feat: add calendar export endpoints for ICS and Google Calendar

src/calendar.rs

@@ -0,0 +1,462 @@
+//! Shared calendar generation logic for ICS files and Google Calendar URLs.
+//!
+//! Used by both the Discord bot commands and the web API endpoints.
+
+use crate::data::models::DbMeetingTime;
+use chrono::{Datelike, Duration, NaiveDate, NaiveTime, Weekday};
+
+/// Course metadata needed for calendar generation (shared interface between bot and web).
+pub struct CalendarCourse {
+    pub crn: String,
+    pub subject: String,
+    pub course_number: String,
+    pub title: String,
+    pub sequence_number: Option<String>,
+    pub primary_instructor: Option<String>,
+}
+
+impl CalendarCourse {
+    /// Display title like "CS 1083 - Introduction to Computer Science"
+    pub fn display_title(&self) -> String {
+        format!("{} {} - {}", self.subject, self.course_number, self.title)
+    }
+
+    /// Filename-safe identifier: "CS_1083_001"
+    pub fn filename_stem(&self) -> String {
+        format!(
+            "{}_{}{}",
+            self.subject.replace(' ', "_"),
+            self.course_number,
+            self.sequence_number
+                .as_deref()
+                .map(|s| format!("_{s}"))
+                .unwrap_or_default()
+        )
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Date parsing helpers
+// ---------------------------------------------------------------------------
+
+/// Parse a date string in either MM/DD/YYYY or YYYY-MM-DD format.
+fn parse_date(s: &str) -> Option<NaiveDate> {
+    NaiveDate::parse_from_str(s, "%m/%d/%Y")
+        .or_else(|_| NaiveDate::parse_from_str(s, "%Y-%m-%d"))
+        .ok()
+}
+
+/// Parse an HHMM time string into `NaiveTime`.
+fn parse_hhmm(s: &str) -> Option<NaiveTime> {
+    if s.len() != 4 {
+        return None;
+    }
+    let hours = s[..2].parse::<u32>().ok()?;
+    let minutes = s[2..].parse::<u32>().ok()?;
+    NaiveTime::from_hms_opt(hours, minutes, 0)
+}
+
+/// Active weekdays for a meeting time.
+fn active_weekdays(mt: &DbMeetingTime) -> Vec<Weekday> {
+    let mapping: [(bool, Weekday); 7] = [
+        (mt.monday, Weekday::Mon),
+        (mt.tuesday, Weekday::Tue),
+        (mt.wednesday, Weekday::Wed),
+        (mt.thursday, Weekday::Thu),
+        (mt.friday, Weekday::Fri),
+        (mt.saturday, Weekday::Sat),
+        (mt.sunday, Weekday::Sun),
+    ];
+    mapping
+        .iter()
+        .filter(|(active, _)| *active)
+        .map(|(_, day)| *day)
+        .collect()
+}
+
+/// ICS two-letter day code for RRULE BYDAY.
+fn ics_day_code(day: Weekday) -> &'static str {
+    match day {
+        Weekday::Mon => "MO",
+        Weekday::Tue => "TU",
+        Weekday::Wed => "WE",
+        Weekday::Thu => "TH",
+        Weekday::Fri => "FR",
+        Weekday::Sat => "SA",
+        Weekday::Sun => "SU",
+    }
+}
+
+/// Location string from a `DbMeetingTime`.
+fn location_string(mt: &DbMeetingTime) -> String {
+    let building = mt
+        .building_description
+        .as_deref()
+        .or(mt.building.as_deref())
+        .unwrap_or("");
+    let room = mt.room.as_deref().unwrap_or("");
+    let combined = format!("{building} {room}").trim().to_string();
+    if combined.is_empty() {
+        "Online".to_string()
+    } else {
+        combined
+    }
+}
+
+/// Days display string (e.g. "MWF", "TTh").
+fn days_display(mt: &DbMeetingTime) -> String {
+    let weekdays = active_weekdays(mt);
+    if weekdays.is_empty() {
+        return "TBA".to_string();
+    }
+    weekdays
+        .iter()
+        .map(|d| ics_day_code(*d))
+        .collect::<Vec<_>>()
+        .join("")
+}
+
+/// Escape text for ICS property values.
