assist-rs 0.1.0

//! Data file management for ASSIST.
//!
//! ASSIST needs three kinds of files to run end-to-end:
//!
//! 1. Planetary + asteroid ephemerides (`de440.bsp`, `sb441-n16.bsp`)
//! 2. MPC observatory codes (`obscodes_extended.json`) for observer lookups
//! 3. Earth orientation binary PCK kernels (`earth_*.bpc`) for sub-mas
//!    ITRF93 → ICRF rotation of ground-based observatories. Three kernels
//!    together span 1962 → ~2125: historical, current high-precision, and
//!    long-term predict.
//!
//! [`DataManager`] downloads these to a local cache directory on demand and
//! returns resolved paths for [`crate::Ephemeris::from_paths`],
//! [`crate::ObservatoryTable::from_json`], and
//! [`crate::earth_orientation::EarthOrientation::from_paths`].
//!
//! # Default data directory
//!
//! `$ASSIST_DATA_DIR` if set, otherwise `$XDG_CACHE_HOME/assist-rs/` or
//! `~/.cache/assist-rs/`.
//!
//! # Example
//!
//! ```no_run
//! use assist_rs::data::DataManager;
//!
//! let dm = DataManager::new();
//! let paths = dm.ensure_ready()?;
//! # Ok::<(), assist_rs::data::DataError>(())
//! ```
//!
//! Each downloaded file gets a `<filename>.meta.json` sidecar with MD5 hash,
//! Content-Length, and Last-Modified from the HTTP response. On subsequent
//! runs, non-static files (the MPC obscodes file and
//! `earth_latest_high_prec.bpc`) are checked via HEAD and re-downloaded if
//! the MD5 doesn't match or the remote metadata differs.

use std::fmt;
use std::fs::{self, File};
use std::io::{self, BufWriter, Read, Write};
use std::path::{Path, PathBuf};

use serde::{Deserialize, Serialize};

// ─── Kernel catalog ─────────────────────────────────────────────────────────

struct KernelEntry {
    filename: &'static str,
    url: &'static str,
    gzipped: bool,
    is_static: bool,
}

const DEFAULT_KERNELS: &[KernelEntry] = &[
    KernelEntry {
        filename: "de440.bsp",
        url: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/planets/de440.bsp",
        gzipped: false,
        is_static: true,
    },
    KernelEntry {
        filename: "sb441-n16.bsp",
        url: "https://ssd.jpl.nasa.gov/ftp/eph/small_bodies/asteroids_de441/sb441-n16.bsp",
        gzipped: false,
        is_static: true,
    },
    KernelEntry {
        filename: "obscodes_extended.json",
        url: "https://minorplanetcenter.net/Extended_Files/obscodes_extended.json.gz",
        gzipped: true,
        is_static: false,
    },
    // Earth orientation binary PCKs. NAIF periodically republishes the
    // historical and predict kernels with filenames encoding their coverage;
    // bump the filenames here when upstream does. `earth_latest_high_prec.bpc`
    // is a stable endpoint NAIF updates ~weekly.
    KernelEntry {
        filename: "earth_latest_high_prec.bpc",
        url: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_latest_high_prec.bpc",
        gzipped: false,
        is_static: false,
    },
    KernelEntry {
        filename: "earth_620120_250826.bpc",
        url: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_620120_250826.bpc",
        gzipped: false,
        is_static: true,
    },
    KernelEntry {
        filename: "earth_2025_250826_2125_predict.bpc",
        url: "https://naif.jpl.nasa.gov/pub/naif/generic_kernels/pck/earth_2025_250826_2125_predict.bpc",
        gzipped: false,
        is_static: true,
    },
];

// ─── Sidecar metadata ──────────────────────────────────────────────────────

#[derive(Debug, Serialize, Deserialize)]
struct FileMeta {
    url: String,
    downloaded_at: u64,
    content_length: Option<u64>,
    last_modified: Option<String>,
    md5: String,
}

