//! Runner updates (oxygenhub#322, OxygenFlow docs/jetstream.md §8.2):
//! which build each runner should run, under the policy the site, its
//! owner, its test groups and the runner itself set, the nearest setting
//! winning. Off unless some level turns updates on.

use crate::db::runner_updates::{self as rdb, Group, Policy};
use crate::db::runners::Runner;
use crate::db::{self, Pool};
use flow_core::api::{UpdateOffer, UpdatePolicy};
use std::collections::{BTreeSet, HashMap};

/// The site setting naming the repository whose releases carry runner
/// builds (`owner/name`), each an asset `flow-OS-ARCH`.
pub const SETTING_REPO: &str = "runner_updates_repo";

/// A runner's place, 0 to 99, for percentage groups: a stable hash of its
/// id, so a group's share is the same machines every rollout, and a
/// smaller share sits inside a larger one.
pub fn bucket(runner_id: i64) -> i64 {
    let h = blake3::hash(format!("runner {runner_id}").as_bytes());
    let mut first = [0u8; 8];
    first.copy_from_slice(&h.as_bytes()[..8]);
    (u64::from_le_bytes(first) % 100) as i64
}

/// Whether a group may hold the runner at all: a site group holds any, an
/// owner's group only that owner's runners.
pub fn in_reach(g: &Group, r: &Runner) -> bool {
    g.owner.is_empty() || g.owner == r.scope_owner
}

/// Every level's settings and the groups, read once.
#[derive(Clone, Debug, Default)]
pub struct Levels {
    pub policies: HashMap<(String, String), Policy>,
    pub groups: Vec<Group>,
    /// Chosen members, as (group, runner).
    pub chosen: BTreeSet<(i64, i64)>,
}

impl Levels {
    pub async fn load(pool: &Pool) -> sqlx::Result<Levels> {
        let policies = rdb::policies(pool).await?.into_iter().map(|p| ((p.scope.clone(), p.key.clone()), p)).collect();
        Ok(Levels { policies, groups: rdb::groups(pool).await?, chosen: rdb::members(pool).await?.into_iter().collect() })
    }

    pub fn member(&self, g: &Group, r: &Runner) -> bool {
        in_reach(g, r) && (self.chosen.contains(&(g.id, r.id)) || g.percent.is_some_and(|p| bucket(r.id) < p))
    }

    /// The runner's groups, nearest first: its owner's, then the site's.
    pub fn groups_of(&self, r: &Runner) -> Vec<&Group> {
        let mut gs: Vec<&Group> = self.groups.iter().filter(|g| self.member(g, r)).collect();
        gs.sort_by_key(|g| (g.owner.is_empty(), g.name.clone()));
        gs
    }

    fn get(&self, scope: &str, key: &str) -> Option<&Policy> {
        self.policies.get(&(scope.to_string(), key.to_string()))
    }

    /// The levels that apply to `r`, nearest first, each with its name.
    fn chain(&self, r: &Runner) -> Vec<(String, &Policy)> {
        let mut out = vec![];
        if let Some(p) = self.get("runner", &r.id.to_string()) {
            out.push(("runner".to_string(), p));
        }
        for g in self.groups_of(r) {
            if let Some(p) = self.get("group", &g.id.to_string()) {
                out.push((format!("group {}", g.name), p));
            }
        }
        if !r.scope_owner.is_empty() {
            if let Some(p) = self.get("owner", &r.scope_owner) {
                out.push((format!("owner {}", r.scope_owner), p));
            }
        }
        if let Some(p) = self.get("site", "") {
            out.push(("site".to_string(), p));
        }
        out
    }

    /// The policy for `r`: each setting from the nearest level that sets it.
    pub fn resolve(&self, r: &Runner) -> UpdatePolicy {
        let chain = self.chain(r);
        fn pick<T>(chain: &[(String, &Policy)], f: impl Fn(&Policy) -> Option<T>) -> (Option<T>, String) {
            chain.iter().find_map(|(name, p)| f(p).map(|v| (Some(v), name.clone()))).unwrap_or((None, "default".into()))
        }
        let (updates, u_from) = pick(&chain, |p| p.updates);
        let (channel, c_from) = pick(&chain, |p| p.channel.clone().filter(|c| !c.is_empty()));
        let (window, w_from) = pick(&chain, |p| Some((p.window_from? as u8, p.window_to? as u8)));
        let (dry_run, d_from) = pick(&chain, |p| p.dry_run);
        UpdatePolicy {
            updates: updates.unwrap_or(false),
            channel: channel.unwrap_or_else(|| "stable".into()),
            window,
            dry_run: dry_run.unwrap_or(false),
            from: vec![u_from, c_from, w_from, d_from],
        }
    }
}

/// Whether hour `h` (UTC) falls in `[from, to)`, which may wrap past midnight.
pub fn in_window((from, to): (u8, u8), h: u8) -> bool {
    if from <= to {
        from <= h && h < to
    } else {
        h >= from || h < to
    }
}

