//! Swarm-level config-PR status, kept current by both a webhook nudge and a
//! periodic poll.
//!
//! swarm-ui's config-PR panel needs a *swarm*-level answer to "does agent X
//! have an open config PR" that does not depend on which hive currently
//! hosts X being reachable.
//!
//! Both paths write the same [`ConfigPrCache`]:
//!
//! - [`spawn`] — a periodic full rescan. The backstop: catches anything a
//!   missed delivery loses, and is what populates the cache before the first
//!   delivery ever arrives.
//! - [`ConfigPrCache::apply_webhook_delivery`] — called from
//!   `crate::webhook::post_webhook_forge` on a verified `ConfigPr` delivery.
//!   The low-latency path: a PR opening or closing shows up immediately
//!   instead of waiting up to `POLL_INTERVAL`.
//!
//! [`merged`] reads the same delivery for a merge, which the webhook handler
//! turns into a deploy. The poll has no counterpart: it lists open PRs only,
//! so a merge whose delivery is lost deploys nothing.

use std::collections::HashMap;
use std::sync::{Arc, Mutex};

use serde::Deserialize;

use crate::forge::{Client, ConfigPrStatus};

/// The handful of fields this cache needs out of a Forgejo `pull_request`
/// webhook payload — not a full typed mirror of the event (Forgejo's own
/// schema has dozens more), just enough to know which agent, which PR, and
/// whether it's still open.
#[derive(Deserialize)]
pub struct ConfigPrWebhookPayload {
    /// `"closed"` on both a merge and a close without merging; `merged`
    /// tells them apart.
    #[serde(default)]
    action: String,
    pull_request: WebhookPullRequest,
    repository: WebhookRepository,
}

#[derive(Deserialize)]
struct WebhookPullRequest {
    number: u64,
    /// Forgejo sends `"open"` or `"closed"` here — merged and
    /// closed-without-merging are indistinguishable at this field, but this
    /// cache only ever answers "is there an open PR," so the distinction
    /// doesn't matter to it.
    state: String,
    html_url: Option<String>,
    #[serde(default)]
    merged: bool,
    /// The commit the merge left on the base branch.
    #[serde(default)]
    merge_commit_sha: Option<String>,
    /// The branch the PR targets. Only a merge into `main` is deployed: the
    /// hive builds its config repo's `main`.
    #[serde(default)]
    base: Option<WebhookBranch>,
}

#[derive(Deserialize)]
struct WebhookBranch {
    #[serde(rename = "ref")]
    name: String,
}

/// A config PR that was just merged: whose config, and the commit to deploy.
#[derive(Debug, PartialEq, Eq)]
pub struct MergedConfigPr {
    pub agent: String,
    pub rev: String,
}

/// The merge a verified `ConfigPr` delivery reports, if it reports one.
///
/// Only the `closed` action counts: Forgejo also sends `merged: true` on
/// later events about an already-merged PR (a label or an edit), and those
/// must not deploy it again. So does only a merge into `main`. A body that
/// does not parse is `None`; [`ConfigPrCache::apply_webhook_delivery`]
/// already logs it.
pub fn merged(body: &[u8]) -> Option<MergedConfigPr> {
    let payload: ConfigPrWebhookPayload = serde_json::from_slice(body).ok()?;
    let into_main = payload
        .pull_request
        .base
        .as_ref()
        .is_some_and(|base| base.name == "main");
    if payload.action != "closed" || !payload.pull_request.merged || !into_main {
        return None;
    }
    let Some(rev) = payload.pull_request.merge_commit_sha else {
        tracing::warn!(
            agent = %payload.repository.name,
            pr = payload.pull_request.number,
            "config-pr webhook: merged PR carries no merge_commit_sha; nothing deployed"
        );
        return None;
    };
    Some(MergedConfigPr {
        agent: payload.repository.name,
        rev,
    })
}

#[derive(Deserialize)]
struct WebhookRepository {
    /// The config repo's name IS the agent's name — same convention
    /// `Client::list_open_config_prs` relies on.
    name: String,
}

/// How often to rescan `agent-configs/*`.
const POLL_INTERVAL: std::time::Duration = std::time::Duration::from_mins(5);

