//! `$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"

//! ```

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,

}

#[derive(Clone, Debug, Deserialize)]

pub struct RunnerConfig {

    pub hub: String,

    pub token: String,

    pub ca: Option<PathBuf>,

    pub name: Option<String>,

}

#[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 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()

        };

        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"))

    }

    /// 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 mut got = hash_file(path)?;

        if got != blake3_hex {

            // The read may have come from bad cached pages rather than the

            // disk (oxygenflow#22: a RAM fault on Earth failed every job for

            // hours while the file was intact): drop the file's pages and

            // read it again from the disk before giving up.

            drop_cached(path);

            let again = hash_file(path)?;

            if again == blake3_hex {

                eprintln!(

                    "warning: {} hashed {got} from the page cache but {again} from the disk: the cached copy was bad (check this machine's memory)",

                    path.display()

                );

            }

            got = again;

        }

        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())

    }

}

/// Ask the kernel to forget a file's cached pages, so the next read comes

/// from the disk. Best effort: dirty pages and other platforms stay.

fn drop_cached(path: &Path) {

    #[cfg(target_os = "linux")]

    if let Ok(f) = std::fs::File::open(path) {

        use std::os::fd::AsRawFd;

        // SAFETY: a valid descriptor; the advice only affects caching.

        unsafe {

            libc::posix_fadvise(f.as_raw_fd(), 0, 0, libc::POSIX_FADV_DONTNEED);

        }

    }

    #[cfg(not(target_os = "linux"))]

    let _ = path;

}

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())

}