/// Parse `02-05` (hours, UTC) as a window; blank is none.
pub fn parse_window(s: &str) -> Result<Option<(u8, u8)>, String> {
    let s = s.trim();
    if s.is_empty() {
        return Ok(None);
    }
    let (a, b) = s.split_once('-').ok_or("a window is two hours, from-to, e.g. 02-05")?;
    let hour = |x: &str| x.trim().trim_end_matches(":00").parse::<u8>().ok().filter(|h| *h < 24);
    match (hour(a), hour(b)) {
        (Some(a), Some(b)) if a != b => Ok(Some((a, b))),
        _ => Err("a window is two different hours from 0 to 23, from-to, e.g. 02-05".into()),
    }
}

/// A channel as written: `stable`, `canary`, or a version.
pub fn valid_channel(c: &str) -> bool {
    matches!(c, "stable" | "canary") || (!c.is_empty() && c.split('.').all(|p| !p.is_empty() && p.bytes().all(|b| b.is_ascii_digit())))
}

/// The version in a runner's or a tag's words: `0.3.1 (build)` → `0.3.1`,
/// `v0.3.1` → `0.3.1`.
pub fn version_of(s: &str) -> String {
    s.split_whitespace().next().unwrap_or("").trim_start_matches('v').to_string()
}

fn older(a: &str, b: &str) -> bool {
    let parts = |v: &str| v.split('.').map(|p| p.parse::<u64>().unwrap_or(0)).collect::<Vec<_>>();
    parts(a) < parts(b)
}

/// The version a runner's report says rolled back: `rolled back from flow
/// 0.4.0 to 0.3.1: …` (the runner's words, oxygenflow spec §11.5.3) → `0.4.0`.
pub fn rolled_back_version(note: &str) -> Option<String> {
    let v = note.strip_prefix("rolled back from flow ")?.split_whitespace().next()?;
    v.split('.').all(|p| !p.is_empty() && p.bytes().all(|b| b.is_ascii_digit())).then(|| v.to_string())
}

/// The release asset a runner on `os` and `arch` runs: `flow-linux-x86_64`,
/// `flow-windows-x86_64.exe`.
pub fn asset_for(os: &str, arch: &str) -> String {
    format!("flow-{os}-{arch}{}", if os == "windows" { ".exe" } else { "" })
}

/// The build `r` should install under `policy` at hour `hour` (UTC), or
/// why there is none.
pub async fn offer(pool: &Pool, r: &Runner, policy: &UpdatePolicy, hour: u8) -> sqlx::Result<(Option<UpdateOffer>, String)> {
    if !policy.updates {
        return Ok((None, format!("updates are off ({})", policy.from[0])));
    }
    let Some(spec) = db::accounts::setting(pool, SETTING_REPO).await?.filter(|s| !s.trim().is_empty()) else {
        return Ok((None, "no runner releases repository is set (Admin › Runners › Updates)".into()));
    };
    let Some((owner, name)) = spec.trim().split_once('/') else {
        return Ok((None, format!("the runner releases repository {spec:?} is not owner/name")));
    };
    let Some(repo) = db::repos::get(pool, owner, name).await? else {
        return Ok((None, format!("the runner releases repository {spec} does not exist")));
    };
    let releases = db::releases::list(pool, repo.id).await?;
    let release = match policy.channel.as_str() {
        "stable" => releases.iter().find(|x| !x.prerelease),
        "canary" => releases.first(),
        v => releases.iter().find(|x| version_of(&x.tag) == v),
    };
    let Some(release) = release else {
        return Ok((None, format!("{spec} has no release for the {} channel", policy.channel)));
    };
    let (want, have) = (version_of(&release.tag), version_of(&r.version));
    if want == have {
        return Ok((None, format!("up to date: flow {have} ({} channel)", policy.channel)));
    }
    if let Some(h) = rdb::held(pool, &want).await? {
        return Ok((
            None,
            format!("flow {want} is held: it rolled back on {} ({}); lift the hold on Admin › Runners › Updates", h.runner, h.why),
        ));
    }
    let going_back = older(&want, &have);
    if going_back && matches!(policy.channel.as_str(), "stable" | "canary") {
        return Ok((None, format!("runs flow {have}, newer than the {} channel's {want}", policy.channel)));
    }
    let file = asset_for(&r.os, &r.arch);
    let assets = db::releases::assets(pool, release.id).await?;
    let Some(a) = assets.iter().find(|a| a.name == file) else {
        return Ok((None, format!("{spec} {} has no {file}", release.tag)));
    };
    if let Some(w) = policy.window.filter(|w| !in_window(*w, hour)) {
        return Ok((None, format!("flow {want} waits for its window, {:02}:00–{:02}:00 UTC", w.0, w.1)));
    }
    let note = format!(
        "flow {want} ({} channel){}",
        policy.channel,
        if policy.dry_run { ": dry run, check it and say what would happen" } else { "" }
    );
    Ok((
        Some(UpdateOffer {
            version: want,
            tag: release.tag.clone(),
            asset: a.name.clone(),
            url: format!("/{owner}/{name}/asset/{}/{}", a.id, a.name),
            blake3: a.hash.clone(),
            size: a.size as u64,
            older: going_back,
        }),
        note,
    ))
}

