ghostty/macos/Sources/Features/Terminal/TerminalRestorable.swift

import Cocoa

/// The state stored for terminal window restoration.
class TerminalRestorableState: Codable {
    static let selfKey = "state"
    static let versionKey = "version"
    static let version: Int = 2

    let focusedSurface: String?
    let surfaceTree: Ghostty.SplitNode?

    init(from controller: TerminalController) {
        self.focusedSurface = controller.focusedSurface?.uuid.uuidString
        self.surfaceTree = controller.surfaceTree
    }

    init?(coder aDecoder: NSCoder) {
        // If the version doesn't match then we can't decode. In the future we can perform
        // version upgrading or something but for now we only have one version so we
        // don't bother.
        guard aDecoder.decodeInteger(forKey: Self.versionKey) == Self.version else {
            return nil
        }

        guard let v = aDecoder.decodeObject(of: CodableBridge<Self>.self, forKey: Self.selfKey) else {
            return nil
        }

        self.surfaceTree = v.value.surfaceTree
        self.focusedSurface = v.value.focusedSurface
    }

    func encode(with coder: NSCoder) {
        coder.encode(Self.version, forKey: Self.versionKey)
        coder.encode(CodableBridge(self), forKey: Self.selfKey)
    }
}

enum TerminalRestoreError: Error {
    case delegateInvalid
    case identifierUnknown
    case stateDecodeFailed
    case windowDidNotLoad
}

/// The NSWindowRestoration implementation that is called when a terminal window needs to be restored.
/// The encoding of a terminal window is handled elsewhere (usually NSWindowDelegate).
class TerminalWindowRestoration: NSObject, NSWindowRestoration {
    static func restoreWindow(
        withIdentifier identifier: NSUserInterfaceItemIdentifier,
        state: NSCoder,
        completionHandler: @escaping (NSWindow?, Error?) -> Void
    ) {
        // Verify the identifier is what we expect
        guard identifier == .init(String(describing: Self.self)) else {
            completionHandler(nil, TerminalRestoreError.identifierUnknown)
            return
        }

        // The app delegate is definitely setup by now. If it isn't our AppDelegate
        // then something is royally fucked up but protect against it anyhow.
        guard let appDelegate = NSApplication.shared.delegate as? AppDelegate else {
            completionHandler(nil, TerminalRestoreError.delegateInvalid)
            return
        }

        // If our configuration is "never" then we never restore the state
        // no matter what. Note its safe to use "ghostty.config" directly here
        // because window restoration is only ever invoked on app start so we
        // don't have to deal with config reloads.
        if (appDelegate.ghostty.config.windowSaveState == "never") {
            completionHandler(nil, nil)
            return
        }

        // Decode the state. If we can't decode the state, then we can't restore.
        guard let state = TerminalRestorableState(coder: state) else {
            completionHandler(nil, TerminalRestoreError.stateDecodeFailed)
            return
        }

        // The window creation has to go through our terminalManager so that it
        // can be found for events from libghostty. This uses the low-level
        // createWindow so that AppKit can place the window wherever it should
        // be.
        let c = appDelegate.terminalManager.createWindow(withSurfaceTree: state.surfaceTree)
        guard let window = c.window else {
            completionHandler(nil, TerminalRestoreError.windowDidNotLoad)
            return
        }

        // Setup our restored state on the controller
        if let focusedStr = state.focusedSurface,
           let focusedUUID = UUID(uuidString: focusedStr),
           let view = c.surfaceTree?.findUUID(uuid: focusedUUID) {
            c.focusedSurface = view
            restoreFocus(to: view, inWindow: window)
        }

        completionHandler(window, nil)
    }

    /// This restores the focus state of the surfaceview within the given window. When restoring,
    /// the view isn't immediately attached to the window since we have to wait for SwiftUI to
    /// catch up. Therefore, we sit in an async loop waiting for the attachment to happen.
    private static func restoreFocus(to: Ghostty.SurfaceView, inWindow: NSWindow, attempts: Int = 0) {
        // For the first attempt, we schedule it immediately. Subsequent events wait a bit
        // so we don't just spin the CPU at 100%. Give up after some period of time.
        let after: DispatchTime
        if (attempts == 0) {
            after = .now()
        } else if (attempts > 40) {
            // 2 seconds, give up
            return
        } else {
            after = .now() + .milliseconds(50)
        }

        DispatchQueue.main.asyncAfter(deadline: after) {
            // If the view is not attached to a window yet then we repeat.
            guard let viewWindow = to.window else {
                restoreFocus(to: to, inWindow: inWindow, attempts: attempts + 1)
                return
            }

            // If the view is attached to some other window, we give up
            guard viewWindow == inWindow else { return }

            inWindow.makeFirstResponder(to)

            // If the window is main, then we also make sure it comes forward. This
            // prevents a bug found in #1177 where sometimes on restore the windows
            // would be behind other applications.
            if (viewWindow.isMainWindow) {
                viewWindow.orderFront(nil)
            }
        }
    }
}