import UIKit

@MainActor
final class MilestoneEditorViewController: UIViewController, UITextFieldDelegate {
    private let context: AppContext
    private let owner: String
    private let repository: String
    private let id: Int64?
    private let saved: (Int64) -> Void
    private let scrollView = UIScrollView()
    private let stack = UIStackView()
    private let titleField = UITextField()
    private let descriptionView = UITextView()
    private let closedSwitch = UISwitch()
    private let dueSwitch = UISwitch()
    private let duePicker = UIDatePicker()
    private let spinner = UIActivityIndicatorView(style: .medium)
    private var task: Task<Void, Never>?

    init(
        context: AppContext,
        owner: String,
        repository: String,
        id: Int64? = nil,
        saved: @escaping (Int64) -> Void
    ) {
        self.context = context
        self.owner = owner
        self.repository = repository
        self.id = id
        self.saved = saved
        super.init(nibName: nil, bundle: nil)
        title = id == nil ? "New Milestone" : "Edit Milestone"
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError("init(coder:) is not supported") }

    deinit { task?.cancel() }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemGroupedBackground
        navigationItem.leftBarButtonItem = UIBarButtonItem(
            barButtonSystemItem: .cancel,
            target: self,
            action: #selector(cancel)
        )
        navigationItem.rightBarButtonItem = UIBarButtonItem(customView: spinner)
        spinner.startAnimating()
        configureForm()
        task = Task { await load() }
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        if id == nil { titleField.becomeFirstResponder() }
    }

    private func configureForm() {
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.keyboardDismissMode = .interactive
        view.addSubview(scrollView)
        stack.axis = .vertical
        stack.spacing = 12
        stack.translatesAutoresizingMaskIntoConstraints = false
        stack.isHidden = true
        scrollView.addSubview(stack)

        titleField.placeholder = "Title"
        titleField.delegate = self
        titleField.font = .preferredFont(forTextStyle: .headline)
        titleField.adjustsFontForContentSizeCategory = true
        titleField.borderStyle = .roundedRect
        titleField.autocapitalizationType = .sentences
        titleField.returnKeyType = .next
        titleField.accessibilityLabel = "Milestone title"
        titleField.addTarget(self, action: #selector(titleChanged), for: .editingChanged)

        let descriptionLabel = UILabel()
        descriptionLabel.text = "Description"
        descriptionLabel.font = .preferredFont(forTextStyle: .headline)
        descriptionLabel.adjustsFontForContentSizeCategory = true
        descriptionView.font = .preferredFont(forTextStyle: .body)
        descriptionView.adjustsFontForContentSizeCategory = true
        descriptionView.backgroundColor = .secondarySystemGroupedBackground
        descriptionView.layer.cornerRadius = 10
        descriptionView.textContainerInset = UIEdgeInsets(top: 12, left: 8, bottom: 12, right: 8)
        descriptionView.autocapitalizationType = .sentences
        descriptionView.accessibilityLabel = "Milestone description"

        let closedLabel = UILabel()
        closedLabel.text = "Closed"
        closedLabel.font = .preferredFont(forTextStyle: .body)
        closedLabel.adjustsFontForContentSizeCategory = true
        let closedRow = UIStackView(arrangedSubviews: [closedLabel, closedSwitch])
        closedRow.alignment = .center
        closedSwitch.accessibilityLabel = "Closed milestone"

        let dueLabel = UILabel()
        dueLabel.text = "Due Date"
        dueLabel.font = .preferredFont(forTextStyle: .body)
        dueLabel.adjustsFontForContentSizeCategory = true
        let dueRow = UIStackView(arrangedSubviews: [dueLabel, dueSwitch])
        dueRow.alignment = .center
        dueSwitch.accessibilityLabel = "Set due date"
        dueSwitch.addTarget(self, action: #selector(dueChanged), for: .valueChanged)
        duePicker.datePickerMode = .date
        duePicker.preferredDatePickerStyle = .inline
        duePicker.isHidden = true

        stack.addArrangedSubview(titleField)
        stack.addArrangedSubview(descriptionLabel)
        stack.addArrangedSubview(descriptionView)
        stack.addArrangedSubview(closedRow)
        stack.addArrangedSubview(dueRow)
        stack.addArrangedSubview(duePicker)
        NSLayoutConstraint.activate([
            scrollView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
            scrollView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
            scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
            scrollView.bottomAnchor.constraint(equalTo: view.keyboardLayoutGuide.topAnchor),
            stack.leadingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leadingAnchor, constant: 16),
            stack.trailingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.trailingAnchor, constant: -16),
            stack.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor, constant: 16),
            stack.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor, constant: -16),
            stack.widthAnchor.constraint(equalTo: scrollView.frameLayoutGuide.widthAnchor, constant: -32),
            descriptionView.heightAnchor.constraint(greaterThanOrEqualToConstant: 180),
        ])
    }

    private func load() async {
        do {
            let page = try await context.core.milestoneEditor(
                owner: owner,
                repository: repository,
                id: id
            )
            guard !Task.isCancelled else { return }
            titleField.text = page.title
            descriptionView.text = page.description
            closedSwitch.isOn = page.closed
            if let timestamp = page.dueDate {
                dueSwitch.isOn = true
                duePicker.date = localDate(forUTCTimestamp: timestamp)
                duePicker.isHidden = false
            }
            stack.isHidden = false
        } catch {
            if !Task.isCancelled { show(error: error) }
        }
        restoreSaveButton()
    }

    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        descriptionView.becomeFirstResponder()
        return true
    }

    @objc private func dueChanged() {
        duePicker.isHidden = !dueSwitch.isOn
    }

    @objc private func titleChanged() {
        navigationItem.rightBarButtonItem?.isEnabled = !(titleField.text ?? "")
            .trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
    }

    @objc private func save() {
        view.endEditing(true)
        navigationItem.leftBarButtonItem?.isEnabled = false
        navigationItem.rightBarButtonItem = UIBarButtonItem(customView: spinner)
        spinner.startAnimating()
        task?.cancel()
        task = Task {
            do {
                let id = try await context.core.saveMilestone(
                    owner: owner,
                    repository: repository,
                    id: id,
                    draft: MilestoneEditorPage(
                        title: titleField.text ?? "",
                        description: descriptionView.text ?? "",
                        dueDate: dueSwitch.isOn ? utcTimestamp(forLocalDate: duePicker.date) : nil,
                        closed: closedSwitch.isOn
                    )
                )
                guard !Task.isCancelled else { return }
                saved(id)
            } catch {
                if !Task.isCancelled {
                    show(error: error)
                    restoreSaveButton()
                }
            }
        }
    }

    private func restoreSaveButton() {
        spinner.stopAnimating()
        navigationItem.leftBarButtonItem?.isEnabled = true
        navigationItem.rightBarButtonItem = UIBarButtonItem(
            title: "Save",
            style: .done,
            target: self,
            action: #selector(save)
        )
        titleChanged()
    }

    @objc private func cancel() { dismiss(animated: true) }
}