/*
 * Posture classifier — flowchart `Posture classification` 기반 (2026-06-22).
 *
 * 단순화: 3 state (SUPINE/SITTING/STANDING) → **2 state (LYING / NON_LYING)**.
 *  - 낙상 예방 목적상 sitting/standing 구분 불필요. "누웠나, 일어났나" 만 중요.
 *
 * 단계:
 *   1. Acc magnitude 게이트: 0.8 ≤ |a| ≤ 1.2 → motion/bad sample 거부
 *   2. Gyro magnitude 게이트: |g| ≤ 9.16 dps → 회전 중 sample 거부
 *   3. Pitch 계산: atan(ax / sqrt(ay² + az²)) × 180/π
 *   4. 분류 (|pitch| 기준, threshold = GreenZoneConstants.pitchLyingThreshold):
 *        > threshold → LYING (누움)
 *        ≤ threshold → NON_LYING (앉음/섬)
 *      threshold default = 25°, dev 모드 설정에서 변경 가능.
 */
package com.example.medilightv2android.managers

import com.example.medilightv2android.ble.ImuSample
import kotlin.math.abs
import kotlin.math.atan
import kotlin.math.sqrt

enum class Posture { UNKNOWN, LYING, NON_LYING }

object ImuPostureClassifier {

    // 게이트 임계값 — flowchart 그대로
    private const val ACC_MAG_MIN = 0.8f
    private const val ACC_MAG_MAX = 1.2f
    private const val GYRO_MAG_MAX_DPS = 9.16f

    /** 자세 + 진단 정보 (UI/log용). */
    data class Result(
        val posture: Posture,
        val pitchDeg: Float,
        val accMag: Float,
        val gyroMagDps: Float,
        val reason: String,
    )

    fun classify(samples: List<ImuSample>): Result {
        if (samples.isEmpty()) {
            return Result(Posture.UNKNOWN, 0f, 0f, 0f, "no samples")
        }

        var sumAx = 0f; var sumAy = 0f; var sumAz = 0f
        var sumGx = 0f; var sumGy = 0f; var sumGz = 0f
        for (s in samples) {
            sumAx += s.ax; sumAy += s.ay; sumAz += s.az
            sumGx += s.gx; sumGy += s.gy; sumGz += s.gz
        }
        val n = samples.size
        val ax = sumAx / n; val ay = sumAy / n; val az = sumAz / n
        val gx = sumGx / n; val gy = sumGy / n; val gz = sumGz / n

        val accMag = sqrt(ax * ax + ay * ay + az * az)
        val gyroMag = sqrt(gx * gx + gy * gy + gz * gz)

        if (accMag < ACC_MAG_MIN || accMag > ACC_MAG_MAX) {
            return Result(Posture.UNKNOWN, 0f, accMag, gyroMag,
                "acc mag out of range (%.2f)".format(accMag))
        }
        if (gyroMag > GYRO_MAG_MAX_DPS) {
            return Result(Posture.UNKNOWN, 0f, accMag, gyroMag,
                "moving (gyro %.1f dps)".format(gyroMag))
        }

        val pitch = (atan(ax / sqrt(ay * ay + az * az)) * 180.0 / Math.PI).toFloat()
        val absPitch = abs(pitch)
        val thr = GreenZoneConstants.pitchLyingThreshold

        val posture = if (absPitch > thr) Posture.LYING else Posture.NON_LYING
        return Result(posture, pitch, accMag, gyroMag, "ok")
    }
}