package classes

import (
	"context"
	"errors"

	chatclasses "git.golem15.com/golem15/sm-chat-plugin/classes"
	chatmodels "git.golem15.com/golem15/sm-chat-plugin/models"
	chanclasses "git.golem15.com/golem15/sm-chatchannels-plugin/classes"
	chanmodels "git.golem15.com/golem15/sm-chatchannels-plugin/models"
	userclasses "git.golem15.com/golem15/sm-user-plugin/classes"
	usermodels "git.golem15.com/golem15/sm-user-plugin/models"
	"git.golem15.com/golem15/summercms/modules/lagoon"
	"gorm.io/gorm"
)

// chatGeneralLock is the transaction advisory lock that serialises finding
// or creating ogólny, so members bootstrapping at the same moment end with
// one group conversation and one channel.
const chatGeneralLock int64 = 0x6a7a626d63686174

// chatGroupNames are the display names of the default group codes; any
// other code is named after itself.
var chatGroupNames = map[string]string{
	"studenci":    "Studenci",
	"moderatorzy": "Moderatorzy czatu",
}

// chatMembersSQL selects the ids of the users in the group with code ?
// that are not deleted.
const chatMembersSQL = `SELECT DISTINCT users_groups.user_id
FROM users_groups
JOIN user_groups ON user_groups.id = users_groups.user_group_id
JOIN users ON users.id = users_groups.user_id
WHERE user_groups.code = ? AND users.deleted_at IS NULL`

// chatConversationsSQL selects the ids of the conversations of context
// bm/1 (ogólny and every DM).
const chatConversationsSQL = `SELECT id FROM golem15_chat_conversations WHERE context_type = ? AND context_id = ?`

// EnsureChatGroups creates a user group for each code that has none and
// returns how many it created. It never assigns a user to a group: members
// are added by hand in the backend.
func EnsureChatGroups(ctx context.Context, db *gorm.DB, codes ...string) (int64, error) {
	if db == nil {
		return 0, errors.New("jz.bm: chat groups need a database")
	}
	var created int64
	seen := map[string]bool{}
	for _, code := range codes {
		if code == "" || seen[code] {
			continue
		}
		seen[code] = true
		name := chatGroupNames[code]
		if name == "" {
			name = code
		}
		res := db.WithContext(ctx).Exec(`INSERT INTO user_groups (name, code, description, created_at, updated_at)
SELECT ?, ?, ?, NOW(), NOW()
WHERE NOT EXISTS (SELECT 1 FROM user_groups WHERE code = ?)`, name, code, "Czat BM (jz.bm)", code)
		if res.Error != nil {
			return created, res.Error
		}
		created += res.RowsAffected
	}
	return created, nil
}

// EnsureGeneral finds or creates the group conversation of context bm/1
// (golem15.chat GetGroupChat, which also joins actorID) and adopts it as
// the system default channel ogólny, so mentions accrue on it. Adoption is
// idempotent. actorID must be a chat-group member.
func EnsureGeneral(ctx context.Context, db *gorm.DB, chat *chatclasses.Service, channels *chanclasses.ChannelService, actorID uint) (*chatmodels.Conversation, *chanmodels.Channel, error) {
	if db == nil || chat == nil || channels == nil {
		return nil, nil, errors.New("jz.bm: ogólny needs the database and the chat services")
	}
	var conv *chatmodels.Conversation
	var ch *chanmodels.Channel
	err := lagoon.Transaction(ctx, db, func(ctx context.Context, tx *gorm.DB) error {
		if err := tx.Exec("SELECT pg_advisory_xact_lock(?)", chatGeneralLock).Error; err != nil {
			return err
		}
		c, err := chat.WithDB(tx).GetGroupChat(ctx, actorID, ChatContextType, ChatContextID)
		if err != nil {
			return err
		}
		yes := true
		adopted, err := channels.WithDB(tx).AdoptConversation(ctx, ChatContextType, ChatContextID, c.ID, chanclasses.AdoptConversationInput{
			Name:      ChatGeneralName,
			Slug:      ChatGeneralSlug,
			IsSystem:  &yes,
			IsDefault: &yes,
		})
		if err != nil {
			return err
		}
		conv, ch = c, adopted
		return nil
	})
	if err != nil {
		return nil, nil, err
	}
	return conv, ch, nil
}

