use std::collections::HashMap;
use std::fs;
use std::path::Path;

use chrono::{Datelike, NaiveDate, Weekday};

use crate::error::StreamdError;
use crate::models::{SpecialDayType, Timesheet};

use super::config::{RepositoryConfig, TimesheetConfig};
use super::report::{DayReport, DayType, DayWarning, MonthReport, ReportWarning, TimesheetReport};
use super::validation::find_overlapping_timecards;

/// Load repository configuration from .streamd.toml file.
pub fn load_repository_config(base_folder: &Path) -> Result<RepositoryConfig, StreamdError> {
    let config_path = base_folder.join(".streamd.toml");

    if !config_path.exists() {
        return Ok(RepositoryConfig::default());
    }

    let content = fs::read_to_string(&config_path)?;
    let config: RepositoryConfig = toml::from_str(&content)?;

    // Validate timesheet config if present
    if let Some(ref timesheet) = config.timesheet {
        timesheet.validate()?;
    }

    Ok(config)
}

/// Calculate total hours worked from timecards.
fn calculate_timecard_hours(timesheet: &Timesheet) -> f64 {
    timesheet
        .timecards
        .iter()
        .map(|tc| {
            let duration = tc.to_time - tc.from_time;
            duration.num_minutes() as f64 / 60.0
        })
        .sum()
}

/// Determine the day type based on timesheet data.
fn determine_day_type(date: NaiveDate, timesheet: Option<&Timesheet>, has_period: bool) -> DayType {
    let weekday = date.weekday();

    // Check weekend first
    if weekday == Weekday::Sat || weekday == Weekday::Sun {
        return DayType::Weekend;
    }

    // Check if outside any period
    if !has_period {
        return DayType::OutsidePeriod;
    }

    // Check special day types from timesheet
    if let Some(ts) = timesheet {
        if let Some(special) = ts.special_day_type {
            match special {
                SpecialDayType::Vacation => return DayType::Vacation,
                SpecialDayType::Holiday => return DayType::Holiday,
                SpecialDayType::Undertime => return DayType::FlexDay,
                SpecialDayType::Weekend => return DayType::Weekend,
            }
        }

        if ts.is_sick_leave {
            return DayType::SickLeave;
        }

        // Has timecards or special type
        return DayType::Regular;
    }

    // No timesheet entry for a weekday = Missing
    DayType::Missing
}

/// Calculate expected hours for a day based on period config and day type.
fn calculate_expected_hours(day_type: DayType, hours_per_day: f64, _date: NaiveDate) -> f64 {
    match day_type {
        DayType::Regular => hours_per_day,
        DayType::SickLeave => hours_per_day,
        DayType::Vacation => hours_per_day,
        DayType::Holiday => 0.0,
        DayType::FlexDay => hours_per_day,
        DayType::Weekend => 0.0,
        DayType::Missing => hours_per_day,
        DayType::OutsidePeriod => 0.0,
    }
}

/// Calculate actual hours for a day based on day type rules.
fn calculate_actual_hours(day_type: DayType, timecard_hours: f64, expected_hours: f64) -> f64 {
    match day_type {
        DayType::Regular => timecard_hours,
        DayType::SickLeave => expected_hours.max(timecard_hours),
        DayType::Vacation => expected_hours + timecard_hours,
        DayType::Holiday => timecard_hours,
        DayType::FlexDay => 0.0,
        DayType::Weekend => timecard_hours,
        DayType::Missing => 0.0,
        DayType::OutsidePeriod => timecard_hours,
    }
}

/// Generate a timesheet report from timesheets and configuration.
pub fn generate_report(
    timesheets: &[Timesheet],
    config: &TimesheetConfig,
) -> Result<TimesheetReport, StreamdError> {
    if config.periods.is_empty() {
        return Ok(TimesheetReport::new());
    }

    // Index timesheets by date for quick lookup
    let timesheets_by_date: HashMap<NaiveDate, &Timesheet> =
        timesheets.iter().map(|ts| (ts.date, ts)).collect();

    // Find the date range to report on
    let earliest_period_start = config.periods.iter().map(|p| p.start).min().unwrap();
    let latest_period_end = config.periods.iter().map(|p| p.end).max().unwrap();

    // Limit to today
    let today = chrono::Local::now().date_naive();
    let end_date = latest_period_end.min(today);

    // Group by month and generate reports
    let mut month_reports: Vec<MonthReport> = Vec::new();
    let mut all_warnings: Vec<ReportWarning> = Vec::new();
    let mut cumulative_balance: f64 = 0.0;