// ─── AssistDataPaths ────────────────────────────────────────────────────────

/// Resolved paths to all data files ASSIST needs.
#[derive(Debug, Clone)]
pub struct AssistDataPaths {
    /// DE440 planetary ephemeris SPK.
    pub planets: PathBuf,
    /// SB441 N=16 small-body perturber SPK.
    pub asteroids: PathBuf,
    /// MPC observatory codes JSON (decompressed).
    pub obscodes: PathBuf,
    /// Current high-precision Earth orientation PCK, updated ~weekly by NAIF.
    /// Covers approximately 2000 to the near future.
    pub eop_high_prec: PathBuf,
    /// Historical Earth orientation PCK (1962 → ~present).
    pub eop_historical: PathBuf,
    /// Long-term Earth orientation predict PCK (~2025 → 2125).
    pub eop_predict: PathBuf,
}

impl AssistDataPaths {
    /// The three EOP kernel paths in SPICE-idiomatic load order
    /// (predict, historical, current) — pass this directly to
    /// [`crate::earth_orientation::EarthOrientation::from_paths`] so the
    /// current high-precision kernel wins wherever it has coverage.
    pub fn eop_kernels(&self) -> [&PathBuf; 3] {
        [&self.eop_predict, &self.eop_historical, &self.eop_high_prec]
    }
}

// ─── DataError ──────────────────────────────────────────────────────────────

/// Errors from the data manager.
#[derive(Debug)]
pub enum DataError {
    /// Required files are missing (offline mode).
    MissingFiles(Vec<String>),
    /// HTTP request failed.
    Http(String),
    /// I/O error.
    Io(io::Error),
}

impl fmt::Display for DataError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::MissingFiles(files) => write!(f, "missing data files: {}", files.join(", ")),
            Self::Http(msg) => write!(f, "HTTP error: {msg}"),
            Self::Io(e) => write!(f, "I/O error: {e}"),
        }
    }
}

impl std::error::Error for DataError {}

// ─── DataManager ────────────────────────────────────────────────────────────

/// Manages downloading and caching of the files ASSIST needs.
///
/// Files are stored in a local data directory. Default location is
/// `$ASSIST_DATA_DIR` if set, otherwise `$XDG_CACHE_HOME/assist-rs/` or
/// `~/.cache/assist-rs/`.
pub struct DataManager {
    data_dir: PathBuf,
}

impl Default for DataManager {
    fn default() -> Self {
        Self::new()
    }
}

impl DataManager {
    /// Create a `DataManager` with the default data directory.
    pub fn new() -> Self {
        let data_dir = std::env::var("ASSIST_DATA_DIR")
            .map(PathBuf::from)
            .unwrap_or_else(|_| {
                if let Ok(xdg) = std::env::var("XDG_CACHE_HOME") {
                    PathBuf::from(xdg).join("assist-rs")
                } else {
                    let home = std::env::var("HOME").expect("HOME environment variable not set");
                    PathBuf::from(home).join(".cache").join("assist-rs")
                }
            });
        Self { data_dir }
    }

    /// Create a `DataManager` with a custom data directory.
    pub fn with_dir(dir: impl Into<PathBuf>) -> Self {
        Self {
            data_dir: dir.into(),
        }
    }

    /// The data directory path.
    pub fn data_dir(&self) -> &Path {
        &self.data_dir
    }

    fn paths(&self) -> AssistDataPaths {
        AssistDataPaths {
            planets: self.data_dir.join("de440.bsp"),
            asteroids: self.data_dir.join("sb441-n16.bsp"),
            obscodes: self.data_dir.join("obscodes_extended.json"),
            eop_high_prec: self.data_dir.join("earth_latest_high_prec.bpc"),
            eop_historical: self.data_dir.join("earth_620120_250826.bpc"),
            eop_predict: self.data_dir.join("earth_2025_250826_2125_predict.bpc"),
        }
    }

    /// Return paths if all data files exist. No network access.
    pub fn offline(&self) -> Result<AssistDataPaths, DataError> {
        let missing: Vec<String> = DEFAULT_KERNELS
            .iter()
            .filter(|e| !self.data_dir.join(e.filename).exists())
            .map(|e| e.filename.to_string())
            .collect();
        if !missing.is_empty() {
            return Err(DataError::MissingFiles(missing));
        }
        Ok(self.paths())
    }

