package gateway

import (
	"strconv"
	"sync"
	"time"

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

// Metrics collector tuning. Compile-time constants.
const (
	// metricsWindow bounds how long request timestamps are retained for QPS.
	metricsWindow = 2 * time.Second
	// metricsQPSSpan is the sliding window over which QPS is measured.
	metricsQPSSpan = time.Second
)

// AdminMetrics is the wire shape of GET /api/v1/admin/observability/metrics.
// LLM/Token cost is deliberately absent: the gateway does not track token usage or
// spend, and a fabricated number would violate the "不伪造指标" red line.
type AdminMetrics struct {
	TotalRequests  int64            `json:"totalRequests"`
	QPS            float64          `json:"qps"`
	AvgLatencyMs   float64          `json:"avgLatencyMs"`
	MaxLatencyMs   int64            `json:"maxLatencyMs"`
	PerMethod      map[string]int64 `json:"perMethod"`
	PerPath        map[string]int64 `json:"perPath"`
	StatusCounts   map[string]int64 `json:"statusCounts"`
	LLMCalls       int64            `json:"llmCalls"`
	SubagentEvents int64            `json:"subagentEvents"`
}

// MetricsCollector accumulates request metrics and derived counters for the admin
// observability panel. It is concurrency-safe.
type MetricsCollector struct {
	mu        sync.Mutex
	total     int64
	perMethod map[string]int64
	perPath   map[string]int64
	statuses  map[int]int64
	sumDur    int64
	maxDur    int64
	recent    []time.Time
	llm       int64
	subagent  int64
}

// newMetricsCollector builds an empty metrics collector.
func newMetricsCollector() *MetricsCollector {
	return &MetricsCollector{
		perMethod: make(map[string]int64),
		perPath:   make(map[string]int64),
		statuses:  make(map[int]int64),
	}
}

// Record counts one request with the given method, path, status and duration.
func (m *MetricsCollector) Record(method, path string, status int, durMs int64) {
	m.mu.Lock()
	defer m.mu.Unlock()
	now := time.Now()
	m.total++
	m.perMethod[method]++
	m.perPath[path]++
	m.statuses[status]++
	m.sumDur += durMs
	if durMs > m.maxDur {
		m.maxDur = durMs
	}
	m.recent = append(m.recent, now)
	m.prune(now)
}

// Observe increments the LLM/subagent counters when a span of that kind is
// recorded. It is called by ObserveSpan so the counters reflect real work.
func (m *MetricsCollector) Observe(rec trace.SpanRecord) {
	m.mu.Lock()
	defer m.mu.Unlock()
	switch rec.Kind {
	case trace.SpanKindLLM:
		m.llm++
	case trace.SpanKindSubagent:
		m.subagent++
	}
}

// prune drops request times older than metricsWindow so recent stays small. The
// caller must hold m.mu.
func (m *MetricsCollector) prune(now time.Time) {
	min := now.Add(-metricsWindow)
	i := 0
	for i < len(m.recent) && m.recent[i].Before(min) {
		i++
	}
	if i > 0 {
		m.recent = append([]time.Time(nil), m.recent[i:]...)
	}
}

// Snapshot returns a point-in-time copy of the metrics. qps counts the requests
// started within metricsQPSSpan of now.
func (m *MetricsCollector) Snapshot(now time.Time) AdminMetrics {
	m.mu.Lock()
	defer m.mu.Unlock()
	statuses := make(map[string]int64, len(m.statuses))
	for k, v := range m.statuses {
		statuses[strconv.Itoa(k)] = v
	}
	var qps int64
	for _, t := range m.recent {
		if now.Sub(t) <= metricsQPSSpan {
			qps++
		}
	}
	avg := int64(0)
	if m.total > 0 {
		avg = m.sumDur / m.total
	}
	return AdminMetrics{
		TotalRequests:  m.total,
		QPS:            float64(qps),
		AvgLatencyMs:   float64(avg),
		MaxLatencyMs:   m.maxDur,
		PerMethod:      m.perMethod,
		PerPath:        m.perPath,
		StatusCounts:   statuses,
		LLMCalls:       m.llm,
		SubagentEvents: m.subagent,
	}
}