// MediaPipe hand landmark indices and the bone connections between them.
// See: https://developers.google.com/mediapipe/solutions/vision/hand_landmarker
//
// 21 landmarks per hand, each normalized to [0,1] in image space.

export const LANDMARK = {
  WRIST: 0,
  THUMB_CMC: 1,
  THUMB_MCP: 2,
  THUMB_IP: 3,
  THUMB_TIP: 4,
  INDEX_MCP: 5,
  INDEX_PIP: 6,
  INDEX_DIP: 7,
  INDEX_TIP: 8,
  MIDDLE_MCP: 9,
  MIDDLE_PIP: 10,
  MIDDLE_DIP: 11,
  MIDDLE_TIP: 12,
  RING_MCP: 13,
  RING_PIP: 14,
  RING_DIP: 15,
  RING_TIP: 16,
  PINKY_MCP: 17,
  PINKY_PIP: 18,
  PINKY_DIP: 19,
  PINKY_TIP: 20,
} as const;

/** Pairs of landmark indices that form the hand skeleton, for overlay drawing. */
export const HAND_CONNECTIONS: ReadonlyArray<readonly [number, number]> = [
  // Thumb
  [0, 1],
  [1, 2],
  [2, 3],
  [3, 4],
  // Index
  [0, 5],
  [5, 6],
  [6, 7],
  [7, 8],
  // Middle
  [5, 9],
  [9, 10],
  [10, 11],
  [11, 12],
  // Ring
  [9, 13],
  [13, 14],
  [14, 15],
  [15, 16],
  // Pinky
  [13, 17],
  [17, 18],
  [18, 19],
  [19, 20],
  // Palm base
  [0, 17],
];

export interface NormalizedLandmark {
  x: number;
  y: number;
  z: number;
  visibility?: number;
}

/** Euclidean distance between two normalized landmarks (x/y plane). */
export function dist2d(a: NormalizedLandmark, b: NormalizedLandmark): number {
  const dx = a.x - b.x;
  const dy = a.y - b.y;
  return Math.hypot(dx, dy);
}

/** Midpoint of two normalized landmarks (x/y plane). */
export function midpoint(a: NormalizedLandmark, b: NormalizedLandmark): { x: number; y: number } {
  return { x: (a.x + b.x) / 2, y: (a.y + b.y) / 2 };
}