package service

import (
	"archive/tar"
	"compress/gzip"
	"context"
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/google/uuid"

	"openvpn-manager/internal/config"
	"openvpn-manager/internal/model"
	"openvpn-manager/internal/store"
	"openvpn-manager/pkg/openvpn"
)

// Service 业务逻辑聚合，供 API 层调用。
// 任何对实例/用户/证书/备份的变更都应经过这里，从而写入审计日志。
type Service struct {
	Cfg   *config.Config
	Store *store.Store
	Ovm   *openvpn.Manager
}

func New(cfg *config.Config, st *store.Store, ovm *openvpn.Manager) *Service {
	return &Service{Cfg: cfg, Store: st, Ovm: ovm}
}

func (s *Service) audit(c context.Context, action, target, detail, result, ip string) {
	username, _ := c.Value("user").(string)
	if username == "" {
		username = "system"
	}
	_ = s.Store.AppendAudit(model.AuditLog{
		ID:     uuid.NewString(),
		Time:   time.Now(),
		User:   username,
		Action: action,
		Target: target,
		Result: result,
		Detail: detail,
		IP:     ip,
	})
}

// AuditForAPI 在 API 层被调用时手动写入(因为 gin context 转为 context.Context)。
func (s *Service) AuditForAPI(c *gin.Context, action, target, detail, result string) {
	username, _ := c.Get("user")
	un, _ := username.(string)
	if un == "" {
		un = "system"
	}
	_ = s.Store.AppendAudit(model.AuditLog{
		ID:     uuid.NewString(),
		Time:   time.Now(),
		User:   un,
		Action: action,
		Target: target,
		Result: result,
		Detail: detail,
		IP:     c.ClientIP(),
	})
}

// CreateInstance 新建一个 OpenVPN 实例，并签发服务端证书、生成 server.conf。
func (s *Service) CreateInstance(in model.Instance) (*model.Instance, error) {
	if in.Name == "" {
		return nil, fmt.Errorf("name required")
	}
	if in.Port == 0 {
		return nil, fmt.Errorf("port required")
	}
	if in.Proto == "" {
		in.Proto = "udp"
	}
	if in.Dev == "" {
		in.Dev = "tun"
	}
	if in.Subnet == "" {
		in.Subnet = "10.8.0.0/24"
	}
	if in.AccessMode == "" {
		in.AccessMode = model.AccessOpen
	}
	// 校验白名单 CIDR
	for _, c := range in.AllowNetworks {
		if err := openvpn.ValidateCIDR(c); err != nil {
			return nil, fmt.Errorf("instance allow_networks: %w", err)
		}
	}
	// 名称查重
	if _, err := s.Store.GetInstanceByName(in.Name); err == nil {
		return nil, fmt.Errorf("instance %s already exists", in.Name)
	}
	// 确保 CA
	if err := s.Ovm.EnsureCA(); err != nil {
		return nil, err
	}
	in.ID = uuid.NewString()
	in.Status = "stopped"
	in.CreatedAt = time.Now()
	in.UpdatedAt = time.Now()
	// 创建实例目录
	if err := os.MkdirAll(s.Cfg.InstanceDir(in.Name), 0o755); err != nil {
		return nil, err
	}
	if err := os.MkdirAll(filepath.Join(s.Cfg.InstanceDir(in.Name), "logs"), 0o755); err != nil {
		return nil, err
	}
	// 签发服务端证书
	if err := s.Ovm.IssueServerCert(in.Name); err != nil {
		return nil, fmt.Errorf("issue server cert: %w", err)
	}
	// 写 server.conf + 白名单脚本
	ccdDir := filepath.Join(s.Cfg.InstanceDir(in.Name), "ccd")
	if err := s.Ovm.WriteServerConf(&in, ccdDir); err != nil {
		return nil, fmt.Errorf("write conf: %w", err)
	}
	if in.AccessMode == model.AccessWhitelist {
		if _, err := s.Ovm.AllowNetworksScript(in.Name, in.AllowNetworks); err != nil {
			return nil, fmt.Errorf("gen whitelist scripts: %w", err)
		}
	}
	if err := s.Store.UpsertInstance(in); err != nil {
		return nil, err
	}
	return &in, nil
}