    // Iterate through all dates in the range
    let mut current_date = earliest_period_start;
    let mut current_month: Option<(i32, u32)> = None;
    let mut current_month_days: Vec<DayReport> = Vec::new();

    while current_date <= end_date {
        let year = current_date.year();
        let month = current_date.month();

        // Check if we've moved to a new month
        if current_month != Some((year, month)) {
            // Save the previous month if it had days
            if let Some((prev_year, prev_month)) = current_month {
                if !current_month_days.is_empty() {
                    let month_report =
                        MonthReport::new(prev_year, prev_month).with_days(current_month_days);
                    cumulative_balance += month_report.diff();
                    month_reports.push(month_report);
                }
            }
            current_month = Some((year, month));
            current_month_days = Vec::new();
        }

        // Find if this date falls within a period
        let period = config.find_period(current_date);
        let has_period = period.is_some();
        let hours_per_day = period.map(|p| p.hours_per_day()).unwrap_or(0.0);

        // Get timesheet for this date
        let timesheet = timesheets_by_date.get(&current_date).copied();
        let timecard_hours = timesheet.map(calculate_timecard_hours).unwrap_or(0.0);

        // Determine day type
        let day_type = determine_day_type(current_date, timesheet, has_period);

        // Skip weekends with no work and days outside periods with no work
        let should_include = match day_type {
            DayType::Weekend => timecard_hours > 0.0,
            DayType::OutsidePeriod => timecard_hours > 0.0,
            _ => has_period, // Only include days within periods
        };

        if should_include {
            // Calculate expected and actual hours
            let expected_hours = calculate_expected_hours(day_type, hours_per_day, current_date);
            let actual_hours = calculate_actual_hours(day_type, timecard_hours, expected_hours);

            let mut day_report =
                DayReport::new(current_date, expected_hours, actual_hours, day_type);

            // Collect warnings
            let mut day_warnings: Vec<DayWarning> = Vec::new();

            // Warning: Missing without explanation
            if day_type == DayType::Missing {
                day_warnings.push(DayWarning::MissingWithoutExplanation);
                all_warnings.push(ReportWarning::new(
                    current_date,
                    DayWarning::MissingWithoutExplanation,
                ));
            }

            // Warning: Overlapping timecards
            if let Some(ts) = timesheet {
                let overlaps = find_overlapping_timecards(&ts.timecards);
                for (first, second) in overlaps {
                    let warning = DayWarning::OverlappingTimecards { first, second };
                    day_warnings.push(warning.clone());
                    all_warnings.push(ReportWarning::new(current_date, warning));
                }
            }

            // Warning: Work outside period
            if day_type == DayType::OutsidePeriod && timecard_hours > 0.0 {
                let warning = DayWarning::OutsidePeriod {
                    hours_worked: timecard_hours,
                };
                day_warnings.push(warning.clone());
                all_warnings.push(ReportWarning::new(current_date, warning));
            }

            day_report = day_report.with_warnings(day_warnings);
            current_month_days.push(day_report);
        }

        // Move to next day
        current_date = current_date.succ_opt().unwrap_or(current_date);
        if current_date == end_date && current_date <= latest_period_end {
            // We've hit end_date, process this day then stop
        }
    }

    // Don't forget the last month
    if let Some((year, month)) = current_month {
        if !current_month_days.is_empty() {
            let month_report = MonthReport::new(year, month).with_days(current_month_days);
            cumulative_balance += month_report.diff();
            month_reports.push(month_report);
        }
    }

    // Sort months in ascending order (oldest first, newest at bottom)
    month_reports.sort_by(|a, b| {
        let a_date = (a.year, a.month);
        let b_date = (b.year, b.month);
        a_date.cmp(&b_date)
    });

    Ok(TimesheetReport::new()
        .with_months(month_reports)
        .with_cumulative_balance(cumulative_balance)
        .with_warnings(all_warnings))
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::models::Timecard;
    use crate::timesheet::Period;
    use chrono::NaiveTime;

    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()
    }

    fn make_timesheet(date: NaiveDate, cards: Vec<(u32, u32, u32, u32)>) -> Timesheet {
        Timesheet {
            date,
            is_sick_leave: false,
            special_day_type: None,
            timecards: cards
                .into_iter()
                .map(|(fh, fm, th, tm)| Timecard::new(time(fh, fm), time(th, tm)))
                .collect(),
        }
    }

    fn make_config(start: NaiveDate, end: NaiveDate, hours_per_week: f64) -> TimesheetConfig {
        TimesheetConfig {
            periods: vec![Period {
                start,
                end,
                hours_per_week,
            }],
        }
    }

