tix-tracker 0.12.0

//! Explicit lifecycle controls with append-only History (mission
//! `recurring-issues-01M3C7G7`, WP05; `data-model.md` §4/§7 and
//! `contracts/series-generator.md`).
//!
//! # A lifecycle is a set of decisions, not a process
//!
//! Nothing here runs on a timer, on refresh, or because detection said something
//! was due. [`apply`] performs exactly one **confirmed** action on one series and
//! returns what happened. Detection reads state; this writes it; and only a caller
//! who confirmed the action can reach the write (C-003).
//!
//! # The six actions, and what each one does to the schedule
//!
//! Every action is a state change on the *series definition issue*
//! (`series.state`, `series.skipped`, `series.next_cursor`), applied in one
//! [`Store::transaction`] with one appended History entry. "Next candidate" is the
//! `next_cursor` the detector reads, so the table below is the documented
//! next-candidate behaviour `data-model.md` §4 asks for:
//!
//! | action   | `state`            | `skipped`  | `next_cursor` | next candidate is |
//! |----------|--------------------|------------|---------------|-------------------|
//! | `pause`  | `active` → `paused`| unchanged  | unchanged     | none — generation is suspended until `resume` |
//! | `resume` | `paused` → `active`| unchanged  | unchanged     | whatever the cursor says |
//! | `end`    | any → `ended`      | unchanged  | unchanged     | none — `ended` is terminal |
//! | `skip`   | unchanged          | + the date | → the date    | the date after the skipped one |
//! | `defer`  | unchanged          | unchanged  | → the date    | the date after the deferred one; the deferred date stays **explicitly** generatable |
//! | `ignore` | unchanged          | + the date | → the date    | the date after it |
//!
//! `skip` and `ignore` have the *same schedule effect* on purpose: a schedule has
//! exactly one way to say "this date is not happening" (the date is recorded, so
//! generation can never recreate it). What differs is the decision in the log —
//! "not doing this one" versus "stop offering this one" — and the log is where a
//! reader looks for a decision. `defer` is the one that keeps the date available:
//! it only moves the cursor, so an explicit `generate` for that date still works.
//!
//! # It decides against the file, not a caller's snapshot
//!
//! [`apply`] takes a [`Store`] and reads the series itself. A caller's
//! [`SeriesIndex`] is a *snapshot* — one built to render a list or a warning is a
//! keystroke old by the time an action arrives — and deciding "is this series
//! already paused?" from it can apply the same action twice and append two events.
//! The index stays the right input for detection, which is read-only and may be
//! minutes stale; a state transition is not, so this layer re-reads.
//!
//! # Idempotence, and the terminal case
//!
//! An action that is already in effect is a **no-op**: pausing a paused series,
//! resuming an active one, ending an ended one, skipping a date that is already
//! recorded, deferring a date the cursor is already past. A no-op appends nothing,
//! which is what makes "repeated actions have exact event counts" true.
//!
//! `ended` is terminal for everything except `end` itself (which is a no-op):
//! pausing, resuming, skipping, deferring or ignoring an ended series is a
//! **rejection**, with nothing written.
//!
//! # History
//!
//! Each applied action appends **one** [`HistoryEventKind::TransitionAccepted`]
//! entry to the defining issue, carrying the actor, the action, the occurrence key
//! where there is one, and the reason where one was given. That is the crate's
//! existing "an accepted decision about this issue's state was applied" kind, and a
//! series definition is an issue whose state these actions change; writing a
//! second audit log, or a kind per action, would fragment the one log the mission's
//! C-007 points at. Prior entries are never rewritten: the history is append-only
//! by construction ([`crate::model::History::append_now`] pushes).

use crate::error::render_diagnostics;
use crate::model::HistoryEventKind;
use crate::recurrence::rule::DateKey;
use crate::recurrence::series::{KeyState, OccurrenceKey, SeriesId, SeriesIndex, SeriesLifecycle};
use crate::storage::Store;

