Stock graph

StockGraph.swift

import Charts
import SwiftUI

let oneDay: TimeInterval = 60 * 60 * 24

struct ContentView: View {
  var body: some View {
    let history = loadHistory()
      .filter { $0.id > Date.now.addingTimeInterval(-oneDay * 30) }
    let analysis = TradingAnalysis(history: history)

    VStack {
      HStack {
        Text("AAPL")
        Text(formattedDollars(analysis.lastChange))
          .foregroundStyle(analysis.lastChange > 0 ? .green : .red)
      }
      Chart(history, content: { day in
        RuleMark(
          x: .value("Date", day.id),
          yStart: .value("Low", day.low),
          yEnd: .value("High", day.high)
        )
        .lineStyle(.init(lineWidth: 1))
        .foregroundStyle(.gray)

        RuleMark(
          x: .value("Date", day.id),
          yStart: .value("Open", day.open),
          yEnd: .value("Close", day.close)
        )
        .lineStyle(.init(lineWidth: 4))
        .foregroundStyle(day.open < day.close ? .green : .red)
      })
      .chartXScale(domain: analysis.xRange)
      .chartYScale(domain: analysis.yRange)
    }
    .padding()
  }
}

struct TradingAnalysis {
  let xRange: ClosedRange<Date>
  let yRange: ClosedRange<Double>
  let lastChange: Double

  init(history: [TradingDay]) {
    if let min = history.map({ $0.id }).min(),
       let max = history.map({ $0.id }).max() {
      self.xRange = min.addingTimeInterval(-oneDay)...max.addingTimeInterval(oneDay)
    } else {
      self.xRange = Date.now.addingTimeInterval(-oneDay)...Date.now
    }
    if let min = history.map({ $0.low }).min(),
       let max = history.map({ $0.high }).max() {
      let size = max - min
      self.yRange = (min - size * 0.1)...(max + size * 0.1)
    } else {
      self.yRange = 0...100
    }
    if let last = history.last {
      self.lastChange = last.close - last.open
    } else {
      self.lastChange = 0
    }
  }
}

struct TradingDay: Identifiable {
  let id: Date
  let low: Double
  let high: Double
  let open: Double
  let close: Double
}

/// History loaded from CSV export of https://finance.yahoo.com/quote/AAPL/history/
func loadHistory() -> [TradingDay] {
  guard let url = Bundle.main.url(forResource: "AAPL", withExtension: "csv"),
        let csv = try? String(contentsOf: url, encoding: .utf8) else {
    return []
  }
  let lines = csv.components(separatedBy: .newlines)
  return lines
    .map { $0.components(separatedBy: ",") }
    .dropFirst()
    .compactMap {
      guard let date = parseDate($0[0]),
            let high = Double($0[2]),
            let low = Double($0[3]),
            let open = Double($0[1]),
            let close = Double($0[4]) else {
        return nil
      }
      return TradingDay(id: date, low: low, high: high, open: open, close: close)
    }
}

func parseDate(_ string: String) -> Date? {
  let formatter = DateFormatter()
  formatter.dateFormat = "yyyy-MM-dd"
  return formatter.date(from: string)
}

func formattedDollars(_ dollars: Double) -> String {
  let formatter = NumberFormatter()
  formatter.maximumFractionDigits = 2
  formatter.minimumFractionDigits = 2
  formatter.positivePrefix = "+"
  return formatter.string(from: dollars as NSNumber) ?? ""
}

#Preview {
  ContentView()
}