import SwiftUI

struct StatsHeroRow: View {
    let totals: StatsTotals
    let daily: [StatsDailyEntry]
    @Binding var selectedMetric: StatsMetric

    var body: some View {
        HStack(spacing: 0) {
            heroBox(title: "Sessions", value: "\(totals.sessions)",
                    trend: trendInfo(values: daily.map { Double($0.sessions) }, costMetric: false),
                    metric: .sessions)
            Divider().frame(height: 44)
            heroBox(title: "Cost", value: SessionFormatting.costString(totals.cost),
                    trend: trendInfo(values: daily.map { $0.cost }, costMetric: true),
                    metric: .cost)
            Divider().frame(height: 44)
            heroBox(title: "Tokens", value: totals.tokens.formattedTokenCount(),
                    trend: trendInfo(values: daily.map { Double($0.tokens) }, costMetric: false),
                    metric: .tokens)
        }
        .frame(maxWidth: .infinity)
        .padding(.vertical, 4)
        .background(Color.themeBgHighlight, in: RoundedRectangle(cornerRadius: 12))
    }

    // MARK: - Hero box

    private func heroBox(title: String, value: String, trend: TrendInfo?, metric: StatsMetric) -> some View {
        Button {
            selectedMetric = metric
        } label: {
            VStack(spacing: 4) {
                Text(title)
                    .font(.caption)
                    .foregroundStyle(.themeComment)
                Text(value)
                    .font(.title3.weight(.semibold).monospacedDigit())
                    .foregroundStyle(.themeFg)
                if let trend {
                    Label(trend.label, systemImage: trend.arrow)
                        .font(.caption2)
                        .foregroundStyle(trend.color)
                }
            }
            .frame(maxWidth: .infinity)
            .padding(.vertical, 8)
            .overlay(alignment: .bottom) {
                if selectedMetric == metric {
                    RoundedRectangle(cornerRadius: 1)
                        .fill(Color.themeBlue)
                        .frame(width: 32, height: 2)
                        .padding(.bottom, 2)
                }
            }
        }
        .buttonStyle(.plain)
    }

    // MARK: - Trend

    private struct TrendInfo {
        let arrow: String
        let label: String
        let color: Color
    }

    private func trendInfo(values: [Double], costMetric: Bool) -> TrendInfo? {
        guard values.count >= 2 else { return nil }

        let mid = values.count / 2
        let firstHalf = values.prefix(mid).reduce(0, +)
        let secondHalf = values.suffix(from: mid).reduce(0, +)

        guard firstHalf > 0 else { return nil }

        let delta = (secondHalf - firstHalf) / firstHalf
        guard abs(delta) >= 0.05 else { return nil }

        let rising = delta > 0
        let pct = String(format: "%.0f%%", abs(delta) * 100)

        if costMetric {
            return TrendInfo(
                arrow: rising ? "arrow.up.right" : "arrow.down.right",
                label: pct,
                color: rising ? .themeOrange : .themeGreen
            )
        } else {
            return TrendInfo(
                arrow: rising ? "arrow.up.right" : "arrow.down.right",
                label: pct,
                color: .themeComment
            )
        }
    }

    // MARK: - Formatting


}