feat: holiday exclusion logic for ICS command

src/bot/commands/ics.rs

@@ -2,10 +2,110 @@
 
 use crate::banner::{Course, MeetingScheduleInfo};
 use crate::bot::{Context, Error, utils};
-use chrono::Utc;
+use chrono::{Datelike, NaiveDate, Utc};
 use serenity::all::CreateAttachment;
 use tracing::info;
 
+/// Represents a holiday or special day that should be excluded from class schedules
+#[derive(Debug, Clone)]
+enum Holiday {
+    /// A single-day holiday
+    Single { month: u32, day: u32 },
+    /// A multi-day holiday range
+    Range {
+        month: u32,
+        start_day: u32,
+        end_day: u32,
+    },
+}
+
+impl Holiday {
+    /// Check if a specific date falls within this holiday
+    fn contains_date(&self, date: NaiveDate) -> bool {
+        match self {
+            Holiday::Single { month, day, .. } => date.month() == *month && date.day() == *day,
+            Holiday::Range {
+                month,
+                start_day,
+                end_day,
+                ..
+            } => date.month() == *month && date.day() >= *start_day && date.day() <= *end_day,
+        }
+    }
+
+    /// Get all dates in this holiday for a given year
+    fn get_dates_for_year(&self, year: i32) -> Vec<NaiveDate> {
+        match self {
+            Holiday::Single { month, day, .. } => {
+                if let Some(date) = NaiveDate::from_ymd_opt(year, *month, *day) {
+                    vec![date]
+                } else {
+                    Vec::new()
+                }
+            }
+            Holiday::Range {
+                month,
+                start_day,
+                end_day,
+                ..
+            } => {
+                let mut dates = Vec::new();
+                for day in *start_day..=*end_day {
+                    if let Some(date) = NaiveDate::from_ymd_opt(year, *month, day) {
+                        dates.push(date);
+                    }
+                }
+                dates
+            }
+        }
+    }
+}
+
+/// University holidays that should be excluded from class schedules
+const UNIVERSITY_HOLIDAYS: &[(&'static str, Holiday)] = &[
+    ("Labor Day", Holiday::Single { month: 9, day: 1 }),
+    (
+        "Fall Break",
+        Holiday::Range {
+            month: 10,
+            start_day: 13,
+            end_day: 14,
+        },
+    ),
+    (
+        "Unspecified Holiday",
+        Holiday::Single { month: 11, day: 26 },
+    ),
+    (
+        "Thanksgiving",
+        Holiday::Range {
+            month: 11,
+            start_day: 28,
+            end_day: 29,
+        },
+    ),
+    ("Student Study Day", Holiday::Single { month: 12, day: 5 }),
+    (
+        "Winter Holiday",
+        Holiday::Range {
+            month: 12,
+            start_day: 23,
+            end_day: 31,
+        },
+    ),
+    ("New Year's Day", Holiday::Single { month: 1, day: 1 }),
+    ("MLK Day", Holiday::Single { month: 1, day: 20 }),
+    (
+        "Spring Break",
+        Holiday::Range {
+            month: 3,
+            start_day: 10,
+            end_day: 15,
+        },
+    ),
+    ("Student Study Day", Holiday::Single { month: 5, day: 9 }),
+];
+
 /// Generate an ICS file for a course
 #[poise::command(slash_command, prefix_command)]
 pub async fn ics(
@@ -40,7 +140,8 @@ pub async fn ics(
     });
 
     // Generate ICS content
-    let ics_content = generate_ics_content(&course, &term, &sorted_meeting_times)?;
+    let (ics_content, excluded_holidays) =
+        generate_ics_content(&course, &term, &sorted_meeting_times)?;
 
     // Create file attachment
     let filename = format!(
@@ -52,9 +153,8 @@ pub async fn ics(
 
     let file = CreateAttachment::bytes(ics_content.into_bytes(), filename.clone());
 
-    ctx.send(
-        poise::CreateReply::default()
-            .content(format!(
+    // Build response content
+    let mut response_content = format!(
         "📅 Generated ICS calendar for **{}**\n\n**Meeting Times:**\n{}",
         course.display_title(),
         sorted_meeting_times
@@ -73,7 +173,29 @@ pub async fn ics(
             })
             .collect::<Vec<_>>()
             .join("\n")
-            ))
+    );
+
+    // Add holiday exclusion information
+    if !excluded_holidays.is_empty() {
+        let count = excluded_holidays.len();
+        let count_text = if count == 1 {
+            "1 date was".to_string()
+        } else {
+            format!("{} dates were", count)
+        };
+        response_content.push_str(&format!("\n\n{} excluded from the ICS file:\n", count_text));
+        response_content.push_str(
+            &excluded_holidays
+                .iter()
+                .map(|s| format!("- {}", s))
+                .collect::<Vec<_>>()
+                .join("\n"),
+        );
+    }
+
+    ctx.send(
+        poise::CreateReply::default()
+            .content(response_content)
             .attachment(file),
     )
     .await?;
@@ -87,8 +209,9 @@ fn generate_ics_content(
     course: &Course,
     term: &str,
     meeting_times: &[MeetingScheduleInfo],
-) -> Result<String, anyhow::Error> {
+) -> Result<(String, Vec<String>), anyhow::Error> {
     let mut ics_content = String::new();
+    let mut excluded_holidays = Vec::new();
 
