digital-psychology/apps/api/internal/star/synastry/synastry.go

// Package synastry computes love/friend/marriage match indices from two natal charts.
package synastry

import (
	"fmt"

	"github.com/yuxingu/digital-psychology/apps/api/internal/star/natal"
)

// Indices are 0–100 match scores.
type Indices struct {
	Love      int    `json:"love_index"`
	Friend    int    `json:"friend_index"`
	Marriage  int    `json:"marriage_index"`
	LoveNote  string `json:"love_note"`
	FriendNote string `json:"friend_note"`
	MarriageNote string `json:"marriage_note"`
	Summary   string `json:"summary"`
}

// Compute returns match indices for charts A and B.
func Compute(a, b natal.Chart, aName, bName string) Indices {
	if aName == "" {
		aName = "我"
	}
	if bName == "" {
		bName = "TA"
	}
	sunDiff := natal.AngleDiff(a.Sun.Lon, b.Sun.Lon)
	moonDiff := natal.AngleDiff(a.Moon.Lon, b.Moon.Lon)
	venA := bodyLon(a, "venus")
	venB := bodyLon(b, "venus")
	marsA := bodyLon(a, "mars")
	marsB := bodyLon(b, "mars")
	venDiff := natal.AngleDiff(venA, venB)
	marsVen := natal.AngleDiff(marsA, venB)
	venMars := natal.AngleDiff(venA, marsB)

	// Closer aspects (0/60/120 soft; 90/180 hard but charged) → higher score blended
	love := clamp(58+aspectBoost(sunDiff)+aspectBoost(moonDiff)+aspectBoost(venDiff)+aspectBoost(marsVen)/2+aspectBoost(venMars)/2, 42, 98)
	friend := clamp(60+aspectBoost(sunDiff)+aspectBoost(moonDiff)*3/2+elemBoost(a.Sun, b.Sun), 45, 97)
	marriage := clamp(55+aspectBoost(sunDiff)+aspectBoost(moonDiff)+aspectBoost(venDiff)+houseBoost(a, b), 40, 96)

	return Indices{
		Love: love, Friend: friend, Marriage: marriage,
		LoveNote:     fmt.Sprintf("%s与%s恋爱指数 %d：太阳相距约%.0f°，金星互动影响吸引力。", aName, bName, love, sunDiff),
		FriendNote:   fmt.Sprintf("友情指数 %d：月亮与太阳元素是否合拍，决定轻松感。", friend),
		MarriageNote: fmt.Sprintf("婚姻/长期指数 %d：看重稳定与共同节奏，而非一时火花。", marriage),
		Summary:      fmt.Sprintf("%s × %s：恋爱 %d · 友情 %d · 婚姻 %d", aName, bName, love, friend, marriage),
	}
}

func bodyLon(c natal.Chart, key string) float64 {
	for _, p := range c.Planets {
		if p.Key == key {
			return p.Lon
		}
	}
	return 0
}

func aspectBoost(diff float64) int {
	// reward conjunction, sextile, trine; mild for square/opposition
	targets := []float64{0, 60, 90, 120, 180}
	best := 180.0
	for _, t := range targets {
		d := abs(diff - t)
		if d < best {
			best = d
		}
	}
	switch {
	case best <= 8:
		if near(diff, 90) || near(diff, 180) {
			return 8
		}
		return 14
	case best <= 12:
		return 8
	default:
		return int(6 - best/30)
	}
}

func near(diff, target float64) bool {
	return abs(diff-target) <= 10
}

func elemBoost(a, b natal.Body) int {
	if a.Element == b.Element {
		return 6
	}
	// fire-air / earth-water traditionally supportive
	pair := a.Element + b.Element
	if pair == "火风" || pair == "风火" || pair == "土水" || pair == "水土" {
		return 4
	}
	return 0
}

func houseBoost(a, b natal.Chart) int {
	// same rising modality → slight boost
	if a.Rise.Modality == b.Rise.Modality {
		return 4
	}
	return 0
}

func clamp(v, lo, hi int) int {
	if v < lo {
		return lo
	}
	if v > hi {
		return hi
	}
	return v
}

func abs(x float64) float64 {
	if x < 0 {
		return -x
	}
	return x
}

// AsMap for JSON.
func (i Indices) AsMap() map[string]any {
	return map[string]any{
		"love_index": i.Love, "friend_index": i.Friend, "marriage_index": i.Marriage,
		"love_note": i.LoveNote, "friend_note": i.FriendNote, "marriage_note": i.MarriageNote,
		"summary": i.Summary,
	}
}