workouts/Workouts/ExerciseFigure/ExerciseFigureView.swift

//
// ExerciseFigureView.swift
// Workouts
//
// Copyright 2026 Rouslan Zenetl. All Rights Reserved.
//

import SwiftUI

/// The looping animated stick-figure for the run screen's bottom half, rendered with
/// `Canvas` + `TimelineView(.animation)` from the bundled anatomical rig data (see
/// `Exercise Library/SYSTEM.md` for the visual language).
///
/// The solver hands back a depth-sorted draw order per frame (far parts first, the head
/// always last so overhead arms pass behind the face) and a near/far tag per limb: the
/// member nearer the camera draws in the dark ink at the heavier width, the far member
/// in the light ink one step thinner and nudged by the readability offset. Working parts
/// swap the same near/far inks for the accent teals; the spine is always dark.

/// Everything the renderer needs for one exercise, resolved once from the bundle.
struct FigureAnimation {
    let timeline: MotionTimeline
    /// Parts drawn in the working accent color (`arm_r`, `leg_l`, `spine`, …).
    let working: Set<String>
    /// Limbs fully occluded in this view — never drawn.
    let hide: Set<String>
    /// Equipment layer (see SYSTEM.md "The props layer").
    let props: [MotionProp]

    init?(exerciseName: String) {
        guard
            let resources = ExerciseMotionLibrary.resources(for: exerciseName),
            let timeline = MotionTimeline(motion: resources.motion, profile: resources.profile)
        else { return nil }
        self.timeline = timeline
        self.working = Set(resources.motion.working ?? [])
        self.hide = Set(resources.motion.hide ?? [])
        self.props = resources.motion.props ?? []
    }

    /// Drawable geometry at `time`, with limbs listed in `hide` dropped so neither they
    /// nor any prop riding them are drawn.
    func geometry(at time: Double) -> FigureGeometry {
        var geo = timeline.geometry(at: time)
        for name in hide {
            if let limb = FigureLimb(rawValue: name) { geo.limbs[limb] = nil }
        }
        return geo
    }
}

/// Bottom-half slot for the run screen: the looping figure when a bundled motion
/// matches the exercise name, or empty space (the pre-figure layout) when none does.
struct ExerciseFigureSlot: View {
    let exerciseName: String

    @State private var figure: FigureAnimation?

    var body: some View {
        ZStack {
            if let figure {
                ExerciseFigureView(figure: figure)
            } else {
                Color.clear
            }
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .task(id: exerciseName) {
            figure = FigureAnimation(exerciseName: exerciseName)
        }
    }
}

/// Draws one `FigureAnimation`, looping forever. The 320×180 design canvas is scaled
/// uniformly to fit the available space (stroke widths scale with it).
struct ExerciseFigureView: View {
    let figure: FigureAnimation

    /// Design-canvas metrics, shared with the reference renderer.
    private static let designSize = CGSize(width: 320, height: 180)
    private static let groundY: CGFloat = 152

    var body: some View {
        TimelineView(.animation) { context in
            Canvas { graphics, size in
                var ctx = graphics
                draw(&ctx, size: size, time: context.date.timeIntervalSinceReferenceDate)
            }
        }
        .accessibilityLabel("Animated form guide")
        .accessibilityHidden(false)
    }

    private func draw(_ ctx: inout GraphicsContext, size: CGSize, time: Double) {
        let scale = min(size.width / Self.designSize.width, size.height / Self.designSize.height)
        guard scale > 0 else { return }
        ctx.translateBy(x: (size.width - Self.designSize.width * scale) / 2,
                        y: (size.height - Self.designSize.height * scale) / 2)
        ctx.scaleBy(x: scale, y: scale)

        let geo = figure.geometry(at: time)

        // Ground line.
        stroke(&ctx, [CGPoint(x: 16, y: Self.groundY + 4),
                      CGPoint(x: Self.designSize.width - 16, y: Self.groundY + 4)],
               color: .figureGround, width: 3)

        // Equipment behind the figure: scene shapes and cables.
        drawBackgroundProps(&ctx, geo)

        // Parts far-to-near. The head paints last (opaque), preceded by the joint-attached
        // equipment so bars/pads sit over the limbs but behind the face.
        for part in geo.order {
            switch part {
            case "head":
                drawAttachedProps(&ctx, geo)
                drawHead(&ctx, geo)
            case "spine":
                drawSpine(&ctx, geo)
            default:
                guard let limb = FigureLimb(rawValue: part), let points = geo.limbs[limb] else { continue }
                let shade = geo.shade[limb] ?? .near
                stroke(&ctx, points, color: ink(part, shade: shade), width: shade == .near ? 6 : 5)
            }
        }
    }

