agents-tools 0.1.0

use std::collections::{HashMap, HashSet};
use std::fs::{self, Permissions};
use std::io::Write;
use std::path::{Component, Path, PathBuf};
use std::sync::{Arc, Mutex, OnceLock, Weak};

use anyhow::{Context, Result as AnyResult, bail};
use atomic_write_file::AtomicWriteFile;
use serde::Serialize;

use crate::{ApplyDiffError, ApplyDiffMode, apply_diff_to_text, apply_diff_to_text_with_mode};

static PATH_LOCKS: OnceLock<Mutex<HashMap<PathBuf, Weak<Mutex<()>>>>> = OnceLock::new();

/// The kind of filesystem change made by [`apply_diff`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
#[serde(rename_all = "snake_case")]
pub enum FileChangeKind {
    /// A previously absent path now contains a file.
    Added,
    /// An existing file's contents changed without changing its path.
    Updated,
    /// A previously existing file was removed.
    Deleted,
    /// A file was installed at a new path and removed from its previous path.
    Moved,
}

/// A committed file change.
#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
pub struct AppliedFile {
    /// The path after the change, relative to the supplied root.
    pub path: PathBuf,
    /// The previous path when the file was moved.
    #[serde(skip_serializing_if = "Option::is_none")]
    pub previous_path: Option<PathBuf>,
    /// The observable kind of committed change.
    pub kind: FileChangeKind,
}

/// A logical file transaction that could not be applied.
#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
pub struct FailedFile {
    /// The primary path named by the failed operation.
    pub path: PathBuf,
    /// Every path participating in the same atomic file transaction.
    pub related_paths: Vec<PathBuf>,
    /// A contextual description of why the logical file did not commit.
    pub message: String,
}

/// The result of applying a multi-file patch.
///
/// Invalid patch envelopes return an [`ApplyDiffError`]. Failures involving an
/// individual file are collected here so unrelated files can still commit.
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize)]
pub struct ApplyDiffReport {
    /// Filesystem changes that committed successfully.
    pub applied: Vec<AppliedFile>,
    /// Logical files that remained unchanged because planning or commit failed.
    pub failed: Vec<FailedFile>,
}

impl ApplyDiffReport {
    /// Returns `true` when no logical file failed.
    ///
    /// A successful report can still have an empty [`applied`](Self::applied)
    /// list when every requested update was a no-op.
    pub fn is_success(&self) -> bool {
        self.failed.is_empty()
    }
}

/// Applies a complete patch to files beneath `root`.
///
/// The patch must use `*** Begin Patch` and `*** End Patch`, with one or more
/// `*** Add File:`, `*** Update File:`, or `*** Delete File:` blocks. Update
/// blocks may include `*** Move to:` immediately after their file header.
///
/// Each logical file is independent: failures do not prevent unrelated files
/// from committing. All blocks connected through the same paths are first
/// applied in memory and then committed together, so a failed file is never
/// left partially edited.
///
/// Paths must be non-empty and relative, may not contain `.` or `..`, and may
/// not traverse symbolic links. Existing files must be regular UTF-8 files.
/// Missing parent directories for added or moved files are created as needed.
///
/// Updates are installed with atomic replacement on Linux, macOS, and Windows.
/// Overlapping paths are serialized within this process. Before each commit,
/// the current file is compared with the snapshot used for planning; an
/// observed external modification becomes a [`FailedFile`] conflict.
///
/// # Errors
///
/// Returns [`ApplyDiffError`] before applying file operations when `root` is not
/// an accessible directory, the patch envelope is malformed, an operation path
/// is unsafe, or the envelope contains no operations. File-specific errors are
/// returned in [`ApplyDiffReport::failed`] instead.
///
/// # Example
///
/// ```no_run
/// use std::path::Path;
/// use agents_tools::apply_diff;
///
/// # fn update_workspace(root: &Path) -> Result<(), agents_tools::ApplyDiffError> {
/// let report = apply_diff(
///     root,
///     "*** Begin Patch\n*** Update File: settings.txt\n-old\n+new\n*** End Patch",
/// )?;
///
/// for change in &report.applied {
///     println!("{:?}: {}", change.kind, change.path.display());
/// }
/// for failure in &report.failed {
///     eprintln!("{}: {}", failure.path.display(), failure.message);
/// }
/// # Ok(())
/// # }
/// ```
pub fn apply_diff(root: impl AsRef<Path>, patch: &str) -> Result<ApplyDiffReport, ApplyDiffError> {
    let root = root.as_ref();
    let metadata = fs::metadata(root).map_err(|error| {
        ApplyDiffError::new(format!(
            "Cannot access patch root {}: {error}",
            root.display()
        ))
    })?;
    if !metadata.is_dir() {
        return Err(ApplyDiffError::new(format!(
            "Patch root is not a directory: {}",
            root.display()
        )));
    }

