//! `DocxConverter` — converts word-processor documents (`.docx`, `.doc`,
//! `.odt`, `.rtf`) to PDF using LibreOffice in headless mode
//! (`soffice --convert-to pdf`).
//!
//! Used by the file viewer (`GET /api/file?…&compile-docx=true`) to render
//! word documents as PDFs on demand — the word-family twin of
//! [`crate::latex::LatexCompiler`].
//!
//! ## Caching (content-addressed)
//!
//! Unlike a `.tex` source, a word document is **self-contained**: images,
//! styles and fonts travel inside the file itself, so there is no dependency
//! graph to track and the `.fls`-sidecar machinery of the LaTeX cache would
//! buy nothing. The cache key is a short SHA-256 of the document bytes: any
//! edit changes the hash and invalidates naturally, and two paths holding the
//! same document share one cached PDF.
//!
//! One artefact lives under `<tmp>/skald-docx/`:
//!
//! | Artefact             | Key                        | Purpose           |
//! |----------------------|----------------------------|-------------------|
//! | `<content-hash>.pdf` | SHA-256 of the file bytes  | The converted PDF |
//!
//! ## Container-shuttled inputs
//!
//! [`DocxConverter::convert_bytes`] exists for documents that live **only
//! inside a user's container** (`/tmp/…`): the caller pulls the bytes out
//! (`container::exec_fs::read`) and the converter works on a host-side
//! scratch copy. This is correct precisely because the format is
//! self-contained — a bare copy loses nothing. (LaTeX deliberately does not
//! get this treatment: a shuttled `.tex` would silently lose its relative
//! `\input` / `\includegraphics` dependencies.)
//!
//! ## LibreOffice quirks this lives with
//!
//! - `soffice` locks its user-profile directory, so concurrent conversions —
//!   or a stale lock left by a killed run — make later invocations fail.
//!   Every conversion therefore gets a **private profile**
//!   (`-env:UserInstallation`) inside its per-run scratch directory, which is
//!   removed afterwards.
//! - A failed conversion does not always exit non-zero: a missing output
//!   file is treated as a failure too, with the captured output as detail.
//! - The scratch copy's **name** is how soffice picks its import filter, so
//!   the shuttled input keeps the caller's extension (`input.docx`,
//!   `input.odt`, …).
//!
//! ## Failure modes
//! - `ToolMissing` — no LibreOffice on the host (neither `soffice` /
//!   `libreoffice` on PATH nor the macOS app bundle).
//! - `Timeout` — conversion exceeded [`CONVERT_TIMEOUT_SECS`].
//! - `Failed { output }` — non-zero exit or missing output file; carries the
//!   captured stdout/stderr so the viewer can surface it.
//! - `Io` — underlying I/O error (reading the source, writing the cache…).

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

use sha2::{Digest, Sha256};
use tokio::process::Command;

/// Hard ceiling for a single conversion. A cold `soffice` start with a fresh
/// profile takes a few seconds; large documents add a few more — 60 s leaves
/// generous headroom while still bounding a hung run.
const CONVERT_TIMEOUT_SECS: u64 = 60;

/// Subdirectory of the OS temp dir holding cached PDFs and per-run scratch
/// directories.
const CACHE_DIR_NAME: &str = "skald-docx";

/// The word-processor extensions this converter accepts — the single source
/// of truth the HTTP layer (`api/files.rs::is_word_doc`) shares, so the
/// query flag and the converter can never disagree on the family.
pub const WORD_EXTS: &[&str] = &["docx", "doc", "odt", "rtf"];

/// A successfully converted PDF.
pub struct ConvertedPdf {
    pub bytes: Vec<u8>,
    /// `true` when served from cache without invoking `soffice`. Informational
    /// only; kept on the struct so the API stays stable (mirrors
    /// `latex::CompiledPdf`).
    #[allow(dead_code)]
    pub from_cache: bool,
}

/// Why a conversion request did not yield a PDF.
#[derive(Debug)]
pub enum ConvertError {
    /// No LibreOffice binary is reachable on the host.
    ToolMissing,
    /// `soffice` ran but failed (non-zero exit, or no output file). Carries
    /// the captured process output.
    Failed { output: String },
    /// Conversion did not finish within [`CONVERT_TIMEOUT_SECS`].
    Timeout,
    /// Underlying I/O error (reading the source, writing the cache, etc.).
    Io(std::io::Error),
}

impl std::fmt::Display for ConvertError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::ToolMissing => write!(f, "LibreOffice is not available on the server"),
            Self::Failed { output } => write!(f, "conversion failed:\n{output}"),
            Self::Timeout => write!(f, "conversion aborted (timeout {CONVERT_TIMEOUT_SECS}s)"),
            Self::Io(e) => write!(f, "I/O error: {e}"),
        }
    }
}

