kotej/App/TabsModel.swift

import Foundation
import Observation

/// Holds the open comparisons. Each tab is an independent `ComparisonModel`, so
/// switching tabs keeps every scan, selection and set of options intact.
@MainActor
@Observable
final class TabsModel {
    private(set) var tabs: [ComparisonModel]
    var selectedID: ComparisonModel.ID

    init() {
        let first = ComparisonModel()
        tabs = [first]
        selectedID = first.id
    }

    var selected: ComparisonModel {
        tabs.first { $0.id == selectedID } ?? tabs[0]
    }

    @discardableResult
    func newTab() -> ComparisonModel {
        let tab = ComparisonModel()
        tabs.append(tab)
        selectedID = tab.id
        return tab
    }

    func close(_ tab: ComparisonModel) {
        guard let index = tabs.firstIndex(where: { $0.id == tab.id }) else { return }
        tabs.remove(at: index)
        // Never leave the window without a tab; reuse an empty one instead.
        if tabs.isEmpty {
            let fresh = ComparisonModel()
            tabs = [fresh]
            selectedID = fresh.id
            return
        }
        if selectedID == tab.id {
            selectedID = tabs[min(index, tabs.count - 1)].id
        }
    }

    func closeSelected() { close(selected) }

    /// Opens an arbitrary pair, either replacing the current comparison or in a
    /// new tab, which is what makes a hand-picked pair the new base.
    func openPair(left: URL, right: URL, inNewTab: Bool) {
        let target = inNewTab ? newTab() : selected
        target.setBoth(left: left, right: right)
        selectedID = target.id
    }

    /// Opens a comparison in a tab: reuses the current one while it's still empty
    /// (the common case right after launch) and otherwise starts a new one, so an
    /// in-progress comparison is never overwritten.
    func open(left: URL?, right: URL?) {
        let target = selected.isPristine ? selected : newTab()
        if let left { target.setSide(.left, to: left) }
        if let right { target.setSide(.right, to: right) }
        selectedID = target.id
    }
}