feat(viewer): directory-tree browser + plain-text viewer

Explorer drawer was a flat list of all 353 disc files and only textures had a
preview. Two additions:

1. Directory tree — the left drawer is now a collapsible `📁` tree, rebuilt each
   frame from the path list (ui.rs: build_tree / split_for_tree / render_dir).
   Filtering narrows leaves and auto-expands matches; `.p00…p04` data segments
   nest under a virtual `<stem>.pak` node. Selection still keys off the original
   file index, so the loader pipeline is untouched.

2. Plain-text viewer — config.ini and any file that sniffs as text now show
   read-only, selectable, monospace content with a Wrap toggle and an encoding
   label. Detection/decoding live in the Bevy-free formats crate:
   vfs::is_probably_text + vfs::decode_text (BOM-aware UTF-8/UTF-16LE/BE, BOM-less
   UTF-16LE heuristic, NUL-reject + 95%-printable fallback) — pure std, WASM-safe,
   unit-tested (6 new tests), and reused by the CLI sniffer (new cyan `txt`).

New TextPreview resource (registered unconditionally so it exists on wasm);
populated in apply_loaded_texture with a 2 MiB char-boundary-safe cap. Also fixes
a latent bug: switching from a texture to a non-texture left stale preview state —
both texture and text state now reset on every selection.

ViewerState gains text_wrap. Formats tests: 22 pass; workspace compiles.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/sylpheed-cli/src/main.rs

@@ -272,6 +272,7 @@ fn cmd_sniff(dir: &Path, unknown_only: bool) -> Result<()> {
             "bin" => label.red().to_string(),
             "xpr" => label.green().to_string(),
             "dds" => label.green().to_string(),
+            "txt" => label.cyan().to_string(),
             _ => label.yellow().to_string(),
         };
 

crates/sylpheed-formats/src/vfs.rs

@@ -108,7 +108,12 @@ impl GameAssets {
 /// Use this to identify unknown file types during reverse engineering.
 pub fn identify_format(bytes: &[u8]) -> FileFormat {
     if bytes.len() < 4 {
-        return FileFormat::Unknown;
+        // Very short files can still be text (e.g. a one-line config).
+        return if is_probably_text(bytes) {
+            FileFormat::Text
+        } else {
+            FileFormat::Unknown
+        };
     }
     match &bytes[..4] {
         b"XPR2" => FileFormat::Xpr2Texture,
@@ -116,6 +121,10 @@ pub fn identify_format(bytes: &[u8]) -> FileFormat {
         b"XWB\0" => FileFormat::XwbAudio, // Xbox Wave Bank
         [0x89, b'P', b'N', b'G'] => FileFormat::Png,
         b"DDS " => FileFormat::Dds,
+        // No binary magic matched — fall back to a content heuristic so text
+        // configs (`config.ini`, etc.) are recognised even though they have no
+        // signature.
+        _ if is_probably_text(bytes) => FileFormat::Text,
         _ => FileFormat::Unknown,
     }
 }
@@ -127,6 +136,8 @@ pub enum FileFormat {
     XwbAudio,
     Png,
     Dds,
+    /// Plain text (ASCII / UTF-8 / UTF-16) — `.ini` and similar.
+    Text,
     Unknown,
 }
 