     // ICS header
     ics_content.push_str("BEGIN:VCALENDAR\r\n");
@@ -106,14 +229,15 @@ fn generate_ics_content(
 
     // Generate events for each meeting time
     for (index, meeting_time) in meeting_times.iter().enumerate() {
-        let event_content = generate_event_content(course, meeting_time, index)?;
+        let (event_content, holidays) = generate_event_content(course, meeting_time, index)?;
         ics_content.push_str(&event_content);
+        excluded_holidays.extend(holidays);
     }
 
     // ICS footer
     ics_content.push_str("END:VCALENDAR\r\n");
 
-    Ok(ics_content)
+    Ok((ics_content, excluded_holidays))
 }
 
 /// Generate ICS event content for a single meeting time
@@ -121,7 +245,7 @@ fn generate_event_content(
     course: &Course,
     meeting_time: &MeetingScheduleInfo,
     index: usize,
-) -> Result<String, anyhow::Error> {
+) -> Result<(String, Vec<String>), anyhow::Error> {
     let course_title = course.display_title();
     let instructor_name = course.primary_instructor_name();
     let location = meeting_time.place_string();
@@ -194,13 +318,112 @@ fn generate_event_content(
                 by_day.join(","),
                 until_date
             ));
+
+            // Add holiday exceptions (EXDATE) if the class would meet on holiday dates
+            let holiday_exceptions = get_holiday_exceptions(meeting_time);
+            if let Some(exdate_property) = generate_exdate_property(&holiday_exceptions, start_utc)
+            {
+                event_content.push_str(&format!("{}\r\n", exdate_property));
+            }
+
+            // Collect holiday names for reporting
+            let mut holiday_names = Vec::new();
+            for (holiday_name, holiday) in UNIVERSITY_HOLIDAYS {
+                for &exception_date in &holiday_exceptions {
+                    if holiday.contains_date(exception_date) {
+                        holiday_names.push(format!(
+                            "{} ({})",
+                            holiday_name,
+                            exception_date.format("%a, %b %d")
+                        ));
+                    }
+                }
+            }
+            holiday_names.sort();
+            holiday_names.dedup();
+
+            return Ok((event_content, holiday_names));
         }
     }
 
     // Event footer
     event_content.push_str("END:VEVENT\r\n");
 
-    Ok(event_content)
+    Ok((event_content, Vec::new()))
+}
+
+/// Convert chrono::Weekday to the custom DayOfWeek enum
+fn chrono_weekday_to_day_of_week(weekday: chrono::Weekday) -> crate::banner::meetings::DayOfWeek {
+    use crate::banner::meetings::DayOfWeek;
+    match weekday {
+        chrono::Weekday::Mon => DayOfWeek::Monday,
+        chrono::Weekday::Tue => DayOfWeek::Tuesday,
+        chrono::Weekday::Wed => DayOfWeek::Wednesday,
+        chrono::Weekday::Thu => DayOfWeek::Thursday,
+        chrono::Weekday::Fri => DayOfWeek::Friday,
+        chrono::Weekday::Sat => DayOfWeek::Saturday,
+        chrono::Weekday::Sun => DayOfWeek::Sunday,
+    }
+}
+
+/// Check if a class meets on a specific date based on its meeting days
+fn class_meets_on_date(meeting_time: &MeetingScheduleInfo, date: NaiveDate) -> bool {
+    let weekday = chrono_weekday_to_day_of_week(date.weekday());
+    let meeting_days = meeting_time.days_of_week();
+
+    meeting_days.contains(&weekday)
+}
+
+/// Get holiday dates that fall within the course date range and would conflict with class meetings
+fn get_holiday_exceptions(meeting_time: &MeetingScheduleInfo) -> Vec<NaiveDate> {
+    let mut exceptions = Vec::new();
+
+    // Get the year range from the course date range
+    let start_year = meeting_time.date_range.start.year();
+    let end_year = meeting_time.date_range.end.year();
+
+    for (_, holiday) in UNIVERSITY_HOLIDAYS {
+        // Check for the holiday in each year of the course
+        for year in start_year..=end_year {
+            let holiday_dates = holiday.get_dates_for_year(year);
+
+            for holiday_date in holiday_dates {
+                // Check if the holiday falls within the course date range
+                if holiday_date >= meeting_time.date_range.start
+                    && holiday_date <= meeting_time.date_range.end
+                {
+                    // Check if the class would actually meet on this day
+                    if class_meets_on_date(meeting_time, holiday_date) {
+                        exceptions.push(holiday_date);
+                    }
+                }
+            }
+        }
+    }
+
+    exceptions
+}
+
+/// Generate EXDATE property for holiday exceptions
+fn generate_exdate_property(
+    exceptions: &[NaiveDate],
+    start_time: chrono::DateTime<Utc>,
+) -> Option<String> {
+    if exceptions.is_empty() {
+        return None;
+    }
+
+    let mut exdate_values = Vec::new();
+
+    for &exception_date in exceptions {
+        // Create a datetime for the exception using the same time as the start time
+        let exception_datetime = exception_date.and_time(start_time.time()).and_utc();
+
+        let exdate_str = exception_datetime.format("%Y%m%dT%H%M%SZ").to_string();
+        exdate_values.push(exdate_str);
+    }
+
+    Some(format!("EXDATE:{}", exdate_values.join(",")))
 }
 
 /// Escape text for ICS format