import SwiftUI

struct SessionView: View {
    @EnvironmentObject private var analytics: HermesAnalyticsClient
    @EnvironmentObject private var localization: LocalizationStore
    @EnvironmentObject private var repository: HermesRepository

    let onRetry: () -> Void

    var body: some View {
        let session = repository.currentSession
        let bannerMessage = hermesUserFacingErrorMessage(
            localization: localization,
            localeCode: localization.localeCode,
            error: repository.errorCause
        )
        let statusText: String
        if session != nil {
            statusText = localization.string(for: "session.status_ready")
        } else if bannerMessage != nil {
            statusText = localization.string(for: "session.status_error")
        } else {
            statusText = localization.string(for: "session.status_loading")
        }

        return VStack(alignment: .leading, spacing: HermesTheme.sectionSpacing) {
            HermesSectionHeader(
                title: localization.string(for: "session.title"),
                subtitle: localization.string(for: "session.subtitle")
            )

            if session == nil {
                if let bannerMessage {
                    sessionErrorState(
                        message: bannerMessage,
                        retryText: localization.string(for: "common.retry"),
                        onRetry: onRetry
                    )
                } else {
                    sessionLoadingState(
                        title: statusText,
                        subtitle: localization.string(for: "session.note")
                    )
                }
            } else {
                sessionStatusBadge(text: statusText, warning: bannerMessage != nil)

                if let bannerMessage {
                    sessionBanner(message: bannerMessage)
                }

                sessionRow(label: localization.string(for: "session.id_label"), value: session?.sessionId.uuidString ?? "--")
                sessionRow(label: localization.string(for: "session.user_id_label"), value: session?.userId.uuidString ?? "--")
                sessionRow(
                    label: localization.string(for: "session.locale_label"),
                    value: localization.localeName(for: session?.localeCode ?? localization.localeCode)
                )
                sessionRow(label: localization.string(for: "session.started_label"), value: session.map { Self.compactDateFormatter.string(from: $0.startedAt) } ?? "--")
                sessionRow(label: localization.string(for: "session.variant_label"), value: session?.experimentVariant ?? "--")
                sessionRow(label: localization.string(for: "session.app_version_label"), value: session?.appVersion ?? "--")
                sessionRow(label: localization.string(for: "session.device_model_label"), value: session?.deviceModel ?? "--")
                sessionRow(label: localization.string(for: "session.os_version_label"), value: session?.osVersion ?? "--")

                Text(localization.string(for: "session.note"))
                    .font(.callout)
                    .foregroundStyle(HermesTheme.textSecondary)
            }
        }
        .hermesCard()
        .onAppear {
            analytics.track("screen_viewed", attributes: ["screen_name": "session"])
        }
    }

    @ViewBuilder
    private func sessionLoadingState(title: String, subtitle: String) -> some View {
        VStack(alignment: .leading, spacing: 8) {
            Text(title)
                .font(.headline.weight(.semibold))
                .foregroundStyle(HermesTheme.textPrimary)
            Text(subtitle)
                .font(.callout)
                .foregroundStyle(HermesTheme.textSecondary)
        }
    }

    @ViewBuilder
    private func sessionErrorState(message: String, retryText: String, onRetry: @escaping () -> Void) -> some View {
        VStack(alignment: .leading, spacing: 12) {
            Text(message)
                .font(.callout)
                .foregroundStyle(HermesTheme.warning)

            Button {
                onRetry()
            } label: {
                Text(retryText)
            }
            .buttonStyle(HermesSecondaryButtonStyle())
        }
    }

    @ViewBuilder
    private func sessionStatusBadge(text: String, warning: Bool) -> some View {
        Text(text)
            .font(.caption.weight(.semibold))
            .foregroundStyle(warning ? HermesTheme.warning : HermesTheme.accent)
            .padding(.horizontal, 12)
            .padding(.vertical, 8)
            .background((warning ? HermesTheme.warning : HermesTheme.accent).opacity(0.16))
            .clipShape(Capsule())
    }

    @ViewBuilder
    private func sessionBanner(message: String) -> some View {
        Text(message)
            .font(.callout)
            .foregroundStyle(HermesTheme.warning)
            .padding(.horizontal, 12)
            .padding(.vertical, 10)
            .frame(maxWidth: .infinity, alignment: .leading)
            .background(HermesTheme.warning.opacity(0.12))
            .clipShape(RoundedRectangle(cornerRadius: HermesTheme.insetRadius, style: .continuous))
    }

    @ViewBuilder
    private func sessionRow(label: String, value: String) -> some View {
        HStack {
            Text(label)
                .font(.callout)
                .foregroundStyle(HermesTheme.textSecondary)
            Spacer(minLength: 12)
            Text(value)
                .font(.callout.weight(.semibold))
                .foregroundStyle(HermesTheme.textPrimary)
        }
    }

    private static let compactDateFormatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.timeZone = .current
        formatter.dateFormat = "yyyy-MM-dd HH:mm"
        return formatter
    }()
}