import SwiftUI

struct CalendarMonthView: View {
  @ObservedObject var model: CalendarModel
  @Environment(\.controlSize) private var controlSize
  private var compact: Bool {
    #if os(macOS)
    controlSize == .small
    #else
    false
    #endif
  }
  @Environment(\.dynamicTypeSize) private var typeSize
  private let accent = Color(red: 0.78, green: 0.22, blue: 0.29)
  var body: some View { VStack(spacing: 0) { monthHeader; monthGrid } }
  private var monthHeader: some View {
    ViewThatFits(in: .horizontal) {
      HStack {
        Text(model.display(model.monthStart, template: "MMMM yyyy")).font(.title2.bold())
        Spacer()
        monthControls
      }
      VStack(alignment: .leading) {
        Text(model.display(model.monthStart, template: "MMMM yyyy")).font(.title2.bold())
        monthControls
      }
    }.padding(.vertical, compact ? 4 : 16)
  }
  private var monthControls: some View {
    HStack {
      Button("Previous month", systemImage: "chevron.left") { move(-1) }.labelStyle(.iconOnly).frame(minWidth: compact ? 28 : 44, minHeight: compact ? 28 : 44)
      Button("Today") { model.date = Date() }.frame(minHeight: compact ? 28 : 44)
      Button("Next month", systemImage: "chevron.right") { move(1) }.labelStyle(.iconOnly).frame(minWidth: compact ? 28 : 44, minHeight: compact ? 28 : 44)
    }.buttonStyle(.borderless)
  }
  private func move(_ amount: Int) { model.date = model.calendar.date(byAdding: .month, value: amount, to: model.date) ?? model.date }
  private var monthGrid: some View {
    Grid(horizontalSpacing: 4, verticalSpacing: 4) {
      GridRow {
        ForEach(Array(model.weekdayLabels.enumerated()), id: \.offset) { _, label in
          Text(typeSize.isAccessibilitySize ? String(label.prefix(1)) : label)
            .font(.caption).foregroundStyle(.secondary).accessibilityHidden(true)
        }
      }
      ForEach(0..<6) { week in
        GridRow {
          ForEach(Array(model.days.dropFirst(week * 7).prefix(7)), id: \.self) { day in
            dayButton(day)
          }
        }
      }
    }.padding(.bottom, 12)
  }
  private func dayButton(_ day: Date) -> some View {
    let selected = model.calendar.isDate(day, inSameDayAs: model.date)
    let today = model.calendar.isDate(day, inSameDayAs: Date())
    let count = model.dayEvents(day).count
    let current = model.calendar.isDate(day, equalTo: model.monthStart, toGranularity: .month)
    return Button { model.date = day } label: {
      VStack(spacing: 3) {
        Text("\(model.calendar.component(.day, from: day))")
          .font(.body.monospacedDigit()).bold(today).lineLimit(1).minimumScaleFactor(0.7)
        Circle().fill(count == 0 ? .clear : selected ? .white : accent).frame(width: 4, height: 4)
      }.frame(maxWidth: .infinity, minHeight: compact ? 28 : 44)
        .foregroundStyle(selected ? .white : current ? Color.primary : Color.secondary)
        .background(selected ? accent : .clear, in: RoundedRectangle(cornerRadius: 9))
        .overlay { RoundedRectangle(cornerRadius: 9).strokeBorder(today ? accent : .clear, lineWidth: 2) }
    }.buttonStyle(.plain)
      .accessibilityLabel(model.display(day, template: "EEEE d MMMM yyyy"))
      .accessibilityValue("\(today ? "Today. " : "")\(count) events")
      .accessibilityAddTraits(selected ? .isSelected : [])
  }
}