package telemetry

import (
	"context"
	"errors"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	otlploggrpc "go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc"
	otlpmetricgrpc "go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
	otlptracegrpc "go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
	"go.opentelemetry.io/otel/log/global"
	"go.opentelemetry.io/otel/propagation"
	sdklog "go.opentelemetry.io/otel/sdk/log"
	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
	"go.opentelemetry.io/otel/sdk/resource"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.24.0"
)

// Config holds OTel bootstrap configuration.
type Config struct {
	// ServiceName identifies the service in traces, metrics, and logs.
	ServiceName string `env:"OTEL_SERVICE_NAME,required"`
	// ServiceVersion is the deployed version (e.g. "1.4.2").
	ServiceVersion string `env:"OTEL_SERVICE_VERSION" envDefault:"unknown"`
	// Environment is the deployment environment (e.g. "production", "staging").
	Environment string `env:"OTEL_ENVIRONMENT" envDefault:"development"`
	// OTLPEndpoint is the OTLP gRPC collector address (e.g. "alloy:4317").
	OTLPEndpoint string `env:"OTEL_EXPORTER_OTLP_ENDPOINT,required"`
	// OTLPInsecure disables TLS for the OTLP connection. Set true in development.
	OTLPInsecure bool `env:"OTEL_EXPORTER_OTLP_INSECURE" envDefault:"false"`
}

// New bootstraps the full OTel SDK:
//   - TracerProvider  → OTLP gRPC → Grafana Alloy → Tempo
//   - MeterProvider   → OTLP gRPC → Grafana Alloy → Mimir
//   - LoggerProvider  → OTLP gRPC → Grafana Alloy → Loki
//
// Sets the three OTel globals so all micro-libs using the global API
// auto-instrument without importing this module.
//
// The returned shutdown function flushes all exporters and must be called
// before process exit (defer it in main or wire it into the launcher).
// Returns (shutdown, nil) on success, (nil, err) on failure.
func New(ctx context.Context, cfg Config) (func(context.Context) error, error) {
	res := newResource(cfg)

	// --- TracerProvider (traces → Tempo) ---
	traceOpts := []otlptracegrpc.Option{
		otlptracegrpc.WithEndpoint(cfg.OTLPEndpoint),
	}
	if cfg.OTLPInsecure {
		traceOpts = append(traceOpts, otlptracegrpc.WithInsecure())
	}
	traceExporter, err := otlptracegrpc.New(ctx, traceOpts...)
	if err != nil {
		return nil, err
	}
	tp := sdktrace.NewTracerProvider(
		sdktrace.WithBatcher(traceExporter),
		sdktrace.WithResource(res),
	)
	otel.SetTracerProvider(tp)
	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(
		propagation.TraceContext{},
		propagation.Baggage{},
	))

	// --- MeterProvider (metrics → Mimir) ---
	metricOpts := []otlpmetricgrpc.Option{
		otlpmetricgrpc.WithEndpoint(cfg.OTLPEndpoint),
	}
	if cfg.OTLPInsecure {
		metricOpts = append(metricOpts, otlpmetricgrpc.WithInsecure())
	}
	metricExporter, err := otlpmetricgrpc.New(ctx, metricOpts...)
	if err != nil {
		_ = tp.Shutdown(ctx)
		return nil, err
	}
	mp := sdkmetric.NewMeterProvider(
		sdkmetric.WithReader(sdkmetric.NewPeriodicReader(metricExporter)),
		sdkmetric.WithResource(res),
	)
	otel.SetMeterProvider(mp)

	// --- LoggerProvider (logs → Loki) ---
	logOpts := []otlploggrpc.Option{
		otlploggrpc.WithEndpoint(cfg.OTLPEndpoint),
	}
	if cfg.OTLPInsecure {
		logOpts = append(logOpts, otlploggrpc.WithInsecure())
	}
	logExporter, err := otlploggrpc.New(ctx, logOpts...)
	if err != nil {
		_ = tp.Shutdown(ctx)
		_ = mp.Shutdown(ctx)
		return nil, err
	}
	lp := sdklog.NewLoggerProvider(
		sdklog.WithProcessor(sdklog.NewBatchProcessor(logExporter)),
		sdklog.WithResource(res),
	)
	global.SetLoggerProvider(lp)

	shutdown := func(ctx context.Context) error {
		return errors.Join(
			tp.Shutdown(ctx),
			mp.Shutdown(ctx),
			lp.Shutdown(ctx),
		)
	}
	return shutdown, nil
}

// newResource builds an OTel resource with service identity and environment attributes.
func newResource(cfg Config) *resource.Resource {
	r, _ := resource.Merge(
		resource.Default(),
		resource.NewWithAttributes(
			semconv.SchemaURL,
			semconv.ServiceName(cfg.ServiceName),
			semconv.ServiceVersion(cfg.ServiceVersion),
			attribute.String("deployment.environment", cfg.Environment),
		),
	)
	return r
}