//! The contract between the monitor, which produces round reports, and the notification
//! sinks, which consume them. Neither side knows about the other.

use std::{net::IpAddr, time::Duration};

/// `Ok(rtt)` when the probe succeeded, `Err(reason)` otherwise.
pub type ProbeOutcome = Result<Duration, String>;

pub fn describe(outcome: &ProbeOutcome) -> String {
    match outcome {
        Ok(rtt) => format!("{:.0}ms", rtt.as_secs_f64() * 1000.0),
        Err(reason) => reason.clone(),
    }
}

/// Everything one check round of one group produced.
#[derive(Debug, Clone, PartialEq)]
pub struct RoundReport {
    pub group: String,
    /// "A" or "AAAA": the record type this group reads and writes.
    pub record_type: &'static str,
    pub dry_run: bool,
    /// Every member IP probed this round; empty if the round failed before probing.
    pub ips: Vec<IpStatus>,
    pub events: Vec<Event>,
    /// The group's records after this round; `None` if they are unknown.
    pub dns_now: Option<Vec<IpAddr>>,
    /// Set on every failing round, while `Event::CheckFailed` fires only on the first.
    pub error: Option<String>,
}

#[derive(Debug, Clone, PartialEq)]
pub struct IpStatus {
    pub ip: IpAddr,
    /// Member names whose records point at this IP.
    pub members: Vec<String>,
    /// Debounced health, which is what decides DNS.
    pub up: bool,
    /// This round's raw probe result.
    pub probe: ProbeOutcome,
}

#[derive(Debug, Clone, PartialEq)]
pub enum Event {
    /// First round after startup; the report's `ips` is the full snapshot.
    Started { missing: Vec<String> },
    /// A member name now points at different IPs than last round.
    MemberChanged {
        member: String,
        old: Vec<IpAddr>,
        new: Vec<IpAddr>,
    },
    /// Debounced health flipped, or an IP that just appeared failed its first probe.
    HealthChanged {
        ip: IpAddr,
        members: Vec<String>,
        up: bool,
        probe: ProbeOutcome,
    },
    /// Records were written (or would have been, in a dry run).
    DnsUpdated {
        added: Vec<IpAddr>,
        removed: Vec<IpAddr>,
    },
    /// Every member is down; DNS is left as it was. Fires once per outage.
    NoHealthyMembers,
    CheckFailed { error: String },
    CheckRecovered,
}