package route

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"time"

	"maps/router/internal/geo"
)

// Valhalla is a client for a Valhalla routing API
// (e.g. the hosted https://valhalla1.openstreetmap.de or a self-hosted
// valhalla instance). Note: hosted instances strip route geometry, so
// Route.Geometry will be nil.
type Valhalla struct {
	BaseURL string
	HTTP    *http.Client
	name    string
}

func NewValhalla(baseURL string) *Valhalla {
	return &Valhalla{
		BaseURL: baseURL,
		HTTP:    &http.Client{Timeout: 60 * time.Second},
		name:    "valhalla(" + baseURL + ")",
	}
}

func (v *Valhalla) Name() string { return v.name }

func (v *Valhalla) costing(p Profile) string {
	if p == ProfileWalk {
		return "pedestrian"
	}
	return "auto"
}

type vLocation struct {
	Lat float64 `json:"lat"`
	Lon float64 `json:"lon"`
}

type vRouteReq struct {
	Locations []vLocation `json:"locations"`
	Costing   string      `json:"costing"`
	Polyline  bool        `json:"polyline"`
}

type vLeg struct {
	Summary struct {
		Time   float64 `json:"time"`
		Length float64 `json:"length"` // km
	} `json:"summary"`
}

type vTrip struct {
	Summary struct {
		Time   float64 `json:"time"`
		Length float64 `json:"length"` // km
		MinLat float64 `json:"min_lat"`
		MaxLat float64 `json:"max_lat"`
		MinLon float64 `json:"min_lon"`
		MaxLon float64 `json:"max_lon"`
	} `json:"summary"`
	Legs []vLeg `json:"legs"`
}

type vResp struct {
	Trip    vTrip  `json:"trip"`
	Message string `json:"message"`
	Error   string `json:"error"`
}

func (v *Valhalla) Route(ctx context.Context, profile Profile, pts []geo.Point) (*Route, error) {
	if len(pts) < 2 {
		return nil, fmt.Errorf("route: need >= 2 points, got %d", len(pts))
	}
	req := vRouteReq{Costing: v.costing(profile), Polyline: true}
	for _, p := range pts {
		req.Locations = append(req.Locations, vLocation{p.Lat, p.Lon})
	}
	body, _ := json.Marshal(req)
	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, v.BaseURL+"/route", bytes.NewReader(body))
	if err != nil {
		return nil, err
	}
	httpReq.Header.Set("Content-Type", "application/json")
	resp, err := v.HTTP.Do(httpReq)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	raw, err := io.ReadAll(io.LimitReader(resp.Body, 20<<20))
	if err != nil {
		return nil, err
	}
	var vr vResp
	if err := json.Unmarshal(raw, &vr); err != nil {
		return nil, fmt.Errorf("valhalla: bad response (%s): %q", resp.Status, string(raw[:min(len(raw), 200)]))
	}
	if vr.Message != "" {
		return nil, fmt.Errorf("valhalla: %s", vr.Message)
	}
	if vr.Error != "" {
		return nil, fmt.Errorf("valhalla: %s", vr.Error)
	}
	out := &Route{
		Duration: vr.Trip.Summary.Time,
		Distance: vr.Trip.Summary.Length * 1000,
		BBox: BBox{
			MinLat: vr.Trip.Summary.MinLat, MaxLat: vr.Trip.Summary.MaxLat,
			MinLon: vr.Trip.Summary.MinLon, MaxLon: vr.Trip.Summary.MaxLon,
		},
	}
	for _, l := range vr.Trip.Legs {
		out.Legs = append(out.Legs, Leg{Duration: l.Summary.Time, Distance: l.Summary.Length * 1000})
	}
	// Geometry: decode encoded polyline if the instance returns it.
	if pl, ok := decodePolylineField(raw); ok {
		out.Geometry = pl
	}
	return out, nil
}

// decodePolylineField checks for trip.polyline (encoded polyline v0) —
// hosted instances omit it; self-hosted valhalla with "polyline":true
// returns it.
func decodePolylineField(raw []byte) ([]geo.Point, bool) {
	var probe struct {
		Trip struct {
			Polyline string `json:"polyline"`
		} `json:"trip"`
	}
	if err := json.Unmarshal(raw, &probe); err != nil || probe.Trip.Polyline == "" {
		return nil, false
	}
	return decodePolyline(probe.Trip.Polyline), true
}

// decodePolyline decodes a Google encoded polyline (precision 1e-5 or 1e-6).
func decodePolyline(s string) []geo.Point {
	var pts []geo.Point
	lat, lon := 0, 0
	i := 0
	for i < len(s) {
		var dlat, dlon int
		shift := 0
		for {
			b := int(s[i]) - 63
			i++
			dlat |= (b & 0x1f) << shift
			if b&0x20 == 0 {
				break
			}
			shift += 5
		}
		shift = 0
		for {
			b := int(s[i]) - 63
			i++
			dlon |= (b & 0x1f) << shift
			if b&0x20 == 0 {
				break
			}
			shift += 5
		}
		lat += dlat&1 ^ dlat>>1
		lon += dlon&1 ^ dlon>>1
		pts = append(pts, geo.Point{Lat: float64(lat) / 1e5, Lon: float64(lon) / 1e5})
	}
	return pts
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}