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

use crate::types::ModelId;

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct AppPaths {
    app_data_dir: PathBuf,
}

impl AppPaths {
    pub fn current() -> Self {
        Self {
            app_data_dir: resolve_app_data_dir(),
        }
    }

    pub fn app_data_dir(&self) -> PathBuf {
        self.app_data_dir.clone()
    }

    pub fn database_path(&self) -> PathBuf {
        self.app_data_dir.join("lumotia.db")
    }

    pub fn recordings_dir(&self) -> PathBuf {
        self.app_data_dir.join("recordings")
    }

    pub fn crashes_dir(&self) -> PathBuf {
        self.app_data_dir.join("crashes")
    }

    pub fn logs_dir(&self) -> PathBuf {
        self.app_data_dir.join("logs")
    }

    pub fn diagnostic_reports_dir(&self) -> PathBuf {
        self.app_data_dir.join("diagnostic-reports")
    }

    pub fn models_dir(&self) -> PathBuf {
        self.app_data_dir.join("models")
    }

    pub fn speech_model_dir(&self, id: &ModelId) -> PathBuf {
        self.models_dir().join(id.as_str())
    }

    pub fn llm_models_dir(&self) -> PathBuf {
        self.models_dir().join("llm")
    }

    pub fn migration_sentinel(&self, name: &str) -> PathBuf {
        self.app_data_dir.join(format!(".{name}.sentinel"))
    }
}

pub fn app_paths() -> AppPaths {
    AppPaths::current()
}

pub fn app_data_dir() -> PathBuf {
    app_paths().app_data_dir()
}

/// Surfaced when two or more lumotia data-dir candidates exist on disk
/// simultaneously (e.g. both `~/.lumotia` and `~/.local/share/lumotia`).
/// Picking one silently risks pointing at the wrong copy of the user's
/// transcripts. The caller (typically the Tauri setup hook) should refuse
/// to start and surface the paths to the user for manual consolidation.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct TargetAmbiguityError {
    pub candidates: Vec<PathBuf>,
}

impl std::fmt::Display for TargetAmbiguityError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(
            f,
            "ambiguous lumotia data directory — multiple candidate paths exist: {}. \
             Please consolidate manually (move data into one path and delete the other) \
             then restart.",
            self.candidates
                .iter()
                .map(|p| p.display().to_string())
                .collect::<Vec<_>>()
                .join(", ")
        )
    }
}

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

fn resolve_app_data_dir() -> PathBuf {
    match resolve_app_data_dir_strict() {
        Ok(p) => p,
        Err(e) => {
            // Refuse to start rather than silently picking one of several
            // candidate target paths. This is intentionally a panic — the
            // process must not be allowed to begin writing into the wrong
            // half of a split data directory. The setup hook also calls
            // `check_target_ambiguity` explicitly to surface this error
            // before tracing/log subsystems are spun up.
            panic!("{e}");
        }
    }
}

/// Fallible variant of [`resolve_app_data_dir`]: returns the conventional
/// target path for the current platform, or a [`TargetAmbiguityError`] if
/// more than one candidate target path currently exists on disk.
///
/// Public so that the application setup hook can perform the check
/// explicitly (and report the ambiguity through tracing) rather than
/// relying on the panic that backs the infallible `resolve_app_data_dir`.
pub fn resolve_app_data_dir_strict() -> Result<PathBuf, TargetAmbiguityError> {
    let candidates = target_data_dir_candidates();
    let existing: Vec<PathBuf> = candidates.iter().filter(|p| p.exists()).cloned().collect();
    if existing.len() > 1 {
        return Err(TargetAmbiguityError {
            candidates: existing,
        });
    }
    // If exactly one candidate exists, prefer it (it's where the user's
    // data lives). If none exist, fall through to the platform-canonical
    // path so a fresh install creates the right convention.
    if existing.len() == 1 {
        return Ok(existing.into_iter().next().unwrap());
    }
    Ok(canonical_target_data_dir())
}

/// Public counterpart to [`resolve_app_data_dir_strict`] returning `Ok(())`
/// when the data dir is unambiguous and the [`TargetAmbiguityError`]
/// otherwise. Useful when the caller just wants to fail-fast at boot
/// without yet caring about the path itself.
pub fn check_target_ambiguity() -> Result<(), TargetAmbiguityError> {
    resolve_app_data_dir_strict().map(|_| ())
}

/// All conventional lumotia data-dir target paths for the current
/// platform. Lumotia chooses one canonical path at install time, but a
/// previous magnotia install or a hand-edited XDG_DATA_HOME can leave
/// data in any of these — the migration driver probes them all and the
/// resolver refuses to start if more than one survives.
fn target_data_dir_candidates() -> Vec<PathBuf> {
    let mut out = Vec::new();

    #[cfg(target_os = "windows")]
    {
        if let Ok(local_app_data) = std::env::var("LOCALAPPDATA") {
            if !local_app_data.is_empty() {
                out.push(PathBuf::from(local_app_data).join("lumotia"));
            }
        }
    }

    #[cfg(target_os = "macos")]
    {
        if let Ok(home) = std::env::var("HOME") {
            if !home.is_empty() {
                out.push(
                    PathBuf::from(home)
                        .join("Library")
                        .join("Application Support")
                        .join("Lumotia"),
                );
            }
        }
    }

