package tracing

import (
	"context"
	"errors"
	"fmt"

	"git.lzcwy.cn/zhengchiliu/zt-closet-manage-backend/pkg/setting"

	"go.opentelemetry.io/contrib/instrumentation/runtime"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc"
	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
	logglobal "go.opentelemetry.io/otel/log/global"
	metricnoop "go.opentelemetry.io/otel/metric/noop"
	"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"
	"go.opentelemetry.io/otel/trace"
	"go.opentelemetry.io/otel/trace/noop"
)

// defaultServiceName 缺省服务名。
const defaultServiceName = "zt-closet-manage-backend"

// noopShutdown 安全的空关闭函数。
func noopShutdown(context.Context) error { return nil }

// NewOTelProvider 初始化 OpenTelemetry 三大信号（Traces/Metrics/Logs）并通过 OTLP gRPC 导出。
//
// 返回：
//   - trace.Tracer：全局 Tracer（供 global.Tracer 使用）；
//   - func(ctx) error：聚合的优雅关闭函数，进程退出时调用以 flush 三个 Provider；
//   - error：初始化错误。
//
// 行为约定：
//   - cfg.Enabled=false：返回 no-op Tracer 与空 Shutdown，不建立任何导出器（业务层 Tracer.Start 仍安全）。
//   - cfg.Insecure=true：OTLP gRPC 使用非 TLS（内网采集器）。
//   - 导出器采用惰性连接，采集器不可用时不阻断启动，仅后台重试。
func NewOTelProvider(cfg *setting.OtelSettingS) (trace.Tracer, func(context.Context) error, error) {
	name := defaultServiceName
	if cfg != nil && cfg.ServiceName != "" {
		name = cfg.ServiceName
	}

	// 未启用：降级为 no-op。
	if cfg == nil || !cfg.Enabled {
		return noop.NewTracerProvider().Tracer(name), noopShutdown, nil
	}

	ctx := context.Background()

	res, err := resource.New(ctx, resource.WithAttributes(
		attribute.String("service.name", name),
		attribute.String("service.version", valueOr(cfg.ServiceVersion, "unknown")),
		attribute.String("deployment.environment", valueOr(cfg.Environment, "unknown")),
	))
	if err != nil {
		return noop.NewTracerProvider().Tracer(name), noopShutdown, fmt.Errorf("otel build resource: %w", err)
	}

	endpoint := cfg.ExporterEndpoint

	// ===== Traces =====
	traceOpts := []otlptracegrpc.Option{otlptracegrpc.WithEndpoint(endpoint)}
	if cfg.Insecure {
		traceOpts = append(traceOpts, otlptracegrpc.WithInsecure())
	}
	traceExp, err := otlptracegrpc.New(ctx, traceOpts...)
	if err != nil {
		return noop.NewTracerProvider().Tracer(name), noopShutdown, fmt.Errorf("otel trace exporter: %w", err)
	}

	ratio := cfg.SamplerRatio
	if ratio <= 0 {
		ratio = 1.0
	}
	tp := sdktrace.NewTracerProvider(
		sdktrace.WithBatcher(traceExp),
		sdktrace.WithResource(res),
		sdktrace.WithSampler(sdktrace.ParentBased(sdktrace.TraceIDRatioBased(ratio))),
	)
	otel.SetTracerProvider(tp)
	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(
		propagation.TraceContext{},
		propagation.Baggage{},
	))

	// ===== Metrics =====
	metricOpts := []otlpmetricgrpc.Option{otlpmetricgrpc.WithEndpoint(endpoint)}
	if cfg.Insecure {
		metricOpts = append(metricOpts, otlpmetricgrpc.WithInsecure())
	}
	metricExp, err := otlpmetricgrpc.New(ctx, metricOpts...)
	if err != nil {
		// 已建 trace，尽力关闭并恢复全局默认 provider，避免留下已关闭的 provider。
		_ = tp.Shutdown(ctx)
		otel.SetTracerProvider(noop.NewTracerProvider())
		return noop.NewTracerProvider().Tracer(name), noopShutdown, fmt.Errorf("otel metric exporter: %w", err)
	}
	mp := sdkmetric.NewMeterProvider(
		sdkmetric.WithResource(res),
		sdkmetric.WithReader(sdkmetric.NewPeriodicReader(metricExp)),
	)
	otel.SetMeterProvider(mp)

	// Go runtime 指标采集（GC、goroutine、内存等）。
	if rerr := runtime.Start(runtime.WithMeterProvider(mp)); rerr != nil {
		// 非致命，仅记录。
		fmt.Printf("otel runtime metrics start failed: %v\n", rerr)
	}

	// ===== Logs =====
	logOpts := []otlploggrpc.Option{otlploggrpc.WithEndpoint(endpoint)}
	if cfg.Insecure {
		logOpts = append(logOpts, otlploggrpc.WithInsecure())
	}
	logExp, err := otlploggrpc.New(ctx, logOpts...)
	if err != nil {
		_ = tp.Shutdown(ctx)
		_ = mp.Shutdown(ctx)
		otel.SetTracerProvider(noop.NewTracerProvider())
		otel.SetMeterProvider(metricnoop.NewMeterProvider())
		return noop.NewTracerProvider().Tracer(name), noopShutdown, fmt.Errorf("otel log exporter: %w", err)
	}
	lp := sdklog.NewLoggerProvider(
		sdklog.WithResource(res),
		sdklog.WithProcessor(sdklog.NewBatchProcessor(logExp)),
	)
	logglobal.SetLoggerProvider(lp)

	// 聚合优雅关闭：依次 flush/关闭三个 Provider。
	shutdown := func(ctx context.Context) error {
		return errors.Join(
			tp.Shutdown(ctx),
			mp.Shutdown(ctx),
			lp.Shutdown(ctx),
		)
	}

	return tp.Tracer(name), shutdown, nil
}

// valueOr 返回 v，v 为空时返回 def。
func valueOr(v, def string) string {
	if v == "" {
		return def
	}
	return v
}