use std::sync::Arc;

use api_types::{AuthMode, Credentials, LoginReq, LoginResp, Me, OkResp, RootInfo, UserInfo};
use axum::Json;
use axum::extract::State;
use axum::http::{HeaderMap, StatusCode, Uri, header};
use axum::response::{IntoResponse, Response};
use serde::Deserialize;

use crate::api::common::{
    SessionUser, display_name, hash_password, session_auth, validate_account_name,
    validate_password,
};
use crate::auth::{self, clear_session_cookie, parse_session_cookie, session_cookie};
use crate::db::{RootRow, User};
use crate::error::{ApiError, AppState};

/// GET /api/auth/me
///
/// - No users at all → `200 {"first_boot": true}`
/// - No/invalid session → `401`
/// - Valid session → user info + visible roots
pub async fn me(
    State(state): State<Arc<AppState>>,
    headers: HeaderMap,
) -> Result<Json<Me>, ApiError> {
    if state.db.user_count().await? == 0 {
        return Ok(Json(Me {
            first_boot: true,
            user: None,
            roots: Vec::new(),
            allow_writable_shares: false,
            thumbnails_available: state.thumbs.is_some(),
            public_url: state.public_url.clone(),
        }));
    }

    let (user, roots) = session_auth(&headers, &state).await?;
    Ok(Json(me_for(&state, &user, roots).await?))
}

/// Build the `/api/auth/me` payload for an authenticated user.
async fn me_for(state: &AppState, user: &User, roots: Vec<RootRow>) -> Result<Me, ApiError> {
    let roots: Vec<RootInfo> = roots
        .into_iter()
        .map(|r| RootInfo {
            id: r.id,
            name: display_name(state, &r.path),
            path: r.path,
            mode: r.mode,
        })
        .collect();

    Ok(Me {
        first_boot: false,
        user: Some(UserInfo {
            id: user.id,
            name: user.name.clone(),
            is_admin: user.is_admin,
            single_click_open: user.single_click,
            thumbnails: user.thumbnails,
            language: user.language.clone(),
            // A removed root leaves a stale id behind; the client never
            // sees it.
            default_root_id: user
                .default_root_id
                .filter(|id| roots.iter().any(|r| r.id == *id)),
            auth_mode: user.auth_mode,
            has_password: user.has_password,
        }),
        roots,
        allow_writable_shares: state.db.allow_writable_shares().await?,
        thumbnails_available: state.thumbs.is_some(),
        public_url: state.public_url.clone(),
    })
}

/// PUT /api/auth/me
///
/// Update the signed-in user's profile settings. Each field is optional;
/// omitted fields are left untouched. Returns the fresh `/me` payload so
/// clients can apply the change immediately.
#[derive(Deserialize)]
pub(crate) struct ProfilePatch {
    #[serde(default)]
    pub single_click_open: Option<bool>,
    pub thumbnails: Option<bool>,
    #[serde(default, deserialize_with = "patch_field")]
    pub language: Option<Option<String>>,
    /// `null` clears the default root (back to the root picker).
    #[serde(default, deserialize_with = "patch_field")]
    pub default_root_id: Option<Option<i64>>,
}

/// Deserializes a nullable patch field into the three-state value:
/// `"de"` → `Some(Some("de"))`, `null` → `Some(None)` (a missing field
/// never calls this and stays `None` via `#[serde(default)]`). The inner
/// `Option<T>` already maps `null` → `None` and a value → `Some`, so only
/// the outer wrap is custom.
fn patch_field<'de, D, T>(deserializer: D) -> Result<Option<Option<T>>, D::Error>
where
    D: serde::Deserializer<'de>,
    T: serde::Deserialize<'de>,
{
    serde::Deserialize::deserialize(deserializer).map(Some)
}

/// A language tag we are willing to store: short, ASCII letters/digits and
/// `-`/`_` (BCP-47 style). Checked at the trust boundary so a raw API
/// client cannot write arbitrary blobs into the DB.
fn valid_language(tag: &str) -> bool {
    !tag.is_empty()
        && tag.len() <= 12
        && tag
            .bytes()
            .all(|b| b.is_ascii_alphanumeric() || b == b'-' || b == b'_')
}

pub async fn update_profile(
    State(state): State<Arc<AppState>>,
    SessionUser { mut user, roots }: SessionUser,
    Json(body): Json<ProfilePatch>,
) -> Result<Json<Me>, ApiError> {
    if let Some(Some(ref tag)) = body.language
        && !valid_language(tag)
    {
        return Err(ApiError::localized(
            StatusCode::BAD_REQUEST,
            "invalid language tag",
            "err_invalid_language",
        ));
    }
    if let Some(v) = body.single_click_open {
        state.db.set_user_single_click(user.id, v).await?;
        user.single_click = v;
    }
    if let Some(v) = body.thumbnails {
        state.db.set_user_thumbnails(user.id, v).await?;
        user.thumbnails = v;
    }
    if let Some(lang) = body.language {
        state.db.set_user_language(user.id, lang.as_deref()).await?;
        user.language = lang;
    }
    if let Some(root_id) = body.default_root_id {
        if let Some(id) = root_id
            && !roots.iter().any(|r| r.id == id)
        {
            return Err(ApiError::localized(
                StatusCode::BAD_REQUEST,
                "not one of your folders",
                "err_invalid_default_root",
            ));
        }
        state.db.set_user_default_root(user.id, root_id).await?;
        user.default_root_id = root_id;
    }
    Ok(Json(me_for(&state, &user, roots).await?))
}

fn already_set_up() -> ApiError {
    ApiError::localized(
        StatusCode::CONFLICT,
        "server is already set up",
        "err_already_set_up",
    )
}

