package service

import (
	"sort"
	"sync"
	"time"
)

// Dependency 依赖名称。
type Dependency string

const (
	DependencyPostgres Dependency = "postgresql"
	DependencyRedis    Dependency = "redis"
	DependencyMQTT     Dependency = "mqtt"
	DependencyIoTDB    Dependency = "iotdb"
	DependencyS3       Dependency = "s3"
	DependencyAI       Dependency = "ai"
	DependencyWVP      Dependency = "wvp"
	DependencyWechat   Dependency = "wechat"
	DependencyWeather  Dependency = "weather"
)

// DependencyMetric 依赖调用指标。
type DependencyMetric struct {
	Requests      int64      `json:"requests"`
	Failures      int64      `json:"failures"`
	LastLatencyMs float64    `json:"lastLatencyMs"`
	P50LatencyMs  float64    `json:"p50LatencyMs"`
	P95LatencyMs  float64    `json:"p95LatencyMs"`
	LastSuccessAt *time.Time `json:"lastSuccessAt,omitempty"`
	LastFailureAt *time.Time `json:"lastFailureAt,omitempty"`
	LastError     string     `json:"lastError,omitempty"`
}

var dependencyMetrics sync.Map

// RecordDependency 记录一次依赖调用。
func RecordDependency(dep Dependency, err error, latency time.Duration) {
	now := time.Now()
	value, _ := dependencyMetrics.LoadOrStore(dep, &DependencyMetric{})
	metric := value.(*DependencyMetric)
	metric.Requests++
	metric.LastLatencyMs = float64(latency.Microseconds()) / 1000
	if err != nil {
		metric.Failures++
		metric.LastFailureAt = &now
		metric.LastError = err.Error()
	} else {
		metric.LastSuccessAt = &now
		metric.LastError = ""
	}
}

// DependencySnapshot 返回当前依赖指标快照。
func DependencySnapshot() map[Dependency]DependencyMetric {
	result := map[Dependency]DependencyMetric{}
	dependencyMetrics.Range(func(key, value interface{}) bool {
		dep := key.(Dependency)
		metric := *value.(*DependencyMetric)
		result[dep] = metric
		return true
	})
	return result
}

// RecordDependencyHistogram 预留直方图能力；当前仅更新最近一次指标。
func RecordDependencyHistogram(dep Dependency, err error, latency time.Duration, samples []float64) {
	RecordDependency(dep, err, latency)
	if len(samples) == 0 {
		return
	}
	value, _ := dependencyMetrics.LoadOrStore(dep, &DependencyMetric{})
	metric := value.(*DependencyMetric)
	sort.Float64s(samples)
	metric.P50LatencyMs = percentile(samples, 0.5)
	metric.P95LatencyMs = percentile(samples, 0.95)
}

func percentile(sorted []float64, p float64) float64 {
	if len(sorted) == 0 {
		return 0
	}
	idx := int(float64(len(sorted)-1) * p)
	return sorted[idx]
}