//! Synchronize Folder: bring a folder of the library up to date with what is on disk, as
//! Lightroom Classic's Synchronize Folder does.
//!
//! A [scan](scan_with) compares the folder (and the folders inside it) with the library and finds
//! three kinds of change, touching nothing:
//!
//! - **new** files: supported files the library doesn't have, by path or by content (the import
//!   scan's duplicate rules, [`crate::import::scan_with`]);
//! - **missing** photos: library photos in the folder whose file is gone (the Missing Photos rule,
//!   [`crate::cmd::missing::checked_path`]);
//! - **metadata** updates: photos whose XMP sidecar file was saved after the photo came into the
//!   library or was last edited here, and says something the library doesn't (rating, flag,
//!   label, metadata, capture time or develop settings). Reading one makes the sidecar win, as
//!   Read Metadata from File does. Embedded XMP in a raw is not a sidecar and is not looked at.
//!
//! [`synchronize`] then imports the new files (in place), moves the missing photos to Recently
//! Deleted and reads the metadata updates — each only when chosen — as one undo step.
//!
//! The scan runs without the session ([`SyncInput`] + [`scan_with`]), so the app can run it on a
//! worker thread: a folder on a sleeping network share must never stall a frame.
//!
//! Limits: a sidecar the library itself wrote (auto-write on) agrees with it and is never an
//! update; one written here before auto-write was turned off, followed by changes made only in
//! the library, is listed as an update even though the library is newer (there is no record of
//! when a photo's metadata last changed here). Reading updates is therefore never the default.

use std::collections::HashMap;
use std::path::Path;
use std::sync::Arc;

use lightcraft_catalog::{Catalog, Filter, Op, Photo, PhotoId, Sort, Source};
use serde::Serialize;

use crate::import::{ImportCandidate, ImportMode, ImportOptions, ScanInput, ScanProgress};
use crate::media::ProbeInfo;
use crate::sidecar::SidecarNaming;
use crate::{EngineError, Result, Session};

/// The largest XMP sidecar read when looking for metadata updates; a bigger one is skipped.
const MAX_SIDECAR_BYTES: u64 = 16 * 1024 * 1024;

/// What a scan of a folder needs, taken from the session so it can run on a worker thread.
pub struct SyncInput {
    folder: String,
    scan: ScanInput,
    /// The library's photos in the folder, each with how its sidecar is named.
    photos: Vec<(Arc<Photo>, SidecarNaming)>,
    /// For the colour label names a sidecar may use.
    labels: Catalog,
}

/// What changed in a folder since it came into the library.
#[derive(Clone, Debug, Default, Serialize)]
pub struct FolderChanges {
    /// The folder, as asked for.
    pub path: String,
    /// Files to import.
    pub new: Vec<ImportCandidate>,
    /// Files whose content the library already has (under another path).
    pub duplicates: usize,
    /// Supported files that couldn't be read.
    pub unreadable: Vec<ImportCandidate>,
    /// Photos whose file is gone.
    pub missing: Vec<FolderPhoto>,
    /// Photos whose sidecar has news.
    pub metadata: Vec<FolderPhoto>,
    /// Photos whose file was renamed or moved within the folder (found by its content).
    pub moved: Vec<FolderMoved>,
    /// The folder itself is not there (moved or renamed whole, or on a disk that isn't
    /// connected): nothing else is reported, rather than every photo as missing.
    pub offline: bool,
    /// The probes of the new files, kept for the import that follows.
    #[serde(skip)]
    probes: HashMap<String, ProbeInfo>,
    /// The folder's photos as the scan saw them: the scan is current while they are the same
    /// records (any change to one replaces it in the catalog).
    #[serde(skip)]
    seen: Vec<Arc<Photo>>,
}

/// A photo of the folder and its file.
#[derive(Clone, Debug, PartialEq, Eq, Serialize)]
pub struct FolderPhoto {
    pub id: u64,
    pub path: String,
}

/// A photo whose file is now somewhere else in the folder.
#[derive(Clone, Debug, PartialEq, Eq, Serialize)]
pub struct FolderMoved {
    pub id: u64,
    pub from: String,
    pub to: String,
}

/// What [`synchronize`] does with the changes found.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct SyncChoice {
    pub import_new: bool,
    pub relink_moved: bool,
    pub remove_missing: bool,
    pub read_metadata: bool,
}

impl Default for SyncChoice {
    /// Lightroom Classic's defaults: import the new files, leave the rest to be looked at; and
    /// photos whose file moved follow it (nothing is lost, and undo puts them back).
    fn default() -> Self {
        SyncChoice { import_new: true, relink_moved: true, remove_missing: false, read_metadata: false }
    }
}

