Future,
        S::Future,
    >;

    fn poll_ready(
        &mut self,
        cx: &mut std::task::Context<'_>,
    ) -> std::task::Poll<Result<(), Self::Error>> {
        self.inner.poll_ready(cx)
    }

    fn call(&mut self, req: Request) -> Self::Future {
        if req.headers().contains_key(http::HeaderName::from(
            jacquard_common::xrpc::Header::AtprotoProxy,
        )) {
            let path = req.uri().path();
            let method = path.trim_start_matches("/");

            if is_protected_method(method) {
                return Either::Right(self.inner.call(req));
            }

            // If the age assurance override is set and this is an age assurance call then we dont want to proxy even if the client requests it
            if tranquil_config::get().server.age_assurance_override
                && (path.ends_with("app.bsky.ageassurance.getState")
                    || path.ends_with("app.bsky.unspecced.getAgeAssuranceState"))
            {
                return Either::Right(self.inner.call(req));
            }

            Either::Left(self.handler.call(req))
        } else {
            Either::Right(self.inner.call(req))
        }
    }
}

async fn proxy_handler(
    State(state): State<AppState>,
    uri: http::Uri,
    method_verb: Method,
    headers: HeaderMap,
    RawQuery(query): RawQuery,
    body: Bytes,
) -> Response {
    // This layer is nested under /xrpc in an axum router so the extracted uri will look like /<method> and thus we can just strip the /
    let method = uri.path().trim_start_matches("/");
    if is_protected_method(method) {
        warn!(method = %method, "Attempted to proxy protected method");
        return ApiError::InvalidRequest(format!("Cannot proxy protected method: {}", method))
            .into_response();
    }

    let Some(proxy_header) =
        get_header_str(&headers, crate::util::HEADER_ATPROTO_PROXY).map(String::from)
    else {
        return ApiError::InvalidRequest("Missing required atproto-proxy header".into())
            .into_response();
    };

    let Some((did, service_id)) = proxy_header.split_once("#") else {
        return ApiError::InvalidRequest(
            "Invalid atproto-proxy header. Missing service identifier.".into(),
        )
        .into_response();
    };
    let Ok(did) = did.parse::<Did>() else {
        return ApiError::InvalidRequest("Invalid DID in atproto-proxy header".into())
            .into_response();
    };
    let Ok(resolved) = state.did_resolver.resolve_service(&did, service_id).await else {
        error!(did = %did, service_id = %service_id, "Could not resolve service DID");
        return ApiError::UpstreamFailure.into_response();
    };

    let target_url = match &query {
        Some(q) => format!("{}/xrpc/{}?{}", resolved.url, method, q),
        None => format!("{}/xrpc/{}", resolved.url, method),
    };
    info!("Proxying {} request to {}", method_verb, target_url);

    let client = proxy_client();
    let mut request_builder = client.request(method_verb.clone(), &target_url);

    let mut auth_header_val = headers.get(http::header::AUTHORIZATION).cloned();
    if let Some(extracted) = crate::auth::extract_auth_token_from_header(
        crate::util::get_header_str(&headers, http::header::AUTHORIZATION),
    ) {
        let token = extracted.token;
        let dpop_proof = crate::util::get_header_str(&headers, crate::util::HEADER_DPOP);
        let http_uri = crate::util::build_full_url(&format!("/xrpc{}", uri));

        match crate::auth::validate_token_with_dpop(
            state.repos.user.as_ref(),
            state.repos.oauth.as_ref(),
            &token,
            extracted.scheme,
            dpop_proof,
            method_verb.as_str(),
            &http_uri,
            crate::auth::AccountRequirement::Active,
        )
        .await
        {
            Ok(auth_user) => {
                let Ok(method_nsid) = method.parse::<Nsid>() else {
                    return ApiError::InvalidRequest(format!("Invalid XRPC method: {}", method))
                        .into_response();
                };
                if let Err(e) = crate::auth::scope_check::check_rpc_scope(
                    &auth_user.auth_source,
                    auth_user.scope.as_deref(),
                    &resolved.did,
                    &method_nsid,
                ) {
                    return e.into_response();
                }

