package conversation

import (
	"database/sql"
	"errors"
	"fmt"
	"slices"
	"strings"
	"time"

	sqids "github.com/sqids/sqids-go"
	"gorm.io/gorm"
)

// Repo exposes low-level message and conversation management. See
// Service for high-level helpers
type Repo interface {
	LoadConversationList() (ConversationList, error)

	FindConversationByShortName(shortName string) (*Conversation, error)
	ConversationShortNameCompletions(search string) []string
	GetConversationByID(int uint) (*Conversation, error)
	GetRootMessages(conversationID uint) ([]Message, error)

	CreateConversation(title string) (*Conversation, error)
	UpdateConversation(*Conversation) error
	DeleteConversation(*Conversation) error
	DeleteConversationById(id uint) error

	GetMessageByID(messageID uint) (*Message, error)

	SaveMessage(message Message) (*Message, error)
	UpdateMessage(message *Message) error
	DeleteMessage(message *Message, prune bool) error
	CloneBranch(toClone Message) (*Message, uint, error)
	Reply(to *Message, messages ...Message) ([]Message, error)

	PathToRoot(message *Message) ([]Message, error)
	PathToLeaf(message *Message) ([]Message, error)

	// Retrieves and return the "selected thread" of the conversation.
	// The "selected thread" of the conversation is a chain of messages
	// starting from the Conversation's SelectedRoot Message, following each
	// Message's SelectedReply until the tail Message is reached.
	GetSelectedThread(*Conversation) ([]Message, error)

	// Start a new conversation with the given messages
	StartConversation(messages ...Message) (*Conversation, []Message, error)

	CloneConversation(toClone Conversation) (*Conversation, uint, error)
}

type repo struct {
	db    *gorm.DB
	sqids *sqids.Sqids
}

func NewRepo(db *gorm.DB) (Repo, error) {
	models := []any{
		&Conversation{},
		&Message{},
	}

	for _, x := range models {
		err := db.AutoMigrate(x)
		if err != nil {
			return nil, fmt.Errorf("Could not perform database migrations: %v", err)
		}
	}

	_sqids, _ := sqids.New(sqids.Options{MinLength: 4})
	return &repo{db, _sqids}, nil
}

type ConversationListItem struct {
	ID            uint
	ShortName     string
	Title         string
	LastMessageAt time.Time
}

type ConversationList struct {
	Total int
	Items []ConversationListItem
}

// LoadConversationList loads existing conversations, ordered by the date
// of their latest message, from most recent to oldest.
func (s *repo) LoadConversationList() (ConversationList, error) {
	list := ConversationList{}

	var convos []Conversation
	err := s.db.Order("last_message_at DESC").Find(&convos).Error
	if err != nil {
		return list, err
	}

	for _, c := range convos {
		list.Items = append(list.Items, ConversationListItem{
			ID:            c.ID,
			ShortName:     c.ShortName.String,
			Title:         c.Title,
			LastMessageAt: c.LastMessageAt,
		})
	}

	list.Total = len(list.Items)
	return list, nil
}

func (s *repo) FindConversationByShortName(shortName string) (*Conversation, error) {
	if shortName == "" {
		return nil, errors.New("shortName is empty")
	}
	var conversation Conversation
	err := s.db.Preload("SelectedRoot").Where("short_name = ?", shortName).Find(&conversation).Error
	return &conversation, err
}

func (s *repo) ConversationShortNameCompletions(shortName string) []string {
	var conversations []Conversation
	// ignore error for completions
	s.db.Find(&conversations)
	completions := make([]string, 0, len(conversations))
	for _, conversation := range conversations {
		if shortName == "" || strings.HasPrefix(conversation.ShortName.String, shortName) {
			completions = append(completions, fmt.Sprintf("%s\t%s", conversation.ShortName.String, conversation.Title))
		}
	}
	return completions
}

