//! Nextcloud connector — the only [`RemoteBackend`] implementation.
//!
//! Hand-rolled over `reqwest` rather than built on a WebDAV crate (D7). No
//! mature Nextcloud crate exists, and the operations that matter here are
//! Nextcloud extensions: `oc:fileid`, propagating directory ETags, chunked
//! upload v2, and Login Flow v2. A general WebDAV client exposes none of them.

use std::ops::Range;

use async_trait::async_trait;
use dr_sync::{
    Capabilities, ChangeDetection, ChunkConstraints, Cursor, Precondition, RemoteBackend,
    RemoteChange, RemoteEntry, RemoteError, RemoteId, RemotePath, ServerPreviews, Validator,
};

pub mod auth;
pub mod desktop_client;
mod propfind;
pub mod session;

pub use auth::{AppCredentials, LoginFlow};
pub use desktop_client::DesktopClient;
pub use session::{Session, SessionError, SessionStore};

/// Chunk sizes Nextcloud's chunked upload v2 accepts.
const CHUNKS: ChunkConstraints = ChunkConstraints {
    min_chunk: 5 * 1024 * 1024,
    max_chunk: 5 * 1024 * 1024 * 1024,
    // Below the 5 MB floor a single PUT is simpler and no slower.
    single_shot_below: 5 * 1024 * 1024,
    max_chunks: 10_000,
};

/// TRACES: FR-NC-12 | M-5
/// A connected Nextcloud account.
pub struct NextcloudBackend {
    client: reqwest::Client,
    server: String,
    login: String,
    password: String,
    /// `/remote.php/dav/files/<user>/` — the prefix stripped from hrefs.
    dav_base: String,
    caps: Capabilities,
}

impl NextcloudBackend {
    /// Build a backend from credentials obtained via [`auth`].
    pub fn new(creds: &AppCredentials, user_id: &str) -> Result<Self, RemoteError> {
        let client = http_client("DarkRoom")?;

        let server = creds.server.trim_end_matches('/').to_string();
        let dav_base = format!("/remote.php/dav/files/{user_id}/");

        Ok(Self {
            client,
            server,
            login: creds.login_name.clone(),
            password: creds.app_password.clone(),
            dav_base,
            caps: Capabilities {
                // The property that makes a no-op sync one request (ARCH §8.1).
                change_detection: ChangeDetection::PropagatingEtags,
                stable_ids: true,
                range_reads: true,
                chunked_upload: Some(CHUNKS),
                bulk_upload: true,
                conditional_write: true,
                // Stock Nextcloud ships no RAW preview provider (ARCH §6.7).
                // Probed per-account at setup and upgraded where present.
                server_previews: ServerPreviews::CommonFormatsOnly,
            },
        })
    }

    fn url_for(&self, path: &RemotePath) -> String {
        let p = path.as_str();
        if p.is_empty() {
            format!("{}{}", self.server, self.dav_base)
        } else {
            format!("{}{}{}", self.server, self.dav_base, encode_path(p))
        }
    }

    fn url_for_id(&self, id: &RemoteId) -> Result<String, RemoteError> {
        match id {
            RemoteId::Path(p) => Ok(self.url_for(p)),
            // A stable id alone is not addressable over WebDAV; the caller
            // holds the path alongside it in the catalog.
            RemoteId::Stable(_) => Err(RemoteError::Unsupported(
                "fetch by fileid requires a path; use RemoteId::Path",
            )),
        }
    }

    async fn propfind(
        &self,
        path: &RemotePath,
        depth: &str,
        body: &'static str,
    ) -> Result<String, RemoteError> {
        let resp = self
            .client
            .request(
                reqwest::Method::from_bytes(b"PROPFIND").expect("valid method"),
                self.url_for(path),
            )
            .basic_auth(&self.login, Some(&self.password))
            .header("Depth", depth)
            .header(reqwest::header::CONTENT_TYPE, "application/xml")
            .body(body)
            .send()
            .await
            .map_err(|e| RemoteError::Network(e.to_string()))?;

        map_status(resp.status(), path.as_str())?;
        resp.text()
            .await
            .map_err(|e| RemoteError::Network(e.to_string()))
    }
}

