//! `/api/schedules` — the operator's scheduled prompts. Each has an id, a
//! name, a body, a cadence and the agents it goes to.
//!
//! **Two buckets.** Every schedule in the swarm is one document under one key
//! ([`DEFINITIONS_KEY`] in [`DEFINITIONS_BUCKET`]), which only this daemon
//! reads or writes. Every change is one compare-and-set on that key, so a
//! schedule exists for all of its agents or for none of them.
//!
//! Each agent reads only its own key of `agent-schedules`
//! (`swarm_queue_client::agent_schedules`), which holds the schedules naming
//! it, without their names or other agents. That key is a projection of the
//! definitions: after a change this daemon rewrites the key of each agent the
//! change touched, and [`spawn_reconcile`] rewrites every agent's key every
//! [`RECONCILE_INTERVAL`], so a projection write that failed is repaired
//! within that interval. A projection keeps each schedule's id, which the
//! agent keys its fired-slot record on, so dropping an agent and adding it
//! back does not refire a slot.

use std::collections::BTreeSet;
use std::sync::Arc;
use std::time::Duration;

use anyhow::Context as _;
use async_nats::jetstream::kv::{CreateErrorKind, Operation, Store, UpdateErrorKind};
use axum::Json;
use axum::extract::{Path, State};
use axum::http::StatusCode;
use problem_details::ProblemDetails;
use serde::{Deserialize, Deserializer, Serialize};
use swarm_queue_client::agent_schedules::{self, AgentSchedules, Schedule};
use utoipa::ToSchema;

use crate::agent_renewal::unix_now;
use crate::wanted::WantedWriter;
use crate::{AppState, error_problem};

/// The bucket holding every schedule definition. Agents hold no grant on it.
pub const DEFINITIONS_BUCKET: &str = "schedule-definitions";

/// The one key in [`DEFINITIONS_BUCKET`].
pub const DEFINITIONS_KEY: &str = "all";

/// How many times a losing writer re-reads and re-applies, as in
/// `wanted::MAX_ATTEMPTS`.
const MAX_ATTEMPTS: usize = 5;

/// Length of a minted schedule id.
const ID_LEN: usize = 8;

/// How often [`spawn_reconcile`] rewrites every agent's key. Also the
/// longest a failed projection write leaves an agent behind.
const RECONCILE_INTERVAL: Duration = Duration::from_mins(1);

/// Every schedule in the swarm: the value under [`DEFINITIONS_KEY`].
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
struct Definitions {
    #[serde(default)]
    schedules: Vec<Definition>,
}

/// One schedule as the operator defines it.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
struct Definition {
    id: String,
    name: String,
    agents: BTreeSet<String>,
    body: String,
    anchor_unix: i64,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    interval_seconds: Option<u64>,
    #[serde(default)]
    paused: bool,
}

impl Definition {
    /// What an agent sees of this schedule.
    fn for_agent(&self) -> Schedule {
        Schedule {
            id: self.id.clone(),
            body: self.body.clone(),
            anchor_unix: self.anchor_unix,
            interval_seconds: self.interval_seconds,
            paused: self.paused,
        }
    }

    /// The next fire time after `now`, or `None` when nothing will fire:
    /// paused, or a one-shot whose time has passed.
    fn next_fire(&self, now: i64) -> Option<i64> {
        if self.paused {
            return None;
        }
        if now < self.anchor_unix {
            return Some(self.anchor_unix);
        }
        let interval = i64::try_from(self.interval_seconds?).ok()?;
        Some(self.for_agent().latest_slot(now)? + interval)
    }
}

/// `agent`'s key: the schedules that name it, in definition order.
fn projection(definitions: &Definitions, agent: &str) -> AgentSchedules {
    AgentSchedules {
        schedules: definitions
            .schedules
            .iter()
            .filter(|d| d.agents.contains(agent))
            .map(Definition::for_agent)
            .collect(),
    }
}