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

impl From<std::io::Error> for ConvertError {
    fn from(e: std::io::Error) -> Self { Self::Io(e) }
}

/// Stateless-ish facade around `soffice`. Owns only the cache root path; safe
/// to share via `Arc` (constructed once and stored on `Skald`).
#[derive(Clone)]
pub struct DocxConverter {
    cache_dir: PathBuf,
}

impl DocxConverter {
    pub fn new() -> Self {
        Self { cache_dir: std::env::temp_dir().join(CACHE_DIR_NAME) }
    }

    /// Convert a word document at `path` (a host file) to PDF, serving from
    /// the content-addressed cache when possible.
    pub async fn convert_path(&self, path: &Path) -> Result<ConvertedPdf, ConvertError> {
        let bytes = tokio::fs::read(path).await?;
        let key = content_hash(&bytes);
        if let Some(hit) = self.cached(&key).await {
            return Ok(hit);
        }
        let scratch = self.cache_dir.join(format!("run-{}", unique_suffix()));
        let pdf_bytes = self.run_soffice(&scratch, path).await?;
        self.store(&key, &pdf_bytes).await;
        tracing::info!(file = ?path, "word document converted (cache miss)");
        Ok(ConvertedPdf { bytes: pdf_bytes, from_cache: false })
    }

    /// Convert a word document that exists only as bytes — a file shuttled
    /// out of a user's container (see the module docs). `ext` (the caller's
    /// file extension) selects the import filter through the scratch copy's
    /// file name.
    pub async fn convert_bytes(&self, bytes: &[u8], ext: &str) -> Result<ConvertedPdf, ConvertError> {
        let key = content_hash(bytes);
        if let Some(hit) = self.cached(&key).await {
            return Ok(hit);
        }
        // Probe before touching the disk: with no converter installed the
        // request fails without leaving a scratch copy behind.
        let soffice = find_soffice().await.ok_or(ConvertError::ToolMissing)?;
        let scratch = self.cache_dir.join(format!("run-{}", unique_suffix()));
        tokio::fs::create_dir_all(&scratch).await?;
        let input = scratch.join(format!("input.{}", sanitize_ext(ext)));
        if let Err(e) = tokio::fs::write(&input, bytes).await {
            let _ = cleanup_dir(&scratch).await;
            return Err(ConvertError::Io(e));
        }
        let pdf_bytes = self.run_soffice_with(&soffice, &scratch, &input).await?;
        self.store(&key, &pdf_bytes).await;
        tracing::info!(ext, "word document converted from shuttled bytes (cache miss)");
        Ok(ConvertedPdf { bytes: pdf_bytes, from_cache: false })
    }

    /// Look up a cached PDF by content key.
    async fn cached(&self, key: &str) -> Option<ConvertedPdf> {
        let path = self.cache_dir.join(format!("{key}.pdf"));
        match tokio::fs::read(&path).await {
            Ok(bytes) => {
                tracing::debug!(cached_pdf = ?path, "word-doc cache hit");
                Some(ConvertedPdf { bytes, from_cache: true })
            }
            Err(_) => None,
        }
    }

    /// Persist a converted PDF under its content key. A write failure is
    /// non-fatal: the next request simply converts again.
    async fn store(&self, key: &str, bytes: &[u8]) {
        let path = self.cache_dir.join(format!("{key}.pdf"));
        if let Err(e) = tokio::fs::write(&path, bytes).await {
            tracing::warn!(cached_pdf = ?path, error = %e, "word-doc cache write failed");
        }
    }

    /// [`run_soffice_with`] with the binary probed first. Used by the
    /// host-path entry point, which has nothing to prepare.
    async fn run_soffice(&self, scratch: &Path, input: &Path) -> Result<Vec<u8>, ConvertError> {
        let soffice = find_soffice().await.ok_or(ConvertError::ToolMissing)?;
        self.run_soffice_with(&soffice, scratch, input).await
    }