/// What [`synchronize`] did.
#[derive(Clone, Debug, Default, PartialEq, Eq, Serialize)]
pub struct SyncReport {
    pub imported: usize,
    pub relinked: usize,
    pub removed: usize,
    pub read: usize,
    /// (path or photo, why) for what couldn't be done.
    pub failed: Vec<(String, String)>,
}

fn invalid(msg: impl Into<String>) -> EngineError {
    EngineError::Other(msg.into())
}

impl SyncInput {
    /// The scan of folder `path`: a folder the library holds photos in, not the startup disk. A
    /// whole disk or share, or a folder that holds disks (`/Volumes`, `/mnt`…), only with `disk`
    /// (as for Remove Disk from Library: its missing photos can be a whole disk's).
    pub fn new(s: &mut Session, path: &str, disk: bool) -> Result<SyncInput> {
        let path = path.trim();
        if path.is_empty() {
            return Err(invalid("missing `path`"));
        }
        if lightcraft_catalog::folders::is_startup_disk(path) {
            return Err(invalid("choose a folder, not the whole startup disk"));
        }
        let f = Filter { library_folder: Some(path.to_string()), ..Default::default() };
        let ids = s.catalog.query(&f, &Sort::default());
        if ids.is_empty() {
            return Err(invalid(format!("{path}: no photo in the library was imported from it")));
        }
        if !disk && (lightcraft_catalog::folders::is_disk_root(path) || crate::cmd::library::covers_other_disks(s, path, &ids)) {
            return Err(invalid(format!("{path} is a whole disk or holds disks: pass `disk: true` to synchronize it")));
        }
        let photos = ids.iter().filter_map(|id| s.catalog.photo(*id).map(|p| (Arc::clone(p), s.sidecar_naming(*id)))).collect();
        let (scan, _) = ScanInput::new(s, &[path.to_string()]);
        Ok(SyncInput { folder: path.to_string(), scan, photos, labels: s.catalog.clone() })
    }
}

/// Find what changed in the folder (see the module docs). Reads the disk, never the session.
///
/// Both halves wait on the disk (a network share answers each file slowly), so they run at once:
/// the look for new files (which probes them on its own threads) beside the checks of the
/// library's photos, which run on several threads too. Stops early when `progress.cancel` is set.
pub fn scan_with(input: SyncInput, progress: &ScanProgress) -> FolderChanges {
    let SyncInput { folder, scan, photos, labels } = input;
    let seen: Vec<Arc<Photo>> = photos.iter().map(|(p, _)| Arc::clone(p)).collect();
    if !cfg!(target_arch = "wasm32") && !Path::new(&folder).is_dir() {
        return FolderChanges { path: folder, seen, offline: true, ..Default::default() };
    }
    // (no threads on the web: one after the other there)
    #[cfg(target_arch = "wasm32")]
    let (out, checks) = (crate::import::scan_with(scan, std::slice::from_ref(&folder), progress), check_photos(&photos, &labels, progress));
    #[cfg(not(target_arch = "wasm32"))]
    let (out, checks) = std::thread::scope(|sc| {
        let photos = &photos;
        let labels = &labels;
        let checks = sc.spawn(move || check_photos(photos, labels, progress));
        let out = crate::import::scan_with(scan, std::slice::from_ref(&folder), progress);
        // (a check that panicked counts as nothing found; the scan still reports the rest)
        (out, checks.join().unwrap_or_default())
    });
    let mut changes = FolderChanges { path: folder, seen, ..Default::default() };
    for ((p, _), check) in photos.iter().zip(checks) {
        let Some(file) = crate::cmd::missing::checked_path(p) else { continue };
        let found = FolderPhoto { id: p.id.0, path: file.to_string() };
        match check {
            Check::Missing => changes.missing.push(found),
            Check::News => changes.metadata.push(found),
            Check::Nothing => {}
        }
    }
    // a missing photo's content found under another name in the folder: the file was renamed or
    // moved, and the photo (with its edits) follows it rather than going missing
    let mut gone_by_hash: HashMap<&str, &str> = HashMap::new();
    for m in &changes.missing {
        if let Some(h) = labels.photo(PhotoId(m.id)).and_then(|p| p.content_hash.as_deref()) {
            gone_by_hash.entry(h).or_insert(m.path.as_str());
        }
    }
    let mut moved_from: HashMap<String, String> = HashMap::new();
    for c in out.candidates {
        let hash = out.probes.get(&c.path).and_then(|i| i.content_hash.as_deref());
        if c.error.is_none()
            && c.duplicate.as_deref() != Some("path")
            && let Some(from) = hash.and_then(|h| gone_by_hash.remove(h))
        {
            moved_from.insert(from.to_string(), c.path.clone());
            continue;
        }
        let browsed = c.existing.and_then(|id| labels.photo(PhotoId(id))).is_some_and(|p| p.local && !p.deleted);
        match (c.duplicate.as_deref(), &c.error) {
            // a file only looked at in Local is not in the library yet: it is new
            (Some("path"), _) if browsed => changes.new.push(c),
            (Some("path"), _) => {}
            (Some(_), _) => changes.duplicates += 1,
            (None, Some(_)) => changes.unreadable.push(c),
            (None, None) => changes.new.push(c),
        }
    }
    let missing = std::mem::take(&mut changes.missing);
    for m in missing {
        match moved_from.get(&m.path) {
            Some(to) => changes.moved.push(FolderMoved { id: m.id, from: m.path, to: to.clone() }),
            None => changes.missing.push(m),
        }
    }
    changes.probes = out.probes;
    changes
}

