monochromatic-git-policy-cli 0.1.2

//! What:
//!  The paths both the prepared commit and the landed history changed since the preparation base,
//!       with the three tree entries subsumption compares.
//! Why:
//!  Subsumption decides per shared path; the listing is two `git diff-tree` runs whatever the history length,
//!       and paths stay Latin-1 decoded so every byte survives and encodes back exactly.
//!
//! In TS you'd write (pseudocode):
//! ```ts
//! await listSharedPaths({ gitPath, shadowPath, mergeBase, current, prepared });
//! ```

/// Shadow runs for the two listings.
use super::replay_shadow::run_shadow_checked;
/// The shadow runner's context and failure.
use super::transaction_git::{GitContext, GitFailure};
/// `Path` names the shadow and the working directory.
use std::path::Path;

/// Git's absent-entry mode in raw diff output.
const ABSENT_MODE: &str = "000000";

/// What:
///  One tree entry: its mode and object ID.
/// Why:
///   Subsumption compares modes as well as objects, and a regular file's mode decides the synthetic base.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// type TreeEntry = { mode: string; oid: string };
/// ```
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct TreeEntry {
    /// Git mode, such as `100644`.
    pub mode: String,
    /// Object ID.
    pub oid: String,
}

/// What:
///  One change of a raw diff record: the path and its entries before and after.
/// Why:
///   Both listings produce these; a path missing from one side has an absent entry.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// type RawChange = { path; fromMode; fromOid; toMode; toOid };
/// ```
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct RawChange {
    /// Path, Latin-1 decoded.
    pub path: String,
    /// Entry before the change, absent for an addition.
    pub from: Option<TreeEntry>,
    /// Entry after the change, absent for a deletion.
    pub to: Option<TreeEntry>,
}

/// What:
///  One path both sides changed, with its three entries.
/// Why:
///   The subsumption rules read the base, landed, and prepared entries together.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// type SharedPath = { path; base: SideEntry; landed: SideEntry; prepared: SideEntry };
/// ```
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct SharedPath {
    /// Repository path, Latin-1 decoded.
    pub path: String,
    /// Preparation base entry, absent when the path was added after it.
    pub base: Option<TreeEntry>,
    /// Landed entry, absent when the landed history deleted the path.
    pub landed: Option<TreeEntry>,
    /// Prepared entry, absent when the prepared commit deleted the path.
    pub prepared: Option<TreeEntry>,
}

/// What:
///  Raw diff output that does not have the expected shape.
/// Why:
///   A malformed record cannot be attributed, so the replay fails rather than guess.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// throw new TypeError('malformed raw diff record');
/// ```
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct RawFormatError(pub String);

/// What:
///  Converts one raw mode and object ID into an entry, absent for the all-zero mode.
/// Why:
///   Git writes `000000` for an absent side of a raw record.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// entryOf({ mode, oid }); // ABSENT_ENTRY for mode 000000
/// ```
fn entry_of(mode: &str, oid: &str) -> Option<TreeEntry> {
    if mode == ABSENT_MODE {
        return None;
    }
    return Some(TreeEntry {
        mode: String::from(mode),
        oid: String::from(oid),
    });
}

/// What:
///  Parses `git diff-tree -r -z --raw --no-renames --no-abbrev` output:
///       a `:` header of five fields followed by the path, both NUL-terminated.
/// Why:
///   Each path appears once because renames are off, so the parser keeps records in output order.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// parseRawChanges(text); // RawChange[]
/// ```
pub fn parse_raw_changes(output: &str) -> Result<Vec<RawChange>, RawFormatError> {
    // `mut` lets the records be collected as the output is walked.
    let mut changes: Vec<RawChange> = Vec::new();
    let tokens: Vec<&str> = output.split('\0').collect();
    let mut cursor: usize = 0;
    while cursor < tokens.len() {
        let header: &str = tokens[cursor];
        cursor += 1;
        if header.is_empty() {
            continue;
        }
        let fields: Vec<&str> = header.trim_start_matches(':').split(' ').collect();
        let path: &str = match tokens.get(cursor) {
            Some(found) => found,
            None => return Err(RawFormatError(format!("raw record {header} has no path"))),
        };
        cursor += 1;
        if fields.len() != 5 || !header.starts_with(':') {
            return Err(RawFormatError(format!("malformed raw record {header}")));
        }
        changes.push(RawChange {
            path: String::from(path),
            from: entry_of(fields[0], fields[2]),
            to: entry_of(fields[1], fields[3]),
        });
    }
    return Ok(changes);
}

