import Cocoa
import Carbon

// Global shortcuts:
//   Left Shift x2   — capture the current selection into the active section
//   Right Shift x2  — show/hide the panel
//   Cmd+Shift+C     — capture (fallback, no Accessibility needed)
//   Cmd+Shift+Space — show/hide the panel (fallback)
//
// The double-Shift gestures come from a CGEvent tap on flagsChanged, which
// needs Accessibility access. The Carbon hotkeys work without it.
final class HotkeyManager {
    static let shared = HotkeyManager()

    var onCapture: (() -> Void)?
    var onTogglePanel: (() -> Void)?

    private var eventTap: CFMachPort?
    private var runLoopSource: CFRunLoopSource?
    private var eventHandlerRef: EventHandlerRef?
    private var hotKeyRefs: [EventHotKeyRef?] = []
    private let signature: OSType = 0x50524D50 // "PRMP"

    private var lastLeftShiftRelease: TimeInterval = 0
    private var lastRightShiftRelease: TimeInterval = 0
    private let doubleTapInterval: TimeInterval = 0.35

    private init() {}

    var isListening: Bool { eventTap != nil }

    func start() {
        startEventTap()
        registerFallbackHotkeys()
    }

    // MARK: - Double-Shift event tap

    private func startEventTap() {
        let mask = CGEventMask(1 << CGEventType.flagsChanged.rawValue)
        guard let tap = CGEvent.tapCreate(
            tap: .cgSessionEventTap,
            place: .headInsertEventTap,
            options: .defaultTap,
            eventsOfInterest: mask,
            callback: hotkeyEventCallback,
            userInfo: Unmanaged.passUnretained(self).toOpaque()
        ) else { return }
        eventTap = tap
        let source = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, tap, 0)
        runLoopSource = source
        CFRunLoopAddSource(CFRunLoopGetMain(), source, .commonModes)
        CGEvent.tapEnable(tap: tap, enable: true)
    }

    fileprivate func handle(proxy: CGEventTapProxy, type: CGEventType, event: CGEvent) -> Unmanaged<CGEvent>? {
        if type == .tapDisabledByTimeout || type == .tapDisabledByUserInput {
            if let tap = eventTap { CGEvent.tapEnable(tap: tap, enable: true) }
            return Unmanaged.passUnretained(event)
        }
        guard type == .flagsChanged else { return Unmanaged.passUnretained(event) }

        let keyCode = event.getIntegerValueField(.keyboardEventKeycode)
        let shiftIsDown = event.flags.contains(.maskShift)
        guard !shiftIsDown else { return Unmanaged.passUnretained(event) } // only count releases

        let now = ProcessInfo.processInfo.systemUptime
        switch keyCode {
        case 56: // left shift
            if now - lastLeftShiftRelease < doubleTapInterval {
                lastLeftShiftRelease = 0
                fire { $0.onCapture?() }
            } else {
                lastLeftShiftRelease = now
            }
        case 60: // right shift
            if now - lastRightShiftRelease < doubleTapInterval {
                lastRightShiftRelease = 0
                fire { $0.onTogglePanel?() }
            } else {
                lastRightShiftRelease = now
            }
        default:
            break
        }
        return Unmanaged.passUnretained(event)
    }

    private func fire(_ action: @escaping (HotkeyManager) -> Void) {
        DispatchQueue.main.async { action(self) }
    }

    // MARK: - Carbon fallback hotkeys

    private func registerFallbackHotkeys() {
        var eventType = EventTypeSpec(
            eventClass: OSType(kEventClassKeyboard),
            eventKind: UInt32(kEventHotKeyPressed)
        )
        InstallEventHandler(GetApplicationEventTarget(), { _, event, _ in
            var hotKeyID = EventHotKeyID()
            let status = GetEventParameter(
                event,
                EventParamName(kEventParamDirectObject),
                EventParamType(typeEventHotKeyID),
                nil,
                MemoryLayout<EventHotKeyID>.size,
                nil,
                &hotKeyID
            )
            guard status == noErr else { return noErr }
            DispatchQueue.main.async {
                switch hotKeyID.id {
                case 1: HotkeyManager.shared.onTogglePanel?()
                case 2: HotkeyManager.shared.onCapture?()
                default: break
                }
            }
            return noErr
        }, 1, &eventType, nil, &eventHandlerRef)

        registerHotkey(id: 1, keyCode: UInt32(kVK_Space), modifiers: UInt32(cmdKey | shiftKey))
        registerHotkey(id: 2, keyCode: UInt32(kVK_ANSI_C), modifiers: UInt32(cmdKey | shiftKey))
    }

    private func registerHotkey(id: UInt32, keyCode: UInt32, modifiers: UInt32) {
        var ref: EventHotKeyRef?
        let hotKeyID = EventHotKeyID(signature: signature, id: id)
        RegisterEventHotKey(keyCode, modifiers, hotKeyID, GetApplicationEventTarget(), 0, &ref)
        hotKeyRefs.append(ref)
    }
}

private func hotkeyEventCallback(
    proxy: CGEventTapProxy,
    type: CGEventType,
    event: CGEvent,
    refcon: UnsafeMutableRawPointer?
) -> Unmanaged<CGEvent>? {
    guard let refcon else { return Unmanaged.passUnretained(event) }
    let manager = Unmanaged<HotkeyManager>.fromOpaque(refcon).takeUnretainedValue()
    return manager.handle(proxy: proxy, type: type, event: event)
}