+fn escape_ics(text: &str) -> String {
+    text.replace('\\', "\\\\")
+        .replace(';', "\\;")
+        .replace(',', "\\,")
+        .replace('\n', "\\n")
+        .replace('\r', "")
+}
+
+// ---------------------------------------------------------------------------
+// University holidays (ported from bot/commands/ics.rs)
+// ---------------------------------------------------------------------------
+
+/// Find the nth occurrence of a weekday in a given month/year (1-based).
+fn nth_weekday_of_month(year: i32, month: u32, weekday: Weekday, n: u32) -> Option<NaiveDate> {
+    let first = NaiveDate::from_ymd_opt(year, month, 1)?;
+    let days_ahead = (weekday.num_days_from_monday() as i64
+        - first.weekday().num_days_from_monday() as i64)
+        .rem_euclid(7) as u32;
+    let day = 1 + days_ahead + 7 * (n - 1);
+    NaiveDate::from_ymd_opt(year, month, day)
+}
+
+/// Compute a consecutive range of dates starting from `start` for `count` days.
+fn date_range(start: NaiveDate, count: i64) -> Vec<NaiveDate> {
+    (0..count)
+        .filter_map(|i| start.checked_add_signed(Duration::days(i)))
+        .collect()
+}
+
+/// Compute university holidays for a given year.
+fn compute_holidays_for_year(year: i32) -> Vec<(&'static str, Vec<NaiveDate>)> {
+    let mut holidays = Vec::new();
+
+    // Labor Day: 1st Monday of September
+    if let Some(d) = nth_weekday_of_month(year, 9, Weekday::Mon, 1) {
+        holidays.push(("Labor Day", vec![d]));
+    }
+
+    // Fall Break: Mon-Tue of Columbus Day week
+    if let Some(mon) = nth_weekday_of_month(year, 10, Weekday::Mon, 2) {
+        holidays.push(("Fall Break", date_range(mon, 2)));
+    }
+
+    // Day before Thanksgiving
+    if let Some(thu) = nth_weekday_of_month(year, 11, Weekday::Thu, 4)
+        && let Some(wed) = thu.checked_sub_signed(Duration::days(1))
+    {
+        holidays.push(("Day Before Thanksgiving", vec![wed]));
+    }
+
+    // Thanksgiving: 4th Thursday + Friday
+    if let Some(thu) = nth_weekday_of_month(year, 11, Weekday::Thu, 4) {
+        holidays.push(("Thanksgiving", date_range(thu, 2)));
+    }
+
+    // Winter Holiday: Dec 23-31
+    if let Some(start) = NaiveDate::from_ymd_opt(year, 12, 23) {
+        holidays.push(("Winter Holiday", date_range(start, 9)));
+    }
+
+    // New Year's Day
+    if let Some(d) = NaiveDate::from_ymd_opt(year, 1, 1) {
+        holidays.push(("New Year's Day", vec![d]));
+    }
+
+    // MLK Day: 3rd Monday of January
+    if let Some(d) = nth_weekday_of_month(year, 1, Weekday::Mon, 3) {
+        holidays.push(("MLK Day", vec![d]));
+    }
+
+    // Spring Break: full week starting 2nd Monday of March
+    if let Some(mon) = nth_weekday_of_month(year, 3, Weekday::Mon, 2) {
+        holidays.push(("Spring Break", date_range(mon, 6)));
+    }
+
+    holidays
+}
+
+/// Get holiday dates within a date range that fall on specific weekdays.
+fn holiday_exceptions(start: NaiveDate, end: NaiveDate, weekdays: &[Weekday]) -> Vec<NaiveDate> {
+    let start_year = start.year();
+    let end_year = end.year();
+
+    (start_year..=end_year)
+        .flat_map(compute_holidays_for_year)
+        .flat_map(|(_, dates)| dates)
+        .filter(|&date| date >= start && date <= end && weekdays.contains(&date.weekday()))
+        .collect()
+}
+
+/// Names of excluded holidays (for user-facing messages).
+fn excluded_holiday_names(
+    start: NaiveDate,
+    end: NaiveDate,
+    exceptions: &[NaiveDate],
+) -> Vec<String> {
+    let start_year = start.year();
+    let end_year = end.year();
+    let all_holidays: Vec<_> = (start_year..=end_year)
+        .flat_map(compute_holidays_for_year)
+        .collect();
+
+    let mut names = Vec::new();
+    for (holiday_name, holiday_dates) in &all_holidays {
+        for &exc in exceptions {
+            if holiday_dates.contains(&exc) {
+                names.push(format!("{} ({})", holiday_name, exc.format("%a, %b %d")));
+            }
+        }
+    }
+    names.sort();
+    names.dedup();
+    names
+}
+
+// ---------------------------------------------------------------------------
+// ICS generation
+// ---------------------------------------------------------------------------
+
+/// Result from ICS generation, including the file content and excluded holiday names.