    let root = fs::canonicalize(root).map_err(|error| {
        ApplyDiffError::new(format!(
            "Cannot resolve patch root {}: {error}",
            root.display()
        ))
    })?;
    let operations = parse_patch(patch)?;
    let groups = group_operations(operations);
    let mut report = ApplyDiffReport::default();

    for group in groups {
        let locks = path_locks(&root, &group.paths);
        let _guards: Vec<_> = locks
            .iter()
            .map(|lock| lock.lock().unwrap_or_else(|poisoned| poisoned.into_inner()))
            .collect();
        match apply_group(&root, &group) {
            Ok(changes) => report.applied.extend(changes),
            Err(error) => report.failed.push(FailedFile {
                path: group.operations[0].source.clone(),
                related_paths: sorted_paths(&group.paths),
                message: format!("{error:#}"),
            }),
        }
    }

    Ok(report)
}

#[derive(Debug, Clone)]
enum OperationKind {
    Add,
    Update { destination: Option<PathBuf> },
    Delete,
}

#[derive(Debug, Clone)]
struct Operation {
    index: usize,
    source: PathBuf,
    body: String,
    kind: OperationKind,
}

impl Operation {
    fn paths(&self) -> Vec<PathBuf> {
        let mut paths = vec![self.source.clone()];
        if let OperationKind::Update {
            destination: Some(destination),
        } = &self.kind
        {
            paths.push(destination.clone());
        }
        paths
    }
}

#[derive(Debug)]
struct OperationGroup {
    operations: Vec<Operation>,
    paths: HashSet<PathBuf>,
}

fn parse_patch(patch: &str) -> Result<Vec<Operation>, ApplyDiffError> {
    let normalized = patch.replace("\r\n", "\n").replace('\r', "\n");
    let mut lines: Vec<&str> = normalized.lines().collect();
    while lines.first().is_some_and(|line| line.trim().is_empty()) {
        lines.remove(0);
    }
    while lines.last().is_some_and(|line| line.trim().is_empty()) {
        lines.pop();
    }

    if lines.first().copied() != Some("*** Begin Patch") {
        return Err(ApplyDiffError::new(
            "Patch must start with `*** Begin Patch`",
        ));
    }
    if lines.last().copied() != Some("*** End Patch") {
        return Err(ApplyDiffError::new("Patch must end with `*** End Patch`"));
    }

    let mut operations = Vec::new();
    let mut cursor = 1;
    while cursor + 1 < lines.len() {
        if lines[cursor].trim().is_empty() {
            cursor += 1;
            continue;
        }

        let header = lines[cursor];
        let (kind, path_text) = if let Some(path) = header.strip_prefix("*** Add File: ") {
            ("add", path)
        } else if let Some(path) = header.strip_prefix("*** Update File: ") {
            ("update", path)
        } else if let Some(path) = header.strip_prefix("*** Delete File: ") {
            ("delete", path)
        } else {
            return Err(ApplyDiffError::new(format!(
                "Invalid patch header: {header}"
            )));
        };

