import UIKit

@MainActor
final class NavigationSettingsViewController: UITableViewController {
    private let context: AppContext
    private var selected: [PrimaryDestination]

    init(context: AppContext) {
        self.context = context
        selected = context.primaryDestinations
        super.init(style: .insetGrouped)
        title = "Primary Navigation"
        navigationItem.rightBarButtonItem = editButtonItem
    }

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

    private var available: [PrimaryDestination] {
        PrimaryDestination.allCases.filter { !selected.contains($0) }
    }

    override func numberOfSections(in tableView: UITableView) -> Int { 2 }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        section == 0 ? selected.count : available.count
    }

    override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
        section == 0 ? "Shown After Home" : "Available Destinations"
    }

    override func tableView(_ tableView: UITableView, titleForFooterInSection section: Int) -> String? {
        section == 0
            ? "Tap Edit to add, remove, or reorder up to four destinations. Home is always first."
            : "Destinations not in the tab bar remain available as buttons on Home."
    }

    override func tableView(
        _ tableView: UITableView,
        cellForRowAt indexPath: IndexPath
    ) -> UITableViewCell {
        let destination = indexPath.section == 0 ? selected[indexPath.row] : available[indexPath.row]
        let cell = UITableViewCell(style: .default, reuseIdentifier: nil)
        var content = cell.defaultContentConfiguration()
        content.text = destination.title
        content.image = UIImage(systemName: destination.symbolName)
        content.imageProperties.tintColor = .tintColor
        if indexPath.section == 1 && selected.count == 4 {
            content.textProperties.color = .secondaryLabel
            content.imageProperties.tintColor = .tertiaryLabel
        }
        cell.selectionStyle = .none
        cell.contentConfiguration = content
        return cell
    }

    override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
        tableView.isEditing && (indexPath.section == 0 || selected.count < 4)
    }

    override func tableView(_ tableView: UITableView, canMoveRowAt indexPath: IndexPath) -> Bool {
        tableView.isEditing && indexPath.section == 0
    }

    override func tableView(
        _ tableView: UITableView,
        moveRowAt sourceIndexPath: IndexPath,
        to destinationIndexPath: IndexPath
    ) {
        guard sourceIndexPath.section == 0, destinationIndexPath.section == 0 else {
            tableView.reloadData()
            return
        }
        let destination = selected.remove(at: sourceIndexPath.row)
        selected.insert(destination, at: destinationIndexPath.row)
        save()
    }

    override func tableView(
        _ tableView: UITableView,
        targetIndexPathForMoveFromRowAt sourceIndexPath: IndexPath,
        toProposedIndexPath proposedDestinationIndexPath: IndexPath
    ) -> IndexPath {
        guard proposedDestinationIndexPath.section == 0 else {
            return IndexPath(row: max(selected.count - 1, 0), section: 0)
        }
        return proposedDestinationIndexPath
    }

    override func tableView(
        _ tableView: UITableView,
        editingStyleForRowAt indexPath: IndexPath
    ) -> UITableViewCell.EditingStyle {
        if indexPath.section == 0 { return .delete }
        return selected.count < 4 ? .insert : .none
    }

    override func tableView(
        _ tableView: UITableView,
        commit editingStyle: UITableViewCell.EditingStyle,
        forRowAt indexPath: IndexPath
    ) {
        switch (editingStyle, indexPath.section) {
        case (.delete, 0):
            selected.remove(at: indexPath.row)
        case (.insert, 1) where selected.count < 4:
            selected.append(available[indexPath.row])
        default:
            return
        }
        save()
        tableView.reloadData()
    }

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.deselectRow(at: indexPath, animated: true)
    }

    private func save() {
        do {
            try context.core.setPrimaryDestinations(destinations: selected)
            context.applyPrimaryDestinations()
        } catch {
            selected = context.primaryDestinations
            tableView.reloadData()
            show(error: error)
        }
    }
}