#[async_trait]
impl RemoteBackend for NextcloudBackend {
    fn capabilities(&self) -> &Capabilities {
        &self.caps
    }

    fn name(&self) -> &str {
        "Nextcloud"
    }

    async fn list(
        &self,
        dir: &RemotePath,
        _since: Option<&Validator>,
    ) -> Result<Vec<RemoteEntry>, RemoteError> {
        // Depth 1 only. Depth: infinity is frequently disabled and
        // prohibitively expensive where it is not (ARCH §8.4).
        let xml = self.propfind(dir, "1", propfind::PROPFIND_BODY).await?;
        propfind::parse_multistatus(&xml, &self.dav_base)
    }

    async fn dir_validator(&self, dir: &RemotePath) -> Result<Validator, RemoteError> {
        // The pruning probe: Depth 0, ETag only. Against the root this is the
        // single request that proves a 50k-image library unchanged.
        let xml = self
            .propfind(dir, "0", propfind::PROPFIND_ETAG_ONLY)
            .await?;
        propfind::parse_self_etag(&xml)
    }

    async fn delta(&self, _cursor: &Cursor) -> Result<(Vec<RemoteChange>, Cursor), RemoteError> {
        // Verified absent: Nextcloud's Directory.php does not implement
        // ISyncCollection, and sync tokens exist only for CalDAV/CardDAV
        // (ARCH §6.6). The engine falls back to ETag pruning.
        Err(RemoteError::Unsupported(
            "Nextcloud has no RFC 6578 sync-collection for files",
        ))
    }

    async fn get(&self, id: &RemoteId, range: Option<Range<u64>>) -> Result<Vec<u8>, RemoteError> {
        let url = self.url_for_id(id)?;
        let mut req = self
            .client
            .get(&url)
            .basic_auth(&self.login, Some(&self.password));

        let wanted = range.clone();
        if let Some(r) = &range {
            req = req.header(
                reqwest::header::RANGE,
                format!("bytes={}-{}", r.start, r.end.saturating_sub(1)),
            );
        }

        let resp = req
            .send()
            .await
            .map_err(|e| RemoteError::Network(e.to_string()))?;
        let status = resp.status();
        map_status(status, &url)?;

        let body = resp
            .bytes()
            .await
            .map_err(|e| RemoteError::Network(e.to_string()))?
            .to_vec();

        // Nextcloud does not advertise Accept-Ranges, so support is detected
        // by the response code rather than by probing with HEAD (ARCH §6.7).
        // A 200 to a ranged request means the server ignored it and sent
        // everything; slice locally so callers still get what they asked for.
        if let Some(r) = wanted {
            if status.as_u16() == 200 && body.len() as u64 > r.end {
                let start = r.start.min(body.len() as u64) as usize;
                let end = r.end.min(body.len() as u64) as usize;
                return Ok(body[start..end].to_vec());
            }
        }

        Ok(body)
    }

    async fn put(
        &self,
        path: &RemotePath,
        body: Vec<u8>,
        precond: Option<Precondition>,
    ) -> Result<Validator, RemoteError> {
        // Chunked upload is an implementation detail of put, chosen by size —
        // exposing it on the trait would leak this protocol (ARCH §8.3).
        if body.len() as u64 >= CHUNKS.single_shot_below {
            return Err(RemoteError::Unsupported(
                "chunked upload v2 not implemented yet",
            ));
        }

        let mut req = self
            .client
            .put(self.url_for(path))
            .basic_auth(&self.login, Some(&self.password));

        match &precond {
            Some(Precondition::IfMatch(v)) => {
                req = req.header(reqwest::header::IF_MATCH, format!("\"{}\"", v.as_str()));
            }
            Some(Precondition::IfAbsent) => {
                req = req.header(reqwest::header::IF_NONE_MATCH, "*");
            }
            None => {}
        }

        let resp = req
            .body(body)
            .send()
            .await
            .map_err(|e| RemoteError::Network(e.to_string()))?;
        map_status(resp.status(), path.as_str())?;