/// The six lifecycle actions (`data-model.md` §7).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum LifecycleAction {
    /// Suspend generation until an explicit resume.
    Pause,
    /// Resume a paused series. Never inferred from a refresh.
    Resume,
    /// End the series. Terminal for generation.
    End,
    /// Record one occurrence date as skipped, so it is never generated.
    Skip,
    /// Move the candidate on without recording the date as skipped.
    Defer,
    /// Stop offering one occurrence date: recorded, like `skip`, as a decision.
    Ignore,
}

impl LifecycleAction {
    /// Every action, in the order a surface should offer them.
    pub const ALL: [Self; 6] = [
        Self::Pause,
        Self::Resume,
        Self::End,
        Self::Skip,
        Self::Defer,
        Self::Ignore,
    ];

    /// The stable spelling the CLI and the MCP tools print.
    pub const fn as_str(self) -> &'static str {
        match self {
            Self::Pause => "pause",
            Self::Resume => "resume",
            Self::End => "end",
            Self::Skip => "skip",
            Self::Defer => "defer",
            Self::Ignore => "ignore",
        }
    }

    /// Whether the action is about one occurrence and therefore needs a key.
    pub const fn needs_key(self) -> bool {
        matches!(self, Self::Skip | Self::Defer | Self::Ignore)
    }

    /// Whether the action changes the series' lifecycle state (as opposed to one
    /// occurrence's standing).
    pub const fn changes_state(self) -> bool {
        matches!(self, Self::Pause | Self::Resume | Self::End)
    }
}

/// One confirmed lifecycle action on one series (T023/T024).
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct LifecycleRequest {
    /// The series to act on.
    pub series_id: SeriesId,
    /// Which action.
    pub action: LifecycleAction,
    /// The occurrence key, required by `skip`/`defer`/`ignore`.
    pub occurrence_key: Option<OccurrenceKey>,
    /// Who acted; lands in the History entry.
    pub actor: String,
    /// Why, when the caller gave one.
    pub reason: Option<String>,
    /// Whether the caller confirmed the action. Unconfirmed requests are inert.
    pub confirmed: bool,
}

impl LifecycleRequest {
    /// A request that is **not** yet confirmed.
    pub fn new(series_id: SeriesId, action: LifecycleAction, actor: impl Into<String>) -> Self {
        Self {
            series_id,
            action,
            occurrence_key: None,
            actor: actor.into(),
            reason: None,
            confirmed: false,
        }
    }

    /// Name the occurrence the action is about.
    pub fn about(mut self, key: OccurrenceKey) -> Self {
        self.occurrence_key = Some(key);
        self
    }

    /// Record why.
    pub fn because(mut self, reason: impl Into<String>) -> Self {
        self.reason = Some(reason.into());
        self
    }

    /// Record the confirmation.
    pub fn confirm(mut self) -> Self {
        self.confirmed = true;
        self
    }
}

/// Why a lifecycle action was refused.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum LifecycleDiagnosticKind {
    /// The request was not confirmed, so nothing was even read.
    NotConfirmed,
    /// No series with that id is defined.
    UnknownSeries,
    /// The series has ended; only `end` is idempotent on it, and it is a no-op.
    EndedSeries,
    /// The action is about an occurrence but no key was given.
    MissingKey,
    /// The key names a different series than the request.
    KeySeriesMismatch,
    /// The action is about an occurrence that already exists, so there is nothing
    /// to skip, defer or ignore.
    AlreadyGenerated,
    /// The issue defining the series could not be read.
    DefinitionUnreadable,
    /// The store refused the write.
    Refused,
}

impl LifecycleDiagnosticKind {
    /// The stable spelling the CLI and the MCP tools print.
    pub const fn as_str(self) -> &'static str {
        match self {
            Self::NotConfirmed => "not_confirmed",
            Self::UnknownSeries => "unknown_series",
            Self::EndedSeries => "series_ended",
            Self::MissingKey => "missing_occurrence_key",
            Self::KeySeriesMismatch => "occurrence_key_series_mismatch",
            Self::AlreadyGenerated => "occurrence_already_generated",
            Self::DefinitionUnreadable => "definition_unreadable",
            Self::Refused => "refused",
        }
    }
}