/// One schedule as the API shows it.
#[derive(Debug, Serialize, ToSchema)]
pub struct ScheduleView {
    id: String,
    /// The operator's title for it.
    name: String,
    /// The agents it fires in, sorted.
    agents: Vec<String>,
    /// The prompt, delivered to each agent verbatim.
    body: String,
    /// The first fire time, unix seconds.
    anchor_unix: i64,
    /// Seconds between fires; `null` for a one-shot.
    interval_seconds: Option<u64>,
    paused: bool,
    /// The next fire time on the schedule's grid, unix seconds, computed when
    /// the response is built; `null` when paused or a one-shot whose time
    /// has passed. Says nothing about whether an agent fired an earlier one.
    next_fire_unix: Option<i64>,
}

impl ScheduleView {
    fn new(d: &Definition, now: i64) -> Self {
        Self {
            id: d.id.clone(),
            name: d.name.clone(),
            agents: d.agents.iter().cloned().collect(),
            body: d.body.clone(),
            anchor_unix: d.anchor_unix,
            interval_seconds: d.interval_seconds,
            paused: d.paused,
            next_fire_unix: d.next_fire(now),
        }
    }
}

/// A new schedule.
#[derive(Debug, Clone, Deserialize, ToSchema)]
pub struct AddScheduleRequest {
    /// The title. Must not be empty.
    name: String,
    /// The agents to fire in, at least one. Each must be declared on a hive.
    agents: Vec<String>,
    /// The prompt, delivered verbatim. Must not be empty.
    body: String,
    /// The first fire time, unix seconds. Defaults to now.
    anchor_unix: Option<i64>,
    /// Seconds between fires, at least 1. Absent for a one-shot.
    interval_seconds: Option<u64>,
    #[serde(default)]
    paused: bool,
}

/// A partial change to one schedule; an absent field is left as it is.
#[derive(Debug, Clone, Default, Deserialize, ToSchema)]
pub struct EditScheduleRequest {
    name: Option<String>,
    body: Option<String>,
    anchor_unix: Option<i64>,
    /// A number sets the interval; `null` makes the schedule a one-shot.
    #[serde(default)]
    #[schema(value_type = Option<u64>)]
    interval_seconds: IntervalEdit,
    paused: Option<bool>,
    /// Agents to add. Each must be declared on a hive; one already targeted
    /// is left as it is.
    #[serde(default)]
    add_agents: Vec<String>,
    /// Agents to remove. Each must be a current target, and at least one
    /// target must remain.
    #[serde(default)]
    remove_agents: Vec<String>,
}

/// What an edit does to the interval: an absent field keeps it, `null` makes
/// a one-shot, a number sets it.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
enum IntervalEdit {
    #[default]
    Keep,
    Set(Option<u64>),
}

impl<'de> Deserialize<'de> for IntervalEdit {
    fn deserialize<D: Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
        Option::<u64>::deserialize(d).map(Self::Set)
    }
}

/// Why a change was refused before it was written.
#[derive(Debug, PartialEq, Eq)]
enum Refusal {
    Invalid(String),
    NotDeclared(String),
    NoSuchSchedule(String),
}

fn invalid(why: &str) -> Refusal {
    Refusal::Invalid(why.to_owned())
}

fn check_text(value: &str, what: &str) -> Result<(), Refusal> {
    if value.trim().is_empty() {
        return Err(Refusal::Invalid(format!("the {what} is empty")));
    }
    Ok(())
}

fn check_interval(interval: Option<u64>) -> Result<(), Refusal> {
    if interval == Some(0) {
        return Err(invalid(
            "interval_seconds must be at least 1; omit it for a one-shot",
        ));
    }
    Ok(())
}

/// `names` as agent identifiers, each declared on some hive per `live`.
fn check_agents(names: &[String], live: &BTreeSet<String>) -> Result<BTreeSet<String>, Refusal> {
    let mut agents = BTreeSet::new();
    for name in names {
        let agent = hive_types::Ident::parse(name)
            .map(hive_types::Ident::into_string)
            .map_err(|why| Refusal::Invalid(format!("agent {name:?}: {why}")))?;
        if !live.contains(&agent) {
            return Err(Refusal::NotDeclared(agent));
        }
        agents.insert(agent);
    }
    Ok(agents)
}

