package health

import (
	"encoding/json"
	"net"
	"net/http"
	"strings"
	"sync"
	"time"

	"go.uber.org/zap"
	"golang.org/x/time/rate"

	"github.com/veylant/ia-gateway/internal/apierror"
	"github.com/veylant/ia-gateway/internal/pii"
)

// PlaygroundAnalyzeRequest is the JSON body for POST /playground/analyze.
type PlaygroundAnalyzeRequest struct {
	Text string `json:"text"`
}

// PlaygroundAnalyzeResponse is the JSON response for POST /playground/analyze.
type PlaygroundAnalyzeResponse struct {
	Entities      []PlaygroundEntity `json:"entities"`
	AnonymizedText string            `json:"anonymized_text"`
}

// PlaygroundEntity is a detected PII entity returned by the playground endpoint.
type PlaygroundEntity struct {
	Type       string  `json:"type"`
	Value      string  `json:"value,omitempty"` // original value (shown in UI badge)
	Pseudonym  string  `json:"pseudonym,omitempty"`
	Start      int     `json:"start"`
	End        int     `json:"end"`
	Confidence float64 `json:"confidence"`
	Layer      string  `json:"layer"`
}

// playgroundIPLimiter holds per-IP token bucket limiters.
// Limiters are evicted after 5 minutes of inactivity.
type playgroundIPLimiter struct {
	mu       sync.Mutex
	limiters map[string]*ipEntry
}

type ipEntry struct {
	limiter  *rate.Limiter
	lastSeen time.Time
}

var globalPlaygroundLimiter = &playgroundIPLimiter{
	limiters: make(map[string]*ipEntry),
}

func (p *playgroundIPLimiter) get(ip string) *rate.Limiter {
	p.mu.Lock()
	defer p.mu.Unlock()

	entry, ok := p.limiters[ip]
	if !ok {
		// 20 req/min per IP, burst of 5.
		entry = &ipEntry{limiter: rate.NewLimiter(rate.Every(3*time.Second), 5)}
		p.limiters[ip] = entry
	}
	entry.lastSeen = time.Now()

	// Evict stale entries (>5 min inactive) to prevent unbounded memory growth.
	for k, v := range p.limiters {
		if time.Since(v.lastSeen) > 5*time.Minute {
			delete(p.limiters, k)
		}
	}
	return entry.limiter
}

// PlaygroundAnalyzeHandler returns an HTTP handler for POST /playground/analyze.
// The endpoint is public (no JWT required) and rate-limited to 20 req/min per IP.
// If piiClient is nil the handler returns a simulated response so the playground
// page remains usable even when the PII sidecar is not running.
func PlaygroundAnalyzeHandler(piiClient *pii.Client, logger *zap.Logger) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		// IP-based rate limiting.
		ip := clientIP(r)
		if !globalPlaygroundLimiter.get(ip).Allow() {
			apierror.WriteError(w, apierror.NewRateLimitError(
				"playground rate limit exceeded — max 20 requests/minute per IP",
			))
			return
		}

		// Parse request body.
		var req PlaygroundAnalyzeRequest
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			apierror.WriteError(w, apierror.NewBadRequestError("invalid JSON: "+err.Error()))
			return
		}

		var resp PlaygroundAnalyzeResponse

		if req.Text == "" {
			resp = PlaygroundAnalyzeResponse{Entities: []PlaygroundEntity{}, AnonymizedText: ""}
			writeJSON(w, resp)
			return
		}

		// Delegate to PII service if available.
		if piiClient != nil {
			result, err := piiClient.Detect(r.Context(), req.Text, "playground", "public-playground", true, false)
			if err == nil {
				entities := make([]PlaygroundEntity, 0, len(result.Entities))
				for _, e := range result.Entities {
					entities = append(entities, PlaygroundEntity{
						Type:       e.EntityType,
						Value:      req.Text[clamp(int(e.Start), 0, len(req.Text)):clamp(int(e.End), 0, len(req.Text))],
						Pseudonym:  e.Pseudonym,
						Start:      int(e.Start),
						End:        int(e.End),
						Confidence: float64(e.Confidence),
						Layer:      e.DetectionLayer,
					})
				}
				resp = PlaygroundAnalyzeResponse{
					Entities:       entities,
					AnonymizedText: result.AnonymizedText,
				}
				writeJSON(w, resp)
				return
			}
			logger.Warn("playground PII detection failed — using simulated response", zap.Error(err))
		}

		// PII service unavailable: return a deterministic simulated response so the
		// playground page still demonstrates the feature.
		resp = simulatedResponse(req.Text)
		writeJSON(w, resp)
	}
}

// simulatedResponse returns a static example response when the PII service is down.
func simulatedResponse(text string) PlaygroundAnalyzeResponse {
	return PlaygroundAnalyzeResponse{
		Entities: []PlaygroundEntity{
			{Type: "PERSON", Value: "(example)", Pseudonym: "[PERSON_1]", Start: 0, End: 0, Confidence: 0.99, Layer: "simulated"},
			{Type: "EMAIL_ADDRESS", Value: "(example)", Pseudonym: "[EMAIL_1]", Start: 0, End: 0, Confidence: 0.99, Layer: "simulated"},
		},
		AnonymizedText: strings.TrimSpace(text) + "\n\n[PII service offline — showing example output]",
	}
}

// clientIP extracts the real client IP from the request, respecting X-Real-IP
// and X-Forwarded-For headers set by Traefik / Nginx.
func clientIP(r *http.Request) string {
	if ip := r.Header.Get("X-Real-IP"); ip != "" {
		if parsed := net.ParseIP(strings.TrimSpace(ip)); parsed != nil {
			return parsed.String()
		}
	}
	if forwarded := r.Header.Get("X-Forwarded-For"); forwarded != "" {
		// X-Forwarded-For may be a comma-separated list; use the first (client) IP.
		parts := strings.SplitN(forwarded, ",", 2)
		if parsed := net.ParseIP(strings.TrimSpace(parts[0])); parsed != nil {
			return parsed.String()
		}
	}
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return r.RemoteAddr
	}
	return host
}

func clamp(v, min, max int) int {
	if v < min {
		return min
	}
	if v > max {
		return max
	}
	return v
}

func writeJSON(w http.ResponseWriter, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusOK)
	_ = json.NewEncoder(w).Encode(v)
}