        let source = validate_relative_path(path_text)?;
        cursor += 1;

        let destination = if kind == "update" {
            lines
                .get(cursor)
                .and_then(|line| {
                    line.strip_prefix("*** Move to: ")
                        .map(validate_relative_path)
                })
                .transpose()?
        } else {
            None
        };
        if destination.is_some() {
            cursor += 1;
        }

        let body_start = cursor;
        while cursor + 1 < lines.len() && !is_file_header(lines[cursor]) {
            cursor += 1;
        }
        let body = lines[body_start..cursor].join("\n");

        let kind = match kind {
            "add" => OperationKind::Add,
            "update" => OperationKind::Update { destination },
            "delete" => {
                if !body.trim().is_empty() {
                    return Err(ApplyDiffError::new(format!(
                        "Delete block for {} cannot contain a patch body",
                        source.display()
                    )));
                }
                OperationKind::Delete
            }
            _ => unreachable!(),
        };

        operations.push(Operation {
            index: operations.len(),
            source,
            body,
            kind,
        });
    }

    if operations.is_empty() {
        return Err(ApplyDiffError::new("Patch contains no file operations"));
    }
    Ok(operations)
}

fn is_file_header(line: &str) -> bool {
    line.starts_with("*** Add File: ")
        || line.starts_with("*** Update File: ")
        || line.starts_with("*** Delete File: ")
        || line == "*** End Patch"
}

fn validate_relative_path(path: &str) -> Result<PathBuf, ApplyDiffError> {
    let path = Path::new(path.trim());
    if path.as_os_str().is_empty() || path.is_absolute() {
        return Err(ApplyDiffError::new(format!(
            "Patch path must be a non-empty relative path: {}",
            path.display()
        )));
    }
    if path
        .components()
        .any(|component| !matches!(component, Component::Normal(_)))
    {
        return Err(ApplyDiffError::new(format!(
            "Patch path contains an unsafe component: {}",
            path.display()
        )));
    }
    Ok(path.to_path_buf())
}

fn group_operations(operations: Vec<Operation>) -> Vec<OperationGroup> {
    let mut groups: Vec<OperationGroup> = Vec::new();
    for operation in operations {
        let operation_paths: HashSet<PathBuf> = operation.paths().into_iter().collect();
        let matching: Vec<usize> = groups
            .iter()
            .enumerate()
            .filter_map(|(index, group)| {
                (!group.paths.is_disjoint(&operation_paths)).then_some(index)
            })
            .collect();

        if matching.is_empty() {
            groups.push(OperationGroup {
                operations: vec![operation],
                paths: operation_paths,
            });
            continue;
        }

        let target = matching[0];
        groups[target].operations.push(operation);
        groups[target].paths.extend(operation_paths);
        for index in matching.into_iter().skip(1).rev() {
            let merged = groups.remove(index);
            groups[target].operations.extend(merged.operations);
            groups[target].paths.extend(merged.paths);
        }
        groups[target]
            .operations
            .sort_by_key(|operation| operation.index);
    }
    groups.sort_by_key(|group| group.operations[0].index);
    groups
}

#[derive(Clone)]
struct FileState {
    text: String,
    permissions: Option<Permissions>,
}

fn apply_group(root: &Path, group: &OperationGroup) -> AnyResult<Vec<AppliedFile>> {
    let mut initial = HashMap::new();
    for path in &group.paths {
        initial.insert(path.clone(), read_file(root, path)?);
    }
    let mut current = initial.clone();