impl AddScheduleRequest {
    fn into_definition(
        self,
        id: String,
        now: i64,
        live: &BTreeSet<String>,
    ) -> Result<Definition, Refusal> {
        check_text(&self.name, "name")?;
        check_text(&self.body, "body")?;
        check_interval(self.interval_seconds)?;
        let agents = check_agents(&self.agents, live)?;
        if agents.is_empty() {
            return Err(invalid("a schedule needs at least one agent"));
        }
        Ok(Definition {
            id,
            name: self.name,
            agents,
            body: self.body,
            anchor_unix: self.anchor_unix.unwrap_or(now),
            interval_seconds: self.interval_seconds,
            paused: self.paused,
        })
    }
}

impl EditScheduleRequest {
    /// Apply the edit to schedule `id`, returning it as changed and every
    /// agent it named before or after.
    fn apply(
        self,
        definitions: &mut Definitions,
        id: &str,
        live: &BTreeSet<String>,
    ) -> Result<(Definition, BTreeSet<String>), Refusal> {
        if let Some(name) = &self.name {
            check_text(name, "name")?;
        }
        if let Some(body) = &self.body {
            check_text(body, "body")?;
        }
        if let IntervalEdit::Set(interval) = self.interval_seconds {
            check_interval(interval)?;
        }
        let added = check_agents(&self.add_agents, live)?;
        let d = definitions
            .schedules
            .iter_mut()
            .find(|d| d.id == id)
            .ok_or_else(|| Refusal::NoSuchSchedule(id.to_owned()))?;
        let mut agents = d.agents.clone();
        agents.extend(added);
        for name in &self.remove_agents {
            if !agents.remove(name) {
                return Err(Refusal::Invalid(format!(
                    "agent {name:?} is not a target of schedule {id:?}"
                )));
            }
        }
        if agents.is_empty() {
            return Err(invalid(
                "this would leave the schedule with no agents; remove the schedule instead",
            ));
        }
        let touched = d.agents.union(&agents).cloned().collect();
        d.agents = agents;
        if let Some(name) = self.name {
            d.name = name;
        }
        if let Some(body) = self.body {
            d.body = body;
        }
        if let Some(anchor) = self.anchor_unix {
            d.anchor_unix = anchor;
        }
        if let IntervalEdit::Set(interval) = self.interval_seconds {
            d.interval_seconds = interval;
        }
        if let Some(paused) = self.paused {
            d.paused = paused;
        }
        Ok((d.clone(), touched))
    }
}

/// Remove schedule `id`, returning the agents it named.
fn remove(definitions: &mut Definitions, id: &str) -> Result<BTreeSet<String>, Refusal> {
    let at = definitions
        .schedules
        .iter()
        .position(|d| d.id == id)
        .ok_or_else(|| Refusal::NoSuchSchedule(id.to_owned()))?;
    Ok(definitions.schedules.remove(at).agents)
}

/// A fresh id: lowercase letters only, so the agent's todo key
/// `schedule:<id>` can never equal one hive-c0re pushes for its numeric ids.
fn mint_id(taken: &Definitions) -> anyhow::Result<String> {
    loop {
        let mut bytes = [0u8; ID_LEN];
        getrandom::fill(&mut bytes)
            .map_err(|e| anyhow::anyhow!("drawing a schedule id from the kernel's CSPRNG: {e}"))?;
        let id: String = bytes.iter().map(|b| char::from(b'a' + b % 26)).collect();
        if !taken.schedules.iter().any(|d| d.id == id) {
            return Ok(id);
        }
    }
}

/// The failure of one request, as the problem it answers with.
enum Failure {
    Refused(Refusal),
    Queue(anyhow::Error),
}

impl From<anyhow::Error> for Failure {
    fn from(e: anyhow::Error) -> Self {
        Self::Queue(e)
    }
}

impl From<Refusal> for Failure {
    fn from(r: Refusal) -> Self {
        Self::Refused(r)
    }
}

fn problem(failure: Failure) -> ProblemDetails {
    match failure {
        Failure::Refused(Refusal::Invalid(why)) => error_problem(StatusCode::BAD_REQUEST, &why),
        Failure::Refused(Refusal::NotDeclared(agent)) => error_problem(
            StatusCode::BAD_REQUEST,
            &format!("no hive's wanted state declares an agent {agent:?} that is not destroyed"),
        ),
        Failure::Refused(Refusal::NoSuchSchedule(id)) => {
            error_problem(StatusCode::NOT_FOUND, &format!("no schedule {id:?}"))
        }
        Failure::Queue(e) => {
            tracing::warn!(error = %format!("{e:#}"), "schedules: queue failure");
            error_problem(crate::wanted_error_status(&e), &format!("{e:#}"))
        }
    }
}