    /// Ensure all three files exist, downloading any that are missing, locally
    /// corrupted, or stale upstream.
    ///
    /// For each file:
    ///
    /// - If the file is missing → download.
    /// - Else if a sidecar exists, compare the local file's MD5 against the
    ///   stored MD5. Mismatch implies local corruption or tampering →
    ///   re-download. An error computing the MD5 (e.g. unreadable file) is
    ///   propagated, not swallowed.
    /// - Else if the file is non-static (e.g. `obscodes_extended.json`), HEAD
    ///   the remote and re-download if `Content-Length` or `Last-Modified`
    ///   differs from the sidecar. Network failures here are propagated —
    ///   callers that need offline-tolerant behavior should use
    ///   [`Self::offline`] instead.
    /// - Else (static file, MD5 matches, or no sidecar to check against) →
    ///   keep the cached copy.
    pub fn ensure_ready(&self) -> Result<AssistDataPaths, DataError> {
        fs::create_dir_all(&self.data_dir).map_err(DataError::Io)?;

        for entry in DEFAULT_KERNELS {
            let path = self.data_dir.join(entry.filename);
            let meta_path = self.data_dir.join(format!("{}.meta.json", entry.filename));

            if !path.exists() {
                eprintln!("Downloading {}...", entry.filename);
                download(entry, &path, &meta_path)?;
                continue;
            }

            let Ok(meta) = read_meta(&meta_path) else {
                // No sidecar — can't validate, assume caller knows what they
                // put in the cache directory.
                continue;
            };

            // Integrity check: the local file's MD5 must match what we
            // recorded when we downloaded it. Catches on-disk corruption and
            // deliberate replacement. An error here means we can't even
            // read the local file — propagate rather than silently trust
            // an unverifiable cache entry.
            if !local_md5_matches(&path, &meta.md5)? {
                eprintln!("Re-downloading {} (local MD5 mismatch)...", entry.filename);
                download(entry, &path, &meta_path)?;
                continue;
            }

            if entry.is_static {
                continue;
            }

            // Staleness check: failure here is most often a network outage.
            // Surface it rather than silently serving a possibly-stale cache;
            // offline callers should use `offline()` instead of `ensure_ready`.
            if is_stale(entry.url, &meta)? {
                eprintln!("Updating {} (remote changed)...", entry.filename);
                download(entry, &path, &meta_path)?;
            }
        }

        Ok(self.paths())
    }

    /// Remove the data directory and all its contents.
    pub fn clean(&self) -> Result<(), DataError> {
        if self.data_dir.exists() {
            fs::remove_dir_all(&self.data_dir).map_err(DataError::Io)?;
        }
        Ok(())
    }
}

// ─── Private helpers ────────────────────────────────────────────────────────

fn is_stale(url: &str, meta: &FileMeta) -> Result<bool, DataError> {
    let response = ureq::head(url)
        .call()
        .map_err(|e| DataError::Http(format!("HEAD {url}: {e}")))?;

    let remote_length: Option<u64> = response
        .headers()
        .get("content-length")
        .and_then(|v| v.to_str().ok())
        .and_then(|v| v.parse().ok());

    let remote_modified: Option<&str> = response
        .headers()
        .get("last-modified")
        .and_then(|v| v.to_str().ok());

    if let (Some(remote), Some(local)) = (remote_length, meta.content_length) {
        if remote != local {
            return Ok(true);
        }
    }

    if let (Some(remote), Some(local)) = (remote_modified, meta.last_modified.as_deref()) {
        if remote != local {
            return Ok(true);
        }
    }

    Ok(false)
}

fn download(entry: &KernelEntry, path: &Path, meta_path: &Path) -> Result<(), DataError> {
    let response = ureq::get(entry.url)
        .call()
        .map_err(|e| DataError::Http(format!("GET {}: {e}", entry.url)))?;

    let content_length: Option<u64> = response
        .headers()
        .get("content-length")
        .and_then(|v| v.to_str().ok())
        .and_then(|v| v.parse().ok());

    let last_modified: Option<String> = response
        .headers()
        .get("last-modified")
        .and_then(|v| v.to_str().ok())
        .map(|v| v.to_string());

    if let Some(size) = content_length {
        eprintln!("  {} ({:.1} MB)", entry.filename, size as f64 / 1_048_576.0);
    }

    let tmp_path = path.with_extension("tmp");
    {
        let mut body = response.into_body();
        let file = File::create(&tmp_path).map_err(DataError::Io)?;
        let mut writer = BufWriter::new(file);
        if entry.gzipped {
            let mut decoder = flate2::read::GzDecoder::new(body.as_reader());
            io::copy(&mut decoder, &mut writer).map_err(DataError::Io)?;
        } else {
            io::copy(&mut body.as_reader(), &mut writer).map_err(DataError::Io)?;
        }
        writer.flush().map_err(DataError::Io)?;
    }

    let md5_hex = compute_md5(&tmp_path)?;

    fs::rename(&tmp_path, path).map_err(DataError::Io)?;

    let now = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .unwrap()
        .as_secs();
    let meta = FileMeta {
        url: entry.url.to_string(),
        downloaded_at: now,
        content_length,
        last_modified,
        md5: md5_hex,
    };
    let json =
        serde_json::to_string_pretty(&meta).map_err(|e| DataError::Io(io::Error::other(e)))?;
    fs::write(meta_path, json).map_err(DataError::Io)?;

