//! Device sign-in (oxygenhub#67), in the shape of RFC 8628: an app that

//! cannot take a password asks for a code, the user approves it on the web

//! (signed in, with their second factor), and the app's next poll gets a

//! token with the scopes the user allowed.

use crate::db::{self, accounts};

use crate::Shared;

use axum::extract::State;

use axum::http::StatusCode;

use axum::response::{IntoResponse, Response};

use axum::Json;

use serde::Deserialize;

use serde_json::json;

/// How long a code lasts, and how often an app may poll.

const LIFETIME_MS: i64 = 15 * 60 * 1000;

const INTERVAL_S: i64 = 5;

/// User codes: consonants only, so no word is spelt and none is mistaken

/// for another letter or a digit.

const USER_ALPHABET: &[u8] = b"BCDFGHJKLMNPQRSTVWXZ";

#[derive(Deserialize)]

pub struct CodeRequest {

    /// What the app calls itself, shown when the user approves it.

    #[serde(default)]

    client: String,

    #[serde(default)]

    scopes: Vec<String>,

}

/// A user code, `XXXX-XXXX`.

fn user_code() -> String {

    use rand::RngCore;

    let mut b = [0u8; 8];

    rand::rngs::OsRng.fill_bytes(&mut b);

    let c: String = b.iter().map(|x| USER_ALPHABET[*x as usize % USER_ALPHABET.len()] as char).collect();

    format!("{}-{}", &c[..4], &c[4..])

}

/// A user code as typed: upper case, spaces and dashes ignored.

pub fn normalize_user_code(s: &str) -> String {

    let c: String = s.chars().filter(|c| c.is_ascii_alphanumeric()).map(|c| c.to_ascii_uppercase()).collect();

    if c.len() == 8 {

        format!("{}-{}", &c[..4], &c[4..])

    } else {

        c

    }

}

fn oauth_error(status: StatusCode, error: &str, detail: &str) -> Response {

    (status, Json(json!({ "error": error, "error_description": detail }))).into_response()

}

/// `POST /api/v1/device/code`: a device code to poll with and a user code

/// to show. No token needed.

pub async fn code(State(app): State<Shared>, Json(req): Json<CodeRequest>) -> Response {

    let known = |s: &str| crate::web::settings::SCOPES.iter().any(|(k, _)| *k == s);

    let mut scopes: Vec<&str> = req.scopes.iter().map(String::as_str).filter(|s| known(s)).collect();

    if scopes.len() != req.scopes.len() {

        return oauth_error(StatusCode::BAD_REQUEST, "invalid_scope", "unknown scope");

    }

    if scopes.is_empty() {

        scopes = vec!["repo:read", "user:read"];

    }

    let client: String = req.client.trim().chars().filter(|c| !c.is_control()).take(80).collect();

    let client = if client.is_empty() { "an app".to_string() } else { client };

    let device = format!("oxydev_{}", crate::auth::random_hex(32));

    let hash = crate::auth::token_hash(&device);

    let expires = db::now_ms() + LIFETIME_MS;

    // A clash of user codes is unlikely; try a few.

    for _ in 0..4 {

        let user = user_code();

        match accounts::create_device_code(&app.db, &hash, &user, &client, &scopes.join(","), expires).await {

            Ok(_) => {

                let base = app.config.base_url().trim_end_matches('/').to_string();

                return Json(json!({

                    "device_code": device,

                    "user_code": user,

                    "verification_uri": format!("{base}/device"),

                    "verification_uri_complete": format!("{base}/device?code={user}"),

                    "expires_in": LIFETIME_MS / 1000,

                    "interval": INTERVAL_S,

                }))

                .into_response();

            }

            Err(sqlx::Error::Database(e)) if e.is_unique_violation() => continue,

            Err(e) => return oauth_error(StatusCode::INTERNAL_SERVER_ERROR, "server_error", &e.to_string()),

        }

    }

    oauth_error(StatusCode::SERVICE_UNAVAILABLE, "server_error", "no free user code; try again")

}

#[derive(Deserialize)]

pub struct TokenRequest {

    device_code: String,

}

/// `POST /api/v1/device/token`: the token once the user approved, or why

/// not yet (`authorization_pending`, `slow_down`, `access_denied`,

/// `expired_token`), as RFC 8628 has it.

pub async fn token(State(app): State<Shared>, Json(req): Json<TokenRequest>) -> Response {

    let hash = crate::auth::token_hash(req.device_code.trim());

    let d = match accounts::device_by_hash(&app.db, &hash).await {

        Ok(Some(d)) => d,

        Ok(None) => return oauth_error(StatusCode::BAD_REQUEST, "expired_token", "no such device code, or it was used"),

        Err(e) => return oauth_error(StatusCode::INTERNAL_SERVER_ERROR, "server_error", &e.to_string()),

    };

    let now = db::now_ms();

    if d.expires_ms < now {

        let _ = accounts::delete_device(&app.db, d.id).await;

        return oauth_error(StatusCode::BAD_REQUEST, "expired_token", "the code expired; ask for a new one");

    }

    if d.denied {

        let _ = accounts::delete_device(&app.db, d.id).await;

        return oauth_error(StatusCode::BAD_REQUEST, "access_denied", "the user denied the request");

    }

    let Some(account_id) = d.account_id else {

        let _ = accounts::device_polled(&app.db, d.id).await;

        if now - d.last_poll_ms < INTERVAL_S * 1000 {

            return oauth_error(StatusCode::BAD_REQUEST, "slow_down", "poll no more often than the interval");

        }

        return oauth_error(StatusCode::BAD_REQUEST, "authorization_pending", "not yet approved");

    };

    // One poll takes the approval: the token is made only by the poll

    // that removed the code.

    match accounts::delete_device(&app.db, d.id).await {

        Ok(true) => {}

        Ok(false) => return oauth_error(StatusCode::BAD_REQUEST, "expired_token", "the code was used"),

        Err(e) => return oauth_error(StatusCode::INTERNAL_SERVER_ERROR, "server_error", &e.to_string()),

    }

    let account = match accounts::account_by_id(&app.db, account_id).await {

        Ok(Some(a)) => a,

        _ => return oauth_error(StatusCode::BAD_REQUEST, "access_denied", "the approving account is gone"),

    };

    let (secret, token_hash) = crate::auth::new_token();

    let name = format!("device: {}", d.client);

    if let Err(e) = accounts::create_token(&app.db, account_id, &name, &token_hash, &d.approved_scopes, "", None).await {

        return oauth_error(StatusCode::INTERNAL_SERVER_ERROR, "server_error", &e.to_string());

    }

    accounts::audit(&app.db, Some(&account), "token.device", &name, &d.approved_scopes).await.ok();

    Json(json!({

        "access_token": secret,

        "token_type": "bearer",

        "scope": d.approved_scopes.replace(',', " "),

        "username": account.username,

    }))

    .into_response()

}