package api

import (
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"time"

	"codeberg.org/SquidSE/ClusterCanvas/service/internal/auth"
	"codeberg.org/SquidSE/ClusterCanvas/service/internal/settings"
)

type userPublic struct {
	ID                string    `json:"id"`
	Username          string    `json:"username"`
	Enabled           bool      `json:"enabled"`
	TOTPConfirmed     bool      `json:"totp_confirmed"`
	GroupNames        []string  `json:"group_names"`
	CreatedAt         time.Time `json:"created_at"`
	PasswordChangedAt time.Time `json:"password_changed_at"`
	IsAdmin           bool      `json:"is_admin"`
	CanDelete         bool      `json:"can_delete"`
}

type usersResponse struct {
	Users []userPublic `json:"users"`
}

type createUserRequest struct {
	Username   string   `json:"username"`
	Password   string   `json:"password"`
	GroupNames []string `json:"group_names"`
}

type patchUserRequest struct {
	GroupNames  *[]string `json:"group_names"`
	Password    *string   `json:"password"`
	DisableTOTP *bool     `json:"disable_totp"`
}

type deleteUserRequest struct {
	CurrentPassword string `json:"current_password"`
	TOTPCode        string `json:"totp_code"`
}

func (app *App) usersGetHandler(writer http.ResponseWriter, request *http.Request) {
	if err := app.requireKey(); err != nil {
		writeJSON(writer, http.StatusServiceUnavailable, apiErrorResponse{Error: err.Error()})
		return
	}

	store, err := settings.LoadPasswords(app.ConfigDir, app.Key)
	if err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	writeJSON(writer, http.StatusOK, usersResponse{Users: toPublicUsers(store.Users)})
}

func (app *App) usersCreateHandler(writer http.ResponseWriter, request *http.Request) {
	if err := app.authorizeUsersWrite(request); err != nil {
		writeJSON(writer, http.StatusForbidden, apiErrorResponse{Error: err.Error()})
		return
	}
	if err := app.requireKey(); err != nil {
		writeJSON(writer, http.StatusServiceUnavailable, apiErrorResponse{Error: err.Error()})
		return
	}

	var payload createUserRequest
	if err := json.NewDecoder(request.Body).Decode(&payload); err != nil {
		writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: "invalid JSON body"})
		return
	}

	username := strings.TrimSpace(payload.Username)
	if username == "" {
		writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: "username is required"})
		return
	}
	if err := auth.ValidatePassword(payload.Password, username); err != nil {
		writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: err.Error()})
		return
	}

	settingsPayload, err := loadSettingsOrDefault(app.ConfigDir)
	if err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	groupNames, err := validateGroupNames(payload.GroupNames, settingsPayload.Groups)
	if err != nil {
		writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: err.Error()})
		return
	}

	store, err := settings.LoadPasswords(app.ConfigDir, app.Key)
	if err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	for _, existing := range store.Users {
		if strings.EqualFold(existing.Username, username) {
			writeJSON(writer, http.StatusConflict, apiErrorResponse{Error: "username already exists"})
			return
		}
	}

	hash, err := auth.HashPassword(payload.Password)
	if err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}
	userID, err := newUserID()
	if err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	now := time.Now().UTC()
	store.Users = append(store.Users, settings.UserCredential{
		ID:                userID,
		Username:          username,
		PasswordHash:      hash,
		Enabled:           true,
		GroupNames:        groupNames,
		CreatedAt:         now,
		PasswordChangedAt: now,
	})

	if err := settings.SavePasswords(app.ConfigDir, store, app.Key); err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	writeJSON(writer, http.StatusOK, usersResponse{Users: toPublicUsers(store.Users)})
}

func (app *App) usersPatchHandler(writer http.ResponseWriter, request *http.Request) {
	if err := app.authorizeUsersWrite(request); err != nil {
		writeJSON(writer, http.StatusForbidden, apiErrorResponse{Error: err.Error()})
		return
	}
	if err := app.requireKey(); err != nil {
		writeJSON(writer, http.StatusServiceUnavailable, apiErrorResponse{Error: err.Error()})
		return
	}

	if err := app.requireGraceReauth(request); err != nil {
		if err.Error() == reauthRequiredMessage {
			writeReauthRequired(writer)
			return
		}
		writeJSON(writer, http.StatusUnauthorized, apiErrorResponse{Error: err.Error()})
		return
	}

	userID := strings.TrimSpace(request.URL.Query().Get("id"))
	if userID == "" {
		writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: "missing user id"})
		return
	}

	var payload patchUserRequest
	if err := json.NewDecoder(request.Body).Decode(&payload); err != nil {
		writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: "invalid JSON body"})
		return
	}
	if payload.GroupNames == nil && payload.Password == nil && payload.DisableTOTP == nil {
		writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: "no fields to update"})
		return
	}

	settingsPayload, err := loadSettingsOrDefault(app.ConfigDir)
	if err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	store, err := settings.LoadPasswords(app.ConfigDir, app.Key)
	if err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	index := -1
	for i := range store.Users {
		if store.Users[i].ID == userID {
			index = i
			break
		}
	}
	if index < 0 {
		writeJSON(writer, http.StatusNotFound, apiErrorResponse{Error: "user not found"})
		return
	}

