package common

import (
	"errors"
	"fmt"
	"io/fs"
	"os"
	"os/user"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"syscall"

	"code.gitea.io/sdk/gitea"
)

var (
	ErrorPIDInUse = errors.New("daemon is already running")
	ErrLockFailed = errors.New("failed to acquire a lock on the PID file")
	ErrBlankCert  = errors.New("cert is blank")
)

type Domain struct {
	name        *string
	config      *AppConfig
	description *string
	gtClient    *gitea.Client
}

// 0x01
func createPIDFile() {
	file, err := os.Create("/var/run/certman.pid")
	if err != nil {
		fmt.Printf("0x01: Error creating PID file: %v\n", err)
		return
	}
	err = file.Close()
	if err != nil {
		fmt.Printf("0x01: Error closing PID file: %v\n", err)
		return
	}
}

// 0x02
func ClearPIDFile() {
	file, err := os.OpenFile("/var/run/certman.pid", os.O_RDWR|os.O_CREATE, 0644)
	if err != nil {
		fmt.Printf("0x02: Error opening PID file: %v\n", err)
		return
	}
	defer file.Close()

	err = file.Truncate(0)
	if err != nil {
		fmt.Printf("0x02: Error writing PID file: %v\n", err)
		return
	}
}

// 0x03
func CreateOrUpdatePIDFile(filename string) error {
	pidBytes, err := os.ReadFile(filename)
	if err != nil {
		fmt.Printf("0x03: Error reading PID file: %v\n", err)
		return err
	}

	pidStr := strings.TrimSpace(string(pidBytes))
	isPidFileEmpty := pidStr == ""

	if !isPidFileEmpty {
		pid, err := strconv.Atoi(pidStr)
		if err != nil {
			fmt.Printf("0x03: Error parsing PID file: %v\n", err)
			return err
		}

		isProcActive, err := isProcessActive(pid)
		if err != nil {
			fmt.Printf("0x03: Error checking if process is active: %v\n", err)
			return err

		}
		if isProcActive {
			return ErrorPIDInUse
		}
	}

	pidFile, err := os.OpenFile(filename, os.O_RDWR|os.O_CREATE, 0644)
	if err != nil {
		if os.IsNotExist(err) {
			createPIDFile()
		} else {
			fmt.Printf("0x03: Error opening PID file: %v\n", err)
			return err
		}
	}
	defer pidFile.Close()

	if err := syscall.Flock(int(pidFile.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
		if errors.Is(err, syscall.EWOULDBLOCK) {
			return ErrLockFailed
		}
		return fmt.Errorf("error locking PID file: %w", err)
	}
	curPid := os.Getpid()
	if _, err := pidFile.Write([]byte(strconv.Itoa(curPid))); err != nil {
		return fmt.Errorf("error writing pid to PID file: %w", err)
	}

	return nil
}

// 0x04
// isProcessActive checks whether the process with the provided PID is running.
func isProcessActive(pid int) (bool, error) {
	if pid <= 0 {
		return false, errors.New("invalid process ID")
	}
	process, err := os.FindProcess(pid)
	if err != nil {
		// On Unix systems, os.FindProcess always succeeds and returns a process with the given pid, irrespective of whether the process exists.
		return false, nil
	}

	err = process.Signal(syscall.Signal(0))
	if err != nil {
		if errors.Is(err, syscall.ESRCH) {
			// The process does not exist
			return false, nil
		} else if errors.Is(err, os.ErrProcessDone) {
			return false, nil
		}
		// Some other unexpected error
		return false, err
	}

	// The process exists and is active
	return true, nil
}

// 0x05
func DaemonProcess() (*os.Process, error) {
	pidBytes, err := os.ReadFile("/var/run/certman.pid")
	if err != nil {
		fmt.Printf("0x05: Error getting PID from /var/run/certman.pid: %v\n", err)
		return nil, err
	}
	pidStr := strings.TrimSpace(string(pidBytes))
	daemonPid, err := strconv.Atoi(pidStr)
	if err != nil {
		fmt.Printf("0x05: Error converting PID string to int (%s): %v\n", pidStr, err)
		return nil, err
	}
	isProcActive, err := isProcessActive(daemonPid)
	if err != nil {
		fmt.Printf("0x05: Error checking if process is active: %v\n", err)
	}
	if !isProcActive {
		return nil, errors.New("process is not active")
	}
	proc, err := os.FindProcess(daemonPid)
	if err != nil {
		fmt.Printf("0x05: Error finding process with PID %d: %v\n", daemonPid, err)
		return nil, err
	}
	return proc, nil
}

