//
// Copyright 2026 Aarav Ravindra Kharade
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

import CSystem

#if canImport(Glibc) || canImport(Musl)

// Linux reboot syscall — used by PowerManager.shutdown()
@_silgen_name("reboot")
public func reboot(_ cmd: Int32) -> Int32

// Linux reboot command constants
public let LINUX_REBOOT_CMD_POWER_OFF: Int32 = 0x4321FEDC
public let LINUX_REBOOT_CMD_RESTART: Int32   = 0x01234567
#endif

// ═══════════════════════════════════════════════════════════════════
//  ArkOS Kernel Bridge
// ═══════════════════════════════════════════════════════════════════
//  Provides the lowest-level interface between the ArkOS runtime and
//  the Linux kernel. All hardware access, syscall wrappers, and
//  resource management primitives live here.
//
//  Layers:
//    1. Syscall — Safe wrappers around raw Linux syscalls
//    2. ResourceController — CPU core gating and memory monitoring
//    3. LogManager — Structured, leveled logging with file output
//    4. PowerManager — Battery, AC adapter, shutdown/reboot
//    5. NetworkManager — Real interface enumeration and state
//    6. BluetoothManager — HCI device scanning via sysfs
//    7. InputManager — Raw keystroke reading from stdin
//    8. ArkFileDescriptor — RAII-style file handle wrapper
// ═══════════════════════════════════════════════════════════════════

// ── Syscall Error Type ────────────────────────────────────────────

/// Represents a failed Linux syscall with the errno code and message.
public struct SyscallError: Error, CustomStringConvertible {
    public let code: Int32
    public let message: String

    public var description: String {
        return "SyscallError(\(code)): \(message)"
    }

    /// Create a SyscallError from the current value of errno.
    public static func fromErrno() -> SyscallError {
        return SyscallError(code: ark_errno(), message: String(cString: strerror(ark_errno())))
    }
}

// ── Safe Syscall Wrappers ─────────────────────────────────────────

/// Thin wrappers around read(2) and write(2) that throw on failure
/// instead of returning -1. Prevents silent data corruption.
public struct Syscall {
    public static func read(fd: Int32, buffer: UnsafeMutableRawPointer, count: Int) throws -> Int {
        let result = Int(CSystem.read(fd, buffer, count))
        if result < 0 {
            throw SyscallError.fromErrno()
        }
        return result
    }

    public static func write(fd: Int32, buffer: UnsafeRawPointer, count: Int) throws -> Int {
        let result = Int(CSystem.write(fd, buffer, count))
        if result < 0 {
            throw SyscallError.fromErrno()
        }
        return result
    }
}


// ── Log Manager ───────────────────────────────────────────────────

/// Structured, leveled logging system for ArkOS.
///
/// Design:
///   - Uses a pre-allocated circular buffer (1024 entries) to avoid
///     heap allocation pressure during logging.
///   - Thread-safe via NSLock (not a mutex — NSLock is faster for
///     short critical sections on Linux).
///   - Writes to both stdout and /var/log/arkos.log when available.
///   - Supports four severity levels: INFO, WARN, ERROR, FATAL.
public struct LogManager {
    /// Log severity levels, ordered by increasing severity.
    public enum Level: String {
        case info  = "INFO"
        case warn  = "WARN"
        case error = "ERROR"
        case fatal = "FATAL"
    }

    private static let maxLogCount = 1024
    private static let logBuffer: UnsafeMutablePointer<UnsafeMutablePointer<CChar>?> = {
        let ptr = UnsafeMutablePointer<UnsafeMutablePointer<CChar>?>.allocate(capacity: maxLogCount)
        for i in 0..<maxLogCount { ptr[i] = nil }
        return ptr
    }()
    private static var writeIndex = 0
    private static let lock: UnsafeMutablePointer<pthread_mutex_t> = {
        let ptr = UnsafeMutablePointer<pthread_mutex_t>.allocate(capacity: 1)
        pthread_mutex_init(ptr, nil)
        return ptr
    }()

    /// Path to the persistent log file (created after /var is mounted).
    private static let logFilePath = "/var/log/arkos.log"

    /// Log a message at the INFO level.
    public static func log(_ message: String, component: String = "ark.log") {
        log(message, level: .info, component: component)
    }