/// POST /api/auth/setup — create the first admin account.
/// Only available while no users exist.
pub async fn setup(
    State(state): State<Arc<AppState>>,
    Json(body): Json<Credentials>,
) -> Result<Response, ApiError> {
    let name = body.name.trim();
    validate_account_name(name)?;
    validate_password(&body.password)?;
    // A cheap pre-check: it keeps a POST to an already-configured server from
    // paying for an Argon2 hash. `create_admin` re-checks atomically.
    if state.db.user_count().await? > 0 {
        return Err(already_set_up());
    }

    let pass_hash = hash_password(&body.password).await?;
    // `None` = another setup request won the race between the check above and
    // this insert.
    let Some(user) = state.db.create_admin(name, &pass_hash).await? else {
        return Err(already_set_up());
    };

    let token = auth::random_token();
    state.db.create_session(user.id, &token).await?;

    let mut res = Json(OkResp {}).into_response();
    res.headers_mut().insert(
        header::SET_COOKIE,
        session_cookie(&token, state.https).parse().unwrap(),
    );
    Ok(res)
}

/// POST /api/auth/login — the password leg of signing in.
///
/// A correct password signs in, unless the account also requires a passkey:
/// then a challenge comes back instead of a session. A wrong password gets
/// the same error either way.
///
/// `state_id` is the other order. A passkey sign-in that landed on an account
/// requiring both legs parks the identified user under that handle, so this
/// route already knows who is asking and only needs the password.
pub async fn login(
    State(state): State<Arc<AppState>>,
    uri: Uri,
    headers: HeaderMap,
    Json(body): Json<LoginReq>,
) -> Result<Response, ApiError> {
    let name = match &body.state_id {
        Some(state_id) => {
            let Some(crate::webauthn::Pending::NeedsPassword { user_id }) =
                crate::webauthn::take(state_id)
            else {
                return Err(ApiError::localized(
                    StatusCode::BAD_REQUEST,
                    "that took too long, please try again",
                    "err_challenge_expired",
                ));
            };
            match state.db.find_user_by_id(user_id).await? {
                Some(u) => u.name,
                None => return Err(invalid_credentials()),
            }
        }
        None => match body.name.as_deref().map(str::trim) {
            Some(n) if !n.is_empty() => n.to_string(),
            _ => return Err(invalid_credentials()),
        },
    };

    // Online guessing gets slower per failed attempt on this name.
    let delay = auth::login_delay(&name);
    if !delay.is_zero() {
        tokio::time::sleep(delay).await;
    }
    let verified = state.db.verify_password(&name, &body.password).await?;
    auth::record_login(&name, verified.is_some());
    let Some(user) = verified else {
        return Err(invalid_credentials());
    };

    // A passkey is also required, and this request did not come from one.
    if user.auth_mode == AuthMode::Both && body.state_id.is_none() {
        return second_factor(&state, &user, &uri, &headers).await;
    }
    crate::api::passkeys::sign_in(&state, user.id).await
}

fn invalid_credentials() -> ApiError {
    ApiError::localized(
        StatusCode::UNAUTHORIZED,
        "invalid name or password",
        "err_invalid_credentials",
    )
}

/// The password passed; ask for the passkey that must follow it.
///
/// The relying party is built here rather than taken as an extractor. It needs
/// a domain name, and most sign-ins do not need it at all — an extractor on
/// `login` would fail every sign-in on a server reached by bare IP.
async fn second_factor(
    state: &AppState,
    user: &crate::db::User,
    uri: &Uri,
    headers: &HeaderMap,
) -> Result<Response, ApiError> {
    let rp = crate::webauthn::relying_party(state, uri, headers)?;
    let keys: Vec<webauthn_rs::prelude::Passkey> =
        crate::api::passkeys::load_passkeys(state, user.id)
            .await?
            .into_iter()
            .map(|(_, k)| k)
            .collect();
    // Only reachable if every stored passkey became unreadable: the mode
    // cannot be set without one, and the last one cannot be deleted under it.
    if keys.is_empty() {
        return Err(ApiError::new(
            StatusCode::INTERNAL_SERVER_ERROR,
            "this account requires a passkey but has none",
        ));
    }
    let (options, auth) = rp.start_passkey_authentication(&keys).map_err(|e| {
        tracing::warn!(error = ?e, "cannot start the second factor");
        ApiError::localized(
            StatusCode::INTERNAL_SERVER_ERROR,
            "that passkey could not be used",
            "err_passkey_failed",
        )
    })?;
    let challenge = crate::api::passkeys::challenge(
        crate::webauthn::Pending::Authenticate {
            user_id: user.id,
            state: Box::new(auth),
            second_factor: true,
        },
        &options,
    )?;
    Ok(Json(LoginResp {
        ok: false,
        passkey_challenge: Some(challenge),
        ..Default::default()
    })
    .into_response())
}

/// POST /api/auth/logout
pub async fn logout(State(state): State<Arc<AppState>>, headers: HeaderMap) -> Response {
    if let Some(token) = parse_session_cookie(&headers) {
        let _ = state.db.delete_session(&token).await;
    }
    let mut res = Json(OkResp {}).into_response();
    res.headers_mut().insert(
        header::SET_COOKIE,
        clear_session_cookie(state.https).parse().unwrap(),
    );
    res
}