package cloud

import (
	"bytes"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"time"
)

// FetchDailyBill 通过 AWS Cost Explorer 按服务和区域同步指定日的未摊销成本。 // Logan.Li
func (p *AWSProvider) FetchDailyBill(billingDate string) ([]CloudBillingRecord, error) {
	day, err := time.Parse("2006-01-02", billingDate)
	if err != nil {
		return nil, fmt.Errorf("账单日期格式错误: %w", err)
	}
	payload, err := json.Marshal(map[string]interface{}{
		"TimePeriod": map[string]string{
			"Start": day.Format("2006-01-02"),
			"End":   day.AddDate(0, 0, 1).Format("2006-01-02"),
		},
		"Granularity": "DAILY",
		"Metrics":     []string{"UnblendedCost"},
		"GroupBy": []map[string]string{
			{"Type": "DIMENSION", "Key": "SERVICE"},
			{"Type": "DIMENSION", "Key": "REGION"},
		},
	})
	if err != nil {
		return nil, fmt.Errorf("构造 AWS Cost Explorer 请求失败: %w", err)
	}
	body, err := p.callCostExplorer(payload)
	if err != nil {
		return nil, err
	}
	return parseAWSCostExplorerBill(billingDate, body)
}

// callCostExplorer 使用 SigV4 调用 Cost Explorer；该服务固定使用 us-east-1。 // Logan.Li
func (p *AWSProvider) callCostExplorer(payload []byte) ([]byte, error) {
	const host = "ce.us-east-1.amazonaws.com"
	now := time.Now().UTC()
	date := now.Format("20060102")
	amzDate := now.Format("20060102T150405Z")
	payloadHash := sha256Hex(string(payload))
	canonicalHeaders := "content-type:application/x-amz-json-1.1\n" +
		"host:" + host + "\n" +
		"x-amz-date:" + amzDate + "\n" +
		"x-amz-target:AWSInsightsIndexService.GetCostAndUsage\n"
	signedHeaders := "content-type;host;x-amz-date;x-amz-target"
	canonicalRequest := "POST\n/\n\n" + canonicalHeaders + "\n" + signedHeaders + "\n" + payloadHash
	credentialScope := date + "/us-east-1/ce/aws4_request"
	stringToSign := "AWS4-HMAC-SHA256\n" + amzDate + "\n" + credentialScope + "\n" + sha256Hex(canonicalRequest)
	kDate := hmacSHA256([]byte("AWS4"+p.secretKey), date)
	kRegion := hmacSHA256(kDate, "us-east-1")
	kService := hmacSHA256(kRegion, "ce")
	signingKey := hmacSHA256(kService, "aws4_request")
	signature := hex.EncodeToString(hmacSHA256(signingKey, stringToSign))

	req, err := http.NewRequest(http.MethodPost, "https://"+host+"/", bytes.NewReader(payload))
	if err != nil {
		return nil, fmt.Errorf("创建 AWS Cost Explorer 请求失败: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-amz-json-1.1")
	req.Header.Set("X-Amz-Date", amzDate)
	req.Header.Set("X-Amz-Target", "AWSInsightsIndexService.GetCostAndUsage")
	req.Header.Set("Authorization", "AWS4-HMAC-SHA256 Credential="+p.accessKey+"/"+credentialScope+", SignedHeaders="+signedHeaders+", Signature="+signature)
	resp, err := (&http.Client{Timeout: 30 * time.Second}).Do(req)
	if err != nil {
		return nil, fmt.Errorf("请求 AWS Cost Explorer 失败: %w", err)
	}
	defer resp.Body.Close()
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("读取 AWS Cost Explorer 响应失败: %w", err)
	}
	if resp.StatusCode < http.StatusOK || resp.StatusCode >= http.StatusMultipleChoices {
		return nil, fmt.Errorf("AWS Cost Explorer 返回 HTTP %d: %s", resp.StatusCode, string(body))
	}
	return body, nil
}

func parseAWSCostExplorerBill(billingDate string, body []byte) ([]CloudBillingRecord, error) {
	var response struct {
		ResultsByTime []struct {
			Groups []struct {
				Keys    []string `json:"Keys"`
				Metrics map[string]struct {
					Amount string `json:"Amount"`
					Unit   string `json:"Unit"`
				} `json:"Metrics"`
			} `json:"Groups"`
		} `json:"ResultsByTime"`
	}
	if err := json.Unmarshal(body, &response); err != nil {
		return nil, fmt.Errorf("解析 AWS Cost Explorer 响应失败: %w", err)
	}
	records := make([]CloudBillingRecord, 0)
	for _, result := range response.ResultsByTime {
		for _, group := range result.Groups {
			metric, ok := group.Metrics["UnblendedCost"]
			if !ok {
				continue
			}
			amount, err := strconv.ParseFloat(metric.Amount, 64)
			if err != nil {
				return nil, fmt.Errorf("解析 AWS 成本金额失败: %w", err)
			}
			service, region := "AWS", "global"
			if len(group.Keys) > 0 && group.Keys[0] != "" {
				service = group.Keys[0]
			}
			if len(group.Keys) > 1 && group.Keys[1] != "" {
				region = group.Keys[1]
			}
			records = append(records, CloudBillingRecord{BillingDate: billingDate, Provider: "aws", Cost: amount, Currency: metric.Unit, Service: service, Region: region, Description: "AWS Cost Explorer UnblendedCost"})
		}
	}
	return records, nil
}