/// The latest full scan, replaced atomically each cycle.
///
/// A full replace rather than an incremental merge: `Client::list_open_config_prs`
/// already returns the complete current set (an agent with no open PR is
/// simply absent), so merging would need its own stale-entry eviction to
/// avoid an agent's long-closed PR lingering forever — the same reconcile
/// problem `hive-c0re`'s poller solves for its approvals. A full replace
/// sidesteps needing that logic twice: the map at any moment is nothing more
/// than "the last successful scan's answer."
pub struct ConfigPrCache(Mutex<HashMap<String, ConfigPrStatus>>);

impl ConfigPrCache {
    fn new() -> Self {
        Self(Mutex::new(HashMap::new()))
    }

    /// `agent`'s open PR, if the last successful scan found one.
    ///
    /// Returns `None` both when the agent has no open PR and when no scan
    /// has completed yet — the caller (`GET /api/agents/<name>/config-pr`)
    /// treats both as "nothing to show," which is the honest answer for a
    /// value that's a best-effort cache, not a live read.
    pub fn get(&self, agent: &str) -> Option<ConfigPrStatus> {
        self.0
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
            .get(agent)
            .cloned()
    }

    /// Every agent with an open PR, per the last successful scan (plus any
    /// webhook upserts since). The bulk counterpart to [`Self::get`] — for
    /// `GET /api/config-prs` (swarm-ui's config-PR table), which needs every
    /// agent's status in one round trip rather than one request per agent.
    pub fn snapshot(&self) -> HashMap<String, ConfigPrStatus> {
        self.0
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
            .clone()
    }

    /// ⚠️ Can race [`Self::apply_webhook_delivery`]: a scan started before a
    /// PR opened may finish *after* the webhook already upserted it, and
    /// this snapshot — taken before that PR existed — will overwrite the
    /// fresh entry. Self-heals within one `POLL_INTERVAL` (the next scan
    /// sees the PR), so not worth coordinating against; noted per argus's
    /// review rather than left implicit.
    fn replace(&self, scan: HashMap<String, ConfigPrStatus>) {
        *self
            .0
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner) = scan;
    }

    /// Apply one verified `ConfigPr` webhook delivery's raw body to the
    /// cache — the low-latency counterpart to [`spawn`]'s periodic rescan.
    ///
    /// A parse failure is logged and dropped, not propagated: the caller
    /// (`crate::webhook::post_webhook_forge`) already returned 200 to
    /// Forgejo (HMAC verification, not payload parsing, is what a retry
    /// could fix), and the next poll tick reconciles whatever this delivery
    /// would have changed — same "poll as backstop" property [`spawn`]'s
    /// doc comment describes, just exercised on the failure path instead of
    /// the steady-state one.
    ///
    /// An `open` PR is upserted unconditionally. A `closed` one is removed
    /// only if the cached entry's PR number still matches — guards against
    /// an out-of-order delivery (a stale `closed` for PR #1 arriving after a
    /// newer `opened` for PR #2 on the same repo) wiping out a genuinely
    /// current entry.
    pub fn apply_webhook_delivery(&self, body: &[u8]) {
        let payload: ConfigPrWebhookPayload = match serde_json::from_slice(body) {
            Ok(p) => p,
            Err(e) => {
                tracing::warn!(
                    error = %e,
                    "config-pr webhook: payload did not parse, cache unchanged (next poll reconciles)"
                );
                return;
            }
        };
        let mut map = self
            .0
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner);
        if payload.pull_request.state == "open" {
            map.insert(
                payload.repository.name,
                ConfigPrStatus {
                    pr_number: payload.pull_request.number,
                    html_url: payload.pull_request.html_url,
                },
            );
        } else if map
            .get(&payload.repository.name)
            .is_some_and(|cached| cached.pr_number == payload.pull_request.number)
        {
            map.remove(&payload.repository.name);
        }
    }
}

/// Build an empty cache and spawn the periodic scan that keeps it current.
///
/// The scan runs immediately on the first tick (`tokio::time::interval`'s
/// default), so the cache is populated on startup rather than staying empty
/// for a full `POLL_INTERVAL` after boot.
pub fn spawn(client: Arc<Client>) -> Arc<ConfigPrCache> {
    let cache = Arc::new(ConfigPrCache::new());
    let cache_for_task = Arc::clone(&cache);
    tokio::spawn(async move {
        let mut ticker = tokio::time::interval(POLL_INTERVAL);
        loop {
            ticker.tick().await;
            match client.list_open_config_prs().await {
                Ok(scan) => cache_for_task.replace(scan),
                Err(e) => {
                    tracing::warn!(
                        error = %format!("{e:#}"),
                        "config-pr poll: scan failed, cache keeps its last value"
                    );
                }
            }
        }
    });
    cache
}

