//! TRACES: FR-NC-7a | FR-NC-7b
//! Where an uploaded original lands on the server.
//!
//! FR-NC-7 says how the bytes travel — chunked upload v2, `MKCOL`, `MOVE` of
//! the `.file` pseudo-entry. This says *where they go*, which the transport
//! deliberately has no opinion about.
//!
//! # The template is expanded on the ingest side, not here
//!
//! An upload receives folder *segments*, already expanded and already checked
//! to be ordinary names (`dr_ingest::layout`). That split is what makes
//! FR-NC-7a's first consequence true: the destination is a pure function of
//! capture metadata and the template, so two devices uploading the same frame
//! compute the same path. If this module re-derived the folders from whatever
//! the local library happened to look like, two machines with differently
//! organised libraries would file the same photograph in two different places
//! on one server.
//!
//! # What this deliberately does not do
//!
//! It does not move anything already on the server. FR-NC-7a's second
//! consequence: the template governs placement *on upload only*, because the
//! remote library is reachable by other clients and restructuring it under
//! them is not ours to do.

use crate::{EntryKind, RemoteBackend, RemoteError, RemotePath, Validator};

/// The folder an original belongs in, under a library root.
///
/// Segments are joined one at a time rather than formatted into a string,
/// because [`RemotePath::join`] is what normalises separators — a segment
/// arriving with a stray slash must not silently become two levels.
pub fn destination(library: &RemotePath, folders: &[String]) -> RemotePath {
    folders
        .iter()
        .filter(|s| !s.is_empty())
        .fold(library.clone(), |acc, seg| acc.join(seg))
}

/// TRACES: FR-NC-7a | FR-CAT-11
/// What became of an original the caller offered.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Placed {
    /// Sent now.
    Uploaded {
        path: RemotePath,
        validator: Validator,
    },
    /// The server already held this photograph, so nothing was transferred.
    ///
    /// The case a re-inserted card produces: the shoot was imported and
    /// uploaded last week, and the card has not been formatted since. Worth a
    /// variant of its own rather than folding into `Uploaded`, because the two
    /// are different answers to "is my work backed up" — and because a caller
    /// counting bytes moved must not count these.
    AlreadyThere { path: RemotePath },
}

impl Placed {
    /// Where the photograph is on the server, however it got there.
    pub fn path(&self) -> &RemotePath {
        match self {
            Placed::Uploaded { path, .. } | Placed::AlreadyThere { path } => path,
        }
    }
}

/// Upload one original into its dated folder, unless it is already there.
///
/// Creates the folders if they are missing — `create_dir` makes parents and
/// succeeds on one that already exists, so the second import of a day costs
/// one request rather than a conflict.
///
/// Returns where the photograph is, which may not be the name that was asked
/// for: two cameras produce `IMG_0001.CR3` and the second must not overwrite
/// the first. The caller records the returned path, never the one it passed.
///
/// `size` is what decides between "already there" and "a different photograph
/// with the same name". See [`resolve`].
pub async fn upload_original(
    backend: &dyn RemoteBackend,
    library: &RemotePath,
    folders: &[String],
    name: &str,
    body: Vec<u8>,
) -> Result<Placed, RemoteError> {
    let dir = destination(library, folders);
    backend.create_dir(&dir).await?;

    match resolve(backend, &dir, name, body.len() as u64).await? {
        Resolution::AlreadyThere => Ok(Placed::AlreadyThere {
            path: dir.join(name),
        }),
        Resolution::Use(name) => {
            let path = dir.join(&name);
            let validator = backend.put(&path, body, None).await?;
            Ok(Placed::Uploaded { path, validator })
        }
    }
}

/// What to do about a name in the destination folder.
#[derive(Debug, Clone, PartialEq, Eq)]
enum Resolution {
    /// Write under this name.
    Use(String),
    /// The photograph is already on the server. Send nothing.
    AlreadyThere,
}

/// Decide what to call an original in a remote folder, or that it is already
/// there.
///
/// One listing rather than a probe per candidate: a day folder is listed in a
/// single `PROPFIND` and the answer covers every collision in it, where
/// probing would be a round trip per attempt over a link that may be mobile
/// data.
///
/// **Name plus length decides "already there".** A card that was imported and
/// uploaded last week and has not been formatted since is the ordinary case,
/// and re-uploading it would double the storage and fill the folder with `-1`
/// copies of a shoot that is already safe. The same length under the same name
/// in the folder this photograph belongs in is that photograph in every case
/// that is not deliberately constructed — and a camera that reuses a filename
/// after `IMG_9999` writes a *different* number of bytes essentially always,
/// which is what leaves the rename below for the case it is actually for.
///
/// A folder that cannot be listed yields the original name rather than an
/// error. That is the safe direction on a server that has just been asked to
/// create the folder: the alternative is failing an upload because a listing
/// raced the `MKCOL`.
async fn resolve(
    backend: &dyn RemoteBackend,
    dir: &RemotePath,
    name: &str,
    size: u64,
) -> Result<Resolution, RemoteError> {
    let taken: std::collections::HashMap<String, u64> = match backend.list(dir, None).await {
        Ok(entries) => entries
            .into_iter()
            .filter(|e| e.kind == EntryKind::File)
            .map(|e| (e.path.name().to_string(), e.size))
            .collect(),
        Err(RemoteError::NotFound(_)) => Default::default(),
        Err(e) => return Err(e),
    };

