Calculate the column widths using cassowary

fdehau/tui-rs#499 (comment)

Cargo.toml

@@ -9,6 +9,7 @@ edition = "2018"
 [dependencies]
 git2 = "0.13"
 crossterm = { version = "0.19" }
-tui = { version = "0.14", default-features = false, features = ['crossterm'] }
+tui = { version = "0.16", default-features = false, features = ['crossterm'] }
+cassowary = "0.3"  # keep this in sync /w tui?
 clap = { version = "3.0.0-beta.2" }
 chrono = "0.4.19"

src/main.rs

@@ -30,6 +30,10 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let tick_rate = std::time::Duration::from_millis(200);
     let mut handler = controller::EventHandler::new(tick_rate);
 
+    let bounds: Vec<_> = (0..6).map(|_| cassowary::Variable::new()).collect();
+    let window_width = cassowary::Variable::new();
+    let mut column_solver = widgets::commit_list_column_width_solver(&bounds, &window_width);
+
     // TODO: use RAII for this somehow
     crossterm::execute!(std::io::stdout(), crossterm::terminal::EnterAlternateScreen)?;
     crossterm::terminal::enable_raw_mode().expect("can run in raw mode");
@@ -85,17 +89,18 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
             drop(commits);
             app_model.resize_revision_window(length);
 
+            column_solver
+                .suggest_value(window_width, chunk_commit.width as f64)
+                .expect("constraints solver failed");
+            let column_widths = widgets::solver_changes_to_lengths(&column_solver, &bounds);
+
             let list = tui::widgets::Table::new(commit_items)
                 .block(commits_block)
                 .highlight_style(
                     tui::style::Style::default().add_modifier(tui::style::Modifier::BOLD),
                 )
                 // TODO: https://github.com/fdehau/tui-rs/issues/499
-                .widths(&[
-                    tui::layout::Constraint::Length(84),
-                    tui::layout::Constraint::Length(40),
-                    tui::layout::Constraint::Length(10), // Commit date (truncates time by default)
-                ]);
+                .widths(column_widths.as_slice());
 
             let (details_index, details_window, details_length) = app_model.diff_line_scroll();
             let details_scroll = widgets::VerticalBar {

src/widgets.rs

@@ -1,3 +1,6 @@
+use cassowary::strength::{REQUIRED, STRONG, WEAK};
+use cassowary::WeightedRelation::*;
+use cassowary::{Solver, Variable};
 use tui::buffer::Buffer;
 use tui::layout::Rect;
 use tui::style::Style;
@@ -46,3 +49,57 @@ impl Widget for VerticalBar {
         buf.set_style(window_area, self.style);
     }
 }
+
+// bounds consists of pairs of variables representing left and right position of the column
+pub fn commit_list_column_width_solver(bounds: &[Variable], window_width: &Variable) -> Solver {
+    let mut solver = Solver::new();
+    solver
+        .add_constraints(&[
+            *window_width | GE(REQUIRED) | 0.0, // positive window width
+            bounds[0] | EQ(REQUIRED) | 0.0,     // left align
+            bounds[3] | EQ(REQUIRED) | bounds[4] - 1.0, // right align
+            bounds[5] | EQ(REQUIRED) | *window_width, // right align
+            bounds[2] | GE(REQUIRED) | bounds[1], // no overlap
+            bounds[4] | GE(REQUIRED) | bounds[3], // no overlap
+            // positive widths
+            bounds[0] | LE(REQUIRED) | bounds[1],
+            bounds[2] | LE(REQUIRED) | bounds[3],
+            bounds[4] | LE(REQUIRED) | bounds[5],
+            // preferred widths:
+            bounds[1] - bounds[0] | EQ(WEAK) | *window_width * (72.0 / 100.0),
+            bounds[3] - bounds[2] | EQ(WEAK) | *window_width * (18.0 / 100.0),
+            bounds[5] - bounds[4] | EQ(WEAK) | *window_width * (9.0 / 100.0),
+            // constrain some columns to a range:
+            bounds[3] - bounds[2] | LE(REQUIRED) | 40.0,
+            bounds[3] - bounds[2] | GE(STRONG) | 20.0,
+            bounds[5] - bounds[4] | LE(REQUIRED) | 15.0,
+            bounds[5] - bounds[4] | GE(STRONG) | 10.0,
+            // require one column to have a minimum size
+            bounds[1] - bounds[0] | GE(STRONG) | 50.0,
+            // fixed length
+            //box1.right - box1.left | EQ(WEAK) | 79.0,
+            //box2.right - box2.left | EQ(WEAK) | 20.0,
+            //box3.right - box3.left | EQ(WEAK) | 10.0,
+        ])
+        .unwrap();
+    solver
+        .add_edit_variable(*window_width, STRONG)
+        .expect("Unable to add edit variable");
+
+    solver
+}
+
+pub fn solver_changes_to_lengths(
+    solver: &Solver,
+    bounds: &[Variable],
+) -> Vec<tui::layout::Constraint> {
+    let widths: Vec<_> = bounds
+        .windows(2)
+        .map(|bounds| solver.get_value(bounds[1]) - solver.get_value(bounds[0]))
+        .collect();
+    vec![
+        tui::layout::Constraint::Length((widths[0] + widths[1]) as u16),
+        tui::layout::Constraint::Length((widths[2] + widths[3]) as u16),
+        tui::layout::Constraint::Length((widths[4]) as u16),
+    ]
+}