        resp.headers()
            .get(reqwest::header::ETAG)
            .and_then(|v| v.to_str().ok())
            .map(Validator::new)
            .ok_or_else(|| RemoteError::Protocol("no ETag on PUT response".into()))
    }

    async fn delete(
        &self,
        id: &RemoteId,
        precond: Option<Precondition>,
    ) -> Result<(), RemoteError> {
        let url = self.url_for_id(id)?;
        let mut req = self
            .client
            .delete(&url)
            .basic_auth(&self.login, Some(&self.password));

        if let Some(Precondition::IfMatch(v)) = &precond {
            req = req.header(reqwest::header::IF_MATCH, format!("\"{}\"", v.as_str()));
        }

        let resp = req
            .send()
            .await
            .map_err(|e| RemoteError::Network(e.to_string()))?;
        map_status(resp.status(), &url)
    }

    async fn thumbnail(&self, id: &RemoteId, size: u32) -> Result<Option<Vec<u8>>, RemoteError> {
        let RemoteId::Stable(file_id) = id else {
            return Ok(None);
        };

        // forceIcon=false is mandatory: the default returns a generic
        // mimetype icon for files the server cannot render, which would
        // otherwise be cached as though it were a thumbnail (ARCH §6.7).
        let url = format!(
            "{}/core/preview?fileId={file_id}&x={size}&y={size}&a=true&forceIcon=false",
            self.server
        );

        let resp = self
            .client
            .get(&url)
            .basic_auth(&self.login, Some(&self.password))
            .send()
            .await
            .map_err(|e| RemoteError::Network(e.to_string()))?;

        // 404 means no preview for this file — expected for RAW, and a
        // fall-through rather than an error.
        if resp.status().as_u16() == 404 {
            return Ok(None);
        }
        map_status(resp.status(), &url)?;

        Ok(Some(
            resp.bytes()
                .await
                .map_err(|e| RemoteError::Network(e.to_string()))?
                .to_vec(),
        ))
    }
}

/// Build an HTTP client with the crypto provider already installed.
///
/// Every entry point that creates a client must go through here. The auth
/// flow runs *before* a backend exists, so leaving the install to
/// `NextcloudBackend::new` means `auth::begin` panics on first use — which is
/// exactly what happened.
pub fn http_client(user_agent: &str) -> Result<reqwest::Client, RemoteError> {
    install_crypto_provider();
    reqwest::Client::builder()
        .user_agent(user_agent.to_string())
        .build()
        .map_err(|e| RemoteError::Network(e.to_string()))
}

/// Install the rustls crypto provider, once per process.
///
/// Required because we build reqwest with `rustls-no-provider` rather than
/// `rustls`: the default provider is aws-lc-rs, whose `aws-lc-sys` crate is C
/// and does not cross-compile for Android. `ring` is pure Rust apart from a
/// small assembly core that builds fine under the NDK.
///
/// Done here rather than left to callers so there is no way to construct a
/// client that panics on first use.
fn install_crypto_provider() {
    use std::sync::Once;
    static ONCE: Once = Once::new();
    ONCE.call_once(|| {
        // Errs only if a provider is already installed, which is fine.
        let _ = rustls::crypto::ring::default_provider().install_default();
    });
}

/// Translate an HTTP status into a typed error.
fn map_status(status: reqwest::StatusCode, what: &str) -> Result<(), RemoteError> {
    match status.as_u16() {
        200..=299 => Ok(()),
        401 | 403 => Err(RemoteError::AuthFailed),
        404 => Err(RemoteError::NotFound(what.to_string())),
        // Drives the sidecar merge path rather than an overwrite (ARCH §8.5).
        412 => Err(RemoteError::PreconditionFailed),
        507 => Err(RemoteError::QuotaExceeded),
        s => Err(RemoteError::Server {
            status: s,
            detail: what.to_string(),
        }),
    }
}

