//! The big picture: totals against your targets, balance, and trends.

use jiff::civil::{Date, Time, Weekday};
use jiff::tz::TimeZone;
use jiff::{SignedDuration, Timestamp, ToSpan};

use super::days_in;
use crate::domain::WorkDay;
use crate::time::DateRange;
use crate::time::resolve::on_date;

/// Time worked in some range of dates.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub struct Totals {
    pub worked: SignedDuration,
    pub days_worked: usize,
}

impl Totals {
    fn of<'a>(days: impl Iterator<Item = &'a WorkDay>) -> Totals {
        days.filter(|day| !day.is_empty()).fold(Totals::default(), |totals, day| Totals {
            worked: totals.worked + day.worked(),
            days_worked: totals.days_worked + 1,
        })
    }

    /// Average time per day worked (not per calendar day).
    pub fn average_day(&self) -> Option<SignedDuration> {
        let days = i32::try_from(self.days_worked).ok().filter(|days| *days > 0)?;
        Some(self.worked / days)
    }
}

/// When a work day started and ended, in minutes after midnight of its date.
/// A night shift ending at 04:10 the next morning ends at minute 1690 (28:10).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct DaySpan {
    pub date: Date,
    pub start_minute: i64,
    pub end_minute: i64,
}

/// What the overview needs from the settings.
#[derive(Debug, Clone, Copy)]
pub struct Targets {
    pub daily: SignedDuration,
    pub week_start: Weekday,
}

#[derive(Debug, Clone, PartialEq)]
pub struct Overview {
    pub this_week: Totals,
    pub last_week: Totals,
    pub this_month: Totals,
    /// Everything in the selected period.
    pub period: Totals,
    /// Over the selected period: for each day worked, time worked minus the
    /// daily target, added up. Positive means you worked more than planned.
    pub balance: SignedDuration,
    /// Time worked per week, oldest first, ending with this week:
    /// (first date of the week, total).
    pub weeks: Vec<(Date, SignedDuration)>,
    /// First start and last end of every day worked in the period.
    pub spans: Vec<DaySpan>,
}

pub fn overview(
    days: &[WorkDay],
    today: Date,
    period: DateRange,
    targets: Targets,
    zone: &TimeZone,
    week_count: usize,
) -> Overview {
    let this_week = DateRange::week_of(today, targets.week_start);
    let period_totals = Totals::of(days_in(days, period));

    let balance =
        days_in(days, period).filter(|day| !day.is_empty()).map(|day| day.worked() - targets.daily).sum();

    let weeks = (0..week_count)
        .rev()
        .map(|weeks_ago| {
            let week_start = this_week.first().saturating_sub((7 * weeks_ago as i64).days());
            let week = DateRange::week_of(week_start, targets.week_start);
            (week.first(), Totals::of(days_in(days, week)).worked)
        })
        .collect();

    let spans = days_in(days, period).filter_map(|day| day_span(day, zone)).collect();

    Overview {
        this_week: Totals::of(days_in(days, this_week)),
        last_week: Totals::of(days_in(days, this_week.previous())),
        this_month: Totals::of(days_in(days, DateRange::month_of(today))),
        period: period_totals,
        balance,
        weeks,
        spans,
    }
}

fn day_span(day: &WorkDay, zone: &TimeZone) -> Option<DaySpan> {
    let midnight = on_date(day.date(), Time::midnight(), zone).timestamp();
    let minutes_after_midnight = |instant: Timestamp| instant.duration_since(midnight).as_mins();
    Some(DaySpan {
        date: day.date(),
        start_minute: minutes_after_midnight(day.first_start()?),
        end_minute: minutes_after_midnight(day.last_end()?),
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::domain::{Journal, ShiftState};
    use jiff::Zoned;
    use jiff::civil::date;

    fn at(day: i8, hour: i8) -> Zoned {
        date(2026, 9, day).at(hour, 0, 0, 0).to_zoned(TimeZone::UTC).unwrap()
    }

    #[test]
    fn night_shift_spans_go_past_24h() {
        let segment = crate::domain::Segment::new(at(24, 22).timestamp(), at(25, 4).timestamp()).unwrap();
        let journal =
            Journal::from_parts(vec![(date(2026, 9, 24), vec![segment])], ShiftState::Idle).unwrap();
        let days = journal.snapshot(at(26, 12).timestamp());
        let targets = Targets { daily: SignedDuration::from_hours(8), week_start: Weekday::Monday };
        let today = date(2026, 9, 26);
        let result = overview(&days, today, DateRange::last_days(today, 7), targets, &TimeZone::UTC, 4);

        assert_eq!(
            result.spans,
            vec![DaySpan { date: date(2026, 9, 24), start_minute: 22 * 60, end_minute: 28 * 60 }]
        );
        assert_eq!(result.this_week.worked, SignedDuration::from_hours(6));
        assert_eq!(result.balance, SignedDuration::from_hours(-2));
        assert_eq!(result.weeks.len(), 4);
    }
}