//! One event through every flow: the ops to queue and the issue's next
//! snapshot. No I/O, so the whole decision is testable.

use std::collections::BTreeSet;

use swarm_wire::router_todo::Op;

use crate::event::{Delivery, Snapshot, fields, is_assign};
use swarm_wire::notify_flows::Flow;

use crate::flow::{Action, evaluate};

/// What one event comes to.
#[derive(Debug, PartialEq, Eq)]
pub struct Routed {
    /// The ops to queue, one per agent that exists.
    pub actions: Vec<Action>,
    /// Recipients that are not agents of this swarm, so got nothing.
    pub skipped: Vec<String>,
    pub next: Snapshot,
}

/// Run `flows` over one delivery of `event_type` on an issue whose snapshot is
/// `snapshot`. `is_agent` says whether a recipient is an agent of this swarm.
pub fn route(
    event_type: &str,
    delivery: &Delivery,
    snapshot: &Snapshot,
    flows: &[Flow],
    is_agent: impl Fn(&str) -> bool,
) -> Routed {
    let fields = fields(event_type, delivery, snapshot);
    let mut actions = Vec::new();
    let mut skipped = Vec::new();
    for action in flows.iter().flat_map(|f| evaluate(f, event_type, &fields)) {
        if is_agent(&action.agent) {
            actions.push(action);
        } else if !skipped.contains(&action.agent) {
            skipped.push(action.agent);
        }
    }
    let mut next = snapshot.clone();
    if is_assign(event_type) {
        // A skipped assignee is left out of the snapshot, so the next assign
        // event counts it as added again: an agent assigned before it is in
        // the roster gets its todo once it is.
        let mut assignees = delivery.assignees.clone();
        assignees.retain(|a| !skipped.contains(a));
        next.assignees = Some(assignees);
    }
    let mut cleared = BTreeSet::new();
    for action in &actions {
        match action.op.op {
            Op::Upsert => {
                next.holders.insert(action.agent.clone());
            }
            Op::Clear => {
                cleared.insert(action.agent.clone());
            }
        }
    }
    next.holders.retain(|h| !cleared.contains(h));
    Routed {
        actions,
        skipped,
        next,
    }
}

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

    fn delivery(action: &str, assignees: &[&str]) -> Delivery {
        Delivery {
            action: action.to_owned(),
            repo: "o/r".to_owned(),
            repo_id: 1,
            number: 9,
            title: "t".to_owned(),
            url: "u".to_owned(),
            sender: "mara".to_owned(),
            is_pull: false,
            assignees: assignees.iter().map(|a| (*a).to_owned()).collect(),
        }
    }

    fn agents(a: &Routed) -> Vec<(&str, Op)> {
        a.actions
            .iter()
            .map(|x| (x.agent.as_str(), x.op.op))
            .collect()
    }

    /// Assign, reassign, close: the three built-ins in the order an issue
    /// meets them, carrying the snapshot from one event to the next.
    #[test]
    fn an_issue_assigned_reassigned_and_closed_queues_and_clears_its_todos() {
        let flows = builtins();
        let is_agent = |a: &str| a != "mara";

        let one = route(
            "issue_assign",
            &delivery("assigned", &["atlas", "mara"]),
            &Snapshot::default(),
            &flows,
            is_agent,
        );
        assert_eq!(agents(&one), [("atlas", Op::Upsert)]);
        assert_eq!(one.skipped, ["mara"]);
        assert_eq!(one.next.holders, BTreeSet::from(["atlas".to_owned()]));

        let two = route(
            "issue_assign",
            &delivery("unassigned", &["mara"]),
            &one.next,
            &flows,
            is_agent,
        );
        assert_eq!(agents(&two), [("atlas", Op::Upsert)]);
        assert!(two.actions[0].op.summary.contains("not assigned"));

        let three = route(
            "issue_assign",
            &delivery("assigned", &["mara", "iris"]),
            &two.next,
            &flows,
            is_agent,
        );
        assert_eq!(agents(&three), [("iris", Op::Upsert)]);

        let closed = route(
            "issues",
            &delivery("closed", &["mara", "iris"]),
            &three.next,
            &flows,
            is_agent,
        );
        // Per agent the clear comes before the closed todo that its prefix would take.
        let mut got = agents(&closed);
        got.sort_by_key(|(a, _)| *a);
        assert_eq!(
            got,
            [
                ("atlas", Op::Clear),
                ("atlas", Op::Upsert),
                ("iris", Op::Clear),
                ("iris", Op::Upsert)
            ]
        );
        assert!(closed.next.holders.is_empty());
        // A close leaves the assignee snapshot as the last assign set it.
        assert_eq!(closed.next.assignees, three.next.assignees);
    }

    /// An agent assigned before it reports status gets nothing then, and its
    /// todo on the next assign event, once it is in the roster.
    #[test]
    fn an_assignee_not_yet_in_the_roster_gets_its_todo_on_the_next_assign() {
        let flows = builtins();
        let early = route(
            "issue_assign",
            &delivery("assigned", &["nova"]),
            &Snapshot::default(),
            &flows,
            |_| false,
        );
        assert!(early.actions.is_empty());
        assert_eq!(early.skipped, ["nova"]);
        assert_eq!(early.next.assignees, Some(BTreeSet::new()));

        let later = route(
            "issue_assign",
            &delivery("assigned", &["nova", "atlas"]),
            &early.next,
            &flows,
            |_| true,
        );
        let mut got = agents(&later);
        got.sort_unstable_by_key(|(a, _)| *a);
        assert_eq!(got, [("atlas", Op::Upsert), ("nova", Op::Upsert)]);
        assert_eq!(
            later.next.assignees,
            Some(BTreeSet::from(["atlas".to_owned(), "nova".to_owned()]))
        );
    }

    #[test]
    fn an_event_no_flow_matches_changes_nothing() {
        let before = Snapshot {
            assignees: Some(BTreeSet::from(["atlas".to_owned()])),
            holders: BTreeSet::from(["atlas".to_owned()]),
        };
        let r = route(
            "issue_comment",
            &delivery("created", &[]),
            &before,
            &builtins(),
            |_| true,
        );
        assert!(r.actions.is_empty());
        assert_eq!(r.next, before);
    }
}