package controller

import (
	"fmt"
	"math"
	"net/http"
	"sort"
	"time"

	"ezops/model"

	"github.com/gin-gonic/gin"
)

// billingMonthCost 表示月度费用汇总。 // Logan.Li
type billingMonthCost struct {
	Month string  `json:"month"`
	Cost  float64 `json:"cost"`
}

// billingAttribution 表示可复核的费用变化归因。 // Logan.Li
type billingAttribution struct {
	Dimension    string  `json:"dimension"`
	Name         string  `json:"name"`
	BaselineCost float64 `json:"baseline_cost"`
	CurrentCost  float64 `json:"current_cost"`
	Delta        float64 `json:"delta"`
	Contribution float64 `json:"contribution"`
}

// GetBillingCostAnalysis 返回月度趋势和同期费用归因，AI 只负责解释确定性结果。 // Logan.Li
func (h *BillingHandler) GetBillingCostAnalysis(c *gin.Context) {
	now := time.Now()
	currentStart := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, now.Location())
	baselineStart := currentStart.AddDate(0, -1, 0)
	baselineEndDay := now.Day()
	baselineLastDay := baselineStart.AddDate(0, 1, -1).Day()
	if baselineEndDay > baselineLastDay {
		baselineEndDay = baselineLastDay
	}
	baselineEnd := time.Date(baselineStart.Year(), baselineStart.Month(), baselineEndDay, 23, 59, 59, 0, now.Location())
	analysisStart := currentStart.AddDate(0, -5, 0)
	currency := c.DefaultQuery("currency", "CNY")

	query := h.db.Model(&model.CloudBilling{}).Where("billing_date >= ? AND currency = ?", analysisStart.Format("2006-01-02"), currency)
	type monthRow struct {
		Month string
		Cost  float64
	}
	var monthRows []monthRow
	query.Select("SUBSTR(billing_date, 1, 7) AS month, COALESCE(SUM(cost), 0) AS cost").
		Group("SUBSTR(billing_date, 1, 7)").Order("month ASC").Scan(&monthRows)
	months := make([]billingMonthCost, 0, len(monthRows))
	for _, row := range monthRows {
		months = append(months, billingMonthCost{Month: row.Month, Cost: roundBilling(row.Cost)})
	}

	baselineStartDate := baselineStart.Format("2006-01-02")
	baselineEndDate := baselineEnd.Format("2006-01-02")
	currentStartDate := currentStart.Format("2006-01-02")
	currentEndDate := now.Format("2006-01-02")
	baselineCost := h.sumBillingPeriod(baselineStartDate, baselineEndDate, currency)
	currentCost := h.sumBillingPeriod(currentStartDate, currentEndDate, currency)
	totalDelta := currentCost - baselineCost

	attributions := make([]billingAttribution, 0, 24)
	for _, dimension := range []string{"provider", "account_name", "service", "region"} {
		attributions = append(attributions, h.billingDimensionAttribution(
			dimension, baselineStartDate, baselineEndDate, currentStartDate, currentEndDate, currency, totalDelta,
		)...)
	}
	sort.Slice(attributions, func(i, j int) bool {
		return math.Abs(attributions[i].Delta) > math.Abs(attributions[j].Delta)
	})
	if len(attributions) > 20 {
		attributions = attributions[:20]
	}

	var dataThrough string
	h.db.Model(&model.CloudBilling{}).Where("currency = ?", currency).Select("COALESCE(MAX(billing_date), '')").Scan(&dataThrough)
	c.JSON(http.StatusOK, model.Response{Code: 200, Message: "success", Data: gin.H{
		"analysis_start":       analysisStart.Format("2006-01-02"),
		"analysis_end":         currentEndDate,
		"data_through":         dataThrough,
		"currency":             currency,
		"incomplete_period":    true,
		"months":               months,
		"baseline_period":      fmt.Sprintf("%s - %s", baselineStartDate, baselineEndDate),
		"comparison_period":    fmt.Sprintf("%s - %s", currentStartDate, currentEndDate),
		"baseline_cost":        roundBilling(baselineCost),
		"comparison_cost":      roundBilling(currentCost),
		"total_delta":          roundBilling(totalDelta),
		"attributions":         attributions,
		"contribution_formula": "(当前期费用 - 基准期费用) / (当前期总费用 - 基准期总费用)",
	}})
}

// sumBillingPeriod 汇总指定币种和日期范围费用。 // Logan.Li
func (h *BillingHandler) sumBillingPeriod(startDate, endDate, currency string) float64 {
	var total float64
	h.db.Model(&model.CloudBilling{}).
		Where("billing_date BETWEEN ? AND ? AND currency = ?", startDate, endDate, currency).
		Select("COALESCE(SUM(cost), 0)").Scan(&total)
	return total
}

// billingDimensionAttribution 计算单一维度的同期费用变化贡献。 // Logan.Li
func (h *BillingHandler) billingDimensionAttribution(dimension, baselineStart, baselineEnd, currentStart, currentEnd, currency string, totalDelta float64) []billingAttribution {
	type dimensionRow struct {
		Name string
		Cost float64
	}
	load := func(startDate, endDate string) []dimensionRow {
		var rows []dimensionRow
		h.db.Model(&model.CloudBilling{}).
			Select(dimension+" AS name, COALESCE(SUM(cost), 0) AS cost").
			Where("billing_date BETWEEN ? AND ? AND currency = ?", startDate, endDate, currency).
			Group(dimension).Scan(&rows)
		return rows
	}
	baseline := map[string]float64{}
	current := map[string]float64{}
	for _, row := range load(baselineStart, baselineEnd) {
		baseline[row.Name] = row.Cost
	}
	for _, row := range load(currentStart, currentEnd) {
		current[row.Name] = row.Cost
	}
	for name := range baseline {
		if _, ok := current[name]; !ok {
			current[name] = 0
		}
	}
	result := make([]billingAttribution, 0, len(current))
	for rawName, currentCost := range current {
		name := rawName
		if rawName == "" {
			name = "未分类"
		}
		baselineCost := baseline[rawName]
		delta := currentCost - baselineCost
		if math.Abs(delta) < 0.01 {
			continue
		}
		contribution := 0.0
		if math.Abs(totalDelta) >= 0.01 {
			contribution = delta / totalDelta * 100
		}
		result = append(result, billingAttribution{
			Dimension: dimension, Name: name, BaselineCost: roundBilling(baselineCost),
			CurrentCost: roundBilling(currentCost), Delta: roundBilling(delta), Contribution: roundBilling(contribution),
		})
	}
	return result
}

// roundBilling 统一费用和百分比精度。 // Logan.Li
func roundBilling(value float64) float64 {
	return math.Round(value*100) / 100
}