//! Tools for moving the repository to a given revision

use std::{

    fs::Permissions,

    io::Write,

    os::unix::fs::{MetadataExt, PermissionsExt},

    path::Path,

    time::Duration,

};

use crate::{

    dirstate::{ParentFileData, TruncatedTimestamp},

    dirstate_tree::{

        dirstate_map::DirstateEntryReset, on_disk::write_tracked_key,

    },

    errors::{HgError, IoResultExt},

    operations::{list_rev_tracked_files, ExpandedManifestEntry},

    progress::Progress,

    repo::Repo,

    sparse,

    utils::{

        files::{filesystem_now, get_path_from_bytes},

        hg_path::{hg_path_to_path_buf, HgPath, HgPathError},

        path_auditor::PathAuditor,

    },

    vfs::{is_on_nfs_mount, VfsImpl},

};

use crossbeam_channel::{Receiver, Sender};

use rayon::prelude::*;

fn write_dirstate(repo: &Repo) -> Result<(), HgError> {

    repo.write_dirstate()

        .map_err(|e| HgError::abort(e.to_string(), exit_codes::ABORT, None))?;

    write_tracked_key(repo)

}

/// Update the current working copy of `repo` to the given revision `to`, from

/// the null revision and set + write out the dirstate to reflect that.

///

/// Do not call this outside of a Python context. This does *not* handle any

/// of the checks, hooks, lock taking needed to setup and get out of this

/// update from the null revision.

pub fn update_from_null(

    repo: &Repo,

    to: UncheckedRevision,

    progress: &dyn Progress,

) -> Result<usize, HgError> {

    // Ignore the warnings, they've been displayed by Python already

    // TODO non-Python clients: display narrow warnings

    let (narrow_matcher, _) = narrow::matcher(repo)?;

    let files_for_rev = list_rev_tracked_files(repo, to, narrow_matcher)

        .map_err(handle_revlog_error)?;

    repo.manually_set_parents(DirstateParents {

        p1: repo.node(to).expect("update target should exist"),

        p2: NULL_NODE,

    })?;

    // Filter the working copy according to the sparse spec

    let tracked_files: Result<Vec<_>, _> = if !repo.has_sparse() {

        files_for_rev.iter().collect()

    } else {

        // Ignore the warnings, they've been displayed by Python already

        // TODO non-Python clients: display sparse warnings

        let (sparse_matcher, _) = sparse::matcher(repo)?;

        files_for_rev

            .iter()

            .filter(|f| {

                match f {

                    Ok(f) => sparse_matcher.matches(f.0),

                    Err(_) => true, // Errors stop the update, include them

                }

            })

            .collect()

    };

    let tracked_files = tracked_files?;

    if tracked_files.is_empty() {

        // Still write the dirstate because we might not be in the null

        // revision.

        // This can happen in narrow repos where all paths are excluded in

        // this revision.

        write_dirstate(repo)?;

        return Ok(0);

    }

    let store_vfs = &repo.store_vfs();

    let options = default_revlog_options(

        repo.config(),

        repo.requirements(),

    )?;

    let (errors_sender, errors_receiver) = crossbeam_channel::unbounded();

    let (files_sender, files_receiver) = crossbeam_channel::unbounded();

    let working_directory_path = &repo.working_directory_path();

    let files_count = tracked_files.len();

    let chunks = chunk_tracked_files(tracked_files);

    progress.update(0, Some(files_count as u64));

    create_working_copy(

        chunks,

        working_directory_path,

        store_vfs,

        options,

        files_sender,

        errors_sender,

        progress,

    );

    let errors: Vec<HgError> = errors_receiver.iter().collect();

    if !errors.is_empty() {

        log::debug!("{} errors during update (see trace logs)", errors.len());

        for error in errors.iter() {

            log::trace!("{}", error);

        }

        // Best we can do is raise the first error (in order of the channel)

        return Err(errors.into_iter().next().expect("can never be empty"));

    }

    // TODO try to run this concurrently to update the dirstate while we're

    // still writing out the working copy to see if that improves performance.

    let total = update_dirstate(repo, files_receiver)?;

    write_dirstate(repo)?;

    Ok(total)

}

fn handle_revlog_error(e: RevlogError) -> HgError {

    match e {

        e => HgError::abort(

            format!("revlog error: {}", e),

            exit_codes::ABORT,

            None,

        ),

    }

}

/// Preallocated size of Vec holding directory contents. This aims at

/// preventing the need for re-allocating the Vec in most cases.