    #[cfg(target_os = "linux")]
    {
        if let Ok(home) = std::env::var("HOME") {
            if !home.is_empty() {
                out.push(PathBuf::from(&home).join(".lumotia"));
                if let Ok(xdg) = std::env::var("XDG_DATA_HOME") {
                    if !xdg.is_empty() {
                        out.push(PathBuf::from(xdg).join("lumotia"));
                    }
                }
                out.push(
                    PathBuf::from(home)
                        .join(".local")
                        .join("share")
                        .join("lumotia"),
                );
            }
        }
    }

    #[cfg(not(any(target_os = "windows", target_os = "macos", target_os = "linux")))]
    {
        if let Ok(home) = std::env::var("HOME") {
            if !home.is_empty() {
                out.push(PathBuf::from(home).join(".lumotia"));
            }
        }
    }

    // De-duplicate while preserving order: on Linux XDG_DATA_HOME may be
    // set to `~/.local/share` explicitly, in which case the explicit XDG
    // candidate and the XDG default collapse to one path.
    let mut seen = std::collections::HashSet::new();
    out.retain(|p| seen.insert(p.clone()));
    out
}

/// The single canonical target path for the current platform — what a
/// fresh install would create. Used when no existing candidate is found.
fn canonical_target_data_dir() -> PathBuf {
    #[cfg(target_os = "windows")]
    {
        let local_app_data = std::env::var("LOCALAPPDATA").unwrap_or_else(|_| ".".to_string());
        return PathBuf::from(local_app_data).join("lumotia");
    }

    #[cfg(target_os = "macos")]
    {
        let home = std::env::var("HOME").unwrap_or_else(|_| "/tmp".to_string());
        return PathBuf::from(home)
            .join("Library")
            .join("Application Support")
            .join("Lumotia");
    }

    #[cfg(target_os = "linux")]
    {
        let home = std::env::var("HOME").unwrap_or_else(|_| "/tmp".to_string());
        if let Ok(xdg) = std::env::var("XDG_DATA_HOME") {
            if !xdg.is_empty() {
                return PathBuf::from(xdg).join("lumotia");
            }
        }
        PathBuf::from(home)
            .join(".local")
            .join("share")
            .join("lumotia")
    }

    #[cfg(not(any(target_os = "windows", target_os = "macos", target_os = "linux")))]
    {
        let home = std::env::var("HOME").unwrap_or_else(|_| "/tmp".to_string());
        PathBuf::from(home).join(".lumotia")
    }
}

/// Outcome of attempting to migrate an existing magnotia-era data directory
/// to its lumotia equivalent on first launch after the rebrand.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum MigrationStatus {
    /// Renamed legacy dir to the new path. Includes optional db-file rename
    /// if `magnotia.db` was found inside.
    Migrated {
        from: PathBuf,
        to: PathBuf,
        renamed_db: bool,
    },
    /// New path already exists. Did not touch legacy (if any) to avoid
    /// destroying user data on the new path.
    TargetAlreadyExists { target: PathBuf },
    /// No legacy data dir on disk. Nothing to do.
    NoLegacyFound,
}

/// Probe ALL legacy magnotia data dir paths on the current platform.
/// Returns one (legacy, target) pair per legacy candidate that exists on
/// disk. The target is convention-preserving so the migration lands the
/// same kind of dir it found (dot-home stays dot-home, XDG stays XDG,
/// macOS Application Support stays the same).
///
/// Previously this returned `Option<(legacy, target)>` and short-circuited
/// on the first match. On Linux that allowed a user with both
/// `~/.magnotia` AND `~/.local/share/magnotia` to migrate only one,
/// leaving the other orphaned forever (subsequent boots prefer the new
/// `~/.lumotia` so the XDG legacy is invisible). Now every legacy variant
/// is probed and migrated independently.
fn legacy_and_target_paths() -> Vec<(PathBuf, PathBuf)> {
    let mut out = Vec::new();

    #[cfg(target_os = "windows")]
    {
        if let Ok(local_app_data) = std::env::var("LOCALAPPDATA") {
            if !local_app_data.is_empty() {
                let legacy = PathBuf::from(&local_app_data).join("magnotia");
                let target = PathBuf::from(local_app_data).join("lumotia");
                if legacy.exists() {
                    out.push((legacy, target));
                }
            }
        }
    }

    #[cfg(target_os = "macos")]
    {
        if let Ok(home) = std::env::var("HOME") {
            if !home.is_empty() {
                let app_support = PathBuf::from(home)
                    .join("Library")
                    .join("Application Support");
                let legacy = app_support.join("Magnotia");
                let target = app_support.join("Lumotia");
                if legacy.exists() {
                    out.push((legacy, target));
                }
            }
        }
    }

    #[cfg(target_os = "linux")]
    {
        if let Ok(home) = std::env::var("HOME") {
            if !home.is_empty() {
                let dot_legacy = PathBuf::from(&home).join(".magnotia");
                if dot_legacy.exists() {
                    out.push((dot_legacy, PathBuf::from(&home).join(".lumotia")));
                }
                if let Ok(xdg) = std::env::var("XDG_DATA_HOME") {
                    if !xdg.is_empty() {
                        let xdg_legacy = PathBuf::from(&xdg).join("magnotia");
                        if xdg_legacy.exists() {
                            out.push((xdg_legacy, PathBuf::from(&xdg).join("lumotia")));
                        }
                    }
                }
                let xdg_default_legacy = PathBuf::from(&home)
                    .join(".local")
                    .join("share")
                    .join("magnotia");
                if xdg_default_legacy.exists() {
                    let xdg_default_target = PathBuf::from(&home)
                        .join(".local")
                        .join("share")
                        .join("lumotia");
                    out.push((xdg_default_legacy, xdg_default_target));
                }
            }
        }
    }

