//! hg-edge.mozilla.org changeset ingestion via `json-log` revset queries.
//!
//! Uses the `json-log?rev=author(term)` endpoint which returns changesets
//! by the *author* (not the pusher), so it captures commits landed by
//! sheriffs on behalf of the contributor.
//!
//! Repos are discovered within configured groups (e.g. `build`) via the
//! `/{group}/?style=json` index, plus any individually listed repos
//! (e.g. `mozilla-central`). Once the first successful scan completes
//! (poller state is touched), all subsequent polls are skipped — the
//! data is historical and will not change.

use std::sync::Arc;

use async_trait::async_trait;
use chrono::{DateTime, TimeZone, Utc};
use moments_core::{EventSource, EventWriter, PollerStateStore, SourceError};
use moments_entities::{Event, Source};
use reqwest::{Client, header};
use serde_json::Value;
use tracing::{debug, warn};

const SOURCE_NAME: &str = "hg";
const USER_AGENT: &str = concat!(
    "moments/",
    env!("CARGO_PKG_VERSION"),
    " (+https://rob.tn)"
);
/// Maximum changesets returned per json-log request.
const REV_COUNT: u32 = 500;

#[derive(Clone, Debug)]
pub struct HgConfig {
    pub host: String,
    /// Substrings matched via `author(term)` revset queries.
    pub author_terms: Vec<String>,
    /// Repo groups to scan — each is enumerated via `/{group}/?style=json`.
    pub groups: Vec<String>,
    /// Individual repos to scan (e.g. `mozilla-central`).
    pub repos: Vec<String>,
}

impl Default for HgConfig {
    fn default() -> Self {
        Self {
            host: "hg-edge.mozilla.org".into(),
            author_terms: vec!["rthijssen".into(), "grenade".into()],
            groups: vec!["build".into(), "integration".into()],
            repos: vec!["mozilla-central".into()],
        }
    }
}

pub struct HgSource {
    client: Client,
    writer: Arc<dyn EventWriter>,
    state: Arc<dyn PollerStateStore>,
    config: HgConfig,
}

impl HgSource {
    pub fn new(
        client: Client,
        writer: Arc<dyn EventWriter>,
        state: Arc<dyn PollerStateStore>,
        config: HgConfig,
    ) -> Self {
        Self {
            client,
            writer,
            state,
            config,
        }
    }

    /// Discover repos in a group via `/{group}/?style=json`.
    async fn discover_repos(&self, group: &str) -> Result<Vec<String>, SourceError> {
        let url = format!("https://{}/{}/?style=json", self.config.host, group);
        let resp = self
            .client
            .get(&url)
            .header(header::USER_AGENT, USER_AGENT)
            .send()
            .await
            .map_err(|e| SourceError::Http(e.to_string()))?;
        if !resp.status().is_success() {
            warn!(group, status = %resp.status(), "failed to discover repos in group");
            return Ok(vec![]);
        }
        let body: Value = resp
            .json()
            .await
            .map_err(|e| SourceError::Parse(e.to_string()))?;
        Ok(body
            .get("entries")
            .and_then(Value::as_array)
            .map(|entries| {
                entries
                    .iter()
                    .filter_map(|e| {
                        e.get("name")
                            .and_then(Value::as_str)
                            .map(|name| format!("{group}/{name}"))
                    })
                    .collect()
            })
            .unwrap_or_default())
    }

    fn log_url(&self, repo: &str, author_term: &str) -> String {
        format!(
            "https://{}/{}/json-log?rev=author({})&style=json&revcount={}",
            self.config.host, repo, author_term, REV_COUNT
        )
    }

    async fn scan_repo(&self, repo: &str) -> Result<usize, SourceError> {
        let mut all_events = Vec::new();
        for term in &self.config.author_terms {
            let url = self.log_url(repo, term);
            let resp = self
                .client
                .get(&url)
                .header(header::USER_AGENT, USER_AGENT)
                .send()
                .await
                .map_err(|e| SourceError::Http(e.to_string()))?;
            if !resp.status().is_success() {
                return Err(SourceError::Http(format!("{} GET {}", resp.status(), url)));
            }
            let body: Value = resp
                .json()
                .await
                .map_err(|e| SourceError::Parse(e.to_string()))?;

