// Package observability provides OpenTelemetry tracing, Prometheus metrics, and structured logging
package observability

import (
	"context"
	"fmt"
	"net/http"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
	"go.opentelemetry.io/otel/propagation"
	"go.opentelemetry.io/otel/sdk/resource"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.21.0"
	"go.opentelemetry.io/otel/trace"
	"go.uber.org/zap"
	"google.golang.org/grpc"
	"google.golang.org/grpc/status"
)

// Config for observability
type Config struct {
	ServiceName     string
	ServiceVersion  string
	TracingEnabled  bool
	TracingEndpoint string
	MetricsEnabled  bool
	MetricsPort     int
}

// Metrics for the RAG service
var (
	queryCounter = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Name: "amaniquery_queries_total",
			Help: "Total number of queries processed",
		},
		[]string{"status", "cache_hit", "strategy"},
	)

	queryDuration = promauto.NewHistogramVec(
		prometheus.HistogramOpts{
			Name:    "amaniquery_query_duration_seconds",
			Help:    "Query processing duration in seconds",
			Buckets: []float64{0.1, 0.25, 0.5, 1, 2.5, 5, 10},
		},
		[]string{"strategy"},
	)

	retrievalDuration = promauto.NewHistogramVec(
		prometheus.HistogramOpts{
			Name:    "amaniquery_retrieval_duration_seconds",
			Help:    "Document retrieval duration in seconds",
			Buckets: []float64{0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1},
		},
		[]string{"type"},
	)

	generationDuration = promauto.NewHistogram(
		prometheus.HistogramOpts{
			Name:    "amaniquery_generation_duration_seconds",
			Help:    "LLM generation duration in seconds",
			Buckets: []float64{0.5, 1, 2.5, 5, 10, 30},
		},
	)

	tokensUsed = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Name: "amaniquery_tokens_total",
			Help: "Total tokens used",
		},
		[]string{"type"},
	)

	cacheHits = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Name: "amaniquery_cache_hits_total",
			Help: "Cache hit count",
		},
		[]string{"tier"},
	)

	cacheMisses = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Name: "amaniquery_cache_misses_total",
			Help: "Cache miss count",
		},
		[]string{"tier"},
	)

	documentsIndexed = promauto.NewCounter(
		prometheus.CounterOpts{
			Name: "amaniquery_documents_indexed_total",
			Help: "Total documents indexed",
		},
	)

	activeConnections = promauto.NewGauge(
		prometheus.GaugeOpts{
			Name: "amaniquery_active_connections",
			Help: "Number of active connections",
		},
	)

	errorCounter = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Name: "amaniquery_errors_total",
			Help: "Total errors by type",
		},
		[]string{"type", "component"},
	)
)

// InitProvider initializes the OpenTelemetry tracer provider
func InitProvider(cfg Config) (func(context.Context) error, error) {
	if !cfg.TracingEnabled {
		return func(ctx context.Context) error { return nil }, nil
	}

	ctx := context.Background()

	// Create resource
	res, err := resource.Merge(
		resource.Default(),
		resource.NewWithAttributes(
			semconv.SchemaURL,
			semconv.ServiceName(cfg.ServiceName),
			semconv.ServiceVersion(cfg.ServiceVersion),
		),
	)
	if err != nil {
		return nil, err
	}

	// Create OTLP exporter
	exporter, err := otlptracegrpc.New(ctx,
		otlptracegrpc.WithEndpoint(cfg.TracingEndpoint),
		otlptracegrpc.WithInsecure(),
	)
	if err != nil {
		return nil, err
	}

	// Create tracer provider
	tp := sdktrace.NewTracerProvider(
		sdktrace.WithBatcher(exporter),
		sdktrace.WithResource(res),
		sdktrace.WithSampler(sdktrace.AlwaysSample()),
	)

	// Set global tracer provider
	otel.SetTracerProvider(tp)
	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(
		propagation.TraceContext{},
		propagation.Baggage{},
	))

	return tp.Shutdown, nil
}

// StartMetricsServer starts the Prometheus metrics server
func StartMetricsServer(port int) *http.Server {
	mux := http.NewServeMux()
	mux.Handle("/metrics", promhttp.Handler())
	mux.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
		w.Write([]byte("OK"))
	})

	server := &http.Server{
		Addr:    fmt.Sprintf(":%d", port),
		Handler: mux,
	}

	go func() {
		if err := server.ListenAndServe(); err != http.ErrServerClosed {
			// Log error
		}
	}()

	return server
}

// RecordQuery records query metrics
func RecordQuery(status string, cacheHit bool, strategy string, duration time.Duration) {
	cacheHitStr := "false"
	if cacheHit {
		cacheHitStr = "true"
	}
	queryCounter.WithLabelValues(status, cacheHitStr, strategy).Inc()
	queryDuration.WithLabelValues(strategy).Observe(duration.Seconds())
}

