//! Moving the working copy to another state (spec §12.3, §7.7).

use super::*;

#[derive(Debug, Default, Clone, PartialEq, Eq)]

pub struct CheckoutReport {

    pub written: usize,

    pub removed: usize,

    pub conflicted: bool,

    /// Nested repositories that could not be moved, and other remarks.

    pub notes: Vec<String>,

    /// How many changes of the state left behind the new one lacks.

    pub lacks: usize,

}

/// Text files rendered at a time by a checkout: bounds its memory.

const CHECKOUT_BATCH: usize = 2048;

impl Repo {

    /// Move the working copy to the state whose heads are `heads` (spec §12.3):

    /// the working directory is rewritten to that state and a fresh

    /// working-copy change is started on it. The bookmark does not move.

    pub fn checkout(

        &self,

        heads: &[ChangeHash],

        discard: bool,

        command: &str,

    ) -> Result<CheckoutReport> {

        self.checkout_keeping(heads, discard, command, &BTreeSet::new())

    }

    /// [`Repo::checkout`], leaving the nested repositories at

    /// `keep_subrepos` as they are (their pins are carried work).

    pub(crate) fn checkout_keeping(

        &self,

        heads: &[ChangeHash],

        discard: bool,

        command: &str,

        keep_subrepos: &BTreeSet<String>,

    ) -> Result<CheckoutReport> {

        let _wc = self.lock_working_copy()?;

        let _all = crate::timing::phase("checkout");

        // A working copy clean by the manifest needs no snapshot; otherwise a

        // status snapshot records what changed, and rewrites the manifest

        // with the graph key of every file it proves unchanged. Either way

        // the manifest then says, for each file on disk, which graph it

        // renders, so the base state itself is not needed (oxygen#35).

        let changed_paths: Vec<String> = if self.clean_by_manifest()? {

            Vec::new()

        } else {

            let snap = self.snapshot_status(command)?;

            self.refuse_dirty(&snap, discard)?;

            snap.statuses.iter().map(|s| s.path.clone()).collect()

        };

        let (_, wc_now) = self.working_copy()?;

        let old_manifest = self.read_manifest()?.map(|(_, _, m)| m).unwrap_or_default();

        let changed: HashSet<&str> = changed_paths.iter().map(String::as_str).collect();

        // The target's history; its file graphs are built a batch at a time

        // for the files that must be written, and dropped after. It becomes

        // the working copy's base, which the state index holds.

        let mut target = self.load_state_indexed(heads)?;

        let heads = target.maximal(heads);

        let tv = crate::timing::phase("checkout: target view");

        let tview = target.tree().view();

        drop(tv);

        let mut report = CheckoutReport::default();

        // Paths this file system cannot hold side by side (spec §7.7).

        report.notes.extend(

            self.platform

                .problems(tview.entries.keys().map(String::as_str)),

        );

        report.conflicted = tview.is_conflicted();

        report.lacks = self.count_lacking(&wc_now.deps, &target)?;

        // Remove what the base or the working copy has and the target does

        // not. A nested repository is never deleted (spec §7.8).

        let mut dirs_to_prune: BTreeSet<PathBuf> = BTreeSet::new();

        let gone: BTreeSet<&str> = old_manifest

            .entries

            .keys()

            .map(String::as_str)

            .chain(changed.iter().copied())

            .filter(|p| !tview.entries.contains_key(*p))

            .collect();

        for path in gone {

            let dir = self.root.join(path);

            if dir.join(OXY_DIR).exists() || dir.join(".git").exists() {

                report

                    .notes

                    .push(format!("{path}: nested repository left in place"));

                continue;

            }

            let full = self.safe_path(path)?;

            if fs::symlink_metadata(&full).is_err() {

                continue;

            }

            fs::remove_file(&full)?;

            report.removed += 1;

            if let Some(parent) = full.parent() {

                dirs_to_prune.insert(parent.to_path_buf());

            }

        }

        // The manifest after the checkout, built from what is known.

        let plan = crate::timing::phase("checkout: plan");

        let mut entries: BTreeMap<String, FsEntry> = BTreeMap::new();

        let hex = |b: &[u8]| *blake3::hash(b).as_bytes();

