package auth

import (
	"errors"
	"log/slog"
	"net/http"
	"strconv"
	"time"

	"github.com/mithral/vellum/internal/httpx"
)

// Handlers serves the authentication and user-management endpoints.
type Handlers struct {
	auth *Authenticator
	log  *slog.Logger
}

// NewHandlers builds the auth HTTP layer.
func NewHandlers(a *Authenticator, log *slog.Logger) *Handlers {
	return &Handlers{auth: a, log: log}
}

// Register mounts the routes onto the shared mux.
func (h *Handlers) Register(mux *http.ServeMux) {
	// Public.
	mux.HandleFunc("POST /api/v1/auth/login", h.handleLogin)
	mux.HandleFunc("POST /api/v1/auth/logout", h.handleLogout)
	mux.HandleFunc("GET /api/v1/auth/me", h.handleMe)

	// Authenticated.
	mux.Handle("POST /api/v1/auth/password", h.auth.Require(h.handleChangePassword))

	// Admin: user management.
	mux.Handle("GET /api/v1/users", h.auth.RequireAdmin(http.HandlerFunc(h.handleListUsers)))
	mux.Handle("POST /api/v1/users", h.auth.RequireAdmin(http.HandlerFunc(h.handleCreateUser)))
	mux.Handle("GET /api/v1/users/{id}/grants", h.auth.RequireAdmin(http.HandlerFunc(h.handleListGrants)))
	mux.Handle("PUT /api/v1/users/{id}/grants/{libraryID}", h.auth.RequireAdmin(http.HandlerFunc(h.handlePutGrant)))
	mux.Handle("DELETE /api/v1/users/{id}/grants/{libraryID}", h.auth.RequireAdmin(http.HandlerFunc(h.handleDeleteGrant)))
}

// ── types ──────────────────────────────────────────────────────────────

// userDTO is the client-facing shape of a user. It never includes a hash.
type userDTO struct {
	ID          int64  `json:"id"`
	Username    string `json:"username"`
	DisplayName string `json:"display_name"`
	IsAdmin     bool   `json:"is_admin"`
	CreatedAt   string `json:"created_at"`
}

func toDTO(u User) userDTO {
	return userDTO{
		ID:          u.ID,
		Username:    u.Username,
		DisplayName: u.DisplayName,
		IsAdmin:     u.IsAdmin,
		CreatedAt:   u.CreatedAt.UTC().Format(time.RFC3339),
	}
}

// ── handlers ───────────────────────────────────────────────────────────

func (h *Handlers) handleLogin(w http.ResponseWriter, r *http.Request) {
	var req struct {
		Username    string `json:"username"`
		Password    string `json:"password"`
		DeviceLabel string `json:"device_label"`
	}
	if err := httpx.DecodeJSON(r, &req); err != nil {
		httpx.WriteError(w, http.StatusBadRequest, err.Error())
		return
	}
	if req.Username == "" || req.Password == "" {
		httpx.WriteError(w, http.StatusBadRequest, "username and password are required")
		return
	}

	ip := h.auth.ClientIP(r)
	if !h.auth.AllowLogin(ip, req.Username) {
		h.log.Warn("login rate limited", "ip", ip, "username", req.Username)
		httpx.WriteError(w, http.StatusTooManyRequests, "too many login attempts, try again later")
		return
	}

	u, err := Authenticate(r.Context(), h.auth.DB, req.Username, req.Password)
	if err != nil {
		if errors.Is(err, ErrInvalidCredentials) {
			h.log.Info("login failed", "ip", ip, "username", req.Username)
			// Same message for unknown user and wrong password.
			httpx.WriteError(w, http.StatusUnauthorized, "invalid username or password")
			return
		}
		h.log.Error("login error", "err", err)
		httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	token, err := CreateSession(r.Context(), h.auth.DB, u.ID, h.auth.CookieTTL,
		req.DeviceLabel, ip, r.UserAgent())
	if err != nil {
		h.log.Error("create session", "err", err)
		httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	h.auth.SetSessionCookie(w, token, time.Now().Add(h.auth.CookieTTL))
	h.auth.ResetLogin(ip, req.Username)
	h.log.Info("login ok", "user", u.Username, "ip", ip)
	httpx.WriteJSON(w, http.StatusOK, map[string]any{
		"user":       toDTO(u),
		"expires_in": int(h.auth.CookieTTL.Seconds()),
	})
}

func (h *Handlers) handleLogout(w http.ResponseWriter, r *http.Request) {
	if token, err := h.auth.TokenFromRequest(r); err == nil {
		if err := DeleteSession(r.Context(), h.auth.DB, token); err != nil {
			h.log.Warn("delete session", "err", err)
		}
	}
	h.auth.ClearSessionCookie(w)
	httpx.WriteJSON(w, http.StatusOK, map[string]string{"status": "logged out"})
}

func (h *Handlers) handleMe(w http.ResponseWriter, r *http.Request) {
	u, ok := CurrentUser(r.Context())
	if !ok {
		httpx.WriteError(w, http.StatusUnauthorized, "not authenticated")
		return
	}

	libs, err := VisibleLibraryIDs(r.Context(), h.auth.DB, u)
	if err != nil {
		h.log.Error("visible libraries", "err", err)
		httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	if libs == nil {
		libs = []int64{}
	}