/// Open a bucket only this daemon writes, creating it if nothing has yet.
async fn open_or_create_definitions(client: &async_nats::Client) -> anyhow::Result<Store> {
    let js = async_nats::jetstream::new(client.clone());
    if let Ok(store) = js.get_key_value(DEFINITIONS_BUCKET).await {
        return Ok(store);
    }
    js.create_key_value(async_nats::jetstream::kv::Config {
        bucket: DEFINITIONS_BUCKET.to_owned(),
        description: "Every scheduled prompt the swarm controller keeps".to_owned(),
        history: 1,
        ..Default::default()
    })
    .await
    .with_context(|| format!("creating the {DEFINITIONS_BUCKET} bucket"))
}

/// The value of `key` decoded, with the revision to write it back against.
/// An absent or deleted key is the default value.
pub(crate) async fn read<T: Default + serde::de::DeserializeOwned>(
    store: &Store,
    key: &str,
) -> anyhow::Result<(T, Option<u64>)> {
    let Some(entry) = store
        .entry(key)
        .await
        .with_context(|| format!("reading {key}"))?
    else {
        return Ok((T::default(), None));
    };
    if entry.operation != Operation::Put {
        return Ok((T::default(), Some(entry.revision)));
    }
    let value =
        serde_json::from_slice(&entry.value).with_context(|| format!("{key} is not decodable"))?;
    Ok((value, Some(entry.revision)))
}

/// Write `value` to `key` against `revision`. `Ok(false)` when another write
/// landed first.
pub(crate) async fn write<T: Serialize>(
    store: &Store,
    key: &str,
    value: &T,
    revision: Option<u64>,
) -> anyhow::Result<bool> {
    let encoded = serde_json::to_vec(value)?;
    match revision {
        Some(revision) => match store.update(key, encoded.into(), revision).await {
            Ok(_) => Ok(true),
            Err(e) if matches!(e.kind(), UpdateErrorKind::WrongLastRevision) => Ok(false),
            Err(e) => Err(e).with_context(|| format!("writing {key}")),
        },
        None => match store.create(key, encoded.into()).await {
            Ok(_) => Ok(true),
            Err(e) if matches!(e.kind(), CreateErrorKind::AlreadyExists) => Ok(false),
            Err(e) => Err(e).with_context(|| format!("writing {key}")),
        },
    }
}

/// Apply `change` to the definitions and write them back, re-reading and
/// re-applying when another write landed in between.
async fn commit<T>(
    store: &Store,
    mut change: impl FnMut(&mut Definitions) -> Result<T, Failure>,
) -> Result<T, Failure> {
    for _ in 0..MAX_ATTEMPTS {
        let (mut definitions, revision) = read::<Definitions>(store, DEFINITIONS_KEY).await?;
        let out = change(&mut definitions)?;
        if write(store, DEFINITIONS_KEY, &definitions, revision).await? {
            return Ok(out);
        }
        tracing::debug!("schedules: definitions write lost a race, retrying");
    }
    Err(
        anyhow::anyhow!("gave up writing the schedules after {MAX_ATTEMPTS} conflicting writes")
            .into(),
    )
}