+pub struct IcsResult {
+    pub content: String,
+    pub filename: String,
+    /// Holiday dates excluded via EXDATE rules, for user-facing messages.
+    #[allow(dead_code)]
+    pub excluded_holidays: Vec<String>,
+}
+
+/// Generate an ICS calendar file for a course.
+pub fn generate_ics(
+    course: &CalendarCourse,
+    meeting_times: &[DbMeetingTime],
+) -> Result<IcsResult, anyhow::Error> {
+    let mut ics = String::new();
+    let mut all_excluded = Vec::new();
+
+    // Header
+    ics.push_str("BEGIN:VCALENDAR\r\n");
+    ics.push_str("VERSION:2.0\r\n");
+    ics.push_str("PRODID:-//Banner Bot//Course Calendar//EN\r\n");
+    ics.push_str("CALSCALE:GREGORIAN\r\n");
+    ics.push_str("METHOD:PUBLISH\r\n");
+    ics.push_str(&format!(
+        "X-WR-CALNAME:{}\r\n",
+        escape_ics(&course.display_title())
+    ));
+
+    for (index, mt) in meeting_times.iter().enumerate() {
+        let (event, holidays) = generate_ics_event(course, mt, index)?;
+        ics.push_str(&event);
+        all_excluded.extend(holidays);
+    }
+
+    ics.push_str("END:VCALENDAR\r\n");
+
+    Ok(IcsResult {
+        content: ics,
+        filename: format!("{}.ics", course.filename_stem()),
+        excluded_holidays: all_excluded,
+    })
+}
+
+/// Generate a single VEVENT for one meeting time.
+fn generate_ics_event(
+    course: &CalendarCourse,
+    mt: &DbMeetingTime,
+    index: usize,
+) -> Result<(String, Vec<String>), anyhow::Error> {
+    let start_date = parse_date(&mt.start_date)
+        .ok_or_else(|| anyhow::anyhow!("Invalid start_date: {}", mt.start_date))?;
+    let end_date = parse_date(&mt.end_date)
+        .ok_or_else(|| anyhow::anyhow!("Invalid end_date: {}", mt.end_date))?;
+
+    let start_time = mt.begin_time.as_deref().and_then(parse_hhmm);
+    let end_time = mt.end_time.as_deref().and_then(parse_hhmm);
+
+    // DTSTART/DTEND: first occurrence with time, or all-day on start_date
+    let (dtstart, dtend) = match (start_time, end_time) {
+        (Some(st), Some(et)) => {
+            let s = start_date.and_time(st).and_utc();
+            let e = start_date.and_time(et).and_utc();
+            (
+                s.format("%Y%m%dT%H%M%SZ").to_string(),
+                e.format("%Y%m%dT%H%M%SZ").to_string(),
+            )
+        }
+        _ => {
+            let s = start_date.and_hms_opt(0, 0, 0).unwrap().and_utc();
+            let e = start_date.and_hms_opt(0, 0, 0).unwrap().and_utc();
+            (
+                s.format("%Y%m%dT%H%M%SZ").to_string(),
+                e.format("%Y%m%dT%H%M%SZ").to_string(),
+            )
+        }
+    };
+
+    let event_title = if index > 0 {
+        format!("{} (Meeting {})", course.display_title(), index + 1)
+    } else {
+        course.display_title()
+    };
+
+    let instructor = course.primary_instructor.as_deref().unwrap_or("Staff");
+
+    let description = format!(
+        "CRN: {}\\nInstructor: {}\\nDays: {}\\nMeeting Type: {}",
+        course.crn,
+        instructor,
+        days_display(mt),
+        mt.meeting_type,
+    );
+
+    let location = location_string(mt);
+
+    let uid = format!(
+        "{}-{}-{}@banner-bot.local",
+        course.crn,
+        index,
+        start_date
+            .and_hms_opt(0, 0, 0)
+            .unwrap()
+            .and_utc()
+            .timestamp()
+    );
+
+    let mut event = String::new();
+    event.push_str("BEGIN:VEVENT\r\n");
+    event.push_str(&format!("UID:{uid}\r\n"));
+    event.push_str(&format!("DTSTART:{dtstart}\r\n"));
+    event.push_str(&format!("DTEND:{dtend}\r\n"));
+    event.push_str(&format!("SUMMARY:{}\r\n", escape_ics(&event_title)));
+    event.push_str(&format!("DESCRIPTION:{}\r\n", escape_ics(&description)));
