Add support to allow the week day start in cal to be configured via a flag (#1996)

* Add support to allow the week day start in cal to be configurable

* Fix variable name

* Use a flag instead of a configuration setting for specifying the starting day of the week

crates/nu-cli/src/commands/cal.rs

@@ -24,6 +24,12 @@ impl WholeStreamCommand for Cal {
                 "Display a year-long calendar for the specified year",
                 None,
             )
+            .named(
+                "week-start",
+                SyntaxShape::String,
+                "Display the calendar with the specified day as the first day of the week",
+                None,
+            )
             .switch(
                 "month-names",
                 "Display the month names instead of integers",
@@ -55,6 +61,11 @@ impl WholeStreamCommand for Cal {
                 example: "cal --full-year 2012",
                 result: None,
             },
+            Example {
+                description: "This month's calendar with the week starting on monday",
+                example: "cal --week-start monday",
+                result: None,
+            },
         ]
     }
 }
@@ -226,11 +237,7 @@ fn add_month_to_table(
         },
     };
 
-    let day_limit =
-        month_helper.number_of_days_in_month + month_helper.day_number_of_week_month_starts_on;
-    let mut day_count: u32 = 1;
-
-    let days_of_the_week = [
+    let mut days_of_the_week = [
         "sunday",
         "monday",
         "tuesday",
@@ -240,12 +247,43 @@ fn add_month_to_table(
         "saturday",
     ];
 
+    let mut week_start_day = days_of_the_week[0].to_string();
+
+    if let Some(week_start_value) = args.get("week-start") {
+        if let Ok(day) = week_start_value.as_string() {
+            if days_of_the_week.contains(&day.as_str()) {
+                week_start_day = day;
+            } else {
+                return Err(ShellError::labeled_error(
+                    "The specified week start day is invalid",
+                    "invalid week start day",
+                    week_start_value.tag(),
+                ));
+            }
+        }
+    }
+
+    let week_start_day_offset = days_of_the_week.len()
+        - days_of_the_week
+            .iter()
+            .position(|day| *day == week_start_day)
+            .unwrap_or(0);
+
+    days_of_the_week.rotate_right(week_start_day_offset);
+
+    let mut total_start_offset: u32 =
+        month_helper.day_number_of_week_month_starts_on + week_start_day_offset as u32;
+    total_start_offset %= days_of_the_week.len() as u32;
+
+    let mut day_number: u32 = 1;
+    let day_limit: u32 = total_start_offset + month_helper.number_of_days_in_month;
+
     let should_show_year_column = args.has("year");
     let should_show_quarter_column = args.has("quarter");
     let should_show_month_column = args.has("month");
     let should_show_month_names = args.has("month-names");
 
-    while day_count <= day_limit {
+    while day_number <= day_limit {
         let mut indexmap = IndexMap::new();
 
         if should_show_year_column {
@@ -273,19 +311,18 @@ fn add_month_to_table(
         }
 
         for day in &days_of_the_week {
-            let should_add_day_number_to_table = (day_count <= day_limit)
-                && (day_count > month_helper.day_number_of_week_month_starts_on);
+            let should_add_day_number_to_table =
+                (day_number > total_start_offset) && (day_number <= day_limit);
 
             let mut value = UntaggedValue::nothing().into_value(tag);
 
             if should_add_day_number_to_table {
-                let day_count_with_offset =
-                    day_count - month_helper.day_number_of_week_month_starts_on;
+                let adjusted_day_number = day_number - total_start_offset;
 
-                value = UntaggedValue::int(day_count_with_offset).into_value(tag);
+                value = UntaggedValue::int(adjusted_day_number).into_value(tag);
 
                 if let Some(current_day) = current_day_option {
-                    if current_day == day_count_with_offset {
+                    if current_day == adjusted_day_number {
                         // TODO: Update the value here with a color when color support is added
                         // This colors the current day
                     }
@@ -294,7 +331,7 @@ fn add_month_to_table(
 
             indexmap.insert((*day).to_string(), value);
 
-            day_count += 1;
+            day_number += 1;
         }
 
         calendar_vec_deque

crates/nu-cli/tests/commands/cal.rs

@@ -52,6 +52,20 @@ fn cal_rows_in_2020() {
     assert!(actual.out.contains("62"));
 }
 
+#[test]
+fn cal_week_day_start_monday() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        cal --full-year 2020 -m --month-names --week-start monday | where month == january | to json
+        "#
+    ));
+
+    let cal_january_json = r#"[{"month":"january","monday":null,"tuesday":null,"wednesday":1,"thursday":2,"friday":3,"saturday":4,"sunday":5},{"month":"january","monday":6,"tuesday":7,"wednesday":8,"thursday":9,"friday":10,"saturday":11,"sunday":12},{"month":"january","monday":13,"tuesday":14,"wednesday":15,"thursday":16,"friday":17,"saturday":18,"sunday":19},{"month":"january","monday":20,"tuesday":21,"wednesday":22,"thursday":23,"friday":24,"saturday":25,"sunday":26},{"month":"january","monday":27,"tuesday":28,"wednesday":29,"thursday":30,"friday":31,"saturday":null,"sunday":null}]"#;
+
+    assert_eq!(actual.out, cal_january_json);
+}
+
 #[test]
 fn cal_sees_pipeline_year() {
     let actual = nu!(

docs/commands/cal.md

@@ -8,6 +8,7 @@ Use `cal` to display a calendar.
 * `-q`, `--quarter`: Display the quarter column
 * `-m`, `--month`: Display the month column
 * `--full-year` \<integer>: Display a year-long calendar for the specified year
+* `--week-start` \<string>: Display the calendar with the specified day as the first day of the week
 * `--month-names`: Display the month names instead of integers
 
 ## Examples
@@ -188,3 +189,16 @@ Use `cal` to display a calendar.
  1 │ 2020 │ november │      8 │      9 │      10 │        11 │       12 │     13 │       14
 ───┴──────┴──────────┴────────┴────────┴─────────┴───────────┴──────────┴────────┴──────────
 ```
+
+```shell
+> cal -ymq --month-names --week-start-day monday
+───┬──────┬─────────┬───────┬────────┬─────────┬───────────┬──────────┬────────┬──────────┬────────
+ # │ year │ quarter │ month │ monday │ tuesday │ wednesday │ thursday │ friday │ saturday │ sunday
+───┼──────┼─────────┼───────┼────────┼─────────┼───────────┼──────────┼────────┼──────────┼────────
+ 0 │ 2020 │       2 │ june  │      1 │       2 │         3 │        4 │      5 │        6 │      7
+ 1 │ 2020 │       2 │ june  │      8 │       9 │        10 │       11 │     12 │       13 │     14
+ 2 │ 2020 │       2 │ june  │     15 │      16 │        17 │       18 │     19 │       20 │     21
+ 3 │ 2020 │       2 │ june  │     22 │      23 │        24 │       25 │     26 │       27 │     28
+ 4 │ 2020 │       2 │ june  │     29 │      30 │           │          │        │          │
+───┴──────┴─────────┴───────┴────────┴─────────┴───────────┴──────────┴────────┴──────────┴────────
+```