SwiftでCSVが簡単に出力できる

import SwiftUI
import SwiftYFinance
import Charts

struct ContentView: View {
    var body: some View {
        Text("TODO")
            .task {
                let stockData = await fetchStockData()
                saveCSV(stockData: stockData)
            }
    }
    
    func saveCSV(stockData: [[String]]) {
        // CSV文字列を生成
        var csvText = Constant.header.joined(separator: ",") + "\n" // ヘッダー行
        for row in stockData {
            csvText += row.joined(separator: ",") + "\n" // 各データ行
        }
        
        // ファイルの保存先パス
        let fileName = "output.csv"
        let path = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0].appendingPathComponent(fileName)
        
        // CSVを保存
        do {
            try csvText.write(to: path, atomically: true, encoding: .utf8)
            print("😺CSV file saved at: \(path)")
        } catch {
            print("Failed to create file: \(error)")
        }
    }
    
    func fetchStockData() async -> [[String]] {
        var stocks: [[String]] = .init()
        
        for stock in Constant.ipo2021 {
            do {
                // `SwiftYFinance.chartDataBy`を非同期呼び出しに変換
                let data = try await fetchChartData(
                    identifier: "\(stock.code).T",
                    start: stock.startDate,
                    end: stock.endDate
                )
                
                // データを加工
                let value: [[String]] = data.compactMap {
                    guard let open = $0.open,
                          let close = $0.close,
                          let high = $0.high,
                          let low = $0.low else {
                        return []
                    }
                    return [open.description, close.description, high.description, low.description]
                }
                
                var resultValue = value.flatMap { $0 }
                resultValue.insert(stock.market.rawValue, at: 0)
                resultValue.insert(stock.code, at: 0)
                stocks.append(resultValue)
            } catch {
                print("エラー: \(error.localizedDescription)")
            }
        }
        
        return stocks
    }
    
    private func fetchChartData(identifier: String, start: Date, end: Date) async throws -> [StockChartData] {
        return try await withCheckedThrowingContinuation { continuation in
            SwiftYFinance.chartDataBy(identifier: identifier, start: start, end: end) { data, error in
                if let error = error {
                    continuation.resume(throwing: error)
                    return
                }
                
                guard let data = data else {
                    continuation.resume(throwing: NSError(domain: "DataError", code: -1, userInfo: nil))
                    return
                }
                
                continuation.resume(returning: data)
            }
        }
    }
}