/// One actionable reason a lifecycle action was refused.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct LifecycleDiagnostic {
    /// What was wrong.
    pub kind: LifecycleDiagnosticKind,
    /// One sentence saying what to do about it.
    pub message: String,
}

impl LifecycleDiagnostic {
    fn new(kind: LifecycleDiagnosticKind, message: impl Into<String>) -> Self {
        Self {
            kind,
            message: message.into(),
        }
    }

    /// Render through the crate's one diagnostic renderer.
    pub fn render(&self) -> String {
        render_diagnostics(
            "E-tix-series",
            std::iter::once((self.kind.as_str(), self.message.as_str())),
        )
    }
}

/// The result of one lifecycle action (the outcome matrix T026 asks for).
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum LifecycleOutcome {
    /// The action took effect and one History entry was appended.
    Applied {
        /// The series.
        series_id: SeriesId,
        /// What was applied.
        action: LifecycleAction,
        /// The lifecycle state afterwards.
        state: SeriesLifecycle,
        /// The occurrence the action was about, when it was about one.
        key: Option<OccurrenceKey>,
        /// The sentence written to History.
        detail: String,
    },
    /// The action was already in effect: nothing was written, including no event.
    NoOp {
        /// The series.
        series_id: SeriesId,
        /// What was asked for.
        action: LifecycleAction,
        /// One sentence saying why nothing changed.
        message: String,
    },
    /// The action was refused. Nothing was written.
    Rejected {
        /// Every reason, in the order they were found.
        diagnostics: Vec<LifecycleDiagnostic>,
    },
}

impl LifecycleOutcome {
    /// Whether the action took effect.
    pub fn is_applied(&self) -> bool {
        matches!(self, Self::Applied { .. })
    }

    /// Whether it was already in effect.
    pub fn is_noop(&self) -> bool {
        matches!(self, Self::NoOp { .. })
    }

    /// Whether it was refused.
    pub fn is_rejected(&self) -> bool {
        matches!(self, Self::Rejected { .. })
    }

    /// The stable word a surface prints: `applied`, `no-op` or `rejected`.
    pub fn as_str(&self) -> &'static str {
        match self {
            Self::Applied { .. } => "applied",
            Self::NoOp { .. } => "no-op",
            Self::Rejected { .. } => "rejected",
        }
    }

    /// One line for a surface.
    pub fn render(&self) -> String {
        match self {
            Self::Applied { action, detail, .. } => format!("{}: {detail}", action.as_str()),
            Self::NoOp {
                action, message, ..
            } => {
                format!("{}: no-op: {message}", action.as_str())
            }
            Self::Rejected { diagnostics } => {
                let first = diagnostics
                    .first()
                    .map(LifecycleDiagnostic::render)
                    .unwrap_or_else(|| "rejected".to_string());
                if diagnostics.len() > 1 {
                    format!("{first} (and {} more)", diagnostics.len() - 1)
                } else {
                    first
                }
            }
        }
    }
}

/// Apply one confirmed lifecycle action (T023-T026).
///
/// Reads the series **from the store** (see the module docs: a state transition
/// must decide against the file), writes through the same store, and returns an
/// outcome for every decision it makes; only a genuine read failure propagates.
#[allow(clippy::too_many_lines)]
pub fn apply(store: &Store, request: &LifecycleRequest) -> crate::error::Result<LifecycleOutcome> {
    // Consent first, and before the store is touched.
    if !request.confirmed {
        return Ok(rejected(LifecycleDiagnostic::new(
            LifecycleDiagnosticKind::NotConfirmed,
            "a lifecycle action must be confirmed: no refresh, timer or detection \
             can apply one",
        )));
    }
    // One read of the repository: the series identity, the occurrence keys and the
    // definition issue all come from it, so nothing is decided from a snapshot that
    // may already be out of date.
    let issues = store.list()?;
    let index = SeriesIndex::build(&issues);
    let Some(series) = index.series_by_id(&request.series_id) else {
        return Ok(rejected(LifecycleDiagnostic::new(
            LifecycleDiagnosticKind::UnknownSeries,
            format!("no series `{}` is defined", request.series_id),
        )));
    };
    let action = request.action;