/// What:
///  Lists the raw changes between two commits in the shadow.
/// Why:
///   Two runs, one per side of the replay, keep the process count fixed.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// rawChanges({ gitPath, shadowPath, from, to }); // ReadonlyMap<path, RawChange>
/// ```
fn raw_changes(
    context: &GitContext,
    shadow: &Path,
    cwd: &Path,
    from: &str,
    to: &str,
) -> Result<Vec<RawChange>, SharedPathError> {
    let output = run_shadow_checked(
        context,
        shadow,
        cwd,
        &[
            "diff-tree",
            "-r",
            "-z",
            "--raw",
            "--no-renames",
            "--no-abbrev",
            from,
            to,
        ],
        None,
        None,
        &[],
    )
    .map_err(SharedPathError::Git)?;
    let text: String = output.stdout.iter().map(|byte| { return char::from(*byte); }).collect();
    return parse_raw_changes(text.as_str()).map_err(SharedPathError::Format);
}

/// What:
///  A shared-path listing failure:
///       a Git command failed, or its output had an unexpected shape.
/// Why:
///   Replay reports either as `transaction-failed`.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// throw new CommitTransactionGitError(...);
/// ```
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum SharedPathError {
    /// A Git command failed.
    Git(GitFailure),
    /// The raw output had an unexpected shape.
    Format(RawFormatError),
}

/// What:
///  Lists the paths both the landed history and the prepared commit changed since the preparation base,
///       in the landed listing's order, with the three entries.
/// Why:
///   The landed listing decides the order subsumption and the synthetic base follow.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// await listSharedPaths({ gitPath, shadowPath, mergeBase, current, prepared });
/// ```
pub fn list_shared_paths(
    context: &GitContext,
    shadow: &Path,
    cwd: &Path,
    merge_base: &str,
    current: &str,
    prepared: &str,
) -> Result<Vec<SharedPath>, SharedPathError> {
    let landed: Vec<RawChange> = raw_changes(context, shadow, cwd, merge_base, current)?;
    let mine: Vec<RawChange> = raw_changes(context, shadow, cwd, merge_base, prepared)?;
    let shared: Vec<SharedPath> = landed
        .into_iter()
        .filter_map(|change| {
            let own: &RawChange = mine.iter().find(|candidate| { return candidate.path == change.path; })?;
            return Some(SharedPath {
                path: change.path,
                base: change.from,
                landed: change.to,
                prepared: own.to.clone(),
            });
        })
        .collect();
    return Ok(shared);
}

/// What:
///  Whether two entries name the same mode and object, or are both absent.
/// Why:
///   An identical prepared and landed entry is subsumed without any text check.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// sameEntry({ left, right });
/// ```
pub fn same_entry(left: &Option<TreeEntry>, right: &Option<TreeEntry>) -> bool {
    return left == right;
}

/// What:
///  Whether all three entries are regular files, so only their bytes can decide the path.
/// Why:
///   Symbolic links and submodules never take the text check.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// isRegularTriple(shared);
/// ```
pub fn is_regular_triple(shared: &SharedPath) -> bool {
    return [&shared.base, &shared.landed, &shared.prepared]
        .iter()
        .all(|side| { return side.as_ref().is_some_and(|entry| { return is_regular_mode(entry.mode.as_str()); }); });
}

/// What:
///  Whether the text check can decide a path:
///       landed and prepared are regular files, and the base is one too or absent.
/// Why:
///   An addition on both sides is read against an empty base, so it is a candidate.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// isTextCandidate(shared);
/// ```
pub fn is_text_candidate(shared: &SharedPath) -> bool {
    let changed_regular: bool = [&shared.landed, &shared.prepared]
        .iter()
        .all(|side| { return side.as_ref().is_some_and(|entry| { return is_regular_mode(entry.mode.as_str()); }); });
    let base_regular: bool = match &shared.base {
        None => true,
        Some(entry) => is_regular_mode(entry.mode.as_str()),
    };
    return changed_regular && base_regular;
}

/// What:
///  Whether a mode is a regular file mode, `100644` or `100755`.
/// Why:
///   Only these modes are text candidates.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// REGULAR_MODES.has(mode);
/// ```
fn is_regular_mode(mode: &str) -> bool {
    return mode == "100644" || mode == "100755";
}

#[cfg(test)]
#[path = "replay_shared_paths_tests.rs"]
mod tests;