import type { HandSample, Point2D } from './types'

/** VisionKit 文档：1=布/开掌，3=握拳 */
const GESTURE_OPEN = 1
const GESTURE_FIST = 3

/**
 * OpenPose-21 指尖索引（相对手腕距离用于连续 openness）
 * 0 wrist, 4 thumb tip, 8 index, 12 middle, 16 ring, 20 pinky
 */
const TIP_INDEXES = [4, 8, 12, 16, 20]

function dist(a: Point2D, b: Point2D) {
    const dx = a.x - b.x
    const dy = a.y - b.y
    return Math.sqrt(dx * dx + dy * dy)
}

function clamp01(v: number) {
    return Math.max(0, Math.min(1, v))
}

/** 离散手势 → 开合度；未知手势返回 null（交给几何或保持） */
export function opennessFromGesture(gesture?: number): number | null {
    if (gesture === GESTURE_OPEN) return 1
    if (gesture === GESTURE_FIST) return 0
    return null
}

/**
 * 用指尖到手腕的平均距离 / 掌宽 估计 openness。
 * 握力环场景开合幅度偏小，映射区间比裸掌更紧一些。
 */
export function opennessFromLandmarks(points?: Point2D[]): number | null {
    if (!points || points.length < 21) return null
    const wrist = points[0]
    const mcpIndex = points[5]
    const mcpPinky = points[17]
    const palmWidth = dist(mcpIndex, mcpPinky)
    if (palmWidth < 1e-6) return null

    let tipSum = 0
    for (const i of TIP_INDEXES) {
        tipSum += dist(points[i], wrist)
    }
    const tipMean = tipSum / TIP_INDEXES.length
    // 握力环：握紧约 0.9~1.35 掌宽，半开约 1.5~2.2 掌宽
    const ratio = tipMean / palmWidth
    return clamp01((ratio - 0.95) / 1.15)
}

export function mergeOpenness(sample: Pick<HandSample, 'gesture' | 'points'>): number | null {
    const fromGeom = opennessFromLandmarks(sample.points)
    const fromGesture = opennessFromGesture(sample.gesture)

    if (fromGeom != null && fromGesture != null) {
        // 几何为主：离散手势（布/拳）在捏环时容易误判，只做轻牵引
        return clamp01(fromGeom * 0.85 + fromGesture * 0.15)
    }
    if (fromGeom != null) return fromGeom
    if (fromGesture != null) return fromGesture
    return null
}