    for operation in &group.operations {
        match &operation.kind {
            OperationKind::Add => {
                if current.get(&operation.source).is_some_and(Option::is_some) {
                    bail!("File already exists: {}", operation.source.display());
                }
                let text = apply_diff_to_text_with_mode("", &operation.body, ApplyDiffMode::Create)
                    .map_err(anyhow::Error::new)?;
                current.insert(
                    operation.source.clone(),
                    Some(FileState {
                        text,
                        permissions: None,
                    }),
                );
            }
            OperationKind::Update { destination } => {
                let Some(mut state) = current.get(&operation.source).cloned().flatten() else {
                    bail!("File does not exist: {}", operation.source.display());
                };
                state.text =
                    apply_diff_to_text(&state.text, &operation.body).map_err(anyhow::Error::new)?;

                if let Some(destination) = destination {
                    if destination != &operation.source
                        && current.get(destination).is_some_and(Option::is_some)
                    {
                        bail!("Move destination already exists: {}", destination.display());
                    }
                    current.insert(operation.source.clone(), None);
                    current.insert(destination.clone(), Some(state));
                } else {
                    current.insert(operation.source.clone(), Some(state));
                }
            }
            OperationKind::Delete => {
                if !current.get(&operation.source).is_some_and(Option::is_some) {
                    bail!("File does not exist: {}", operation.source.display());
                }
                current.insert(operation.source.clone(), None);
            }
        }
    }

    let changes = describe_changes(group, &initial, &current);
    commit_group(root, &initial, &current)?;
    Ok(changes)
}

fn read_file(root: &Path, relative: &Path) -> AnyResult<Option<FileState>> {
    ensure_safe_components(root, relative)?;
    let path = root.join(relative);
    let metadata = match fs::symlink_metadata(&path) {
        Ok(metadata) => metadata,
        Err(error) if error.kind() == std::io::ErrorKind::NotFound => return Ok(None),
        Err(error) => {
            return Err(error).with_context(|| format!("Cannot inspect {}", relative.display()));
        }
    };
    if metadata.file_type().is_symlink() {
        bail!("Symbolic links are not patchable: {}", relative.display());
    }
    if !metadata.is_file() {
        bail!("Path is not a regular file: {}", relative.display());
    }
    let bytes = fs::read(&path).with_context(|| format!("Cannot read {}", relative.display()))?;
    let text = String::from_utf8(bytes)
        .with_context(|| format!("File is not valid UTF-8: {}", relative.display()))?;
    Ok(Some(FileState {
        text,
        permissions: Some(metadata.permissions()),
    }))
}

fn ensure_safe_components(root: &Path, relative: &Path) -> AnyResult<()> {
    let mut current = root.to_path_buf();
    let component_count = relative.components().count();
    for (index, component) in relative.components().enumerate() {
        current.push(component.as_os_str());
        let metadata = match fs::symlink_metadata(&current) {
            Ok(metadata) => metadata,
            Err(error) if error.kind() == std::io::ErrorKind::NotFound => return Ok(()),
            Err(error) => {
                return Err(error)
                    .with_context(|| format!("Cannot inspect {}", relative.display()));
            }
        };
        if metadata.file_type().is_symlink() {
            bail!("Symbolic links are not patchable: {}", relative.display());
        }
        if index + 1 < component_count && !metadata.is_dir() {
            bail!("Path component is not a directory: {}", relative.display());
        }
    }
    Ok(())
}

fn describe_changes(
    group: &OperationGroup,
    initial: &HashMap<PathBuf, Option<FileState>>,
    current: &HashMap<PathBuf, Option<FileState>>,
) -> Vec<AppliedFile> {
    let initial_present: Vec<_> = initial
        .iter()
        .filter_map(|(path, state)| state.is_some().then_some(path.clone()))
        .collect();
    let current_present: Vec<_> = current
        .iter()
        .filter_map(|(path, state)| state.is_some().then_some(path.clone()))
        .collect();
    let has_move = group.operations.iter().any(|operation| {
        matches!(
            operation.kind,
            OperationKind::Update {
                destination: Some(_)
            }
        )
    });