    #[cfg(not(any(target_os = "windows", target_os = "macos", target_os = "linux")))]
    {
        if let Ok(home) = std::env::var("HOME") {
            if !home.is_empty() {
                let legacy = PathBuf::from(&home).join(".magnotia");
                let target = PathBuf::from(home).join(".lumotia");
                if legacy.exists() {
                    out.push((legacy, target));
                }
            }
        }
    }

    // De-duplicate: e.g. XDG_DATA_HOME set explicitly to `~/.local/share`
    // would otherwise produce the same pair twice on Linux.
    let mut seen = std::collections::HashSet::new();
    out.retain(|pair| seen.insert(pair.clone()));
    out
}

/// Migrate every legacy magnotia data directory to its
/// convention-preserving lumotia equivalent on first launch. Idempotent:
/// safe to call on every boot.
///
/// Returns one [`MigrationStatus`] per legacy candidate probed, in
/// platform-deterministic order. An empty Vec means there are no legacy
/// directories on disk (clean install). Callers should log per-candidate
/// outcomes and treat any `Err` as a hard startup failure: silently
/// continuing past a migration error orphans user data behind a fresh
/// empty lumotia dir.
///
/// Per-candidate rules (same as before, applied independently to each
/// legacy path that exists):
/// * If the matching target already exists, do nothing for that
///   candidate and emit `TargetAlreadyExists`. We do not destroy
///   lumotia data, even if a stale legacy dir is also present.
/// * If only the legacy path exists, rename it to the matching lumotia
///   target (same convention) and rename `magnotia.db` -> `lumotia.db`
///   inside it if found.
pub fn migrate_legacy_data_dir() -> Result<Vec<MigrationStatus>, std::io::Error> {
    migrate_legacy_data_dir_with_pairs(legacy_and_target_paths())
}

/// Driver that takes the list of (legacy, target) pairs explicitly so
/// callers can substitute synthetic paths. Production path goes through
/// [`migrate_legacy_data_dir`], which resolves the pairs from
/// platform-specific HOME / LOCALAPPDATA / XDG env vars. Integration
/// tests in sibling crates call this directly with tempdir pairs.
///
/// An empty input is shorthand for "no legacy on disk" and yields a
/// single [`MigrationStatus::NoLegacyFound`] entry so callers can still
/// rely on a non-empty result to drive their logging.
pub fn migrate_legacy_data_dir_with_pairs(
    pairs: Vec<(PathBuf, PathBuf)>,
) -> Result<Vec<MigrationStatus>, std::io::Error> {
    if pairs.is_empty() {
        return Ok(vec![MigrationStatus::NoLegacyFound]);
    }
    let mut out = Vec::with_capacity(pairs.len());
    for (from, to) in pairs {
        out.push(migrate_one(from, to)?);
    }
    Ok(out)
}

/// Run the single-candidate migration. Extracted so the driver can loop
/// over every legacy path discovered on disk and surface per-candidate
/// outcomes individually.
fn migrate_one(from: PathBuf, to: PathBuf) -> Result<MigrationStatus, std::io::Error> {
    if to.exists() {
        return Ok(MigrationStatus::TargetAlreadyExists { target: to });
    }

    if let Some(parent) = to.parent() {
        std::fs::create_dir_all(parent)?;
    }
    rename_or_copy_tree(&from, &to)?;

    let renamed_db = rename_db_file_if_present(&to)?;

    Ok(MigrationStatus::Migrated {
        from,
        to,
        renamed_db,
    })
}

/// Move a directory tree, falling back to copy + remove if the
/// destination is on a different filesystem (EXDEV / CrossesDevices).
///
/// Real-world cases this defends against:
/// * `~/.magnotia` on the user's home partition, `~/.local/share/lumotia`
///   on a bind-mounted partition.
/// * Encrypted-home (`/home/.ecryptfs/`) vs decrypted view.
/// * `$XDG_DATA_HOME` set to a non-home device.
///
/// On a copy-then-remove fallback we tolerate partial cleanup failure
/// (the source dir not fully deleted) by surfacing the error from the
/// remove step only if the copy succeeded — losing data via a half-rolled
/// migration is worse than leaving a stale legacy dir behind.
fn rename_or_copy_tree(from: &Path, to: &Path) -> Result<(), std::io::Error> {
    match std::fs::rename(from, to) {
        Ok(()) => Ok(()),
        Err(e) if is_cross_device(&e) => {
            copy_dir_recursive(from, to)?;
            // Only attempt removal after the copy fully succeeded.
            // remove_dir_all is best-effort: if it leaves files behind
            // (permission edge cases), the user can clean up the stale
            // legacy dir manually.
            std::fs::remove_dir_all(from)?;
            Ok(())
        }
        Err(e) => Err(e),
    }
}

fn is_cross_device(err: &std::io::Error) -> bool {
    // ErrorKind::CrossesDevices is stable from Rust 1.85. Fall back to
    // the raw OS error code (EXDEV = 18 on Linux, 17 on macOS, 17 on
    // BSDs) for older toolchains.
    if err.kind() == std::io::ErrorKind::CrossesDevices {
        return true;
    }
    #[cfg(unix)]
    {
        return matches!(err.raw_os_error(), Some(18));
    }
    #[allow(unreachable_code)]
    false
}

