//! github.com's half of the poller — the protocol code that only this
//! binary links.
//!
//! Plain `reqwest`: the typed Forgejo client cannot address a different
//! API surface, and GitHub's payloads differ enough (string thread ids,
//! its own `subject.type` vocabulary, no `subject.state`) that the
//! tolerant parse in the shared library is the right common layer, not
//! the client.

use std::sync::atomic::{AtomicBool, Ordering};

use hive_forge_notify::notify::UNREAD_FETCH_LIMIT;
use hive_forge_notify::source::Source;
use tracing::{debug, warn};

/// GitHub's REST base. `docs/integrations/github.md` scopes the integration to
/// github.com only — the same constraint the `gh` wrapper and the git
/// credential helper already carry — so this is a constant rather than
/// another operator-entered URL.
pub const API_BASE: &str = "https://api.github.com";

/// Value of the `X-GitHub-Api-Version` header. GitHub dates its REST
/// versions; pinning one means a future default bump cannot silently
/// reshape the payloads this daemon parses.
const API_VERSION: &str = "2022-11-28";

/// `User-Agent` for GitHub calls. GitHub rejects requests without one.
const USER_AGENT: &str = "hyperhive-forge-notify";

/// github.com, via a personal access token.
pub struct GithubSource {
    /// [`API_BASE`] everywhere but the tests, which point it at a local stub.
    api_base: String,
    token: String,
    /// Set once a 401 has been logged at `warn`. A source holds one token,
    /// so this caps the warning at one per token value.
    warned_unauthorized: AtomicBool,
}

impl GithubSource {
    pub fn new(api_base: &str, token: &str) -> Self {
        Self {
            api_base: api_base.to_owned(),
            token: token.to_owned(),
            warned_unauthorized: AtomicBool::new(false),
        }
    }
}

impl Source for GithubSource {
    /// Namespaced, so a github thread id cannot collide with a forge one
    /// on a shared todo key.
    fn key_prefix(&self) -> &'static str {
        "gh:"
    }

    fn name(&self) -> &'static str {
        "github"
    }

    /// `Bearer`, not Forgejo's `token` — plus the version and user-agent
    /// headers GitHub requires. Sending the wrong scheme does not error:
    /// it authenticates as *nobody* and silently drops to the
    /// unauthenticated rate limit, which is why the rate-limit header is
    /// the only cheap way to tell the two apart.
    fn authorize(&self, rb: reqwest::RequestBuilder) -> reqwest::RequestBuilder {
        rb.header("Authorization", format!("Bearer {}", self.token))
            .header("Accept", "application/vnd.github+json")
            .header("X-GitHub-Api-Version", API_VERSION)
            .header("User-Agent", USER_AGENT)
    }

    async fn own_login(&self, client: &reqwest::Client) -> String {
        let url = format!("{}/user", self.api_base);
        let Ok(resp) = self.authorize(client.get(&url)).send().await else {
            return String::new();
        };
        if !resp.status().is_success() {
            return String::new();
        }
        resp.json::<serde_json::Value>()
            .await
            .ok()
            .and_then(|v| v["login"].as_str().map(str::to_owned))
            .unwrap_or_default()
    }

    async fn list_unread(
        &self,
        client: &reqwest::Client,
    ) -> Option<(Vec<serde_json::Value>, Option<u64>)> {
        let url = format!(
            "{}/notifications?all=false&per_page={UNREAD_FETCH_LIMIT}",
            self.api_base
        );
        let resp = match self.authorize(client.get(&url)).send().await {
            Ok(resp) => resp,
            Err(e) => {
                debug!("forge_notify: github poll request failed: {e}");
                return None;
            }
        };
        // Read the cadence hint before the status check: GitHub sends it
        // on an empty page too, and that is exactly the tick where we
        // most want to learn we are polling too fast.
        let poll_interval = resp
            .headers()
            .get("x-poll-interval")
            .and_then(|v| v.to_str().ok())
            .and_then(|v| v.parse::<u64>().ok());
        let status = resp.status();
        if !status.is_success() {
            // 403 with a rate-limit body and 401 on a revoked PAT are
            // both "stay quiet and retry", not fatal: the unit must not
            // restart-loop on a credential the operator fixes out of band.
            // A 401 is the one an operator must act on, so it is a `warn`.
            if status == reqwest::StatusCode::UNAUTHORIZED
                && !self.warned_unauthorized.swap(true, Ordering::Relaxed)
            {
                warn!(
                    "forge_notify: github refused the PAT (401) — no notifications \
                     until github-token holds a working one"
                );
            } else {
                debug!("forge_notify: github poll status {status}");
            }
            return None;
        }
        let raw = resp.text().await.ok()?;

        match serde_json::from_str(&raw) {
            Ok(values) => Some((values, poll_interval)),
            Err(e) => {
                warn!("forge_notify: github response parse error: {e}");
                None
            }
        }
    }

    async fn mark_read(&self, client: &reqwest::Client, id: &str) {
        let url = format!("{}/notifications/threads/{id}", self.api_base);
        match self.authorize(client.patch(&url)).send().await {
            Ok(resp) if resp.status().is_success() => {
                debug!(%id, "forge_notify: marked read (github)");
            }
            Ok(resp) => {
                warn!(%id, status = %resp.status(), "forge_notify: github mark-read non-2xx — notification will resurface");
            }
            Err(e) => {
                warn!(%id, error = ?e, "forge_notify: github mark-read failed — notification will resurface");
            }
        }
    }
}