func (s *repo) GetConversationByID(id uint) (*Conversation, error) {
	var conversation Conversation
	err := s.db.Preload("SelectedRoot").Where("id = ?", id).Find(&conversation).Error
	if err != nil {
		return nil, fmt.Errorf("Cannot get conversation %d: %v", id, err)
	}

	rootMessages, err := s.GetRootMessages(id)
	if err != nil {
		return nil, fmt.Errorf("Could not load conversation's root messages %d: %v", id, err)
	}
	conversation.RootMessages = rootMessages
	return &conversation, nil
}

func (s *repo) CreateConversation(title string) (*Conversation, error) {
	// Create the new conversation
	c := &Conversation{Title: title}
	err := s.db.Create(c).Error
	if err != nil {
		return nil, err
	}
	// Generate and save its "short name"
	shortName, _ := s.sqids.Encode([]uint64{uint64(c.ID)})
	c.ShortName = sql.NullString{String: shortName, Valid: true}
	err = s.db.Updates(c).Error
	if err != nil {
		return nil, err
	}
	return c, nil
}

func (s *repo) UpdateConversation(c *Conversation) error {
	if c == nil || c.ID == 0 {
		return fmt.Errorf("Conversation is nil or invalid (missing ID)")
	}
	return s.db.Updates(c).Error
}

func (s *repo) DeleteConversation(c *Conversation) error {
	if c == nil || c.ID == 0 {
		return fmt.Errorf("Conversation is nil or invalid (missing ID)")
	}
	return s.DeleteConversationById(c.ID)
}

func (s *repo) DeleteConversationById(id uint) error {
	if id == 0 {
		return fmt.Errorf("Invalid conversation ID: %d", id)
	}
	err := s.db.Where("conversation_id = ?", id).Delete(&Message{}).Error
	if err != nil {
		return err
	}
	return s.db.Where("id = ?", id).Delete(&Conversation{}).Error
}

func (s *repo) SaveMessage(m Message) (*Message, error) {
	if m.Conversation == nil {
		return nil, fmt.Errorf("Can't save a message without a conversation (this is a bug)")
	}
	newMessage := m
	newMessage.ID = 0
	newMessage.CreatedAt = time.Now()
	return &newMessage, s.db.Create(&newMessage).Error
}

func (s *repo) UpdateMessage(m *Message) error {
	if m == nil || m.ID == 0 {
		return fmt.Errorf("Message is nil or invalid (missing ID)")
	}
	return s.db.Updates(m).Error
}

func (s *repo) DeleteMessage(message *Message, prune bool) error {
	return s.db.Delete(&message).Error
}

func (s *repo) GetMessageByID(messageID uint) (*Message, error) {
	var message Message
	err := s.db.Preload("Parent").Preload("Replies").Preload("SelectedReply").Where("id = ?", messageID).Find(&message).Error
	return &message, err
}

// Reply to a message with a series of messages (each followed by the next)
func (s *repo) Reply(to *Message, messages ...Message) ([]Message, error) {
	var savedMessages []Message

	err := s.db.Transaction(func(tx *gorm.DB) error {
		currentParent := to
		for i := range messages {
			parent := currentParent
			message := messages[i]
			message.Parent = parent
			message.Conversation = parent.Conversation
			message.ID = 0
			message.CreatedAt = time.Time{}

			if err := tx.Create(&message).Error; err != nil {
				return err
			}

			// update parent selected reply
			parent.Replies = append(parent.Replies, message)
			parent.SelectedReply = &message
			if err := tx.Model(parent).Update("selected_reply_id", message.ID).Error; err != nil {
				return err
			}

			savedMessages = append(savedMessages, message)
			currentParent = &message
		}
		return nil
	})

	if err != nil {
		return savedMessages, err
	}

	to.Conversation.LastMessageAt = savedMessages[len(savedMessages)-1].CreatedAt
	err = s.UpdateConversation(to.Conversation)
	return savedMessages, err
}