    Ok(())
}

fn read_meta(path: &Path) -> Result<FileMeta, DataError> {
    let content = fs::read_to_string(path).map_err(DataError::Io)?;
    serde_json::from_str(&content)
        .map_err(|e| DataError::Io(io::Error::new(io::ErrorKind::InvalidData, e)))
}

/// Compare the MD5 of `path` against `expected_hex`. Returns `Ok(true)` on
/// match. Skips the check (returns `Ok(true)`) when the sidecar MD5 is empty,
/// which covers legacy sidecars written before MD5 was recorded.
fn local_md5_matches(path: &Path, expected_hex: &str) -> Result<bool, DataError> {
    if expected_hex.is_empty() {
        return Ok(true);
    }
    let actual = compute_md5(path)?;
    Ok(actual.eq_ignore_ascii_case(expected_hex))
}

fn compute_md5(path: &Path) -> Result<String, DataError> {
    let mut file = File::open(path).map_err(DataError::Io)?;
    let mut context = md5::Context::new();
    let mut buffer = [0u8; 65536];
    loop {
        let n = file.read(&mut buffer).map_err(DataError::Io)?;
        if n == 0 {
            break;
        }
        context.consume(&buffer[..n]);
    }
    Ok(format!("{:x}", context.compute()))
}

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

    /// Known-answer MD5 tests from RFC 1321 (plus the empty string) so the
    /// hash agrees with what the rest of the world calls MD5.
    #[test]
    fn compute_md5_matches_rfc1321_vectors() {
        let dir = tempfile::tempdir().unwrap();
        let cases: &[(&[u8], &str)] = &[
            (b"", "d41d8cd98f00b204e9800998ecf8427e"),
            (b"abc", "900150983cd24fb0d6963f7d28e17f72"),
            (
                b"The quick brown fox jumps over the lazy dog",
                "9e107d9d372bb6826bd81d3542a419d6",
            ),
        ];
        for (i, (payload, expected)) in cases.iter().enumerate() {
            let path = dir.path().join(format!("case_{i}.bin"));
            fs::write(&path, payload).unwrap();
            let got = compute_md5(&path).unwrap();
            assert_eq!(
                got,
                *expected,
                "case {i}: {:?}",
                std::str::from_utf8(payload)
            );
        }
    }

    #[test]
    fn local_md5_matches_detects_correct_and_incorrect_hashes() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("payload.txt");
        fs::write(&path, b"hello").unwrap();
        let actual = compute_md5(&path).unwrap();

        // Exact match.
        assert!(local_md5_matches(&path, &actual).unwrap());
        // Case-insensitive match.
        assert!(local_md5_matches(&path, &actual.to_uppercase()).unwrap());
        // Mismatch.
        assert!(!local_md5_matches(&path, "0".repeat(32).as_str()).unwrap());
    }

    #[test]
    fn local_md5_matches_skips_check_when_sidecar_has_empty_hash() {
        // Legacy sidecars written before MD5 was recorded will have md5 = "";
        // the helper must not refuse to validate them (we'd re-download every
        // start), nor error on the missing file check.
        let dir = tempfile::tempdir().unwrap();
        let nonexistent = dir.path().join("not_there.bin");
        assert!(local_md5_matches(&nonexistent, "").unwrap());
    }

    /// When a sidecar declares a real MD5 but the underlying file is
    /// missing/unreadable, the helper must propagate the I/O error rather
    /// than silently returning `false` (which would trigger a re-download)
    /// or `true` (which would mask the corruption). `ensure_ready` relies on
    /// this to surface unverifiable cache entries to the caller instead of
    /// the previous `eprintln!` + continue behaviour.
    #[test]
    fn local_md5_matches_propagates_io_error_on_missing_file() {
        let dir = tempfile::tempdir().unwrap();
        let missing = dir.path().join("absent.bin");
        let err = local_md5_matches(&missing, "deadbeef").unwrap_err();
        assert!(
            matches!(err, DataError::Io(_)),
            "expected DataError::Io, got {err:?}"
        );
    }

