//! User-triggered FIPS upgrade from upstream GitHub releases.
//!
//! Flow (no auto-update, no background polling — user clicks a button):
//!   1. Query GitHub for the latest *stable* release of `jmcorgan/fips`
//!      (`/releases/latest` returns the newest non-prerelease, non-draft
//!      tag, so release candidates like `v0.4.0-rc1` are skipped).
//!   2. Compare its tag (e.g. `v0.3.0`) with the installed daemon version
//!      reported by `fipsctl --version`. A dev/pre-release build of the
//!      same number (`0.3.0-dev`) counts as older than the released tag.
//!   3. Pick the Debian package asset matching the host architecture
//!      (`fips_<ver>_amd64.deb` / `_arm64.deb`) plus `checksums-linux.txt`.
//!   4. Download both, SHA256-verify the .deb against the checksums file.
//!   5. `sudo dpkg -i` the verified .deb, then restart the active fips unit.
//!
//! Upstream began publishing tagged releases with `.deb` artefacts and
//! `checksums-linux.txt` (verified present as of v0.1.0 → v0.4.0-rc1), so
//! the apply path is fully wired against those assets.

use anyhow::{Context, Result};
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};

use super::{service, UPSTREAM_REPO};

const GITHUB_API: &str = "https://api.github.com";
const USER_AGENT: &str = "archipelago-fips-updater";

/// Result of `check()` — what the dashboard renders.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct UpdateCheck {
    /// Currently installed daemon version (from `fipsctl --version`).
    pub current: Option<String>,
    /// Tag of the latest stable upstream release, e.g. `v0.3.0`.
    pub latest_version: String,
    /// True when the installed version is older than `latest_version`.
    pub update_available: bool,
    /// Release channel this check tracked. Currently always "stable".
    pub channel: String,
    /// Browser download URL of the architecture-matched .deb for the
    /// latest release, when one exists (informational; apply() re-resolves).
    pub asset_url: Option<String>,
    /// Human-readable note for the UI.
    pub notes: String,
}

/// One GitHub release as we consume it.
#[derive(Debug, Clone, Deserialize)]
struct Release {
    tag_name: String,
    #[serde(default)]
    prerelease: bool,
    #[serde(default)]
    draft: bool,
    #[serde(default)]
    assets: Vec<Asset>,
}

#[derive(Debug, Clone, Deserialize)]
struct Asset {
    name: String,
    browser_download_url: String,
}

fn http_client() -> Result<reqwest::Client> {
    reqwest::Client::builder()
        .user_agent(USER_AGENT)
        .timeout(std::time::Duration::from_secs(30))
        .build()
        .context("Build HTTP client")
}

/// Debian architecture string for the host (`amd64` / `arm64`). Returns
/// the raw `std::env::consts::ARCH` for anything we don't map, so the
/// asset lookup simply finds nothing and surfaces a clear error.
fn deb_arch() -> &'static str {
    match std::env::consts::ARCH {
        "x86_64" => "amd64",
        "aarch64" => "arm64",
        other => other,
    }
}

/// Query GitHub for the latest stable release and compare to the installed
/// version. Never errors on "no package installed" — that is itself a valid
/// state where an update is available.
pub async fn check() -> Result<UpdateCheck> {
    let current = service::daemon_version().await.ok();
    let client = http_client()?;
    let release = fetch_latest_stable(&client).await?;

    let update_available = match &current {
        Some(v) => version_is_older(v, &release.tag_name),
        None => true,
    };

    let asset_url = release
        .assets
        .iter()
        .find(|a| is_deb_for_arch(&a.name))
        .map(|a| a.browser_download_url.clone());

    let notes = if update_available {
        format!(
            "Update available: {} (installed: {})",
            release.tag_name,
            current.as_deref().unwrap_or("not installed")
        )
    } else {
        format!("Up to date ({})", release.tag_name)
    };

    Ok(UpdateCheck {
        current,
        latest_version: release.tag_name,
        update_available,
        channel: "stable".to_string(),
        asset_url,
        notes,
    })
}

/// Download, verify, and install the latest stable FIPS release, then
/// restart the daemon. Steps: resolve release → match .deb for this arch
/// → download .deb + checksums → SHA256-verify → `sudo dpkg -i` → restart.
pub async fn apply() -> Result<()> {
    let client = http_client()?;
    let release = fetch_latest_stable(&client).await?;

    let deb = release
        .assets
        .iter()
        .find(|a| is_deb_for_arch(&a.name))
        .ok_or_else(|| {
            anyhow::anyhow!(
                "release {} has no .deb for architecture {}",
                release.tag_name,
                deb_arch()
            )
        })?;
    let checksums = release
        .assets
        .iter()
        .find(|a| a.name == "checksums-linux.txt")
        .ok_or_else(|| {
            anyhow::anyhow!("release {} has no checksums-linux.txt", release.tag_name)
        })?;

