/*
   GoToSocial
   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU Affero General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Affero General Public License for more details.

   You should have received a copy of the GNU Affero General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package transport

import (
	"context"
	"crypto"
	"encoding/json"
	"fmt"
	"net/url"
	"sync"

	"github.com/go-fed/httpsig"
	"github.com/spf13/viper"
	"github.com/superseriousbusiness/activity/pub"
	"github.com/superseriousbusiness/activity/streams"
	"github.com/superseriousbusiness/gotosocial/internal/config"
	"github.com/superseriousbusiness/gotosocial/internal/db"
	"github.com/superseriousbusiness/gotosocial/internal/federation/federatingdb"
)

// Controller generates transports for use in making federation requests to other servers.
type Controller interface {
	NewTransport(pubKeyID string, privkey crypto.PrivateKey) (Transport, error)
	NewTransportForUsername(ctx context.Context, username string) (Transport, error)
}

type controller struct {
	db       db.DB
	clock    pub.Clock
	client   pub.HttpClient
	appAgent string

	// dereferenceFollowersShortcut is a shortcut to dereference followers of an
	// account on this instance, without making any external api/http calls.
	//
	// It is passed to new transports, and should only be invoked when the iri.Host == this host.
	dereferenceFollowersShortcut func(ctx context.Context, iri *url.URL) ([]byte, error)

	// dereferenceUserShortcut is a shortcut to dereference followers an account on
	// this instance, without making any external api/http calls.
	//
	// It is passed to new transports, and should only be invoked when the iri.Host == this host.
	dereferenceUserShortcut func(ctx context.Context, iri *url.URL) ([]byte, error)
}

func dereferenceFollowersShortcut(federatingDB federatingdb.DB) func(context.Context, *url.URL) ([]byte, error) {
	return func(ctx context.Context, iri *url.URL) ([]byte, error) {
		followers, err := federatingDB.Followers(ctx, iri)
		if err != nil {
			return nil, err
		}

		i, err := streams.Serialize(followers)
		if err != nil {
			return nil, err
		}

		return json.Marshal(i)
	}
}

func dereferenceUserShortcut(federatingDB federatingdb.DB) func(context.Context, *url.URL) ([]byte, error) {
	return func(ctx context.Context, iri *url.URL) ([]byte, error) {
		user, err := federatingDB.Get(ctx, iri)
		if err != nil {
			return nil, err
		}

		i, err := streams.Serialize(user)
		if err != nil {
			return nil, err
		}

		return json.Marshal(i)
	}
}

// NewController returns an implementation of the Controller interface for creating new transports
func NewController(db db.DB, federatingDB federatingdb.DB, clock pub.Clock, client pub.HttpClient) Controller {
	applicationName := viper.GetString(config.Keys.ApplicationName)
	host := viper.GetString(config.Keys.Host)
	appAgent := fmt.Sprintf("%s %s", applicationName, host)

	return &controller{
		db:                           db,
		clock:                        clock,
		client:                       client,
		appAgent:                     appAgent,
		dereferenceFollowersShortcut: dereferenceFollowersShortcut(federatingDB),
		dereferenceUserShortcut:      dereferenceUserShortcut(federatingDB),
	}
}

// NewTransport returns a new http signature transport with the given public key id (a URL), and the given private key.
func (c *controller) NewTransport(pubKeyID string, privkey crypto.PrivateKey) (Transport, error) {
	prefs := []httpsig.Algorithm{httpsig.RSA_SHA256}
	digestAlgo := httpsig.DigestSha256
	getHeaders := []string{httpsig.RequestTarget, "host", "date"}
	postHeaders := []string{httpsig.RequestTarget, "host", "date", "digest"}

	getSigner, _, err := httpsig.NewSigner(prefs, digestAlgo, getHeaders, httpsig.Signature, 120)
	if err != nil {
		return nil, fmt.Errorf("error creating get signer: %s", err)
	}

	postSigner, _, err := httpsig.NewSigner(prefs, digestAlgo, postHeaders, httpsig.Signature, 120)
	if err != nil {
		return nil, fmt.Errorf("error creating post signer: %s", err)
	}

	sigTransport := pub.NewHttpSigTransport(c.client, c.appAgent, c.clock, getSigner, postSigner, pubKeyID, privkey)

	return &transport{
		client:                       c.client,
		appAgent:                     c.appAgent,
		gofedAgent:                   "(go-fed/activity v1.0.0)",
		clock:                        c.clock,
		pubKeyID:                     pubKeyID,
		privkey:                      privkey,
		sigTransport:                 sigTransport,
		getSigner:                    getSigner,
		getSignerMu:                  &sync.Mutex{},
		dereferenceFollowersShortcut: c.dereferenceFollowersShortcut,
		dereferenceUserShortcut:      c.dereferenceUserShortcut,
	}, nil
}

func (c *controller) NewTransportForUsername(ctx context.Context, username string) (Transport, error) {
	// We need an account to use to create a transport for dereferecing something.
	// If a username has been given, we can fetch the account with that username and use it.
	// Otherwise, we can take the instance account and use those credentials to make the request.
	var u string
	if username == "" {
		u = viper.GetString(config.Keys.Host)
	} else {
		u = username
	}

	ourAccount, err := c.db.GetLocalAccountByUsername(ctx, u)
	if err != nil {
		return nil, fmt.Errorf("error getting account %s from db: %s", username, err)
	}

	transport, err := c.NewTransport(ourAccount.PublicKeyURI, ourAccount.PrivateKey)
	if err != nil {
		return nil, fmt.Errorf("error creating transport for user %s: %s", username, err)
	}
	return transport, nil
}