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

    fn runner(id: i64, owner: &str) -> Runner {
        Runner { id, scope_owner: owner.into(), version: "0.3.1 (build)".into(), ..Runner::default() }
    }

    #[test]
    fn a_smaller_share_sits_inside_a_larger_one_and_is_about_its_size() {
        let ten: Vec<i64> = (1..=1000).filter(|id| bucket(*id) < 10).collect();
        let fifty: Vec<i64> = (1..=1000).filter(|id| bucket(*id) < 50).collect();
        assert!(ten.iter().all(|id| fifty.contains(id)));
        assert!((60..=140).contains(&ten.len()), "{}", ten.len());
        assert_eq!(bucket(7), bucket(7), "stable");
    }

    #[test]
    fn the_nearest_level_wins_each_setting() {
        let mut l = Levels::default();
        let pol = |scope: &str, key: &str, f: &dyn Fn(&mut Policy)| {
            let mut p = Policy { scope: scope.into(), key: key.into(), ..Policy::default() };
            f(&mut p);
            ((scope.to_string(), key.to_string()), p)
        };
        l.policies.extend([
            pol("site", "", &|p| {
                p.updates = Some(false);
                p.channel = Some("stable".into());
            }),
            pol("owner", "acme", &|p| p.updates = Some(true)),
            pol("group", "1", &|p| p.channel = Some("canary".into())),
            pol("runner", "3", &|p| p.updates = Some(false)),
        ]);
        l.groups.push(Group { id: 1, owner: "acme".into(), name: "canary".into(), percent: None, created_ms: 0 });
        l.chosen.insert((1, 2));
        l.chosen.insert((1, 9));

        let site_runner = l.resolve(&runner(1, ""));
        assert!(!site_runner.updates, "off at the site");
        assert_eq!(site_runner.from, ["site", "site", "default", "default"]);

        let canary = l.resolve(&runner(2, "acme"));
        assert!(canary.updates && canary.channel == "canary");
        assert_eq!(canary.from[..2], ["owner acme".to_string(), "group canary".to_string()]);

        let held = l.resolve(&runner(3, "acme"));
        assert!(!held.updates, "the runner's own setting wins");
        assert_eq!(held.channel, "stable");

        assert!(l.groups_of(&runner(9, "other")).is_empty(), "an owner's group holds only its own runners");
        assert!(!Levels::default().resolve(&runner(4, "")).updates, "off unless chosen");
    }

    #[test]
    fn a_percentage_group_takes_its_share_of_the_runners_in_reach() {
        let mut l = Levels::default();
        l.groups.push(Group { id: 5, owner: String::new(), name: "farm 20%".into(), percent: Some(20), created_ms: 0 });
        let n = (1..=500).filter(|id| !l.groups_of(&runner(*id, "")).is_empty()).count();
        assert!((60..=140).contains(&n), "{n}");
    }

    #[test]
    fn windows_and_channels_read_as_written() {
        assert_eq!(parse_window("02-05"), Ok(Some((2, 5))));
        assert_eq!(parse_window(" 22:00-04:00 "), Ok(Some((22, 4))));
        assert_eq!(parse_window(""), Ok(None));
        assert!(parse_window("5").is_err() && parse_window("3-3").is_err() && parse_window("1-24").is_err());
        assert!(in_window((2, 5), 2) && in_window((2, 5), 4) && !in_window((2, 5), 5));
        assert!(in_window((22, 4), 23) && in_window((22, 4), 1) && !in_window((22, 4), 12));
        assert!(valid_channel("stable") && valid_channel("canary") && valid_channel("0.3.4"));
        assert!(!valid_channel("latest") && !valid_channel("0.3.") && !valid_channel(""));
        assert_eq!(version_of("v0.3.2"), "0.3.2");
        assert_eq!(version_of("0.3.1 (local build)"), "0.3.1");
        assert_eq!(asset_for("linux", "riscv64"), "flow-linux-riscv64");
        assert_eq!(asset_for("windows", "x86_64"), "flow-windows-x86_64.exe");
        assert_eq!(
            rolled_back_version("rolled back from flow 0.4.0 to 0.3.1: 3 starts without reaching the hub").as_deref(),
            Some("0.4.0")
        );
        assert_eq!(rolled_back_version("runs flow 0.4.0 (was 0.3.1); proven"), None);
    }
}