    private func drawHead(_ ctx: inout GraphicsContext, _ geo: FigureGeometry) {
        let r = geo.headRadius
        let headRect = CGRect(x: geo.headCenter.x - r, y: geo.headCenter.y - r, width: 2 * r, height: 2 * r)
        let headPath = Path(ellipseIn: headRect)
        ctx.fill(headPath, with: .color(.figureHeadFill))
        ctx.stroke(headPath, with: .color(.figureNear), lineWidth: 6)
        if let noseStart = geo.noseStart, let noseEnd = geo.noseEnd {
            stroke(&ctx, [noseStart, noseEnd], color: .figureNear, width: 4)
        }
    }

    private func drawSpine(_ ctx: inout GraphicsContext, _ geo: FigureGeometry) {
        var path = Path()
        path.move(to: geo.spineStart)
        path.addQuadCurve(to: geo.spineEnd, control: geo.spineControl)
        ctx.stroke(path, with: .color(ink("spine", shade: .near)),
                   style: StrokeStyle(lineWidth: 6, lineCap: .round, lineJoin: .round))
    }

    // MARK: Props

    /// Prop joint refs → (limb, chain index): extremities are index 2, mid joints
    /// (elbows/knees) index 1, so equipment can ride either joint. Kept 1:1 with
    /// the reference renderer's `JOINT_LIMB` (legs now end in a foot bone, so a foot
    /// prop rides the ankle at index 2).
    private static let propJoints: [String: (limb: FigureLimb, index: Int)] = [
        "hand_r": (.armR, 2), "elbow_r": (.armR, 1),
        "hand_l": (.armL, 2), "elbow_l": (.armL, 1),
        "foot_r": (.legR, 2), "knee_r": (.legR, 1),
        "foot_l": (.legL, 2), "knee_l": (.legL, 1),
    ]

    /// The joint point a prop follows (plus the unit direction of the bone ending
    /// at the first joint, for perpendicular items). Nil when any referenced limb
    /// isn't drawn this frame.
    private func jointAnchor(_ geo: FigureGeometry, _ ref: PropJointRef) -> (point: CGPoint, direction: CGVector)? {
        var points: [CGPoint] = []
        var direction: CGVector?
        for name in ref.names {
            guard let joint = Self.propJoints[name],
                  let chain = geo.limbs[joint.limb], chain.count > joint.index else { return nil }
            let a = chain[joint.index - 1]
            let b = chain[joint.index]
            points.append(b)
            if direction == nil {
                let d = max(hypot(b.x - a.x, b.y - a.y), 1)
                direction = CGVector(dx: (b.x - a.x) / d, dy: (b.y - a.y) / d)
            }
        }
        guard let direction, !points.isEmpty else { return nil }
        let center = CGPoint(x: points.reduce(0) { $0 + $1.x } / CGFloat(points.count),
                             y: points.reduce(0) { $0 + $1.y } / CGFloat(points.count))
        return (center, direction)
    }

    private func drawBackgroundProps(_ ctx: inout GraphicsContext, _ geo: FigureGeometry) {
        for prop in figure.props {
            switch prop.type {
            case "scene":
                for shape in prop.shapes ?? [] { drawSceneShape(&ctx, shape) }
            case "cable":
                guard let from = prop.from, from.count == 2, let to = prop.to,
                      let anchor = jointAnchor(geo, to) else { continue }
                stroke(&ctx, [CGPoint(x: from[0], y: from[1]), anchor.point],
                       color: .figureEquipment, width: prop.w ?? 2)
            default:
                break
            }
        }
    }

    /// Bars sit at a fixed world angle (default horizontal); dumbbells and pads
    /// default to perpendicular to the lower bone. Kept 1:1 with the reference
    /// renderer's `resolve_props` — change them in lockstep.
    private func drawAttachedProps(_ ctx: inout GraphicsContext, _ geo: FigureGeometry) {
        for prop in figure.props {
            let defaults: (halfLen: Double, width: Double, plateR: Double)
            switch prop.type {
            case "bar": defaults = (24, 4, 0)
            case "dumbbell": defaults = (7, 3, 4.5)
            case "pad": defaults = (8, 7, 0)
            default: continue
            }
            guard let at = prop.at, let anchor = jointAnchor(geo, at) else { continue }
            let axis: CGVector
            if prop.type == "bar" || prop.angle != nil {
                axis = MotionSolver.direction(prop.angle ?? 0)
            } else {
                axis = CGVector(dx: -anchor.direction.dy, dy: anchor.direction.dx)
            }
            let h = prop.halfLen ?? defaults.halfLen
            let a = CGPoint(x: anchor.point.x - axis.dx * h, y: anchor.point.y - axis.dy * h)
            let b = CGPoint(x: anchor.point.x + axis.dx * h, y: anchor.point.y + axis.dy * h)
            stroke(&ctx, [a, b], color: .figureProp, width: prop.w ?? defaults.width)
            let plateR = prop.plateR ?? defaults.plateR
            if plateR > 0 {
                for end in [a, b] {
                    let rect = CGRect(x: end.x - plateR, y: end.y - plateR,
                                      width: 2 * plateR, height: 2 * plateR)
                    ctx.fill(Path(ellipseIn: rect), with: .color(.figureProp))
                }
            }
        }
    }