    #[test]
    fn test_calculate_timecard_hours() {
        let ts = make_timesheet(date(2026, 3, 2), vec![(9, 0, 12, 0), (13, 0, 17, 0)]);
        let hours = calculate_timecard_hours(&ts);
        assert!((hours - 7.0).abs() < 0.0001);
    }

    #[test]
    fn test_calculate_timecard_hours_with_minutes() {
        let ts = make_timesheet(date(2026, 3, 2), vec![(9, 0, 12, 30), (13, 0, 17, 15)]);
        let hours = calculate_timecard_hours(&ts);
        assert!((hours - 7.75).abs() < 0.0001);
    }

    #[test]
    fn test_day_type_regular() {
        // Monday with timesheet
        let ts = make_timesheet(date(2026, 3, 2), vec![(9, 0, 17, 0)]);
        let day_type = determine_day_type(date(2026, 3, 2), Some(&ts), true);
        assert_eq!(day_type, DayType::Regular);
    }

    #[test]
    fn test_day_type_weekend() {
        // Saturday
        let day_type = determine_day_type(date(2026, 3, 7), None, true);
        assert_eq!(day_type, DayType::Weekend);
    }

    #[test]
    fn test_day_type_missing() {
        // Monday with no timesheet
        let day_type = determine_day_type(date(2026, 3, 2), None, true);
        assert_eq!(day_type, DayType::Missing);
    }

    #[test]
    fn test_day_type_vacation() {
        let ts = Timesheet {
            date: date(2026, 3, 2),
            is_sick_leave: false,
            special_day_type: Some(SpecialDayType::Vacation),
            timecards: vec![],
        };
        let day_type = determine_day_type(date(2026, 3, 2), Some(&ts), true);
        assert_eq!(day_type, DayType::Vacation);
    }

    #[test]
    fn test_day_type_sick_leave() {
        let ts = Timesheet {
            date: date(2026, 3, 2),
            is_sick_leave: true,
            special_day_type: None,
            timecards: vec![],
        };
        let day_type = determine_day_type(date(2026, 3, 2), Some(&ts), true);
        assert_eq!(day_type, DayType::SickLeave);
    }

    #[test]
    fn test_day_type_holiday() {
        let ts = Timesheet {
            date: date(2026, 3, 2),
            is_sick_leave: false,
            special_day_type: Some(SpecialDayType::Holiday),
            timecards: vec![],
        };
        let day_type = determine_day_type(date(2026, 3, 2), Some(&ts), true);
        assert_eq!(day_type, DayType::Holiday);
    }

    #[test]
    fn test_day_type_flex_day() {
        let ts = Timesheet {
            date: date(2026, 3, 2),
            is_sick_leave: false,
            special_day_type: Some(SpecialDayType::Undertime),
            timecards: vec![],
        };
        let day_type = determine_day_type(date(2026, 3, 2), Some(&ts), true);
        assert_eq!(day_type, DayType::FlexDay);
    }

    #[test]
    fn test_day_type_outside_period() {
        let day_type = determine_day_type(date(2026, 3, 2), None, false);
        assert_eq!(day_type, DayType::OutsidePeriod);
    }

    #[test]
    fn test_expected_hours_regular() {
        let hours = calculate_expected_hours(DayType::Regular, 7.6, date(2026, 3, 2));
        assert!((hours - 7.6).abs() < 0.0001);
    }

    #[test]
    fn test_expected_hours_holiday() {
        let hours = calculate_expected_hours(DayType::Holiday, 7.6, date(2026, 3, 2));
        assert!((hours - 0.0).abs() < 0.0001);
    }

    #[test]
    fn test_expected_hours_weekend() {
        let hours = calculate_expected_hours(DayType::Weekend, 7.6, date(2026, 3, 7));
        assert!((hours - 0.0).abs() < 0.0001);
    }

    #[test]
    fn test_actual_hours_regular() {
        let hours = calculate_actual_hours(DayType::Regular, 8.0, 7.6);
        assert!((hours - 8.0).abs() < 0.0001);
    }

    #[test]
    fn test_actual_hours_sick_leave_max() {
        // Sick leave: max(expected, worked)
        let hours = calculate_actual_hours(DayType::SickLeave, 3.0, 7.6);
        assert!((hours - 7.6).abs() < 0.0001);
    }

    #[test]
    fn test_actual_hours_sick_leave_worked_more() {
        // Sick leave where worked > expected
        let hours = calculate_actual_hours(DayType::SickLeave, 9.0, 7.6);
        assert!((hours - 9.0).abs() < 0.0001);
    }

    #[test]
    fn test_actual_hours_vacation() {
        // Vacation: expected + worked
        let hours = calculate_actual_hours(DayType::Vacation, 2.0, 7.6);
        assert!((hours - 9.6).abs() < 0.0001);
    }

