container/Sources/ContainerLog/OSLogHandler.swift

//===----------------------------------------------------------------------===//
// Copyright © 2025 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 Foundation
import Logging
import os

import struct Logging.Logger

public struct OSLogHandler: LogHandler {
    private let logger: os.Logger

    public var logLevel: Logger.Level = .info
    private var formattedMetadata: String?

    public var metadata = Logger.Metadata() {
        didSet {
            self.formattedMetadata = self.formatMetadata(self.metadata)
        }
    }

    public subscript(metadataKey metadataKey: String) -> Logger.Metadata.Value? {
        get {
            self.metadata[metadataKey]
        }
        set {
            self.metadata[metadataKey] = newValue
        }
    }

    public init(label: String, category: String) {
        self.logger = os.Logger(subsystem: label, category: category)
    }
}

extension OSLogHandler {
    public func log(
        level: Logger.Level,
        message: Logger.Message,
        metadata: Logger.Metadata?,
        source: String,
        file: String,
        function: String,
        line: UInt
    ) {
        var formattedMetadata = self.formattedMetadata
        if let metadataOverride = metadata, !metadataOverride.isEmpty {
            formattedMetadata = self.formatMetadata(
                self.metadata.merging(metadataOverride) {
                    $1
                }
            )
        }

        var finalMessage = message.description
        if let formattedMetadata {
            finalMessage += " " + formattedMetadata
        }

        self.logger.log(
            level: level.toOSLogLevel(),
            "\(finalMessage, privacy: .public)"
        )
    }

    private func formatMetadata(_ metadata: Logger.Metadata) -> String? {
        if metadata.isEmpty {
            return nil
        }
        return metadata.map {
            "[\($0)=\($1)]"
        }.joined(separator: " ")
    }
}

extension Logger.Level {
    func toOSLogLevel() -> OSLogType {
        switch self {
        case .debug, .trace:
            return .debug
        case .info:
            return .info
        case .notice:
            return .default
        case .error, .warning:
            return .error
        case .critical:
            return .fault
        }
    }
}