// Package adminapi serves /_warp/admin/v1: the API behind the admin panel.
//
// It is deliberately not part of the Matrix spec. Everything a client needs
// goes through the Client-Server API; this is the operator's surface, and
// the only thing in Warp that is ours rather than Matrix's.
//
// Authentication is a normal Matrix access token belonging to an account
// with the admin flag, so the panel logs in the way any client does and
// there is no second credential to manage.
//
// Phase 1 is the skeleton PLAN.md section 7 asks for: the two runtime
// switches, user listing and creation, and the dashboard counters. Full user
// management, registration tokens, the federation allow/deny list editor and
// the audit log arrive in Phase 9.
package adminapi

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

	"github.com/dariuszjaniak/warp/server/internal/buildinfo"
	"github.com/dariuszjaniak/warp/server/internal/federation"
	"github.com/dariuszjaniak/warp/server/internal/httputil"
	"github.com/dariuszjaniak/warp/server/internal/roomserver"
	"github.com/dariuszjaniak/warp/server/internal/settings"
	"github.com/dariuszjaniak/warp/server/internal/storage"
	"github.com/dariuszjaniak/warp/server/internal/userapi"
)

// Prefix is the path every admin endpoint lives under.
const Prefix = "/_warp/admin/v1"

// AdminAPI serves the admin endpoints.
type AdminAPI struct {
	serverName string
	users      *userapi.API
	rooms      *roomserver.API
	settings   *settings.Service
	federation *federation.Gate
	database   storage.Database
	fedStatus  FederationStatus
	log        *slog.Logger
}

// Options configure the component.
type Options struct {
	ServerName string
	Users      *userapi.API

	// Rooms is the roomserver component. A server that started without a
	// signing key has none, and the room endpoints then report that rather
	// than failing on the first call.
	Rooms *roomserver.API

	Settings   *settings.Service
	Federation *federation.Gate

	// FederationStatus reports on the federation module. Nil on a server
	// without one, and the destinations endpoints then say so.
	FederationStatus FederationStatus

	// Database is used for the driver name the dashboard shows and for the
	// migration state; the admin API does not write to it directly.
	Database storage.Database

	Logger *slog.Logger
}

// New builds the component.
func New(opts Options) (*AdminAPI, error) {
	switch {
	case opts.ServerName == "":
		return nil, errors.New("adminapi: ServerName must not be empty")
	case opts.Users == nil:
		return nil, errors.New("adminapi: Users must not be nil")
	case opts.Settings == nil:
		return nil, errors.New("adminapi: Settings must not be nil")
	}
	if opts.Federation == nil {
		opts.Federation = federation.NewGate(nil, nil)
	}
	if opts.Logger == nil {
		opts.Logger = slog.Default()
	}
	return &AdminAPI{
		serverName: opts.ServerName,
		users:      opts.Users,
		rooms:      opts.Rooms,
		settings:   opts.Settings,
		federation: opts.Federation,
		database:   opts.Database,
		fedStatus:  opts.FederationStatus,
		log:        opts.Logger,
	}, nil
}

// RegisterRoutes adds the admin endpoints to the router.
func (a *AdminAPI) RegisterRoutes(r *httputil.Router) {
	a.handle(r, "GET "+Prefix+"/federation", a.handleGetFederation)
	a.handle(r, "PUT "+Prefix+"/federation", a.handlePutFederation)
	a.handle(r, "GET "+Prefix+"/federation/destinations", a.handleGetDestinations)
	a.handle(r, "POST "+Prefix+"/federation/destinations/{serverName}/reset", a.handleResetDestination)
	a.handle(r, "GET "+Prefix+"/registration", a.handleGetRegistration)
	a.handle(r, "PUT "+Prefix+"/registration", a.handlePutRegistration)
	a.handle(r, "GET "+Prefix+"/users", a.handleGetUsers)
	a.handle(r, "POST "+Prefix+"/users", a.handlePostUsers)
	a.handle(r, "GET "+Prefix+"/stats", a.handleGetStats)

	a.handle(r, "GET "+Prefix+"/rooms", a.handleGetRooms)
	a.handle(r, "GET "+Prefix+"/rooms/{roomID}", a.handleGetRoom)
	a.handle(r, "DELETE "+Prefix+"/rooms/{roomID}", a.handleDeleteRoom)
	a.handle(r, "POST "+Prefix+"/rooms/{roomID}/force_leave", a.handleForceLeave)
}