            if let Some(entries) = body.get("entries").and_then(Value::as_array) {
                for entry in entries {
                    let node = entry.get("node").and_then(Value::as_str).unwrap_or("");
                    if node.is_empty() {
                        continue;
                    }
                    let occurred_at = entry
                        .get("date")
                        .and_then(Value::as_array)
                        .and_then(|a| parse_hg_date(a))
                        .unwrap_or_else(Utc::now);

                    let mut payload = entry.clone();
                    if let Some(obj) = payload.as_object_mut() {
                        obj.insert("_repo".into(), Value::String(repo.into()));
                        obj.insert(
                            "_host".into(),
                            Value::String(self.config.host.clone()),
                        );
                    }
                    all_events.push(Event {
                        id: format!("hg:{repo}:{node}"),
                        source: Source::Hg,
                        action: "Commit".into(),
                        occurred_at,
                        public: true,
                        payload,
                    });
                }
            }
        }
        Ok(self.writer.upsert_events(&all_events).await?)
    }
}

#[async_trait]
impl EventSource for HgSource {
    fn name(&self) -> &'static str {
        SOURCE_NAME
    }

    async fn poll(&self) -> Result<usize, SourceError> {
        // hg repos are archived — one complete scan is sufficient.
        if self.state.load(SOURCE_NAME).await?.is_some() {
            debug!("hg already backfilled, skipping");
            return Ok(0);
        }

        let mut repos: Vec<String> = self.config.repos.clone();
        for group in &self.config.groups {
            let discovered = self.discover_repos(group).await?;
            debug!(group, repos = discovered.len(), "discovered hg repos");
            repos.extend(discovered);
        }

        let mut total = 0usize;
        for repo in &repos {
            match self.scan_repo(repo).await {
                Ok(n) => {
                    if n > 0 {
                        debug!(repo, ingested = n, "hg repo scan complete");
                    }
                    total += n;
                }
                Err(e) => {
                    warn!(repo, error = %e, "hg repo scan failed; continuing");
                }
            }
        }
        self.state.touch(SOURCE_NAME).await?;
        debug!(ingested = total, "hg backfill complete");
        Ok(total)
    }
}

/// Parse a hgweb date array `[seconds, tz_offset_secs]` into UTC.
fn parse_hg_date(arr: &[Value]) -> Option<DateTime<Utc>> {
    let secs = arr.first()?.as_f64()? as i64;
    Utc.timestamp_opt(secs, 0).single()
}

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

    #[test]
    fn parse_hg_date_handles_seconds() {
        let arr = vec![Value::from(1_700_000_000_f64), Value::from(0_f64)];
        let dt = parse_hg_date(&arr).expect("parses");
        assert_eq!(dt.timestamp(), 1_700_000_000);
    }

    #[test]
    fn log_url_uses_revset_author_query() {
        let src = HgSource {
            client: Client::new(),
            writer: Arc::new(NoopWriter),
            state: Arc::new(NoopState),
            config: HgConfig::default(),
        };
        let url = src.log_url("mozilla-central", "thijssen");
        assert!(url.contains("json-log?rev=author(thijssen)"));
        assert!(url.contains("revcount=500"));
    }

    // Tiny stub impls just so we can construct an HgSource for unit tests.
    struct NoopWriter;
    #[async_trait]
    impl EventWriter for NoopWriter {
        async fn upsert_events(
            &self,
            _events: &[Event],
        ) -> Result<usize, moments_core::StoreError> {
            Ok(0)
        }
        async fn upsert_repo_languages(
            &self,
            _languages: &[moments_entities::RepoLanguage],
        ) -> Result<usize, moments_core::StoreError> {
            Ok(0)
        }
    }
    struct NoopState;
    #[async_trait]
    impl PollerStateStore for NoopState {
        async fn load(
            &self,
            _source: &str,
        ) -> Result<Option<moments_core::PollerState>, moments_core::StoreError> {
            Ok(None)
        }
        async fn save(
            &self,
            _source: &str,
            _etag: Option<&str>,
            _last_modified: Option<DateTime<Utc>>,
        ) -> Result<(), moments_core::StoreError> {
            Ok(())
        }
        async fn touch(&self, _source: &str) -> Result<(), moments_core::StoreError> {
            Ok(())
        }
    }
}