//===----------------------------------------------------------------------===//
// Copyright © 2026 Apple Inc. and the container project authors.
//
// 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
//
//   https://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 ContainerizationError
import Foundation

/// Boot-time configuration for a container machine.
///
/// These values can be modified without recreating the container machine.
/// Changes take effect on the next boot. `nil` values mean
/// "use the container runtime default."
public struct MachineConfig: Codable, Sendable {
    public static let `default`: MachineConfig = try! .init(cpus: nil, memory: nil, homeMount: nil)

    public static var defaultCPUs: Int {
        max(ProcessInfo.processInfo.processorCount / 2, 4)
    }

    public static var defaultMemory: MemorySize {
        let bytes = max(ProcessInfo.processInfo.physicalMemory / 2, 1024 * 1024 * 1024)
        let gb = bytes / (1024 * 1024 * 1024)
        return try! MemorySize("\(gb)gb")
    }

    public static let defaultHomeMount: HomeMountOption = .rw

    /// Home mount option for the /Users/<name> directory.
    public enum HomeMountOption: String, Sendable, Codable {
        case ro
        case rw
        case none
    }

    /// Number of virtual CPUs.
    public let cpus: Int
    /// Memory in bytes.
    public let memory: MemorySize
    /// Home mount configuration. nil = system default.
    public let homeMount: HomeMountOption

    /// Settable keys and their descriptions, for CLI help text generation.
    public static let settableKeys: [(key: String, valueName: String, description: String)] = [
        ("cpus", "<number>", "Number of virtual CPUs"),
        ("memory", "<size>", "Memory allocation (e.g., 2G, 1G). Default: half of system memory"),
        ("home-mount", "<string>", "User home directory mount option (ro, rw, none). Default: rw"),
    ]

    public init(cpus: Int?, memory: MemorySize?, homeMount: HomeMountOption?) throws {
        self.cpus = cpus ?? Self.defaultCPUs
        self.memory = memory ?? Self.defaultMemory
        self.homeMount = homeMount ?? Self.defaultHomeMount

        try self.validate()
    }

    public init(from decoder: any Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)

        let cpus = try container.decodeIfPresent(Int.self, forKey: .cpus)
        let memory = try container.decodeIfPresent(MemorySize.self, forKey: .memory)
        let homeMount = try container.decodeIfPresent(HomeMountOption.self, forKey: .homeMount)

        try self.init(cpus: cpus, memory: memory, homeMount: homeMount)
    }

    private func validate() throws {
        guard self.cpus > 0 else {
            throw ContainerizationError(
                .invalidArgument,
                message: "invalid CPU count '\(self.cpus)'. Must be a positive integer (e.g., 4)."
            )
        }

        guard self.memory.toUInt64(unit: .bytes) >= 1024 * 1024 * 1024 else {
            throw ContainerizationError(
                .invalidArgument,
                message: "invalid memory value '\(self.memory)'. Must be greater than 1gb."
            )
        }
    }
}

extension MachineConfig {
    /// Generate a help discussion string listing all settable keys.
    public static func helpText() -> String {
        settableKeys.map { entry in
            let label = "\(entry.key)=\(entry.valueName)"
            let padding = String(repeating: " ", count: max(1, 24 - label.count))
            return "\(label)\(padding)\(entry.description)"
        }.joined(separator: "\n")
    }

    /// Create a new MachineConfig from `self`, applying fields defined in `kwargs`
    /// This function is used in both `machine create` and `machine set`
    public func with(_ kwargs: [String: String]) throws -> MachineConfig {
        let validKeys = Set(Self.settableKeys.map(\.key))
        let unknownKeys = Set(kwargs.keys).subtracting(validKeys)
        guard unknownKeys.isEmpty else {
            throw ContainerizationError(
                .invalidArgument,
                message: "unknown fields '\(unknownKeys.joined(separator: ", "))'. Valid: \(validKeys.joined(separator: ", "))")
        }

        let cpus = try kwargs["cpus"].map { try Self.parseInt($0, for: "cpus") }
        let memory = try kwargs["memory"].map { try MemorySize($0) }
        let homeMount = try kwargs["home-mount"].map { try Self.parseHomeMount($0) }

        return try .init(
            cpus: cpus ?? self.cpus,
            memory: memory ?? self.memory,
            homeMount: homeMount ?? self.homeMount
        )
    }

    /// Parse and validate a CPU count from user input.
    private static func parseInt(_ value: String, for key: String) throws -> Int {
        guard let num = Int(value) else {
            throw ContainerizationError(
                .invalidArgument,
                message: "failed to parse \(value) for \(key)"
            )
        }
        return num
    }

    /// Parse and validate a home mount option from user input.
    private static func parseHomeMount(_ value: String) throws -> MachineConfig.HomeMountOption {
        guard let opt = MachineConfig.HomeMountOption(rawValue: value) else {
            throw ContainerizationError(
                .invalidArgument,
                message: "invalid home mount option '\(value)'. Valid options: ro, rw, none"
            )
        }
        return opt
    }
}