    // Download the .deb (bytes) and the checksums (text).
    let deb_bytes = client
        .get(&deb.browser_download_url)
        .send()
        .await
        .context("download .deb")?
        .error_for_status()
        .context(".deb download HTTP error")?
        .bytes()
        .await
        .context("read .deb body")?;
    let checksums_text = client
        .get(&checksums.browser_download_url)
        .send()
        .await
        .context("download checksums")?
        .error_for_status()
        .context("checksums download HTTP error")?
        .text()
        .await
        .context("read checksums body")?;

    // Verify SHA256 against the checksums manifest (sha256sum format:
    // "<hex>␠␠<filename>"). The filename column may include a leading
    // "*" (binary mode) or a path prefix, so match on the basename.
    let expected = checksums_text
        .lines()
        .filter_map(|line| {
            let mut parts = line.split_whitespace();
            let hash = parts.next()?;
            let name = parts.next()?.trim_start_matches('*');
            let base = name.rsplit('/').next().unwrap_or(name);
            (base == deb.name).then(|| hash.to_lowercase())
        })
        .next()
        .ok_or_else(|| anyhow::anyhow!("checksums-linux.txt has no entry for {}", deb.name))?;

    let actual = {
        let mut hasher = Sha256::new();
        hasher.update(&deb_bytes);
        hex::encode(hasher.finalize())
    };
    if actual != expected {
        anyhow::bail!(
            "SHA256 mismatch for {}: expected {}, got {}",
            deb.name,
            expected,
            actual
        );
    }

    // Stage the verified .deb in /tmp (shared with the host — the
    // service runs with PrivateTmp=no) and install it.
    let dest = std::env::temp_dir().join(&deb.name);
    tokio::fs::write(&dest, &deb_bytes)
        .await
        .with_context(|| format!("write {}", dest.display()))?;

    // Run dpkg via `systemd-run` rather than `sudo dpkg` directly. The
    // archipelago service runs under `ProtectSystem=strict`, so `/usr`
    // and `/var/lib/dpkg` are read-only *inside the service's mount
    // namespace* — and a `sudo` child inherits that namespace, so a
    // bare `sudo dpkg -i` fails with "Read-only file system" on the
    // dpkg database. `systemd-run` asks PID 1 to launch the command in
    // a fresh transient scope outside our sandbox, where the real
    // (writable) host filesystem is visible. `--wait` blocks until it
    // finishes and propagates the exit status; `--pipe` forwards
    // dpkg's output; `--collect` reaps the unit even on failure.
    //
    // dpkg flags, both load-bearing for this package specifically:
    //   --force-confold:  the fips package ships conffiles under
    //     /etc/fips that archipelago rewrites at install time, so dpkg
    //     hits an interactive "keep/replace?" conffile prompt. With our
    //     closed stdin that aborts the configure step ("EOF on stdin at
    //     conffile prompt") and leaves the package half-unpacked
    //     (status `iU`), which `fips.status` then reports as
    //     `installed:false`. confold = keep our managed config, no prompt.
    //   --force-downgrade: ISO/dev nodes carry `0.3.0-dev-1`, which dpkg
    //     orders as NEWER than the stable tag `0.3.0` (a trailing
    //     `-dev` sorts above the bare release). Moving a dev build onto
    //     the stable line is therefore a dpkg "downgrade"; without this
    //     flag dpkg warns and exits non-zero. Our own version_is_older()
    //     gate already decided this is the wanted direction.
    // DEBIAN_FRONTEND=noninteractive belt-and-suspenders against any
    // other maintainer-script prompt.
    let dpkg = tokio::process::Command::new("sudo")
        .args([
            "-n",
            "systemd-run",
            "--collect",
            "--wait",
            "--quiet",
            "--pipe",
            "--",
            "env",
            "DEBIAN_FRONTEND=noninteractive",
            "dpkg",
            "--force-confold",
            "--force-downgrade",
            "-i",
        ])
        .arg(&dest)
        .output()
        .await
        .context("sudo systemd-run dpkg -i failed to launch")?;
    // Best-effort cleanup regardless of dpkg result.
    let _ = tokio::fs::remove_file(&dest).await;
    if !dpkg.status.success() {
        anyhow::bail!(
            "dpkg -i {} exited {}: {}",
            deb.name,
            dpkg.status,
            String::from_utf8_lossy(&dpkg.stderr).trim()
        );
    }

    // Restart whichever fips unit is supervising the daemon so the new
    // binary takes over.
    let unit = service::active_unit().await;
    service::restart(unit)
        .await
        .with_context(|| format!("restart {} after install", unit))?;
    Ok(())
}

