use std::borrow::Cow;

use anyhow::{Context as _, Result};
use axum::{
    extract::{Path, Query, State},
    response::{IntoResponse, Redirect, Response},
    routing::{get, post},
    Router,
};
use axum_extra::extract::Form;
use diesel::prelude::*;
use oauth2::{
    basic::BasicClient, reqwest::async_http_client, AuthUrl, AuthorizationCode, ClientId,
    ClientSecret, CsrfToken, RedirectUrl, TokenResponse, TokenUrl,
};
use serde::Deserialize;
use uuid::Uuid;

use crate::{
    app_error::AppError,
    app_state::{AppState, DbConn, ReqwestClient},
    channels::{self, BackendConfig, Channel, OAuthTokens, SlackBackendConfig},
    guards,
    settings::{Settings, SlackSettings},
    users::CurrentUser,
};

/// Creates a new OAuth2 client to be stored in global application state.
pub fn new_oauth_client(settings: &Settings) -> Result<BasicClient> {
    Ok(BasicClient::new(
        ClientId::new(settings.slack.client_id.clone()),
        Some(ClientSecret::new(settings.slack.client_secret.clone())),
        AuthUrl::new(settings.slack.auth_url.clone())
            .context("failed to create new authorization server URL")?,
        Some(
            TokenUrl::new(format!("{}/oauth.v2.access", settings.slack.api_root))
                .context("failed to create new token endpoint URL")?,
        ),
    ))
}

/// Creates a router which can be nested within the higher level app router.
pub fn new_router() -> Router<AppState> {
    Router::new()
        .route(
            "/teams/{team_id}/channels/{channel_id}/slack-auth/login",
            post(start_login),
        )
        .route(
            "/teams/{team_id}/channels/{channel_id}/slack-auth/callback",
            get(callback),
        )
        .route(
            "/teams/{team_id}/channels/{channel_id}/slack-auth/revoke",
            post(revoke),
        )
}

#[derive(Deserialize)]
struct StartLoginFormBody {
    csrf_token: String,
}

/// HTTP get handler for /login
async fn start_login(
    State(app_state): State<AppState>,
    State(Settings {
        base_path,
        frontend_host,
        ..
    }): State<Settings>,
    DbConn(db_conn): DbConn,
    CurrentUser(current_user): CurrentUser,
    Path((team_id, channel_id)): Path<(Uuid, Uuid)>,
    Form(form): Form<StartLoginFormBody>,
) -> Result<Response, AppError> {
    guards::require_valid_csrf_token(&form.csrf_token, &current_user, &db_conn).await?;
    guards::require_team_membership(&current_user, &team_id, &db_conn).await?;

    let channel = db_conn
        .interact(move |conn| -> Result<Channel, AppError> {
            Channel::all()
                .filter(Channel::with_id(&channel_id))
                .filter(Channel::with_team(&team_id))
                .first(conn)
                .optional()?
                .ok_or(AppError::NotFound(
                    "channel with that ID and team not found".to_owned(),
                ))
        })
        .await
        .unwrap()?;

    let csrf_token = CsrfToken::new_random();
    let SlackBackendConfig {
        conversation_id, ..
    } = channel
        .backend_config
        .try_into()
        .map_err(|_| anyhow::anyhow!("channel does not have a Slack backend"))?;
    let slack_config = SlackBackendConfig {
        conversation_id,
        oauth_state: Some(csrf_token.clone()),
        oauth_tokens: None,
    };

    const SCOPE_CHANNELS_READ: &str = "channels:read";
    const SCOPE_CHAT_WRITE_PUBLIC: &str = "chat:write.public";

    let (auth_url, _csrf_token) = app_state
        .slack_oauth_client
        .authorize_url(|| csrf_token)
        .add_scopes([
            oauth2::Scope::new(SCOPE_CHANNELS_READ.to_owned()),
            oauth2::Scope::new(SCOPE_CHAT_WRITE_PUBLIC.to_owned()),
        ])
        .set_redirect_uri(Cow::Owned(
            RedirectUrl::new(format!(
                "{}{}/en/teams/{}/channels/{}/slack-auth/callback",
                frontend_host, base_path, team_id, channel_id
            ))
            .context("failed to create redirection URL")?,
        ))
        .url();

    db_conn
        .interact(move |conn| -> Result<()> {
            diesel::update(channels::table.filter(Channel::with_id(&channel.id)))
                .set(channels::dsl::backend_config.eq(Into::<BackendConfig>::into(slack_config)))
                .execute(conn)
                .map(|_| ())
                .map_err(Into::into)
        })
        .await
        .unwrap()?;

    Ok(Redirect::to(auth_url.as_ref()).into_response())
}

#[derive(Debug, Deserialize)]
struct AuthRequestQuery {
    code: String,
    /// CSRF token
    state: String,
}