// CloneBranch returns a deep clone of the given message and its replies, returning
// a new message object. The new message will be attached to the same parent as
// the messageToClone
func (s *repo) CloneBranch(messageToClone Message) (*Message, uint, error) {
	newMessage := messageToClone
	newMessage.ID = 0
	newMessage.Replies = nil
	newMessage.SelectedReplyID = nil
	newMessage.SelectedReply = nil

	originalReplies := messageToClone.Replies

	if err := s.db.Create(&newMessage).Error; err != nil {
		return nil, 0, fmt.Errorf("Could not clone message: %s", err)
	}

	var replyCount uint = 0
	for _, reply := range originalReplies {
		replyCount++

		newReply := reply
		newReply.ConversationID = messageToClone.ConversationID
		newReply.ParentID = &newMessage.ID
		newReply.Parent = &newMessage

		res, c, err := s.CloneBranch(newReply)
		if err != nil {
			return nil, 0, err
		}
		newMessage.Replies = append(newMessage.Replies, *res)
		replyCount += c

		if reply.ID == *messageToClone.SelectedReplyID {
			newMessage.SelectedReplyID = &res.ID
			if err := s.UpdateMessage(&newMessage); err != nil {
				return nil, 0, fmt.Errorf("Could not update parent select reply ID: %v", err)
			}
		}
	}
	return &newMessage, replyCount, nil
}

func fetchMessages(db *gorm.DB) ([]Message, error) {
	var messages []Message
	if err := db.Preload("Conversation").Find(&messages).Error; err != nil {
		return nil, fmt.Errorf("Could not fetch messages: %v", err)
	}

	messageMap := make(map[uint]Message)
	for i, message := range messages {
		messageMap[messages[i].ID] = message
	}

	// Create a map to store replies by their parent ID
	repliesMap := make(map[uint][]Message)
	for i, message := range messages {
		if messages[i].ParentID != nil {
			repliesMap[*messages[i].ParentID] = append(repliesMap[*messages[i].ParentID], message)
		}
	}

	// Assign replies, parent, and selected reply to each message
	for i := range messages {
		if replies, exists := repliesMap[messages[i].ID]; exists {
			messages[i].Replies = make([]Message, len(replies))
			for j, m := range replies {
				messages[i].Replies[j] = m
			}
		}
		if messages[i].ParentID != nil {
			if parent, exists := messageMap[*messages[i].ParentID]; exists {
				messages[i].Parent = &parent
			}
		}
		if messages[i].SelectedReplyID != nil {
			if selectedReply, exists := messageMap[*messages[i].SelectedReplyID]; exists {
				messages[i].SelectedReply = &selectedReply
			}
		}
	}
	return messages, nil
}

func (r repo) GetRootMessages(conversationID uint) ([]Message, error) {
	var rootMessages []Message
	err := r.db.Where("conversation_id = ? AND parent_id IS NULL", conversationID).Find(&rootMessages).Error
	if err != nil {
		return nil, fmt.Errorf("Could not retrieve root messages for conversation %d: %v", conversationID, err)
	}
	return rootMessages, nil
}

func (s *repo) buildPath(message *Message, getNext func(*Message) *uint) ([]Message, error) {
	var messages []Message
	messages, err := fetchMessages(s.db.Where("conversation_id = ?", message.ConversationID))
	if err != nil {
		return nil, err
	}

	// Create a map to store messages by their ID
	messageMap := make(map[uint]*Message, len(messages))
	for i := range messages {
		messageMap[messages[i].ID] = &messages[i]
	}

	// Construct Replies
	repliesMap := make(map[uint][]*Message, len(messages))
	for _, m := range messageMap {
		if m.ParentID == nil {
			continue
		}
		if p, ok := messageMap[*m.ParentID]; ok {
			repliesMap[p.ID] = append(repliesMap[p.ID], m)
		}
	}

	// Add replies to messages
	for _, m := range messageMap {
		if replies, ok := repliesMap[m.ID]; ok {
			m.Replies = make([]Message, len(replies))
			for idx, reply := range replies {
				m.Replies[idx] = *reply
			}
		}
	}

