//! Directory walk + image detection (M1).
//!
//! Plain recursive scan of the roots (Pictures + DCIM on Android). This is
//! what makes the app testable without MediaStore; MediaStore integration is
//! a later refinement (HANDOFF.md §7.4).

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

/// One image on disk. `mtime` is nanoseconds since the Unix epoch (i64).
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Entry {
    pub path: String,
    pub mtime: i64,
    pub size: i64,
}

/// Lower-case image extensions we index. HEIC is the Android camera default.
pub const IMAGE_EXTS: &[&str] = &[
    "jpg", "jpeg", "png", "webp", "heic", "heif", "bmp", "tif", "tiff",
];

/// Scan roots. `GALLERY_SCAN_DIRS` (colon-separated) overrides — test hook.
pub fn roots() -> Vec<PathBuf> {
    if let Ok(d) = std::env::var("GALLERY_SCAN_DIRS") {
        return d
            .split(':')
            .filter(|s| !s.is_empty())
            .map(PathBuf::from)
            .collect();
    }
    #[cfg(target_os = "android")]
    {
        let ext = PathBuf::from("/storage/emulated/0");
        vec![ext.join("Pictures"), ext.join("DCIM")]
    }
    #[cfg(not(target_os = "android"))]
    {
        let home = std::env::var_os("HOME").map(PathBuf::from).unwrap_or_default();
        vec![home.join("Pictures"), home.join("DCIM")]
    }
}

/// Recursively collect all image entries below `roots`.
/// `on_progress(n)` is called every 512 files found.
pub fn walk(roots: &[PathBuf], on_progress: &dyn Fn(usize)) -> Vec<Entry> {
    walk_stream(roots, &|batch| on_progress(batch.len()))
}

/// Like `walk`, but streams progress: `on_batch(&entries)` receives ALL
/// entries collected so far every 512 new files, so the UI can show results
/// while the scan is still running (first launch must not wait for the full
/// DB build).
pub fn walk_stream(roots: &[PathBuf], on_batch: &dyn Fn(&[Entry])) -> Vec<Entry> {
    let mut out = Vec::new();
    for r in roots {
        if r.is_dir() {
            walk_dir(r, &mut out, on_batch);
        }
    }
    out
}

fn walk_dir(dir: &Path, out: &mut Vec<Entry>, on_batch: &dyn Fn(&[Entry])) {
    let Ok(rd) = std::fs::read_dir(dir) else { return };
    for ent in rd.flatten() {
        let p = ent.path();
        let Ok(ft) = ent.file_type() else { continue };
        if ft.is_dir() {
            // Skip hidden dirs (.thumbnails, .trash, …) — metadata, not photos.
            if p.file_name().and_then(|n| n.to_str()).is_some_and(|n| n.starts_with('.')) {
                continue;
            }
            // Don't follow symlinked dirs (loop protection).
            if !p.is_symlink() {
                walk_dir(&p, out, on_batch);
            }
            continue;
        }
        if !ft.is_file() {
            continue;
        }
        let Some(ext) = p.extension().and_then(|e| e.to_str()) else { continue };
        if !IMAGE_EXTS.contains(&ext.to_ascii_lowercase().as_str()) {
            continue;
        }
        let Ok(md) = std::fs::metadata(&p) else { continue };
        let mtime = md
            .modified()
            .ok()
            .and_then(|t| t.duration_since(std::time::UNIX_EPOCH).ok())
            .map(|d| d.as_nanos() as i64)
            .unwrap_or(0);
        out.push(Entry {
            path: p.to_string_lossy().into_owned(),
            mtime,
            size: md.len() as i64,
        });
        if out.len() % 512 == 0 {
            on_batch(out);
        }
    }
}

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

    fn make_tree(root: &Path, n_files: usize, subdirs: usize) {
        for d in 0..subdirs {
            let dir = root.join(format!("dir{d}"));
            std::fs::create_dir_all(&dir).unwrap();
        }
        for i in 0..n_files {
            let dir = if i % 2 == 0 { root.join(format!("dir{}", i % subdirs)) } else { root.to_path_buf() };
            let mut f = std::fs::File::create(dir.join(format!("img{i}.jpg"))).unwrap();
            f.write_all(&vec![0u8; i % 64]).unwrap();
        }
    }

    #[test]
    fn finds_images_skips_others() {
        let dir = tempfile::tempdir().unwrap();
        std::fs::write(dir.path().join("a.jpg"), b"x").unwrap();
        std::fs::write(dir.path().join("B.PNG"), b"x").unwrap();
        std::fs::write(dir.path().join("c.txt"), b"x").unwrap();
        std::fs::create_dir_all(dir.path().join("d")).unwrap();
        std::fs::write(dir.path().join("d").join("e.heic"), b"x").unwrap();
        let out = walk(&[dir.path().to_path_buf()], &|_| {});
        assert_eq!(out.len(), 3);
        assert!(out.iter().all(|e| e.size == 1));
    }

    #[test]
    fn accepts_5k_files_under_2s() {
        let dir = tempfile::tempdir().unwrap();
        make_tree(dir.path(), 5000, 8);
        let t = std::time::Instant::now();
        let out = walk(&[dir.path().to_path_buf()], &|_| {});
        let elapsed = t.elapsed();
        assert_eq!(out.len(), 5000);
        assert!(
            elapsed.as_millis() < 2000,
            "scan took {:?} (> 2 s)",
            elapsed
        );
    }
}