import SnapKit
import UIKit

/// 日清页顶部可横滑的周/月日历组件。
@MainActor
final class OfflineCollectionCalendarView: UIView {
    var onDateSelected: ((String) -> Void)?
    var onModeChanged: (() -> Void)?

    private let titleLabel = UILabel()
    private let toggleButton = UIButton(type: .system)
    private let nextButton = UIButton(type: .system)
    private let rowsStack = UIStackView()
    private var rowStacks: [UIStackView] = []
    private var dayButtons: [OfflineCollectionDayButton] = []
    private var pendingDates: Set<String> = []
    private var state = OfflineCollectionCalendarState(selectedDate: Date(), maximumDate: Date())
    private let calendar = OfflineCollectionDate.calendar

    override var intrinsicContentSize: CGSize {
        CGSize(width: UIView.noIntrinsicMetric, height: state.mode == .week ? 160 : 378)
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        setupUI()
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    /// 使用选中日、服务端今日和待补缴日期刷新组件。
    func apply(selectedDate: String, maximumDate: String, pendingDates: Set<String>) {
        guard let selected = OfflineCollectionDate.date(from: selectedDate),
              let maximum = OfflineCollectionDate.date(from: maximumDate) else { return }
        self.pendingDates = pendingDates
        state = OfflineCollectionCalendarState(
            selectedDate: selected,
            maximumDate: maximum,
            mode: state.mode,
            calendar: calendar
        )
        reloadDates()
    }

    private func setupUI() {
        backgroundColor = .white
        layer.cornerRadius = AppRadius.lg
        layer.shadowColor = UIColor(hex: 0x8FA0B8).cgColor
        layer.shadowOpacity = 0.12
        layer.shadowRadius = 10
        layer.shadowOffset = CGSize(width: 0, height: 4)

        titleLabel.font = .systemFont(ofSize: 20, weight: .bold)
        titleLabel.textColor = UIColor(hex: 0x081739)
        toggleButton.configuration = .plain()
        toggleButton.configuration?.baseForegroundColor = UIColor(hex: 0x081739)
        toggleButton.configuration?.imagePlacement = .trailing
        toggleButton.configuration?.imagePadding = 8
        toggleButton.configuration?.contentInsets = NSDirectionalEdgeInsets(top: 7, leading: 14, bottom: 7, trailing: 12)
        toggleButton.layer.cornerRadius = 9
        toggleButton.layer.borderWidth = 1
        toggleButton.layer.borderColor = UIColor(hex: 0xE2E7EF).cgColor
        toggleButton.addTarget(self, action: #selector(toggleMode), for: .touchUpInside)
        toggleButton.accessibilityIdentifier = "offlineCollection.calendar.toggle"

        nextButton.setImage(UIImage(systemName: "chevron.right"), for: .normal)
        nextButton.tintColor = UIColor(hex: 0x081739)
        nextButton.accessibilityLabel = "下一页"
        nextButton.addTarget(self, action: #selector(nextPage), for: .touchUpInside)
        nextButton.snp.makeConstraints { make in make.width.height.equalTo(44) }

        let spacer = UIView()
        let header = UIStackView(arrangedSubviews: [titleLabel, spacer, toggleButton, nextButton])
        header.axis = .horizontal
        header.alignment = .center
        header.spacing = 8

        let weekdayStack = UIStackView()
        weekdayStack.axis = .horizontal
        weekdayStack.distribution = .fillEqually
        ["一", "二", "三", "四", "五", "六", "日"].forEach { value in
            let label = UILabel()
            label.text = value
            label.font = .systemFont(ofSize: 13, weight: .medium)
            label.textColor = UIColor(hex: 0x657084)
            label.textAlignment = .center
            weekdayStack.addArrangedSubview(label)
        }

        rowsStack.axis = .vertical
        rowsStack.distribution = .fillEqually
        rowsStack.spacing = 1
        for _ in 0 ..< 6 {
            let row = UIStackView()
            row.axis = .horizontal
            row.distribution = .fillEqually
            for _ in 0 ..< 7 {
                let button = OfflineCollectionDayButton()
                button.addTarget(self, action: #selector(dayTapped(_:)), for: .touchUpInside)
                dayButtons.append(button)
                row.addArrangedSubview(button)
            }
            rowStacks.append(row)
            rowsStack.addArrangedSubview(row)
        }

        addSubview(header)
        addSubview(weekdayStack)
        addSubview(rowsStack)
        header.snp.makeConstraints { make in
            make.top.equalToSuperview().offset(14)
            make.leading.equalToSuperview().offset(16)
            make.trailing.equalToSuperview().inset(10)
            make.height.equalTo(44)
        }
        weekdayStack.snp.makeConstraints { make in
            make.top.equalTo(header.snp.bottom).offset(8)
            make.leading.trailing.equalToSuperview().inset(10)
            make.height.equalTo(24)
        }
        rowsStack.snp.makeConstraints { make in
            make.top.equalTo(weekdayStack.snp.bottom).offset(4)
            make.leading.trailing.equalToSuperview().inset(10)
            make.bottom.equalToSuperview().inset(12)
        }