+    event.push_str(&format!("LOCATION:{}\r\n", escape_ics(&location)));
+
+    let weekdays = active_weekdays(mt);
+    let mut holiday_names = Vec::new();
+
+    if let (false, Some(st)) = (weekdays.is_empty(), start_time) {
+        let by_day: Vec<&str> = weekdays.iter().map(|d| ics_day_code(*d)).collect();
+        let until = end_date.format("%Y%m%dT000000Z").to_string();
+
+        event.push_str(&format!(
+            "RRULE:FREQ=WEEKLY;BYDAY={};UNTIL={}\r\n",
+            by_day.join(","),
+            until,
+        ));
+
+        // Holiday exceptions
+        let exceptions = holiday_exceptions(start_date, end_date, &weekdays);
+        if !exceptions.is_empty() {
+            let start_utc = start_date.and_time(st).and_utc();
+            let exdates: Vec<String> = exceptions
+                .iter()
+                .map(|&d| {
+                    d.and_time(start_utc.time())
+                        .and_utc()
+                        .format("%Y%m%dT%H%M%SZ")
+                        .to_string()
+                })
+                .collect();
+            event.push_str(&format!("EXDATE:{}\r\n", exdates.join(",")));
+        }
+
+        holiday_names = excluded_holiday_names(start_date, end_date, &exceptions);
+    }
+
+    event.push_str("END:VEVENT\r\n");
+    Ok((event, holiday_names))
+}
+
+// ---------------------------------------------------------------------------
+// Google Calendar URL generation
+// ---------------------------------------------------------------------------
+
+/// Generate a Google Calendar "add event" URL for a single meeting time.
+pub fn generate_gcal_url(
+    course: &CalendarCourse,
+    mt: &DbMeetingTime,
+) -> Result<String, anyhow::Error> {
+    let start_date = parse_date(&mt.start_date)
+        .ok_or_else(|| anyhow::anyhow!("Invalid start_date: {}", mt.start_date))?;
+    let end_date = parse_date(&mt.end_date)
+        .ok_or_else(|| anyhow::anyhow!("Invalid end_date: {}", mt.end_date))?;
+
+    let start_time = mt.begin_time.as_deref().and_then(parse_hhmm);
+    let end_time = mt.end_time.as_deref().and_then(parse_hhmm);
+
+    let dates_text = match (start_time, end_time) {
+        (Some(st), Some(et)) => {
+            let s = start_date.and_time(st);
+            let e = start_date.and_time(et);
+            format!(
+                "{}/{}",
+                s.format("%Y%m%dT%H%M%S"),
+                e.format("%Y%m%dT%H%M%S")
+            )
+        }
+        _ => {
+            let s = start_date.format("%Y%m%d").to_string();
+            format!("{s}/{s}")
+        }
+    };
+
+    let instructor = course.primary_instructor.as_deref().unwrap_or("Staff");
+
+    let details = format!(
+        "CRN: {}\nInstructor: {}\nDays: {}",
+        course.crn,
+        instructor,
+        days_display(mt),
+    );
+
+    let location = location_string(mt);
+
+    let weekdays = active_weekdays(mt);
+    let recur = if !weekdays.is_empty() && start_time.is_some() {
+        let by_day: Vec<&str> = weekdays.iter().map(|d| ics_day_code(*d)).collect();
+        let until = end_date.format("%Y%m%dT000000Z").to_string();
+        format!(
+            "RRULE:FREQ=WEEKLY;BYDAY={};UNTIL={}",
+            by_day.join(","),
+            until
+        )
+    } else {
+        String::new()
+    };
+
+    let course_text = course.display_title();
+
+    let params: Vec<(&str, &str)> = vec![
+        ("action", "TEMPLATE"),
+        ("text", &course_text),
+        ("dates", &dates_text),
+        ("details", &details),
+        ("location", &location),
+        ("trp", "true"),
+        ("ctz", "America/Chicago"),
+        ("recur", &recur),
+    ];
+
+    let url = url::Url::parse_with_params("https://calendar.google.com/calendar/render", &params)?;
+    Ok(url.to_string())
+}