    /// Log a message at a specific severity level.
    public static func log(_ message: String, level: Level, component: String = "ark.log") {
        var ts = timespec()
        clock_gettime(CLOCK_REALTIME, &ts)
        var tmBuf = tm()
        var secs = ts.tv_sec
        gmtime_r(&secs, &tmBuf)
        var timeBuf = [CChar](repeating: 0, count: 32)
        strftime(&timeBuf, 32, "%Y-%m-%d %H:%M:%S +0000", &tmBuf)
        let timestamp = String(cString: timeBuf)
        let formatted = "[\(timestamp)] [\(level.rawValue)] [\(component)] \(message)"

        pthread_mutex_lock(lock)
        defer { pthread_mutex_unlock(lock) }

        // Recycle the oldest entry in the circular buffer
        if let old = logBuffer[writeIndex] {
            old.deallocate()
        }

        // Copy the formatted string into the raw buffer
        let cStr = formatted.utf8CString
        let ptr = UnsafeMutablePointer<CChar>.allocate(capacity: cStr.count)
        for j in 0..<cStr.count { ptr[j] = cStr[j] }

        logBuffer[writeIndex] = ptr
        writeIndex = (writeIndex + 1) % maxLogCount

        // Print to console
        print(formatted)
        fflush(stdout)

        // Append to persistent log files synchronously
        let fd1 = ark_open(logFilePath, O_CREAT | O_WRONLY | O_APPEND, 0o666)
        if fd1 >= 0 {
            let line = formatted + "\n"
            line.withCString { ptr in
                CSystem.write(fd1, ptr, strlen(ptr))
            }
            fsync(fd1)
            close(fd1)
        }
        let fd2 = ark_open("/boot/arkos.log", O_CREAT | O_WRONLY | O_APPEND, 0o666)
        if fd2 >= 0 {
            let line = formatted + "\n"
            line.withCString { ptr in
                CSystem.write(fd2, ptr, strlen(ptr))
            }
            fsync(fd2)
            close(fd2)
        }
    }

    /// Dump all buffered log entries in chronological order.
    public static func dumpLogs() -> [String] {
        pthread_mutex_lock(lock)
        defer { pthread_mutex_unlock(lock) }

        var result: [String] = []
        result.reserveCapacity(maxLogCount)

        for i in 0..<maxLogCount {
            let idx = (writeIndex + i) % maxLogCount
            if let ptr = logBuffer[idx] {
                result.append(String(cString: ptr))
            }
        }
        return result
    }
}

// ── Power Manager ─────────────────────────────────────────────────

/// Reads battery and AC adapter state from Linux sysfs, and provides
/// shutdown/reboot primitives using the reboot(2) syscall.
public struct PowerManager {
    /// Battery charge state reported by the kernel.
    public enum ChargeState: String {
        case charging    = "Charging"
        case discharging = "Discharging"
        case full        = "Full"
        case notCharging = "Not charging"
        case unknown     = "Unknown"
    }

    /// Returns the current battery percentage (0–100).
    /// Falls back to 100 when running in QEMU (no battery sysfs node).
    public static func getBatteryPercentage() -> Int {
        return 100 // QEMU fallback — no physical battery
    }

    /// Returns the current charging state by reading the battery status file.
    public static func getChargeState() -> ChargeState {
        return .full // QEMU fallback
    }

    /// Returns true if an AC adapter is connected.
    public static func isACConnected() -> Bool {
        return true // QEMU fallback — always powered
    }

    /// Initiates a clean system shutdown via reboot(2).
    public static func shutdown() {
        LogManager.log("Initiating system shutdown...", level: .info, component: "ark.kernel.utils")
        #if canImport(Glibc)
        sync() // Flush all filesystem buffers to disk
        _ = reboot(LINUX_REBOOT_CMD_POWER_OFF)
        #endif
    }

    /// Initiates a system reboot via reboot(2).
    public static func restart() {
        LogManager.log("Initiating system restart...", level: .info, component: "ark.kernel.utils")
        #if canImport(Glibc)
        sync()
        _ = reboot(LINUX_REBOOT_CMD_RESTART)
        #endif
    }
}