/// Rewrite `agent`'s key from the current definitions.
///
/// The agent key's revision is read before the definitions, so a write based
/// on definitions older than another writer's fails its revision check and
/// is redone from fresh ones.
async fn project(definitions: &Store, agents: &Store, agent: &str) -> anyhow::Result<()> {
    for _ in 0..MAX_ATTEMPTS {
        let (current, revision) = read::<AgentSchedules>(agents, agent).await?;
        let (all, _) = read::<Definitions>(definitions, DEFINITIONS_KEY).await?;
        let wanted = projection(&all, agent);
        if current == wanted {
            return Ok(());
        }
        if write(agents, agent, &wanted, revision).await? {
            return Ok(());
        }
    }
    anyhow::bail!(
        "gave up writing the schedules of {agent} after {MAX_ATTEMPTS} conflicting writes"
    )
}

/// [`project`] each of `touched`, logging a failure: the definitions are
/// already written, and [`spawn_reconcile`] repairs the agent's key.
async fn project_all(client: &async_nats::Client, definitions: &Store, touched: &BTreeSet<String>) {
    let agents = match agent_schedules::open_or_create(client).await {
        Ok(store) => store,
        Err(e) => {
            tracing::warn!(
                error = %swarm_queue_client::chain(&e),
                "schedules: opening the agent-schedules bucket failed; the reconcile pass retries"
            );
            return;
        }
    };
    for agent in touched {
        if let Err(e) = project(definitions, &agents, agent).await {
            tracing::warn!(
                %agent,
                error = %format!("{e:#}"),
                "schedules: rewriting the agent's key failed; the reconcile pass retries"
            );
        }
    }
}

/// Rewrite every agent's key from the definitions, now and every
/// [`RECONCILE_INTERVAL`] after: the agents the definitions name, and every
/// live agent, so one dropped from its last schedule is emptied too.
pub(crate) fn spawn_reconcile(
    client: async_nats::Client,
    wanted: Arc<WantedWriter>,
    hives: Vec<String>,
) {
    tokio::spawn(async move {
        let mut ticker = tokio::time::interval(RECONCILE_INTERVAL);
        loop {
            ticker.tick().await;
            if swarm_queue_client::ensure_connected(&client).is_err() {
                continue;
            }
            let store = match open_or_create_definitions(&client).await {
                Ok(store) => store,
                Err(e) => {
                    tracing::warn!(error = %format!("{e:#}"), "schedules: reconcile could not open the definitions");
                    continue;
                }
            };
            let all = match read::<Definitions>(&store, DEFINITIONS_KEY).await {
                Ok((all, _)) => all,
                Err(e) => {
                    tracing::warn!(error = %format!("{e:#}"), "schedules: reconcile could not read the definitions");
                    continue;
                }
            };
            let mut agents = crate::subagent_term::live_agents(&wanted, &hives).await;
            agents.extend(all.schedules.iter().flat_map(|d| d.agents.iter().cloned()));
            project_all(&client, &store, &agents).await;
        }
    });
}

/// The connected queue client, or the problem.
pub(crate) fn queue(state: &AppState) -> Result<async_nats::Client, (StatusCode, String)> {
    let status = state.status.as_ref().ok_or_else(|| {
        (
            StatusCode::SERVICE_UNAVAILABLE,
            "no swarm queue is configured on this host".to_owned(),
        )
    })?;
    let client = status.queue_client();
    swarm_queue_client::ensure_connected(&client).map_err(|e| {
        (
            StatusCode::SERVICE_UNAVAILABLE,
            swarm_queue_client::chain(&e),
        )
    })?;
    Ok(client)
}

pub(crate) fn refused((status, detail): (StatusCode, String)) -> ProblemDetails {
    error_problem(status, &detail)
}

/// Every agent some hive declares and has not destroyed.
pub(crate) async fn live(state: &AppState) -> Result<BTreeSet<String>, ProblemDetails> {
    let Some(wanted) = state.wanted.as_ref() else {
        return Err(error_problem(
            StatusCode::SERVICE_UNAVAILABLE,
            "no swarm queue is configured on this host",
        ));
    };
    let hives: Vec<String> = state.hives.iter().map(|h| h.name.clone()).collect();
    Ok(crate::subagent_term::live_agents(wanted, &hives).await)
}

