import SwiftUI

struct MapEdges: View {

  let mapSize: CGSize
  let lineWidth: CGFloat
  let vertexSize: CGSize
  let edges: [MapEdge]

  let arrowheadSize = CGFloat(10.0)

  var body: some View {
    ForEach(edges, id: \.id) { edge in
      Path { path in

        // First we transform edges from percentage to map coordinates
        let origin = CGPoint(x: w(edge.origin.x), y: h(edge.origin.y))
        let destination = CGPoint(x: w(edge.destination.x), y: h(edge.destination.y))

        let slope = (destination.y - origin.y) / (destination.x - origin.x)
        let angle = atan(slope)
        let multiplier = CGFloat(slope < 0 ? -1.0 : 1.0)
        let upperAngle = angle - CGFloat.pi / 4.0
        let lowerAngle = angle + CGFloat.pi / 4.0

        let offsetOrigin = CGPoint(
          x: origin.x + multiplier * (vertexSize.width / 2.0) * cos(angle),
          y: origin.y + multiplier * (vertexSize.height / 2.0) * sin(angle))
        let offsetDestination = CGPoint(
          x: destination.x - multiplier * (vertexSize.width / 2.0) * cos(angle),
          y: destination.y - multiplier * (vertexSize.height / 2.0) * sin(angle))

        path.move(to: offsetOrigin)
        path.addLine(to: offsetDestination)

        if edge.arrowhead {
          path.move(to: offsetDestination)
          path.addLine(
            to: CGPoint(
              x: offsetDestination.x - multiplier * arrowheadSize * cos(upperAngle),
              y:
                offsetDestination.y - multiplier * arrowheadSize * sin(upperAngle)))

          path.move(to: offsetDestination)
          path.addLine(
            to: CGPoint(
              x: offsetDestination.x - multiplier * arrowheadSize * cos(lowerAngle),
              y:
                offsetDestination.y - multiplier * arrowheadSize * sin(lowerAngle)))
        }
        path.move(to: offsetDestination)
        path.closeSubpath()
      }.applying(
        CGAffineTransform(translationX: vertexSize.width / 2.0, y: vertexSize.height / 2.0)
      ).stroke(Color.map.vertexColor, lineWidth: lineWidth)
    }
  }

  func h(_ dimension: CGFloat) -> CGFloat {
    max(0.0, min(mapSize.height, dimension * mapSize.height / 100.0))
  }

  func w(_ dimension: CGFloat) -> CGFloat {
    max(0.0, min(mapSize.width, dimension * mapSize.width / 100.0))
  }
}

#Preview {
  MapEdges(
    mapSize: CGSize(width: 400.0, height: 400.0), lineWidth: 1.0,
    vertexSize: CGSize(width: 25.0, height: 25.0),
    edges: [
      MapEdge(
        id: 1, origin: CGPoint(x: 2.0, y: 34.0), destination: CGPoint(x: 23.0, y: 76.2),
        arrowhead: true)
    ])
}