package tracing

import (
	"context"

	"github.com/go-logr/logr"
	"go.opentelemetry.io/otel/trace"
	logf "sigs.k8s.io/controller-runtime/pkg/log"
)

// baseLoggerKey stores the pre-enrichment logger. logr sinks never see a
// context, so trace IDs must ride on the logger as WithValues — and zap does
// not dedupe repeated keys, so each nested span must re-derive from the same
// base instead of stacking traceID/spanID onto an already-enriched logger.
type baseLoggerKey struct{}

// Start begins a span from the global tracer and returns a context whose
// logf.FromContext logger carries the span's traceID/spanID. With tracing
// disabled the span is a no-op with an invalid span context and the logger
// is left untouched.
//
// Trade-off, documented: values pushed via logf.IntoContext *between* two
// Start calls are dropped by the inner Start's re-derivation. Nothing
// first-party does that; controller-runtime's per-reconcile logger
// (reconcileID etc.) is captured as the base and survives.
func Start(ctx context.Context, name string, opts ...trace.SpanStartOption) (context.Context, trace.Span) {
	return StartSpan(ctx, newOptions(nil).tracer(), name, opts...)
}

// StartSpan is Start with an explicit tracer, for decorators that carry
// their own (test-injected) TracerProvider.
func StartSpan(ctx context.Context, tracer trace.Tracer, name string, opts ...trace.SpanStartOption) (context.Context, trace.Span) {
	ctx, span := tracer.Start(ctx, name, opts...)
	sc := span.SpanContext()
	if !sc.IsValid() {
		return ctx, span
	}
	base, ok := ctx.Value(baseLoggerKey{}).(logr.Logger)
	if !ok {
		base = logf.FromContext(ctx)
		ctx = context.WithValue(ctx, baseLoggerKey{}, base)
	}
	return logf.IntoContext(ctx, withSpanValues(base, sc)), span
}

// ContextWithLogger seeds ctx with base as both the current logger and the
// base for span enrichment. If ctx already carries a valid span (the HTTP
// middleware calls this inside the otelhttp handler), the logger is
// enriched immediately.
func ContextWithLogger(ctx context.Context, base logr.Logger) context.Context {
	ctx = context.WithValue(ctx, baseLoggerKey{}, base)
	if sc := trace.SpanContextFromContext(ctx); sc.IsValid() {
		return logf.IntoContext(ctx, withSpanValues(base, sc))
	}
	return logf.IntoContext(ctx, base)
}

// withSpanValues uses lowerCamel keys to match the house style
// (reconcileID, providerID); Grafana/Loki derived fields must match
// "traceID", not the trace_id default.
func withSpanValues(base logr.Logger, sc trace.SpanContext) logr.Logger {
	return base.WithValues("traceID", sc.TraceID().String(), "spanID", sc.SpanID().String())
}