    /// Run one conversion of `input` with output to `scratch` (a per-run
    /// unique directory, removed before returning regardless of outcome) and
    /// return the produced PDF bytes.
    ///
    /// `soffice` gets a **private user profile** inside the scratch dir:
    /// the profile is locked while in use, so a shared one would make
    /// concurrent conversions fail — and a stale lock from a killed run
    /// would make every later one fail.
    async fn run_soffice_with(
        &self,
        soffice: &Path,
        scratch: &Path,
        input: &Path,
    ) -> Result<Vec<u8>, ConvertError> {
        tokio::fs::create_dir_all(scratch).await?;
        let profile = scratch.join("profile");

        let mut cmd = Command::new(soffice);
        cmd.args(["--headless", "--norestore", "--nolockcheck", "--nologo"]);
        // `profile` is always absolute (cache_dir lives under temp_dir), so
        // `file://` + path yields a valid `file:///…` URL on unix hosts.
        cmd.arg(format!("-env:UserInstallation=file://{}", profile.display()));
        cmd.args(["--convert-to", "pdf", "--outdir"]);
        cmd.arg(scratch);
        cmd.arg(input);
        cmd.stdout(std::process::Stdio::piped());
        cmd.stderr(std::process::Stdio::piped());
        // If our future is dropped (e.g. on shutdown) ensure the process dies.
        cmd.kill_on_drop(true);

        let output = match tokio::time::timeout(
            Duration::from_secs(CONVERT_TIMEOUT_SECS),
            cmd.output(),
        ).await {
            Ok(Ok(o))  => o,
            Ok(Err(e)) => {
                let _ = cleanup_dir(scratch).await;
                return Err(ConvertError::Io(e));
            }
            Err(_) => {
                // Timeout: the future is dropped here; `kill_on_drop`
                // terminates `soffice`.
                let _ = cleanup_dir(scratch).await;
                return Err(ConvertError::Timeout);
            }
        };

        let stem = input
            .file_stem()
            .and_then(|s| s.to_str())
            .unwrap_or("output")
            .to_string();
        let pdf_path = scratch.join(format!("{stem}.pdf"));

        // soffice can exit 0 without producing anything (unreadable input,
        // unknown filter): the output file is the real success signal.
        let pdf_bytes = match tokio::fs::read(&pdf_path).await {
            Ok(b) => b,
            Err(_) if !output.status.success() => {
                let _ = cleanup_dir(scratch).await;
                return Err(ConvertError::Failed { output: process_output(&output) });
            }
            Err(e) => {
                let _ = cleanup_dir(scratch).await;
                return Err(ConvertError::Failed {
                    output: format!(
                        "soffice exited successfully but produced no PDF ({e})\n{}",
                        process_output(&output)
                    ),
                });
            }
        };

        let _ = cleanup_dir(scratch).await;
        Ok(pdf_bytes)
    }
}

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

// ── Helpers ─────────────────────────────────────────────────────────────────
//
// `content_hash` / `unique_suffix` / `find_on_path` / `cleanup_dir` mirror the
// private helpers of the same names in `latex/compiler.rs`. Kept as local
// copies so neither module reaches into the other; if a third converter ever
// appears, extraction into a shared module becomes the obvious move.

/// First 5 bytes (10 hex chars) of SHA-256 — enough to avoid collisions in
/// practice while keeping cache filenames short.
fn content_hash(bytes: &[u8]) -> String {
    let mut hasher = Sha256::new();
    hasher.update(bytes);
    let digest = hasher.finalize();
    digest.iter().take(5).map(|b| format!("{b:02x}")).collect()
}

/// Per-run unique suffix (PID + nanosecond timestamp) to namespace the
/// scratch directory and avoid races between concurrent conversions.
fn unique_suffix() -> String {
    use std::time::{SystemTime, UNIX_EPOCH};
    let pid = std::process::id();
    let nanos = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|d| d.as_nanos())
        .unwrap_or(0);
    format!("{pid}-{nanos:x}")
}

/// Locate a LibreOffice binary: `soffice` / `libreoffice` on PATH, then the
/// standard macOS app-bundle location (an installed LibreOffice that was
/// never linked onto PATH).
async fn find_soffice() -> Option<PathBuf> {
    for name in ["soffice", "libreoffice"] {
        if let Some(p) = find_on_path(name).await {
            return Some(p);
        }
    }
    let app_bundle = PathBuf::from("/Applications/LibreOffice.app/Contents/MacOS/soffice");
    if tokio::fs::metadata(&app_bundle).await.map(|m| m.is_file()).unwrap_or(false) {
        return Some(app_bundle);
    }
    None
}

