package placement

import (
	"errors"
	"fmt"
	"maps"
	"math"
	"strings"
	"sync"
	"sync/atomic"

	locodedb "git.frostfs.info/TrueCloudLab/frostfs-locode-db/pkg/locode/db"
	locodebolt "git.frostfs.info/TrueCloudLab/frostfs-locode-db/pkg/locode/db/boltdb"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/netmap"
)

const (
	attrPrefix = "$attribute:"

	geoDistance = "$geoDistance"
)

type Metric interface {
	CalculateValue(*netmap.NodeInfo, *netmap.NodeInfo) int
}

type metricsParser struct {
	locodeDBPath string
	locodes      map[string]locodedb.Point
}

type MetricParser interface {
	ParseMetrics([]string) ([]Metric, error)
}

func NewMetricsParser(locodeDBPath string) (MetricParser, error) {
	return &metricsParser{
		locodeDBPath: locodeDBPath,
	}, nil
}

func (p *metricsParser) initLocodes() error {
	if len(p.locodes) != 0 {
		return nil
	}
	if len(p.locodeDBPath) > 0 {
		p.locodes = make(map[string]locodedb.Point)
		locodeDB := locodebolt.New(locodebolt.Prm{
			Path: p.locodeDBPath,
		},
			locodebolt.ReadOnly(),
		)
		err := locodeDB.Open()
		if err != nil {
			return err
		}
		defer locodeDB.Close()
		err = locodeDB.IterateOverLocodes(func(k string, v locodedb.Point) {
			p.locodes[k] = v
		})
		if err != nil {
			return err
		}
		return nil
	}
	return errors.New("set path to locode database")
}

func (p *metricsParser) ParseMetrics(priority []string) ([]Metric, error) {
	var metrics []Metric
	for _, raw := range priority {
		if attr, found := strings.CutPrefix(raw, attrPrefix); found {
			metrics = append(metrics, NewAttributeMetric(attr))
		} else if raw == geoDistance {
			err := p.initLocodes()
			if err != nil {
				return nil, err
			}
			if len(p.locodes) == 0 {
				return nil, fmt.Errorf("provide locodes database for metric %s", raw)
			}
			m := NewGeoDistanceMetric(p.locodes)
			metrics = append(metrics, m)
		} else {
			return nil, fmt.Errorf("unsupported priority metric %s", raw)
		}
	}
	return metrics, nil
}

// attributeMetric describes priority metric based on attribute.
type attributeMetric struct {
	attribute string
}

// CalculateValue return [0] if from and to contains attribute attributeMetric.attribute and
// the value of attribute is the same. In other case return [1].
func (am *attributeMetric) CalculateValue(from *netmap.NodeInfo, to *netmap.NodeInfo) int {
	fromAttr := from.Attribute(am.attribute)
	toAttr := to.Attribute(am.attribute)
	if len(fromAttr) > 0 && len(toAttr) > 0 && fromAttr == toAttr {
		return 0
	}
	return 1
}

func NewAttributeMetric(attr string) Metric {
	return &attributeMetric{attribute: attr}
}

// geoDistanceMetric describes priority metric based on attribute.
type geoDistanceMetric struct {
	locodes  map[string]locodedb.Point
	distance *atomic.Pointer[map[string]int]
	mtx      sync.Mutex
}

func NewGeoDistanceMetric(locodes map[string]locodedb.Point) Metric {
	d := atomic.Pointer[map[string]int]{}
	m := make(map[string]int)
	d.Store(&m)
	gm := &geoDistanceMetric{
		locodes:  locodes,
		distance: &d,
	}
	return gm
}

// CalculateValue return distance in kilometers between current node and provided,
// if coordinates for provided node found. In other case return math.MaxInt.
func (gm *geoDistanceMetric) CalculateValue(from *netmap.NodeInfo, to *netmap.NodeInfo) int {
	fl := from.LOCODE()
	tl := to.LOCODE()
	if fl == tl {
		return 0
	}
	m := gm.distance.Load()
	if v, ok := (*m)[fl+tl]; ok {
		return v
	}
	return gm.calculateDistance(fl, tl)
}

func (gm *geoDistanceMetric) calculateDistance(from, to string) int {
	gm.mtx.Lock()
	defer gm.mtx.Unlock()
	od := gm.distance.Load()
	if v, ok := (*od)[from+to]; ok {
		return v
	}
	nd := maps.Clone(*od)
	var dist int
	pointFrom, okFrom := gm.locodes[from]
	pointTo, okTo := gm.locodes[to]
	if okFrom && okTo {
		dist = int(distance(pointFrom.Latitude(), pointFrom.Longitude(), pointTo.Latitude(), pointTo.Longitude()))
	} else {
		dist = math.MaxInt
	}
	nd[from+to] = dist
	gm.distance.Store(&nd)

	return dist
}

// distance return amount of KM between two points.
// Parameters are latitude and longitude of point 1 and 2 in decimal degrees.
// Original implementation can be found here https://www.geodatasource.com/developers/go.
func distance(lt1 float64, ln1 float64, lt2 float64, ln2 float64) float64 {
	radLat1 := math.Pi * lt1 / 180
	radLat2 := math.Pi * lt2 / 180
	radTheta := math.Pi * (ln1 - ln2) / 180

	dist := math.Sin(radLat1)*math.Sin(radLat2) + math.Cos(radLat1)*math.Cos(radLat2)*math.Cos(radTheta)

	if dist > 1 {
		dist = 1
	}

	dist = math.Acos(dist)
	dist = dist * 180 / math.Pi
	dist = dist * 60 * 1.1515 * 1.609344

	return dist
}