	target := &store.Users[index]
	passwordChanged := false

	if payload.GroupNames != nil {
		groupNames, err := validateGroupNames(*payload.GroupNames, settingsPayload.Groups)
		if err != nil {
			writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: err.Error()})
			return
		}
		wasAdmin := userIsAdministrator(*target)
		wouldBeAdmin := false
		for _, name := range groupNames {
			if name == settings.AdministratorsGroupName {
				wouldBeAdmin = true
				break
			}
		}
		if wasAdmin && !wouldBeAdmin && countAdministrators(store.Users) <= 1 {
			writeJSON(writer, http.StatusConflict, apiErrorResponse{
				Error: "cannot remove the last administrator from the Administrators group",
			})
			return
		}
		target.GroupNames = groupNames
	}

	if payload.Password != nil {
		if err := auth.ValidatePassword(*payload.Password, target.Username); err != nil {
			writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: err.Error()})
			return
		}
		hash, err := auth.HashPassword(*payload.Password)
		if err != nil {
			writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
			return
		}
		target.PasswordHash = hash
		target.PasswordChangedAt = time.Now().UTC()
		passwordChanged = true
	}

	if payload.DisableTOTP != nil && *payload.DisableTOTP {
		target.TOTPSecret = ""
		target.TOTPConfirmed = false
	}

	if err := settings.SavePasswords(app.ConfigDir, store, app.Key); err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	if passwordChanged && app.Sessions != nil {
		_ = app.Sessions.InvalidateUserSessions(userID)
	}

	writeJSON(writer, http.StatusOK, usersResponse{Users: toPublicUsers(store.Users)})
}

func (app *App) usersDeleteHandler(writer http.ResponseWriter, request *http.Request) {
	if err := app.authorizeUsersWrite(request); err != nil {
		writeJSON(writer, http.StatusForbidden, apiErrorResponse{Error: err.Error()})
		return
	}
	if err := app.requireKey(); err != nil {
		writeJSON(writer, http.StatusServiceUnavailable, apiErrorResponse{Error: err.Error()})
		return
	}

	userID := strings.TrimSpace(request.URL.Query().Get("id"))
	if userID == "" {
		writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: "missing user id"})
		return
	}

	var payload deleteUserRequest
	if err := json.NewDecoder(request.Body).Decode(&payload); err != nil {
		writeJSON(writer, http.StatusBadRequest, apiErrorResponse{Error: "invalid JSON body"})
		return
	}

	if err := app.requireInlineReauth(request, payload.CurrentPassword, payload.TOTPCode); err != nil {
		writeJSON(writer, http.StatusUnauthorized, apiErrorResponse{Error: err.Error()})
		return
	}

	store, err := settings.LoadPasswords(app.ConfigDir, app.Key)
	if err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	adminCount := countAdministrators(store.Users)
	remaining := make([]settings.UserCredential, 0, len(store.Users))
	found := false
	for _, user := range store.Users {
		if user.ID != userID {
			remaining = append(remaining, user)
			continue
		}
		found = true
		if userIsAdministrator(user) && adminCount <= 1 {
			writeJSON(writer, http.StatusConflict, apiErrorResponse{
				Error: "cannot delete the last administrator",
			})
			return
		}
	}

	if !found {
		writeJSON(writer, http.StatusNotFound, apiErrorResponse{Error: "user not found"})
		return
	}

	store.Users = remaining
	if err := settings.SavePasswords(app.ConfigDir, store, app.Key); err != nil {
		writeJSON(writer, http.StatusInternalServerError, apiErrorResponse{Error: err.Error()})
		return
	}

	if app.Sessions != nil {
		_ = app.Sessions.InvalidateUserSessions(userID)
	}

	writeJSON(writer, http.StatusOK, usersResponse{Users: toPublicUsers(store.Users)})
}

func validateGroupNames(names []string, groups []settings.Group) ([]string, error) {
	if names == nil {
		return []string{}, nil
	}
	known := make(map[string]struct{}, len(groups))
	for _, group := range groups {
		known[group.Name] = struct{}{}
	}
	result := make([]string, 0, len(names))
	seen := make(map[string]struct{}, len(names))
	for _, name := range names {
		trimmed := strings.TrimSpace(name)
		if trimmed == "" {
			continue
		}
		if _, ok := known[trimmed]; !ok {
			return nil, fmt.Errorf("unknown group: %s", trimmed)
		}
		if _, ok := seen[trimmed]; ok {
			continue
		}
		seen[trimmed] = struct{}{}
		result = append(result, trimmed)
	}
	return result, nil
}

func toPublicUsers(users []settings.UserCredential) []userPublic {
	adminCount := countAdministrators(users)
	result := make([]userPublic, 0, len(users))
	for _, user := range users {
		isAdmin := userIsAdministrator(user)
		groupNames := user.GroupNames
		if groupNames == nil {
			groupNames = []string{}
		}
		result = append(result, userPublic{
			ID:                user.ID,
			Username:          user.Username,
			Enabled:           user.Enabled,
			TOTPConfirmed:     user.TOTPConfirmed,
			GroupNames:        groupNames,
			CreatedAt:         user.CreatedAt,
			PasswordChangedAt: user.PasswordChangedAt,
			IsAdmin:           isAdmin,
			CanDelete:         !(isAdmin && adminCount <= 1),
		})
	}
	return result
}

func userIsAdministrator(user settings.UserCredential) bool {
	for _, groupName := range user.GroupNames {
		if groupName == settings.AdministratorsGroupName {
			return true
		}
	}
	return false
}

func countAdministrators(users []settings.UserCredential) int {
	count := 0
	for _, user := range users {
		if userIsAdministrator(user) {
			count++
		}
	}
	return count
}