	httpx.WriteJSON(w, http.StatusOK, map[string]any{
		"user":              toDTO(u),
		"visible_libraries": libs,
	})
}

func (h *Handlers) handleChangePassword(w http.ResponseWriter, r *http.Request, u User) {
	var req struct {
		CurrentPassword string `json:"current_password"`
		NewPassword     string `json:"new_password"`
	}
	if err := httpx.DecodeJSON(r, &req); err != nil {
		httpx.WriteError(w, http.StatusBadRequest, err.Error())
		return
	}
	if len(req.NewPassword) < 8 {
		httpx.WriteError(w, http.StatusBadRequest, "new password must be at least 8 characters")
		return
	}

	if _, err := Authenticate(r.Context(), h.auth.DB, u.Username, req.CurrentPassword); err != nil {
		httpx.WriteError(w, http.StatusUnauthorized, "current password is incorrect")
		return
	}
	if err := SetPassword(r.Context(), h.auth.DB, u.ID, req.NewPassword); err != nil {
		h.log.Error("change password", "err", err)
		httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	// SetPassword revoked every session, including this one.
	h.auth.ClearSessionCookie(w)
	httpx.WriteJSON(w, http.StatusOK, map[string]string{"status": "password changed, please log in again"})
}

// ── admin: users ───────────────────────────────────────────────────────

func (h *Handlers) handleListUsers(w http.ResponseWriter, r *http.Request) {
	users, err := ListUsers(r.Context(), h.auth.DB)
	if err != nil {
		h.log.Error("list users", "err", err)
		httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	out := make([]userDTO, 0, len(users))
	for _, u := range users {
		out = append(out, toDTO(u))
	}
	httpx.WriteJSON(w, http.StatusOK, map[string]any{"users": out})
}

func (h *Handlers) handleCreateUser(w http.ResponseWriter, r *http.Request) {
	var req struct {
		Username    string `json:"username"`
		DisplayName string `json:"display_name"`
		Password    string `json:"password"`
		IsAdmin     bool   `json:"is_admin"`
	}
	if err := httpx.DecodeJSON(r, &req); err != nil {
		httpx.WriteError(w, http.StatusBadRequest, err.Error())
		return
	}
	if len(req.Password) < 8 {
		httpx.WriteError(w, http.StatusBadRequest, "password must be at least 8 characters")
		return
	}

	u, err := CreateUser(r.Context(), h.auth.DB, req.Username, req.DisplayName, req.Password, req.IsAdmin)
	switch {
	case errors.Is(err, ErrUserExists):
		httpx.WriteError(w, http.StatusConflict, "username already taken")
		return
	case errors.Is(err, ErrInvalidUsername):
		httpx.WriteError(w, http.StatusBadRequest, err.Error())
		return
	case err != nil:
		h.log.Error("create user", "err", err)
		httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
		return
	}

	h.log.Info("user created", "username", u.Username, "admin", u.IsAdmin)
	httpx.WriteJSON(w, http.StatusCreated, map[string]any{"user": toDTO(u)})
}

// ── admin: grants ──────────────────────────────────────────────────────

func (h *Handlers) handleListGrants(w http.ResponseWriter, r *http.Request) {
	userID, ok := pathInt(w, r, "id")
	if !ok {
		return
	}
	grants, err := LibraryGrants(r.Context(), h.auth.DB, userID)
	if err != nil {
		h.log.Error("list grants", "err", err)
		httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	httpx.WriteJSON(w, http.StatusOK, map[string]any{"grants": grants})
}

func (h *Handlers) handlePutGrant(w http.ResponseWriter, r *http.Request) {
	userID, ok := pathInt(w, r, "id")
	if !ok {
		return
	}
	libraryID, ok := pathInt(w, r, "libraryID")
	if !ok {
		return
	}

	req := struct {
		CanRead     *bool `json:"can_read"`
		CanDownload *bool `json:"can_download"`
	}{}
	if err := httpx.DecodeJSON(r, &req); err != nil {
		httpx.WriteError(w, http.StatusBadRequest, err.Error())
		return
	}
	canRead := true
	if req.CanRead != nil {
		canRead = *req.CanRead
	}
	canDownload := false
	if req.CanDownload != nil {
		canDownload = *req.CanDownload
	}

	if err := GrantLibrary(r.Context(), h.auth.DB, userID, libraryID, canRead, canDownload); err != nil {
		h.log.Error("grant library", "err", err)
		httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	httpx.WriteJSON(w, http.StatusOK, map[string]any{
		"user_id":      userID,
		"library_id":   libraryID,
		"can_read":     canRead,
		"can_download": canDownload,
	})
}

func (h *Handlers) handleDeleteGrant(w http.ResponseWriter, r *http.Request) {
	userID, ok := pathInt(w, r, "id")
	if !ok {
		return
	}
	libraryID, ok := pathInt(w, r, "libraryID")
	if !ok {
		return
	}
	if err := RevokeLibrary(r.Context(), h.auth.DB, userID, libraryID); err != nil {
		h.log.Error("revoke library", "err", err)
		httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

func pathInt(w http.ResponseWriter, r *http.Request, name string) (int64, bool) {
	raw := r.PathValue(name)
	n, err := strconv.ParseInt(raw, 10, 64)
	if err != nil || n <= 0 {
		httpx.WriteError(w, http.StatusBadRequest, "invalid "+name)
		return 0, false
	}
	return n, true
}