monochromatic-git-policy-cli 0.5.4

//! What:
//!  The shared clock of every wait notice:
//!  when the first line of a wait is due,
//!  how often it repeats,
//!  and the place in line a queued commit holds.
//! Why:
//!  A commit that queues behind other commits, a lock, a reservation or a child process must say so,
//!  and say it again at a steady interval,
//!  or the caller cannot tell a queued commit from a hung one (issue 1811).
//!  Each wait loop feeds its elapsed time to a `Ticker` and prints a line when the ticker says one is due,
//!  so the decision is a function of elapsed time alone and a test can drive it with chosen durations.
//!  The interval comes from `CLI_GIT_WAIT_NOTICE_SECONDS` at the production entry of each wait.
//!
//! In TS you'd write (pseudocode):
//! ```ts
//! const ticker = new Ticker(Cadence.fromEnvironment());
//! while (waiting) { if (ticker.due(elapsedMs)) stderr.write(line(elapsedMs)); await wait(pollMs); }
//! ```

/// Positive-seconds parsing shared with the lock wait limits.
use super::bounded_push::positive_seconds;
/// Borrowed OS text of the environment value.
use std::ffi::OsStr;
/// `Write` is the sink a notice goes to.
use std::io::Write;
/// Time spans and the monotonic clock.
use std::time::{Duration, Instant};

/// Environment variable that sets, in whole seconds, how often a waiting command repeats its notice.
pub const NOTICE_INTERVAL_VARIABLE: &str = "CLI_GIT_WAIT_NOTICE_SECONDS";

/// How often a waiting command repeats its notice when the variable is absent or unusable.
pub const DEFAULT_NOTICE_INTERVAL: Duration = Duration::from_secs(10);

/// How long a wait stays silent before its first notice:
///  a landing that holds the lock normally ends within this,
///  so brief contention between healthy commits prints nothing.
pub const NOTICE_GRACE: Duration = Duration::from_secs(1);

/// The shortest interval a ticker divides by, so a zero interval cannot divide by zero.
const SHORTEST_INTERVAL: Duration = Duration::from_millis(1);

/// What:
///  When a wait's notices are due:
///  the grace before the first and the interval between the rest.
/// Why:
///   One value travels from the production entry to the wait loop,
///  and tests choose short ones instead of waiting out the defaults.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// type Cadence = { graceMs: number; intervalMs: number };
/// ```
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Cadence {
    /// Silence before the first notice.
    pub grace: Duration,
    /// Time between two notices.
    pub interval: Duration,
}

impl Cadence {
    /// The cadence for an interval:
    ///  the standard grace, but never longer than the interval itself.
    ///
    /// In TS you'd write (pseudocode):
    /// ```ts
    /// { graceMs: Math.min(GRACE_MS, intervalMs), intervalMs }
    /// ```
    pub fn from_interval(interval: Duration) -> Self {
        return Self {
            grace: interval.min(NOTICE_GRACE),
            interval,
        };
    }

    /// The cadence when nothing configures it.
    pub fn standard() -> Self {
        return Self::from_interval(DEFAULT_NOTICE_INTERVAL);
    }

    /// The cadence for a value of the variable;
    ///  a missing, zero or malformed value falls back to the standard one.
    ///
    /// In TS you'd write (pseudocode):
    /// ```ts
    /// Cadence.fromInterval(positiveSeconds(value) ?? DEFAULT_INTERVAL)
    /// ```
    pub fn from_value(value: Option<&OsStr>) -> Self {
        let Some(text) = value else {
            return Self::standard();
        };
        return match positive_seconds(NOTICE_INTERVAL_VARIABLE, text) {
            Some(interval) => Self::from_interval(interval),
            None => Self::standard(),
        };
    }

    /// The cadence this process runs under:
    ///  the variable in its environment, or the standard one.
    pub fn from_environment() -> Self {
        return Self::from_value(std::env::var_os(NOTICE_INTERVAL_VARIABLE).as_deref());
    }
}

/// What:
///  Decides, from elapsed time alone,
///  whether a notice is due,
///  and when the next one will be.
/// Why:
///   A wait loop polls at its own pace.
///  The ticker answers "is a line due now" once per due notice,
///  however late the poll comes,
///  and never answers twice for the same interval.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// class Ticker { due(elapsedMs: number): boolean; nextInMs(elapsedMs: number): number }
/// ```
#[derive(Clone, Copy, Debug)]
pub struct Ticker {
    /// The interval between notices.
    interval: Duration,
    /// When the first notice is due.
    first_at: Duration,
    /// How many notices were already due.
    printed: u32,
}

impl Ticker {
    /// A ticker whose first notice comes after the cadence's grace.
    pub fn new(cadence: Cadence) -> Self {
        return Self {
            interval: cadence.interval.max(SHORTEST_INTERVAL),
            first_at: cadence.grace,
            printed: 0,
        };
    }

    /// A ticker for a wait that printed its first line when it began:
    ///  the next notice comes one interval later.
    pub fn announced_at_start(cadence: Cadence) -> Self {
        return Self {
            interval: cadence.interval.max(SHORTEST_INTERVAL),
            first_at: Duration::ZERO,
            printed: 1,
        };
    }

    /// How many notices are due after `waited`.
    fn due_count(&self, waited: Duration) -> u32 {
        if waited < self.first_at {
            return 0;
        }
        let after_first: u128 = (waited - self.first_at).as_nanos() / self.interval.as_nanos();
        return u32::try_from(after_first.saturating_add(1)).unwrap_or(u32::MAX);
    }

