feat: add stats view mode with streaks and completion rate

Add a fifth view mode, Stats, to the `v` cycle
(day -> week -> month -> year -> stats). For each habit it shows the
current streak, longest streak, total completions, and a completion
rate over the span since the first reached day. The current streak
tolerates a still-open today by counting back from yesterday when today
is not yet done.

Streaks fold in archived months via the preloaded archived_reached set,
so they span data that has been archived out of the live record, not
just the current file. Also document the new mode in the keys help text.

Author: 1995parham

src/app/impl_self.rs

@@ -367,7 +367,7 @@ impl App {
                                 "w"     | "write" => "write current state to disk   (alias: w)",
                                 "h"|"?" | "help" => "help [<command>|commands|keys]     (aliases: h, ?)",
                                 "cmds"  | "commands" => "add, delete, month-{prev,next}, archive, help, quit",
-                                "keys" => "hjkl: move | HJKL: cursor | n/Enter: +1 | p/BS: -1 | v: cycle view (day/week/month/year) | V: all week | []: month | Esc: reset",
+                                "keys" => "hjkl: move | HJKL: cursor | n/Enter: +1 | p/BS: -1 | v: cycle view (day/week/month/year/stats) | []: month | Esc: reset",
                                 "wq" =>   "write current state to disk and quit dijo",
                                 _ => "unknown command or help topic.",
                             }

src/app/impl_view.rs

@@ -98,7 +98,8 @@ impl View for App {
                     ViewMode::Day => ViewMode::Week,
                     ViewMode::Week => ViewMode::Month,
                     ViewMode::Month => ViewMode::Year,
-                    ViewMode::Year => ViewMode::Day,
+                    ViewMode::Year => ViewMode::Stats,
+                    ViewMode::Stats => ViewMode::Day,
                 };
                 for habit in self.habits.iter_mut() {
                     habit.inner_data_mut_ref().set_view_mode(next);

src/habit/prelude.rs

@@ -14,6 +14,7 @@ pub enum ViewMode {
     Week,
     Month,
     Year,
+    Stats,
 }
 
 impl fmt::Display for ViewMode {
@@ -23,6 +24,7 @@ impl fmt::Display for ViewMode {
             ViewMode::Week => write!(f, "WEEK"),
             ViewMode::Month => write!(f, "MONTH"),
             ViewMode::Year => write!(f, "YEAR"),
+            ViewMode::Stats => write!(f, "STATS"),
         }
     }
 }

src/views.rs

@@ -4,6 +4,8 @@ use cursive::theme::{ColorStyle, Effect, Style};
 use cursive::view::{CannotFocus, View};
 use cursive::{Printer, Vec2};
 
+use std::collections::HashSet;
+
 use chrono::prelude::*;
 use chrono::{Local, NaiveDate};
 
@@ -232,11 +234,88 @@ where
             }
         };
 
+        let draw_stats = |printer: &Printer| {
+            let today = Local::now().date_naive();
+
+            // every day this habit reached its goal, including months that
+            // have since been archived out of the live record
+            let mut reached: Vec<NaiveDate> = self
+                .get_dates()
+                .into_iter()
+                .filter(|&d| self.reached_goal(d))
+                .chain(archived.iter().copied())
+                .collect();
+            reached.sort_unstable();
+            reached.dedup();
+
+            let total = reached.len() as u32;
+            let reached_set: HashSet<NaiveDate> = reached.iter().copied().collect();
+
+            // longest run of consecutive reached days
+            let mut longest = 0u32;
+            let mut run = 0u32;
+            let mut prev: Option<NaiveDate> = None;
+            for &d in &reached {
+                run = match prev {
+                    Some(p) if p.succ_opt() == Some(d) => run + 1,
+                    _ => 1,
+                };
+                longest = longest.max(run);
+                prev = Some(d);
+            }
+
+            // current streak: count back from today, tolerating a still-open
+            // today (start from yesterday if today isn't done yet)
+            let mut current = 0u32;
+            let mut day = if reached_set.contains(&today) {
+                Some(today)
+            } else {
+                today.pred_opt()
+            };
+            while let Some(d) = day {
+                if reached_set.contains(&d) {
+                    current += 1;
+                    day = d.pred_opt();
+                } else {
+                    break;
+                }
+            }
+
+            // completion rate over the span since the first reached day
+            let rate = match reached.first() {
+                Some(&first) => {
+                    let span = (today - first).num_days() + 1;
+                    if span > 0 {
+                        (total as i64 * 100 / span) as u32
+                    } else {
+                        0
+                    }
+                }
+                None => 0,
+            };
+
+            let lines = [
+                format!("Current  {current:>4} days"),
+                format!("Longest  {longest:>4} days"),
+                format!("Done     {total:>4} time{}", if total == 1 { "" } else { "s" }),
+                format!("Rate     {rate:>4} %"),
+            ];
+            for (i, line) in lines.iter().enumerate() {
+                let style = if i == 0 && current > 0 {
+                    goal_reached_style
+                } else {
+                    Style::none()
+                };
+                printer.with_style(style, |p| p.print((2, i + 2), line));
+            }
+        };
+
         match self.inner_data_ref().view_mode() {
             ViewMode::Day => draw_day(printer),
             ViewMode::Week => draw_week(printer),
             ViewMode::Month => draw_month(printer),
             ViewMode::Year => draw_year(printer),
+            ViewMode::Stats => draw_stats(printer),
         };
     }