@@ -138,7 +149,162 @@ impl FileFormat {
             Self::XwbAudio => "xwb",
             Self::Png => "png",
             Self::Dds => "dds",
+            Self::Text => "txt",
             Self::Unknown => "bin",
         }
     }
 }
+
+// ── Text detection & decoding (pure std, WASM-safe) ───────────────────────────
+
+/// True if `b` is a byte we'd expect inside a text file: common whitespace,
+/// printable ASCII, or any high byte (UTF-8 continuation / Latin-1). Mirrors the
+/// printable convention used by the IDXD string-pool extractor.
+#[inline]
+fn is_text_byte(b: u8) -> bool {
+    matches!(b, b'\t' | b'\n' | b'\r') || (0x20..0x7f).contains(&b) || b >= 0x80
+}
+
+/// Heuristic sniff for whether `bytes` is human-readable text.
+///
+/// Recognises UTF-8 / UTF-16 BOMs outright, BOM-less UTF-16LE by its
+/// characteristic odd-position NUL bytes, and otherwise requires a byte sample
+/// to be almost entirely text bytes with no embedded NUL (NUL is the strongest
+/// binary signal). Decoding is left to [`decode_text`].
+pub fn is_probably_text(bytes: &[u8]) -> bool {
+    if bytes.is_empty() {
+        return false;
+    }
+    // Byte-order marks are unambiguous.
+    if bytes.starts_with(&[0xEF, 0xBB, 0xBF]) // UTF-8
+        || bytes.starts_with(&[0xFF, 0xFE])   // UTF-16LE
+        || bytes.starts_with(&[0xFE, 0xFF])
+    // UTF-16BE
+    {
+        return true;
+    }
+
+    // Cap the scan so huge files stay cheap.
+    let sample = &bytes[..bytes.len().min(4096)];
+
+    // BOM-less UTF-16LE: ASCII text encodes as `<char> 0x00 <char> 0x00 …`, so
+    // roughly half the bytes (the odd positions) are NUL and the even bytes are
+    // printable.
+    if sample.len() >= 16 {
+        let nul_odd = sample.iter().skip(1).step_by(2).filter(|&&b| b == 0).count();
+        if nul_odd * 2 >= sample.len() / 2 {
+            let printable_even = sample.iter().step_by(2).filter(|&&b| is_text_byte(b)).count();
+            if printable_even * 2 >= sample.len() / 2 - 2 {
+                return true;
+            }
+        }
+    }
+
+    // Single-byte (ASCII / UTF-8): an embedded NUL means binary; otherwise
+    // require the overwhelming majority to be text bytes.
+    if sample.contains(&0) {
+        return false;
+    }
+    let text = sample.iter().filter(|&&b| is_text_byte(b)).count();
+    text * 100 >= sample.len() * 95
+}
+
+/// Decode `bytes` to a `String`, returning `(text, encoding_label)`.
+///
+/// Honours UTF-8 / UTF-16LE / UTF-16BE BOMs and BOM-less UTF-16LE, falling back
+/// to lossy UTF-8. Never fails — undecodable sequences become U+FFFD. Pure std,
+/// so both the viewer and CLI can share it.
+pub fn decode_text(bytes: &[u8]) -> (String, &'static str) {
+    if let Some(rest) = bytes.strip_prefix(&[0xEF, 0xBB, 0xBF]) {
+        return (String::from_utf8_lossy(rest).into_owned(), "UTF-8 (BOM)");
+    }
+    if let Some(rest) = bytes.strip_prefix(&[0xFF, 0xFE]) {
+        return (decode_utf16(rest, false), "UTF-16LE (BOM)");
+    }
+    if let Some(rest) = bytes.strip_prefix(&[0xFE, 0xFF]) {
+        return (decode_utf16(rest, true), "UTF-16BE (BOM)");
+    }
+    // BOM-less UTF-16LE detection (same signal as `is_probably_text`).
+    let sample = &bytes[..bytes.len().min(4096)];
+    if sample.len() >= 16 {
+        let nul_odd = sample.iter().skip(1).step_by(2).filter(|&&b| b == 0).count();
+        if nul_odd * 2 >= sample.len() / 2 {
+            return (decode_utf16(bytes, false), "UTF-16LE");
+        }
+    }
+    (String::from_utf8_lossy(bytes).into_owned(), "UTF-8 / ASCII")
+}
+
+fn decode_utf16(bytes: &[u8], big_endian: bool) -> String {
+    let units: Vec<u16> = bytes
+        .chunks_exact(2)
+        .map(|c| {
+            if big_endian {
+                u16::from_be_bytes([c[0], c[1]])
+            } else {
+                u16::from_le_bytes([c[0], c[1]])
+            }
+        })
+        .collect();
+    String::from_utf16_lossy(&units)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ascii_config_is_text() {
+        let ini = b"[Video]\r\nWidth=1280\r\nHeight=720\r\n";
+        assert!(is_probably_text(ini));
+        assert_eq!(identify_format(ini), FileFormat::Text);
+        let (text, enc) = decode_text(ini);
+        assert!(text.contains("Width=1280"));
+        assert_eq!(enc, "UTF-8 / ASCII");
+    }
+
+    #[test]
+    fn magic_takes_precedence_over_text() {
+        // An XPR2 header happens to start with printable bytes; the magic match
+        // must win so it's never misfiled as text.
+        let mut xpr = b"XPR2".to_vec();
+        xpr.extend_from_slice(&[0u8; 32]);
+        assert_eq!(identify_format(&xpr), FileFormat::Xpr2Texture);
+    }
+
+    #[test]
+    fn binary_with_nul_is_not_text() {
+        let bin = [0u8, 1, 2, 0xFF, 0x00, 0x89, 0x10, 0x00, 0x42];
+        assert!(!is_probably_text(&bin));
+        assert_eq!(identify_format(&bin), FileFormat::Unknown);
+    }
+
+    #[test]
+    fn utf16le_bom_is_text_and_decodes() {
+        let data = [0xFF, 0xFE, b'H', 0x00, b'i', 0x00];
+        assert!(is_probably_text(&data));
+        assert_eq!(identify_format(&data), FileFormat::Text);
+        let (text, enc) = decode_text(&data);
+        assert_eq!(text, "Hi");
+        assert_eq!(enc, "UTF-16LE (BOM)");
+    }
+
+    #[test]
+    fn bomless_utf16le_detected() {
+        // "Hello, world!!!!" as UTF-16LE, no BOM (>=16 bytes so the heuristic runs).
+        let mut data = Vec::new();
+        for &b in b"Hello, world!!!!" {
+            data.push(b);
+            data.push(0);
+        }
+        assert!(is_probably_text(&data));
+        let (text, enc) = decode_text(&data);
+        assert_eq!(text, "Hello, world!!!!");
+        assert_eq!(enc, "UTF-16LE");
+    }
+
+    #[test]
+    fn empty_is_not_text() {
+        assert!(!is_probably_text(&[]));
+    }
+}