// adminHandler is a handler that has already been shown to be an admin.
type adminHandler func(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error

// handle registers an admin-only endpoint.
//
// Admin endpoints are not rate limited. They are reachable only with an
// admin token, and an operator bulk-loading users through the panel is
// exactly the traffic a limiter would get in the way of.
func (a *AdminAPI) handle(r *httputil.Router, pattern string, h adminHandler) {
	r.HandleFunc(pattern, func(w http.ResponseWriter, req *http.Request) error {
		auth, err := a.requireAdmin(req)
		if err != nil {
			return err
		}
		return h(w, req, auth)
	})
}

// requireAdmin resolves the access token and insists on the admin flag.
//
// A non-admin token gets M_FORBIDDEN rather than a 404: the caller is a
// legitimate user of this server who is not allowed here, and pretending
// the endpoint does not exist would only make the panel harder to debug.
func (a *AdminAPI) requireAdmin(r *http.Request) (userapi.Authenticated, error) {
	token := accessTokenFrom(r)
	if token == "" {
		return userapi.Authenticated{}, httputil.MissingToken()
	}

	auth, err := a.users.Authenticate(r.Context(), token)
	switch {
	case err == nil:
	case errors.Is(err, userapi.ErrNoSuchToken):
		return userapi.Authenticated{}, httputil.UnknownToken(false)
	case errors.Is(err, userapi.ErrTokenExpired):
		return userapi.Authenticated{}, httputil.UnknownToken(true)
	case errors.Is(err, userapi.ErrAccountDeactivated):
		return userapi.Authenticated{}, httputil.UserDeactivated()
	default:
		return userapi.Authenticated{}, err
	}

	if !auth.Admin {
		return userapi.Authenticated{}, httputil.Forbidden("This endpoint requires a server administrator")
	}
	return auth, nil
}

// accessTokenFrom reads the bearer token. The admin panel is a normal
// Matrix client, so it sends the header form; the query parameter is not
// accepted here, because an admin token in a URL ends up in access logs.
func accessTokenFrom(r *http.Request) string {
	header := r.Header.Get("Authorization")
	const prefix = "Bearer "
	if len(header) <= len(prefix) || !equalFoldASCII(header[:len(prefix)], prefix) {
		return ""
	}
	return header[len(prefix):]
}

// equalFoldASCII compares two ASCII strings case-insensitively. The scheme
// of an Authorization header is case-insensitive per RFC 9110.
func equalFoldASCII(a, b string) bool {
	if len(a) != len(b) {
		return false
	}
	for i := range len(a) {
		x, y := a[i], b[i]
		if 'A' <= x && x <= 'Z' {
			x += 'a' - 'A'
		}
		if 'A' <= y && y <= 'Z' {
			y += 'a' - 'A'
		}
		if x != y {
			return false
		}
	}
	return true
}

// switchResponse is the shape both runtime switches report.
type switchResponse struct {
	Enabled bool `json:"enabled"`

	// Toggleable is false when the config file pinned the setting, in
	// which case the panel shows the switch greyed out rather than letting
	// an operator flip something that will bounce.
	Toggleable bool `json:"toggleable"`
}

// switchRequest is the body of either PUT.
type switchRequest struct {
	Enabled *bool `json:"enabled"`
}

// federationResponse adds the allow and deny lists to the switch.
type federationResponse struct {
	switchResponse
	Allowlist []string `json:"allowlist"`
	Denylist  []string `json:"denylist"`
}

// handleGetFederation implements GET /_warp/admin/v1/federation.
func (a *AdminAPI) handleGetFederation(w http.ResponseWriter, _ *http.Request, _ userapi.Authenticated) error {
	allowlist, denylist := a.federation.Policy().Lists()
	httputil.WriteJSON(w, http.StatusOK, federationResponse{
		switchResponse: switchResponse{
			Enabled:    a.settings.FederationEnabled(),
			Toggleable: a.settings.FederationToggleable(),
		},
		// Editing these is Phase 9; they are reported now because the
		// dashboard has to show which servers a running Warp will talk to.
		Allowlist: allowlist,
		Denylist:  denylist,
	})
	return nil
}

