use chrono::NaiveTime;

use crate::models::Timecard;

/// Check if two time ranges overlap.
fn timecards_overlap(a: &Timecard, b: &Timecard) -> bool {
    a.from_time < b.to_time && b.from_time < a.to_time
}

/// Find all overlapping timecard pairs for a day.
/// Returns a list of tuples containing the two overlapping timecards.
pub fn find_overlapping_timecards(
    timecards: &[Timecard],
) -> Vec<((NaiveTime, NaiveTime), (NaiveTime, NaiveTime))> {
    let mut overlaps = Vec::new();
    for i in 0..timecards.len() {
        for j in (i + 1)..timecards.len() {
            if timecards_overlap(&timecards[i], &timecards[j]) {
                overlaps.push((
                    (timecards[i].from_time, timecards[i].to_time),
                    (timecards[j].from_time, timecards[j].to_time),
                ));
            }
        }
    }
    overlaps
}

#[cfg(test)]
mod tests {
    use super::*;

    fn time(hour: u32, min: u32) -> NaiveTime {
        NaiveTime::from_hms_opt(hour, min, 0).unwrap()
    }

    fn card(from_h: u32, from_m: u32, to_h: u32, to_m: u32) -> Timecard {
        Timecard::new(time(from_h, from_m), time(to_h, to_m))
    }

    #[test]
    fn test_no_overlap_adjacent_timecards() {
        let timecards = vec![card(9, 0, 12, 0), card(13, 0, 17, 0)];
        let overlaps = find_overlapping_timecards(&timecards);
        assert!(overlaps.is_empty());
    }

    #[test]
    fn test_no_overlap_exact_touch() {
        // Touching at 12:00 is NOT an overlap (end time = start time)
        let timecards = vec![card(9, 0, 12, 0), card(12, 0, 17, 0)];
        let overlaps = find_overlapping_timecards(&timecards);
        assert!(overlaps.is_empty());
    }

    #[test]
    fn test_partial_overlap() {
        let timecards = vec![card(9, 0, 12, 30), card(12, 0, 13, 0)];
        let overlaps = find_overlapping_timecards(&timecards);
        assert_eq!(overlaps.len(), 1);
        assert_eq!(overlaps[0].0, (time(9, 0), time(12, 30)));
        assert_eq!(overlaps[0].1, (time(12, 0), time(13, 0)));
    }

    #[test]
    fn test_full_containment() {
        // One timecard fully contains another
        let timecards = vec![card(9, 0, 17, 0), card(10, 0, 11, 0)];
        let overlaps = find_overlapping_timecards(&timecards);
        assert_eq!(overlaps.len(), 1);
    }

    #[test]
    fn test_exact_match_overlap() {
        let timecards = vec![card(9, 0, 12, 0), card(9, 0, 12, 0)];
        let overlaps = find_overlapping_timecards(&timecards);
        assert_eq!(overlaps.len(), 1);
    }

    #[test]
    fn test_multiple_overlaps_same_day() {
        // First overlaps with second, and second overlaps with third
        let timecards = vec![card(9, 0, 11, 0), card(10, 0, 13, 0), card(12, 0, 15, 0)];
        let overlaps = find_overlapping_timecards(&timecards);
        // 9-11 overlaps with 10-13, and 10-13 overlaps with 12-15
        assert_eq!(overlaps.len(), 2);
    }

    #[test]
    fn test_single_timecard_no_overlap() {
        let timecards = vec![card(9, 0, 17, 0)];
        let overlaps = find_overlapping_timecards(&timecards);
        assert!(overlaps.is_empty());
    }

    #[test]
    fn test_empty_timecards_no_overlap() {
        let timecards: Vec<Timecard> = vec![];
        let overlaps = find_overlapping_timecards(&timecards);
        assert!(overlaps.is_empty());
    }

    #[test]
    fn test_three_timecards_all_overlap() {
        // All three overlap with each other
        let timecards = vec![card(9, 0, 15, 0), card(10, 0, 16, 0), card(11, 0, 17, 0)];
        let overlaps = find_overlapping_timecards(&timecards);
        // 9-15 with 10-16, 9-15 with 11-17, and 10-16 with 11-17
        assert_eq!(overlaps.len(), 3);
    }
}