///

/// The value is arbitrarily picked as a little over an average number of files

/// per directory done by looking at a few larger open-source repos.

/// Most of the runtime is IO anyway, so this doesn't matter too much.

const FILES_PER_DIRECTORY: usize = 16;

/// Chunk files per directory prefix, so almost every directory is handled

/// in a separate thread, which works around the FS inode mutex.

/// Chunking less (and doing approximately `files_count`/`threads`) actually

/// ends up being less performant: my hypothesis is `rayon`'s work stealing

/// being more efficient with tasks of varying lengths.

#[logging_timer::time("trace")]

fn chunk_tracked_files(

    tracked_files: Vec<ExpandedManifestEntry>,

) -> Vec<(&HgPath, Vec<ExpandedManifestEntry>)> {

    let files_count = tracked_files.len();

    let mut chunks = Vec::with_capacity(files_count / FILES_PER_DIRECTORY);

    let mut current_chunk = Vec::with_capacity(FILES_PER_DIRECTORY);

    let mut last_directory = tracked_files[0].0.parent();

    for file_info in tracked_files {

        let current_directory = file_info.0.parent();

        let different_directory = current_directory != last_directory;

        if different_directory {

            chunks.push((last_directory, current_chunk));

            current_chunk = Vec::with_capacity(FILES_PER_DIRECTORY);

        }

        current_chunk.push(file_info);

        last_directory = current_directory;

    }

    chunks.push((last_directory, current_chunk));

    chunks

}

#[logging_timer::time("trace")]

fn create_working_copy<'a: 'b, 'b>(

    chunks: Vec<(&HgPath, Vec<ExpandedManifestEntry<'a>>)>,

    working_directory_path: &Path,

    store_vfs: &VfsImpl,

    options: RevlogOpenOptions,

    files_sender: Sender<(&'b HgPath, u32, usize, TruncatedTimestamp)>,

    error_sender: Sender<HgError>,

    progress: &dyn Progress,

) {

    let auditor = PathAuditor::new(working_directory_path);

    chunks.into_par_iter().for_each(|(dir_path, chunk)| {

        if let Err(e) = working_copy_worker(

            dir_path,

            chunk,

            working_directory_path,

            store_vfs,

            options,

            &files_sender,

            progress,

            &auditor,

        ) {

            error_sender

                .send(e)

                .expect("channel should not be disconnected")

        }

    });

}

/// Represents a work unit for a single thread, responsible for this set of

/// files and restoring them to the working copy.

#[allow(clippy::too_many_arguments)]

fn working_copy_worker<'a: 'b, 'b>(

    dir_path: &HgPath,

    chunk: Vec<ExpandedManifestEntry<'a>>,

    working_directory_path: &Path,

    store_vfs: &VfsImpl,

    options: RevlogOpenOptions,

    files_sender: &Sender<(&'b HgPath, u32, usize, TruncatedTimestamp)>,

    progress: &dyn Progress,

    auditor: &PathAuditor,

) -> Result<(), HgError> {

    let dir_path =

        hg_path_to_path_buf(dir_path).expect("invalid path in manifest");

    let dir_path = working_directory_path.join(dir_path);

    std::fs::create_dir_all(&dir_path).when_writing_file(&dir_path)?;

    for (file, file_node, flags) in chunk {

        auditor.audit_path(file)?;

        let flags = flags.map(|f| f.into());

        let path =

            working_directory_path.join(get_path_from_bytes(file.as_bytes()));

        // Treemanifest is not supported

        assert!(flags != Some(b't'));

        let filelog = Filelog::open_vfs(store_vfs, file, options)?;

        let filelog_revision_data = &filelog

            .data_for_node(file_node)

            .map_err(handle_revlog_error)?;

        let file_data = filelog_revision_data.file_data()?;

        if flags == Some(b'l') {

            let target = get_path_from_bytes(file_data);

            if let Err(e) = std::os::unix::fs::symlink(target, &path) {

                // If the path already exists either:

                //   - another process created this file while ignoring the

                //     lock => error

                //   - our check for the fast path is incorrect => error

                //   - this is a malicious repo/bundle and this is symlink that

                //     tries to write things where it shouldn't be able to.

                match e.kind() {

                    std::io::ErrorKind::AlreadyExists => {

                        let metadata = std::fs::symlink_metadata(&path)

