//
//  DayMath.swift
//  Haru_Danim
//
//  "하루 시작 시간" 기준의 논리적 하루 계산과 세션 분할 (CLAUDE.md §4.3)
//

import Foundation

/// 논리적 하루(하루 시작 시간 반영), 주/월 범위, 세션 분할 계산
struct DayMath {
    let settings: TrackingSettings

    init(settings: TrackingSettings = .current()) {
        self.settings = settings
    }

    var calendar: Calendar { settings.calendar }

    // MARK: 논리적 하루

    /// `date`가 속하는 논리적 하루의 키(해당 달력일의 자정 Date).
    /// 예: 하루 시작 06:00일 때 7/7 05:00 → 7/6이 키.
    func dayKey(for date: Date) -> Date {
        let startOfDay = calendar.startOfDay(for: date)
        let boundary = calendar.date(byAdding: .minute, value: settings.dayStartMinutes, to: startOfDay)!
        if date < boundary {
            return calendar.date(byAdding: .day, value: -1, to: startOfDay)!
        }
        return startOfDay
    }

    /// 키(자정 Date)가 가리키는 논리적 하루의 실제 시각 범위
    func dayRange(forKey key: Date) -> Range<Date> {
        let start = calendar.date(byAdding: .minute, value: settings.dayStartMinutes, to: key)!
        let nextKey = calendar.date(byAdding: .day, value: 1, to: key)!
        let end = calendar.date(byAdding: .minute, value: settings.dayStartMinutes, to: nextKey)!
        return start..<end
    }

    func dayRange(containing date: Date) -> Range<Date> {
        dayRange(forKey: dayKey(for: date))
    }

    // MARK: 주 / 월 범위

    /// `date`가 속한 논리적 하루를 포함하는 주(주 시작 요일 설정 반영)의 범위
    func weekRange(containing date: Date) -> Range<Date> {
        var key = dayKey(for: date)
        while calendar.component(.weekday, from: key) != calendar.firstWeekday {
            key = calendar.date(byAdding: .day, value: -1, to: key)!
        }
        let lastKey = calendar.date(byAdding: .day, value: 6, to: key)!
        return dayRange(forKey: key).lowerBound..<dayRange(forKey: lastKey).upperBound
    }

    /// `date`가 속한 논리적 하루를 포함하는 달의 범위
    func monthRange(containing date: Date) -> Range<Date> {
        let key = dayKey(for: date)
        let comps = calendar.dateComponents([.year, .month], from: key)
        let firstKey = calendar.date(from: comps)!
        let dayCount = calendar.range(of: .day, in: .month, for: firstKey)!.count
        let lastKey = calendar.date(byAdding: .day, value: dayCount - 1, to: firstKey)!
        return dayRange(forKey: firstKey).lowerBound..<dayRange(forKey: lastKey).upperBound
    }

    /// 범위에 포함된 논리적 하루 키 목록
    func dayKeys(in range: Range<Date>) -> [Date] {
        var keys: [Date] = []
        var key = dayKey(for: range.lowerBound)
        while dayRange(forKey: key).lowerBound < range.upperBound {
            keys.append(key)
            key = calendar.date(byAdding: .day, value: 1, to: key)!
        }
        return keys
    }

    // MARK: 세션 분할 (하루 경계 걸침 처리)

    struct DaySegment {
        let dayKey: Date
        let range: Range<Date>
    }

    /// 시작~종료 구간을 논리적 하루 경계 기준으로 분할
    func splitByDay(start: Date, end: Date) -> [DaySegment] {
        guard start < end else { return [] }
        var segments: [DaySegment] = []
        var cursor = start
        while cursor < end {
            let key = dayKey(for: cursor)
            let dayEnd = dayRange(forKey: key).upperBound
            let segmentEnd = min(dayEnd, end)
            segments.append(DaySegment(dayKey: key, range: cursor..<segmentEnd))
            cursor = segmentEnd
        }
        return segments
    }
}

// MARK: - 집계

/// 행동별 시간/횟수 집계 (분할 규칙은 구간 겹침으로 자연히 반영됨)
struct Aggregator {
    let math: DayMath

    init(math: DayMath = DayMath()) {
        self.math = math
    }

    /// 지정 구간 내 행동의 총 시간(초). 진행 중 세션은 `now`까지 계산.
    func seconds(for action: Action, in range: Range<Date>, now: Date = .now) -> TimeInterval {
        action.sessions.reduce(0) { total, session in
            let end = session.endAt ?? now
            let overlapStart = max(session.startAt, range.lowerBound)
            let overlapEnd = min(end, range.upperBound)
            return total + max(0, overlapEnd.timeIntervalSince(overlapStart))
        }
    }

    /// 지정 구간 내 행동의 총 횟수
    func count(for action: Action, in range: Range<Date>) -> Int {
        action.countEntries
            .filter { range.contains($0.timestamp) }
            .reduce(0) { $0 + $1.amount }
    }

    func seconds(for actions: [Action], in range: Range<Date>, now: Date = .now) -> TimeInterval {
        actions.reduce(0) { $0 + seconds(for: $1, in: range, now: now) }
    }

    func count(for actions: [Action], in range: Range<Date>) -> Int {
        actions.reduce(0) { $0 + count(for: $1, in: range) }
    }

    /// 오늘(논리적 하루)의 값 — 메인 버튼 표시용
    func todayValue(for action: Action, now: Date = .now) -> Double {
        let range = math.dayRange(containing: now)
        switch action.trackingType {
        case .time: return seconds(for: action, in: range, now: now)
        case .count: return Double(count(for: action, in: range))
        }
    }
}