        // Text files to render, attribute files first (the others need them).

        let mut texts: Vec<(String, NodeId, Mode)> = Vec::new();

        for (path, e) in tview.entries.iter() {

            if e.kind == NodeKind::Dir || !self.in_scope(path) {

                continue;

            }

            // The manifest entry of a file the working copy has not changed,

            // with the right executable bit.

            let exec_ok =

                |m: &prompt::ManifestEntry| !self.platform.exec_bits || m.exec == e.mode.exec;

            let entry = old_manifest

                .entries

                .get(path)

                .filter(|m| !changed.contains(path.as_str()) && exec_ok(m));

            if e.kind == NodeKind::File && !e.mode.opaque {

                // The manifest proves the file on disk equal to the rendering

                // of a graph whose key is the target's: nothing to read,

                // render or write.

                let key = target.graph_key(&e.node);

                let proven = |m: &&prompt::ManifestEntry| {

                    !is_attributes(path) && key.is_some() && m.graph == key

                };

                match entry.filter(proven) {

                    Some(m) => {

                        entries.insert(

                            path.clone(),

                            FsEntry {

                                content_hash: Some(m.hash),

                                graph_key: m.graph,

                                unchanged: true,

                                stat: Some((m.size, m.mtime_ns)),

                                ..FsEntry::new(NodeKind::File, e.mode.exec, Vec::new())

                            },

                        );

                    }

                    None => texts.push((path.clone(), e.node, e.mode)),

                }

                continue;

            }

            // Opaque files, symlinks and subrepos: their blobs.

            let blobs = target.live_blobs(&e.node);

            if blobs.len() > 1 {

                report.conflicted = true;

            }

            let Some(blob) = blobs.first().copied() else {

                continue;

            };

            if e.kind == NodeKind::Subrepo {

                if keep_subrepos.contains(path) {

                    continue;

                }

                let pin = crate::subrepo::Pin::decode(&self.read_blob(&blob)?)?;

                let sync = self.sync_subrepo(path, &pin, false)?;

                if matches!(

                    sync,

                    SubrepoSync::Updated | SubrepoSync::KeptBookmark { .. }

                ) {

                    report.written += 1;

                }

                report.notes.extend(sync.note(path));

                continue;

            }

            if let Some(m) = entry

                .filter(|m| e.kind == NodeKind::File && blobs.len() == 1 && m.blob == Some(blob))

            {

                entries.insert(

                    path.clone(),

                    FsEntry {

                        content_hash: Some(m.hash),

                        blob: (e.kind == NodeKind::File).then_some(blob),

                        stat: Some((m.size, m.mtime_ns)),

                        ..FsEntry::new(e.kind, e.mode.exec, Vec::new())

                    },

                );

                continue;

            }

            let bytes = self.read_blob(&blob)?;

            let full = self.root.join(path);

            if e.kind == NodeKind::Symlink {

                let same = fs::read_link(&full)

                    .is_ok_and(|t| t.to_string_lossy().as_bytes() == bytes.as_slice());

                if !same {

                    self.write_symlink(path, &bytes)?;

                    report.written += 1;

                }

                entries.insert(

                    path.clone(),

                    FsEntry {

                        content_hash: Some(hex(&bytes)),

                        ..FsEntry::new(NodeKind::Symlink, false, Vec::new())

                    },

                );

            } else {

                if !self.same_on_disk(&full, &bytes, e.mode.exec) {

                    self.write_file(path, &bytes, e.mode.exec)?;

                    report.written += 1;

                }

                entries.insert(

                    path.clone(),

                    FsEntry {

                        content_hash: Some(hex(&bytes)),

                        blob: (blobs.len() == 1).then_some(blob),

                        ..FsEntry::new(NodeKind::File, e.mode.exec, Vec::new())

                    },

                );

            }

            for (i, b) in blobs.iter().enumerate().skip(1) {

                self.write_file(

                    &format!("{path}.oxy-conflict-{}", i + 1),

                    &self.read_blob(b)?,

                    e.mode.exec,

                )?;

            }

        }

        drop(plan);

        let _render = crate::timing::phase("checkout: render and write");

        // Render and write text files a batch at a time; attribute files

        // come first, since the others' line endings and locks follow them.

        texts.sort_by_key(|(p, _, _)| !is_attributes(p));

        let keys: HashMap<NodeId, [u8; 32]> = texts

            .iter()

            .filter_map(|(_, n, _)| Some((*n, target.graph_key(n)?)))