    if has_move && initial_present.len() == 1 && current_present.len() == 1 {
        let previous = &initial_present[0];
        let path = &current_present[0];
        if previous != path {
            return vec![AppliedFile {
                path: path.clone(),
                previous_path: Some(previous.clone()),
                kind: FileChangeKind::Moved,
            }];
        }
    }

    let mut paths = sorted_paths(&group.paths);
    let mut changes = Vec::new();
    for path in paths.drain(..) {
        match (
            initial.get(&path).and_then(Option::as_ref),
            current.get(&path).and_then(Option::as_ref),
        ) {
            (None, Some(_)) => changes.push(AppliedFile {
                path,
                previous_path: None,
                kind: FileChangeKind::Added,
            }),
            (Some(_), None) => changes.push(AppliedFile {
                path,
                previous_path: None,
                kind: FileChangeKind::Deleted,
            }),
            (Some(before), Some(after)) if !states_equal(before, after) => {
                changes.push(AppliedFile {
                    path,
                    previous_path: None,
                    kind: FileChangeKind::Updated,
                })
            }
            _ => {}
        }
    }
    changes
}

fn states_equal(left: &FileState, right: &FileState) -> bool {
    left.text == right.text && permissions_equal(&left.permissions, &right.permissions)
}

fn optional_states_equal(left: Option<&FileState>, right: Option<&FileState>) -> bool {
    match (left, right) {
        (None, None) => true,
        (Some(expected), Some(actual)) => {
            expected.text == actual.text
                && (expected.permissions.is_none()
                    || permissions_equal(&expected.permissions, &actual.permissions))
        }
        _ => false,
    }
}

#[cfg(unix)]
fn permissions_equal(left: &Option<Permissions>, right: &Option<Permissions>) -> bool {
    use std::os::unix::fs::PermissionsExt;
    left.as_ref().map(PermissionsExt::mode) == right.as_ref().map(PermissionsExt::mode)
}

#[cfg(not(unix))]
fn permissions_equal(left: &Option<Permissions>, right: &Option<Permissions>) -> bool {
    left.as_ref().map(Permissions::readonly) == right.as_ref().map(Permissions::readonly)
}

struct PreparedChange {
    relative: PathBuf,
    full: PathBuf,
    initial: Option<FileState>,
    final_state: Option<FileState>,
    writer: Option<AtomicWriteFile>,
    committed: bool,
}

fn commit_group(
    root: &Path,
    initial: &HashMap<PathBuf, Option<FileState>>,
    current: &HashMap<PathBuf, Option<FileState>>,
) -> AnyResult<()> {
    let mut changed_paths: Vec<PathBuf> = initial
        .keys()
        .filter(
            |path| match (initial[*path].as_ref(), current[*path].as_ref()) {
                (None, None) => false,
                (Some(before), Some(after)) => !states_equal(before, after),
                _ => true,
            },
        )
        .cloned()
        .collect();
    changed_paths.sort_by(|left, right| {
        current[left]
            .is_none()
            .cmp(&current[right].is_none())
            .then_with(|| left.cmp(right))
    });
    if changed_paths.is_empty() {
        return Ok(());
    }

    let mut created_directories = Vec::new();
    for relative in &changed_paths {
        if current[relative].is_some()
            && let Err(error) = create_parent_directories(root, relative, &mut created_directories)
        {
            remove_created_directories(&created_directories);
            return Err(error);
        }
    }

    let mut prepared = Vec::new();
    for relative in changed_paths {
        let full = root.join(&relative);
        let writer = match current[&relative].as_ref() {
            Some(state) => match prepare_atomic_write(&full, state) {
                Ok(writer) => Some(writer),
                Err(error) => {
                    drop(prepared);
                    remove_created_directories(&created_directories);
                    return Err(error)
                        .with_context(|| format!("Cannot prepare {}", relative.display()));
                }
            },
            None => None,
        };
        prepared.push(PreparedChange {
            relative: relative.clone(),
            full,
            initial: initial[&relative].clone(),
            final_state: current[&relative].clone(),
            writer,
            committed: false,
        });
    }