/// `/releases/latest` returns the most recent non-prerelease, non-draft
/// release. We still re-check the flags defensively in case the endpoint
/// or repo settings change.
async fn fetch_latest_stable(client: &reqwest::Client) -> Result<Release> {
    let url = format!("{}/repos/{}/releases/latest", GITHUB_API, UPSTREAM_REPO);
    let resp = client
        .get(&url)
        .header("Accept", "application/vnd.github+json")
        .send()
        .await
        .context("GitHub releases/latest API")?;
    if !resp.status().is_success() {
        anyhow::bail!("GitHub releases/latest API returned {}", resp.status());
    }
    let release: Release = resp.json().await.context("Parse release JSON")?;
    if release.draft || release.prerelease {
        anyhow::bail!(
            "releases/latest returned a {} release ({})",
            if release.draft { "draft" } else { "prerelease" },
            release.tag_name
        );
    }
    Ok(release)
}

fn is_deb_for_arch(name: &str) -> bool {
    name.starts_with("fips_") && name.ends_with(&format!("_{}.deb", deb_arch()))
}

/// Parse the leading `MAJOR.MINOR.PATCH` triple from a version string,
/// plus whether a pre-release suffix (`-dev`, `-rc1`, …) follows it.
fn parse_version(s: &str) -> Option<((u64, u64, u64), bool)> {
    // Take the first whitespace token, drop a leading 'v'.
    let tok = s.split_whitespace().next().unwrap_or(s);
    let tok = tok.strip_prefix('v').unwrap_or(tok);
    // Split off any pre-release / build suffix.
    let (core, rest) = match tok.find(|c: char| c == '-' || c == '+') {
        Some(i) => (&tok[..i], &tok[i..]),
        None => (tok, ""),
    };
    let mut it = core.split('.');
    let major = it.next()?.parse::<u64>().ok()?;
    let minor = it.next().unwrap_or("0").parse::<u64>().ok()?;
    let patch = it.next().unwrap_or("0").parse::<u64>().ok()?;
    let has_prerelease = rest.starts_with('-');
    Some(((major, minor, patch), has_prerelease))
}

/// True when `installed` is strictly older than release tag `latest`.
/// Same numeric triple but `installed` carries a pre-release suffix while
/// `latest` doesn't ⇒ installed is older (e.g. `0.3.0-dev` < `v0.3.0`).
/// If either side can't be parsed, fall back to "differs ⇒ update".
fn version_is_older(installed: &str, latest: &str) -> bool {
    match (parse_version(installed), parse_version(latest)) {
        (Some((ic, ipre)), Some((lc, lpre))) => {
            if ic != lc {
                ic < lc
            } else {
                // Equal cores: a pre-release is older than the final release.
                ipre && !lpre
            }
        }
        _ => {
            // Unparseable: be conservative — offer the update unless the
            // installed string already mentions the latest tag.
            !installed.contains(latest.trim_start_matches('v'))
        }
    }
}

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

    #[test]
    fn test_deb_arch_maps_known() {
        // On the host running tests this is whatever the test arch is;
        // just assert it returns a non-empty, lowercase token.
        let a = deb_arch();
        assert!(!a.is_empty());
        assert_eq!(a, a.to_lowercase());
    }

    #[test]
    fn test_version_older() {
        assert!(version_is_older("0.3.0-dev (rev abc123)", "v0.3.0"));
        assert!(version_is_older("0.2.1", "v0.3.0"));
        assert!(version_is_older("0.3.0-rc1", "v0.3.0"));
        assert!(!version_is_older("0.3.0", "v0.3.0"));
        assert!(!version_is_older("0.4.0", "v0.3.0"));
        assert!(!version_is_older("0.3.1", "v0.3.0"));
    }

    #[test]
    fn test_parse_version() {
        assert_eq!(parse_version("v0.3.0"), Some(((0, 3, 0), false)));
        assert_eq!(parse_version("0.3.0-dev (rev x)"), Some(((0, 3, 0), true)));
        assert_eq!(parse_version("0.4.0-rc1"), Some(((0, 4, 0), true)));
        assert_eq!(parse_version("1.2"), Some(((1, 2, 0), false)));
    }

    #[test]
    fn test_is_deb_for_arch() {
        let arch = deb_arch();
        assert!(is_deb_for_arch(&format!("fips_0.3.0_{}.deb", arch)));
        assert!(!is_deb_for_arch("fips_0.3.0_someotherarch.deb"));
        assert!(!is_deb_for_arch("checksums-linux.txt"));
        assert!(!is_deb_for_arch(&format!(
            "fips-0.3.0-linux-{}.tar.gz",
            arch
        )));
    }

    #[test]
    fn test_update_check_serialises() {
        let uc = UpdateCheck {
            current: Some("0.3.0-dev".to_string()),
            latest_version: "v0.3.0".to_string(),
            update_available: true,
            channel: "stable".to_string(),
            asset_url: Some("https://example/fips_0.3.0_amd64.deb".to_string()),
            notes: "test".to_string(),
        };
        let json = serde_json::to_string(&uc).unwrap();
        assert!(json.contains("latest_version"));
        assert!(json.contains("update_available"));
        assert!(json.contains("stable"));
    }
}