package calculator

import (
	"math"
	"time"

	"github.com/hebl/gofa"
)

func ECItoECEF(j2000X, j2000Y, j2000Z float64, utc time.Time) (float64, float64, float64) {
	j2000Position := [3]float64{j2000X, j2000Y, j2000Z}
	var ecef [3]float64

	// 当前的 TT 时间 (Terrestrial Time)
	var tt1, tt2 float64
	gofa.Dtf2d("UTC",
		utc.Year(),
		int(utc.Month()),
		utc.Day(),
		utc.Hour(),
		utc.Minute(),
		float64(utc.Second()),
		&tt1, &tt2)

	var djm0, mjd float64
	gofa.Cal2jd(int(utc.Year()), int(utc.Month()), int(utc.Day()), &djm0, &mjd)
	var dut1 float64 = 0.0562
	xp := 0.0
	yp := 0.0

	if e, ok := EOP.Get(mjd); ok {
		xp = e.Xp
		yp = e.Yp
		dut1 = e.Dut1
	}

	// 计算 UT1 时间 世界时UT1与协调世界时UTC
	var ut11, ut12 float64
	gofa.Utcut1(tt1, tt2, dut1, &ut11, &ut12)

	// 计算 C2T 矩阵 (ICRS -> CIRS -> ECEF)
	var rc2t [3][3]float64
	gofa.C2t06a(tt1, tt2, ut11, ut12, xp, yp, &rc2t)

	// 计算 ECEF 坐标
	gofa.Rxp(rc2t, j2000Position, &ecef)
	return ecef[0], ecef[1], ecef[2]
}

func ECEFGeocentricToGeodetic(x, y, z float64) (float64, float64, float64) {
	var lat, lon, alt float64
	gofa.Gc2gd(gofa.WGS84, [3]float64{x, y, z}, &lon, &lat, &alt)
	return lat * 180 / math.Pi, lon * 180 / math.Pi, alt
}