    match taken.get(name) {
        None => return Ok(Resolution::Use(name.to_string())),
        Some(&there) if there == size => return Ok(Resolution::AlreadyThere),
        Some(_) => {}
    }

    // A different photograph that happens to share a name. The same suffix
    // convention the local import uses, so one that collided on both sides
    // carries the same name in both places.
    let (stem, ext) = match name.rsplit_once('.') {
        Some((s, e)) if !s.is_empty() => (s, Some(e)),
        _ => (name, None),
    };
    for n in 1..1000 {
        let candidate = match ext {
            Some(ext) => format!("{stem}-{n}.{ext}"),
            None => format!("{stem}-{n}"),
        };
        match taken.get(&candidate) {
            None => return Ok(Resolution::Use(candidate)),
            // The renamed copy is itself already up there: this is the second
            // re-import of a card that legitimately collided once.
            Some(&there) if there == size => return Ok(Resolution::AlreadyThere),
            Some(_) => {}
        }
    }
    Err(RemoteError::Unsupported(
        "a thousand files of the same name in one folder",
    ))
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::types::{RemoteEntry, RemoteId};

    fn segs(v: &[&str]) -> Vec<String> {
        v.iter().map(|s| s.to_string()).collect()
    }

    #[test]
    fn an_original_lands_under_year_then_day() {
        let dest = destination(
            &RemotePath::new("PhotosRaw"),
            &segs(&["2026", "2026-08-22"]),
        );
        assert_eq!(dest.as_str(), "PhotosRaw/2026/2026-08-22");
    }

    #[test]
    fn an_empty_segment_does_not_leave_a_nameless_folder() {
        let dest = destination(&RemotePath::new("PhotosRaw"), &segs(&["2026", "", "x"]));
        assert_eq!(dest.as_str(), "PhotosRaw/2026/x");
    }

    #[test]
    fn a_library_at_the_root_still_works() {
        let dest = destination(&RemotePath::root(), &segs(&["2026", "2026-08-22"]));
        assert_eq!(dest.as_str(), "2026/2026-08-22");
    }

    // The upload path itself needs a backend, which is exercised against a
    // fake in `dr-sync-nextcloud`'s tests and against a real server in S8.
    // What is worth pinning here is the collision rule, since it decides
    // whether a second camera's `IMG_0001.CR3` overwrites the first.
    /// A folder holding files of given name and length.
    struct Listing(Vec<(&'static str, u64)>);

    #[async_trait::async_trait]
    impl RemoteBackend for Listing {
        fn capabilities(&self) -> &crate::Capabilities {
            unimplemented!("not reached by the collision tests")
        }
        fn name(&self) -> &str {
            "listing"
        }
        async fn list(
            &self,
            dir: &RemotePath,
            _since: Option<&Validator>,
        ) -> Result<Vec<RemoteEntry>, RemoteError> {
            Ok(self
                .0
                .iter()
                .map(|(n, size)| RemoteEntry {
                    id: RemoteId::Path(dir.join(n)),
                    path: dir.join(n),
                    kind: EntryKind::File,
                    validator: Validator::new("v"),
                    size: *size,
                    modified: None,
                    has_preview: false,
                    materialised: true,
                })
                .collect())
        }
        async fn dir_validator(&self, _dir: &RemotePath) -> Result<Validator, RemoteError> {
            Err(RemoteError::Unsupported("test backend"))
        }
        async fn delta(
            &self,
            _cursor: &crate::Cursor,
        ) -> Result<(Vec<crate::RemoteChange>, crate::Cursor), RemoteError> {
            Err(RemoteError::Unsupported("test backend"))
        }
        async fn get(
            &self,
            _id: &RemoteId,
            _range: Option<std::ops::Range<u64>>,
        ) -> Result<Vec<u8>, RemoteError> {
            Err(RemoteError::Unsupported("test backend"))
        }
        async fn put(
            &self,
            _path: &RemotePath,
            _body: Vec<u8>,
            _precond: Option<crate::Precondition>,
        ) -> Result<Validator, RemoteError> {
            Ok(Validator::new("v"))
        }
        async fn delete(
            &self,
            _id: &RemoteId,
            _precond: Option<crate::Precondition>,
        ) -> Result<(), RemoteError> {
            Err(RemoteError::Unsupported("test backend"))
        }
        async fn move_to(&self, _from: &RemoteId, _to: &RemotePath) -> Result<(), RemoteError> {
            Err(RemoteError::Unsupported("test backend"))
        }
        async fn create_dir(&self, _path: &RemotePath) -> Result<(), RemoteError> {
            Ok(())
        }
    }

