CSV/TSV Table Viewer

Overview

Ferrite v0.2.5 adds support for viewing CSV and TSV files as formatted tables. When opening .csv or .tsv files, the Rendered view mode displays the data as a scrollable table with fixed-width columns and header highlighting.

Key Files

• src/markdown/csv_viewer.rs - Main CSV viewer module (parsing, widget, state, virtual scrolling)
• src/state.rs - FileType enum with Csv/Tsv variants and is_tabular() helper
• src/app.rs - Integration with view mode system

Implementation Details

File Type Detection

The FileType enum was extended with Csv and Tsv variants:

pub enum FileType {
    Markdown,
    Json,
    Yaml,
    Toml,
    Csv,   // .csv files
    Tsv,   // .tsv files
    Unknown,
}

The is_tabular() helper identifies tabular file types:

pub fn is_tabular(&self) -> bool {
    matches!(self, Self::Csv | Self::Tsv)
}

CSV Parsing

Uses the csv crate (v1.3+) with flexible parsing:

• Auto-delimiter detection: Automatically detects comma, tab, semicolon, or pipe delimiters
• Manual override: Users can manually select delimiter via status bar dropdown
• Header detection: Automatically detects if first row is a header
• Flexible columns: Handles rows with varying column counts
• Column width calculation: Based on first 1,000 rows (sampled for performance), clamped to 50-300px

Virtual Scrolling (Task 15)

For handling large files (10,000+ rows) efficiently:

• No row limit: Parses all rows (removed previous 10,000 row limit)
• Viewport-based rendering: Uses ScrollArea::show_viewport() to determine visible rows
• Buffer rows: Renders 5 extra rows above/below viewport for smooth scrolling
• Memory efficient: Only allocates UI elements for visible rows + buffer
• Column width sampling: Samples first 1,000 rows for width calculation to optimize large file loading

const VIRTUAL_SCROLL_BUFFER: usize = 5; // Extra rows rendered above/below viewport

Table Viewer Widget

The CsvViewer widget provides:

• Header row highlighting (first row styled as bold, auto-detected or manual override)
• Horizontal/vertical scrolling via egui's ScrollArea
• Virtual scrolling for efficient large file handling
• Cell tooltips for truncated content (>50 chars)
• Large file warning (>1MB threshold)
• Theme-aware colors for light/dark modes
• Rainbow column coloring (optional, uses Oklch color space for perceptually even colors)

View Mode Integration

CSV/TSV files follow the same pattern as structured files (JSON/YAML/TOML):

• Raw mode: Plain text editor (FerriteEditor) — always editable, including files ≥ 1 MB
• Rendered mode: Table viewer with inline cell editing for files < 1 MB
• Split mode: Left pane raw editor, right pane table viewer (same editing rules as Rendered)

Rendered Cell Editing (Task 15)

For files under 1 MB (LARGE_FILE_THRESHOLD in csv_viewer.rs):

Action	Behaviour
Double-click	Enter inline edit mode on that cell (single-line TextEdit overlay)
Enter	Commit edit (or start editing the selected cell if not already editing)
Escape	Cancel edit without changing content
Click away	Commit edit when the text field loses focus
Arrow keys	Move selection when the table has focus and no cell is being edited

Commit path: Updates the in-memory CsvData model, re-serializes all rows with csv::Writer (RFC 4180 quoting), writes to Tab::content, and sets CsvViewerOutput.content_changed. central_panel.rs calls prepare_undo_snapshot_hashed() before show(), then record_edit_from_snapshot() and mark_content_edited() when content changed.

Size gating (≥ 1 MB): Rendered table is read-only. A persistent banner explains that cell editing is disabled and directs users to Raw view (Ctrl+E). Lazy row-index parsing is still used for scrolling performance.

Not editable in Rendered mode: Internal “Show Raw” preview inside the CSV widget (csv.show_raw) remains a non-interactive preview; use app-level Raw view for large-file text edits.

Dependencies Used

• csv = "1.3" - CSV parsing with RFC 4180 compliance
• palette = "0.7" - Oklch color space for rainbow column colors

Usage

1. Open any .csv or .tsv file
2. Press Ctrl+E to toggle between Raw and Rendered views
3. In Rendered view, the table displays with:
   • Header row at top (highlighted)
   • Scrollable content with virtual scrolling
   • Hover over truncated cells for full content tooltip
4. Use status bar dropdown to:
   • Change delimiter (auto-detect, comma, tab, semicolon, pipe)
   • Toggle header row on/off

Test Files

Sample test files in test_md/:

• test_data.csv - Employee data with quoted fields and commas
• test_data.tsv - Product catalog with tab-delimited columns
• large_test_data.csv - 20,000 row test file for virtual scrolling
• very_large_test_data.csv - 500,000 row test file for benchmarking

Performance Targets

• 10k+ row files: Smooth 60fps scrolling with virtual scrolling
• 100MB files: Opens in <2 seconds (parsing only, UI-ready)
• Memory: Proportional to file size (no truncation)