/// Percent-encode each path segment, leaving separators intact.
fn encode_path(path: &str) -> String {
    path.split('/')
        .map(|seg| {
            seg.bytes()
                .map(|b| match b {
                    b'A'..=b'Z' | b'a'..=b'z' | b'0'..=b'9' | b'-' | b'_' | b'.' | b'~' => {
                        (b as char).to_string()
                    }
                    _ => format!("%{b:02X}"),
                })
                .collect::<String>()
        })
        .collect::<Vec<_>>()
        .join("/")
}

#[cfg(test)]
mod tests {
    use super::*;

    fn backend() -> NextcloudBackend {
        NextcloudBackend::new(
            &AppCredentials {
                server: "https://cloud.example/".into(),
                login_name: "duncan".into(),
                app_password: "token".into(),
            },
            "duncan",
        )
        .unwrap()
    }

    #[test]
    fn capabilities_declare_the_nextcloud_fast_path() {
        let b = backend();
        let c = b.capabilities();
        // Propagating ETags are what make a no-op sync one request.
        assert_eq!(c.change_detection, ChangeDetection::PropagatingEtags);
        assert!(c.stable_ids);
        assert!(c.range_reads);
        assert!(c.conditional_write);
        // Stock Nextcloud cannot render RAW previews.
        assert_eq!(c.server_previews, ServerPreviews::CommonFormatsOnly);
    }

    #[test]
    fn strategy_selects_etag_pruning() {
        use dr_sync::SyncStrategy;
        let s = SyncStrategy::for_capabilities(backend().capabilities());
        assert_eq!(s, SyncStrategy::EtagPruning);
        assert!(s.has_cheap_noop());
    }

    #[test]
    fn urls_include_the_dav_prefix() {
        let b = backend();
        assert_eq!(
            b.url_for(&RemotePath::new("Photos/2026")),
            "https://cloud.example/remote.php/dav/files/duncan/Photos/2026"
        );
    }

    #[test]
    fn root_url_has_no_trailing_segment() {
        let b = backend();
        assert_eq!(
            b.url_for(&RemotePath::root()),
            "https://cloud.example/remote.php/dav/files/duncan/"
        );
    }

    #[test]
    fn path_segments_are_encoded_but_separators_are_not() {
        assert_eq!(encode_path("My Trip/a b.CR2"), "My%20Trip/a%20b.CR2");
        assert_eq!(encode_path("Photos/2026"), "Photos/2026");
    }

    #[test]
    fn fetching_by_bare_fileid_is_rejected_clearly() {
        // Callers hold the path alongside the id; failing loudly beats
        // constructing a URL that cannot work.
        let b = backend();
        assert!(matches!(
            b.url_for_id(&RemoteId::Stable(42)),
            Err(RemoteError::Unsupported(_))
        ));
    }

    #[test]
    fn statuses_map_to_actionable_errors() {
        use reqwest::StatusCode;
        assert!(map_status(StatusCode::OK, "x").is_ok());
        assert!(matches!(
            map_status(StatusCode::UNAUTHORIZED, "x"),
            Err(RemoteError::AuthFailed)
        ));
        // 412 must be distinguishable — it drives the sidecar merge.
        assert!(matches!(
            map_status(StatusCode::PRECONDITION_FAILED, "x"),
            Err(RemoteError::PreconditionFailed)
        ));
        assert!(matches!(
            map_status(StatusCode::INSUFFICIENT_STORAGE, "x"),
            Err(RemoteError::QuotaExceeded)
        ));
    }

    #[test]
    fn http_client_works_before_any_backend_exists() {
        // The auth flow builds a client before a backend is constructed. If
        // the crypto provider is installed only in NextcloudBackend::new,
        // this panics — which is exactly what happened against the live
        // server.
        let c = http_client("test");
        assert!(c.is_ok(), "client must build without a backend");
    }

    #[tokio::test]
    async fn delta_is_unsupported_and_says_why() {
        // Verified absent in the server; the engine must fall back rather
        // than treat this as a failure.
        let b = backend();
        assert!(matches!(
            b.delta(&Cursor::new("x")).await,
            Err(RemoteError::Unsupported(_))
        ));
    }
}