package classes

import (
	"context"

	chatcontracts "git.golem15.com/golem15/sm-chat-plugin/contracts"
	chancontracts "git.golem15.com/golem15/sm-chatchannels-plugin/contracts"
	userclasses "git.golem15.com/golem15/sm-user-plugin/classes"
	"gorm.io/gorm"
)

var (
	_ chatcontracts.Context        = (*ChatContext)(nil)
	_ chancontracts.AccessResolver = (*ChatAccess)(nil)
)

// The BM chat context: one context of type bm with id 1, whose members are
// the members of one user group.
const (
	// ChatContextType is the context alias (context_type) jz.bm registers on
	// golem15.chat.
	ChatContextType = "bm"
	// ChatContextID is the id of the one BM chat context.
	ChatContextID uint = 1
	// ChatGeneralName is the name of the group conversation and its channel.
	ChatGeneralName = "ogólny"
	// ChatGeneralSlug is the slug of the adopted channel.
	ChatGeneralSlug = "ogolny"
	// ChatBroadcastChannel is the host channel golem15.chat publishes created
	// events to. It must never be empty: an empty host channel silences the
	// conversation channels too. No client can subscribe to it, because the
	// chat authorizer only admits chat:conversation:{id}.
	ChatBroadcastChannel = "chat:context:1"
)

// MemberFunc reports whether userID belongs to the user group with code
// group. IsChatMember is the production check; tests inject their own.
type MemberFunc func(ctx context.Context, db *gorm.DB, userID uint, group string) (bool, error)

// IsChatMember reports whether userID is in the chat group group. No user,
// no group code or no database is never a member.
func IsChatMember(ctx context.Context, db *gorm.DB, userID uint, group string) (bool, error) {
	if userID == 0 || group == "" || db == nil {
		return false, nil
	}
	return userclasses.HasGroupCode(ctx, db, userID, group)
}

// IsChatModerator reports whether userID is in the moderator group
// moderatorGroup.
func IsChatModerator(ctx context.Context, db *gorm.DB, userID uint, moderatorGroup string) (bool, error) {
	return IsChatMember(ctx, db, userID, moderatorGroup)
}

// ChatMemberIDs lists the ids of the users in group that are not deleted,
// ordered by id. A group code with no group row has no member.
func ChatMemberIDs(ctx context.Context, db *gorm.DB, group string) ([]uint, error) {
	ids := []uint{}
	if group == "" || db == nil {
		return ids, nil
	}
	err := db.WithContext(ctx).
		Table("users_groups").
		Joins("JOIN user_groups ON user_groups.id = users_groups.user_group_id").
		Joins("JOIN users ON users.id = users_groups.user_id").
		Where("user_groups.code = ? AND users.deleted_at IS NULL", group).
		Distinct().
		Order("users_groups.user_id").
		Pluck("users_groups.user_id", &ids).Error
	if err != nil {
		return nil, err
	}
	return ids, nil
}

// ChatContext is the golem15.chat context of the BM chat. Membership is the
// user group named by group; nobody oversees other people's chats, so a
// moderator reads no DM and edits no foreign message.
type ChatContext struct {
	db             *gorm.DB
	group          string
	moderatorGroup string
	isMember       MemberFunc
}

// NewChatContext returns the BM chat context over db for the chat group
// code group and the moderator group code moderatorGroup.
func NewChatContext(db *gorm.DB, group, moderatorGroup string) *ChatContext {
	return &ChatContext{db: db, group: group, moderatorGroup: moderatorGroup}
}

// WithMembership replaces the group check (IsChatMember) and returns c.
func (c *ChatContext) WithMembership(fn MemberFunc) *ChatContext {
	c.isMember = fn
	return c
}

func (c *ChatContext) ID() uint                 { return ChatContextID }
func (c *ChatContext) Type() string             { return ChatContextType }
func (c *ChatContext) ChatEnabled() bool        { return true }
func (c *ChatContext) GroupName() string        { return ChatGeneralName }
func (c *ChatContext) BroadcastChannel() string { return ChatBroadcastChannel }

// CanActFor is the default: a user acts only for themself.
func (c *ChatContext) CanActFor(ctx context.Context, actorID, memberID uint) bool {
	return chatcontracts.DefaultCanActFor(ctx, actorID, memberID)
}

// CanOverseeChats is always false. golem15.chat grants an overseer read
// access to every conversation and edits of other people's messages, which
// no BM user gets; moderators delete through a narrower hook.
func (c *ChatContext) CanOverseeChats(context.Context, uint) (bool, error) {
	return false, nil
}

// HasMember reports whether userID is in the chat group.
func (c *ChatContext) HasMember(ctx context.Context, userID uint) (bool, error) {
	if userID == 0 || c.group == "" {
		return false, nil
	}
	if c.isMember != nil {
		return c.isMember(ctx, c.db, userID, c.group)
	}
	return IsChatMember(ctx, c.db, userID, c.group)
}

// Members lists the ids of the chat group's users that are not deleted.
func (c *ChatContext) Members(ctx context.Context) ([]uint, error) {
	return ChatMemberIDs(ctx, c.db, c.group)
}

// ChatContextLoader is the golem15.chat loader of the bm alias. The only
// context is id 1; any other id is unknown (nil, nil), which golem15.chat
// answers with its not-a-member error. The group codes are read per load,
// so a config change needs no re-registration.
func ChatContextLoader(group, moderatorGroup func() string) chatcontracts.Loader {
	return func(_ context.Context, db *gorm.DB, id uint) (chatcontracts.Context, error) {
		if id != ChatContextID {
			return nil, nil
		}
		return NewChatContext(db, group(), moderatorGroup()), nil
	}
}

// ChatAccess is golem15.chatchannels' access policy for BM: chat-group
// members may access context bm/1 and nothing else, and nobody manages it,
// so no channel is ever created through the channel service.
type ChatAccess struct {
	db       func() *gorm.DB
	group    string
	isMember MemberFunc
}

// NewChatAccess returns the access policy for the chat group group. db is
// resolved per check; isMember nil means IsChatMember.
func NewChatAccess(db func() *gorm.DB, group string, isMember MemberFunc) *ChatAccess {
	if isMember == nil {
		isMember = IsChatMember
	}
	return &ChatAccess{db: db, group: group, isMember: isMember}
}

// CanAccessContext is true only for a chat-group member and context bm/1.
// Any error, or no database, denies.
func (a *ChatAccess) CanAccessContext(ctx context.Context, userID uint, contextType string, contextID uint) bool {
	if contextType != ChatContextType || contextID != ChatContextID || userID == 0 || a.group == "" || a.db == nil {
		return false
	}
	db := a.db()
	if db == nil {
		return false
	}
	ok, err := a.isMember(ctx, db, userID, a.group)
	return err == nil && ok
}

// CanManageContext is always false: nobody creates or edits channels.
func (a *ChatAccess) CanManageContext(context.Context, uint, string, uint) bool {
	return false
}