// FindGeneral returns the group conversation of context bm/1, or nil when
// nobody has opened the chat yet.
func FindGeneral(ctx context.Context, db *gorm.DB) (*chatmodels.Conversation, error) {
	var conv chatmodels.Conversation
	err := db.WithContext(ctx).
		Where("type = ? AND context_type = ? AND context_id = ?", chatmodels.TypeGroup, ChatContextType, ChatContextID).
		Order("id").Take(&conv).Error
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	return &conv, nil
}

// SyncChatParticipants makes the chat's participants follow the chat
// group, in one transaction: every member missing from ogólny (generalID)
// joins it, and users no longer in the group lose their participant rows
// in every conversation of context bm/1. Nothing is pruned while no group
// with that code exists, so a mistyped code cannot wipe the DMs. It returns
// how many rows it added and removed.
func SyncChatParticipants(ctx context.Context, db *gorm.DB, generalID uint, group string) (int64, int64, error) {
	if db == nil {
		return 0, 0, errors.New("jz.bm: chat sync needs a database")
	}
	if group == "" {
		return 0, 0, errors.New("jz.bm: chat sync needs a chat group code")
	}
	var added, removed int64
	err := lagoon.Transaction(ctx, db, func(ctx context.Context, tx *gorm.DB) error {
		if generalID != 0 {
			res := tx.Exec(`INSERT INTO golem15_chat_participants (conversation_id, user_id, joined_at)
SELECT ?, m.user_id, NOW() FROM (`+chatMembersSQL+`) m
ON CONFLICT (conversation_id, user_id) DO NOTHING`, generalID, group)
			if res.Error != nil {
				return res.Error
			}
			added = res.RowsAffected
		}
		res := tx.Exec(`DELETE FROM golem15_chat_participants
WHERE conversation_id IN (`+chatConversationsSQL+`)
  AND user_id NOT IN (`+chatMembersSQL+`)
  AND EXISTS (SELECT 1 FROM user_groups WHERE code = ?)`, ChatContextType, ChatContextID, group, group)
		if res.Error != nil {
			return res.Error
		}
		removed = res.RowsAffected
		return nil
	})
	return added, removed, err
}

// PruneChatParticipant removes userID from every conversation of context
// bm/1. It runs when someone outside the chat group asks for the chat.
func PruneChatParticipant(ctx context.Context, db *gorm.DB, userID uint) error {
	if db == nil {
		return errors.New("jz.bm: chat prune needs a database")
	}
	return db.WithContext(ctx).Exec(`DELETE FROM golem15_chat_participants
WHERE user_id = ? AND conversation_id IN (`+chatConversationsSQL+`)`, userID, ChatContextType, ChatContextID).Error
}

// AssignMissingHandles gives every chat-group member without a handle one
// (golem15.user AssignHandle), so they can be @mentioned, and returns how
// many it assigned.
func AssignMissingHandles(ctx context.Context, db *gorm.DB, group string) (int, error) {
	if db == nil {
		return 0, errors.New("jz.bm: handles need a database")
	}
	if group == "" {
		return 0, nil
	}
	var users []usermodels.User
	err := db.WithContext(ctx).
		Where("id IN ("+chatMembersSQL+")", group).
		Where("handle IS NULL OR handle = ''").
		Order("id").Find(&users).Error
	if err != nil {
		return 0, err
	}
	n := 0
	for i := range users {
		if err := userclasses.AssignHandle(ctx, db, &users[i]); err != nil {
			return n, err
		}
		n++
	}
	return n, nil
}