crates/sylpheed-viewer/src/iso_loader.rs

@@ -90,6 +90,22 @@ pub struct FileInfo {
     pub detected_format: Option<FileFormat>,
 }
 
+/// Decoded contents of the currently-selected text file, shown in the central
+/// panel. `content` is `None` whenever the selection isn't text.
+#[derive(Resource, Default)]
+pub struct TextPreview {
+    /// Decoded UTF-8 (any BOM / UTF-16 already resolved), or `None`.
+    pub content: Option<String>,
+    /// Encoding label for the header, e.g. "UTF-16LE (BOM)".
+    pub encoding: String,
+    /// True when the file was larger than `MAX_TEXT_BYTES` and got clipped.
+    pub truncated: bool,
+}
+
+/// Cap on the decoded text we hand to egui — its text layout cost grows
+/// super-linearly, and disc config files are only a few KiB anyway.
+const MAX_TEXT_BYTES: usize = 2 * 1024 * 1024;
+
 // ── SystemSet label ───────────────────────────────────────────────────────────
 
 /// `draw_viewer_ui` runs `.after(IsoLoaderSystemSet)` to see the frame's
@@ -157,7 +173,10 @@ impl Plugin for IsoLoaderPlugin {
             .add_event::<FileSelected>()
             .init_resource::<IsoState>()
             .init_resource::<TexturePreview>()
-            .init_resource::<FileInfo>();
+            .init_resource::<FileInfo>()
+            // Registered unconditionally (even on wasm, where the load systems
+            // below are cfg'd out) so the UI can always read it.
+            .init_resource::<TextPreview>();
 
         #[cfg(not(target_arch = "wasm32"))]
         {
@@ -392,6 +411,7 @@ fn poll_loader_channel(
 fn apply_loaded_texture(
     mut pending: ResMut<PendingFileBytes>,
     mut preview: ResMut<TexturePreview>,
+    mut text_preview: ResMut<TextPreview>,
     mut file_info: ResMut<FileInfo>,
     mut images: ResMut<Assets<Image>>,
     mut contexts: bevy_egui::EguiContexts,
@@ -412,6 +432,9 @@ fn apply_loaded_texture(
         images.remove(handle.id());
     }
     *preview = TexturePreview::default();
+    // Clear stale text too, so switching files never shows a previous file's
+    // content in the wrong panel.
+    *text_preview = TextPreview::default();
 
     // Populate FileInfo for the status / info panel.
     file_info.name = path
@@ -422,6 +445,25 @@ fn apply_loaded_texture(
     file_info.size_bytes = bytes.len();
     file_info.detected_format = Some(fmt);
 