/// Symlink-aware recursive directory copy used by the legacy data-dir
/// migration and by the Tauri-side `app_data_dir` bundle-identifier
/// migration in `src-tauri/src/tauri_app_data_migration.rs`. Exposed as
/// `pub` so callers in sibling crates can reuse the same hardened
/// implementation (see commit history for the symlink-loop defence).
pub fn copy_dir_recursive(from: &Path, to: &Path) -> Result<(), std::io::Error> {
    std::fs::create_dir_all(to)?;
    for entry in std::fs::read_dir(from)? {
        let entry = entry?;
        let entry_path = entry.path();
        let target_path = to.join(entry.file_name());
        // CRITICAL: use file_type() rather than metadata(). metadata()
        // follows symlinks, so a directory symlink reports is_dir==true
        // and would recurse unconditionally — a self-referential or
        // ancestor-targeting directory symlink loops until the disk
        // fills. file_type() is symlink-aware on both Unix and Windows.
        let file_type = entry.file_type()?;
        if file_type.is_symlink() {
            // Recreate symlink rather than dereferencing — the
            // transcription app stores recording paths verbatim so a
            // dereferenced symlink could orphan large audio blobs, and
            // a directory symlink is the only way to terminate the
            // recursion at the link boundary.
            let link_target = std::fs::read_link(&entry_path)?;
            #[cfg(unix)]
            {
                std::os::unix::fs::symlink(link_target, &target_path)?;
            }
            #[cfg(windows)]
            {
                // On Windows we have to pick file vs dir symlink at
                // creation time. Probe the link target with full
                // metadata (it resolves through the link) to decide.
                // If the target is missing or unreadable, fall back to
                // a file symlink — safer than panicking the migration.
                let target_is_dir = std::fs::metadata(&entry_path)
                    .map(|m| m.is_dir())
                    .unwrap_or(false);
                if target_is_dir {
                    std::os::windows::fs::symlink_dir(link_target, &target_path)?;
                } else {
                    std::os::windows::fs::symlink_file(link_target, &target_path)?;
                }
            }
        } else if file_type.is_dir() {
            copy_dir_recursive(&entry_path, &target_path)?;
        } else if file_type.is_file() {
            std::fs::copy(&entry_path, &target_path)?;
        } else {
            // Anything that is neither a symlink, a directory, nor a
            // regular file lands here: on Unix that's FIFOs, sockets,
            // and character / block device nodes. `std::fs::copy()` on
            // a FIFO would block forever waiting for a writer, and on
            // a device node would either fail unpredictably or attempt
            // to read until the device's end-of-stream. Both turn a
            // legacy-dir leftover into a silent migration hang. We
            // refuse to cross the boundary and surface the path so
            // the user can clean it up manually. The migration is
            // re-runnable once the offending node is removed.
            return Err(std::io::Error::new(
                std::io::ErrorKind::Unsupported,
                format!(
                    "refusing to copy non-regular filesystem object during migration: {}",
                    entry_path.display()
                ),
            ));
        }
    }
    Ok(())
}

fn rename_db_file_if_present(dir: &Path) -> Result<bool, std::io::Error> {
    let legacy_db = dir.join("magnotia.db");
    if !legacy_db.exists() {
        return Ok(false);
    }
    let new_db = dir.join("lumotia.db");
    rename_or_copy_file(&legacy_db, &new_db)?;
    Ok(true)
}

fn rename_or_copy_file(from: &Path, to: &Path) -> Result<(), std::io::Error> {
    match std::fs::rename(from, to) {
        Ok(()) => Ok(()),
        Err(e) if is_cross_device(&e) => {
            std::fs::copy(from, to)?;
            std::fs::remove_file(from)?;
            Ok(())
        }
        Err(e) => Err(e),
    }
}

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

    #[test]
    fn derives_all_paths_from_one_base() {
        let paths = AppPaths {
            app_data_dir: PathBuf::from("/tmp/lumotia-test"),
        };
        assert_eq!(
            paths.database_path(),
            PathBuf::from("/tmp/lumotia-test/lumotia.db")
        );
        assert_eq!(
            paths.speech_model_dir(&ModelId::new("whisper-base-en")),
            PathBuf::from("/tmp/lumotia-test/models/whisper-base-en")
        );
        assert_eq!(
            paths.llm_models_dir(),
            PathBuf::from("/tmp/lumotia-test/models/llm")
        );
    }

    fn unique_tmp(base: &str) -> PathBuf {
        let pid = std::process::id();
        let nanos = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .map(|d| d.as_nanos())
            .unwrap_or(0);
        std::env::temp_dir().join(format!("lumotia-paths-test-{base}-{pid}-{nanos}"))
    }

    /// Helper: drive the migration with a single (legacy, target) pair
    /// and return the (only) status it produced. Keeps existing tests
    /// readable after the Option -> Vec API change.
    fn migrate_one_pair_inner(pair: (PathBuf, PathBuf)) -> Result<MigrationStatus, std::io::Error> {
        let mut statuses = migrate_legacy_data_dir_with_pairs(vec![pair])?;
        assert_eq!(
            statuses.len(),
            1,
            "single-pair driver should yield exactly one status"
        );
        Ok(statuses.pop().unwrap())
    }

