//! `$FLOW_HOME` (default `~/.local/share/flow`): the pinned parts of each

//! isolation tier, rootfs images by hash, scratch space and the runner's

//! configuration, all described by `flow.toml`.

//!

//! ```toml

//! [microvm]

//! firecracker = { path = "bin/firecracker", blake3 = "…" }

//! kernel = { path = "kernel/vmlinux", blake3 = "…" }

//! init = { path = "bin/flow-init", blake3 = "…" }

//!

//! [runner]                       # only for `flow runner`

//! hub = "https://hub.example:7343"

//! token = "…"                    # a runner token from the hub's [flow] runner_tokens

//! ca = "/path/to/hub-ca.pem"     # when the hub's certificate is self-signed

//! name = "earth-1"

//! ```

//!

//! A runner signs its receipts with a composite key kept beside `flow.toml`

//! (`runner.key`, `runner.identity`), made on first start.

use anyhow::{bail, Context, Result};

use serde::Deserialize;

use std::collections::HashMap;

use std::path::{Path, PathBuf};

use std::sync::Mutex;

#[derive(Clone, Debug, Deserialize)]

pub struct Pinned {

    pub path: PathBuf,

    pub blake3: String,

}

#[derive(Clone, Debug, Deserialize)]

pub struct MicrovmConfig {

    pub firecracker: Pinned,

    pub kernel: Pinned,

    pub init: Pinned,

}

/// Where `flow runner register` keeps the runner's hub and credential.

pub const RUNNER_TOML: &str = "runner.toml";

#[derive(Clone, Debug, Deserialize)]

pub struct RunnerConfig {

    pub hub: String,

    pub token: String,

    pub ca: Option<PathBuf>,

    pub name: Option<String>,

    /// Jobs run at once (default 1).

    #[serde(default)]

    pub max_jobs: Option<usize>,

    /// Labels the runner offers, e.g. `gpu`, `big-disk`.

    #[serde(default)]

    pub labels: Vec<String>,

    /// Memory (MiB) and vCPUs the jobs running at once may use together.

    #[serde(default)]

    pub memory_mib: Option<u32>,

    #[serde(default)]

    pub cpus: Option<u32>,

}

#[derive(Clone, Debug, Default, Deserialize)]

pub struct Config {

    pub microvm: Option<MicrovmConfig>,

    pub runner: Option<RunnerConfig>,

}

pub struct Home {

    pub root: PathBuf,

    pub config: Config,

    /// Files already verified, by path, with the (len, mtime) they had then.

    verified: Mutex<HashMap<PathBuf, (u64, std::time::SystemTime)>>,

}

impl Home {

    pub fn locate(explicit: Option<&Path>) -> Result<Home> {

        let root = match explicit {

            Some(p) => p.to_path_buf(),

            None => match std::env::var_os("FLOW_HOME") {

                Some(p) => PathBuf::from(p),

                None => PathBuf::from(std::env::var_os("HOME").context("HOME is not set")?).join(".local/share/flow"),

            },

        };

        let file = root.join("flow.toml");

        let mut config: Config = if file.is_file() {

            let text = std::fs::read_to_string(&file).with_context(|| format!("read {}", file.display()))?;

            toml::from_str(&text).with_context(|| format!("parse {}", file.display()))?

        } else {

            Config::default()

        };

        // `flow runner register` writes the runner's hub and credential to

        // runner.toml, which stands in for a [runner] section flow.toml lacks.

        let registered = root.join(RUNNER_TOML);

        if config.runner.is_none() && registered.is_file() {

            let text = std::fs::read_to_string(&registered).with_context(|| format!("read {}", registered.display()))?;

            config.runner = Some(toml::from_str(&text).with_context(|| format!("parse {}", registered.display()))?);

        }

        for d in ["cas", "work", "repos"] {

            std::fs::create_dir_all(root.join(d)).with_context(|| format!("create {}", root.join(d).display()))?;

        }

        Ok(Home { root, config, verified: Mutex::new(HashMap::new()) })

    }

    pub fn resolve(&self, p: &Path) -> PathBuf {

        if p.is_absolute() {

            p.to_path_buf()

        } else {

            self.root.join(p)

        }

    }

    /// Where a rootfs image with this hash lives.

    pub fn rootfs(&self, hash: &str) -> PathBuf {

        self.root.join("cas").join(format!("{hash}.ext4"))