// UpdateInstance 仅更新可热改字段（端口/子网需要重启生效）。
func (s *Service) UpdateInstance(in model.Instance) error {
	old, err := s.Store.GetInstance(in.ID)
	if err != nil {
		return err
	}
	if in.AccessMode == "" {
		in.AccessMode = old.AccessMode
	}
	if in.Cipher == "" {
		in.Cipher = old.Cipher
	}
	if in.AuthDigest == "" {
		in.AuthDigest = old.AuthDigest
	}
	if in.Dev == "" {
		in.Dev = old.Dev
	}
	if in.Subnet == "" {
		in.Subnet = old.Subnet
	}
	for _, c := range in.AllowNetworks {
		if err := openvpn.ValidateCIDR(c); err != nil {
			return fmt.Errorf("instance allow_networks: %w", err)
		}
	}
	in.CreatedAt = old.CreatedAt
	in.UpdatedAt = time.Now()
	in.Status = old.Status
	in.PID = old.PID
	ccdDir := filepath.Join(s.Cfg.InstanceDir(in.Name), "ccd")
	if err := s.Ovm.WriteServerConf(&in, ccdDir); err != nil {
		return err
	}
	if in.AccessMode == model.AccessWhitelist {
		if _, err := s.Ovm.AllowNetworksScript(in.Name, in.AllowNetworks); err != nil {
			return err
		}
	}
	if err := s.Store.UpsertInstance(in); err != nil {
		return err
	}
	// 实例级 allow_networks 变更后,刷新所有用户的 ccd
	inst := in
	for _, u := range s.Store.ListUsers(inst.ID) {
		u := u
		merged := openvpn.MergeAllowNetworks(inst.AllowNetworks, u.AllowNetworks)
		if err := s.writeUserCCD(&inst, &u, merged); err != nil {
			return err
		}
	}
	return nil
}

// DeleteInstance 移除实例及其 PKI/配置。
func (s *Service) DeleteInstance(id string) error {
	in, err := s.Store.GetInstance(id)
	if err != nil {
		return err
	}
	if in.Status == "running" {
		_ = s.StopInstance(id)
	}
	// 清理用户记录与目录
	for _, u := range s.Store.ListUsers(id) {
		_ = s.Store.DeleteUser(u.ID)
	}
	_ = os.RemoveAll(s.Cfg.InstanceDir(in.Name))
	_ = os.RemoveAll(filepath.Join(s.Cfg.ClientsDir(), in.Name))
	return s.Store.DeleteInstance(id)
}

// StartInstance 在前台启动 openvpn。
// 注意：本服务应以 root 运行；非 root 场景下应通过 systemd 单元托管。
func (s *Service) StartInstance(id string) error {
	in, err := s.Store.GetInstance(id)
	if err != nil {
		return err
	}
	if in.Status == "running" {
		return fmt.Errorf("already running")
	}
	conf := s.Ovm.InstanceConf(in.Name)
	if _, err := os.Stat(conf); err != nil {
		return fmt.Errorf("conf missing: %w", err)
	}
	cmd := exec.Command(s.Cfg.OpenVPNBin,
		"--cd", s.Cfg.InstanceDir(in.Name),
		"--config", conf)
	logf, _ := os.OpenFile(filepath.Join(s.Cfg.InstanceDir(in.Name), "logs", "openvpn-stdout.log"),
		os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o644)
	if logf != nil {
		cmd.Stdout = logf
		cmd.Stderr = logf
	}
	if err := cmd.Start(); err != nil {
		return err
	}
	in.Status = "running"
	in.PID = cmd.Process.Pid
	in.UpdatedAt = time.Now()
	_ = s.Store.UpsertInstance(*in)
	// 后台释放
	go func() {
		_ = cmd.Wait()
		// 进程退出时回写状态(简单模型)
		cur, err := s.Store.GetInstance(id)
		if err == nil && cur.PID == cmd.Process.Pid {
			cur.Status = "stopped"
			cur.PID = 0
			cur.UpdatedAt = time.Now()
			_ = s.Store.UpsertInstance(*cur)
		}
	}()
	return nil
}