#[utoipa::path(
    get,
    path = "/api/schedules",
    responses(
        (status = 200, description = "every schedule, sorted by name then id; empty when \
            there are none", body = Vec<ScheduleView>),
        (status = 503, description = "no swarm queue is configured on this host, or it is \
            not connected (problem+json)", body = String),
        (status = 500, description = "the schedules could not be read (problem+json)",
            body = String),
    ),
    tag = "schedules"
)]
pub(crate) async fn list_schedules(
    State(state): State<AppState>,
) -> Result<Json<Vec<ScheduleView>>, ProblemDetails> {
    let client = queue(&state).map_err(refused)?;
    let store = open_or_create_definitions(&client)
        .await
        .map_err(|e| problem(e.into()))?;
    let (mut all, _) = read::<Definitions>(&store, DEFINITIONS_KEY)
        .await
        .map_err(|e| problem(e.into()))?;
    all.schedules
        .sort_by(|a, b| (&a.name, &a.id).cmp(&(&b.name, &b.id)));
    let now = unix_now();
    Ok(Json(
        all.schedules
            .iter()
            .map(|d| ScheduleView::new(d, now))
            .collect(),
    ))
}

#[utoipa::path(
    post,
    path = "/api/schedules",
    request_body = AddScheduleRequest,
    responses(
        (status = 201, description = "the schedule as stored, with its new id",
            body = ScheduleView),
        (status = 400, description = "the name or body is empty, the interval is 0, no \
            agent is named, or an agent is not an identifier or not declared on any hive \
            (problem+json)", body = String),
        (status = 503, description = "no swarm queue is configured on this host, or it is \
            not connected (problem+json)", body = String),
        (status = 500, description = "the schedules could not be written (problem+json)",
            body = String),
    ),
    tag = "schedules"
)]
pub(crate) async fn add_schedule(
    State(state): State<AppState>,
    Json(req): Json<AddScheduleRequest>,
) -> Result<(StatusCode, Json<ScheduleView>), ProblemDetails> {
    let client = queue(&state).map_err(refused)?;
    let live = live(&state).await?;
    let now = unix_now();
    let store = open_or_create_definitions(&client)
        .await
        .map_err(|e| problem(e.into()))?;
    let added = commit(&store, |all| {
        let id = mint_id(all)?;
        let d = req.clone().into_definition(id, now, &live)?;
        all.schedules.push(d.clone());
        Ok(d)
    })
    .await
    .map_err(problem)?;
    tracing::info!(id = %added.id, agents = ?added.agents, "added a schedule");
    project_all(&client, &store, &added.agents).await;
    Ok((StatusCode::CREATED, Json(ScheduleView::new(&added, now))))
}

#[utoipa::path(
    patch,
    path = "/api/schedules/{id}",
    params(("id" = String, Path, description = "schedule to change")),
    request_body = EditScheduleRequest,
    responses(
        (status = 200, description = "the schedule as stored", body = ScheduleView),
        (status = 400, description = "the name or body is empty, the interval is 0, an \
            added agent is not declared on any hive, a removed agent is not a target, or \
            no agent would remain (problem+json)", body = String),
        (status = 404, description = "there is no schedule with this id (problem+json)",
            body = String),
        (status = 503, description = "no swarm queue is configured on this host, or it is \
            not connected (problem+json)", body = String),
        (status = 500, description = "the schedules could not be written (problem+json)",
            body = String),
    ),
    tag = "schedules"
)]
pub(crate) async fn edit_schedule(
    State(state): State<AppState>,
    Path(id): Path<String>,
    Json(req): Json<EditScheduleRequest>,
) -> Result<Json<ScheduleView>, ProblemDetails> {
    let client = queue(&state).map_err(refused)?;
    let live = live(&state).await?;
    let store = open_or_create_definitions(&client)
        .await
        .map_err(|e| problem(e.into()))?;
    let (edited, touched) = commit(&store, |all| Ok(req.clone().apply(all, &id, &live)?))
        .await
        .map_err(problem)?;
    tracing::info!(%id, "edited a schedule");
    project_all(&client, &store, &touched).await;
    Ok(Json(ScheduleView::new(&edited, unix_now())))
}

