package auth

import (
	"fmt"
	"strings"
	"time"

	jwt "github.com/golang-jwt/jwt/v4"
)

type PermMask uint8

const (
	None PermMask = 0
	Read PermMask = 1 << iota
	Write
	Delete
)

func (p PermMask) HasRead() bool   { return p&Read != 0 }
func (p PermMask) HasWrite() bool  { return p&Write != 0 }
func (p PermMask) HasDelete() bool { return p&Delete != 0 }
func ParseMask(s string) PermMask {
	var p PermMask
	for _, r := range strings.ToLower(s) {
		switch r {
		case 'r':
			p |= Read
		case 'w':
			p |= Read | Write
		case 'd':
			p |= Read | Write | Delete
		}
	}
	return p
}

type PathRule struct {
	Dir          string
	Mask         PermMask
	Deny         bool
	ChildrenOnly bool
}
type Account struct {
	Username, Password string
	Mask               PermMask
	Rules              []PathRule
}
type Manager struct {
	Accounts map[string]*Account
	Guest    *Account
}

func ParseRules(values []string) (*Manager, error) {
	m := &Manager{Accounts: map[string]*Account{}}
	for _, value := range values {
		for _, item := range strings.Split(value, "|") {
			if item == "" {
				continue
			}
			fields := strings.Split(item, ":")
			if len(fields) < 3 || len(fields)%2 == 0 {
				continue
			}
			a := &Account{Username: fields[0], Password: fields[1], Mask: ParseMask(fields[2])}
			for i := 3; i+1 < len(fields); i += 2 {
				a.Rules = append(a.Rules, PathRule{Dir: strings.Trim(fields[i], "/"), Mask: ParseMask(fields[i+1])})
			}
			if a.Username == "" {
				m.Guest = a
			} else {
				m.Accounts[a.Username] = a
			}
		}
	}
	if m.Guest == nil {
		m.Guest = &Account{Mask: Read | Write | Delete}
	}
	return m, nil
}

func (m *Manager) Authenticate(user, pwd string) *Account {
	if a, ok := m.Accounts[user]; ok && a.Password == pwd {
		return a
	}
	if user == "" && pwd == "" {
		return m.Guest
	}
	return nil
}
func (a *Account) MaskFor(path string) PermMask {
	return a.maskFor(path, false)
}

// MaskForEntry returns the permission shown for a directory/file while its
// parent directory is being listed. CHFS section rules rule.r/rule.w/rule.d
// affect the contents of the named directory, but the directory entry itself
// keeps the inherited permission until it is opened.
func (a *Account) MaskForEntry(path string) PermMask {
	return a.maskFor(path, true)
}

func (a *Account) maskFor(path string, entry bool) PermMask {
	path = strings.Trim(path, "/")
	best := -1
	mask := a.Mask
	for _, r := range a.Rules {
		d := strings.Trim(r.Dir, "/")
		if !matchPath(d, path) {
			continue
		}
		if entry && r.ChildrenOnly && matchPathExact(d, path) {
			continue
		}
		if len(d) > best {
			best = len(d)
			if r.Deny {
				mask = None
			} else {
				mask = r.Mask
			}
		}
	}
	return mask
}
func matchPath(pattern, path string) bool {
	if pattern == "" {
		return path == ""
	}
	pp := strings.Split(pattern, "/")
	ps := strings.Split(path, "/")
	if len(ps) < len(pp) {
		return false
	}
	for i, p := range pp {
		if !matchSegment(p, ps[i]) {
			return false
		}
	}
	return true
}

func matchSegment(pattern, value string) bool {
	p := []rune(pattern)
	v := []rune(value)
	dp := make([][]bool, len(p)+1)
	for i := range dp {
		dp[i] = make([]bool, len(v)+1)
	}
	dp[0][0] = true
	for i := 1; i <= len(p); i++ {
		if p[i-1] == '*' {
			dp[i][0] = dp[i-1][0]
		}
	}
	for i := 1; i <= len(p); i++ {
		for j := 1; j <= len(v); j++ {
			switch p[i-1] {
			case '*':
				dp[i][j] = dp[i-1][j] || dp[i][j-1]
			case '?':
				dp[i][j] = dp[i-1][j-1]
			default:
				dp[i][j] = dp[i-1][j-1] && p[i-1] == v[j-1]
			}
		}
	}
	return dp[len(p)][len(v)]
}

func matchPathExact(pattern, path string) bool {
	pp := strings.Split(strings.Trim(pattern, "/"), "/")
	ps := strings.Split(strings.Trim(path, "/"), "/")
	if len(pp) != len(ps) {
		return false
	}
	return matchPath(pattern, path)
}

func MatchPath(pattern, path string) bool { return matchPath(pattern, path) }

const jwtSecret = "_pengyichen2015_"

type jwtClaims struct {
	Acc string `json:"acc"`
	jwt.StandardClaims
}

func NewToken(username string, timeoutMinutes int) (string, error) {
	if timeoutMinutes <= 0 {
		timeoutMinutes = 30
	}
	claims := jwtClaims{Acc: username, StandardClaims: jwt.StandardClaims{ExpiresAt: time.Now().Add(time.Duration(timeoutMinutes) * time.Minute).Unix()}}
	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString([]byte(jwtSecret))
}

func GetAccFromToken(raw string) (string, error) {
	if raw == "" {
		return "", fmt.Errorf("empty token")
	}
	var claims jwtClaims
	token, err := jwt.ParseWithClaims(raw, &claims, func(t *jwt.Token) (interface{}, error) {
		if t.Method != jwt.SigningMethodHS256 {
			return nil, fmt.Errorf("unexpected signing method: %s", t.Method.Alg())
		}
		return []byte(jwtSecret), nil
	})
	if err != nil || token == nil || !token.Valid {
		if err == nil {
			err = fmt.Errorf("invalid token")
		}
		return "", err
	}
	if claims.Acc == "" {
		return "", fmt.Errorf("token missing account")
	}
	return claims.Acc, nil
}