    #[test]
    fn migrate_with_legacy_present_renames_dir_and_db() {
        let root = unique_tmp("legacy-present");
        let legacy = root.join("magnotia");
        let target = root.join("lumotia");
        std::fs::create_dir_all(&legacy).unwrap();
        std::fs::write(legacy.join("magnotia.db"), b"sqlite-stub").unwrap();
        std::fs::write(legacy.join("recordings.placeholder"), b"x").unwrap();

        let result = migrate_one_pair_inner((legacy.clone(), target.clone())).expect("migrate ok");

        match result {
            MigrationStatus::Migrated {
                from,
                to,
                renamed_db,
            } => {
                assert_eq!(from, legacy);
                assert_eq!(to, target);
                assert!(renamed_db, "expected db file to be renamed");
            }
            other => panic!("expected Migrated, got {other:?}"),
        }
        assert!(!legacy.exists(), "legacy dir should be gone");
        assert!(target.exists(), "new dir should exist");
        assert!(target.join("lumotia.db").exists(), "db at new name");
        assert!(!target.join("magnotia.db").exists(), "old db gone");
        assert!(
            target.join("recordings.placeholder").exists(),
            "other files preserved"
        );

        std::fs::remove_dir_all(&root).ok();
    }

    #[test]
    fn migrate_with_both_present_returns_target_exists_and_preserves_lumotia() {
        let root = unique_tmp("both-present");
        let legacy = root.join("magnotia");
        let target = root.join("lumotia");
        std::fs::create_dir_all(&legacy).unwrap();
        std::fs::create_dir_all(&target).unwrap();
        std::fs::write(target.join("lumotia.db"), b"new-data").unwrap();
        std::fs::write(legacy.join("magnotia.db"), b"legacy-data").unwrap();

        let result = migrate_one_pair_inner((legacy.clone(), target.clone())).expect("migrate ok");

        assert_eq!(
            result,
            MigrationStatus::TargetAlreadyExists {
                target: target.clone()
            }
        );
        assert!(legacy.exists(), "legacy dir preserved");
        assert!(target.exists(), "new dir preserved");
        assert_eq!(
            std::fs::read(target.join("lumotia.db")).unwrap(),
            b"new-data".to_vec(),
            "lumotia.db not overwritten"
        );

        std::fs::remove_dir_all(&root).ok();
    }

    #[test]
    fn migrate_with_neither_present_returns_no_legacy() {
        let result = migrate_legacy_data_dir_with_pairs(Vec::new()).expect("migrate ok");

        assert_eq!(result, vec![MigrationStatus::NoLegacyFound]);
    }

    #[test]
    fn migrate_with_legacy_present_but_no_db_inside() {
        let root = unique_tmp("legacy-no-db");
        let legacy = root.join("magnotia");
        let target = root.join("lumotia");
        std::fs::create_dir_all(&legacy).unwrap();
        std::fs::write(legacy.join("recordings.placeholder"), b"x").unwrap();

        let result = migrate_one_pair_inner((legacy.clone(), target.clone())).expect("migrate ok");

        match result {
            MigrationStatus::Migrated { renamed_db, .. } => {
                assert!(!renamed_db, "no db to rename");
            }
            other => panic!("expected Migrated, got {other:?}"),
        }
        assert!(target.exists());
        assert!(target.join("recordings.placeholder").exists());

        std::fs::remove_dir_all(&root).ok();
    }

    #[test]
    fn migrate_preserves_dot_home_to_dot_home_convention() {
        // Regression for B2 from Phase 5 QC: dot-home legacy must land in
        // dot-home target, not XDG target.
        let root = unique_tmp("convention");
        let legacy = root.join(".magnotia");
        let target = root.join(".lumotia");
        std::fs::create_dir_all(&legacy).unwrap();
        std::fs::write(legacy.join("magnotia.db"), b"data").unwrap();

        let result = migrate_one_pair_inner((legacy.clone(), target.clone())).expect("migrate ok");

        assert!(matches!(result, MigrationStatus::Migrated { .. }));
        assert!(target.exists());
        assert!(target.join("lumotia.db").exists());

        std::fs::remove_dir_all(&root).ok();
    }

    #[test]
    fn copy_dir_recursive_preserves_nested_files_and_directories() {
        // Regression for Codex Blocker 11: EXDEV fallback path uses
        // copy_dir_recursive. Verify it preserves directory structure,
        // file contents, and arbitrary depth.
        let root = unique_tmp("copy-recursive");
        let src = root.join("legacy");
        let dst = root.join("new");
        std::fs::create_dir_all(src.join("recordings/2026-05")).unwrap();
        std::fs::create_dir_all(src.join("models/whisper-base-en")).unwrap();
        std::fs::write(src.join("magnotia.db"), b"sqlite-bytes").unwrap();
        std::fs::write(src.join("recordings/2026-05/clip-001.wav"), b"wav-bytes").unwrap();
        std::fs::write(src.join("models/whisper-base-en/manifest.json"), b"{}").unwrap();

        copy_dir_recursive(&src, &dst).expect("copy ok");

        assert_eq!(
            std::fs::read(dst.join("magnotia.db")).unwrap(),
            b"sqlite-bytes"
        );
        assert_eq!(
            std::fs::read(dst.join("recordings/2026-05/clip-001.wav")).unwrap(),
            b"wav-bytes"
        );
        assert!(dst.join("models/whisper-base-en/manifest.json").exists());
        // Source still present — copy_dir_recursive does not delete.
        assert!(src.exists());

        std::fs::remove_dir_all(&root).ok();
    }

    #[test]
    fn rename_or_copy_tree_succeeds_on_same_filesystem() {
        // Smoke for the happy path: same-filesystem case uses rename
        // and leaves no source behind.
        let root = unique_tmp("rename-tree");
        let src = root.join("legacy");
        let dst = root.join("new");
        std::fs::create_dir_all(&src).unwrap();
        std::fs::write(src.join("magnotia.db"), b"data").unwrap();

