//! Authenticated-user extractor shared by all protected API routes.

use std::sync::Arc;

use api_types::P_SHARE;
use axum::extract::FromRequestParts;
use axum::http::StatusCode;
use axum::http::request::Parts;

use crate::auth::parse_session_cookie;
use crate::db::{RootRow, ShareRow, User};
use crate::error::{ApiError, AppState};

/// Authorization for the file API: which roots the caller may touch.
///
/// Deliberately carries no [`User`]. A share visitor is anonymous, so there
/// is no identity to expose here. A handler that trusted a user id from this
/// extractor would treat a share visitor as the share's creator.
pub struct AuthUser {
    pub roots: Vec<RootRow>,
    /// Present when authenticated via a public share token. The single entry
    /// in `roots` is the shared item (its path is the share's `target`), so all
    /// file operations are scoped to it.
    pub share: Option<ShareRow>,
}

impl<S> FromRequestParts<S> for AuthUser
where
    S: HasState + Send + Sync,
{
    type Rejection = ApiError;

    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
        let state = state.state();

        // 1. Public share token (`?share=<token>` or `X-Share-Token`). Checked
        //    first: a request that explicitly carries a share token is a share
        //    request, even if a session is also present (so a signed-in user
        //    viewing a share link sees the shared scope).
        if let Some(share_token) = share_token_from_request(parts) {
            return match state.db.share_by_token(&share_token).await? {
                Some(share) if !share.is_expired() => {
                    // The password guards the files, not just the share
                    // page. A check only on resolve would leave the file
                    // API open to anyone holding the link.
                    if share_is_locked(state, &share, &parts.headers).await? {
                        return Err(crate::api::shares::locked_error());
                    }
                    let roots = vec![RootRow {
                        id: share.id,
                        path: share.target.clone(),
                        mode: share.mode,
                    }];
                    Ok(AuthUser {
                        roots,
                        share: Some(share),
                    })
                }
                Some(_) => Err(ApiError::localized(
                    StatusCode::GONE,
                    "this share has expired",
                    "err_share_expired",
                )),
                None => Err(ApiError::localized(
                    StatusCode::NOT_FOUND,
                    "share not found",
                    "err_share_not_found",
                )),
            };
        }

        // 2. Signed-in session. Admins also get the whole server root,
        //    read-only, under `ADMIN_ROOT` (the folder picker in user
        //    management browses it).
        let (user, mut roots) = session_auth(&parts.headers, state).await?;
        if user.is_admin {
            roots.push(RootRow {
                id: api_types::ADMIN_ROOT,
                path: ".".to_string(),
                mode: api_types::Mode::Ro,
            });
        }
        Ok(AuthUser { roots, share: None })
    }
}

/// Extractor for routes that must never be reachable with a share token:
/// share management and admin.
///
/// A share token only proves that the caller holds a share link. It says
/// nothing about *who* the caller is, so it must not stand in for the share
/// creator's identity. Requests that carry one are rejected outright instead
/// of silently falling back to the session, so a share visitor cannot act as
/// the creator by also having a cookie.
pub struct SessionUser {
    pub user: User,
    pub roots: Vec<RootRow>,
}

impl<S> FromRequestParts<S> for SessionUser
where
    S: HasState + Send + Sync,
{
    type Rejection = ApiError;

    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
        if share_token_from_request(parts).is_some() {
            return Err(ApiError::localized(
                StatusCode::FORBIDDEN,
                "a share token cannot be used here; sign in instead",
                "err_share_token_forbidden",
            ));
        }
        let (user, roots) = session_auth(&parts.headers, state.state()).await?;
        Ok(SessionUser { user, roots })
    }
}

/// Authenticate via the session cookie only, returning the user and roots.
pub(crate) async fn session_auth(
    headers: &axum::http::HeaderMap,
    state: &AppState,
) -> Result<(User, Vec<RootRow>), ApiError> {
    let Some(token) = parse_session_cookie(headers) else {
        return Err(ApiError::localized(
            StatusCode::UNAUTHORIZED,
            "not signed in",
            "err_not_signed_in",
        ));
    };
    let Some((user, roots)) = state.db.session_user_with_roots(&token).await? else {
        return Err(ApiError::localized(
            StatusCode::UNAUTHORIZED,
            "session expired, please sign in again",
            "err_session_expired",
        ));
    };
    Ok((user, roots))
}

/// Whether `share` still needs its password entered by this caller.
pub(crate) async fn share_is_locked(
    state: &AppState,
    share: &ShareRow,
    headers: &axum::http::HeaderMap,
) -> Result<bool, ApiError> {
    if share.password_hash.is_none() {
        return Ok(false);
    }
    let Some(unlock) = crate::auth::parse_share_cookie(headers, share.id) else {
        return Ok(true);
    };
    Ok(!state.db.share_unlock_valid(&unlock, share.id).await?)
}

