package main

import (
	"fmt"
	"os"
	"sync"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/trace"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/services/gateway"
)

// newAppTraceWriter builds the composition root's trace writer: the JSONL stderr
// recorder (the local structured log of every span) plus room for the gateway's
// observability sink, which can only be registered once the gateway exists (see
// wireGatewayTraceSink).
func newAppTraceWriter() *traceFanout {
	return newTraceFanout(trace.NewJSONRecorder(os.Stderr))
}

// wireGatewayTraceSink registers the gateway's observability sink on the app's
// trace fanout. It is called from wireFrontend — the first moment the gateway
// exists — because the gateway is built after the loop that emits the spans.
// Without it the admin trace ring buffer is never fed and
// GET /api/v1/admin/observability/trace answers an empty list forever
// (design/19 §2). It is a no-op on a boot without a tracer or gateway.
func wireGatewayTraceSink(a *app, gw *gateway.Server) {
	if a.traceWriter == nil || gw == nil {
		return
	}
	a.traceWriter.Add(gatewaySpanSink{srv: gw})
	a.log.Info("observability trace sink wired")
}

// traceFanout is the composition root's trace.Writer. It fans every completed
// span out to the sinks installed at boot (the JSONL stderr recorder) plus any
// sink registered later in the boot sequence: the gateway's observability buffer
// only exists once wireFrontend has built the gateway, while the loop that emits
// the spans is built earlier in wireRuntime.
//
// It is safe for concurrent use — the loop finishes spans from several
// goroutines (per-step, per-tool-call, sub-agents).
type traceFanout struct {
	mu      sync.RWMutex
	writers []trace.Writer
}

// newTraceFanout builds a fanout over the given writers. Nil writers are dropped.
func newTraceFanout(writers ...trace.Writer) *traceFanout {
	f := &traceFanout{}
	for _, w := range writers {
		f.Add(w)
	}
	return f
}

// Add installs one more sink. A nil writer is ignored.
func (f *traceFanout) Add(w trace.Writer) {
	if w == nil {
		return
	}
	f.mu.Lock()
	defer f.mu.Unlock()
	f.writers = append(f.writers, w)
}

// WriteSpan writes rec to every sink and returns the first error. Every sink is
// tried even after a failure, so one broken sink cannot hide a span from the
// others; the tracer only logs the returned error (trace.Tracer.emit).
func (f *traceFanout) WriteSpan(rec trace.SpanRecord) error {
	f.mu.RLock()
	defer f.mu.RUnlock()
	var firstErr error
	for _, w := range f.writers {
		if w == nil {
			continue
		}
		if err := w.WriteSpan(rec); err != nil && firstErr == nil {
			firstErr = fmt.Errorf("trace fanout: %w", err)
		}
	}
	return firstErr
}

// wireGatewayLogBuffer hands the composition root's log ring buffer to the
// gateway, so GET /api/v1/admin/observability/logs serves the recent backend log
// tail. The logger is built before the gateway (its records must be captured
// from the first log line), so the buffer is injected here, the first moment the
// gateway exists — like wireGatewayTraceSink does for spans. It is a no-op on a
// boot without a gateway.
func wireGatewayLogBuffer(a *app, buf *logger.RingBuffer) {
	if a == nil || a.gw == nil || buf == nil {
		return
	}
	a.gw.SetLogBuffer(buf)
	a.log.Info("observability log buffer wired", "capacity", buf.Len())
}

// gatewaySpanSink adapts *gateway.Server to trace.Writer through its ObserveSpan
// entry point, so an emitted span lands in the admin panel's trace ring buffer
// AND in the LLM/subagent metric counters (ObserveSpan appends to the buffer and
// observes the metrics; the buffer is what GET /api/v1/admin/observability/trace
// serves).
type gatewaySpanSink struct{ srv *gateway.Server }

// WriteSpan feeds rec to the gateway. A missing server is a no-op.
func (g gatewaySpanSink) WriteSpan(rec trace.SpanRecord) error {
	if g.srv == nil {
		return nil
	}
	g.srv.ObserveSpan(rec)
	return nil
}