    /// `read_meta` on a missing sidecar must error — this is the upstream
    /// of `ensure_ready`'s integrity check. (`ensure_ready` itself treats a
    /// missing sidecar separately: it's an explicit `let Ok(meta) = ... else
    /// continue` branch, not an error path.)
    #[test]
    fn read_meta_errors_on_missing_file() {
        let dir = tempfile::tempdir().unwrap();
        let missing = dir.path().join("kernel.meta.json");
        let err = read_meta(&missing).unwrap_err();
        assert!(matches!(err, DataError::Io(_)));
    }

    /// Network failures during the staleness HEAD must propagate as
    /// `DataError::Http` rather than the prior `eprintln!` + continue.
    /// Uses an RFC 6761 `.invalid` TLD which is guaranteed never to
    /// resolve, so the call fails fast at DNS without hitting any real
    /// server or waiting for a TCP timeout.
    #[test]
    fn is_stale_propagates_http_error_on_unreachable_host() {
        let url = "http://nx.invalid/never-resolves";
        let meta = FileMeta {
            url: url.into(),
            downloaded_at: 0,
            content_length: Some(1),
            last_modified: None,
            md5: String::new(),
        };
        let err = is_stale(url, &meta).unwrap_err();
        assert!(
            matches!(err, DataError::Http(_)),
            "expected DataError::Http, got {err:?}"
        );
    }

    /// Every kernel declared in `DEFAULT_KERNELS` must be reachable through
    /// `AssistDataPaths`; otherwise a download happens but the path is never
    /// returned to the caller, creating orphan files in the cache dir.
    #[test]
    fn every_default_kernel_has_a_path_field() {
        let dm = DataManager::with_dir("/tmp/check");
        let paths = dm.paths();
        let all_paths = [
            &paths.planets,
            &paths.asteroids,
            &paths.obscodes,
            &paths.eop_high_prec,
            &paths.eop_historical,
            &paths.eop_predict,
        ];
        for entry in DEFAULT_KERNELS {
            let expected = dm.data_dir.join(entry.filename);
            assert!(
                all_paths.iter().any(|p| **p == expected),
                "kernel {:?} in DEFAULT_KERNELS has no corresponding field in AssistDataPaths",
                entry.filename
            );
        }
        // And the reverse: every returned path must correspond to a declared
        // kernel (guards against dangling fields).
        for p in all_paths {
            let filename = p.file_name().unwrap().to_str().unwrap();
            assert!(
                DEFAULT_KERNELS.iter().any(|e| e.filename == filename),
                "AssistDataPaths field points at {filename:?}, which is not in DEFAULT_KERNELS"
            );
        }
    }

    #[test]
    fn eop_kernels_returns_spice_idiomatic_load_order() {
        // predict → historical → current, so the high-precision kernel wins
        // at epochs it covers (last-in-wins).
        let dm = DataManager::with_dir("/tmp/check");
        let paths = dm.paths();
        let kernels = paths.eop_kernels();
        assert_eq!(kernels[0], &paths.eop_predict);
        assert_eq!(kernels[1], &paths.eop_historical);
        assert_eq!(kernels[2], &paths.eop_high_prec);
    }

    #[test]
    fn meta_round_trips_through_sidecar() {
        // Writing the sidecar and reading it back must preserve every field
        // the staleness check relies on (content_length, last_modified, md5).
        let dir = tempfile::tempdir().unwrap();
        let meta_path = dir.path().join("kernel.meta.json");
        let meta = FileMeta {
            url: "https://example.com/kernel.bsp".into(),
            downloaded_at: 1_700_000_000,
            content_length: Some(42),
            last_modified: Some("Mon, 21 Oct 2024 12:00:00 GMT".into()),
            md5: "d41d8cd98f00b204e9800998ecf8427e".into(),
        };
        let json = serde_json::to_string_pretty(&meta).unwrap();
        fs::write(&meta_path, json).unwrap();

        let back = read_meta(&meta_path).unwrap();
        assert_eq!(back.url, meta.url);
        assert_eq!(back.downloaded_at, meta.downloaded_at);
        assert_eq!(back.content_length, meta.content_length);
        assert_eq!(back.last_modified, meta.last_modified);
        assert_eq!(back.md5, meta.md5);
    }
}