// StopInstance 通过 SIGTERM 停止实例。
func (s *Service) StopInstance(id string) error {
	in, err := s.Store.GetInstance(id)
	if err != nil {
		return err
	}
	if in.PID == 0 {
		in.Status = "stopped"
		return s.Store.UpsertInstance(*in)
	}
	proc, err := os.FindProcess(in.PID)
	if err != nil {
		return err
	}
	if err := proc.Signal(os.Interrupt); err != nil {
		// 兜底：直接 Kill
		_ = proc.Signal(os.Kill)
	}
	in.Status = "stopped"
	in.PID = 0
	in.UpdatedAt = time.Now()
	return s.Store.UpsertInstance(*in)
}

// CreateUser 新建客户端用户并签发证书。
func (s *Service) CreateUser(u model.VPNUser) (*model.VPNUser, error) {
	if u.Username == "" {
		return nil, fmt.Errorf("username required")
	}
	in, err := s.Store.GetInstance(u.InstanceID)
	if err != nil {
		return nil, err
	}
	if _, err := s.Store.GetUserByCN(u.InstanceID, u.Username); err == nil {
		return nil, fmt.Errorf("user %s already exists", u.Username)
	}
	// 校验用户级 CIDR
	for _, c := range u.AllowNetworks {
		if err := openvpn.ValidateCIDR(c); err != nil {
			return nil, fmt.Errorf("user allow_networks: %w", err)
		}
	}
	u.ID = uuid.NewString()
	u.Enabled = true
	u.CreatedAt = time.Now()
	// 签发证书（Manager 按实例名索引 PKI）
	if _, _, err := s.Ovm.IssueCert(in.Name, u.Username); err != nil {
		return nil, err
	}
	// CCD: 合并实例级与用户级白名单(白名单模式才生效)
	merged := openvpn.MergeAllowNetworks(in.AllowNetworks, u.AllowNetworks)
	if err := s.writeUserCCD(in, &u, merged); err != nil {
		return nil, err
	}
	// 预生成 ovpn(以空 host 生成占位，用户在 UI 上下载)
	if _, err := s.Ovm.GenerateClientOVPNFor(&u, in, "vpn.example.com"); err != nil {
		return nil, err
	}
	if err := s.Store.UpsertUser(u); err != nil {
		return nil, err
	}
	return &u, nil
}

// GenerateOVPN 下载/重新生成 .ovpn，remoteHost 由前端传入。
func (s *Service) GenerateOVPN(userID, remoteHost string) (string, error) {
	u, err := s.Store.GetUser(userID)
	if err != nil {
		return "", err
	}
	in, err := s.Store.GetInstance(u.InstanceID)
	if err != nil {
		return "", err
	}
	return s.Ovm.GenerateClientOVPNFor(u, in, remoteHost)
}

// RevokeUser 吊销用户：禁用 + 标记。
func (s *Service) RevokeUser(userID string) error {
	u, err := s.Store.GetUser(userID)
	if err != nil {
		return err
	}
	u.Enabled = false
	now := time.Now()
	u.RevokedAt = &now
	if err := s.Store.UpsertUser(*u); err != nil {
		return err
	}
	// 在 ccd 写入禁用标记
	in, err2 := s.Store.GetInstance(u.InstanceID)
	if err2 == nil {
		body := "# revoked by manager\n"
		_ = s.Ovm.WriteCCD(in.Name, u.Username, body)
	}
	return nil
}