#[utoipa::path(
    delete,
    path = "/api/schedules/{id}",
    params(("id" = String, Path, description = "schedule to remove")),
    responses(
        (status = 204, description = "removed; it fires no more"),
        (status = 404, description = "there is no schedule with this id (problem+json)",
            body = String),
        (status = 503, description = "no swarm queue is configured on this host, or it is \
            not connected (problem+json)", body = String),
        (status = 500, description = "the schedules could not be written (problem+json)",
            body = String),
    ),
    tag = "schedules"
)]
pub(crate) async fn remove_schedule(
    State(state): State<AppState>,
    Path(id): Path<String>,
) -> Result<StatusCode, ProblemDetails> {
    let client = queue(&state).map_err(refused)?;
    let store = open_or_create_definitions(&client)
        .await
        .map_err(|e| problem(e.into()))?;
    let touched = commit(&store, |all| Ok(remove(all, &id)?))
        .await
        .map_err(problem)?;
    tracing::info!(%id, "removed a schedule");
    project_all(&client, &store, &touched).await;
    Ok(StatusCode::NO_CONTENT)
}

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

    fn live() -> BTreeSet<String> {
        ["atlas", "iris", "scribe"].map(str::to_owned).into()
    }

    fn standup() -> Definition {
        Definition {
            id: "abc".to_owned(),
            name: "standup".to_owned(),
            agents: ["atlas", "iris"].map(str::to_owned).into(),
            body: "post the standup".to_owned(),
            anchor_unix: 1000,
            interval_seconds: Some(3600),
            paused: false,
        }
    }

    fn all() -> Definitions {
        Definitions {
            schedules: vec![standup()],
        }
    }

    fn edit(json: &str) -> EditScheduleRequest {
        serde_json::from_str(json).expect("decodes")
    }

    /// Each agent's key carries the schedules naming it, under the same id,
    /// and nothing of the name or the other agents.
    #[test]
    fn an_agents_key_holds_the_schedules_naming_it() {
        let mut defs = all();
        let mut other = standup();
        "xyz".clone_into(&mut other.id);
        other.agents = ["scribe"].map(str::to_owned).into();
        defs.schedules.push(other);
        let atlas = projection(&defs, "atlas");
        assert_eq!(atlas.schedules, vec![standup().for_agent()]);
        assert_eq!(projection(&defs, "scribe").schedules[0].id, "xyz");
        assert!(projection(&defs, "argus").schedules.is_empty());
        let encoded = serde_json::to_string(&atlas).unwrap();
        assert!(!encoded.contains("\"name\""), "{encoded}");
        assert!(!encoded.contains("iris"), "{encoded}");
    }

    /// A body or name edit leaves anchor and interval, and so the fire
    /// times, where they were, and keeps the id.
    #[test]
    fn a_text_edit_leaves_the_cadence_and_id_alone() {
        let mut defs = all();
        let (out, touched) = edit(r#"{"body":"retro","name":"retro"}"#)
            .apply(&mut defs, "abc", &live())
            .unwrap();
        assert_eq!(
            (out.id.as_str(), out.body.as_str(), out.name.as_str()),
            ("abc", "retro", "retro")
        );
        assert_eq!((out.anchor_unix, out.interval_seconds), (1000, Some(3600)));
        assert_eq!(touched, standup().agents);
    }

    /// Adding and removing targets keeps the id, and every agent on either
    /// side of the change is rewritten.
    #[test]
    fn the_agent_set_changes_without_a_new_id() {
        let mut defs = all();
        let (out, touched) = edit(r#"{"add_agents":["scribe"],"remove_agents":["iris"]}"#)
            .apply(&mut defs, "abc", &live())
            .unwrap();
        assert_eq!(out.id, "abc");
        assert_eq!(out.agents, ["atlas", "scribe"].map(str::to_owned).into());
        assert_eq!(
            touched,
            ["atlas", "iris", "scribe"].map(str::to_owned).into()
        );
        assert_eq!(defs.schedules, vec![out]);
    }

