// Package traffic implements the live-traffic pipeline: external incident
// feeds → OSM node-pair speeds → OSRM segment-speed CSV → re-customize.
//
// The matcher works on the OSM side (Overpass returns OSM node IDs directly),
// so no OSRM binary parsing is needed: the segment-speed CSV is keyed by OSM
// node pairs, exactly what the OSRM updater consumes.
package traffic

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"

	"maps/router/internal/geo"
)

const defaultOverpassURL = "https://overpass-api.de/api/interpreter"

// WayNode is one OSM node on a way.
type WayNode struct {
	ID  int64   `json:"id"`
	Lat float64 `json:"lat"`
	Lon float64 `json:"lon"`
}

// Way is a highway way with its full node list.
type Way struct {
	ID      int64     `json:"id"`
	Highway string    `json:"highway"`
	Ref     string    `json:"ref"`
	Nodes   []WayNode `json:"-"`
}

// QueryWaysAround fetches highway ways within radiusM of (lat, lon).
func QueryWaysAround(client *http.Client, overpassURL string, lat, lon, radiusM float64, timeoutSec int) ([]Way, error) {
	if client == nil {
		client = &http.Client{Timeout: time.Duration(timeoutSec+30) * time.Second}
	}
	if overpassURL == "" {
		overpassURL = defaultOverpassURL
	}
	ql := fmt.Sprintf("[out:json][timeout:%d];way(around:%d,%g,%g)[highway];out geom;",
		timeoutSec, int(radiusM), lat, lon)
	req, err := http.NewRequest(http.MethodPost, overpassURL,
		strings.NewReader(url.Values{"data": {ql}}.Encode()))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	// public Overpass WAFs reject the default Go user agent
	req.Header.Set("User-Agent", "voyage-router/0.1 (traffic pipeline; contact: gmp)")
	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("overpass: %w", err)
	}
	defer resp.Body.Close()
	body, err := io.ReadAll(io.LimitReader(resp.Body, 64<<20))
	if err != nil {
		return nil, fmt.Errorf("overpass read: %w", err)
	}
	if resp.StatusCode != 200 {
		return nil, fmt.Errorf("overpass: status %d: %s", resp.StatusCode, truncate(string(body), 200))
	}
	var doc struct {
		Elements []struct {
			Type  string            `json:"type"`
			ID    int64             `json:"id"`
			Tags  map[string]string `json:"tags"`
			Geom  []struct {
				Lat float64 `json:"lat"`
				Lon float64 `json:"lon"`
			} `json:"geometry"`
			NodeIDs []int64 `json:"nodes"` // parallel to Geom
		} `json:"elements"`
	}
	if err := json.Unmarshal(body, &doc); err != nil {
		return nil, fmt.Errorf("overpass json: %w (body: %s)", err, truncate(string(body), 120))
	}
	var ways []Way
	for _, e := range doc.Elements {
		if e.Type != "way" || len(e.Geom) < 2 || len(e.NodeIDs) != len(e.Geom) {
			continue
		}
		w := Way{ID: e.ID, Highway: e.Tags["highway"], Ref: e.Tags["ref"]}
		for i, g := range e.Geom {
			w.Nodes = append(w.Nodes, WayNode{ID: e.NodeIDs[i], Lat: g.Lat, Lon: g.Lon})
		}
		ways = append(ways, w)
	}
	return ways, nil
}

// classRank orders highway classes by importance (higher = more likely the
// intended road for an incident reported near it).
func classRank(h string) int {
	switch h {
	case "motorway":
		return 7
	case "trunk":
		return 6
	case "primary":
		return 5
	case "secondary":
		return 4
	case "tertiary":
		return 3
	case "unclassified":
		return 2
	default:
		return 1
	}
}

// classWindowM is the distance within which a higher-class road beats a
// closer lower-class one: an incident reported "at I-90" means the motorway
// even when a service road or footway is nearer.
const classWindowM = 150.0

// ClosestNodePair finds the highway segment the incident is on and returns
// its two OSM endpoint node IDs. Selection: within classWindowM, the
// highest-class road wins (ties → nearest); beyond it, plain nearest.
func ClosestNodePair(ways []Way, lat, lon float64) (way Way, nodeA, nodeB int64, distM float64, ok bool) {
	p := geo.Point{Lat: lat, Lon: lon}
	type seg struct {
		way   Way
		a, b  int64
		distM float64
		rank  int
	}
	var best *seg
	for _, w := range ways {
		rank := classRank(w.Highway)
		for i := 0; i+1 < len(w.Nodes); i++ {
			d := geo.DistToPolylineMeters(p, []geo.Point{{Lat: w.Nodes[i].Lat, Lon: w.Nodes[i].Lon}, {Lat: w.Nodes[i+1].Lat, Lon: w.Nodes[i+1].Lon}})
			if d > classWindowM && best != nil && best.distM <= classWindowM {
				continue
			}
			better := false
			if best == nil {
				better = true
			} else if rank > best.rank && d <= classWindowM {
				better = true
			} else if rank == best.rank && d < best.distM {
				better = true
			} else if rank < best.rank && best.distM > classWindowM && d < best.distM {
				better = true // nothing in the window; fall back to nearest
			}
			if better {
				best = &seg{way: w, a: w.Nodes[i].ID, b: w.Nodes[i+1].ID, distM: d, rank: rank}
			}
		}
	}
	if best == nil {
		return
	}
	return best.way, best.a, best.b, best.distM, true
}

// ExpandToRadius returns node pairs along the matched way covering ±radiusM
// of the incident point (incidents affect a stretch, not a single edge).
func ExpandToRadius(way Way, hitA, hitB int64, radiusM float64) [][2]int64 {
	found := -1
	for i := 0; i+1 < len(way.Nodes); i++ {
		if way.Nodes[i].ID == hitA && way.Nodes[i+1].ID == hitB {
			found = i
			break
		}
	}
	if found < 0 {
		if hitA != 0 {
			return [][2]int64{{hitA, hitB}}
		}
		return nil
	}
	start := found
	back := 0.0
	for start > 0 && back+segmentLen(way, start-1) <= radiusM {
		back += segmentLen(way, start - 1)
		start--
	}
	end := found
	fwd := 0.0
	for end+1 < len(way.Nodes)-1 && fwd+segmentLen(way, end+1) <= radiusM {
		fwd += segmentLen(way, end+1)
		end++
	}
	var pairs [][2]int64
	for i := start; i <= end; i++ {
		pairs = append(pairs, [2]int64{way.Nodes[i].ID, way.Nodes[i+1].ID})
	}
	return pairs
}

func segmentLen(w Way, i int) float64 {
	return geo.Meters(geo.Point{Lat: w.Nodes[i].Lat, Lon: w.Nodes[i].Lon}, geo.Point{Lat: w.Nodes[i+1].Lat, Lon: w.Nodes[i+1].Lon})
}

func truncate(s string, n int) string {
	if len(s) <= n {
		return s
	}
	return s[:n] + "…"
}