// DeleteUser 删除用户及证书。
func (s *Service) DeleteUser(userID string) error {
	u, err := s.Store.GetUser(userID)
	if err != nil {
		return err
	}
	in, _ := s.Store.GetInstance(u.InstanceID)
	if in != nil {
		_ = s.Ovm.DeleteCCD(in.Name, u.Username)
		_ = os.Remove(filepath.Join(s.Ovm.PKIPath(in.Name), "issued", u.Username+".crt"))
		_ = os.Remove(filepath.Join(s.Ovm.PKIPath(in.Name), "private", u.Username+".key"))
		_ = os.Remove(filepath.Join(s.Cfg.ClientsDir(), in.Name, u.Username+".ovpn"))
	}
	return s.Store.DeleteUser(userID)
}

// UpdateUser 修改用户(主要用于改 allow_networks / static_ip 等)。
func (s *Service) UpdateUser(u model.VPNUser) error {
	old, err := s.Store.GetUser(u.ID)
	if err != nil {
		return err
	}
	for _, c := range u.AllowNetworks {
		if err := openvpn.ValidateCIDR(c); err != nil {
			return fmt.Errorf("user allow_networks: %w", err)
		}
	}
	u.CreatedAt = old.CreatedAt
	u.Enabled = old.Enabled
	u.RevokedAt = old.RevokedAt
	in, err := s.Store.GetInstance(u.InstanceID)
	if err != nil {
		return err
	}
	merged := openvpn.MergeAllowNetworks(in.AllowNetworks, u.AllowNetworks)
	if err := s.writeUserCCD(in, &u, merged); err != nil {
		return err
	}
	return s.Store.UpsertUser(u)
}

// writeUserCCD 把允许网段写进 ccd/<cn>,client-connect 脚本读取后推送 route。
// 文件内容:
//   - 第 1 行 ifconfig-push (固定 IP)
//   - 之后每行一个 CIDR (允许的网段)
// 这样设计既兼容现有 static_ip 场景,又能让 client-connect.sh 简单 grep。
func (s *Service) writeUserCCD(in *model.Instance, u *model.VPNUser, allowNets []string) error {
	var b strings.Builder
	if u.StaticIP != "" {
		b.WriteString("ifconfig-push " + u.StaticIP + " 255.255.255.0\n")
	}
	for _, c := range allowNets {
		b.WriteString(c + "\n")
	}
	return s.Ovm.WriteCCD(in.Name, u.Username, b.String())
}

// CertInfos 汇总所有用户证书的过期时间。
func (s *Service) CertInfos() ([]model.CertInfo, error) {
	var out []model.CertInfo
	now := time.Now()
	for _, in := range s.Store.ListInstances() {
		pki := s.Ovm.PKIPath(in.Name)
		issuedDir := filepath.Join(pki, "issued")
		entries, err := os.ReadDir(issuedDir)
		if err != nil {
			continue
		}
		for _, e := range entries {
			if e.IsDir() || !strings.HasSuffix(e.Name(), ".crt") {
				continue
			}
			cn := strings.TrimSuffix(e.Name(), ".crt")
			if cn == "server" {
				continue
			}
			notAfter, err := s.Ovm.CertNotAfter(filepath.Join(issuedDir, e.Name()))
			if err != nil {
				continue
			}
			out = append(out, model.CertInfo{
				InstanceID: in.ID,
				Username:   cn,
				NotAfter:   notAfter,
				DaysLeft:   int(notAfter.Sub(now).Hours() / 24),
			})
		}
	}
	return out, nil
}

// ListOnline 解析 status 文件获取在线客户端。
func (s *Service) ListOnline(instanceID string) ([]openvpn.StatusEntry, error) {
	in, err := s.Store.GetInstance(instanceID)
	if err != nil {
		return nil, err
	}
	statusPath := filepath.Join(s.Cfg.InstanceDir(in.Name), "status.log")
	return s.Ovm.ParseStatus(statusPath)
}

