feat(timesheet): add report data structures

Add DayReport, DayType, DayWarning, MonthReport, and TimesheetReport
structs for generating timesheet reports. These support:
- Day types (Regular, SickLeave, Vacation, Holiday, FlexDay, Weekend, Missing, OutsidePeriod)
- Warnings for missing days, overlapping timecards, and outside-period work
- Monthly and cumulative calculations

src/timesheet/report.rs

@@ -0,0 +1,322 @@
+use chrono::{NaiveDate, NaiveTime};
+use std::fmt;
+
+/// Type of day for timesheet calculations.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum DayType {
+    /// Regular working day (Mon-Fri).
+    Regular,
+    /// Day with sick leave marker.
+    SickLeave,
+    /// Day with vacation marker.
+    Vacation,
+    /// Day with holiday marker.
+    Holiday,
+    /// Day with flex/undertime marker.
+    FlexDay,
+    /// Weekend day (Sat/Sun).
+    Weekend,
+    /// Missing: weekday with no entries and no explanation.
+    Missing,
+    /// Day outside any configured period.
+    OutsidePeriod,
+}
+
+impl fmt::Display for DayType {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            DayType::Regular => write!(f, ""),
+            DayType::SickLeave => write!(f, "Sick Leave"),
+            DayType::Vacation => write!(f, "Vacation"),
+            DayType::Holiday => write!(f, "Holiday"),
+            DayType::FlexDay => write!(f, "Flex Day"),
+            DayType::Weekend => write!(f, "Weekend"),
+            DayType::Missing => write!(f, "\u{26a0} Missing"),
+            DayType::OutsidePeriod => write!(f, "Outside Period"),
+        }
+    }
+}
+
+/// Warning associated with a specific day.
+#[derive(Debug, Clone, PartialEq)]
+pub enum DayWarning {
+    /// Weekday has no entries and no leave/holiday marker.
+    MissingWithoutExplanation,
+    /// Two timecards overlap.
+    OverlappingTimecards {
+        first: (NaiveTime, NaiveTime),
+        second: (NaiveTime, NaiveTime),
+    },
+    /// Work logged outside any configured period.
+    OutsidePeriod { hours_worked: f64 },
+}
+
+impl fmt::Display for DayWarning {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            DayWarning::MissingWithoutExplanation => {
+                write!(f, "No entries and no leave/holiday marker")
+            }
+            DayWarning::OverlappingTimecards { first, second } => {
+                write!(
+                    f,
+                    "{}-{} overlaps with {}-{}",
+                    first.0.format("%H:%M"),
+                    first.1.format("%H:%M"),
+                    second.0.format("%H:%M"),
+                    second.1.format("%H:%M")
+                )
+            }
+            DayWarning::OutsidePeriod { hours_worked } => {
+                write!(f, "{:.1}h worked (no period configured)", hours_worked)
+            }
+        }
+    }
+}
+
+/// Report for a single day.
+#[derive(Debug, Clone)]
+pub struct DayReport {
+    pub date: NaiveDate,
+    pub expected_hours: f64,
+    pub actual_hours: f64,
+    pub day_type: DayType,
+    pub warnings: Vec<DayWarning>,
+}
+
+impl DayReport {
+    pub fn new(date: NaiveDate, expected_hours: f64, actual_hours: f64, day_type: DayType) -> Self {
+        Self {
+            date,
+            expected_hours,
+            actual_hours,
+            day_type,
+            warnings: Vec::new(),
+        }
+    }
+
+    pub fn with_warning(mut self, warning: DayWarning) -> Self {
+        self.warnings.push(warning);
+        self
+    }
+
+    pub fn with_warnings(mut self, warnings: Vec<DayWarning>) -> Self {
+        self.warnings = warnings;
+        self
+    }
+
+    /// Calculate the difference between actual and expected hours.
+    pub fn diff(&self) -> f64 {
+        self.actual_hours - self.expected_hours
+    }
+
+    /// Check if this day has any warnings.
+    pub fn has_warnings(&self) -> bool {
+        !self.warnings.is_empty()
+    }
+}
+
+/// Report for a single month.
+#[derive(Debug, Clone)]
+pub struct MonthReport {
+    pub year: i32,
+    pub month: u32,
+    pub days: Vec<DayReport>,
+}
+
+impl MonthReport {
+    pub fn new(year: i32, month: u32) -> Self {
+        Self {
+            year,
+            month,
+            days: Vec::new(),
+        }
+    }
+
+    pub fn with_days(mut self, days: Vec<DayReport>) -> Self {
+        self.days = days;
+        self
+    }
+
+    /// Calculate total expected hours for the month.
+    pub fn total_expected(&self) -> f64 {
+        self.days.iter().map(|d| d.expected_hours).sum()
+    }
+
+    /// Calculate total actual hours for the month.
+    pub fn total_actual(&self) -> f64 {
+        self.days.iter().map(|d| d.actual_hours).sum()
+    }
+
+    /// Calculate the difference for the month.
