sub2api/backend/internal/service/usage_billing.go

package service

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"strings"
)

var ErrUsageBillingRequestIDRequired = errors.New("usage billing request_id is required")
var ErrUsageBillingRequestConflict = errors.New("usage billing request fingerprint conflict")

// UsageBillingCommand describes one billable request that must be applied at most once.
type UsageBillingCommand struct {
	RequestID          string
	APIKeyID           int64
	RequestFingerprint string
	RequestPayloadHash string

	UserID              int64
	AccountID           int64
	SubscriptionID      *int64
	AccountType         string
	Model               string
	ServiceTier         string
	ReasoningEffort     string
	BillingType         int8
	InputTokens         int
	OutputTokens        int
	CacheCreationTokens int
	CacheReadTokens     int
	ImageCount          int
	MediaType           string

	BalanceCost         float64
	SubscriptionCost    float64
	APIKeyQuotaCost     float64
	APIKeyRateLimitCost float64
	AccountQuotaCost    float64
}

func (c *UsageBillingCommand) Normalize() {
	if c == nil {
		return
	}
	c.RequestID = strings.TrimSpace(c.RequestID)
	if strings.TrimSpace(c.RequestFingerprint) == "" {
		c.RequestFingerprint = buildUsageBillingFingerprint(c)
	}
}

func buildUsageBillingFingerprint(c *UsageBillingCommand) string {
	if c == nil {
		return ""
	}
	raw := fmt.Sprintf(
		"%d|%d|%d|%s|%s|%s|%s|%d|%d|%d|%d|%d|%d|%s|%d|%0.10f|%0.10f|%0.10f|%0.10f|%0.10f",
		c.UserID,
		c.AccountID,
		c.APIKeyID,
		strings.TrimSpace(c.AccountType),
		strings.TrimSpace(c.Model),
		strings.TrimSpace(c.ServiceTier),
		strings.TrimSpace(c.ReasoningEffort),
		c.BillingType,
		c.InputTokens,
		c.OutputTokens,
		c.CacheCreationTokens,
		c.CacheReadTokens,
		c.ImageCount,
		strings.TrimSpace(c.MediaType),
		valueOrZero(c.SubscriptionID),
		c.BalanceCost,
		c.SubscriptionCost,
		c.APIKeyQuotaCost,
		c.APIKeyRateLimitCost,
		c.AccountQuotaCost,
	)
	if payloadHash := strings.TrimSpace(c.RequestPayloadHash); payloadHash != "" {
		raw += "|" + payloadHash
	}
	sum := sha256.Sum256([]byte(raw))
	return hex.EncodeToString(sum[:])
}

func HashUsageRequestPayload(payload []byte) string {
	if len(payload) == 0 {
		return ""
	}
	sum := sha256.Sum256(payload)
	return hex.EncodeToString(sum[:])
}

func valueOrZero(v *int64) int64 {
	if v == nil {
		return 0
	}
	return *v
}

type UsageBillingApplyResult struct {
	Applied              bool
	APIKeyQuotaExhausted bool
}

type UsageBillingRepository interface {
	Apply(ctx context.Context, cmd *UsageBillingCommand) (*UsageBillingApplyResult, error)
}