/// Extract the share token from a request, if present: a `?share=<token>`
/// query param or an `X-Share-Token` header.
fn share_token_from_request(parts: &Parts) -> Option<String> {
    if let Some(q) = parts.uri.query() {
        for pair in q.split('&') {
            if let Some((k, v)) = pair.split_once('=')
                && k == P_SHARE
                && !v.is_empty()
            {
                return Some(v.to_string());
            }
        }
    }
    parts
        .headers
        .get("x-share-token")
        .and_then(|v| v.to_str().ok())
        .filter(|s| !s.is_empty())
        .map(|s| s.to_string())
}

/// Lets the extractor pull the concrete state type out of a generic `S`.
pub trait HasState {
    fn state(&self) -> &AppState;
}

impl HasState for Arc<AppState> {
    fn state(&self) -> &AppState {
        self
    }
}

// ---------------------------------------------------------------------------
// Shared validation / naming helpers
// ---------------------------------------------------------------------------

/// UI name of a root or share target `rel` (relative to the server root):
/// its last path component, or the configured root name for `.`.
pub(crate) fn display_name(state: &AppState, rel: &str) -> String {
    if rel == "." {
        return state.root_name.clone();
    }
    std::path::Path::new(rel)
        .file_name()
        .map(|s| s.to_string_lossy().into_owned())
        .unwrap_or_else(|| rel.to_string())
}

/// A resolved absolute path re-expressed relative to the server root — the
/// form `shares.target` is stored in, so share lookups and share revokes both
/// speak the same spelling of a path.
pub(crate) fn target_rel(state: &AppState, abs: &std::path::Path) -> String {
    let rel = abs
        .strip_prefix(&state.root)
        .map(|p| p.to_string_lossy().into_owned())
        .unwrap_or_else(|_| ".".to_string());
    // The server root strips to the empty string, which has no last component
    // for [`display_name`] to show. Spell it `.`, the form that already means
    // "the whole root" everywhere else.
    if rel.is_empty() { ".".to_string() } else { rel }
}

pub(crate) fn validate_account_name(name: &str) -> Result<(), ApiError> {
    let n = name.trim();
    if n.is_empty() || n.len() > 64 {
        return Err(ApiError::localized(
            StatusCode::BAD_REQUEST,
            "name must be 1–64 characters",
            "err_name_length",
        ));
    }
    Ok(())
}

/// Run blocking work (filesystem, mostly) on the blocking pool.
///
/// The join itself can only fail if the task panicked or the runtime is
/// shutting down; both are `500`. Every caller used to spell that out, so
/// the `?` on the outer result is the join and the inner one is the work.
pub(crate) async fn blocking<T, E>(
    f: impl FnOnce() -> Result<T, E> + Send + 'static,
) -> Result<T, ApiError>
where
    T: Send + 'static,
    E: Into<ApiError> + Send + 'static,
{
    tokio::task::spawn_blocking(f)
        .await
        .map_err(|_| internal_error())?
        .map_err(Into::into)
}

pub(crate) fn internal_error() -> ApiError {
    ApiError::localized(
        StatusCode::INTERNAL_SERVER_ERROR,
        "internal error",
        "err_internal",
    )
}

/// Hash a password off the async executor. Argon2 is slow by design, so
/// running it inline would block a tokio worker thread for the whole cost.
pub(crate) async fn hash_password(pw: &str) -> Result<String, ApiError> {
    let pw = pw.to_string();
    let _slot = crate::auth::ARGON2_SLOTS.acquire().await;
    tokio::task::spawn_blocking(move || crate::auth::hash_password(&pw))
        .await
        .map_err(|_| {
            ApiError::localized(
                StatusCode::INTERNAL_SERVER_ERROR,
                "internal error",
                "err_internal",
            )
        })?
        .map_err(|e| {
            ApiError::new(
                StatusCode::INTERNAL_SERVER_ERROR,
                format!("hashing failed: {e}"),
            )
        })
}

/// A user-chosen label for a credential: trimmed, bounded, never empty.
pub(crate) fn credential_label(raw: &str, fallback: &str) -> String {
    let trimmed = raw.trim();
    if trimmed.is_empty() {
        return fallback.to_string();
    }
    trimmed.chars().take(64).collect()
}

pub(crate) fn validate_password(pw: &str) -> Result<(), ApiError> {
    if pw.len() < 8 {
        return Err(ApiError::localized(
            StatusCode::BAD_REQUEST,
            "password must be at least 8 characters",
            "err_password_short",
        ));
    }
    Ok(())
}

/// Extractor for admin-only routes: a signed-in user who is an admin.
/// Built on [`SessionUser`], so a share token never grants admin.
pub struct AdminUser {
    pub user: User,
}

impl<S> FromRequestParts<S> for AdminUser
where
    S: HasState + Send + Sync,
{
    type Rejection = ApiError;

    async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
        let auth = SessionUser::from_request_parts(parts, state).await?;
        if !auth.user.is_admin {
            return Err(ApiError::localized(
                StatusCode::FORBIDDEN,
                "admin only",
                "err_admin_only",
            ));
        }
        Ok(AdminUser { user: auth.user })
    }
}