// RecordRetrieval records retrieval metrics
func RecordRetrieval(retrievalType string, duration time.Duration) {
	retrievalDuration.WithLabelValues(retrievalType).Observe(duration.Seconds())
}

// RecordGeneration records LLM generation metrics
func RecordGeneration(duration time.Duration) {
	generationDuration.Observe(duration.Seconds())
}

// RecordTokens records token usage
func RecordTokens(tokenType string, count int) {
	tokensUsed.WithLabelValues(tokenType).Add(float64(count))
}

// RecordCacheHit records a cache hit
func RecordCacheHit(tier string) {
	cacheHits.WithLabelValues(tier).Inc()
}

// RecordCacheMiss records a cache miss
func RecordCacheMiss(tier string) {
	cacheMisses.WithLabelValues(tier).Inc()
}

// RecordDocumentIndexed records a document being indexed
func RecordDocumentIndexed() {
	documentsIndexed.Inc()
}

// RecordError records an error
func RecordError(errorType, component string) {
	errorCounter.WithLabelValues(errorType, component).Inc()
}

// IncrementConnections increments active connections
func IncrementConnections() {
	activeConnections.Inc()
}

// DecrementConnections decrements active connections
func DecrementConnections() {
	activeConnections.Dec()
}

// UnaryServerInterceptor returns a gRPC unary server interceptor for tracing
func UnaryServerInterceptor() grpc.UnaryServerInterceptor {
	return func(
		ctx context.Context,
		req interface{},
		info *grpc.UnaryServerInfo,
		handler grpc.UnaryHandler,
	) (interface{}, error) {
		tracer := otel.Tracer("grpc-server")
		ctx, span := tracer.Start(ctx, info.FullMethod,
			trace.WithSpanKind(trace.SpanKindServer),
		)
		defer span.End()

		start := time.Now()
		resp, err := handler(ctx, req)
		duration := time.Since(start)

		if err != nil {
			span.SetAttributes(attribute.String("error", err.Error()))
			st, _ := status.FromError(err)
			span.SetAttributes(attribute.String("grpc.status_code", st.Code().String()))
		}

		span.SetAttributes(
			attribute.String("grpc.method", info.FullMethod),
			attribute.Int64("grpc.duration_ms", duration.Milliseconds()),
		)

		return resp, err
	}
}

// StreamServerInterceptor returns a gRPC stream server interceptor for tracing
func StreamServerInterceptor() grpc.StreamServerInterceptor {
	return func(
		srv interface{},
		ss grpc.ServerStream,
		info *grpc.StreamServerInfo,
		handler grpc.StreamHandler,
	) error {
		tracer := otel.Tracer("grpc-server")
		ctx, span := tracer.Start(ss.Context(), info.FullMethod,
			trace.WithSpanKind(trace.SpanKindServer),
		)
		defer span.End()

		wrappedStream := &tracedServerStream{
			ServerStream: ss,
			ctx:          ctx,
		}

		err := handler(srv, wrappedStream)
		if err != nil {
			span.SetAttributes(attribute.String("error", err.Error()))
		}

		return err
	}
}

type tracedServerStream struct {
	grpc.ServerStream
	ctx context.Context
}

func (s *tracedServerStream) Context() context.Context {
	return s.ctx
}

// Logger creates a structured logger
func NewLogger(level, format string) (*zap.Logger, error) {
	var config zap.Config
	if format == "json" {
		config = zap.NewProductionConfig()
	} else {
		config = zap.NewDevelopmentConfig()
	}

	switch level {
	case "debug":
		config.Level = zap.NewAtomicLevelAt(zap.DebugLevel)
	case "info":
		config.Level = zap.NewAtomicLevelAt(zap.InfoLevel)
	case "warn":
		config.Level = zap.NewAtomicLevelAt(zap.WarnLevel)
	case "error":
		config.Level = zap.NewAtomicLevelAt(zap.ErrorLevel)
	default:
		config.Level = zap.NewAtomicLevelAt(zap.InfoLevel)
	}

	return config.Build()
}