package api

import (
	"encoding/json"
	"net/http"
	"os"
	"strconv"
	"strings"
	"sync"
	"time"
)

// Metric — один снимок состояния, принятый через POST /metrics.
type Metric struct {
	Timestamp     string  `json:"timestamp"`
	Source        string  `json:"source"`
	Hostname      string  `json:"hostname,omitempty"`
	Status        string  `json:"status,omitempty"`
	MemoryTotalMB float64 `json:"memory_total_mb,omitempty"`
	MemoryFreeMB  float64 `json:"memory_free_mb,omitempty"`
	MemoryAvailMB float64 `json:"memory_available_mb,omitempty"`
	MemoryUsedMB  float64 `json:"memory_used_mb,omitempty"`
	MemoryPercent float64 `json:"memory_percent,omitempty"`
	CpuLoad1m     float64 `json:"cpu_load_1m,omitempty"`
	CpuLoad5m     float64 `json:"cpu_load_5m,omitempty"`
	CpuLoad15m    float64 `json:"cpu_load_15m,omitempty"`
	DiskTotalGB   float64 `json:"disk_total_gb,omitempty"`
	DiskFreeGB    float64 `json:"disk_free_gb,omitempty"`
	DiskUsedGB    float64 `json:"disk_used_gb,omitempty"`
	UptimeSec     float64 `json:"uptime_sec,omitempty"`
	Notes         string  `json:"notes,omitempty"`
}

const maxHistory = 240

// Server хранит историю снимков в памяти.
type Server struct {
	mu      sync.RWMutex
	history []Metric
}

func NewServer() *Server {
	return &Server{}
}

// HandleMetrics — единственный публичный эндпоинт.
// GET  /metrics → отдаёт историю.
// POST /metrics → сохраняет снимок.
func (s *Server) HandleMetrics(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Access-Control-Allow-Origin", "*")
	w.Header().Set("Access-Control-Allow-Headers", "Content-Type, X-Metrics-Token")

	switch r.Method {
	case http.MethodOptions:
		w.WriteHeader(http.StatusNoContent)

	case http.MethodGet:
		s.mu.RLock()
		history := append([]Metric(nil), s.history...)
		s.mu.RUnlock()

		latest := Metric{}
		if len(history) > 0 {
			latest = history[len(history)-1]
		}
		writeJSON(w, http.StatusOK, map[string]any{
			"count":   len(history),
			"latest":  latest,
			"history": history,
		})

	case http.MethodPost:
		if !s.authorized(r) {
			writeJSON(w, http.StatusUnauthorized, map[string]any{"error": "invalid token"})
			return
		}
		var payload map[string]any
		if err := json.NewDecoder(r.Body).Decode(&payload); err != nil {
			writeJSON(w, http.StatusBadRequest, map[string]any{"error": "invalid json"})
			return
		}
		m := normalize(payload)
		s.mu.Lock()
		s.history = append(s.history, m)
		if len(s.history) > maxHistory {
			s.history = append([]Metric(nil), s.history[len(s.history)-maxHistory:]...)
		}
		count := len(s.history)
		s.mu.Unlock()
		writeJSON(w, http.StatusOK, map[string]any{"ok": true, "stored": count})

	default:
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
	}
}

// authorized проверяет METRICS_TOKEN если он задан.
func (s *Server) authorized(r *http.Request) bool {
	expected := strings.TrimSpace(os.Getenv("METRICS_TOKEN"))
	if expected == "" {
		return true
	}
	return strings.TrimSpace(r.Header.Get("X-Metrics-Token")) == expected
}

func writeJSON(w http.ResponseWriter, code int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(code)
	_ = json.NewEncoder(w).Encode(v)
}

// normalize приводит произвольный payload к структуре Metric.
func normalize(p map[string]any) Metric {
	now := time.Now().UTC().Format(time.RFC3339)
	m := Metric{
		Timestamp: now,
		Source:    textVal(p, "source", "function", "name", "host", "hostname", "instance"),
		Hostname:  textVal(p, "hostname", "host", "node", "instance"),
		Status:    textVal(p, "status"),
		Notes:     textVal(p, "notes", "note", "message"),
	}
	if m.Source == "" {
		m.Source = "function"
	}

	m.MemoryTotalMB = numVal(p, "memory_total_mb", "total_memory_mb", "mem_total_mb")
	m.MemoryFreeMB = numVal(p, "memory_free_mb", "free_memory_mb", "mem_free_mb", "free_mb")
	m.MemoryAvailMB = numVal(p, "memory_available_mb", "available_memory_mb", "mem_available_mb")
	m.MemoryUsedMB = numVal(p, "memory_used_mb", "used_memory_mb", "mem_used_mb", "used_mb")
	m.MemoryPercent = numVal(p, "memory_percent", "mem_percent", "memory_usage_percent")

	if m.MemoryUsedMB == 0 && m.MemoryTotalMB > 0 && m.MemoryFreeMB > 0 {
		m.MemoryUsedMB = m.MemoryTotalMB - m.MemoryFreeMB
	}
	if m.MemoryAvailMB == 0 && m.MemoryFreeMB > 0 {
		m.MemoryAvailMB = m.MemoryFreeMB
	}
	if m.MemoryPercent == 0 && m.MemoryTotalMB > 0 && m.MemoryUsedMB > 0 {
		m.MemoryPercent = (m.MemoryUsedMB / m.MemoryTotalMB) * 100
	}

	m.CpuLoad1m = numVal(p, "cpu_load_1m", "loadavg_1m", "load_1m", "load1")
	m.CpuLoad5m = numVal(p, "cpu_load_5m", "loadavg_5m", "load_5m", "load5")
	m.CpuLoad15m = numVal(p, "cpu_load_15m", "loadavg_15m", "load_15m", "load15")

	m.DiskTotalGB = numVal(p, "disk_total_gb", "total_disk_gb")
	m.DiskFreeGB = numVal(p, "disk_free_gb", "free_disk_gb")
	m.DiskUsedGB = numVal(p, "disk_used_gb", "used_disk_gb")
	if m.DiskUsedGB == 0 && m.DiskTotalGB > 0 && m.DiskFreeGB > 0 {
		m.DiskUsedGB = m.DiskTotalGB - m.DiskFreeGB
	}

	m.UptimeSec = numVal(p, "uptime_sec", "uptime", "uptime_seconds")

	if ts := textVal(p, "timestamp", "ts", "collected_at"); ts != "" {
		m.Timestamp = ts
	}
	return m
}

func textVal(p map[string]any, keys ...string) string {
	for _, k := range keys {
		if v, ok := p[k]; ok {
			if s := strings.TrimSpace(anyToString(v)); s != "" {
				return s
			}
		}
	}
	return ""
}

func numVal(p map[string]any, keys ...string) float64 {
	for _, k := range keys {
		if v, ok := p[k]; ok {
			if f, ok := anyToFloat64(v); ok {
				return f
			}
		}
	}
	return 0
}

func anyToString(v any) string {
	switch t := v.(type) {
	case string:
		return t
	case float64:
		return strconv.FormatFloat(t, 'f', -1, 64)
	case json.Number:
		return t.String()
	default:
		return ""
	}
}

func anyToFloat64(v any) (float64, bool) {
	switch t := v.(type) {
	case float64:
		return t, true
	case float32:
		return float64(t), true
	case int:
		return float64(t), true
	case int64:
		return float64(t), true
	case json.Number:
		f, err := t.Float64()
		return f, err == nil
	case string:
		f, err := strconv.ParseFloat(strings.TrimSpace(t), 64)
		return f, err == nil
	default:
		return 0, false
	}
}