    /// Whether a notice is due now that `waited` has passed;
    ///  true once per due notice.
    ///
    /// In TS you'd write (pseudocode):
    /// ```ts
    /// ticker.due(elapsedMs)
    /// ```
    pub fn due(&mut self, waited: Duration) -> bool {
        let count: u32 = self.due_count(waited);
        if count <= self.printed {
            return false;
        }
        self.printed = count;
        return true;
    }

    /// How long after `waited` the next notice is due;
    ///  a watcher sleeps this long.
    ///
    /// In TS you'd write (pseudocode):
    /// ```ts
    /// ticker.nextInMs(elapsedMs)
    /// ```
    pub fn next_in(&self, waited: Duration) -> Duration {
        // The notice after the `printed`th one is due `printed` intervals after the first.
        let due_at: Duration = self.first_at.saturating_add(self.interval.saturating_mul(self.printed));
        return due_at.saturating_sub(waited);
    }
}

/// What:
///  A commit's place among the commits that wait for the same thing.
/// Why:
///   The reservation registry knows the order in which waiting commits will be served,
///  and a commit in line is told its number.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// type QueuePlace = { position: number; waiting: number };
/// ```
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct QueuePlace {
    /// This commit's number, counted from 1;
    ///  the first is served next.
    pub position: usize,
    /// How many commits are in line, this one included.
    pub waiting: usize,
}

/// What:
///  The sentence that tells a commit its place.
/// Why:
///   The line says how many commits are served before this one.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// `This is number ${position} of ${waiting} commits in line.`
/// ```
pub fn queue_place_text(place: QueuePlace) -> String {
    let ahead: usize = place.position.saturating_sub(1);
    return format!(
        "This is number {} of {} commits in line, so {ahead} will be served first.",
        place.position, place.waiting
    );
}

/// What:
///  What one notice of a wait for a child process says.
/// Why:
///   A child whose output goes to a file or a pipe is silent while it runs,
///  so the wait names what it waits for, the child's process, how long it has lasted and where it stops the child.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// type ChildWaitFacts = { waitingFor; pid; waitedMs; limitMs; limitNote; repeat };
/// ```
#[derive(Clone, Copy, Debug)]
pub struct ChildWaitFacts<'facts> {
    /// What the wait is for, in words ("monochromatic-lint to check a.md").
    pub waiting_for: &'facts str,
    /// The child's process.
    pub pid: u32,
    /// How long the wait has lasted.
    pub waited: Duration,
    /// How long the child may run before it is stopped.
    pub limit: Duration,
    /// Where the person changes the limit, spelled to follow "seconds", or empty when nothing changes it.
    pub limit_note: &'facts str,
    /// Whether an earlier notice of this wait already printed the hint.
    pub repeat: bool,
}

/// What:
///  The notice of a wait for a child process.
/// Why:
///   The first notice of a wait adds what to do if the child is stuck, and the repeats stay short.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// `cli-git: still waiting for ${waitingFor} (process ${pid}) after ${waited} seconds; stopping it after ${limit} seconds`
/// ```
pub fn child_wait_line(facts: &ChildWaitFacts<'_>) -> String {
    let hint: &str = if facts.repeat {
        ""
    } else {
        " Hint: it is still running; if it looks stuck, check it with `ps` and report it."
    };
    return format!(
        "cli-git: still waiting for {} (process {}) after {} seconds; stopping it after {} seconds{}.{hint}",
        facts.waiting_for,
        facts.pid,
        facts.waited.as_secs(),
        facts.limit.as_secs(),
        facts.limit_note
    );
}

/// What:
///  Prints a wait's notices to a sink at the pace of its ticker.
/// Why:
///   Wait loops that poll (reservations, child processes, settlement locks) share one printing rule:
///  the line is built only when it is due,
///  so a poll that is not due costs a clock read and nothing else.
///
/// In TS you'd write (pseudocode):
/// ```ts
/// const reporter = new WaitReporter(cadence, stderr); reporter.poll((waitedMs) => line(waitedMs));
/// ```
pub struct WaitReporter<'sink> {
    /// When the wait began.
    started: Instant,
    /// Decides when a line is due.
    ticker: Ticker,
    /// Where the lines go.
    sink: &'sink mut dyn Write,
    /// How many lines were printed.
    printed: u32,
}

impl<'sink> WaitReporter<'sink> {
    /// A reporter whose clock starts now and whose first notice follows the cadence's grace.
    pub fn start(cadence: Cadence, sink: &'sink mut dyn Write) -> Self {
        return Self {
            started: Instant::now(),
            ticker: Ticker::new(cadence),
            sink,
            printed: 0,
        };
    }

    /// Print the line built by `line` when a notice is due;
    ///  `line` gets how long the wait has lasted and whether an earlier notice of this wait was printed.
    ///  Whether one was printed.
    pub fn poll(&mut self, line: impl FnOnce(Duration, bool) -> String) -> bool {
        let waited: Duration = self.started.elapsed();
        if !self.ticker.due(waited) {
            return false;
        }
        let text: String = line(waited, self.printed > 0);
        self.printed += 1;
        // Terminal output error: a notice is advisory; a failed write must not stop the wait.
        let _written = writeln!(self.sink, "{text}");
        return true;
    }
}

/// Cadence, ticker and line controls stay out of the release executable.
#[cfg(test)]
#[path = "wait_progress_tests.rs"]
mod tests;