+    if fmt == FileFormat::Text {
+        let (mut text, encoding) = sylpheed_formats::vfs::decode_text(&bytes);
+        let truncated = text.len() > MAX_TEXT_BYTES;
+        if truncated {
+            // Cut on a char boundary so we never split a codepoint.
+            let end = text
+                .char_indices()
+                .take_while(|(i, _)| *i < MAX_TEXT_BYTES)
+                .last()
+                .map(|(i, c)| i + c.len_utf8())
+                .unwrap_or(0);
+            text.truncate(end);
+        }
+        text_preview.content = Some(text);
+        text_preview.encoding = encoding.to_string();
+        text_preview.truncated = truncated;
+        return; // FileInfo + TextPreview are sufficient for text files.
+    }
+
     if fmt != FileFormat::Xpr2Texture {
         return; // Not a texture — FileInfo is sufficient
     }

crates/sylpheed-viewer/src/lib.rs

@@ -32,6 +32,8 @@ pub struct ViewerState {
     pub current_mode: ViewMode,
     /// Whether to render meshes in wireframe mode (toggle with F2).
     pub wireframe: bool,
+    /// Whether the plain-text viewer wraps long lines.
+    pub text_wrap: bool,
 }
 
 impl Default for ViewerState {
@@ -39,6 +41,7 @@ impl Default for ViewerState {
         Self {
             current_mode: ViewMode::Textures,
             wireframe: false,
+            text_wrap: true,
         }
     }
 }

crates/sylpheed-viewer/src/ui.rs

@@ -10,7 +10,7 @@ use bevy::prelude::*;
 use bevy_egui::{egui, EguiContexts};
 
 use crate::iso_loader::{
-    FileInfo, FileSelected, IsoState, RequestOpenDir, RequestOpenIso, TexturePreview,
+    FileInfo, FileSelected, IsoState, RequestOpenDir, RequestOpenIso, TextPreview, TexturePreview,
     IsoLoaderSystemSet,
 };
 use crate::{ViewerState, ViewMode};
@@ -33,12 +33,91 @@ pub struct FileBrowserState {
     pub filter: String,
 }
 