/// What checking one photo of the folder found.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
enum Check {
    #[default]
    Nothing,
    Missing,
    News,
}

fn check_photo(p: &Photo, naming: SidecarNaming, labels: &Catalog) -> Check {
    let Some(file) = crate::cmd::missing::checked_path(p) else { return Check::Nothing };
    if !Path::new(file).exists() {
        Check::Missing
    } else if p.copy_of.is_none() && sidecar_has_news(labels, p, naming) {
        Check::News
    } else {
        Check::Nothing
    }
}

/// [`check_photo`] for each photo, in order, on several threads (each file is a wait on the
/// disk, not work for the CPU). Photos not reached before a cancel count as nothing found.
fn check_photos(photos: &[(Arc<Photo>, SidecarNaming)], labels: &Catalog, progress: &ScanProgress) -> Vec<Check> {
    use std::sync::atomic::Ordering::Relaxed;
    if cfg!(target_arch = "wasm32") {
        return vec![Check::Nothing; photos.len()];
    }
    #[cfg(not(target_arch = "wasm32"))]
    {
        let n = crate::import::workers(photos.len());
        if n > 1 {
            let next = std::sync::atomic::AtomicUsize::new(0);
            let found = std::sync::Mutex::new(vec![Check::Nothing; photos.len()]);
            std::thread::scope(|sc| {
                for _ in 0..n {
                    sc.spawn(|| {
                        while !progress.cancel.load(Relaxed) {
                            let i = next.fetch_add(1, Relaxed);
                            let Some((p, naming)) = photos.get(i) else { break };
                            let c = check_photo(p, *naming, labels);
                            if let Some(slot) = found.lock().unwrap_or_else(std::sync::PoisonError::into_inner).get_mut(i) {
                                *slot = c;
                            }
                        }
                    });
                }
            });
            return found.into_inner().unwrap_or_else(std::sync::PoisonError::into_inner);
        }
    }
    photos.iter().map(|(p, naming)| if progress.cancel.load(Relaxed) { Check::Nothing } else { check_photo(p, *naming, labels) }).collect()
}

/// [`scan_with`] on the calling thread.
pub fn scan(s: &mut Session, path: &str, disk: bool) -> Result<FolderChanges> {
    let input = SyncInput::new(s, path, disk)?;
    let changes = scan_with(input, &ScanProgress::default());
    if changes.offline {
        return Err(not_there(&changes.path));
    }
    Ok(changes)
}

fn not_there(path: &str) -> EngineError {
    invalid(format!("{path} is not there (moved, renamed, or on a disk that isn't connected)"))
}

impl Session {
    /// The last scan ([`Session::folder_changes`]) if it is of folder `path` and still current:
    /// the folder holds the same photos, none of them changed. What the person was shown is what
    /// gets done. Used once. (Changes elsewhere in the library don't matter.)
    pub fn take_folder_changes(&mut self, path: &str) -> Option<FolderChanges> {
        let c = self.folder_changes.take()?;
        if lightcraft_catalog::query::folder_key(&c.path) != lightcraft_catalog::query::folder_key(path) {
            return None;
        }
        let f = Filter { library_folder: Some(path.to_string()), ..Default::default() };
        let mut now: Vec<PhotoId> = self.catalog.query(&f, &Sort::default());
        let mut then: Vec<PhotoId> = c.seen.iter().map(|p| p.id).collect();
        now.sort();
        then.sort();
        let unchanged = now == then && c.seen.iter().all(|p| self.catalog.photo(p.id).is_some_and(|q| Arc::ptr_eq(p, q)));
        unchanged.then_some(c)
    }
}