        rename_or_copy_tree(&src, &dst).expect("rename ok");

        assert!(!src.exists(), "source removed");
        assert!(dst.exists(), "destination present");
        assert_eq!(std::fs::read(dst.join("magnotia.db")).unwrap(), b"data");

        std::fs::remove_dir_all(&root).ok();
    }

    #[test]
    fn is_cross_device_classifies_exdev_error_kind() {
        // Synthesise an io::Error tagged with CrossesDevices and ensure
        // the classifier returns true. This is the path that triggers
        // the copy-then-delete fallback in rename_or_copy_tree on Rust
        // 1.85+ toolchains.
        let err = std::io::Error::new(std::io::ErrorKind::CrossesDevices, "test exdev");
        assert!(is_cross_device(&err));

        let unrelated = std::io::Error::new(std::io::ErrorKind::NotFound, "test notfound");
        assert!(!is_cross_device(&unrelated));
    }

    #[cfg(unix)]
    #[test]
    fn is_cross_device_classifies_raw_exdev_on_unix() {
        // Belt-and-braces: ensure raw errno 18 (EXDEV on Linux) is
        // classified as cross-device even if the ErrorKind doesn't
        // map to CrossesDevices (older toolchains, future kernel
        // surprises).
        let err = std::io::Error::from_raw_os_error(18);
        assert!(is_cross_device(&err));
    }

    // ------------------------------------------------------------------
    // Defect A regression tests: multi-legacy-candidate + ambiguity guard
    // ------------------------------------------------------------------

    #[test]
    fn migrate_handles_both_dot_home_and_xdg() {
        // Reproduces the multi-legacy orphan scenario: a Linux user with
        // BOTH `~/.magnotia` and `~/.local/share/magnotia` on disk. The
        // old code returned `Option<(legacy, target)>` and short-circuited
        // on the dot-home variant, leaving the XDG legacy orphaned. The
        // new driver loops over the Vec and migrates every candidate.
        let root = unique_tmp("both-legacy");
        let dot_legacy = root.join(".magnotia");
        let dot_target = root.join(".lumotia");
        let xdg_legacy = root.join(".local/share/magnotia");
        let xdg_target = root.join(".local/share/lumotia");
        std::fs::create_dir_all(&dot_legacy).unwrap();
        std::fs::create_dir_all(&xdg_legacy).unwrap();
        std::fs::write(dot_legacy.join("marker"), b"dot-home").unwrap();
        std::fs::write(xdg_legacy.join("marker"), b"xdg").unwrap();

        let statuses = migrate_legacy_data_dir_with_pairs(vec![
            (dot_legacy.clone(), dot_target.clone()),
            (xdg_legacy.clone(), xdg_target.clone()),
        ])
        .expect("migrate ok");

        assert_eq!(
            statuses.len(),
            2,
            "expected one status per legacy candidate"
        );
        for s in &statuses {
            assert!(
                matches!(s, MigrationStatus::Migrated { .. }),
                "expected Migrated, got {s:?}"
            );
        }
        assert!(!dot_legacy.exists(), "dot-home legacy should be gone");
        assert!(!xdg_legacy.exists(), "XDG legacy should be gone");
        assert!(dot_target.exists(), "dot-home target should exist");
        assert!(xdg_target.exists(), "XDG target should exist");
        assert_eq!(
            std::fs::read(dot_target.join("marker")).unwrap(),
            b"dot-home".to_vec(),
            "dot-home content preserved"
        );
        assert_eq!(
            std::fs::read(xdg_target.join("marker")).unwrap(),
            b"xdg".to_vec(),
            "XDG content preserved"
        );

        std::fs::remove_dir_all(&root).ok();
    }

    #[test]
    fn resolve_app_data_dir_refuses_on_multiple_targets() {
        // Reproduces the stray-dot-home orphan scenario: after a partial
        // migration the user may end up with BOTH `~/.lumotia` and
        // `~/.local/share/lumotia` on disk. Picking one silently is
        // worse than failing fast, so the strict resolver must error
        // with both paths surfaced for manual consolidation.
        //
        // We override HOME so the strict resolver scans inside our
        // tempdir, then assert it returns Err with both paths named.
        let root = unique_tmp("ambiguous-target");
        let fake_home = root.join("home");
        std::fs::create_dir_all(&fake_home).unwrap();
        let dot = fake_home.join(".lumotia");
        let xdg_default = fake_home.join(".local/share/lumotia");
        std::fs::create_dir_all(&dot).unwrap();
        std::fs::create_dir_all(&xdg_default).unwrap();

        // Serialise env mutation: HOME / XDG_DATA_HOME are process-global,
        // and other tests in this module rely on them being unchanged.
        // We restore the previous values before returning.
        let prev_home = std::env::var_os("HOME");
        let prev_xdg = std::env::var_os("XDG_DATA_HOME");
        // SAFETY: tests in this module that read HOME serialise on this
        // exact pattern (set, call, restore) and the process is otherwise
        // single-threaded inside a #[test] body.
        std::env::set_var("HOME", &fake_home);
        std::env::remove_var("XDG_DATA_HOME");

        let result = resolve_app_data_dir_strict();

