yog 0.0.3

yog: a balls-oriented session manager for lernie loops (egui frontend)
Documentation 
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//! The §3.8 **mutating fan**'s line grammar (§8.5) — its own file beside
//! [`super::fork`]'s, on the same seam: a family whose gestures read an
//! obligation off the seat rather than a bare tail.

use super::{Context, args, verbs};
use crate::boundary::{Action, Gesture};

/// `/fan <n>` — the §4.10 mutating fan. The obligation is the seat's own: the
/// focused project and the focused ball, exactly as `/close`'s is, so the only
/// word a line carries is **N**, which is the one thing that is yog's policy
/// rather than a derived fact. The prepared start is the seat's too — a fan
/// spreads a `/prepare`, so it refuses for the same reason `/prompt` does when
/// nothing is prepared.
///
/// A **bare project-repo** fan (no ball, the integration branch as target,
/// §4.10 item 8) has no line spelling on purpose: the line supplies what a seat
/// has selected and refuses what it cannot, and reading "no ball selected" as
/// "fan the integration branch" would be a guess at a different gesture. The
/// envelope stays the spelling for that.
pub(super) fn fan(tail: &str, ctx: &Context, verb: &str) -> Result<Gesture, String> {
    let n = args::required(tail, verb, "how many candidates")?;
    Ok(Gesture::Act(Action::Fan {
        prepared: prepared(ctx, verb)?,
        obligation: obligation(ctx, verb)?,
        n: n.parse()
            .map_err(|_| format!("/{verb}: {n:?} is not a count; usage: /fan <n>"))?,
    }))
}

/// `/retire <handle>` — release one candidate, per the project's retention
/// policy. The handle is balls' own opaque name, read off the cohort, and it is
/// required: there is no "the current candidate" for a seat to mean.
pub(super) fn retire(tail: &str, ctx: &Context, verb: &str) -> Result<Gesture, String> {
    Ok(Gesture::Act(Action::Retire {
        obligation: obligation(ctx, verb)?,
        handle: args::required(tail, verb, "the candidate handle")?,
    }))
}

/// The seat's delivery obligation: its focused project and its focused ball.
/// The ball is **required** here even though the type allows none — a bare
/// project-repo obligation is a different gesture (§4.10 item 8) and reading
/// "nothing selected" as "the integration branch" would be a guess at it.
fn obligation(ctx: &Context, verb: &str) -> Result<crate::fan::Obligation, String> {
    Ok(crate::fan::Obligation {
        project: args::project(ctx, verb)?,
        ball: Some(verbs::id("", ctx, verb)?),
    })
}

/// The seat's prepared start, or the refusal naming it — `/prompt`'s own
/// context read, shared with `/fan` because both spend one `/prepare`.
fn prepared(ctx: &Context, verb: &str) -> Result<crate::start::Prepared, String> {
    ctx.prepared
        .clone()
        .ok_or_else(|| format!("/{verb}: nothing is prepared — /prepare first"))
}