    #[test]
    fn test_actual_hours_flex_day() {
        // Flex day: always 0
        let hours = calculate_actual_hours(DayType::FlexDay, 5.0, 7.6);
        assert!((hours - 0.0).abs() < 0.0001);
    }

    #[test]
    fn test_generate_report_empty_config() {
        let config = TimesheetConfig { periods: vec![] };
        let report = generate_report(&[], &config).unwrap();
        assert!(report.months.is_empty());
    }

    #[test]
    fn test_generate_report_single_day() {
        // Monday 2026-03-02
        let timesheets = vec![make_timesheet(date(2026, 3, 2), vec![(9, 0, 17, 0)])];
        let config = make_config(date(2026, 3, 2), date(2026, 3, 2), 40.0);

        let report = generate_report(&timesheets, &config).unwrap();

        assert_eq!(report.months.len(), 1);
        assert_eq!(report.months[0].days.len(), 1);

        let day = &report.months[0].days[0];
        assert_eq!(day.date, date(2026, 3, 2));
        assert!((day.expected_hours - 8.0).abs() < 0.0001);
        assert!((day.actual_hours - 8.0).abs() < 0.0001);
        assert_eq!(day.day_type, DayType::Regular);
    }

    #[test]
    fn test_generate_report_detects_missing_day() {
        // Period covers Mon-Tue, but only Mon has timesheet
        let timesheets = vec![make_timesheet(date(2026, 3, 2), vec![(9, 0, 17, 0)])];
        // March 2 is Monday, March 3 is Tuesday
        let config = make_config(date(2026, 3, 2), date(2026, 3, 3), 40.0);

        let report = generate_report(&timesheets, &config).unwrap();

        assert_eq!(report.months[0].days.len(), 2);

        // First day (Mon) should be regular
        assert_eq!(report.months[0].days[0].day_type, DayType::Regular);

        // Second day (Tue) should be missing
        assert_eq!(report.months[0].days[1].day_type, DayType::Missing);
        assert!(report.months[0].days[1].has_warnings());
    }

    #[test]
    fn test_generate_report_weekend_excluded_if_no_work() {
        // Period covers Mon-Sun, but only Mon has timesheet
        let timesheets = vec![make_timesheet(date(2026, 3, 2), vec![(9, 0, 17, 0)])];
        let config = make_config(date(2026, 3, 2), date(2026, 3, 8), 40.0);

        let report = generate_report(&timesheets, &config).unwrap();

        // Should only include Mon-Fri (5 days), not Sat-Sun
        let days = &report.months[0].days;
        for day in days {
            let weekday = day.date.weekday();
            assert!(weekday != Weekday::Sat && weekday != Weekday::Sun);
        }
    }

    #[test]
    fn test_generate_report_weekend_included_if_work() {
        // Work on Saturday
        let timesheets = vec![
            make_timesheet(date(2026, 3, 2), vec![(9, 0, 17, 0)]),
            make_timesheet(date(2026, 3, 7), vec![(10, 0, 14, 0)]), // Saturday
        ];
        let config = make_config(date(2026, 3, 2), date(2026, 3, 8), 40.0);

        let report = generate_report(&timesheets, &config).unwrap();

        // Should include Saturday
        let has_saturday = report.months[0]
            .days
            .iter()
            .any(|d| d.date == date(2026, 3, 7));
        assert!(has_saturday);
    }

    #[test]
    fn test_generate_report_overlapping_timecards_warning() {
        let ts = Timesheet {
            date: date(2026, 3, 2),
            is_sick_leave: false,
            special_day_type: None,
            timecards: vec![
                Timecard::new(time(9, 0), time(12, 30)),
                Timecard::new(time(12, 0), time(13, 0)),
            ],
        };
        let config = make_config(date(2026, 3, 2), date(2026, 3, 2), 40.0);

        let report = generate_report(&[ts], &config).unwrap();

        assert!(report.has_warnings());
        assert!(report.months[0].days[0].has_warnings());
    }

    #[test]
    fn test_generate_report_cumulative_balance() {
        // Two days: one with 8h (expected 8h), one with 10h (expected 8h)
        let timesheets = vec![
            make_timesheet(date(2026, 3, 2), vec![(9, 0, 17, 0)]), // 8h
            make_timesheet(date(2026, 3, 3), vec![(8, 0, 18, 0)]), // 10h
        ];
        let config = make_config(date(2026, 3, 2), date(2026, 3, 3), 40.0);

        let report = generate_report(&timesheets, &config).unwrap();

        // Balance should be +2h (18h actual - 16h expected)
        assert!((report.cumulative_balance - 2.0).abs() < 0.0001);
    }
}