        // Restore env BEFORE asserting so a panic doesn't poison
        // subsequent tests.
        match prev_home {
            Some(v) => std::env::set_var("HOME", v),
            None => std::env::remove_var("HOME"),
        }
        if let Some(v) = prev_xdg {
            std::env::set_var("XDG_DATA_HOME", v);
        }

        let err = result.expect_err("expected ambiguity error");
        assert!(
            err.candidates.iter().any(|p| p == &dot),
            "error must name dot-home candidate: {err}"
        );
        assert!(
            err.candidates.iter().any(|p| p == &xdg_default),
            "error must name XDG default candidate: {err}"
        );
        let msg = err.to_string();
        assert!(
            msg.contains("ambiguous"),
            "message should flag ambiguity: {msg}"
        );

        std::fs::remove_dir_all(&root).ok();
    }

    // ------------------------------------------------------------------
    // Defect B regression tests: copy_dir_recursive symlink loop
    // ------------------------------------------------------------------

    #[cfg(unix)]
    #[test]
    fn copy_dir_recursive_does_not_loop_on_self_referential_dir_symlink() {
        // The original code used `entry.metadata()` which follows
        // symlinks, so a directory symlink reported is_dir==true and
        // recursed unconditionally. A self-referential dir symlink would
        // then loop until the disk filled. Use file_type() (which does
        // NOT follow symlinks), branch on is_symlink() FIRST, and
        // recreate the link instead of recursing through it.
        let root = unique_tmp("symlink-self");
        let src = root.join("src");
        let dst = root.join("dst");
        std::fs::create_dir_all(&src).unwrap();
        std::fs::write(src.join("regular-file"), b"hello").unwrap();
        // Self-reference: src/oops -> src.
        std::os::unix::fs::symlink(&src, src.join("oops")).unwrap();

        copy_dir_recursive(&src, &dst).expect("copy must terminate, not loop");

        // The regular file should have been copied.
        assert_eq!(std::fs::read(dst.join("regular-file")).unwrap(), b"hello");
        // The self-reference should have been recreated as a symlink,
        // NOT as a directory full of recursive copies.
        let oops = dst.join("oops");
        let oops_meta = std::fs::symlink_metadata(&oops).expect("oops should exist");
        assert!(
            oops_meta.file_type().is_symlink(),
            "dst/oops must be a symlink, not a recursive directory copy"
        );
        // And the link target must be preserved verbatim.
        let link_target = std::fs::read_link(&oops).unwrap();
        assert_eq!(link_target, src, "symlink target should be preserved");

        std::fs::remove_dir_all(&root).ok();
    }

    #[cfg(unix)]
    #[test]
    fn copy_dir_recursive_preserves_directory_symlinks() {
        // A directory symlink to a real sibling dir must be recreated as
        // a symlink in dst (preserving the link-shape), not dereferenced
        // into a recursive copy of the sibling's contents.
        let root = unique_tmp("symlink-dir");
        let src = root.join("src");
        let sibling = root.join("sibling");
        let dst = root.join("dst");
        std::fs::create_dir_all(&src).unwrap();
        std::fs::create_dir_all(&sibling).unwrap();
        std::fs::write(sibling.join("payload"), b"sibling-data").unwrap();
        // src/link -> sibling (directory symlink).
        std::os::unix::fs::symlink(&sibling, src.join("link")).unwrap();

        copy_dir_recursive(&src, &dst).expect("copy ok");

        let dst_link = dst.join("link");
        let meta = std::fs::symlink_metadata(&dst_link).expect("dst/link should exist");
        assert!(
            meta.file_type().is_symlink(),
            "dst/link must remain a symlink, not be replaced with a directory copy"
        );
        // Following the link should still resolve to sibling content;
        // the link target must be preserved verbatim.
        let link_target = std::fs::read_link(&dst_link).unwrap();
        assert_eq!(link_target, sibling, "symlink target should be preserved");
        // And we must NOT have written sibling/payload into dst/link/.
        // (If link is a symlink, reading dst/link/payload would follow
        // it back to sibling/payload, so check on-disk shape instead.)
        let entries: Vec<_> = std::fs::read_dir(&dst).unwrap().collect();
        let dst_link_entry = entries
            .iter()
            .find_map(|e| e.as_ref().ok())
            .filter(|e| e.file_name() == "link");
        if let Some(e) = dst_link_entry {
            assert!(
                e.file_type().unwrap().is_symlink(),
                "directory entry for dst/link must report symlink"
            );
        }

        std::fs::remove_dir_all(&root).ok();
    }

    // ------------------------------------------------------------------
    // Adversarial probes: hostile filesystem objects inside the legacy
    // tree that could turn a benign cross-device migration into a hang,
    // a silent data loss, or an unhelpful panic. These exercise the
    // copy_dir_recursive fall-through after the symlink and directory
    // branches have been ruled out. Same-filesystem rename via
    // `std::fs::rename` is atomic and bypasses these paths entirely; we
    // only need to defend the EXDEV copy fallback.
    // ------------------------------------------------------------------

    #[cfg(unix)]
    #[test]
    fn copy_dir_recursive_rejects_fifo_in_legacy_tree_without_hanging() {
        // A FIFO inside the legacy tree must NOT cause copy_dir_recursive
        // to block on std::fs::copy (open-for-read on a FIFO with no
        // writer blocks indefinitely). The hardened branch surfaces an
        // Unsupported error naming the offending path, leaving the
        // partial destination on disk for the user to consult before
        // retrying.
        let root = unique_tmp("fifo-rejected");
        let src = root.join("legacy");
        let dst = root.join("new");
        std::fs::create_dir_all(&src).unwrap();
        std::fs::write(src.join("regular.txt"), b"normal-data").unwrap();

        let fifo_path = src.join("debug-pipe");
        // mkfifo via the system binary keeps the test free of an extra
        // libc dev-dependency. The migration only needs the FIFO to be
        // present on disk so file_type().is_fifo() returns true.
        let status = std::process::Command::new("mkfifo")
            .arg(&fifo_path)
            .status()
            .expect("mkfifo invocation must run on a unix test host");
        assert!(status.success(), "mkfifo must succeed");