            .collect();

        let mut attrs = crate::attributes::Attributes::default();

        let attr_count = texts.iter().filter(|(p, _, _)| is_attributes(p)).count();

        let mut done = 0usize;

        let mut batches: Vec<&[(String, NodeId, Mode)]> = Vec::new();

        if attr_count > 0 {

            batches.push(&texts[..attr_count]);

        }

        batches.extend(texts[attr_count..].chunks(CHECKOUT_BATCH));

        for batch in batches {

            use rayon::prelude::*;

            let nodes: Vec<NodeId> = batch.iter().map(|(_, n, _)| *n).collect();

            {

                let _t = crate::timing::phase("checkout: build graphs");

                self.load_graphs_of(&mut target, &nodes)?;

            }

            let rendered: Vec<(Vec<u8>, bool)> = {

                let _t = crate::timing::phase("checkout: render");

                nodes

                    .par_iter()

                    .map(|n| {

                        let (bytes, m) = target.render_file(n);

                        (bytes, m.is_conflicted())

                    })

                    .collect()

            };

            target.drop_graphs(&nodes);

            let _t = crate::timing::phase("checkout: write");

            if done == 0 && attr_count > 0 {

                attrs = crate::attributes::Attributes::from_files(

                    batch

                        .iter()

                        .zip(&rendered)

                        .map(|((p, _, _), (b, _))| (p.as_str(), b.as_slice())),

                );

            }

            done += batch.len();

            for ((path, node, mode), (bytes, conflicted)) in batch.iter().zip(rendered) {

                let a = attrs.lookup(path);

                let crlf = a.eol == Some(crate::attributes::Eol::Crlf);

                let on_disk: Vec<u8> = if crlf {

                    crate::attributes::to_crlf(&bytes)

                } else {

                    bytes

                };

                if !self.same_on_disk(&self.root.join(path), &on_disk, mode.exec) {

                    self.write_file(path, &on_disk, mode.exec)?;

                    report.written += 1;

                }

                report.conflicted |= conflicted;

                entries.insert(

                    path.clone(),

                    FsEntry {

                        content_hash: Some(hex(&on_disk)),

                        graph_key: (!conflicted && a.eol.is_none())

                            .then(|| keys.get(node).copied())

                            .flatten(),

                        ..FsEntry::new(NodeKind::File, mode.exec, Vec::new())

                    },

                );

            }

        }

        // Lockable files are read-only until locked (spec §18), whether

        // written now or left as they were.

        for (path, e) in &entries {

            if e.kind == NodeKind::File && attrs.lookup(path).lockable && !self.is_locked(path) {

                let _ = set_readonly(&self.root.join(path), true);

            }

        }

        // Prune directories left empty, deepest first.

        for d in dirs_to_prune.iter().rev() {

            let mut d = d.clone();

            while d != self.root

                && fs::read_dir(&d)

                    .map(|mut i| i.next().is_none())

                    .unwrap_or(false)

            {

                fs::remove_dir(&d)?;

                let Some(p) = d.parent() else { break };

                d = p.to_path_buf();

            }

        }

        drop(_render);

        let recording = crate::timing::phase("checkout: record");

        let (op_ref, op) = self.head_op()?;

        let wc = self.new_working_copy(heads.clone(), "");

        let wc_hash = self.store.put_change(&wc)?;

        let mut view = op.view.clone();

        view.workspaces.insert(self.workspace, wc_hash);

        self.record_op(&[op_ref], command, view)?;

        drop(recording);

        let _t = crate::timing::phase("checkout: manifest");

        // The directories the new tree has, with any the old manifest kept

        // that still exist (holding only ignored files, say), statted now,

        // after the writes: the next check then need not list the tree. A

        // directory written just now is within the racy window, so for a

        // moment the check lists anyway.

