import SwiftUI
import Combine

/// Manages multiple terminal tabs. Singleton shared across all screens —
/// whichever notch is currently open displays these tabs.
@MainActor
class TerminalManager: ObservableObject {

    static let shared = TerminalManager()

    @Published var tabs: [TerminalSession] = []
    @Published var activeTabIndex: Int = 0

    @AppStorage(NotchSettings.Keys.terminalFontSize)
    private var fontSize: Double = NotchSettings.Defaults.terminalFontSize
    @AppStorage(NotchSettings.Keys.terminalTheme)
    private var theme: String = NotchSettings.Defaults.terminalTheme

    private var cancellables = Set<AnyCancellable>()

    private init() {
        newTab()
    }

    // MARK: - Active tab

    var activeTab: TerminalSession? {
        guard tabs.indices.contains(activeTabIndex) else { return nil }
        return tabs[activeTabIndex]
    }

    /// Short title for the closed notch bar — the active tab's process name.
    var activeTitle: String {
        activeTab?.title ?? "shell"
    }

    // MARK: - Tab operations

    func newTab() {
        let session = TerminalSession(
            fontSize: CGFloat(fontSize),
            theme: TerminalTheme.resolve(theme)
        )

        // Forward title changes to trigger view updates in this manager
        session.$title
            .receive(on: RunLoop.main)
            .sink { [weak self] _ in self?.objectWillChange.send() }
            .store(in: &cancellables)

        tabs.append(session)
        activeTabIndex = tabs.count - 1
    }

    func closeTab(at index: Int) {
        guard tabs.indices.contains(index) else { return }
        tabs[index].terminate()
        tabs.remove(at: index)

        // Adjust active index
        if tabs.isEmpty {
            newTab()
        } else if activeTabIndex >= tabs.count {
            activeTabIndex = tabs.count - 1
        }
    }

    func closeActiveTab() {
        closeTab(at: activeTabIndex)
    }

    func switchToTab(at index: Int) {
        guard tabs.indices.contains(index) else { return }
        activeTabIndex = index
    }

    func nextTab() {
        guard tabs.count > 1 else { return }
        activeTabIndex = (activeTabIndex + 1) % tabs.count
    }

    func previousTab() {
        guard tabs.count > 1 else { return }
        activeTabIndex = (activeTabIndex - 1 + tabs.count) % tabs.count
    }

    /// Removes the tab at the given index and returns the session so it
    /// can be hosted in a pop-out window.
    func detachTab(at index: Int) -> TerminalSession? {
        guard tabs.indices.contains(index) else { return nil }
        let session = tabs.remove(at: index)

        if tabs.isEmpty {
            newTab()
        } else if activeTabIndex >= tabs.count {
            activeTabIndex = tabs.count - 1
        }

        return session
    }

    func detachActiveTab() -> TerminalSession? {
        detachTab(at: activeTabIndex)
    }

    /// Updates font size on all existing terminal sessions.
    func updateAllFontSizes(_ size: CGFloat) {
        for tab in tabs {
            tab.updateFontSize(size)
        }
    }

    func updateAllThemes(_ theme: TerminalTheme) {
        for tab in tabs {
            tab.applyTheme(theme)
        }
    }
}