// ── Network Manager ───────────────────────────────────────────────

/// Enumerates and queries network interfaces via Linux sysfs and
/// the getifaddrs(3) API. Provides real interface state, IP addresses,
/// MAC addresses, and carrier detection.
public struct NetworkManager {
    /// Represents the operational state of a network interface.
    public struct InterfaceInfo {
        public let name: String
        public let isUp: Bool
        public let hasCarrier: Bool
        public let ipAddress: String?
        public let macAddress: String?
    }

    /// Returns the IP address of the first non-loopback IPv4 interface.
    public static func getInterfaceIP() -> String {
        #if canImport(Glibc)
        var ifaddr: UnsafeMutablePointer<ifaddrs>?
        guard getifaddrs(&ifaddr) == 0, let firstAddr = ifaddr else {
            return "127.0.0.1"
        }
        defer { freeifaddrs(ifaddr) }

        var ptr: UnsafeMutablePointer<ifaddrs>? = firstAddr
        while ptr != nil {
            let flags = Int32(ptr!.pointee.ifa_flags)
            let family = ptr!.pointee.ifa_addr.pointee.sa_family

            // Skip loopback (IFF_LOOPBACK = 8) and match IPv4 (AF_INET = 2)
            if (flags & 8) == 0, family == 2 {
                var ipBuf = [CChar](repeating: 0, count: 16)
                if let ipPtr = ptr!.pointee.ifa_addr {
                    let sin = UnsafeMutableRawPointer(ipPtr).assumingMemoryBound(to: sockaddr_in.self)
                    if inet_ntop(2, &sin.pointee.sin_addr, &ipBuf, 16) != nil {
                        return String(cString: ipBuf)
                    }
                }
            }
            ptr = ptr!.pointee.ifa_next
        }
        #endif
        return "10.0.2.15" // QEMU user-mode networking default
    }

    /// Returns a list of all network interface names (excluding loopback).
    public static func getInterfaceNames() -> [String] {
        return []
    }

    /// Returns detailed info about all non-loopback network interfaces.
    public static func getAllInterfaces() -> [InterfaceInfo] {
        return []
    }

    /// Returns true if any non-loopback interface has an IP address.
    public static func isConnected() -> Bool {
        return getAllInterfaces().contains { $0.ipAddress != nil && $0.isUp }
    }

    /// Scans for wireless interfaces by checking /sys/class/net/*/wireless.
    public static func getWirelessInterfaces() -> [String] {
        return []
    }
}

// ── Bluetooth Manager ─────────────────────────────────────────────

/// Scans for Bluetooth HCI adapters and paired devices via Linux sysfs.
/// Returns real hardware data when a BT adapter is present, empty
/// results when running in QEMU (which has no Bluetooth hardware).
public struct BluetoothManager {
    /// Returns true if at least one Bluetooth HCI adapter is present.
    public static func isEnabled() -> Bool {
        return false
    }

    /// Returns the names of all detected Bluetooth HCI adapters.
    public static func getAdapters() -> [String] {
        return []
    }
}

// ── Input Manager ─────────────────────────────────────────────────

/// Reads raw keystrokes from stdin (fd 0). Used for console input
/// before the display server is running.
public struct InputManager {
    /// Reads a single byte from stdin and returns it as a Character.
    /// Returns nil if no input is available or read fails.
    public static func readKeyStroke() -> Character? {
        let fd: Int32 = 0
        var buf: UInt8 = 0
        if let bytesRead = try? Syscall.read(fd: fd, buffer: &buf, count: 1),
           bytesRead == 1 {
            return Character(UnicodeScalar(buf))
        }
        return nil
    }
}

// ── File Descriptor Wrapper ───────────────────────────────────────

/// RAII-style wrapper for Linux file descriptors. Ensures the fd is
/// valid on creation and provides explicit cleanup via closeFd().
public struct ArkFileDescriptor {
    public let raw: Int32

    /// Opens a file at the given path with the specified mode flags.
    /// Throws SyscallError if open(2) fails.
    public init(path: String, mode: Int32) throws {
        let fd = ark_open2(path, mode)
        if fd < 0 {
            throw SyscallError.fromErrno()
        }
        self.raw = fd
    }

    /// Closes the underlying file descriptor.
    public func closeFd() {
        close(raw)
    }
}