        if !old_manifest.dirs.is_empty() {

            let mut dirs: BTreeSet<String> =

                old_manifest.dirs.iter().map(|(d, _)| d.clone()).collect();

            dirs.insert(String::new());

            for p in entries.keys() {

                let mut at = p.as_str();

                while let Some((parent, _)) = at.rsplit_once('/') {

                    if !dirs.insert(parent.to_string()) {

                        break;

                    }

                    at = parent;

                }

            }

            use rayon::prelude::*;

            let root = &self.root;

            let dirs: Vec<(String, u128)> = dirs

                .into_par_iter()

                .filter_map(|d| {

                    let m = fs::metadata(root.join(&d)).ok().filter(|m| m.is_dir())?;

                    Some((d, prompt::mtime_ns(&m)))

                })

                .collect();

            let mut dirs = dirs;

            dirs.sort_unstable();

            *self.walked_dirs.borrow_mut() = Some((dirs, old_manifest.nested.clone()));

        }

        self.write_manifest_entries(report.conflicted, false, &entries, &HashMap::new())?;

        let _ = self.run_hook(

            "post-checkout",

            &format!(

                "{{\"event\":\"post-checkout\",\"heads\":{},\"written\":{},\"removed\":{}}}",

                json_array(heads.iter().map(|h| json_str(&h.to_hex()))),

                report.written,

                report.removed

            ),

        );

        Ok(report)

    }

    /// How many changes of the state at `from` the state `to` lacks: a walk

    /// down from `from` that stops at what `to` holds.

    fn count_lacking(&self, from: &[ChangeHash], to: &State) -> Result<usize> {

        let mut seen: HashSet<ChangeHash> = HashSet::new();

        let mut stack: Vec<ChangeHash> = from.to_vec();

        while let Some(h) = stack.pop() {

            if to.contains(&h) || !seen.insert(h) {

                continue;

            }

            stack.extend(self.store.get_change_lazy(&h)?.0.deps);

        }

        Ok(seen.len())

    }

    /// Refuse to leave uncommitted work behind unless `discard`.

    pub(crate) fn refuse_dirty(&self, snap: &SnapshotResult, discard: bool) -> Result<()> {

        if discard || (snap.wc.tree_ops.is_empty() && snap.wc.edits.is_empty()) {

            return Ok(());

        }

        let list: Vec<String> = snap

            .statuses

            .iter()

            .take(8)

            .map(|s| format!("{} {}", status_word(s.status), s.path))

            .collect();

        fail(format!(

            "the working copy has changes ({}{}); commit them, take them along with --carry, or drop them with --discard",

            list.join(", "),

            if snap.statuses.len() > 8 { ", …" } else { "" }

        ))

    }

    /// Whether the file at `full` already holds `bytes` with this executable

    /// bit, so writing it again can be skipped.

    fn same_on_disk(&self, full: &Path, bytes: &[u8], exec: bool) -> bool {

        match fs::symlink_metadata(full) {

            Ok(m) if m.is_file() && m.len() == bytes.len() as u64 => {

                (!self.platform.exec_bits || is_executable(&m) == exec)

                    && fs::read(full).is_ok_and(|b| b == bytes)

            }

            _ => false,

        }

    }

    /// The absolute path for a repository path, refusing anything that would

    /// escape the workspace or write through a symlink (spec §7.7).

    fn safe_path(&self, rel: &str) -> Result<PathBuf> {

        let mut full = self.root.clone();

        let comps: Vec<&str> = rel.split('/').collect();

        for (i, comp) in comps.iter().enumerate() {

            if comp.is_empty() || *comp == "." || *comp == ".." || comp.contains('\\') {

                return fail(format!("refusing unsafe path {rel:?}"));

            }

            if i == 0 && *comp == OXY_DIR {

                return fail(format!("refusing to write inside {OXY_DIR}: {rel:?}"));

            }

            if i + 1 < comps.len() {

                full.push(comp);

                if let Ok(m) = fs::symlink_metadata(&full) {