//===----------------------------------------------------------------------===//
// Copyright © 2025-2026 Apple Inc. and the Containerization 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
import GRPCCore

/// Monotonic deadlines for operations which cross a process or transport boundary.
///
/// Keep generated gRPC calls behind ``performGRPC(operation:deadline:_:)``. Requiring both an
/// operation class and an absolute deadline makes a call which silently falls back to generated
/// default options conspicuous during review and straightforward to reject in CI.
public struct DeadlinePolicy: Sendable {
    public typealias Deadline = ContinuousClock.Instant

    public enum Operation: String, Sendable {
        case dial
        case statistics
        case createProcess
        case startProcess
        case processControl
        case deleteProcess
        case agentClose
        case waitProcess
        case filesystem
    }

    public struct Bounds: Sendable {
        public var dial: Duration = .seconds(3)
        public var statistics: Duration = .seconds(2)
        public var createProcess: Duration = .seconds(10)
        public var startProcess: Duration = .seconds(15)
        public var processControl: Duration = .seconds(3)
        public var deleteProcess: Duration = .seconds(30)
        public var agentClose: Duration = .seconds(3)
        public var waitProcess: Duration = .seconds(30)
        public var filesystem: Duration = .seconds(10)

        public init() {}
    }

    public static let standard = DeadlinePolicy()

    public var bounds: Bounds

    public init(bounds: Bounds = Bounds()) {
        self.bounds = bounds
    }

    public func bound(for operation: Operation) -> Duration {
        switch operation {
        case .dial: bounds.dial
        case .statistics: bounds.statistics
        case .createProcess: bounds.createProcess
        case .startProcess: bounds.startProcess
        case .processControl: bounds.processControl
        case .deleteProcess: bounds.deleteProcess
        case .agentClose: bounds.agentClose
        case .waitProcess: bounds.waitProcess
        case .filesystem: bounds.filesystem
        }
    }

    public func deadline(for operation: Operation, clock: ContinuousClock = .init()) -> Deadline {
        clock.now.advanced(by: bound(for: operation))
    }

    /// Invoke a generated gRPC call with the remaining part of an absolute monotonic deadline.
    /// gRPC aborts the RPC when this timeout expires, so the server operation and client-side
    /// continuation aren't left live after the caller receives a timeout.
    public func performGRPC<Result: Sendable>(
        operation: Operation,
        deadline: Deadline,
        _ call: @Sendable (GRPCCore.CallOptions) async throws -> Result
    ) async throws -> Result {
        let remaining = ContinuousClock().now.duration(to: deadline)
        guard remaining > .zero else {
            throw timeoutError(for: operation)
        }

        var options = GRPCCore.CallOptions.defaults
        options.timeout = remaining
        do {
            return try await call(options)
        } catch let error as RPCError where error.code == .deadlineExceeded {
            throw timeoutError(for: operation, cause: error)
        }
    }

    public func timeoutError(for operation: Operation, cause: (any Error)? = nil) -> ContainerizationError {
        ContainerizationError(
            .timeout,
            message: "\(operation.rawValue) exceeded its monotonic deadline",
            cause: cause
        )
    }
}