        let left = UISwipeGestureRecognizer(target: self, action: #selector(swiped(_:)))
        left.direction = .left
        let right = UISwipeGestureRecognizer(target: self, action: #selector(swiped(_:)))
        right.direction = .right
        addGestureRecognizer(left)
        addGestureRecognizer(right)
        reloadDates()
    }

    private func reloadDates() {
        titleLabel.text = state.monthTitle
        let isMonth = state.mode == .month
        toggleButton.configuration?.title = isMonth ? "周" : "月"
        toggleButton.configuration?.image = UIImage(systemName: isMonth ? "chevron.up" : "chevron.down")
        rowStacks.enumerated().forEach { $0.element.isHidden = !isMonth && $0.offset > 0 }

        let dates = isMonth ? state.monthDates : state.weekDates
        let selectedMonth = calendar.component(.month, from: state.selectedDate)
        for (index, button) in dayButtons.enumerated() {
            guard index < dates.count else {
                button.isHidden = true
                continue
            }
            let date = dates[index]
            let key = OfflineCollectionDate.businessDate(for: date, calendar: calendar)
            button.isHidden = false
            button.apply(
                date: date,
                key: key,
                selected: calendar.isDate(date, inSameDayAs: state.selectedDate),
                pending: pendingDates.contains(key),
                today: calendar.isDate(date, inSameDayAs: state.maximumDate),
                enabled: date <= state.maximumDate,
                inCurrentMonth: !isMonth || calendar.component(.month, from: date) == selectedMonth,
                calendar: calendar
            )
        }
        invalidateIntrinsicContentSize()
    }

    @objc private func toggleMode() {
        state.toggleMode()
        let animations = { [weak self] in
            self?.reloadDates()
            self?.superview?.layoutIfNeeded()
        }
        if UIAccessibility.isReduceMotionEnabled { animations() } else {
            UIView.animate(withDuration: 0.2, animations: animations)
        }
        onModeChanged?()
    }

    @objc private func dayTapped(_ sender: OfflineCollectionDayButton) {
        guard let date = sender.date, state.select(date) else { return }
        reloadDates()
        onDateSelected?(OfflineCollectionDate.businessDate(for: date, calendar: calendar))
    }

    @objc private func swiped(_ gesture: UISwipeGestureRecognizer) {
        let oldDate = state.selectedDate
        let offset = gesture.direction == .left ? 1 : -1
        let date = state.movePage(offset)
        guard !calendar.isDate(oldDate, inSameDayAs: date) else { return }
        let transition: UIView.AnimationOptions = gesture.direction == .left ? .transitionCrossDissolve : .transitionCrossDissolve
        if UIAccessibility.isReduceMotionEnabled { reloadDates() } else {
            UIView.transition(with: rowsStack, duration: 0.18, options: transition) { [weak self] in self?.reloadDates() }
        }
        onDateSelected?(OfflineCollectionDate.businessDate(for: date, calendar: calendar))
    }

    @objc private func nextPage() {
        let oldDate = state.selectedDate
        let date = state.movePage(1)
        guard !calendar.isDate(oldDate, inSameDayAs: date) else { return }
        reloadDates()
        onDateSelected?(OfflineCollectionDate.businessDate(for: date, calendar: calendar))
    }
}

/// 日历中的单个日期按钮，同时表达选中、今日和待补缴状态。
private final class OfflineCollectionDayButton: UIControl {
    private let dayLabel = UILabel()
    private let pendingDot = UIView()
    private(set) var date: Date?

    override init(frame: CGRect) {
        super.init(frame: frame)
        layer.cornerRadius = 10
        dayLabel.font = .systemFont(ofSize: 17, weight: .medium)
        dayLabel.textAlignment = .center
        pendingDot.layer.cornerRadius = 2.5
        addSubview(dayLabel)
        addSubview(pendingDot)
        dayLabel.snp.makeConstraints { make in make.centerX.equalToSuperview(); make.centerY.equalToSuperview().offset(-2) }
        pendingDot.snp.makeConstraints { make in make.top.equalTo(dayLabel.snp.bottom).offset(2); make.centerX.equalToSuperview(); make.width.height.equalTo(5) }
        snp.makeConstraints { make in make.height.greaterThanOrEqualTo(44) }
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    func apply(
        date: Date,
        key: String,
        selected: Bool,
        pending: Bool,
        today: Bool,
        enabled: Bool,
        inCurrentMonth: Bool,
        calendar: Calendar
    ) {
        self.date = date
        isEnabled = enabled
        dayLabel.text = String(calendar.component(.day, from: date))
        pendingDot.isHidden = !pending
        pendingDot.backgroundColor = selected ? .white : AppColor.danger
        backgroundColor = selected ? AppColor.primary : (pending ? UIColor(hex: 0xFFF1F0) : .clear)
        layer.borderWidth = pending && selected ? 2 : (today && !selected ? 1 : 0)
        layer.borderColor = (pending && selected ? AppColor.danger : AppColor.primary).cgColor
        dayLabel.textColor = selected ? .white : (enabled ? (inCurrentMonth ? AppColor.textPrimary : AppColor.textTertiary) : AppColor.textTertiary)
        alpha = enabled ? 1 : 0.35
        accessibilityLabel = "\(key)\(today ? "，今天" : "")\(pending ? "，待补缴" : "")\(selected ? "，已选中" : "")"
        accessibilityTraits = selected ? [.button, .selected] : .button
    }
}