+// ── Directory tree ────────────────────────────────────────────────────────────
+
+/// One directory node in the ephemeral file tree. Rebuilt from the flat path
+/// list each frame; leaves carry their original index into `browser.files` so
+/// selection stays stable regardless of tree shape or filtering.
+#[derive(Default)]
+struct TreeDir {
+    /// Child directories, keyed by name (`BTreeMap` = stable alphabetical order).
+    dirs: std::collections::BTreeMap<String, TreeDir>,
+    /// Leaf files: (display name, original index into `browser.files`).
+    files: Vec<(String, usize)>,
+}
+
+/// Split a full path into (directory components, leaf name), grouping data
+/// segments (`foo.p00`, `foo.p01`, …) under a virtual `foo.pak` directory so a
+/// pack and its segments sit together. Purely cosmetic — indices are untouched.
+fn split_for_tree(full: &str) -> (Vec<String>, String) {
+    let mut comps: Vec<String> = full.split('/').map(str::to_string).collect();
+    let leaf = comps.pop().unwrap_or_default();
+    if let Some((stem, ext)) = leaf.rsplit_once('.') {
+        let e = ext.as_bytes();
+        // `.pNN` where NN are two digits → nest under "<stem>.pak".
+        if e.len() == 3 && e[0] == b'p' && e[1].is_ascii_digit() && e[2].is_ascii_digit() {
+            comps.push(format!("{stem}.pak"));
+        }
+    }
+    (comps, leaf)
+}
+
+/// Build the directory tree, keeping only leaves whose full path contains
+/// `filter` (case-insensitive; empty filter keeps everything).
+fn build_tree(files: &[String], filter: &str) -> TreeDir {
+    let filter = filter.to_lowercase();
+    let mut root = TreeDir::default();
+    for (idx, full) in files.iter().enumerate() {
+        if !filter.is_empty() && !full.to_lowercase().contains(&filter) {
+            continue;
+        }
+        let (dirs, leaf) = split_for_tree(full);
+        let mut node = &mut root;
+        for comp in dirs {
+            node = node.dirs.entry(comp).or_default();
+        }
+        node.files.push((leaf, idx));
+    }
+    root
+}
+
+/// Render a directory node recursively: sub-directories (collapsible) first,
+/// then leaf files as selectable labels.
+fn render_dir(
+    ui: &mut egui::Ui,
+    node: &TreeDir,
+    force_open: bool,
+    selected: &mut Option<usize>,
+    events: &mut EventWriter<FileSelected>,
+    files: &[String],
+) {
+    for (name, child) in &node.dirs {
+        egui::CollapsingHeader::new(format!("📁 {name}"))
+            .id_salt(name)
+            .default_open(force_open)
+            .show(ui, |ui| {
+                render_dir(ui, child, force_open, selected, events, files);
+            });
+    }
+    for (leaf, idx) in &node.files {
+        let is_selected = *selected == Some(*idx);
+        if ui
+            .add(egui::SelectableLabel::new(is_selected, leaf.as_str()))
+            .clicked()
+        {
+            *selected = Some(*idx);
+            events.send(FileSelected(files[*idx].clone()));
+        }
+    }
+}
+
 fn draw_viewer_ui(
     mut contexts: EguiContexts,
     mut viewer: ResMut<ViewerState>,
     mut browser: ResMut<FileBrowserState>,
     iso_state: Res<IsoState>,
     preview: Res<TexturePreview>,
+    text_preview: Res<TextPreview>,
     file_info: Res<FileInfo>,
     mut open_iso_events: EventWriter<RequestOpenIso>,
     mut open_dir_events: EventWriter<RequestOpenDir>,
@@ -138,26 +217,21 @@ fn draw_viewer_ui(
                          or File → Open extracted folder.",
                     );
                 } else {
-                    let filter = browser.filter.to_lowercase();
-                    let filtered: Vec<(usize, String)> = browser
-                        .files
-                        .iter()
-                        .enumerate()
-                        .filter(|(_, f)| {
-                            filter.is_empty() || f.to_lowercase().contains(&filter)
-                        })
-                        .map(|(i, f)| (i, f.clone()))
-                        .collect();
-
-                    for (idx, file) in &filtered {
-                        let is_selected = browser.selected == Some(*idx);
-                        let label =
-                            egui::SelectableLabel::new(is_selected, file.as_str());
-                        if ui.add(label).clicked() {
-                            browser.selected = Some(*idx);
-                            file_selected_events.send(FileSelected(file.clone()));
-                        }
-                    }
+                    // Build a directory tree from the flat path list. Cheap to
+                    // rebuild every frame (a few hundred short paths); cloning
+                    // `files` first sidesteps borrowing `browser` immutably and
+                    // mutably (selected) at the same time.
+                    let files = browser.files.clone();
+                    let tree = build_tree(&files, &browser.filter);
+                    let force_open = !browser.filter.is_empty();
+                    render_dir(
+                        ui,
+                        &tree,
+                        force_open,
+                        &mut browser.selected,
+                        &mut file_selected_events,
+                        &files,
+                    );
                 }
             });
         });
@@ -184,7 +258,37 @@ fn draw_viewer_ui(
     // ── Central area ──────────────────────────────────────────────────────
     if browser.selected.is_some() {
         egui::CentralPanel::default().show(ctx, |ui| {
-            if let Some(egui_id) = preview.egui_id {
+            if let Some(text) = &text_preview.content {
+                // ── Plain-text viewer ──
+                ui.horizontal(|ui| {
+                    ui.heading(&file_info.name);
+                    ui.separator();
+                    ui.label(&text_preview.encoding);
+                    ui.separator();
+                    ui.checkbox(&mut viewer.text_wrap, "Wrap");
+                    if text_preview.truncated {
+                        ui.separator();
+                        ui.colored_label(egui::Color32::YELLOW, "(truncated)");
+                    }
+                });
+                ui.separator();
+
+                egui::ScrollArea::both().show(ui, |ui| {
+                    // Read-only: `&str` is a non-editable TextBuffer, and
+                    // `.interactive(false)` keeps it selectable/copyable.
+                    let mut buf = text.as_str();
+                    let mut edit = egui::TextEdit::multiline(&mut buf)
+                        .font(egui::TextStyle::Monospace)
+                        .code_editor()
+                        .desired_width(f32::INFINITY)
+                        .interactive(false);
+                    if !viewer.text_wrap {
+                        // Don't wrap: let ScrollArea scroll horizontally.
+                        edit = edit.clip_text(false);
+                    }
+                    ui.add(edit);
+                });
+            } else if let Some(egui_id) = preview.egui_id {
                 // Texture preview
                 ui.heading(&file_info.name);
                 ui.label(&preview.format_info);