        // Bound the test against the regression: if a future refactor
        // re-introduces the std::fs::copy fall-through, the FIFO read
        // would hang forever and stall CI. We run copy_dir_recursive
        // on a worker thread and require it to return within a tight
        // budget; a slow CI host gets 5 seconds, which is many orders
        // of magnitude above the expected ~ms return.
        let src_owned = src.clone();
        let dst_owned = dst.clone();
        let handle = std::thread::spawn(move || copy_dir_recursive(&src_owned, &dst_owned));
        let start = std::time::Instant::now();
        let result = loop {
            if handle.is_finished() {
                break handle.join().expect("worker thread must not panic");
            }
            if start.elapsed() > std::time::Duration::from_secs(5) {
                panic!(
                    "copy_dir_recursive hung on a FIFO inside the legacy tree; \
                     suspected regression in the non-regular fall-through guard"
                );
            }
            std::thread::sleep(std::time::Duration::from_millis(10));
        };

        let err = result.expect_err("FIFO inside legacy tree must surface an error");
        assert_eq!(err.kind(), std::io::ErrorKind::Unsupported);
        let msg = err.to_string();
        assert!(
            msg.contains("debug-pipe"),
            "error must name the offending path: {msg}"
        );

        // The partial destination may or may not contain the regular
        // file depending on read_dir iteration order; we don't assert
        // either way. What matters is that the migration returns an
        // error rather than blocking forever.
        std::fs::remove_dir_all(&root).ok();
    }

    #[cfg(unix)]
    #[test]
    fn copy_dir_recursive_surfaces_permission_error_on_unreadable_file() {
        // A legacy file with mode 0000 inside the tree must cause
        // copy_dir_recursive to fail loud with PermissionDenied, not
        // silently skip the file (which would orphan user data). The
        // user can chmod the file and retry.
        use std::os::unix::fs::PermissionsExt;

        let root = unique_tmp("unreadable-file");
        let src = root.join("legacy");
        let dst = root.join("new");
        std::fs::create_dir_all(&src).unwrap();
        let locked = src.join("locked.db");
        std::fs::write(&locked, b"sensitive").unwrap();
        std::fs::set_permissions(&locked, std::fs::Permissions::from_mode(0o000)).unwrap();

        // Belt-and-braces against test-running-as-root: root bypasses
        // DAC permissions and would silently succeed, masking the
        // regression. Skip the assertion in that case so the test is
        // honest about what it proved.
        let running_as_root = effective_uid() == 0;

        let result = copy_dir_recursive(&src, &dst);

        // Restore permissions before TempDir cleanup, regardless of
        // the test outcome, so the tempdir teardown doesn't itself
        // hit EACCES.
        std::fs::set_permissions(&locked, std::fs::Permissions::from_mode(0o600)).ok();

        if running_as_root {
            // Document the bypass; the test still has value in CI
            // where the runner is non-root.
            assert!(
                result.is_ok() || result.is_err(),
                "test result intentionally not asserted under euid 0"
            );
        } else {
            let err = result.expect_err("unreadable file must surface an error");
            assert_eq!(
                err.kind(),
                std::io::ErrorKind::PermissionDenied,
                "expected PermissionDenied, got {err:?}"
            );
        }

        std::fs::remove_dir_all(&root).ok();
    }

    /// Read the effective uid by inspecting a freshly-created file's
    /// owner. Used by the permission-denied probe to skip its core
    /// assertion when the test host runs as root (root bypasses DAC).
    /// Direct over a libc dev-dependency for one helper.
    #[cfg(unix)]
    fn effective_uid() -> u32 {
        use std::os::unix::fs::MetadataExt;
        let tmp = std::env::temp_dir().join(format!("euid-probe-{}", std::process::id()));
        std::fs::write(&tmp, b"x").unwrap();
        let uid = std::fs::metadata(&tmp).unwrap().uid();
        std::fs::remove_file(&tmp).ok();
        uid
    }

    #[cfg(unix)]
    #[test]
    fn copy_dir_recursive_preserves_dangling_symlink_target() {
        // A legacy symlink pointing at a since-deleted target must be
        // recreated as a dangling symlink at the destination — NOT
        // dereferenced (which would fail) and NOT skipped (which would
        // silently drop a piece of the user's directory shape).
        let root = unique_tmp("dangling-symlink");
        let src = root.join("legacy");
        let dst = root.join("new");
        std::fs::create_dir_all(&src).unwrap();
        std::os::unix::fs::symlink("/no/such/path/ever", src.join("orphan")).unwrap();

        copy_dir_recursive(&src, &dst).expect("dangling symlink must not abort the copy");

        let orphan = dst.join("orphan");
        let meta = std::fs::symlink_metadata(&orphan).expect("orphan must exist as a link");
        assert!(
            meta.file_type().is_symlink(),
            "dst/orphan must be a symlink, not a regular file or directory"
        );
        let link_target = std::fs::read_link(&orphan).unwrap();
        assert_eq!(
            link_target,
            std::path::PathBuf::from("/no/such/path/ever"),
            "symlink target must be preserved verbatim"
        );

        std::fs::remove_dir_all(&root).ok();
    }
}