/// HTTP get handler for /callback
async fn callback(
    Query(query): Query<AuthRequestQuery>,
    State(app_state): State<AppState>,
    State(Settings {
        base_path,
        frontend_host,
        ..
    }): State<Settings>,
    DbConn(db_conn): DbConn,
    CurrentUser(current_user): CurrentUser,
    Path((team_id, channel_id)): Path<(Uuid, Uuid)>,
) -> Result<impl IntoResponse, AppError> {
    guards::require_team_membership(&current_user, &team_id, &db_conn).await?;

    let channel = db_conn
        .interact(move |conn| -> Result<Channel, AppError> {
            Channel::all()
                .filter(Channel::with_id(&channel_id))
                .filter(Channel::with_team(&team_id))
                .first(conn)
                .optional()?
                .ok_or(AppError::NotFound(
                    "channel with that ID and team not found".to_owned(),
                ))
        })
        .await
        .unwrap()?;

    let slack_data: SlackBackendConfig = channel
        .backend_config
        .try_into()
        .map_err(|_| anyhow::anyhow!("channel does not have a Slack backend"))?;

    let true_csrf_token = slack_data.oauth_state.ok_or(AppError::BadRequest(
        "No active Slack auth flow.".to_owned(),
    ))?;
    if true_csrf_token.secret() != &query.state {
        tracing::debug!("oauth csrf tokens did not match");
        return Err(AppError::Forbidden(
            "Slack OAuth CSRF tokens do not match.".to_owned(),
        ));
    }

    tracing::debug!("exchanging authorization code");
    let response = app_state
        .slack_oauth_client
        .exchange_code(AuthorizationCode::new(query.code))
        .set_redirect_uri(Cow::Owned(
            RedirectUrl::new(format!(
                "{}{}/en/teams/{}/channels/{}/slack-auth/callback",
                frontend_host, base_path, team_id, channel_id
            ))
            .context("failed to create redirection URL")?,
        ))
        .request_async(async_http_client)
        .await
        .context("failed to exchange slack oauth code")?;
    let slack_data = SlackBackendConfig {
        conversation_id: slack_data.conversation_id,
        oauth_state: None,
        oauth_tokens: Some(OAuthTokens {
            access_token: response.access_token().to_owned(),
            refresh_token: response.refresh_token().map(|value| value.to_owned()),
        }),
    };
    db_conn
        .interact(move |conn| -> Result<()> {
            let n_rows = diesel::update(channels::table.filter(Channel::with_id(&channel_id)))
                .set(channels::dsl::backend_config.eq(BackendConfig::from(slack_data)))
                .execute(conn)?;
            tracing::debug!("updated {} rows", n_rows);
            assert!(n_rows == 1);
            Ok(())
        })
        .await
        .unwrap()?;

    tracing::debug!("successfully authenticated");
    Ok(Redirect::to(&format!(
        "{}/en/teams/{}/channels/{}",
        base_path, team_id, channel_id
    )))
}

#[derive(Deserialize)]
struct RevokeFormBody {
    csrf_token: String,
}

async fn revoke(
    State(Settings {
        base_path,
        slack: SlackSettings { api_root, .. },
        ..
    }): State<Settings>,
    State(ReqwestClient(reqwest_client)): State<ReqwestClient>,
    DbConn(db_conn): DbConn,
    CurrentUser(current_user): CurrentUser,
    Path((team_id, channel_id)): Path<(Uuid, Uuid)>,
    Form(form): Form<RevokeFormBody>,
) -> Result<Response, AppError> {
    guards::require_valid_csrf_token(&form.csrf_token, &current_user, &db_conn).await?;
    guards::require_team_membership(&current_user, &team_id, &db_conn).await?;

    let channel = db_conn
        .interact(move |conn| -> Result<Channel, AppError> {
            Channel::all()
                .filter(Channel::with_id(&channel_id))
                .filter(Channel::with_team(&team_id))
                .first(conn)
                .optional()?
                .ok_or(AppError::NotFound(
                    "channel with that ID and team not found".to_owned(),
                ))
        })
        .await
        .unwrap()?;

    let slack_data: SlackBackendConfig = channel
        .backend_config
        .try_into()
        .map_err(|_| anyhow::anyhow!("channel does not have a Slack backend"))?;

    if let Some(OAuthTokens { access_token, .. }) = slack_data.oauth_tokens {
        #[derive(Deserialize)]
        struct ApiResponse {
            revoked: Option<bool>,
            error: Option<String>,
        }
        tracing::debug!("revoking slack access token via slack api");
        let response: ApiResponse = reqwest_client
            .get(format!("{}/auth.revoke", api_root))
            .bearer_auth(access_token.secret())
            .send()
            .await?
            .error_for_status()?
            .json()
            .await?;
        if response.revoked == Some(true) {
            tracing::debug!("access token revoked successfully; updating backend config");
            let slack_data = SlackBackendConfig {
                conversation_id: slack_data.conversation_id,
                oauth_state: None,
                oauth_tokens: None,
            };
            db_conn
                .interact(move |conn| -> Result<()> {
                    let n_rows =
                        diesel::update(channels::table.filter(Channel::with_id(&channel_id)))
                            .set(channels::dsl::backend_config.eq(BackendConfig::from(slack_data)))
                            .execute(conn)?;
                    tracing::debug!("updated {} rows", n_rows);
                    assert!(n_rows == 1);
                    Ok(())
                })
                .await
                .unwrap()?;
            tracing::debug!("backend config successfully updated");
            Ok(Redirect::to(&format!(
                "{}/en/teams/{}/channels/{}",
                base_path, team_id, channel_id
            ))
            .into_response())
        } else if let Some(message) = response.error {
            Err(anyhow::anyhow!("error while revoking access token: {}", message).into())
        } else {
            Err(anyhow::anyhow!("unknown error while revoking access token").into())
        }
    } else {
        Err(AppError::BadRequest(
            "Channel is not currently authenticated with Slack credentials.".to_owned(),
        ))
    }
}