//
// 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
// ── Resource Controller ───────────────────────────────────────────

/// Manages CPU and memory resources for the ArkOS runtime.
///
/// CPU gating: All background work is dispatched through a concurrent
/// queue to prevent runaway thread creation. The queue width matches
/// the number of available CPU cores detected at startup.
///
/// Memory monitoring: Reads the process RSS from getrusage(2) and
/// compares against the configured cap (default 2 GB).
public struct ResourceController {
    /// Execute a unit of work on a new detached pthread.
    public static func executeOnCorePool(_ work: @escaping () -> Void) {
        // Box the closure into a heap-allocated context
        let ctx = UnsafeMutablePointer<(() -> Void)>.allocate(capacity: 1)
        ctx.initialize(to: work)
        var thread: pthread_t?
        let result = pthread_create(&thread, nil, { arg -> UnsafeMutableRawPointer? in
            let fn = arg!.assumingMemoryBound(to: (() -> Void).self)
            fn.pointee()
            fn.deinitialize(count: 1)
            fn.deallocate()
            return nil
        }, ctx)
        if result == 0 {
            if let t = thread {
                pthread_detach(t)
            }
        } else {
            print("ERROR: pthread_create failed with \(result)")
            ctx.deinitialize(count: 1)
            ctx.deallocate()
        }
    }

    /// Returns the current process peak RSS in bytes.
    /// On Linux, getrusage(2) reports ru_maxrss in kilobytes.
    public static func checkMemoryUsage() -> Int64 {
#if canImport(Glibc) || canImport(CSystem)
        var usage = rusage()
        if getrusage(RUSAGE_SELF, &usage) == 0 {
            return Int64(usage.ru_maxrss) * 1024
        }
        #endif
        return 0
    }

    /// Returns the number of online CPU cores by reading /proc/cpuinfo.
    public static func getCPUCoreCount() -> Int {
        #if canImport(Glibc) || canImport(CSystem)
        let count = sysconf(Int32(_SC_NPROCESSORS_ONLN))
        if count > 0 { return count }
        #endif
        return 1
    }

    /// Returns total system RAM in bytes by reading /proc/meminfo.
    public static func getTotalMemory() -> Int64 {
        if let data = readFileContents("/proc/meminfo") {
            for line in data.split(separator: "\n") {
                if line.hasPrefix("MemTotal:") {
                    let parts = line.split(separator: " ").compactMap { Int64($0) }
                    if let kb = parts.first {
                        return kb * 1024
                    }
                }
            }
        }
        return 0
    }

    /// Returns available system RAM in bytes by reading /proc/meminfo.
    public static func getAvailableMemory() -> Int64 {
        if let data = readFileContents("/proc/meminfo") {
            for line in data.split(separator: "\n") {
                if line.hasPrefix("MemAvailable:") {
                    let parts = line.split(separator: " ").compactMap { Int64($0) }
                    if let kb = parts.first {
                        return kb * 1024
                    }
                }
            }
        }
        return 0
    }

    /// Returns used memory in bytes (total - available).
    public static func getUsedMemory() -> Int64 {
        let total = getTotalMemory()
        let available = getAvailableMemory()
        return max(0, total - available)
    }

    /// Returns the CPU usage as a percentage (0-100).
    /// Reads /proc/stat twice with a 100ms interval and computes the delta.
    public static func getCPUUsage() -> Double {
        func readCPUStat() -> (idle: Int64, total: Int64)? {
            guard let data = readFileContents("/proc/stat") else { return nil }
            let lines = data.split(separator: "\n")
            guard let cpuLine = lines.first(where: { $0.hasPrefix("cpu ") }) else { return nil }
            let fields = cpuLine.split(separator: " ").dropFirst().compactMap { Int64($0) }
            guard fields.count >= 4 else { return nil }
            let idle = fields[3] + (fields.count > 4 ? fields[4] : 0)  // idle + iowait
            let total = fields.reduce(0, +)
            return (idle, total)
        }

        guard let first = readCPUStat() else { return 0.0 }
        usleep(100_000)  // 100ms
        guard let second = readCPUStat() else { return 0.0 }

        let deltaIdle = second.idle - first.idle
        let deltaTotal = second.total - first.total
        guard deltaTotal > 0 else { return 0.0 }

        return Double(deltaTotal - deltaIdle) / Double(deltaTotal) * 100.0
    }
}