+    pub fn diff(&self) -> f64 {
+        self.total_actual() - self.total_expected()
+    }
+
+    /// Get the month name.
+    pub fn month_name(&self) -> &'static str {
+        match self.month {
+            1 => "January",
+            2 => "February",
+            3 => "March",
+            4 => "April",
+            5 => "May",
+            6 => "June",
+            7 => "July",
+            8 => "August",
+            9 => "September",
+            10 => "October",
+            11 => "November",
+            12 => "December",
+            _ => "Unknown",
+        }
+    }
+}
+
+/// A warning to be displayed in the report summary.
+#[derive(Debug, Clone)]
+pub struct ReportWarning {
+    pub date: NaiveDate,
+    pub warning: DayWarning,
+}
+
+impl ReportWarning {
+    pub fn new(date: NaiveDate, warning: DayWarning) -> Self {
+        Self { date, warning }
+    }
+}
+
+/// Complete timesheet report.
+#[derive(Debug, Clone)]
+pub struct TimesheetReport {
+    pub months: Vec<MonthReport>,
+    pub cumulative_balance: f64,
+    pub warnings: Vec<ReportWarning>,
+}
+
+impl TimesheetReport {
+    pub fn new() -> Self {
+        Self {
+            months: Vec::new(),
+            cumulative_balance: 0.0,
+            warnings: Vec::new(),
+        }
+    }
+
+    pub fn with_months(mut self, months: Vec<MonthReport>) -> Self {
+        self.months = months;
+        self
+    }
+
+    pub fn with_cumulative_balance(mut self, balance: f64) -> Self {
+        self.cumulative_balance = balance;
+        self
+    }
+
+    pub fn with_warnings(mut self, warnings: Vec<ReportWarning>) -> Self {
+        self.warnings = warnings;
+        self
+    }
+
+    /// Check if there are any warnings.
+    pub fn has_warnings(&self) -> bool {
+        !self.warnings.is_empty()
+    }
+}
+
+impl Default for TimesheetReport {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn date(year: i32, month: u32, day: u32) -> NaiveDate {
+        NaiveDate::from_ymd_opt(year, month, day).unwrap()
+    }
+
+    fn time(hour: u32, min: u32) -> NaiveTime {
+        NaiveTime::from_hms_opt(hour, min, 0).unwrap()
+    }
+
+    #[test]
+    fn test_day_report_diff() {
+        let report = DayReport::new(date(2026, 3, 2), 7.6, 8.2, DayType::Regular);
+        assert!((report.diff() - 0.6).abs() < 0.0001);
+    }
+
+    #[test]
+    fn test_day_report_negative_diff() {
+        let report = DayReport::new(date(2026, 3, 2), 7.6, 6.0, DayType::Regular);
+        assert!((report.diff() - (-1.6)).abs() < 0.0001);
+    }
+
+    #[test]
+    fn test_month_report_totals() {
+        let month = MonthReport::new(2026, 3).with_days(vec![
+            DayReport::new(date(2026, 3, 2), 7.6, 8.2, DayType::Regular),
+            DayReport::new(date(2026, 3, 3), 7.6, 7.6, DayType::Regular),
+            DayReport::new(date(2026, 3, 4), 7.6, 6.0, DayType::Regular),
+        ]);
+
+        assert!((month.total_expected() - 22.8).abs() < 0.0001);
+        assert!((month.total_actual() - 21.8).abs() < 0.0001);
+        assert!((month.diff() - (-1.0)).abs() < 0.0001);
+    }
+
+    #[test]
+    fn test_month_name() {
+        let month = MonthReport::new(2026, 3);
+        assert_eq!(month.month_name(), "March");
+    }
+
+    #[test]
+    fn test_day_warning_overlap_display() {
+        let warning = DayWarning::OverlappingTimecards {
+            first: (time(9, 0), time(12, 30)),
+            second: (time(12, 0), time(13, 0)),
+        };
+        assert_eq!(warning.to_string(), "09:00-12:30 overlaps with 12:00-13:00");
+    }
+
+    #[test]
+    fn test_day_warning_missing_display() {
+        let warning = DayWarning::MissingWithoutExplanation;
+        assert_eq!(
+            warning.to_string(),
+            "No entries and no leave/holiday marker"
+        );
+    }
+
+    #[test]
+    fn test_day_warning_outside_period_display() {
+        let warning = DayWarning::OutsidePeriod { hours_worked: 3.5 };
+        assert_eq!(warning.to_string(), "3.5h worked (no period configured)");
+    }
+
+    #[test]
+    fn test_day_report_with_warnings() {
+        let report = DayReport::new(date(2026, 3, 2), 7.6, 8.2, DayType::Regular).with_warning(
+            DayWarning::OverlappingTimecards {
+                first: (time(9, 0), time(12, 30)),
+                second: (time(12, 0), time(13, 0)),
+            },
+        );
+
+        assert!(report.has_warnings());
+        assert_eq!(report.warnings.len(), 1);
+    }
+
+    #[test]
+    fn test_timesheeet_report_has_warnings() {
+        let report = TimesheetReport::new().with_warnings(vec![ReportWarning::new(
+            date(2026, 3, 4),
+            DayWarning::MissingWithoutExplanation,
+        )]);
+
+        assert!(report.has_warnings());
+    }
+}