// Package clientapi implements the Client-Server API: the HTTP surface
// clients talk to.
//
// Phase 1 covers everything about identity — registration, login, sessions,
// devices, profiles, account data and capabilities. Rooms, messages and
// /sync arrive in Phases 3 and 4; the route table here is the place they
// will be added.
//
// Handlers are thin. They decode a request, map it onto a userapi call and
// shape the response; the rules live in userapi, and the storage in
// internal/storage. A handler that needs more than that is a sign something
// belongs further down.
package clientapi

import (
	"errors"
	"log/slog"
	"time"

	"github.com/dariuszjaniak/warp/server/internal/config"
	"github.com/dariuszjaniak/warp/server/internal/federation"
	"github.com/dariuszjaniak/warp/server/internal/httputil"
	"github.com/dariuszjaniak/warp/server/internal/ratelimit"
	"github.com/dariuszjaniak/warp/server/internal/settings"
	"github.com/dariuszjaniak/warp/server/internal/userapi"
)

// ClientAPI serves the Client-Server API.
type ClientAPI struct {
	serverName    string
	clientBaseURL string
	users         *userapi.API
	settings      *settings.Service
	federation    *federation.Gate
	registration  config.Registration
	log           *slog.Logger
	now           func() time.Time

	uia      *uiaStore
	clientIP ratelimit.KeyFunc

	// One limiter per endpoint class, so a client hammering /login cannot
	// spend the budget of /profile.
	limitDefault  *ratelimit.Limiter
	limitLogin    *ratelimit.Limiter
	limitRegister *ratelimit.Limiter
}

// Options configure the component.
type Options struct {
	// ServerName is the Matrix server name.
	ServerName string

	// ClientBaseURL is the URL advertised to clients, the same value
	// /.well-known/matrix/client carries. A successful login repeats it so
	// that a client which only knew the server name does not have to fetch
	// the discovery document separately.
	ClientBaseURL string

	// Users is the userapi component.
	Users *userapi.API

	// Settings is the runtime-settings service; the registration switch is
	// read from it on every registration attempt.
	Settings *settings.Service

	// Federation gates the endpoints that would need a remote server.
	Federation *federation.Gate

	// Registration is the file configuration of the registration flow.
	Registration config.Registration

	// RateLimit configures the per-endpoint buckets.
	RateLimit config.RateLimit

	// TrustXForwardedFor takes the client address from the proxy header.
	TrustXForwardedFor bool

	Logger *slog.Logger

	// Now is the clock, so tests can expire sessions without waiting.
	Now func() time.Time
}

// New builds the component.
func New(opts Options) (*ClientAPI, error) {
	if opts.ServerName == "" {
		return nil, errors.New("clientapi: ServerName must not be empty")
	}
	if opts.Users == nil {
		return nil, errors.New("clientapi: Users must not be nil")
	}
	if opts.Settings == nil {
		return nil, errors.New("clientapi: Settings must not be nil")
	}
	if opts.Federation == nil {
		opts.Federation = federation.NewGate(nil, nil)
	}
	if opts.Logger == nil {
		opts.Logger = slog.Default()
	}
	if opts.Now == nil {
		opts.Now = time.Now
	}

	c := &ClientAPI{
		serverName:    opts.ServerName,
		clientBaseURL: opts.ClientBaseURL,
		users:         opts.Users,
		settings:      opts.Settings,
		federation:    opts.Federation,
		registration:  opts.Registration,
		log:           opts.Logger,
		now:           opts.Now,
		uia:           newUIAStore(uiaSessionTTL, opts.Now),
		clientIP:      ratelimit.ClientIP(opts.TrustXForwardedFor),
	}

	if opts.RateLimit.Enabled {
		c.limitDefault = ratelimit.New(bucket(opts.RateLimit.Default))
		c.limitLogin = ratelimit.New(bucket(opts.RateLimit.Login))
		c.limitRegister = ratelimit.New(bucket(opts.RateLimit.Register))
	} else {
		c.limitDefault, c.limitLogin, c.limitRegister =
			ratelimit.Disabled(), ratelimit.Disabled(), ratelimit.Disabled()
	}
	return c, nil
}

func bucket(b config.RateLimitBucket) ratelimit.Policy {
	return ratelimit.Policy{Burst: b.Burst, Interval: b.Interval}
}

