package auth

import (
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"errors"
	"net/http"
	"strconv"
	"strings"
	"time"

	"golang.org/x/crypto/bcrypt"
)

const (
	AdminCookie   = "artifacto_admin"
	adminLifetime = 30 * 24 * time.Hour
)

type ctxKey int

const ctxAdmin ctxKey = 1

type Admin struct {
	passwordHash []byte
	secret       []byte
	secure       bool
}

func NewAdmin(password, secretHex string, secure bool) (*Admin, error) {
	if password == "" {
		return nil, errors.New("ADMIN_PASSWORD required")
	}
	if len(secretHex) < 32 {
		return nil, errors.New("SESSION_SECRET must be >= 32 chars")
	}
	h, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
	if err != nil {
		return nil, err
	}
	return &Admin{passwordHash: h, secret: []byte(secretHex), secure: secure}, nil
}

func (a *Admin) VerifyPassword(p string) bool {
	return bcrypt.CompareHashAndPassword(a.passwordHash, []byte(p)) == nil
}

// Issue returns a signed cookie value "issued_at.sig".
func (a *Admin) Issue() string {
	issued := strconv.FormatInt(time.Now().Unix(), 10)
	return issued + "." + a.sign("admin|"+issued)
}

func (a *Admin) Verify(raw string) bool {
	parts := strings.SplitN(raw, ".", 2)
	if len(parts) != 2 {
		return false
	}
	issued, err := strconv.ParseInt(parts[0], 10, 64)
	if err != nil {
		return false
	}
	if time.Since(time.Unix(issued, 0)) > adminLifetime {
		return false
	}
	expected := a.sign("admin|" + parts[0])
	return hmac.Equal([]byte(expected), []byte(parts[1]))
}

func (a *Admin) sign(s string) string {
	m := hmac.New(sha256.New, a.secret)
	m.Write([]byte(s))
	return base64.RawURLEncoding.EncodeToString(m.Sum(nil))
}

func (a *Admin) SetCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     AdminCookie,
		Value:    a.Issue(),
		Path:     "/",
		HttpOnly: true,
		Secure:   a.secure,
		SameSite: http.SameSiteLaxMode,
		Expires:  time.Now().Add(adminLifetime),
	})
}

func (a *Admin) ClearCookie(w http.ResponseWriter) {
	http.SetCookie(w, &http.Cookie{
		Name:     AdminCookie,
		Value:    "",
		Path:     "/",
		HttpOnly: true,
		Secure:   a.secure,
		SameSite: http.SameSiteLaxMode,
		MaxAge:   -1,
	})
}

// Middleware allows the request through if the admin cookie is valid; otherwise
// redirects to /login (for HTML nav) or returns 401 (for API/HTMX).
func (a *Admin) Middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		c, err := r.Cookie(AdminCookie)
		if err != nil || !a.Verify(c.Value) {
			if isAPI(r) {
				http.Error(w, "unauthorized", http.StatusUnauthorized)
				return
			}
			http.Redirect(w, r, "/login?next="+r.URL.RequestURI(), http.StatusSeeOther)
			return
		}
		ctx := context.WithValue(r.Context(), ctxAdmin, true)
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

func isAPI(r *http.Request) bool {
	if strings.HasPrefix(r.URL.Path, "/api/") {
		return true
	}
	if r.Header.Get("HX-Request") == "true" {
		return true
	}
	return false
}

func IsAdmin(ctx context.Context) bool {
	v, _ := ctx.Value(ctxAdmin).(bool)
	return v
}