import SwiftUI
import UIKit

/// The Nearlight signature element: an upright, softly lit aperture.
///
/// Two capsules in a ZStack — no assets, shaders, blur, or particles. The
/// inner capsule carries a vertical Rosewood gradient; its geometry encodes
/// conversation state and audio level. Noninteractive and accessibility
/// hidden: the companion status text carries meaning.
struct LightwellView: View {
    /// Lightwell presentation state, mapped from session/conversation models.
    enum Phase: Equatable {
        case idle
        case connecting
        case waiting
        case listening(level: Double)
        case thinking
        case speaking(level: Double)
        case tearingDown
        case failed
        /// Input never drives the light (muted or Type mode).
        case readyNoInput
    }

    let phase: Phase
    /// Compact (24×36) in the conversation status strip; full (64×96) on welcome.
    var compact: Bool = false
    @Environment(\.accessibilityReduceMotion) private var reduceMotion
    /// Frame dimensions never animate; inner dimensions multiply by 0.375
    /// in the compact frame.
    private var frameSize: CGSize {
        compact ? CGSize(width: 24, height: 36) : CGSize(width: 64, height: 96)
    }
    private var baseInner: CGSize {
        let base = CGSize(width: 16, height: 40)
        return compact
            ? CGSize(width: base.width * 0.375, height: base.height * 0.375)
            : base
    }

    @Environment(\.colorSchemeContrast) private var contrast

    var body: some View {
        Group {
            if pulseWanted {
                // Isolated TimelineView: ticks only while pending states are
                // showing; pauses when offscreen/inactive automatically.
                TimelineView(.periodic(from: .now, by: 0.05)) { context in
                    lightwell(pulse: pulseValue(at: context.date))
                }
            } else {
                lightwell(pulse: 0)
            }
        }
    }

    private func lightwell(pulse: Double) -> some View {
        let inner = innerSize
        return ZStack {
            Capsule()
                .fill(Nearlight.surface)
            Capsule()
                .fill(innerFill)
                .frame(width: inner.width, height: inner.height)
                .opacity(overallOpacity(pulse: pulse))
        }
        .frame(width: frameSize.width, height: frameSize.height)
        .overlay(
            Capsule().strokeBorder(
                contrast == .increased ? Nearlight.rosewood : Nearlight.quiet,
                lineWidth: 1
            )
        )
        .accessibilityHidden(true)
        .animation(reduceMotion ? nil : Nearlight.settle, value: innerSize)
    }

    /// Increase Contrast promotes the gradient to solid Rosewood.
    private var innerFill: AnyShapeStyle {
        if contrast == .increased {
            return AnyShapeStyle(Nearlight.rosewood)
        }
        return AnyShapeStyle(
            LinearGradient(
                stops: [
                    .init(color: Nearlight.rosewood.opacity(0.35), location: 0),
                    .init(color: Nearlight.rosewood.opacity(1), location: 0.5),
                    .init(color: Nearlight.rosewood.opacity(0.55), location: 1),
                ],
                startPoint: .top, endPoint: .bottom
            )
        )
    }

    /// Whether a pulse TimelineView should run for this phase.
    private var pulseWanted: Bool {
        switch phase {
        case .connecting, .waiting, .thinking: return !reduceMotion
        default: return false
        }
    }

    /// Triangle wave 0→1→0 over the 2.4s cycle from the timeline date.
    private func pulseValue(at date: Date) -> Double {
        let t = date.timeIntervalSinceReferenceDate.truncatingRemainder(dividingBy: 2.4) / 2.4
        return t < 0.5 ? t * 2 : (1 - t) * 2
    }

    /// Inner capsule geometry per spec table. `a` is the smoothed level.
    /// Reduce Motion: static 16×40 (idle/listening) and 16×48 (pending/
    /// thinking/speaking) with no level-driven resizing.
    private var innerSize: CGSize {
        let base = baseInner
        if reduceMotion {
            switch phase {
            case .waiting, .thinking, .speaking:
                return CGSize(width: base.width, height: base.height + (compact ? 3 : 8))
            default:
                return base
            }
        }
        switch phase {
        case .listening(let a):
            let level = min(max(a, 0), 1)
            return CGSize(width: base.width + (compact ? 3 : 8) * level,
                          height: base.height + (compact ? 6 : 16) * level)
        case .speaking(let a):
            let level = min(max(a, 0), 1)
            return CGSize(width: base.width + (compact ? 4.5 : 12) * level,
                          height: base.height + (compact ? 9 : 24) * level)
        case .waiting, .thinking:
            // Pulse drives opacity; height steps up one band.
            return CGSize(width: base.width, height: base.height + (compact ? 3 : 8))
        case .connecting, .idle, .failed, .tearingDown, .readyNoInput:
            return base
        }
    }

    private func overallOpacity(pulse: Double) -> Double {
        switch phase {
        case .connecting, .waiting:
            return 0.45 + 0.45 * pulse
        case .thinking:
            return 0.65 + 0.35 * pulse
        case .idle, .failed, .tearingDown:
            return 0.45
        case .listening, .speaking, .readyNoInput:
            return 1
        }
    }
}