import SwiftUI
import UIKit

// MARK: - 색상 팔레트 (다크 전용)

extension Color {
    init(hex: UInt32) {
        self.init(
            .sRGB,
            red: Double((hex >> 16) & 0xFF) / 255,
            green: Double((hex >> 8) & 0xFF) / 255,
            blue: Double(hex & 0xFF) / 255
        )
    }
}

enum Theme {
    static let bg = Color(hex: 0x0B0E13)
    static let surface = Color(hex: 0x161B25)
    static let surfaceHi = Color(hex: 0x202836)
    static let stroke = Color.white.opacity(0.07)

    static let accent = Color(hex: 0x3BE39F)
    static let accentSoft = Color(hex: 0x3BE39F).opacity(0.14)
    static let onAccent = Color(hex: 0x07281B)

    static let danger = Color(hex: 0xFF7A7A)
    static let warn = Color(hex: 0xFFC94D)
    static let sunday = Color(hex: 0xFF8A80)
    static let saturday = Color(hex: 0x7EB6FF)

    static let textPrimary = Color(hex: 0xF3F6FA)
    static let textSecondary = Color(hex: 0x8D99AD)

    static let accentGradient = LinearGradient(
        colors: [Color(hex: 0x5CF0B6), Color(hex: 0x1FC98B)],
        startPoint: .topLeading,
        endPoint: .bottomTrailing
    )
}

// MARK: - 공용 스타일

struct CardBackground: ViewModifier {
    var cornerRadius: CGFloat = 18

    func body(content: Content) -> some View {
        content
            .background(
                RoundedRectangle(cornerRadius: cornerRadius, style: .continuous)
                    .fill(Theme.surface)
                    .overlay(
                        RoundedRectangle(cornerRadius: cornerRadius, style: .continuous)
                            .strokeBorder(Theme.stroke, lineWidth: 1)
                    )
            )
    }
}

extension View {
    func cardStyle(cornerRadius: CGFloat = 18) -> some View {
        modifier(CardBackground(cornerRadius: cornerRadius))
    }
}

// MARK: - 햅틱

enum Haptics {
    static func success() { UINotificationFeedbackGenerator().notificationOccurred(.success) }
    static func warning() { UINotificationFeedbackGenerator().notificationOccurred(.warning) }
    static func tap() { UIImpactFeedbackGenerator(style: .light).impactOccurred() }
    static func shutter() { UIImpactFeedbackGenerator(style: .medium).impactOccurred() }
}

// MARK: - 달력 유틸

enum KoreanCalendar {
    static let calendar: Calendar = {
        var c = Calendar(identifier: .gregorian)
        c.locale = Locale(identifier: "ko_KR")
        return c
    }()

    static let weekdaySymbols = ["일", "월", "화", "수", "목", "금", "토"]

    /// 해당 월의 그리드 셀 배열. 앞쪽 빈칸은 nil, 이후 1...말일.
    static func gridDays(year: Int, month: Int) -> [Int?] {
        let comps = DateComponents(year: year, month: month, day: 1)
        guard let first = calendar.date(from: comps),
              let range = calendar.range(of: .day, in: .month, for: first) else { return [] }
        let firstWeekday = calendar.component(.weekday, from: first)
        let leading = (firstWeekday - calendar.firstWeekday + 7) % 7
        return Array(repeating: nil, count: leading) + range.map { $0 }
    }

    static func date(year: Int, month: Int, day: Int) -> Date? {
        calendar.date(from: DateComponents(year: year, month: month, day: day))
    }

    static func isToday(year: Int, month: Int, day: Int) -> Bool {
        let t = calendar.dateComponents([.year, .month, .day], from: .now)
        return t.year == year && t.month == month && t.day == day
    }

    /// 오늘부터 해당 날짜까지 남은 일수 (음수면 지난 날짜)
    static func daysFromToday(to date: Date) -> Int {
        let today = calendar.startOfDay(for: .now)
        let target = calendar.startOfDay(for: date)
        return calendar.dateComponents([.day], from: today, to: target).day ?? 0
    }

    static func weekdayColor(columnIndex: Int) -> Color {
        switch columnIndex {
        case 0: return Theme.sunday
        case 6: return Theme.saturday
        default: return Theme.textSecondary
        }
    }
}

// MARK: - 이미지 유틸

extension UIImage {
    func downscaled(maxDimension: CGFloat) -> UIImage {
        let longest = max(size.width, size.height)
        guard longest > maxDimension, longest > 0 else { return self }
        let ratio = maxDimension / longest
        let newSize = CGSize(width: size.width * ratio, height: size.height * ratio)
        let format = UIGraphicsImageRendererFormat.default()
        format.scale = 1
        return UIGraphicsImageRenderer(size: newSize, format: format).image { _ in
            draw(in: CGRect(origin: .zero, size: newSize))
        }
    }
}