/// Whether `p`'s XMP sidecar file was saved after the library last had its say about the photo
/// (imported, or edited here) and says something the library doesn't.
fn sidecar_has_news(labels: &Catalog, p: &Photo, naming: SidecarNaming) -> bool {
    let Source::File { path } = &p.source else { return false };
    let Some(file) = crate::sidecar::find_sidecar(path, naming) else { return false };
    let Ok(meta) = std::fs::metadata(&file) else { return false };
    if meta.len() > MAX_SIDECAR_BYTES {
        return false;
    }
    let saved = meta.modified().ok().and_then(|t| t.duration_since(std::time::UNIX_EPOCH).ok()).map(|d| d.as_secs());
    let Some(saved) = saved.and_then(|s| i64::try_from(s).ok()) else { return false };
    let seen = [Some(p.imported.as_str()), p.edited.as_deref()].into_iter().flatten().filter_map(lightcraft_catalog::stacks::iso_seconds).max();
    if seen.is_some_and(|t| saved <= t) {
        return false;
    }
    let Ok(text) = std::fs::read_to_string(&file) else { return false };
    let Ok(sc) = crate::sidecar::parse_sidecar(&text, p.kind == lightcraft_catalog::MediaKind::Raw) else { return false };
    let sc = sc.resolve_label(labels);
    let mut q = p.clone();
    crate::sidecar::merge_into(&mut q, &sc, "");
    (q.rating, q.flag, q.label, &q.meta, &q.captured, &q.develop) != (p.rating, p.flag, p.label, &p.meta, &p.captured, &p.develop)
}

/// Act on `changes` as `choice` says, as one undo step ("Synchronize Folder"). A missing photo
/// whose file is back by now is left alone. Once the import is in, a part that fails is
/// reported in `failed` and the rest is still done (and still one step).
pub fn synchronize(s: &mut Session, changes: FolderChanges, choice: SyncChoice) -> Result<SyncReport> {
    if changes.offline {
        return Err(not_there(&changes.path));
    }
    let mark = s.commits();
    let mut report = SyncReport::default();
    let FolderChanges { new, missing, metadata, moved, probes, .. } = changes;
    if choice.import_new && !new.is_empty() {
        s.import_probes = probes;
        let files: Vec<String> = new.into_iter().map(|c| c.path).collect();
        let r = crate::import::import_with(s, &files, &ImportOptions { mode: ImportMode::Add, ..Default::default() })?;
        report.imported = r.imported.len();
        report.failed.extend(r.failed);
    }
    if choice.relink_moved {
        // still where the scan found it, and still gone from where the photo says
        let ops: Vec<Op> = moved
            .iter()
            .filter(|m| Path::new(&m.to).is_file() && !Path::new(&m.from).exists() && s.catalog.photo(PhotoId(m.id)).is_some())
            .map(|m| crate::cmd::missing::relink_op(PhotoId(m.id), &m.to))
            .collect();
        if !ops.is_empty() {
            let n = ops.len();
            match s.commit("Relink Moved Photos", Op::Batch { ops }) {
                Ok(()) => report.relinked = n,
                Err(e) => report.failed.push((String::new(), e.to_string())),
            }
        }
    }
    if choice.remove_missing {
        let gone: Vec<PhotoId> = missing.iter().filter(|m| !Path::new(&m.path).exists()).map(|m| PhotoId(m.id)).collect();
        let ops: Vec<Op> = gone
            .iter()
            .filter(|id| s.catalog.photo(**id).is_some_and(|p| p.in_library()))
            .map(|id| Op::SetDeleted { id: *id, deleted: true })
            .collect();
        if !ops.is_empty() {
            let n = ops.len();
            match s.commit("Remove Missing Photos", Op::Batch { ops }) {
                Ok(()) => report.removed = n,
                Err(e) => report.failed.push((String::new(), e.to_string())),
            }
        }
    }
    if choice.read_metadata {
        let mut ops = Vec::new();
        for m in &metadata {
            match s.read_sidecar_op(PhotoId(m.id)) {
                Ok(Some((op, _))) => {
                    ops.push(op);
                    report.read += 1;
                }
                Ok(None) => report.failed.push((m.path.clone(), "no XMP sidecar".into())),
                Err(e) => report.failed.push((m.path.clone(), e.to_string())),
            }
        }
        if !ops.is_empty()
            && let Err(e) = s.commit("Read Metadata from File", Op::Batch { ops })
        {
            report.read = 0;
            report.failed.push((String::new(), e.to_string()));
        }
    }
    // (what was done stays one step even when a later part failed: the report says which)
    let steps = usize::try_from(s.commits().wrapping_sub(mark)).unwrap_or(usize::MAX).min(s.undo.len());
    s.merge_undo(steps, "Synchronize Folder");
    if let Some(last) = s.undo.last_mut().filter(|_| steps == 1) {
        last.label = "Synchronize Folder".into();
    }
    Ok(report)
}