// Client-Server API path prefixes. Warp serves the versioned paths only:
// the r0 prefix was deprecated in Matrix 1.4, and every client that still
// sends it also understands a 404 and falls back to version negotiation
// through /_matrix/client/versions.
const (
	v3 = "/_matrix/client/v3"
	v1 = "/_matrix/client/v1"
)

// RegisterRoutes adds the Client-Server endpoints to the router.
func (c *ClientAPI) RegisterRoutes(r *httputil.Router) {
	// Registration. The token-validity endpoint is v1 because that is the
	// version the spec introduced it at.
	c.public(r, "POST "+v3+"/register", c.limitRegister, c.handleRegister)
	c.public(r, "GET "+v3+"/register/available", c.limitRegister, c.handleRegisterAvailable)
	c.public(r, "GET "+v1+"/register/m.login.registration_token/validity",
		c.limitRegister, c.handleRegistrationTokenValidity)

	// Sessions.
	c.public(r, "GET "+v3+"/login", c.limitDefault, c.handleLoginFlows)
	c.public(r, "POST "+v3+"/login", c.limitLogin, c.handleLogin)
	c.public(r, "POST "+v3+"/refresh", c.limitLogin, c.handleRefresh)
	c.authed(r, "POST "+v3+"/logout", c.limitDefault, c.handleLogout)
	c.authed(r, "POST "+v3+"/logout/all", c.limitDefault, c.handleLogoutAll)

	// Account.
	c.authed(r, "GET "+v3+"/account/whoami", c.limitDefault, c.handleWhoami)
	c.authed(r, "GET "+v3+"/capabilities", c.limitDefault, c.handleCapabilities)

	// Devices.
	c.authed(r, "GET "+v3+"/devices", c.limitDefault, c.handleGetDevices)
	c.authed(r, "GET "+v3+"/devices/{deviceID}", c.limitDefault, c.handleGetDevice)
	c.authed(r, "PUT "+v3+"/devices/{deviceID}", c.limitDefault, c.handlePutDevice)
	c.authed(r, "DELETE "+v3+"/devices/{deviceID}", c.limitDefault, c.handleDeleteDevice)
	c.authed(r, "POST "+v3+"/delete_devices", c.limitDefault, c.handleDeleteDevices)

	// Profiles are world-readable: a client showing a room member's name
	// has no token for that member's server, and the spec makes the GETs
	// unauthenticated for exactly that reason.
	c.public(r, "GET "+v3+"/profile/{userID}", c.limitDefault, c.handleGetProfile)
	c.public(r, "GET "+v3+"/profile/{userID}/displayname", c.limitDefault, c.handleGetDisplayName)
	c.public(r, "GET "+v3+"/profile/{userID}/avatar_url", c.limitDefault, c.handleGetAvatarURL)
	c.authed(r, "PUT "+v3+"/profile/{userID}/displayname", c.limitDefault, c.handlePutDisplayName)
	c.authed(r, "PUT "+v3+"/profile/{userID}/avatar_url", c.limitDefault, c.handlePutAvatarURL)

	// Account data.
	c.authed(r, "GET "+v3+"/user/{userID}/account_data/{dataType}",
		c.limitDefault, c.handleGetAccountData)
	c.authed(r, "PUT "+v3+"/user/{userID}/account_data/{dataType}",
		c.limitDefault, c.handlePutAccountData)
	c.authed(r, "GET "+v3+"/user/{userID}/rooms/{roomID}/account_data/{dataType}",
		c.limitDefault, c.handleGetRoomAccountData)
	c.authed(r, "PUT "+v3+"/user/{userID}/rooms/{roomID}/account_data/{dataType}",
		c.limitDefault, c.handlePutRoomAccountData)

	c.authed(r, "GET "+v3+"/sync", c.limitDefault, c.handleSync)
}

// public registers an endpoint that needs no access token.
func (c *ClientAPI) public(r *httputil.Router, pattern string, limiter *ratelimit.Limiter, h httputil.Handler) {
	r.Handle(pattern, limiter.Middleware(c.clientIP)(httputil.Wrap(h)))
}

// authed registers an endpoint that needs one.
//
// The rate limiter still keys on the client address rather than the user:
// it runs before the token is resolved, and a limiter that had to hit the
// database to find its own key would be a denial of service of its own.
func (c *ClientAPI) authed(r *httputil.Router, pattern string, limiter *ratelimit.Limiter, h AuthedHandler) {
	r.Handle(pattern, limiter.Middleware(c.clientIP)(httputil.Wrap(c.withAuth(h))))
}