                            .when_reading_file(&path)?;

                        if metadata.is_dir() {

                            return Err(HgError::Path(

                                HgPathError::TraversesSymbolicLink {

                                    // Technically it should be one of the

                                    // children, but good enough

                                    path: file

                                        .join(HgPath::new(b"*"))

                                        .to_owned(),

                                    symlink: file.to_owned(),

                                },

                            ));

                        }

                        return Err(e).when_writing_file(&path);

                    }

                    _ => return Err(e).when_writing_file(&path),

                }

            }

        } else {

            let mut f =

                std::fs::File::create(&path).when_writing_file(&path)?;

            f.write_all(file_data).when_writing_file(&path)?;

        }

        if flags == Some(b'x') {

            std::fs::set_permissions(&path, Permissions::from_mode(0o755))

                .when_writing_file(&path)?;

        }

        let metadata =

            std::fs::symlink_metadata(&path).when_reading_file(&path)?;

        let mode = metadata.mode();

        files_sender

            .send((

                file,

                mode,

                file_data.len(),

                TruncatedTimestamp::for_mtime_of(&metadata)

                    .when_reading_file(&path)?,

            ))

            .expect("channel should not be closed");

        progress.increment(1, None);

    }

    Ok(())

}

#[logging_timer::time("trace")]

fn update_dirstate(

    repo: &Repo,

    files_receiver: Receiver<(&HgPath, u32, usize, TruncatedTimestamp)>,

) -> Result<usize, HgError> {

    let mut dirstate = repo

        .dirstate_map_mut()

        .map_err(|e| HgError::abort(e.to_string(), exit_codes::ABORT, None))?;

    // (see the comments in `filter_ambiguous_files` in `merge.py` for more)

    // It turns out that (on Linux at least) the filesystem resolution time

    // for most filesystems is based on the HZ kernel config. Their internal

    // clocks do return nanoseconds if the hardware clock is precise enough,

    // which should be the case on most recent computers but are only updated

    // every few milliseconds at best (every "jiffy").

    //

    // We are still not concerned with fixing the race with other

    // processes that might modify the working copy right after it was created

    // within the same tick, because it is impossible to catch.

    // However, we might as well not race with operations that could run right

    // after this one, especially other Mercurial operations that could be

    // waiting for the wlock to change file contents and the dirstate.

    //

    // Thus: wait until the filesystem clock has ticked to filter ambiguous

    // entries and write the dirstate, but only for dirstate-v2, since v1 only

    // has second-level granularity and waiting for a whole second is too much

    // of a penalty in the general case.

    // Although we're assuming that people running dirstate-v2 on Linux

    // don't have a second-granularity FS (with the exclusion of NFS), users

    // can be surprising, and at some point in the future dirstate-v2 will

    // become the default. To that end, we limit the wait time to 100ms and

    // fall back to the filter method in case of a timeout.

    //

    // +------------+------+--------------+

    // |   version  | wait | filter level |

    // +------------+------+--------------+

    // |     V1     | No   | Second       |

    // |     V2     | Yes  | Nanosecond   |

    // | V2-slow-fs | No   | Second       |

    // +------------+------+--------------+

    let dirstate_v2 = repo.use_dirstate_v2();

    // Let's ignore NFS right off the bat

    let mut fast_enough_fs = !is_on_nfs_mount(repo.working_directory_path());

    let fs_time_now = if dirstate_v2 && fast_enough_fs {

        match wait_until_fs_tick(repo.working_directory_path()) {

            None => None,

            Some(Ok(time)) => Some(time),

            Some(Err(time)) => {

                fast_enough_fs = false;

                Some(time)

            }

        }

    } else {

        filesystem_now(repo.working_directory_path())

            .ok()

            .map(TruncatedTimestamp::from)

    };

    let mut total = 0;

    for (filename, mode, size, mtime) in files_receiver.into_iter() {

        total += 1;

        // When using dirstate-v2 on a filesystem with reasonable performance

        // this is basically always true unless you get a mtime from the

        // far future.

        let has_meaningful_mtime = if let Some(fs_time) = fs_time_now {

            mtime.for_reliable_mtime_of_self(&fs_time).is_some_and(|t| {

                // Dirstate-v1 only has second-level information

                !t.second_ambiguous || dirstate_v2 && fast_enough_fs

            })

        } else {

            // We somehow failed to write to the filesystem, so don't store

            // the cache information.