func LinkFile(source, target, domain, extension string) error {
	if target == "" {
		return ErrBlankCert
	}
	linkInfo, err := os.Stat(target)
	if err != nil {
		if os.IsNotExist(err) {
			err = os.Symlink(source, target)
			if err != nil {
				return err
			}
			return nil
		}
		return err
	}
	if linkInfo.IsDir() {
		target = filepath.Join(target, domain+extension)
		err = os.Symlink(source, target)
		if err != nil {
			return err
		}
	}

	return nil
}

func FileExists(path string) bool {
	_, err := os.Stat(path)
	return err == nil
}

func contains(slice []string, value string) (sliceHas bool, index int) {
	for i, entry := range slice {
		if entry == value {
			return true, i
		}
	}
	return false, -1
}

func insert(a []string, index int, value string) []string {
	last := len(a) - 1
	a = append(a, a[last])
	copy(a[index+1:], a[index:last])
	a[index] = value
	return a
}

func SanitizeDomainKey(s string) string {
	s = strings.TrimSpace(strings.ToLower(s))
	r := strings.NewReplacer("/", "_", "\\", "_", " ", "_", ":", "_")
	return r.Replace(s)
}

func ChownRecursive(path string, uid, gid int) error {
	return filepath.WalkDir(path, func(name string, d fs.DirEntry, err error) error {
		if err != nil {
			return err // Stop if we encounter a permission error on a specific file
		}
		// Apply ownership change to the current item
		return os.Chown(name, uid, gid)
	})
}

func LookupGID(group string) (int, error) {
	g, err := user.LookupGroup(group)
	if err != nil {
		return 0, err
	}
	return strconv.Atoi(g.Gid)
}

// MakeCredential resolves username/groupname to uid/gid for syscall.Credential.
// Note: actually *using* different credentials typically requires the server
// process to have appropriate privileges (often root).
func MakeCredential(username, groupname string) (*syscall.Credential, error) {
	var uid, gid uint32
	var haveUID, haveGID bool

	if username != "" {
		u, err := user.Lookup(username)
		if err != nil {
			return nil, fmt.Errorf("unknown user")
		}
		parsed, err := strconv.ParseUint(u.Uid, 10, 32)
		if err != nil {
			return nil, fmt.Errorf("bad uid")
		}
		uid = uint32(parsed)
		haveUID = true

		// If group not explicitly provided, default to user's primary group.
		if groupname == "" && u.Gid != "" {
			parsedG, err := strconv.ParseUint(u.Gid, 10, 32)
			if err == nil {
				gid = uint32(parsedG)
				haveGID = true
			}
		}
	}

	if groupname != "" {
		g, err := user.LookupGroup(groupname)
		if err != nil {
			return nil, fmt.Errorf("unknown group")
		}
		parsed, err := strconv.ParseUint(g.Gid, 10, 32)
		if err != nil {
			return nil, fmt.Errorf("bad gid")
		}
		gid = uint32(parsed)
		haveGID = true
	}

	// If only group was provided, keep current uid.
	if !haveUID {
		uid = uint32(os.Getuid())
	}
	if !haveGID {
		gid = uint32(os.Getgid())
	}

	return &syscall.Credential{Uid: uid, Gid: gid}, nil
}

func CertsDir(config *AppConfig, domainConfig *DomainConfig) string {
	if config == nil {
		return ""
	}
	if domainConfig == nil {
		return ""
	}

	if domainConfig.Certificates.DataRoot == "" {
		if config.Certificates.DataRoot == "" {
			workDir, err := os.Getwd()
			if err != nil {
				return "./"
			}
			return workDir
		}
		return config.Certificates.DataRoot
	}
	return domainConfig.Certificates.DataRoot
}

var fqdnRegex = regexp.MustCompile(`^(?i:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z]{2,}$`)

func IsValidFQDN(domain string) bool {
	return len(domain) <= 253 && fqdnRegex.MatchString(domain)
}