package gateway

import (
	"context"
	"errors"
	"fmt"
	"strconv"
	"time"

	"glchat/internal/permissions"
	"glchat/internal/store"
)

// Snapshot собирает READY-снапшот из хранилища с учётом прав пользователя
// (AGENT.md 8.3: только серверы и комнаты, которые он видит).
type Snapshot struct {
	store      *store.Store
	calculator *permissions.Calculator
}

// NewSnapshot собирает READY через переданный калькулятор прав: сервер и
// Gateway должны использовать один кэш, иначе инвалидация не видна обоим.
func NewSnapshot(st *store.Store, calculator *permissions.Calculator) *Snapshot {
	if calculator == nil {
		calculator = permissions.NewCalculator(newPermissionSource(st))
	}
	return &Snapshot{store: st, calculator: calculator}
}

var _ SnapshotBuilder = (*Snapshot)(nil)

func (s *Snapshot) Build(ctx context.Context, user *store.User) (*Ready, error) {
	ready := &Ready{
		User: ReadyUser{
			ID:              formatID(user.ID),
			Username:        user.Username,
			DisplayName:     user.DisplayName,
			IsInstanceAdmin: user.IsInstanceAdmin,
			Badges:          user.Badges,
		},
		Guilds:     []ReadyGuild{},
		DMChannels: []ReadyChannel{},
		ReadStates: []ReadyRead{},
	}
	if ready.User.Badges == nil {
		ready.User.Badges = []string{}
	}
	if user.AvatarFileID != nil {
		ready.User.AvatarFileID = formatID(*user.AvatarFileID)
	}

	guilds, err := s.store.ListGuildsForUser(ctx, user.ID)
	if err != nil {
		return nil, fmt.Errorf("list user guilds: %w", err)
	}
	for _, guild := range guilds {
		resolved, err := s.calculator.Guild(ctx, guild.ID, user.ID, user.IsInstanceAdmin)
		if err != nil {
			return nil, err
		}
		// Сервер без VIEW_GUILD не показываем (AGENT.md 6.2).
		if !resolved.Has(permissions.ViewGuild) {
			continue
		}
		readyGuild, err := s.buildGuild(ctx, guild, user, resolved)
		if err != nil {
			return nil, err
		}
		ready.Guilds = append(ready.Guilds, readyGuild)
	}
	return ready, nil
}

func (s *Snapshot) buildGuild(ctx context.Context, guild store.Guild, user *store.User, resolved permissions.Resolved) (ReadyGuild, error) {
	readyGuild := ReadyGuild{
		ID:        formatID(guild.ID),
		Name:      guild.Name,
		OwnerID:   formatID(guild.OwnerID),
		IsMain:    guild.IsMain,
		Channels:  []ReadyChannel{},
		Roles:     []ReadyRole{},
		MemberIDs: []string{},
		MyRoles:   []string{},
		MyPerms:   []string{},
	}

	roles, err := s.store.ListGuildRoles(ctx, guild.ID)
	if err != nil {
		return readyGuild, err
	}
	for _, role := range roles {
		readyGuild.Roles = append(readyGuild.Roles, ReadyRole{
			ID:          formatID(role.ID),
			Name:        role.Name,
			Color:       role.Color,
			Position:    role.Position,
			Permissions: strconv.FormatUint(role.Permissions, 10),
			IsDefault:   role.IsDefault,
			Mentionable: role.Mentionable,
			Hoist:       role.Hoist,
		})
	}
	memberRoles, err := s.store.MemberRoleIDs(ctx, guild.ID, user.ID)
	if err != nil {
		return readyGuild, err
	}
	for _, roleID := range memberRoles {
		readyGuild.MyRoles = append(readyGuild.MyRoles, formatID(roleID))
	}

	channels, err := s.store.ListGuildChannels(ctx, guild.ID)
	if err != nil {
		return readyGuild, err
	}
	for _, channel := range channels {
		// Категории не запрашивают права: они видны вместе с сервером.
		if channel.Type == store.ChannelCategory && !resolved.Has(permissions.ManageChannels) {
			readyGuild.Channels = append(readyGuild.Channels, channelPayload(channel, false, false))
			continue
		}
		channelResolved, err := s.calculator.Channel(ctx, guild.ID, channel.ID, user.ID, user.IsInstanceAdmin)
		if err != nil {
			return readyGuild, err
		}
		if !channelResolved.CanViewChannel() {
			continue
		}
		readyGuild.Channels = append(readyGuild.Channels, channelPayload(channel,
			channelResolved.Can(permissions.SendMessages), channelResolved.Can(permissions.ConnectVoice)))
	}