    /// Poll a future to completion on this thread.
    ///
    /// A hand-rolled poll rather than a runtime dependency for two tests: the
    /// fake backend answers immediately, so a future that came back pending
    /// would mean the fake had grown a suspension the tests do not model.
    fn block_on<F: std::future::Future>(f: F) -> F::Output {
        use std::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
        fn noop(_: *const ()) {}
        fn clone(p: *const ()) -> RawWaker {
            RawWaker::new(p, &VTABLE)
        }
        static VTABLE: RawWakerVTable = RawWakerVTable::new(clone, noop, noop, noop);
        let waker = unsafe { Waker::from_raw(RawWaker::new(std::ptr::null(), &VTABLE)) };
        let mut cx = Context::from_waker(&waker);
        let mut f = std::pin::pin!(f);
        match f.as_mut().poll(&mut cx) {
            Poll::Ready(v) => v,
            Poll::Pending => panic!("the fake backend never yields"),
        }
    }

    #[test]
    fn a_card_already_on_the_server_transfers_nothing() {
        // The ordinary case: last week's shoot was imported and uploaded, and
        // the card has not been formatted since. Re-uploading would double the
        // storage and litter the folder with `-1` copies of safe work.
        let backend = Listing(vec![("IMG_0001.CR3", 3)]);
        let placed = block_on(upload_original(
            &backend,
            &RemotePath::new("PhotosRaw"),
            &segs(&["2026", "2026-08-22"]),
            "IMG_0001.CR3",
            vec![1, 2, 3],
        ))
        .unwrap();
        assert_eq!(
            placed,
            Placed::AlreadyThere {
                path: RemotePath::new("PhotosRaw/2026/2026-08-22/IMG_0001.CR3")
            }
        );
    }

    #[test]
    fn a_second_cameras_img_0001_does_not_overwrite_the_first() {
        // Same name, different length: a genuinely different photograph, which
        // is what the rename is for.
        let backend = Listing(vec![("IMG_0001.CR3", 99)]);
        let placed = block_on(upload_original(
            &backend,
            &RemotePath::new("PhotosRaw"),
            &segs(&["2026", "2026-08-22"]),
            "IMG_0001.CR3",
            vec![1, 2, 3],
        ))
        .unwrap();
        assert_eq!(
            placed.path().as_str(),
            "PhotosRaw/2026/2026-08-22/IMG_0001-1.CR3"
        );
        assert!(matches!(placed, Placed::Uploaded { .. }));
    }

    #[test]
    fn a_free_name_is_used_as_it_is() {
        let backend = Listing(vec![("IMG_0002.CR3", 3)]);
        let placed = block_on(upload_original(
            &backend,
            &RemotePath::new("PhotosRaw"),
            &segs(&["2026", "2026-08-22"]),
            "IMG_0001.CR3",
            vec![1, 2, 3],
        ))
        .unwrap();
        assert_eq!(
            placed.path().as_str(),
            "PhotosRaw/2026/2026-08-22/IMG_0001.CR3"
        );
        assert!(matches!(placed, Placed::Uploaded { .. }));
    }

    #[test]
    fn a_renamed_copy_that_is_already_up_there_is_not_sent_twice() {
        // The card that collided once and is now being re-imported: both the
        // original name and the renamed copy are on the server, and this
        // photograph is the renamed one.
        let backend = Listing(vec![("IMG_0001.CR3", 99), ("IMG_0001-1.CR3", 3)]);
        let placed = block_on(upload_original(
            &backend,
            &RemotePath::new("PhotosRaw"),
            &segs(&["2026", "2026-08-22"]),
            "IMG_0001.CR3",
            vec![1, 2, 3],
        ))
        .unwrap();
        assert!(matches!(placed, Placed::AlreadyThere { .. }), "{placed:?}");
    }

    #[test]
    fn an_empty_folder_takes_the_name_as_offered() {
        let backend = Listing(vec![]);
        let placed = block_on(upload_original(
            &backend,
            &RemotePath::new("PhotosRaw"),
            &segs(&["2026", "2026-08-22"]),
            "IMG_0001.CR3",
            vec![1, 2, 3],
        ))
        .unwrap();
        assert!(matches!(placed, Placed::Uploaded { .. }));
    }
}