	// Build the path
	var path []Message
	nextID := &message.ID

	for {
		current, exists := messageMap[*nextID]
		if !exists {
			return nil, fmt.Errorf("Message with ID %d not found in conversation", *nextID)
		}

		path = append(path, *current)

		nextID = getNext(current)
		if nextID == nil {
			break
		}
	}

	return path, nil
}

// PathToRoot traverses the provided message's Parent until reaching the tree
// root and returns a slice of all messages traversed in chronological order
// (starting with the root and ending with the message provided)
func (s *repo) PathToRoot(message *Message) ([]Message, error) {
	if message == nil || message.ID <= 0 {
		return nil, fmt.Errorf("Message is nil or has invalid ID")
	}

	path, err := s.buildPath(message, func(m *Message) *uint {
		return m.ParentID
	})
	if err != nil {
		return nil, err
	}
	slices.Reverse(path)

	return path, nil
}

// PathToLeaf traverses the provided message's SelectedReply until reaching a
// tree leaf and returns a slice of all messages traversed in chronological
// order (starting with the message provided and ending with the leaf)
func (s *repo) PathToLeaf(message *Message) ([]Message, error) {
	if message == nil || message.ID <= 0 {
		return nil, fmt.Errorf("Message is nil or has invalid ID")
	}

	return s.buildPath(message, func(m *Message) *uint {
		return m.SelectedReplyID
	})
}

func (s *repo) StartConversation(messages ...Message) (*Conversation, []Message, error) {
	if len(messages) == 0 {
		return nil, nil, fmt.Errorf("Must provide at least 1 message")
	}

	// Create new conversation
	conversation, err := s.CreateConversation("")
	if err != nil {
		return nil, nil, err
	}
	messages[0].Conversation = conversation

	// Create first message
	firstMessage, err := s.SaveMessage(messages[0])
	if err != nil {
		return nil, nil, err
	}
	messages[0] = *firstMessage

	// Update conversation's selected root message
	conversation.RootMessages = []Message{messages[0]}
	conversation.SelectedRoot = &messages[0]
	conversation.LastMessageAt = messages[0].CreatedAt

	// Add additional replies to conversation
	if len(messages) > 1 {
		newMessages, err := s.Reply(&messages[0], messages[1:]...)
		if err != nil {
			return nil, nil, err
		}
		messages = append([]Message{messages[0]}, newMessages...)
		conversation.LastMessageAt = messages[len(messages)-1].CreatedAt
	}

	err = s.UpdateConversation(conversation)
	return conversation, messages, err
}

// CloneConversation clones the given conversation and all of its meesages
func (s *repo) CloneConversation(toClone Conversation) (*Conversation, uint, error) {
	rootMessages, err := s.GetRootMessages(toClone.ID)
	if err != nil {
		return nil, 0, fmt.Errorf("Could not create clone: %v", err)
	}

	clone, err := s.CreateConversation(toClone.Title + " - Clone")
	if err != nil {
		return nil, 0, fmt.Errorf("Could not create clone: %v", err)
	}

	var errors []error
	var messageCnt uint = 0
	for _, root := range rootMessages {
		messageCnt++
		newRoot := root
		newRoot.ConversationID = &clone.ID

		cloned, count, err := s.CloneBranch(newRoot)
		if err != nil {
			errors = append(errors, err)
			continue
		}
		messageCnt += count

		if root.ID == *toClone.SelectedRootID {
			clone.SelectedRootID = &cloned.ID
			if err := s.UpdateConversation(clone); err != nil {
				errors = append(errors, fmt.Errorf("Could not set selected root on clone: %v", err))
			}
		}
	}

	if len(errors) > 0 {
		return nil, 0, fmt.Errorf("Messages failed to be cloned: %v", errors)
	}

	return clone, messageCnt, nil
}

func (s *repo) GetSelectedThread(c *Conversation) ([]Message, error) {
	if c.SelectedRoot == nil {
		return nil, fmt.Errorf("No SelectedRoot on conversation - this is a bug")
	}
	return s.PathToLeaf(c.SelectedRoot)
}