/// Return the absolute path of `bin` if it is found on `PATH` and is a regular
/// file. We avoid pulling in the `which` crate for a single lookup.
async fn find_on_path(bin: &str) -> Option<PathBuf> {
    let path_var = std::env::var_os("PATH")?;
    for dir in std::env::split_paths(&path_var) {
        let candidate = dir.join(bin);
        if tokio::fs::metadata(&candidate).await
            .map(|m| m.is_file() || m.file_type().is_symlink())
            .unwrap_or(false)
        {
            return Some(candidate);
        }
    }
    None
}

/// The scratch copy's extension drives soffice's import-filter choice, so it
/// must survive the trip. Anything outside the known word family (or weird
/// bytes) becomes `docx` — which is also what content-sniffing would guess.
fn sanitize_ext(ext: &str) -> String {
    let e = ext.to_ascii_lowercase();
    if WORD_EXTS.contains(&e.as_str()) { e } else { "docx".to_string() }
}

/// Flatten a process's captured stdout+stderr into one displayable string,
/// capped so a noisy run cannot bloat the HTTP error body.
fn process_output(output: &std::process::Output) -> String {
    let mut text = String::new();
    text.push_str(&String::from_utf8_lossy(&output.stdout));
    if !text.is_empty() && !text.ends_with('\n') {
        text.push('\n');
    }
    text.push_str(&String::from_utf8_lossy(&output.stderr));
    let text = text.trim();
    if text.is_empty() {
        return "(no output from soffice)".to_string();
    }
    text.chars().take(4000).collect()
}

/// Recursively remove a scratch directory. Errors are logged and swallowed:
/// leftover dirs only consume a little disk under the OS temp folder.
async fn cleanup_dir(dir: &Path) -> std::io::Result<()> {
    if tokio::fs::try_exists(dir).await.unwrap_or(false) {
        tokio::fs::remove_dir_all(dir).await?;
    }
    Ok(())
}

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

    #[test]
    fn hash_is_10_lowercase_hex_chars() {
        let h = content_hash(b"hello world");
        assert_eq!(h.len(), 10);
        assert!(h.chars().all(|c| c.is_ascii_hexdigit() && !c.is_ascii_uppercase()));
    }

    #[test]
    fn hash_is_deterministic() {
        assert_eq!(content_hash(b"abc"), content_hash(b"abc"));
        assert_ne!(content_hash(b"abc"), content_hash(b"abd"));
    }

    #[test]
    fn sanitize_ext_keeps_the_word_family() {
        for ext in WORD_EXTS {
            assert_eq!(&sanitize_ext(ext), ext);
        }
        assert_eq!(sanitize_ext("DOCX"), "docx");
    }

    #[test]
    fn sanitize_ext_defaults_unknowns_to_docx() {
        assert_eq!(sanitize_ext("pptx"), "docx");
        assert_eq!(sanitize_ext("../../etc/passwd"), "docx");
        assert_eq!(sanitize_ext(""), "docx");
    }

    #[tokio::test]
    async fn cache_round_trip() {
        let dir = std::env::temp_dir().join(format!("skald-docx-test-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).unwrap();

        let converter = DocxConverter { cache_dir: dir.clone() };
        assert!(converter.cached("deadbeef00").await.is_none());
        converter.store("deadbeef00", b"%PDF-fake").await;
        let hit = converter.cached("deadbeef00").await.unwrap();
        assert_eq!(hit.bytes, b"%PDF-fake");
        assert!(hit.from_cache);

        let _ = std::fs::remove_dir_all(&dir);
    }

    /// With no LibreOffice on the host the converter must report ToolMissing —
    /// on a box *with* LibreOffice this test is skipped rather than failed,
    /// since it would otherwise run a real conversion.
    #[tokio::test]
    async fn missing_tool_reports_tool_missing() {
        if find_soffice().await.is_some() {
            eprintln!("LibreOffice present — skipping ToolMissing test");
            return;
        }
        let dir = std::env::temp_dir().join(format!("skald-docx-test-missing-{}", std::process::id()));
        let converter = DocxConverter { cache_dir: dir };
        let result = converter.convert_bytes(b"not a real docx", "docx").await;
        assert!(matches!(result, Err(ConvertError::ToolMissing)));
    }
}