//! Per-request NextCloud session context.
//!
//! Bundles WHO the caller is, the raw wire username they presented,
//! and (for path-scoped endpoints) WHERE they're confined to. Built
//! by `basic_auth_middleware` and stashed in request extensions as
//! `Arc<NcSession>`; handlers extract it via [`SharedNcSession`]
//! (derefs to `NcSession`) — declare `session: SharedNcSession` in
//! the signature.
//!
//! ## Source of truth
//!
//! - `user`: authenticated identity (id, canonical username, role).
//! - `raw_username`: the opaque wire identifier from the Basic Auth
//!   header. Today: plain `user` (single-drive) or `user~{drive_uuid}`
//!   (multi-drive POC). May look different again when future auth
//!   schemes land. **Handlers MUST NOT parse it** — it's used verbatim
//!   only for echoing back into DAV/OCS URLs the client expects to
//!   see (notably OCS `cloud/user`'s `id` field, which NC desktop
//!   splices into every subsequent DAV path it builds) and for
//!   audit logs.
//! - `chroot`: folder the request is jailed inside. `Some` for every
//!   authenticated NC request today (the home folder when no drive
//!   marker is present, or the resolved drive when one is). `None`
//!   is reserved for future routes that don't operate on a single
//!   folder (admin / cross-drive queries).
//!
//! ## Why this lives in middleware, not routes.rs
//!
//! The auth step already has every input needed (raw username from
//! header + drive marker after `~` + authenticated user). Resolving
//! the chroot there means every NC handler — DAV, OCS, uploads,
//! trashbin, sharees, … — gets a uniform `NcSession` regardless of
//! whether its URL carries a `{user}` segment. The URL `{user}`
//! segment becomes informational; the auth header is canonical.

use std::sync::Arc;

use axum::{
    extract::FromRequestParts,
    http::{StatusCode, request::Parts},
    response::{IntoResponse, Response},
};

use crate::application::dtos::folder_dto::FolderDto;
use crate::interfaces::errors::AppError;
use crate::interfaces::middleware::auth::CurrentUser;

#[derive(Debug, Clone)]
pub struct NcSession {
    /// Shared with the `Arc<CurrentUser>` request extension — one identity
    /// build per request instead of a clone per consumer.
    pub user: Arc<CurrentUser>,
    pub raw_username: String,
    /// Shared with `NC_CHROOT_CACHE` (markerless branch) — a cache hit is
    /// an `Arc` bump, not a `FolderDto` deep-clone.
    pub chroot: Option<Arc<FolderDto>>,
}

impl NcSession {
    /// Return the chroot, or 500 if a path-scoped handler is reached
    /// without one. Documents the invariant that every NC route
    /// today is path-scoped — if this fires, route wiring is wrong.
    pub fn require_chroot(&self) -> Result<&FolderDto, AppError> {
        self.chroot.as_deref().ok_or_else(|| {
            AppError::internal_error(
                "NcSession: path-scoped handler reached without a chroot — route wiring bug",
            )
        })
    }

    /// True when the session is scoped to the user's home folder
    /// (no drive marker in the Basic Auth username). Useful for
    /// handlers that want to render a friendlier display when the
    /// user is on their default drive.
    pub fn is_home(&self) -> bool {
        !self.raw_username.contains('~')
    }
}

/// Pull the `{user}` segment out of a NC DAV URL.
///
/// Expected URL shapes:
/// - `/remote.php/dav/files/{user}` (root)
/// - `/remote.php/dav/files/{user}/{*subpath}`
/// - `/remote.php/dav/uploads/{user}/{upload_id}[/{*rest}]`
/// - `/remote.php/dav/trashbin/{user}[/{*subpath}]`
///
/// Returns `None` for anything that doesn't follow this shape (notably
/// the OCS surfaces, where there is no `{user}` segment to compare).
fn extract_url_user(path: &str) -> Option<std::borrow::Cow<'_, str>> {
    let mut segments = path.split('/');
    if !segments.next()?.is_empty() {
        return None;
    }
    if segments.next()? != "remote.php" {
        return None;
    }
    if segments.next()? != "dav" {
        return None;
    }
    let _surface = segments.next()?; // files / uploads / trashbin
    let user_seg = segments.next()?;
    if user_seg.is_empty() {
        return None;
    }
    // Keep the `Cow` — a plain-ASCII username decodes to `Cow::Borrowed`, so the
    // common path allocates nothing; only a percent-encoded username owns. The
    // old `.into_owned()` forced a `String` on EVERY path-scoped NC DAV request
    // (benches/ROUND19.md §M7). The caller compares by slice.
    //
    // Lowercase before returning so cached client URLs like
    // `/dav/files/Alice/...` compare equal to the canonical
    // (lowercase) `session.raw_username`. See
    // `docs/plan/username-lowercase.md § 4. NextCloud DAV surface`.
    //
    // The lowercase transform always allocates (`to_ascii_lowercase`
    // on a `str` returns `String`). Trades the "Cow::Borrowed common
    // path" of the ROUND19 optimisation for correctness of the case-
    // insensitive comparison at line 157 — a `&str` compare with a
    // borrowed segment against a lowercase `session.raw_username`
    // would silently mismatch for `Alice`. The alloc is one small
    // String per NC DAV request; the correctness win is worth it.
    let decoded = urlencoding::decode(user_seg).ok()?;
    Some(std::borrow::Cow::Owned(decoded.to_ascii_lowercase()))
}

/// Axum extractor: the shared handle to the request's [`NcSession`].
///
/// Derefs to `NcSession`, so handler bodies read `session.user`,
/// `session.require_chroot()`, … unchanged. Extraction is one `Arc`
/// refcount increment — the previous extractor deep-cloned the whole
/// session (`CurrentUser` + `raw_username` + chroot `FolderDto`, ~8-9
/// `String` allocs) on every authenticated NC request.
///
/// On path-scoped DAV routes (`/remote.php/dav/{files,uploads,
/// trashbin}/{user}/…`), the URL `{user}` segment is cross-checked
/// against `session.raw_username` and 403'd on mismatch. This is a
/// consistency check, NOT a security boundary — the chroot ACL
/// (`get_folder_with_perms`) is what actually prevents cross-user
/// access. It just surfaces malformed requests early (403) instead
/// of silently letting them through.
#[derive(Debug, Clone)]
pub struct SharedNcSession(Arc<NcSession>);

impl SharedNcSession {
    /// Wrap an already-shared session (used by the bench harness; the
    /// middleware inserts the `Arc` into request extensions directly).
    pub fn from_arc(session: Arc<NcSession>) -> Self {
        Self(session)
    }
}

impl std::ops::Deref for SharedNcSession {
    type Target = NcSession;

    fn deref(&self) -> &NcSession {
        &self.0
    }
}

impl<S: Send + Sync> FromRequestParts<S> for SharedNcSession {
    type Rejection = Response;

    async fn from_request_parts(parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
        let session = parts
            .extensions
            .get::<Arc<NcSession>>()
            .cloned()
            .ok_or_else(|| StatusCode::UNAUTHORIZED.into_response())?;

        if let Some(url_user) = extract_url_user(parts.uri.path())
            && url_user.as_ref() != session.raw_username.as_str()
        {
            return Err(StatusCode::FORBIDDEN.into_response());
        }

        Ok(Self(session))
    }
}