    #[test]
    fn bad_edits_are_refused_before_anything_changes() {
        for (json, id) in [
            (r#"{"interval_seconds":0}"#, "abc"),
            (r#"{"body":"  "}"#, "abc"),
            (r#"{"name":""}"#, "abc"),
            (r#"{"add_agents":["nobody"]}"#, "abc"),
            (r#"{"remove_agents":["scribe"]}"#, "abc"),
            (r#"{"remove_agents":["atlas","iris"]}"#, "abc"),
            (r#"{"body":"x"}"#, "nope"),
        ] {
            let mut defs = all();
            assert!(edit(json).apply(&mut defs, id, &live()).is_err(), "{json}");
            assert_eq!(defs, all(), "{json}");
        }
    }

    #[test]
    fn a_null_interval_makes_a_one_shot_and_an_absent_one_keeps_it() {
        let mut defs = all();
        let (kept, _) = edit(r#"{"paused":true}"#)
            .apply(&mut defs, "abc", &live())
            .unwrap();
        assert_eq!(kept.interval_seconds, Some(3600));
        assert!(kept.paused);
        let (once, _) = edit(r#"{"interval_seconds":null}"#)
            .apply(&mut defs, "abc", &live())
            .unwrap();
        assert_eq!(once.interval_seconds, None);
    }

    #[test]
    fn removing_drops_only_the_named_schedule() {
        let mut defs = all();
        assert_eq!(
            remove(&mut defs, "zzz"),
            Err(Refusal::NoSuchSchedule("zzz".to_owned()))
        );
        assert_eq!(defs, all());
        assert_eq!(remove(&mut defs, "abc").unwrap(), standup().agents);
        assert!(defs.schedules.is_empty());
    }

    #[test]
    fn an_add_needs_a_name_and_declared_agents_and_anchors_at_now() {
        let add = |json: &str| {
            serde_json::from_str::<AddScheduleRequest>(json)
                .unwrap()
                .into_definition("id".to_owned(), 42, &live())
        };
        let d = add(r#"{"name":"n","agents":["iris","atlas","iris"],"body":"hi"}"#).unwrap();
        assert_eq!(
            (d.anchor_unix, d.interval_seconds, d.paused),
            (42, None, false)
        );
        assert_eq!(d.agents, ["atlas", "iris"].map(str::to_owned).into());
        assert!(add(r#"{"name":" ","agents":["iris"],"body":"hi"}"#).is_err());
        assert!(add(r#"{"name":"n","agents":[],"body":"hi"}"#).is_err());
        assert_eq!(
            add(r#"{"name":"n","agents":["nobody"],"body":"hi"}"#),
            Err(Refusal::NotDeclared("nobody".to_owned()))
        );
        assert!(add(r#"{"name":"n","agents":["Not An Ident"],"body":"hi"}"#).is_err());
    }

    #[test]
    fn next_fire_is_the_next_grid_slot_or_none() {
        let mut d = standup();
        assert_eq!(d.next_fire(999), Some(1000));
        assert_eq!(d.next_fire(1000), Some(4600));
        assert_eq!(d.next_fire(4601), Some(8200));
        d.paused = true;
        assert_eq!(d.next_fire(999), None);
        d.paused = false;
        d.interval_seconds = None;
        assert_eq!(d.next_fire(999), Some(1000));
        assert_eq!(d.next_fire(1000), None);
    }

    #[test]
    fn a_view_shows_the_wire_shape() {
        let v = serde_json::to_value(ScheduleView::new(&standup(), 1500)).unwrap();
        assert_eq!(
            v,
            serde_json::json!({
                "id": "abc",
                "name": "standup",
                "agents": ["atlas", "iris"],
                "body": "post the standup",
                "anchor_unix": 1000,
                "interval_seconds": 3600,
                "paused": false,
                "next_fire_unix": 4600,
            })
        );
    }

    /// Letters only: hive-c0re keys its todos `schedule:<number>`, and a
    /// swarm id that could be all digits could collapse into one of them.
    #[test]
    fn minted_ids_are_letters_and_avoid_taken_ones() {
        let defs = all();
        for _ in 0..100 {
            let id = mint_id(&defs).unwrap();
            assert_eq!(id.len(), ID_LEN);
            assert!(id.chars().all(|c| c.is_ascii_lowercase()), "{id}");
            assert_ne!(id, "abc");
        }
    }
}