    private func drawSceneShape(_ ctx: inout GraphicsContext, _ shape: PropSceneShape) {
        let color: Color = shape.color == "prop" ? .figureProp : .figureEquipment
        switch shape.kind {
        case "line":
            guard let pts = shape.pts else { return }
            stroke(&ctx, pts.compactMap { $0.count == 2 ? CGPoint(x: $0[0], y: $0[1]) : nil },
                   color: color, width: shape.w ?? 4)
        case "circle":
            guard let c = shape.c, c.count == 2, let r = shape.r else { return }
            let rect = CGRect(x: c[0] - r, y: c[1] - r, width: 2 * r, height: 2 * r)
            if shape.fill ?? true {
                ctx.fill(Path(ellipseIn: rect), with: .color(color))
            } else {
                ctx.stroke(Path(ellipseIn: rect), with: .color(color), lineWidth: shape.w ?? 3)
            }
        case "rect":
            guard let x = shape.x, let y = shape.y, let w = shape.w, let h = shape.h else { return }
            let path = Path(roundedRect: CGRect(x: x, y: y, width: w, height: h),
                            cornerRadius: shape.r ?? 2)
            ctx.fill(path, with: .color(color))
        default:
            break
        }
    }

    /// Near parts take the dark ink, far parts the light one; working parts swap for the
    /// accent teals. The spine (passed `.near`) is always dark unless it's the working part.
    private func ink(_ part: String, shade: Shade) -> Color {
        if figure.working.contains(part) {
            return shade == .near ? .figureNearWorking : .figureFarWorking
        }
        return shade == .near ? .figureNear : .figureFar
    }

    private func stroke(_ ctx: inout GraphicsContext, _ points: [CGPoint], color: Color, width: CGFloat) {
        var path = Path()
        path.addLines(points)
        ctx.stroke(path, with: .color(color),
                   style: StrokeStyle(lineWidth: width, lineCap: .round, lineJoin: .round))
    }
}

// MARK: - Figure Palette

/// The reference palette (`render.py`), made dark-mode adaptive: the prominent near
/// side stays strong (near-black → light gray), the recessive far side stays muted,
/// and the working teals brighten/desaturate so they read on black. watchOS has no
/// dynamic-provider `UIColor` and renders on black, so it takes the dark variant
/// verbatim.
private extension Color {
    static func figure(light: (Double, Double, Double), dark: (Double, Double, Double)) -> Color {
        #if os(watchOS)
        Color(red: dark.0, green: dark.1, blue: dark.2)
        #else
        Color(UIColor { traits in
            traits.userInterfaceStyle == .dark
                ? UIColor(red: dark.0, green: dark.1, blue: dark.2, alpha: 1)
                : UIColor(red: light.0, green: light.1, blue: light.2, alpha: 1)
        })
        #endif
    }

    /// Near-side limbs, spine, head, nose — the prominent stroke (`#3a3f4b`).
    static let figureNear = figure(light: (0.23, 0.25, 0.29), dark: (0.76, 0.79, 0.83))

    /// Far-side limbs, drawn behind — the recessive stroke (`#a9afba`).
    static let figureFar = figure(light: (0.66, 0.69, 0.73), dark: (0.36, 0.39, 0.43))

    /// Working near-side parts — teal accent (`#0d9488`).
    static let figureNearWorking = figure(light: (0.05, 0.58, 0.53), dark: (0.18, 0.83, 0.75))

    /// Working far-side parts — light teal (`#86cfc5`), kept more muted than the near
    /// so the near/far hierarchy holds in both modes.
    static let figureFarWorking = figure(light: (0.53, 0.81, 0.77), dark: (0.31, 0.56, 0.52))

    /// Scene equipment — seats, benches, frames, cables (`#c5cad4`); sits behind
    /// the figure, one step lighter than the ground line.
    static let figureEquipment = figure(light: (0.77, 0.79, 0.83), dark: (0.25, 0.27, 0.31))

    /// Joint-attached items — bars, dumbbells, pads (`#6b7180`); darker than the
    /// scene so the thing being moved reads over the limbs.
    static let figureProp = figure(light: (0.42, 0.44, 0.50), dark: (0.55, 0.58, 0.63))

    /// Ground line (`#b9bec9`).
    static let figureGround = figure(light: (0.73, 0.75, 0.79), dark: (0.29, 0.31, 0.36))

    /// Opaque head fill — the screen background, so limbs pass behind the face.
    #if os(watchOS)
    static let figureHeadFill = Color.black
    #else
    static let figureHeadFill = Color(.systemBackground)
    #endif
}