package gateway

import (
	"sync"
	"time"

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

// defaultTraceBufCap is how many completed spans the ring buffer holds before the
// oldest is evicted. Compile-time constant.
const defaultTraceBufCap = 512

// AdminTraceSpan is the camelCase wire shape of one traced span. It decouples the
// frontend from the trace package's snake_case SpanRecord.
type AdminTraceSpan struct {
	ID         string         `json:"id"`
	ParentID   string         `json:"parentId,omitempty"`
	Name       string         `json:"name"`
	Kind       string         `json:"kind"`
	Status     string         `json:"status"`
	StartedAt  string         `json:"startedAt"`
	EndedAt    string         `json:"endedAt,omitempty"`
	DurationNs int64          `json:"durationNs"`
	Props      map[string]any `json:"props,omitempty"`
	Events     []trace.Event  `json:"events,omitempty"`
}

// RingBuffer is a concurrency-safe bounded buffer of completed trace spans. The
// oldest span is evicted when the buffer is full, so the admin panel always sees
// the most recent work without unbounded growth.
type RingBuffer struct {
	mu   sync.RWMutex
	buf  []trace.SpanRecord
	next int
	full bool
	cap  int
}

// newRingBuffer builds a ring buffer holding up to cap spans (default when cap<=0).
func newRingBuffer(cap int) *RingBuffer {
	if cap <= 0 {
		cap = defaultTraceBufCap
	}
	return &RingBuffer{buf: make([]trace.SpanRecord, cap), cap: cap}
}

// Append stores rec, evicting the oldest when the buffer is full.
func (r *RingBuffer) Append(rec trace.SpanRecord) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.buf[r.next] = rec
	r.next = (r.next + 1) % r.cap
	if r.next == 0 {
		r.full = true
	}
}

// Snapshot returns up to n most-recent spans, newest first. A non-positive n
// selects defaultObsLimit; n is clamped to maxObsLimit.
func (r *RingBuffer) Snapshot(n int) []trace.SpanRecord {
	if n <= 0 {
		n = defaultObsLimit
	}
	if n > maxObsLimit {
		n = maxObsLimit
	}
	r.mu.RLock()
	defer r.mu.RUnlock()
	count := r.next
	if r.full {
		count = r.cap
	}
	if count > n {
		count = n
	}
	out := make([]trace.SpanRecord, 0, count)
	for i := 0; i < count; i++ {
		idx := (r.next - 1 - i + r.cap*2) % r.cap
		out = append(out, r.buf[idx])
	}
	return out
}

// traceSink adapts a *RingBuffer to trace.Writer so a completed span is appended
// to the gateway's trace buffer.
type traceSink struct{ b *RingBuffer }

// WriteSpan appends rec to the ring buffer.
func (s traceSink) WriteSpan(rec trace.SpanRecord) error {
	if s.b == nil {
		return nil
	}
	s.b.Append(rec)
	return nil
}

// MultiTraceWriter fans a completed span out to several trace.Writers, so a tracer
// can record to both the gateway's ring buffer and a JSONL file in one pass. A nil
// Writer is skipped. It is the composition-root helper the main session uses to
// route the loop tracer's output into the gateway without dropping stderr.
type MultiTraceWriter struct {
	// Writers are the sinks a span is written to. A nil Writer is skipped.
	Writers []trace.Writer
}

// WriteSpan writes rec to every configured Writer.
func (m MultiTraceWriter) WriteSpan(rec trace.SpanRecord) error {
	for _, w := range m.Writers {
		if w == nil {
			continue
		}
		if err := w.WriteSpan(rec); err != nil {
			return err
		}
	}
	return nil
}

// adminSpanOf maps a trace.SpanRecord to the camelCase admin wire shape.
func adminSpanOf(rec trace.SpanRecord) AdminTraceSpan {
	sp := AdminTraceSpan{
		ID:         rec.ID,
		ParentID:   rec.ParentID,
		Name:       rec.Name,
		Kind:       string(rec.Kind),
		Status:     string(rec.Status),
		StartedAt:  rec.StartedAt.UTC().Format(time.RFC3339),
		DurationNs: rec.Duration.Nanoseconds(),
		Props:      rec.Props,
		Events:     rec.Events,
	}
	if !rec.EndedAt.IsZero() {
		sp.EndedAt = rec.EndedAt.UTC().Format(time.RFC3339)
	}
	return sp
}