    }

    /// The rootfs images this home holds: the hashes of `cas/*.ext4`.

    pub fn images(&self) -> Vec<String> {

        let Ok(dir) = std::fs::read_dir(self.root.join("cas")) else {

            return Vec::new();

        };

        let mut out: Vec<String> = dir

            .filter_map(|e| {

                let name = e.ok()?.file_name().into_string().ok()?;

                let hash = name.strip_suffix(".ext4")?;

                (hash.len() == 64 && hash.chars().all(|c| c.is_ascii_hexdigit())).then(|| hash.to_string())

            })

            .collect();

        out.sort();

        out

    }

    /// A pinned file, checked against its BLAKE3 before use (again only

    /// when its size or modification time changed since).

    pub fn verified(&self, path: &Path, blake3_hex: &str) -> Result<PathBuf> {

        let meta = std::fs::metadata(path).with_context(|| format!("{} is missing", path.display()))?;

        let stamp = (meta.len(), meta.modified()?);

        if self.verified.lock().unwrap().get(path) == Some(&stamp) {

            return Ok(path.to_path_buf());

        }

        let got = hash_file(path)?;

        if got != blake3_hex {

            bail!("{} has BLAKE3 {got}, but {blake3_hex} is pinned", path.display());

        }

        self.verified.lock().unwrap().insert(path.to_path_buf(), stamp);

        Ok(path.to_path_buf())

    }

}

pub fn hash_file(path: &Path) -> Result<String> {

    let mut h = blake3::Hasher::new();

    h.update_reader(std::fs::File::open(path).with_context(|| format!("open {}", path.display()))?)?;

    Ok(h.finalize().to_hex().to_string())

}

/// The key a runner signs receipts with (Oxygen spec §14.6).

pub struct RunnerKey {

    pub identity: oxy_core::identity::Identity,

    pub secret: oxy_core::identity::SecretKey,

}

impl Home {

    /// The runner's key, made on first use as `runner.key` (owner-only)

    /// and `runner.identity`, named `name`.

    pub fn runner_key(&self, name: &str) -> Result<RunnerKey> {

        use oxy_core::identity::{Identity, SecretKey};

        let key_path = self.root.join("runner.key");

        let id_path = self.root.join("runner.identity");

        if key_path.exists() {

            let (key, secret) = SecretKey::decode(&std::fs::read(&key_path)?).context("runner.key")?;

            let identity = Identity::decode(&std::fs::read(&id_path)?).context("runner.identity")?;

            if identity.hash() != key {

                bail!("runner.identity does not belong to runner.key");

            }

            return Ok(RunnerKey { identity, secret });

        }

        let secret = SecretKey::generate();

        let now = std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).map(|d| d.as_millis() as u64).unwrap_or(0);

        let identity = secret.identity(&format!("{name} (OxygenFlow runner)"), "", now);

        std::fs::write(&id_path, identity.encode())?;

        let tmp = self.root.join("runner.key.tmp");

        {

            use std::io::Write;

            use std::os::unix::fs::OpenOptionsExt;

            let mut f = std::fs::OpenOptions::new().write(true).create(true).truncate(true).mode(0o600).open(&tmp)?;

            f.write_all(&secret.encode(&identity.hash()))?;

            f.sync_all()?;

        }

        std::fs::rename(&tmp, &key_path)?;

        Ok(RunnerKey { identity, secret })

    }

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn the_runner_key_is_made_once_and_kept_private() {

        use std::os::unix::fs::PermissionsExt;

        let dir = tempfile::tempdir().unwrap();

        let home = Home::locate(Some(dir.path())).unwrap();

        let a = home.runner_key("earth-1").unwrap();

        assert_eq!(a.identity.name, "earth-1 (OxygenFlow runner)");

        let mode = std::fs::metadata(dir.path().join("runner.key")).unwrap().permissions().mode();

        assert_eq!(mode & 0o777, 0o600);

        let b = home.runner_key("renamed").unwrap();

        assert_eq!(a.identity, b.identity, "the same key after a restart");

        let sig = b.secret.sign(oxy_core::identity::Domain::Attest, &b.identity.hash(), &oxy_core::hash::ObjectRef([1; 32]));

        oxy_core::identity::verify(&a.identity, &sig, oxy_core::identity::Domain::Attest, &oxy_core::hash::ObjectRef([1; 32])).unwrap();

    }

}