    for index in 0..prepared.len() {
        if let Err(error) = verify_unchanged(
            root,
            &prepared[index].relative,
            prepared[index].initial.as_ref(),
        )
        .and_then(|()| commit_one(&mut prepared[index]))
        {
            let rollback_errors = rollback_prepared(root, &mut prepared, &created_directories);
            let mut error = error.context(format!(
                "Cannot commit {}",
                prepared[index].relative.display()
            ));
            if !rollback_errors.is_empty() {
                error = error.context(format!(
                    "Rollback conflicts: {}",
                    rollback_errors.join("; ")
                ));
            }
            return Err(error);
        }
    }
    Ok(())
}

fn create_parent_directories(
    root: &Path,
    relative: &Path,
    created: &mut Vec<PathBuf>,
) -> AnyResult<()> {
    let Some(parent) = relative.parent() else {
        return Ok(());
    };
    let mut current = root.to_path_buf();
    for component in parent.components() {
        current.push(component.as_os_str());
        match fs::symlink_metadata(&current) {
            Ok(metadata) if metadata.is_dir() && !metadata.file_type().is_symlink() => {}
            Ok(_) => bail!("Unsafe parent directory: {}", relative.display()),
            Err(error) if error.kind() == std::io::ErrorKind::NotFound => {
                fs::create_dir(&current)
                    .with_context(|| format!("Cannot create {}", current.display()))?;
                created.push(current.clone());
            }
            Err(error) => {
                return Err(error).with_context(|| format!("Cannot inspect {}", current.display()));
            }
        }
    }
    Ok(())
}

fn prepare_atomic_write(target: &Path, state: &FileState) -> AnyResult<AtomicWriteFile> {
    let mut file = AtomicWriteFile::open(target)?;
    file.write_all(state.text.as_bytes())?;
    if let Some(permissions) = &state.permissions {
        file.set_permissions(permissions.clone())?;
    }
    file.sync_all()?;
    Ok(file)
}

fn verify_unchanged(root: &Path, relative: &Path, expected: Option<&FileState>) -> AnyResult<()> {
    ensure_safe_components(root, relative)?;
    let actual = read_file(root, relative)?;
    let unchanged = optional_states_equal(expected, actual.as_ref());
    if !unchanged {
        bail!(
            "File changed concurrently while the patch was being prepared: {}",
            relative.display()
        );
    }
    Ok(())
}

fn commit_one(change: &mut PreparedChange) -> AnyResult<()> {
    // A commit error can be reported after the replacement became visible
    // (for example while synchronizing metadata). Mark it first so rollback
    // inspects the actual state and restores only when our final bytes won.
    change.committed = true;
    match change.writer.take() {
        Some(writer) => writer.commit()?,
        None => remove_file_durably(&change.full)?,
    }
    Ok(())
}

fn remove_file_durably(path: &Path) -> std::io::Result<()> {
    fs::remove_file(path)?;
    sync_parent_directory(path)
}

#[cfg(unix)]
fn sync_parent_directory(path: &Path) -> std::io::Result<()> {
    use std::fs::File;

    File::open(path.parent().unwrap_or_else(|| Path::new(".")))?.sync_all()
}

#[cfg(not(unix))]
fn sync_parent_directory(_path: &Path) -> std::io::Result<()> {
    Ok(())
}