                let key_bytes = match auth_user.key_bytes {
                    Some(kb) => kb,
                    None => match state.repos.user.get_user_info_by_did(&auth_user.did).await {
                        Ok(Some(info)) => match info.key_bytes {
                            Some(key_bytes_enc) => {
                                match crate::config::decrypt_key(
                                    &key_bytes_enc,
                                    info.encryption_version,
                                ) {
                                    Ok(key) => key,
                                    Err(e) => {
                                        error!(error = ?e, "Failed to decrypt user key for proxy");
                                        return ApiError::UpstreamFailure.into_response();
                                    }
                                }
                            }
                            None => {
                                warn!(did = %auth_user.did, "User has no signing key for proxy");
                                return ApiError::UpstreamFailure.into_response();
                            }
                        },
                        Ok(None) => {
                            warn!(did = %auth_user.did, "User not found for proxy service auth");
                            return ApiError::UpstreamFailure.into_response();
                        }
                        Err(e) => {
                            error!(error = ?e, "DB error fetching user key for proxy");
                            return ApiError::UpstreamFailure.into_response();
                        }
                    },
                };

                // getFeed must be audienced to the feed generator, not the AppView.
                let (token_aud, token_lxm) = if method == "app.bsky.feed.getFeed" {
                    match resolve_feed_generator_did(&resolved.url, query.as_deref()).await {
                        Some(feed_did) => (
                            feed_did,
                            "app.bsky.feed.getFeedSkeleton"
                                .parse::<Nsid>()
                                .expect("getFeedSkeleton is a valid NSID"),
                        ),
                        None => {
                            warn!(
                                "getFeed proxy: could not resolve feed generator DID; refusing \
                                 to mint an AppView-audienced token"
                            );
                            return ApiError::InvalidRequest("Could not resolve feed".into())
                                .into_response();
                        }
                    }
                } else {
                    (resolved.did.clone(), method_nsid.clone())
                };

                match crate::auth::create_service_token(
                    &auth_user.did,
                    &token_aud,
                    Some(&token_lxm),
                    &key_bytes,
                ) {
                    Ok(new_token) => {
                        if let Ok(val) =
                            axum::http::HeaderValue::from_str(&format!("Bearer {}", new_token))
                        {
                            auth_header_val = Some(val);
                        }
                    }
                    Err(e) => {
                        error!("Failed to create service token: {:?}", e);
                        return ApiError::UpstreamFailure.into_response();
                    }
                }
            }
            Err(e) => {
                info!(error = ?e, "Proxy token validation failed, returning error to client");
                let mut response = ApiError::from(e).into_response();
                if let Ok(nonce_val) = crate::oauth::verify::generate_dpop_nonce().parse() {
                    response
                        .headers_mut()
                        .insert(crate::util::HEADER_DPOP_NONCE, nonce_val);
                }
                return response;
            }
        }
    }

    if let Some(val) = auth_header_val {
        request_builder = request_builder.header(http::header::AUTHORIZATION, val);
    }
    request_builder = crate::api::proxy_client::HEADERS_TO_FORWARD
        .iter()
        .filter_map(|name| headers.get(name).map(|val| (name, val)))
        .fold(request_builder, |builder, (name, val)| {
            builder.header(name.as_str(), val)
        });
    if !body.is_empty() {
        request_builder = request_builder.body(body);
    }

    match request_builder.send().await {
        Ok(resp) => {
            let status = resp.status();
            let headers = resp.headers().clone();
            let body = match resp.bytes().await {
                Ok(b) => b,
                Err(e) => {
                    error!("Error reading proxy response body: {:?}", e);
                    return ApiError::UpstreamUnavailable("Error reading upstream response".into())
                        .into_response();
                }
            };
            let mut response_builder = Response::builder().status(status);
            response_builder = crate::api::proxy_client::RESPONSE_HEADERS_TO_FORWARD
                .iter()
                .filter_map(|name| headers.get(name).map(|val| (name, val)))
                .fold(response_builder, |builder, (name, val)| {
                    builder.header(name, val)
                });
            match response_builder.body(axum::body::Body::from(body)) {
                Ok(r) => r,
                Err(e) => {
                    error!("Error building proxy response: {:?}", e);
                    ApiError::InternalError(None).into_response()
                }
            }
        }
        Err(e) => {
            error!("Error sending proxy request: {:?}", e);
            if e.is_timeout() {
                ApiError::UpstreamTimeout.into_response()
            } else {
                ApiError::UpstreamFailure.into_response()
            }
        }
    }
}
