// Package clientapproval implements a Hook that fails an Announce based on a
// whitelist or blacklist of BitTorrent client IDs.
package clientapproval

import (
	"context"
	"errors"
	"fmt"

	"github.com/sot-tech/mochi/bittorrent"
	"github.com/sot-tech/mochi/middleware"
	"github.com/sot-tech/mochi/pkg/conf"
	"github.com/sot-tech/mochi/storage"
)

// Name is the name by which this middleware is registered with Conf.
const Name = "client approval"

func init() {
	middleware.RegisterBuilder(Name, build)
}

var (
	// ErrClientUnapproved is the error returned when a client's PeerID is invalid.
	ErrClientUnapproved = bittorrent.ClientError("unapproved client")

	errBothListsProvided = errors.New("using both whitelist and blacklist is invalid")
)

// Config represents all the values required by this middleware to validate
// peers based on their BitTorrent client ID.
type Config struct {
	Whitelist []string
	Blacklist []string
}

type hook struct {
	approved   map[ClientID]struct{}
	unapproved map[ClientID]struct{}
}

func build(options conf.MapConfig, _ storage.PeerStorage) (middleware.Hook, error) {
	var cfg Config

	if err := options.Unmarshal(&cfg); err != nil {
		return nil, fmt.Errorf("middleware %s: %w", Name, err)
	}

	h := &hook{
		approved:   make(map[ClientID]struct{}),
		unapproved: make(map[ClientID]struct{}),
	}

	if len(cfg.Whitelist) > 0 && len(cfg.Blacklist) > 0 {
		return nil, errBothListsProvided
	}

	for _, cidString := range cfg.Whitelist {
		cidBytes := []byte(cidString)
		if len(cidBytes) != 6 {
			return nil, errors.New("client ID " + cidString + " must be 6 bytes")
		}
		var cid ClientID
		copy(cid[:], cidBytes)
		h.approved[cid] = struct{}{}
	}

	for _, cidString := range cfg.Blacklist {
		cidBytes := []byte(cidString)
		if len(cidBytes) != 6 {
			return nil, errors.New("client ID " + cidString + " must be 6 bytes")
		}
		var cid ClientID
		copy(cid[:], cidBytes)
		h.unapproved[cid] = struct{}{}
	}

	return h, nil
}

func (h *hook) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequest, _ *bittorrent.AnnounceResponse) (context.Context, error) {
	clientID := NewClientID(req.ID)

	if len(h.approved) > 0 {
		if _, found := h.approved[clientID]; !found {
			return ctx, ErrClientUnapproved
		}
	}

	if len(h.unapproved) > 0 {
		if _, found := h.unapproved[clientID]; found {
			return ctx, ErrClientUnapproved
		}
	}

	return ctx, nil
}

func (h *hook) HandleScrape(ctx context.Context, _ *bittorrent.ScrapeRequest, _ *bittorrent.ScrapeResponse) (context.Context, error) {
	// Scrapes don't require any protection.
	return ctx, nil
}