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249//! ASCII table renderer with Unicode box-drawing borders for CLI output.
//!
//! Supports column alignment, auto-width, header styling, and optional colored
//! output via the `colored` crate.
use colored::Colorize;
/// Column alignment.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Align {
Left,
Right,
Center,
}
/// A table builder that collects headers and rows, then renders to a
/// Unicode box-drawing string.
pub struct Table {
headers: Vec<String>,
alignments: Vec<Align>,
rows: Vec<Vec<String>>,
}
impl Table {
/// Create a new table with the given column headers.
/// All columns default to left-alignment.
pub fn new(headers: &[&str]) -> Self {
let headers: Vec<String> = headers.iter().map(|h| h.to_string()).collect();
let alignments = vec![Align::Left; headers.len()];
Self {
headers,
alignments,
rows: Vec::new(),
}
}
/// Override the alignment for a specific column (0-indexed).
/// Out-of-range indices are silently ignored.
pub fn align(mut self, col: usize, alignment: Align) -> Self {
if col < self.alignments.len() {
self.alignments[col] = alignment;
}
self
}
/// Add a row. Extra cells are truncated; missing cells are filled with "".
pub fn add_row(&mut self, cells: &[&str]) {
let row: Vec<String> = (0..self.headers.len())
.map(|i| cells.get(i).unwrap_or(&"").to_string())
.collect();
self.rows.push(row);
}
/// Compute the display width of each column (max of header and all cells).
fn column_widths(&self) -> Vec<usize> {
let mut widths: Vec<usize> = self.headers.iter().map(|h| h.len()).collect();
for row in &self.rows {
for (i, cell) in row.iter().enumerate() {
if i < widths.len() {
widths[i] = widths[i].max(cell.len());
}
}
}
widths
}
/// Pad a string to the given width according to alignment.
fn pad(text: &str, width: usize, alignment: Align) -> String {
let len = text.len();
if len >= width {
return text.to_string();
}
let diff = width - len;
match alignment {
Align::Left => format!("{text}{}", " ".repeat(diff)),
Align::Right => format!("{}{text}", " ".repeat(diff)),
Align::Center => {
let left = diff / 2;
let right = diff - left;
format!("{}{text}{}", " ".repeat(left), " ".repeat(right))
}
}
}
/// Build a horizontal border line.
/// `left`, `mid`, `right` are the corner/junction characters.
fn border(widths: &[usize], left: &str, mid: &str, right: &str) -> String {
let segments: Vec<String> = widths.iter().map(|w| "\u{2500}".repeat(w + 2)).collect();
format!("{left}{}{right}", segments.join(mid))
}
/// Render the table to a string with Unicode box-drawing borders.
///
/// Layout:
/// ```text
/// ┌──────┬───────┐
/// │ Name │ Value │
/// ├──────┼───────┤
/// │ foo │ bar │
/// └──────┴───────┘
/// ```
pub fn render(&self) -> String {
let widths = self.column_widths();
let top = Self::border(&widths, "\u{250c}", "\u{252c}", "\u{2510}");
let sep = Self::border(&widths, "\u{251c}", "\u{253c}", "\u{2524}");
let bot = Self::border(&widths, "\u{2514}", "\u{2534}", "\u{2518}");
let mut lines = Vec::new();
// Top border
lines.push(top);
// Header row (bold)
let header_cells: Vec<String> = self
.headers
.iter()
.enumerate()
.map(|(i, h)| format!(" {} ", Self::pad(h, widths[i], self.alignments[i]).bold()))
.collect();
lines.push(format!("\u{2502}{}\u{2502}", header_cells.join("\u{2502}")));
// Separator
lines.push(sep);
// Data rows
for row in &self.rows {
let cells: Vec<String> = row
.iter()
.enumerate()
.map(|(i, cell)| format!(" {} ", Self::pad(cell, widths[i], self.alignments[i])))
.collect();
lines.push(format!("\u{2502}{}\u{2502}", cells.join("\u{2502}")));
}
// Bottom border
lines.push(bot);
lines.join("\n")
}
/// Render the table and print it to stdout.
pub fn print(&self) {
println!("{}", self.render());
}
}
// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn basic_table() {
let mut t = Table::new(&["Name", "Age", "City"]);
t.add_row(&["Alice", "30", "London"]);
t.add_row(&["Bob", "25", "Paris"]);
let rendered = t.render();
let lines: Vec<&str> = rendered.lines().collect();
// 5 lines: top, header, sep, 2 rows, bottom = 6
assert_eq!(lines.len(), 6);
// Top border uses box-drawing
assert!(lines[0].starts_with('\u{250c}'));
assert!(lines[0].ends_with('\u{2510}'));
// Bottom border
assert!(lines[5].starts_with('\u{2514}'));
assert!(lines[5].ends_with('\u{2518}'));
// Header line contains column names (ignore ANSI codes for bold)
assert!(lines[1].contains("Name"));
assert!(lines[1].contains("Age"));
assert!(lines[1].contains("City"));
// Data rows contain cell values
assert!(lines[3].contains("Alice"));
assert!(lines[3].contains("30"));
assert!(lines[3].contains("London"));
assert!(lines[4].contains("Bob"));
assert!(lines[4].contains("25"));
assert!(lines[4].contains("Paris"));
}
#[test]
fn right_alignment() {
let mut t = Table::new(&["Item", "Count"]);
t = t.align(1, Align::Right);
t.add_row(&["apples", "5"]);
t.add_row(&["oranges", "123"]);
let rendered = t.render();
// The "5" should be right-padded on the left within its column
// Find the data line with "5"
let line = rendered.lines().find(|l| l.contains("apples")).unwrap();
// After the second box char, the number should be right-aligned
assert!(line.contains(" 5"));
}
#[test]
fn center_alignment() {
let pad = Table::pad("hi", 6, Align::Center);
assert_eq!(pad, " hi ");
let pad_odd = Table::pad("hi", 7, Align::Center);
assert_eq!(pad_odd, " hi ");
}
#[test]
fn empty_table() {
let t = Table::new(&["A", "B"]);
let rendered = t.render();
let lines: Vec<&str> = rendered.lines().collect();
// top, header, sep, bottom = 4 lines (no data rows)
assert_eq!(lines.len(), 4);
}
#[test]
fn missing_cells_filled() {
let mut t = Table::new(&["X", "Y", "Z"]);
t.add_row(&["only-one"]);
let rendered = t.render();
// Row should still have 3 columns; missing ones are empty
let data_line = rendered.lines().nth(3).unwrap();
// Count box-drawing vertical bars in data line
let bars = data_line.matches('\u{2502}').count();
assert_eq!(bars, 4); // left + 2 inner + right
}
#[test]
fn wide_cells_auto_width() {
let mut t = Table::new(&["ID", "Description"]);
t.add_row(&["1", "A very long description string"]);
let rendered = t.render();
assert!(rendered.contains("A very long description string"));
// The top border should be wide enough to contain the description
let top = rendered.lines().next().unwrap();
// At minimum: 2 padding + description length for second column
assert!(top.len() > 30);
}
}