    // `ended` is terminal for every action but `end` itself (a no-op).
    if series.state == SeriesLifecycle::Ended && action != LifecycleAction::End {
        return Ok(rejected(LifecycleDiagnostic::new(
            LifecycleDiagnosticKind::EndedSeries,
            format!(
                "series `{}` has ended; `end` is terminal, and only `resume` on a \
                 non-ended series or a new series can generate again",
                series.id
            ),
        )));
    }

    // The occurrence-bound actions need a key, and it must name this series.
    let mut date: Option<DateKey> = None;
    if action.needs_key() {
        let Some(key) = request.occurrence_key.as_ref() else {
            return Ok(rejected(LifecycleDiagnostic::new(
                LifecycleDiagnosticKind::MissingKey,
                format!(
                    "`{}` is about one occurrence and needs `--date` (the key \
                     `<series-id>@<YYYY-MM-DD>`)",
                    action.as_str()
                ),
            )));
        };
        let (key_series, key_date) = match OccurrenceKey::parse(key.as_str()) {
            Ok(parts) => parts,
            Err(error) => {
                return Ok(rejected(LifecycleDiagnostic::new(
                    LifecycleDiagnosticKind::MissingKey,
                    error.first().message.clone(),
                )));
            }
        };
        if key_series != request.series_id {
            return Ok(rejected(LifecycleDiagnostic::new(
                LifecycleDiagnosticKind::KeySeriesMismatch,
                format!(
                    "key `{key}` names series `{key_series}` but the request names `{}`",
                    request.series_id
                ),
            )));
        }
        // An occurrence that exists cannot be skipped, deferred or ignored: those
        // actions decide about a date that has not happened. `tix delete` removes
        // an occurrence; this never pretends to.
        if index.key_state(key) == KeyState::Generated {
            return Ok(rejected(LifecycleDiagnostic::new(
                LifecycleDiagnosticKind::AlreadyGenerated,
                format!(
                    "occurrence `{key}` already exists ({}); skipping, deferring or \
                     ignoring it would say something untrue about a file that is there",
                    index
                        .occurrence(key)
                        .map(|record| record.filename.clone())
                        .unwrap_or_else(|| "in the index".to_string())
                ),
            )));
        }
        date = Some(key_date);
    }

    // The no-op matrix: an action already in effect appends nothing.
    match action {
        LifecycleAction::Pause if series.state == SeriesLifecycle::Paused => {
            return Ok(noop(
                series.id.clone(),
                action,
                "the series is already paused",
            ));
        }
        LifecycleAction::Resume if series.state == SeriesLifecycle::Active => {
            return Ok(noop(
                series.id.clone(),
                action,
                "the series is already active",
            ));
        }
        LifecycleAction::End if series.state == SeriesLifecycle::Ended => {
            return Ok(noop(
                series.id.clone(),
                action,
                "the series has already ended",
            ));
        }
        LifecycleAction::Skip | LifecycleAction::Ignore => {
            if let Some(date) = date.as_ref()
                && series.is_skipped(date)
            {
                return Ok(noop(
                    series.id.clone(),
                    action,
                    &format!("`{date}` is already recorded as skipped"),
                ));
            }
        }
        LifecycleAction::Defer => {
            if let Some(date) = date.as_ref()
                && series.next_cursor.as_ref() == Some(date)
            {
                return Ok(noop(
                    series.id.clone(),
                    action,
                    &format!("the cursor is already past `{date}`"),
                ));
            }
            if let Some(date) = date.as_ref()
                && series.is_skipped(date)
            {
                return Ok(noop(
                    series.id.clone(),
                    action,
                    &format!("`{date}` is already recorded as skipped"),
                ));
            }
        }
        _ => {}
    }