            false

        };

        let reset = DirstateEntryReset {

            filename,

            wc_tracked: true,

            p1_tracked: true,

            p2_info: false,

            has_meaningful_mtime,

            parent_file_data_opt: Some(ParentFileData {

                mode_size: Some((

                    mode,

                    size.try_into().expect("invalid file size in manifest"),

                )),

                mtime: Some(mtime),

            }),

            from_empty: true,

        };

        dirstate.reset_state(reset).map_err(|e| {

            HgError::abort(e.to_string(), exit_codes::ABORT, None)

        })?;

    }

    Ok(total)

}

/// Wait until the next update from the filesystem time by writing in a loop

/// a new temporary file inside the working directory and checking if its time

/// differs from the first one observed.

///

/// Returns `None` if we are unable to get the filesystem time,

/// `Some(Err(timestamp))` if we've timed out waiting for the filesystem clock

/// to tick, and `Some(Ok(timestamp))` if we've waited successfully.

///

/// On Linux, your average tick is going to be a "jiffy", or 1/HZ.

/// HZ is your kernel's tick rate (if it has one configured) and the value

/// is the one returned by `grep 'CONFIG_HZ=' /boot/config-$(uname -r)`,

/// again assuming a normal setup.

///

/// In my case (Alphare) at the time of writing, I get `CONFIG_HZ=250`,

/// which equates to 4ms.

///

/// This might change with a series that could make it to Linux 6.12:

/// https://lore.kernel.org/all/20241002-mgtime-v10-8-d1c4717f5284@kernel.org

fn wait_until_fs_tick(

    working_directory_path: &Path,

) -> Option<Result<TruncatedTimestamp, TruncatedTimestamp>> {

    let start = std::time::Instant::now();

    let old_fs_time = filesystem_now(working_directory_path).ok()?;

    let mut fs_time = filesystem_now(working_directory_path).ok()?;

    const FS_TICK_WAIT_TIMEOUT: Duration = Duration::from_millis(100);

    while fs_time == old_fs_time {

        if std::time::Instant::now() - start > FS_TICK_WAIT_TIMEOUT {

            log::trace!(

                "timed out waiting for the fs clock to tick after {:?}",

                FS_TICK_WAIT_TIMEOUT

            );

            return Some(Err(TruncatedTimestamp::from(old_fs_time)));

        }

        fs_time = filesystem_now(working_directory_path).ok()?;

    }

    log::trace!(

        "waited for {:?} before writing the dirstate",

        fs_time.duration_since(old_fs_time)

    );

    Some(Ok(TruncatedTimestamp::from(fs_time)))

}

#[cfg(test)]

mod test {

    use super::*;

    use pretty_assertions::assert_eq;

    #[test]

    fn test_chunk_tracked_files() {

        fn chunk(v: Vec<&'static str>) -> Vec<ExpandedManifestEntry> {

            v.into_iter()

                .map(|f| (HgPath::new(f.as_bytes()), NULL_NODE, None))

                .collect()

        }

        let p = HgPath::new;

        let files = chunk(vec!["a"]);

        let expected = vec![(p(""), chunk(vec!["a"]))];

        assert_eq!(chunk_tracked_files(files), expected);

        let files = chunk(vec!["a", "b", "c"]);

        let expected = vec![(p(""), chunk(vec!["a", "b", "c"]))];

        assert_eq!(chunk_tracked_files(files), expected);

        let files = chunk(vec![

            "dir/a-new",

            "dir/a/mut",

            "dir/a/mut-mut",

            "dir/albert",

            "dir/b",

            "dir/subdir/c",

            "dir/subdir/d",

            "file",

        ]);

        let expected = vec![

            (p("dir"), chunk(vec!["dir/a-new"])),

            (p("dir/a"), chunk(vec!["dir/a/mut", "dir/a/mut-mut"])),

            (p("dir"), chunk(vec!["dir/albert", "dir/b"])),

            (p("dir/subdir"), chunk(vec!["dir/subdir/c", "dir/subdir/d"])),

            (p(""), chunk(vec!["file"])),

        ];

        assert_eq!(chunk_tracked_files(files), expected);

        // Doesn't get split

        let large_dir = vec![

            "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12",

            "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23",

        ];

        let files = chunk(large_dir.clone());

        let expected = vec![(p(""), chunk(large_dir))];

        assert_eq!(chunk_tracked_files(files), expected);

    }

}