// handlePutFederation implements PUT /_warp/admin/v1/federation, the switch
// PLAN.md section 3 describes: no restart, the gate picks it up on the next
// request.
func (a *AdminAPI) handlePutFederation(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error {
	enabled, err := decodeSwitch(w, r)
	if err != nil {
		return err
	}
	if err := a.settings.SetFederationEnabled(r.Context(), enabled); err != nil {
		return toggleError(err, "federation")
	}
	a.log.Info("federation switch changed through the admin API",
		"enabled", enabled, "by", auth.UserID)
	return a.handleGetFederation(w, r, auth)
}

// handleGetRegistration implements GET /_warp/admin/v1/registration.
func (a *AdminAPI) handleGetRegistration(w http.ResponseWriter, _ *http.Request, _ userapi.Authenticated) error {
	httputil.WriteJSON(w, http.StatusOK, switchResponse{
		Enabled:    a.settings.RegistrationEnabled(),
		Toggleable: a.settings.RegistrationToggleable(),
	})
	return nil
}

// handlePutRegistration implements PUT /_warp/admin/v1/registration.
func (a *AdminAPI) handlePutRegistration(w http.ResponseWriter, r *http.Request, auth userapi.Authenticated) error {
	enabled, err := decodeSwitch(w, r)
	if err != nil {
		return err
	}
	if err := a.settings.SetRegistrationEnabled(r.Context(), enabled); err != nil {
		return toggleError(err, "registration")
	}
	a.log.Info("registration switch changed through the admin API",
		"enabled", enabled, "by", auth.UserID)
	return a.handleGetRegistration(w, r, auth)
}

// decodeSwitch reads {"enabled": bool}. The field is a pointer so that a
// body without it is a missing parameter rather than a silent "false".
func decodeSwitch(w http.ResponseWriter, r *http.Request) (bool, error) {
	var req switchRequest
	if err := httputil.DecodeJSON(w, r, &req); err != nil {
		return false, err
	}
	if req.Enabled == nil {
		return false, httputil.MissingParam("enabled is required")
	}
	return *req.Enabled, nil
}

// toggleError turns a refused toggle into the right answer: a setting the
// config file pinned is a 409, because the request was well formed and the
// server's configuration is what stands in the way.
func toggleError(err error, name string) error {
	if errors.Is(err, settings.ErrNotToggleable) {
		return httputil.NewError(http.StatusConflict, httputil.ErrCodeForbidden,
			"The %s switch is pinned by the configuration file (%s.allow_runtime_toggle is false)",
			name, name)
	}
	return err
}

// statsResponse is the dashboard payload: PLAN.md section 8.1 lists users,
// rooms, events, federation status, storage driver and version as the first
// thing the panel shows. The room and event counters join it in Phase 3,
// when there is something to count.
type statsResponse struct {
	ServerName string `json:"server_name"`
	Version    string `json:"version"`
	Database   string `json:"database"`

	Users       int `json:"users"`
	Admins      int `json:"admins"`
	Deactivated int `json:"deactivated"`
	Devices     int `json:"devices"`

	Rooms          int `json:"rooms"`
	PublishedRooms int `json:"published_rooms"`
	Events         int `json:"events"`

	FederationEnabled   bool `json:"federation_enabled"`
	RegistrationEnabled bool `json:"registration_enabled"`
}

// handleGetStats implements GET /_warp/admin/v1/stats.
func (a *AdminAPI) handleGetStats(w http.ResponseWriter, r *http.Request, _ userapi.Authenticated) error {
	stats, err := a.users.Stats(r.Context())
	if err != nil {
		return err
	}
	resp := statsResponse{
		ServerName:          a.serverName,
		Version:             buildinfo.Version,
		Users:               stats.Users,
		Admins:              stats.Admins,
		Deactivated:         stats.Deactivated,
		Devices:             stats.Devices,
		FederationEnabled:   a.settings.FederationEnabled(),
		RegistrationEnabled: a.settings.RegistrationEnabled(),
	}
	if a.database != nil {
		resp.Database = a.database.Driver()
	}
	if a.rooms != nil {
		roomStats, err := a.rooms.Stats(r.Context())
		if err != nil {
			return err
		}
		resp.Rooms = roomStats.Rooms
		resp.PublishedRooms = roomStats.Published
		resp.Events = roomStats.Events
	}
	httputil.WriteJSON(w, http.StatusOK, resp)
	return nil
}