    // The definition issue is where all of this lives.
    let Some(definition) = issues
        .iter()
        .find(|issue| issue.number == series.issue_number)
    else {
        return Ok(rejected(LifecycleDiagnostic::new(
            LifecycleDiagnosticKind::DefinitionUnreadable,
            format!(
                "series `{}` is defined by issue #{} ({}) but that issue could not be read",
                series.id, series.issue_number, series.filename
            ),
        )));
    };

    let before = series.state;
    let after = match action {
        LifecycleAction::Pause => SeriesLifecycle::Paused,
        LifecycleAction::Resume => SeriesLifecycle::Active,
        LifecycleAction::End => SeriesLifecycle::Ended,
        LifecycleAction::Skip | LifecycleAction::Defer | LifecycleAction::Ignore => before,
    };
    let detail = lifecycle_detail(&series.id, action, date.as_ref(), before, after, request);

    let written = store.transaction(|| {
        let mut definition = definition.clone();
        let reference = definition.series.as_mut().ok_or_else(|| {
            crate::error::TixError::InvalidInput(format!(
                "issue #{} no longer carries a series table",
                definition.number
            ))
        })?;
        match action {
            LifecycleAction::Pause | LifecycleAction::Resume | LifecycleAction::End => {
                reference.state = Some(after);
            }
            LifecycleAction::Skip | LifecycleAction::Ignore => {
                // The same schedule effect for both, and no second field to keep in
                // step: the decision is what the History entry records.
                let date = date.expect("a keyed action carries its date");
                if !reference.skipped.iter().any(|raw| raw == date.as_str()) {
                    reference.skipped.push(date.as_str().to_string());
                }
                reference.next_cursor = Some(date.as_str().to_string());
            }
            LifecycleAction::Defer => {
                let date = date.expect("a keyed action carries its date");
                reference.next_cursor = Some(date.as_str().to_string());
            }
        }
        definition.history.append_now(
            &request.actor,
            HistoryEventKind::TransitionAccepted,
            &detail,
        );
        store.update(&definition.filename, &definition)?;
        Ok(())
    });

    match written {
        Ok(()) => Ok(LifecycleOutcome::Applied {
            series_id: series.id.clone(),
            action,
            state: after,
            key: request.occurrence_key.clone(),
            detail,
        }),
        Err(error) => Ok(rejected(LifecycleDiagnostic::new(
            LifecycleDiagnosticKind::Refused,
            format!("the store refused the lifecycle write: {error}"),
        ))),
    }
}

/// The one History sentence an applied action writes.
///
/// It names the action, the occurrence where there is one, the state change where
/// there was one, and the caller's reason when they gave one — so an audit reader
/// never has to reconstruct why from the diff.
fn lifecycle_detail(
    series: &SeriesId,
    action: LifecycleAction,
    date: Option<&DateKey>,
    before: SeriesLifecycle,
    after: SeriesLifecycle,
    request: &LifecycleRequest,
) -> String {
    let mut detail = format!("series `{series}` {}", action.as_str());
    if let Some(date) = date {
        detail.push_str(&format!(" occurrence `{series}@{date}`"));
    }
    if action.changes_state() && before != after {
        detail.push_str(&format!(
            " (state {} -> {})",
            before.as_str(),
            after.as_str()
        ));
    }
    if let Some(reason) = request.reason.as_deref() {
        let reason = reason.trim();
        if !reason.is_empty() {
            detail.push_str(&format!(": {reason}"));
        }
    }
    detail
}

/// One refusal, as an outcome.
fn rejected(diagnostic: LifecycleDiagnostic) -> LifecycleOutcome {
    LifecycleOutcome::Rejected {
        diagnostics: vec![diagnostic],
    }
}

/// One no-op, as an outcome.
fn noop(series_id: SeriesId, action: LifecycleAction, message: &str) -> LifecycleOutcome {
    LifecycleOutcome::NoOp {
        series_id,
        action,
        message: message.to_string(),
    }
}

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

    fn series_id() -> SeriesId {
        SeriesId::parse("s-abc").expect("a valid id")
    }