fn rollback_prepared(
    root: &Path,
    prepared: &mut [PreparedChange],
    created_directories: &[PathBuf],
) -> Vec<String> {
    let mut errors = Vec::new();
    for change in prepared.iter_mut().filter(|change| !change.committed) {
        drop(change.writer.take());
    }
    for change in prepared.iter_mut().rev().filter(|change| change.committed) {
        let actual = match read_file(root, &change.relative) {
            Ok(actual) => actual,
            Err(error) => {
                errors.push(error.to_string());
                continue;
            }
        };
        if optional_states_equal(change.initial.as_ref(), actual.as_ref()) {
            continue;
        }
        if !optional_states_equal(change.final_state.as_ref(), actual.as_ref()) {
            errors.push(format!(
                "{} changed concurrently during rollback",
                change.relative.display()
            ));
            continue;
        }
        let result = match &change.initial {
            Some(initial) => prepare_atomic_write(&change.full, initial)
                .and_then(|writer| writer.commit().map_err(anyhow::Error::new)),
            None => remove_file_durably(&change.full).map_err(anyhow::Error::new),
        };
        if let Err(error) = result {
            errors.push(format!("{}: {error:#}", change.relative.display()));
        }
    }
    remove_created_directories(created_directories);
    errors
}

fn remove_created_directories(paths: &[PathBuf]) {
    for path in paths.iter().rev() {
        let _ = fs::remove_dir(path);
    }
}

fn path_locks(root: &Path, paths: &HashSet<PathBuf>) -> Vec<Arc<Mutex<()>>> {
    let registry = PATH_LOCKS.get_or_init(|| Mutex::new(HashMap::new()));
    let mut registry = registry
        .lock()
        .unwrap_or_else(|poisoned| poisoned.into_inner());
    registry.retain(|_, lock| lock.strong_count() > 0);

    let mut keys: Vec<PathBuf> = paths.iter().map(|path| root.join(path)).collect();
    keys.sort();
    keys.into_iter()
        .map(|key| {
            if let Some(lock) = registry.get(&key).and_then(Weak::upgrade) {
                return lock;
            }
            let lock = Arc::new(Mutex::new(()));
            registry.insert(key, Arc::downgrade(&lock));
            lock
        })
        .collect()
}

fn sorted_paths(paths: &HashSet<PathBuf>) -> Vec<PathBuf> {
    let mut paths: Vec<_> = paths.iter().cloned().collect();
    paths.sort();
    paths
}

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

    #[test]
    fn connected_operations_are_grouped_transitively() {
        let operations = vec![
            Operation {
                index: 0,
                source: PathBuf::from("a"),
                body: String::new(),
                kind: OperationKind::Update {
                    destination: Some(PathBuf::from("b")),
                },
            },
            Operation {
                index: 1,
                source: PathBuf::from("c"),
                body: String::new(),
                kind: OperationKind::Update {
                    destination: Some(PathBuf::from("d")),
                },
            },
            Operation {
                index: 2,
                source: PathBuf::from("b"),
                body: String::new(),
                kind: OperationKind::Update {
                    destination: Some(PathBuf::from("c")),
                },
            },
        ];
        let groups = group_operations(operations);
        assert_eq!(groups.len(), 1);
        assert_eq!(groups[0].operations.len(), 3);
    }

    #[test]
    fn unspecified_creation_permissions_match_the_committed_file() {
        let expected = FileState {
            text: "content".to_owned(),
            permissions: None,
        };
        let actual = FileState {
            text: "content".to_owned(),
            permissions: Some(fs::metadata(".").unwrap().permissions()),
        };

        assert!(optional_states_equal(Some(&expected), Some(&actual)));
    }

    #[test]
    fn rollback_removes_a_committed_add_with_os_assigned_permissions() {
        let root = tempfile::tempdir().unwrap();
        let relative = PathBuf::from("added.txt");
        let full = root.path().join(&relative);
        fs::write(&full, "content").unwrap();
        let mut prepared = vec![PreparedChange {
            relative,
            full: full.clone(),
            initial: None,
            final_state: Some(FileState {
                text: "content".to_owned(),
                permissions: None,
            }),
            writer: None,
            committed: true,
        }];

        let errors = rollback_prepared(root.path(), &mut prepared, &[]);

        assert!(errors.is_empty(), "{errors:?}");
        assert!(!full.exists());
    }
}