// Backup 创建 tar.gz 备份。
func (s *Service) Backup(note string) (*model.Backup, error) {
	if err := os.MkdirAll(s.Cfg.BackupsDir(), 0o755); err != nil {
		return nil, err
	}
	id := uuid.NewString()
	ts := time.Now().Format("20060102-150405")
	fp := filepath.Join(s.Cfg.BackupsDir(), "backup-"+ts+"-"+id[:8]+".tar.gz")
	f, err := os.Create(fp)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	gz := gzip.NewWriter(f)
	defer gz.Close()
	tw := tar.NewWriter(gz)
	defer tw.Close()

	add := func(rel string) error {
		abs := filepath.Join(s.Cfg.DataDir, rel)
		return filepath.Walk(abs, func(path string, info os.FileInfo, err error) error {
			if err != nil {
				return nil
			}
			if info.IsDir() {
				return nil
			}
			hdr, err := tar.FileInfoHeader(info, "")
			if err != nil {
				return nil
			}
			hdr.Name = filepath.ToSlash(filepath.Join(rel, strings.TrimPrefix(path, abs)))
			if err := tw.WriteHeader(hdr); err != nil {
				return nil
			}
			data, err := os.ReadFile(path)
			if err != nil {
				return nil
			}
			_, _ = tw.Write(data)
			return nil
		})
	}
	for _, sub := range []string{"pki", "instances", "clients"} {
		_ = add(sub)
	}
	b := &model.Backup{
		ID:        id,
		CreatedAt: time.Now(),
		Filename:  filepath.Base(fp),
		Note:      note,
		Includes:  []string{"pki", "instances", "clients"},
	}
	fi, _ := os.Stat(fp)
	if fi != nil {
		b.Size = fi.Size()
	}
	_ = s.Store.AddBackup(*b)
	return b, nil
}

// Restore 从备份恢复。会覆盖现有数据。
func (s *Service) Restore(backupID string) error {
	var bk *model.Backup
	for _, b := range s.Store.ListBackups() {
		if b.ID == backupID {
			b := b
			bk = &b
			break
		}
	}
	if bk == nil {
		return fmt.Errorf("backup not found")
	}
	src := filepath.Join(s.Cfg.BackupsDir(), bk.Filename)
	f, err := os.Open(src)
	if err != nil {
		return err
	}
	defer f.Close()
	var r io.Reader = f
	if strings.HasSuffix(src, ".gz") {
		gz, err := gzip.NewReader(f)
		if err != nil {
			return err
		}
		defer gz.Close()
		r = gz
	}
	tr := tar.NewReader(r)
	for {
		hdr, err := tr.Next()
		if err == io.EOF {
			break
		}
		if err != nil {
			return err
		}
		target := filepath.Join(s.Cfg.DataDir, hdr.Name)
		if hdr.FileInfo().IsDir() {
			_ = os.MkdirAll(target, 0o755)
			continue
		}
		_ = os.MkdirAll(filepath.Dir(target), 0o755)
		out, err := os.OpenFile(target, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o600)
		if err != nil {
			return err
		}
		_, _ = io.Copy(out, tr)
		_ = out.Close()
	}
	return nil
}

// DeleteBackup 删除备份文件与索引。
func (s *Service) DeleteBackup(id string) error {
	for _, b := range s.Store.ListBackups() {
		if b.ID == id {
			_ = os.Remove(filepath.Join(s.Cfg.BackupsDir(), b.Filename))
			return s.Store.DeleteBackup(id)
		}
	}
	return fmt.Errorf("not found")
}

// RandomToken 生成短随机串。
func RandomToken(n int) string {
	b := make([]byte, n)
	_, _ = rand.Read(b)
	return hex.EncodeToString(b)
}