story/internal/contentpolicy/classifier.go

package contentpolicy

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"regexp"
	"strings"
	"time"

	"data-terminal-cloud/internal/outbox"
)

type Decision struct {
	AllowOrdinaryStory bool
	Sensitivity        string
	Reason             string
	ProviderRef        string
	RequestRef         string
}

type Classifier interface {
	Classify(context.Context, string) (Decision, error)
}

type LocalClassifier struct{}

var (
	verificationCodePattern = regexp.MustCompile(`(?i)(验证码|校验码|动态码|verification\s*code|otp)[^0-9]{0,8}[0-9]{4,8}`)
	accountNumberPattern    = regexp.MustCompile(`(?:^|[^0-9])[0-9]{12,19}(?:[^0-9]|$)`)
	promptInjectionPattern  = regexp.MustCompile(`(?i)(忽略.{0,16}(以上|之前|所有).{0,16}(指令|规则|提示)|(?:泄露|输出|显示).{0,20}(系统提示|密钥|其他.{0,8}(用户|长者|家庭))|ignore\s+(all\s+)?(previous|prior)\s+instructions|reveal.{0,20}(system\s+prompt|secret|other\s+user))`)
)

var sensitiveMedicalTerms = []string{"艾滋", "hiv", "癌症", "肿瘤", "精神病", "精神科", "诊断结果", "病理报告"}
var paymentTerms = []string{"银行卡", "银行账号", "信用卡", "支付密码", "取款密码", "转账"}

// Classify applies a conservative local safety baseline before ordinary story
// generation. It is intentionally rule-based and must be supplemented by a
// production content-safety service and evaluated policy set.
func Classify(content string) Decision {
	normalized := strings.ToLower(strings.TrimSpace(content))
	if verificationCodePattern.MatchString(normalized) {
		return localDecision(false, "high", "verification_code")
	}
	if accountNumberPattern.MatchString(normalized) && containsAny(normalized, paymentTerms) {
		return localDecision(false, "high", "financial_account")
	}
	if promptInjectionPattern.MatchString(normalized) {
		return localDecision(false, "high", "prompt_injection")
	}
	if containsAny(normalized, sensitiveMedicalTerms) {
		return localDecision(false, "sensitive", "sensitive_medical")
	}
	return localDecision(true, "normal", "")
}

func (LocalClassifier) Classify(_ context.Context, content string) (Decision, error) {
	return Classify(content), nil
}

func localDecision(allow bool, sensitivity, reason string) Decision {
	return Decision{
		AllowOrdinaryStory: allow,
		Sensitivity:        sensitivity,
		Reason:             reason,
		ProviderRef:        "local-content-safety-policy",
	}
}

type ManagedClassifier struct {
	endpoint  string
	apiKey    string
	policyRef string
	client    *http.Client
}

func NewManagedClassifier(endpoint, apiKey, policyRef string, timeout time.Duration) (*ManagedClassifier, error) {
	endpoint = strings.TrimSpace(endpoint)
	apiKey = strings.TrimSpace(apiKey)
	policyRef = strings.TrimSpace(policyRef)
	parsed, err := url.Parse(endpoint)
	if err != nil || parsed.Host == "" || (parsed.Scheme != "http" && parsed.Scheme != "https") {
		return nil, errors.New("content safety endpoint must be an absolute HTTP(S) URL")
	}
	if apiKey == "" || policyRef == "" || timeout <= 0 {
		return nil, errors.New("content safety API key, policy reference and positive timeout are required")
	}
	return &ManagedClassifier{
		endpoint: endpoint, apiKey: apiKey, policyRef: policyRef,
		client: &http.Client{Timeout: timeout},
	}, nil
}

// Classify always applies the local high-risk rules before sending content to
// the managed policy service. Local matches therefore never leave the process.
func (c *ManagedClassifier) Classify(ctx context.Context, content string) (Decision, error) {
	if decision := Classify(content); !decision.AllowOrdinaryStory {
		return decision, nil
	}
	requestBody, err := json.Marshal(struct {
		PolicyRef string `json:"policy_ref"`
		Content   string `json:"content"`
	}{PolicyRef: c.policyRef, Content: content})
	if err != nil {
		return Decision{}, err
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.endpoint, bytes.NewReader(requestBody))
	if err != nil {
		return Decision{}, fmt.Errorf("build content safety request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+c.apiKey)
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("User-Agent", "voice-platform-content-safety/1.0")
	resp, err := c.client.Do(req)
	if err != nil {
		return Decision{}, outbox.Retryable(fmt.Errorf("call content safety service: %w", err))
	}
	defer resp.Body.Close()
	body, readErr := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if readErr != nil {
		return Decision{}, outbox.Retryable(fmt.Errorf("read content safety response: %w", readErr))
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		requestErr := fmt.Errorf("content safety service returned HTTP %d", resp.StatusCode)
		if resp.StatusCode == http.StatusRequestTimeout || resp.StatusCode == http.StatusTooEarly || resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode >= 500 {
			return Decision{}, outbox.Retryable(requestErr)
		}
		return Decision{}, requestErr
	}
	var result struct {
		Decision    string `json:"decision"`
		Sensitivity string `json:"sensitivity"`
		ReasonCode  string `json:"reason_code"`
		RequestRef  string `json:"request_ref"`
	}
	if err = json.Unmarshal(body, &result); err != nil {
		return Decision{}, outbox.Retryable(errors.New("content safety response is not valid JSON"))
	}
	result.Decision = strings.ToUpper(strings.TrimSpace(result.Decision))
	result.Sensitivity = strings.ToLower(strings.TrimSpace(result.Sensitivity))
	result.ReasonCode = strings.ToLower(strings.TrimSpace(result.ReasonCode))
	if (result.Decision != "ALLOW" && result.Decision != "BLOCK" && result.Decision != "REVIEW") ||
		(result.Sensitivity != "normal" && result.Sensitivity != "sensitive" && result.Sensitivity != "high") ||
		!validReasonCode(result.ReasonCode, result.Decision == "ALLOW") {
		return Decision{}, outbox.Retryable(errors.New("content safety response failed schema validation"))
	}
	return Decision{
		AllowOrdinaryStory: result.Decision == "ALLOW",
		Sensitivity:        result.Sensitivity,
		Reason:             result.ReasonCode,
		ProviderRef:        "managed-content-safety:" + c.policyRef,
		RequestRef:         strings.TrimSpace(result.RequestRef),
	}, nil
}

func validReasonCode(value string, allowEmpty bool) bool {
	if value == "" {
		return allowEmpty
	}
	if len(value) > 64 {
		return false
	}
	for _, character := range value {
		if (character < 'a' || character > 'z') && (character < '0' || character > '9') && character != '_' && character != '-' {
			return false
		}
	}
	return true
}

func containsAny(content string, terms []string) bool {
	for _, term := range terms {
		if strings.Contains(content, term) {
			return true
		}
	}
	return false
}