package main

import (
	"context"
	"net/http"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"git.k6n.net/mats/go-cart-actor/pkg/actor"
	"git.k6n.net/mats/go-cart-actor/pkg/order"
)

type orderAlert struct {
	Severity string `json:"severity"` // warn | error
	Message  string `json:"message"`
	OrderId  string `json:"orderId,omitempty"`
}

type statusBucket struct {
	Status order.Status `json:"status"`
	Count  int          `json:"count"`
	Total  int64        `json:"total"`
}

type revenueSnapshot struct {
	Total    int64 `json:"total"`
	Captured int64 `json:"captured"`
	Refunded int64 `json:"refunded"`
	Pending  int64 `json:"pending"`
}

type dailyRevenue struct {
	Date  string `json:"date"` // YYYY-MM-DD
	Total int64  `json:"total"`
}

type orderStatsResponse struct {
	OrdersTotal    int             `json:"ordersTotal"`
	Revenue        revenueSnapshot `json:"revenue"`
	ByStatus       []statusBucket  `json:"byStatus"`
	RecentOrders   []orderSummary  `json:"recentOrders"`
	DailyRevenue30 []dailyRevenue  `json:"dailyRevenue30,omitempty"`
	Alerts         []orderAlert    `json:"alerts"`
}

// statsCache holds an in-memory aggregate of all orders, rebuilt on mutation
// instead of scanning *.events.log on every request.
type statsCache struct {
	mu      sync.RWMutex
	data    orderStatsResponse
	pool    *actor.SimpleGrainPool[order.OrderGrain]
	dataDir string
}

func newStatsCache(dataDir string, pool *actor.SimpleGrainPool[order.OrderGrain]) *statsCache {
	return &statsCache{dataDir: dataDir, pool: pool}
}

// Get returns the cached stats. Call Rebuild() on startup to warm the cache;
// if never built, returns an empty response.
func (c *statsCache) Get() orderStatsResponse {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.data
}

// Rebuild rebuilds the stats cache from disk. Safe to call concurrently;
// intended as a goroutine after each mutation so it never blocks an HTTP
// response.
func (c *statsCache) Rebuild() {
	c.rebuild()
}

func (c *statsCache) rebuild() {
	if c.pool == nil {
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	matches, _ := filepath.Glob(filepath.Join(c.dataDir, "*.events.log"))
	now := time.Now()
	var totalOrders int
	var totalRevenue, capturedRevenue, refundedRevenue int64
	byStatus := map[order.Status]int{}
	statusTotal := map[order.Status]int64{}

	dailyByDay := map[string]int64{}
	for i := 0; i < 30; i++ {
		day := now.AddDate(0, 0, -i).Format("2006-01-02")
		dailyByDay[day] = 0
	}

	var allOrders []orderSummary
	var alerts []orderAlert

	for _, m := range matches {
		base := strings.TrimSuffix(filepath.Base(m), ".events.log")
		raw, err := strconv.ParseUint(base, 10, 64)
		if err != nil {
			continue
		}
		g, err := c.pool.Get(ctx, raw)
		if err != nil || g.Status == order.StatusNew {
			continue
		}
		totalOrders++
		byStatus[g.Status]++
		statusTotal[g.Status] += g.TotalAmount.Int64()

		totalRevenue += g.TotalAmount.Int64()
		capturedRevenue += g.CapturedAmount.Int64()
		refundedRevenue += g.RefundedAmount.Int64()

		if g.PlacedAt != "" {
			if placed, parseErr := time.Parse(time.RFC3339, g.PlacedAt); parseErr == nil {
				dayKey := placed.Format("2006-01-02")
				if _, ok := dailyByDay[dayKey]; ok {
					dailyByDay[dayKey] += g.TotalAmount.Int64()
				}
			}
		}

		allOrders = append(allOrders, orderSummary{
			OrderId:     order.OrderId(raw).String(),
			Reference:   g.OrderReference,
			Status:      g.Status,
			TotalAmount: g.TotalAmount.Int64(),
			Currency:    g.Currency,
			PlacedAt:    g.PlacedAt,
		})

		if g.Status == order.StatusPending {
			alerts = append(alerts, orderAlert{
				Severity: "warn",
				Message:  "Payment still pending",
				OrderId:  order.OrderId(raw).String(),
			})
		}
		if g.Status == order.StatusCancelled {
			alerts = append(alerts, orderAlert{
				Severity: "warn",
				Message:  "Order was cancelled",
				OrderId:  order.OrderId(raw).String(),
			})
		}
	}

	sort.Slice(allOrders, func(i, j int) bool {
		return allOrders[i].PlacedAt > allOrders[j].PlacedAt
	})
	recent := allOrders
	if len(recent) > 10 {
		recent = recent[:10]
	}

	if len(alerts) > 50 {
		alerts = alerts[:50]
	}

	buckets := make([]statusBucket, 0, len(byStatus))
	for st, cnt := range byStatus {
		buckets = append(buckets, statusBucket{Status: st, Count: cnt, Total: statusTotal[st]})
	}
	sort.Slice(buckets, func(i, j int) bool {
		return buckets[i].Count > buckets[j].Count
	})

	var dailyRev []dailyRevenue
	for i := 29; i >= 0; i-- {
		day := now.AddDate(0, 0, -i).Format("2006-01-02")
		dailyRev = append(dailyRev, dailyRevenue{Date: day, Total: dailyByDay[day]})
	}

	c.mu.Lock()
	c.data = orderStatsResponse{
		OrdersTotal: totalOrders,
		Revenue: revenueSnapshot{
			Total:    totalRevenue,
			Captured: capturedRevenue,
			Refunded: refundedRevenue,
			Pending:  totalRevenue - capturedRevenue - refundedRevenue,
		},
		ByStatus:       buckets,
		RecentOrders:   recent,
		DailyRevenue30: dailyRev,
		Alerts:         alerts,
	}
	c.mu.Unlock()
}

// handleStats returns dashboard stats from the in-memory cache (O(1) read,
// rebuilt after each mutation) instead of scanning all *.events.log on every
// request.
func (s *server) handleStats(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, http.StatusOK, s.statsCache.Get())
}