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

    fn payload(agent: &str, number: u64, state: &str) -> Vec<u8> {
        serde_json::json!({
            "pull_request": { "number": number, "state": state, "html_url": "https://forge.example/pr" },
            "repository": { "name": agent },
        })
        .to_string()
        .into_bytes()
    }

    #[test]
    fn an_open_delivery_upserts_the_entry() {
        let cache = ConfigPrCache::new();
        cache.apply_webhook_delivery(&payload("damocles", 5, "open"));
        let status = cache.get("damocles").expect("entry inserted");
        assert_eq!(status.pr_number, 5);
    }

    #[test]
    fn a_closed_delivery_removes_a_matching_entry() {
        let cache = ConfigPrCache::new();
        cache.apply_webhook_delivery(&payload("damocles", 5, "open"));
        cache.apply_webhook_delivery(&payload("damocles", 5, "closed"));
        assert!(cache.get("damocles").is_none());
    }

    #[test]
    fn a_stale_closed_delivery_does_not_clobber_a_newer_open_pr() {
        let cache = ConfigPrCache::new();
        // PR #5 opened, then closed, then a genuinely new PR #6 opens.
        cache.apply_webhook_delivery(&payload("damocles", 5, "open"));
        cache.apply_webhook_delivery(&payload("damocles", 6, "open"));
        // The #5 close event arrives late, after #6 already replaced it.
        cache.apply_webhook_delivery(&payload("damocles", 5, "closed"));
        let status = cache.get("damocles").expect("PR #6 must survive");
        assert_eq!(status.pr_number, 6);
    }

    #[test]
    fn snapshot_returns_every_agent_with_an_open_pr() {
        let cache = ConfigPrCache::new();
        assert!(
            cache.snapshot().is_empty(),
            "an unpopulated cache snapshots empty, not missing"
        );
        cache.apply_webhook_delivery(&payload("damocles", 5, "open"));
        cache.apply_webhook_delivery(&payload("iris", 9, "open"));
        let snapshot = cache.snapshot();
        assert_eq!(snapshot.len(), 2);
        assert_eq!(snapshot["damocles"].pr_number, 5);
        assert_eq!(snapshot["iris"].pr_number, 9);
    }

    fn closed(merged: bool) -> Vec<u8> {
        serde_json::json!({
            "action": "closed",
            "pull_request": {
                "number": 5,
                "state": "closed",
                "html_url": "https://forge.example/pr",
                "merged": merged,
                "merge_commit_sha": merged.then_some("abc123"),
                "base": { "ref": "main" },
            },
            "repository": { "name": "damocles" },
        })
        .to_string()
        .into_bytes()
    }

    #[test]
    fn a_merged_delivery_names_the_agent_and_the_merge_commit() {
        assert_eq!(
            super::merged(&closed(true)),
            Some(super::MergedConfigPr {
                agent: "damocles".to_owned(),
                rev: "abc123".to_owned(),
            })
        );
    }

    #[test]
    fn a_closed_unmerged_delivery_is_not_a_merge() {
        assert_eq!(super::merged(&closed(false)), None);
    }

    #[test]
    fn a_merged_pr_on_a_non_close_action_is_not_a_merge() {
        let mut body: serde_json::Value =
            serde_json::from_slice(&closed(true)).expect("fixture is json");
        body["action"] = "label_updated".into();
        assert_eq!(super::merged(body.to_string().as_bytes()), None);
    }

    #[test]
    fn a_merge_into_another_branch_is_not_deployed() {
        let mut body: serde_json::Value =
            serde_json::from_slice(&closed(true)).expect("fixture is json");
        body["pull_request"]["base"]["ref"] = "staging".into();
        assert_eq!(super::merged(body.to_string().as_bytes()), None);
    }

    #[test]
    fn an_open_delivery_is_not_a_merge() {
        assert_eq!(super::merged(&payload("damocles", 5, "open")), None);
    }

    #[test]
    fn a_malformed_payload_leaves_the_cache_unchanged() {
        let cache = ConfigPrCache::new();
        cache.apply_webhook_delivery(&payload("damocles", 5, "open"));
        cache.apply_webhook_delivery(b"not json");
        let status = cache
            .get("damocles")
            .expect("prior entry must survive a bad delivery");
        assert_eq!(status.pr_number, 5);
    }
}