    #[test]
    fn every_action_has_one_stable_spelling() {
        let spellings: Vec<&str> = LifecycleAction::ALL.iter().map(|a| a.as_str()).collect();
        assert_eq!(
            spellings,
            vec!["pause", "resume", "end", "skip", "defer", "ignore"]
        );
        assert_eq!(LifecycleAction::ALL.len(), 6, "the six actions");
    }

    #[test]
    fn only_the_occurrence_actions_need_a_key_and_only_three_change_state() {
        for action in LifecycleAction::ALL {
            assert_eq!(
                action.needs_key(),
                matches!(
                    action,
                    LifecycleAction::Skip | LifecycleAction::Defer | LifecycleAction::Ignore
                ),
                "{}",
                action.as_str()
            );
            assert_eq!(
                action.changes_state(),
                matches!(
                    action,
                    LifecycleAction::Pause | LifecycleAction::Resume | LifecycleAction::End
                ),
                "{}",
                action.as_str()
            );
        }
    }

    #[test]
    fn a_request_is_unconfirmed_until_it_says_so() {
        let request = LifecycleRequest::new(series_id(), LifecycleAction::Pause, "alice");
        assert!(!request.confirmed);
        assert!(request.occurrence_key.is_none());
        let confirmed = request.clone().confirm();
        assert!(confirmed.confirmed);
        assert_eq!(confirmed.action, LifecycleAction::Pause);
    }

    #[test]
    fn the_detail_names_the_action_the_key_the_state_change_and_the_reason() {
        let date = DateKey::from_date(
            time::Date::from_calendar_date(2026, time::Month::January, 2).expect("a date"),
        );
        let key = OccurrenceKey::new(&series_id(), &date);
        let request = LifecycleRequest::new(series_id(), LifecycleAction::Skip, "alice")
            .about(key)
            .because("release week")
            .confirm();
        let detail = lifecycle_detail(
            &series_id(),
            LifecycleAction::Skip,
            Some(&date),
            SeriesLifecycle::Active,
            SeriesLifecycle::Active,
            &request,
        );
        assert!(detail.contains("series `s-abc` skip"), "{detail}");
        assert!(detail.contains("occurrence `s-abc@2026-01-02`"), "{detail}");
        assert!(detail.contains(": release week"), "{detail}");
        assert!(
            !detail.contains("state"),
            "a keyed action changes no state: {detail}"
        );

        let paused = lifecycle_detail(
            &series_id(),
            LifecycleAction::Pause,
            None,
            SeriesLifecycle::Active,
            SeriesLifecycle::Paused,
            &LifecycleRequest::new(series_id(), LifecycleAction::Pause, "alice"),
        );
        assert!(paused.contains("(state active -> paused)"), "{paused}");
    }

    #[test]
    fn outcomes_have_stable_words_and_render_their_reason() {
        let applied = LifecycleOutcome::Applied {
            series_id: series_id(),
            action: LifecycleAction::Pause,
            state: SeriesLifecycle::Paused,
            key: None,
            detail: "series `s-abc` pause (state active -> paused)".to_string(),
        };
        assert_eq!(applied.as_str(), "applied");
        assert!(applied.is_applied());
        assert!(applied.render().contains("pause"));

        let noop = LifecycleOutcome::NoOp {
            series_id: series_id(),
            action: LifecycleAction::Pause,
            message: "already paused".to_string(),
        };
        assert_eq!(noop.as_str(), "no-op");
        assert!(noop.is_noop());
        assert!(noop.render().contains("already paused"));

        let rejected = LifecycleOutcome::Rejected {
            diagnostics: vec![
                LifecycleDiagnostic::new(
                    LifecycleDiagnosticKind::NotConfirmed,
                    "a lifecycle action must be confirmed",
                ),
                LifecycleDiagnostic::new(LifecycleDiagnosticKind::UnknownSeries, "no series"),
            ],
        };
        assert_eq!(rejected.as_str(), "rejected");
        assert!(rejected.is_rejected());
        assert!(rejected.render().contains("not_confirmed"));
        assert!(rejected.render().contains("and 1 more"));
    }
}