package notices

import (
	"context"
	"database/sql"
	"encoding/json"
	"fmt"
	"log/slog"
	"strings"
	"time"
)

// EmailSender 抽象邮件兜底通道(生产实现按 SMTP/第三方 API 注入,测试用 fake)。
type EmailSender interface {
	Send(ctx context.Context, to, subject, body string) error
}

// validNoticeTypes 与 migrations/sqlite/000026_notices.up.sql 的 CHECK 约束一致,
// 六值全部放行(nodectl 手发场景约束更窄,交由调用层——如 nodectl 命令——自行收紧)。
var validNoticeTypes = map[string]bool{
	"important": true,
	"feature":   true,
	"news":      true,
	"reward":    true,
	"version":   true,
	"promo":     true,
}

// PublishInput 是 Service.Publish 的入参;Email=true 仅 important 类型允许。
type PublishInput struct {
	Type      string
	TitleZH   string
	TitleEN   string
	BodyZH    string
	BodyEN    string
	Link      string
	ExpiresAt *time.Time
	Email     bool // 仅 important 允许 true
}

// Service 承载通知发布/撤回的业务规则:字段校验、审计留痕、important 邮件兜底。
//
// 审计选型(简案,见 task-5-brief):Service 直接持 *sql.DB 自写
// `INSERT INTO audit_log(actor,action,target,meta,at)`,不复用 codes.Store.WriteAuditLog——
// 避免 notices 包为了一个方法反向依赖 codes 包,保持依赖方向干净。actor 固定为 "nodectl"
// (当前唯一调用方是后台管理命令);失败仅记录,不影响主流程(照仓库既有审计写入惯例)。
type Service struct {
	st     *Store
	mailer EmailSender
	db     *sql.DB
}

// NewService 组装通知发布服务。mailer 可为 nil(仅当调用方保证不会传 Email=true 时安全)。
func NewService(st *Store, mailer EmailSender, db *sql.DB) *Service {
	return &Service{st: st, mailer: mailer, db: db}
}

func (s *Service) writeAudit(ctx context.Context, action, target string, meta map[string]any) {
	metaJSON := "null"
	if meta != nil {
		if b, err := json.Marshal(meta); err == nil {
			metaJSON = string(b)
		}
	}
	_, err := s.db.ExecContext(ctx,
		`INSERT INTO audit_log (actor, action, target, meta, at) VALUES (?, ?, ?, ?, ?)`,
		"nodectl", action, target, metaJSON, time.Now().UTC())
	if err != nil {
		// 审计失败不影响主流程,照仓库惯例仅记录。
		slog.Warn("notices: write audit log failed", "action", action, "target", target, "err", err)
	}
}

// Publish 校验并落库一条广播通知;Email=true 时对全体 active 用户尽力发送兜底邮件
// (单个失败仅记录日志、不中断,全部尝试后置位 email_sent_at)。
func (s *Service) Publish(ctx context.Context, in PublishInput) (int64, error) {
	if !validNoticeTypes[in.Type] {
		return 0, fmt.Errorf("notices: invalid type %q", in.Type)
	}
	if strings.TrimSpace(in.TitleZH) == "" {
		return 0, fmt.Errorf("notices: title_zh required")
	}
	if strings.TrimSpace(in.TitleEN) == "" {
		return 0, fmt.Errorf("notices: title_en required")
	}
	if in.Email && in.Type != "important" {
		return 0, fmt.Errorf("notices: email fallback only allowed for type=important, got %q", in.Type)
	}
	if in.Email && s.mailer == nil {
		return 0, fmt.Errorf("notices: email requested but no mailer configured")
	}

	now := time.Now().UTC()
	id, err := s.st.InsertBroadcast(ctx, in.Type, in.TitleZH, in.TitleEN, in.BodyZH, in.BodyEN, in.Link, now, in.ExpiresAt)
	if err != nil {
		return 0, fmt.Errorf("notices: insert broadcast: %w", err)
	}

	s.writeAudit(ctx, "notice_publish", fmt.Sprintf("notice:%d", id), map[string]any{
		"type":     in.Type,
		"title_zh": in.TitleZH,
	})

	if in.Email {
		s.sendEmailFallback(ctx, id, in)
	}

	return id, nil
}

// sendEmailFallback 对全体 active 用户逐个发送兜底邮件;单个失败仅记录日志继续,
// 全部尝试后统一置位 email_sent_at(幂等:Store.MarkEmailSent 只在未发送过时置位)。
func (s *Service) sendEmailFallback(ctx context.Context, id int64, in PublishInput) {
	emails, err := s.st.ListActiveUserEmails(ctx)
	if err != nil {
		slog.Warn("notices: list active user emails failed", "notice_id", id, "err", err)
		return
	}

	subject := fmt.Sprintf("【穿山甲】%s / %s", in.TitleZH, in.TitleEN)
	body := emailBody(in)

	for _, to := range emails {
		if err := s.mailer.Send(ctx, to, subject, body); err != nil {
			slog.Warn("notices: send email fallback failed", "notice_id", id, "to", to, "err", err)
			continue
		}
	}

	if err := s.st.MarkEmailSent(ctx, id, time.Now().UTC()); err != nil {
		slog.Warn("notices: mark email sent failed", "notice_id", id, "err", err)
	}
}

func emailBody(in PublishInput) string {
	var b strings.Builder
	b.WriteString(in.TitleZH)
	b.WriteString(" / ")
	b.WriteString(in.TitleEN)
	b.WriteString("\n\n")
	if in.BodyZH != "" {
		b.WriteString(in.BodyZH)
		b.WriteString("\n\n")
	}
	if in.BodyEN != "" {
		b.WriteString(in.BodyEN)
		b.WriteString("\n\n")
	}
	b.WriteString("在 App 内查看详情 / View details in the app")
	return b.String()
}

// RevokeByID 撤回一条通知并留痕审计;目标不存在或已撤回时返回错误。
func (s *Service) RevokeByID(ctx context.Context, id int64) error {
	if err := s.st.Revoke(ctx, id, time.Now().UTC()); err != nil {
		return fmt.Errorf("notices: revoke %d: %w", id, err)
	}
	s.writeAudit(ctx, "notice_revoke", fmt.Sprintf("notice:%d", id), nil)
	return nil
}