package collector

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"math"
	"net/http"
	"sort"
	"strings"
	"time"

	"go.opentelemetry.io/collector/pdata/pcommon"
	"go.opentelemetry.io/collector/pdata/plog"
)

const (
	maxVitalsBody   = 32 << 10
	maxVitalsString = 300
	maxAttribution  = 24
)

// vitalThresholds are Google's Core Web Vitals boundaries: [good, poor].
// Ratings are recomputed here so a client cannot report a misleading one.
var vitalThresholds = map[string][2]float64{
	"LCP":  {2500, 4000},
	"INP":  {200, 500},
	"CLS":  {0.1, 0.25},
	"FCP":  {1800, 3000},
	"TTFB": {800, 1800},
}

func vitalRating(name string, v float64) string {
	t := vitalThresholds[name]
	switch {
	case v <= t[0]:
		return "good"
	case v <= t[1]:
		return "needs-improvement"
	default:
		return "poor"
	}
}

func formatVital(name string, v float64) string {
	switch name {
	case "CLS":
		return fmt.Sprintf("%.3f", v)
	case "INP", "TTFB":
		return fmt.Sprintf("%dms", int(math.Round(v)))
	default:
		return fmt.Sprintf("%.2fs", v/1000)
	}
}

type vitalMetric struct {
	Value       float64        `json:"value"`
	Delta       float64        `json:"delta,omitempty"`
	ID          string         `json:"id,omitempty"`
	Attribution map[string]any `json:"attribution,omitempty"`
}

// vitalsBeacon is the payload otel-rum.js sends once per page view (and again,
// as a fuller snapshot, if the page is hidden more than once, e.g. INP
// changing after a tab switch). The same pageView id marks snapshots of one load.
type vitalsBeacon struct {
	Service     string                 `json:"service"`
	Environment string                 `json:"environment"`
	Release     string                 `json:"release"`
	Session     string                 `json:"session"`
	PageView    string                 `json:"pageView"`
	URL         string                 `json:"url"`
	UserAgent   string                 `json:"ua"`
	Viewport    string                 `json:"viewport"`
	Navigation  string                 `json:"nav"`
	Connection  string                 `json:"conn"`
	Metrics     map[string]vitalMetric `json:"metrics"`
}

func clip(s string) string {
	if len(s) > maxVitalsString {
		return s[:maxVitalsString]
	}
	return s
}

// cleanAttribution keeps only bounded scalar values.
func cleanAttribution(in map[string]any) map[string]any {
	out := make(map[string]any, len(in))
	keys := make([]string, 0, len(in))
	for k := range in {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	for _, k := range keys {
		if len(out) >= maxAttribution {
			break
		}
		switch v := in[k].(type) {
		case string:
			out[clip(k)] = clip(v)
		case float64:
			if !math.IsNaN(v) && !math.IsInf(v, 0) {
				out[clip(k)] = v
			}
		case bool:
			out[clip(k)] = v
		}
	}
	return out
}

// HandleVitals ingests a Web Vitals beacon and stores it as one INFO log
// record (scope "otel-rum", rum.event=page_vitals), so search, retention and
// the UI treat it like any other frontend telemetry.
func (c *Collector) HandleVitals(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	if !c.checkIngest(w, r) {
		return
	}

	// sendBeacon posts text/plain, so decode regardless of content type.
	var b vitalsBeacon
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, maxVitalsBody)).Decode(&b); err != nil {
		http.Error(w, "invalid vitals payload", http.StatusBadRequest)
		return
	}
	logs, ok := b.toLogs(time.Now())
	if !ok {
		http.Error(w, "no valid metrics", http.StatusBadRequest)
		return
	}
	if err := c.ConsumeLogs(context.Background(), logs); err != nil {
		log.Printf("failed to consume vitals: %v", err)
		http.Error(w, "failed to store vitals", http.StatusInternalServerError)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// toLogs converts the beacon into a single log record; ok is false when it
// carries no recognised, finite metric.
func (b *vitalsBeacon) toLogs(now time.Time) (plog.Logs, bool) {
	metrics := map[string]map[string]any{}
	names := make([]string, 0, len(b.Metrics))
	for name, m := range b.Metrics {
		if _, known := vitalThresholds[name]; !known || math.IsNaN(m.Value) || math.IsInf(m.Value, 0) || m.Value < 0 {
			continue
		}
		entry := map[string]any{"value": m.Value, "rating": vitalRating(name, m.Value)}
		if m.ID != "" {
			entry["id"] = clip(m.ID)
		}
		if len(m.Attribution) > 0 {
			entry["attribution"] = cleanAttribution(m.Attribution)
		}
		metrics[name] = entry
		names = append(names, name)
	}
	if len(names) == 0 {
		return plog.Logs{}, false
	}
	sort.Strings(names)

	parts := make([]string, 0, len(names))
	worst := "good"
	for _, n := range names {
		parts = append(parts, n+" "+formatVital(n, b.Metrics[n].Value))
		switch metrics[n]["rating"] {
		case "poor":
			worst = "poor"
		case "needs-improvement":
			if worst == "good" {
				worst = "needs-improvement"
			}
		}
	}
	message := strings.Join(parts, " · ")
	body, _ := json.Marshal(map[string]any{"message": message, "metrics": metrics})

	service := clip(b.Service)
	if service == "" {
		service = "frontend"
	}

	ld := plog.NewLogs()
	rl := ld.ResourceLogs().AppendEmpty()
	rl.Resource().Attributes().PutStr("service.name", service)
	sl := rl.ScopeLogs().AppendEmpty()
	sl.Scope().SetName("otel-rum")
	rec := sl.LogRecords().AppendEmpty()
	rec.SetTimestamp(pcommon.NewTimestampFromTime(now))
	rec.SetSeverityText("INFO")
	rec.SetSeverityNumber(plog.SeverityNumberInfo)
	rec.Body().SetStr(string(body))

	a := rec.Attributes()
	a.PutStr("source", "frontend")
	a.PutStr("rum.event", "page_vitals")
	a.PutStr("vitals.rating", worst)
	for k, v := range map[string]string{
		"page_view.id":        b.PageView,
		"session.id":          b.Session,
		"browser.url":         b.URL,
		"browser.userAgent":   b.UserAgent,
		"browser.viewport":    b.Viewport,
		"navigation.type":     b.Navigation,
		"network.connection":  b.Connection,
		"service.release":     b.Release,
		"service.environment": b.Environment,
	} {
		if v != "" {
			a.PutStr(k, clip(v))
		}
	}
	// Flat, individually searchable values alongside the structured body.
	for _, n := range names {
		lower := strings.ToLower(n)
		a.PutDouble("vitals."+lower, b.Metrics[n].Value)
		a.PutStr("vitals."+lower+".rating", metrics[n]["rating"].(string))
	}
	return ld, true
}