	members, err := s.store.ListGuildMembers(ctx, guild.ID)
	if err != nil {
		return readyGuild, err
	}
	for _, member := range members {
		readyGuild.MemberIDs = append(readyGuild.MemberIDs, formatID(member.UserID))
		if member.UserID == user.ID {
			readyGuild.MyNickname = member.Nickname
		}
	}
	return readyGuild, nil
}

func channelPayload(channel store.Channel, canSend, canConnect bool) ReadyChannel {
	payload := ReadyChannel{
		ID:         formatID(channel.ID),
		Type:       string(channel.Type),
		Name:       channel.Name,
		Position:   channel.Position,
		UserLimit:  channel.UserLimit,
		Slowmode:   channel.SlowmodeSeconds,
		CanSend:    canSend,
		CanConnect: canConnect,
	}
	if channel.GuildID != nil {
		payload.GuildID = formatID(*channel.GuildID)
	}
	if channel.ParentID != nil {
		payload.ParentID = formatID(*channel.ParentID)
	}
	return payload
}

// permissionSource читает роли, оверрайды и участников для движка прав.
type permissionSource struct{ store *store.Store }

func newPermissionSource(st *store.Store) *permissionSource { return &permissionSource{store: st} }

func (p *permissionSource) GuildRoles(ctx context.Context, guildID uint64) ([]permissions.RoleData, error) {
	roles, err := p.store.ListGuildRoles(ctx, guildID)
	if err != nil {
		return nil, err
	}
	result := make([]permissions.RoleData, 0, len(roles))
	for _, role := range roles {
		result = append(result, permissions.RoleData{
			ID:          role.ID,
			Permissions: permissions.Permission(role.Permissions),
			IsDefault:   role.IsDefault,
			Position:    role.Position,
		})
	}
	return result, nil
}

func (p *permissionSource) MemberRoleIDs(ctx context.Context, guildID, userID uint64) ([]uint64, error) {
	return p.store.MemberRoleIDs(ctx, guildID, userID)
}

func (p *permissionSource) IsMember(ctx context.Context, guildID, userID uint64) (bool, error) {
	if _, err := p.store.GetGuildMember(ctx, guildID, userID); err != nil {
		if errors.Is(err, store.ErrNotFound) {
			return false, nil
		}
		return false, err
	}
	return true, nil
}

func (p *permissionSource) ChannelOverrides(ctx context.Context, channelID uint64) ([]permissions.OverrideData, error) {
	overrides, err := p.store.ListChannelOverrides(ctx, channelID)
	if err != nil {
		return nil, err
	}
	result := make([]permissions.OverrideData, 0, len(overrides))
	for _, override := range overrides {
		result = append(result, permissions.OverrideData{
			TargetType: override.TargetType,
			TargetID:   override.TargetID,
			Allow:      permissions.Permission(override.Allow),
			Deny:       permissions.Permission(override.Deny),
		})
	}
	return result, nil
}

func (p *permissionSource) GuildOwnerID(ctx context.Context, guildID uint64) (uint64, error) {
	guild, err := p.store.GetGuild(ctx, guildID)
	if err != nil {
		return 0, err
	}
	return guild.OwnerID, nil
}

func (p *permissionSource) MemberTimeout(ctx context.Context, guildID, userID uint64) (bool, error) {
	member, err := p.store.GetGuildMember(ctx, guildID, userID)
	if err != nil {
		// Участника нет — тайм-аут не действует; прочие ошибки чтения не
		// должны блокировать выдачу прав (AGENT.md 7.4).
		return false, nil //nolint:nilerr // отсутствие участника не является ошибкой прав
	}
	if member.TimeoutUntil == nil {
		return false, nil
	}
	return member.TimeoutUntil.After(time.Now().UTC()), nil
}

func formatID(id uint64) string {
	if id == 0 {
		return ""
	}
	var buf [20]byte
	pos := len(buf)
	for id > 0 {
		pos--
		buf[pos] = byte('0' + id%10)
		id /= 10
	}
	return string(buf[pos:])
}