package board

import (
	"bytes"
	"encoding/gob"
	"fmt"
	"sort"
	"time"

	"codeflow.dananglin.me.uk/apollo/pelican/internal/db"
	bolt "go.etcd.io/bbolt"
)

// Board is probably the heart of Pelican.
type Board struct {
	db *bolt.DB
}

// Open reads the board from the database.
// If no board exists then a new one will be created.
func Open(path string) (Board, error) {
	database, err := db.OpenDatabase(path)
	if err != nil {
		return Board{}, fmt.Errorf("unable to open the db. %w", err)
	}

	board := Board{
		db: database,
	}

	statusList, err := board.StatusList()
	if err != nil {
		return Board{}, err
	}

	if len(statusList) == 0 {
		newStatusList := defaultStatusList()

		boltItems := make([]db.BoltItem, len(newStatusList))

		for i := range newStatusList {
			boltItems[i] = &newStatusList[i]
		}

		if _, err := db.Write(database, db.WriteModeCreate, db.StatusBucket, boltItems); err != nil {
			return Board{}, fmt.Errorf("unable to save the default status list to the db. %w", err)
		}
	}

	return board, nil
}

// Close closes the project's Kanban board.
func (b *Board) Close() error {
	if b.db == nil {
		return nil
	}

	if err := b.db.Close(); err != nil {
		return fmt.Errorf("error closing the db. %w", err)
	}

	return nil
}

// StatusList returns the ordered list of statuses from the db.
func (b *Board) StatusList() ([]Status, error) {
	data, err := db.ReadAll(b.db, db.StatusBucket)
	if err != nil {
		return nil, fmt.Errorf("unable to read the status list, %w", err)
	}

	statuses := make([]Status, len(data))

	for ind, d := range data {
		buf := bytes.NewBuffer(d)

		decoder := gob.NewDecoder(buf)

		var status Status

		if err := decoder.Decode(&status); err != nil {
			return nil, fmt.Errorf("unable to decode data, %w", err)
		}

		statuses[ind] = status
	}

	sort.Sort(ByStatusPosition(statuses))

	return statuses, nil
}

// Status returns a single status from the database.
func (b *Board) Status(statusID int) (Status, error) {
	data, err := db.Read(b.db, db.StatusBucket, statusID)
	if err != nil {
		return Status{}, fmt.Errorf("unable to read status [%d] from the database; %w", statusID, err)
	}

	if data == nil {
		return Status{}, StatusNotExistError{ID: statusID}
	}

	var status Status

	buf := bytes.NewBuffer(data)

	decoder := gob.NewDecoder(buf)

	if err := decoder.Decode(&status); err != nil {
		return Status{}, fmt.Errorf("unable to decode data into a Status object; %w", err)
	}

	return status, nil
}

// StatusArgs is an argument type for creating or updating statuses.
type StatusArgs struct {
	Name     string
	Position int
}

// CreateStatus creates a status in the database.
func (b *Board) CreateStatus(args StatusArgs) error {
	name := args.Name
	pos := args.Position

	if pos < 1 {
		statuses, err := b.StatusList()
		if err != nil {
			return fmt.Errorf("unable to get the list of statuses; %w", err)
		}

		length := len(statuses)
		if length == 0 {
			pos = 1
		} else {
			pos = statuses[length-1].Position + 1
		}
	}

	status := Status{
		Identity: Identity{ID: -1},
		Name:     name,
		Position: pos,
		CardIds:  nil,
	}

	if _, err := db.Write(b.db, db.WriteModeCreate, db.StatusBucket, []db.BoltItem{&status}); err != nil {
		return fmt.Errorf("unable to write the status to the database; %w", err)
	}

	return nil
}

// UpdateStatusArgs is an argument type required for updating statuses.
type UpdateStatusArgs struct {
	StatusID int
	StatusArgs
}

// UpdateStatus modifies an existing status in the database.
func (b *Board) UpdateStatus(args UpdateStatusArgs) error {
	status, err := b.Status(args.StatusID)
	if err != nil {
		return fmt.Errorf("unable to retrieve the status from the database. %w", err)
	}

	if len(args.Name) > 0 {
		status.Name = args.Name
	}

	if args.Position > 0 {
		status.Position = args.Position
	}

	if _, err := db.Write(b.db, db.WriteModeUpdate, db.StatusBucket, []db.BoltItem{&status}); err != nil {
		return fmt.Errorf("unable to write the status to the db. %w", err)
	}

	return nil
}

// DeleteStatus deletes a status from the database.
// A status can only be deleted if it does not contain any cards.
func (b *Board) DeleteStatus(statusID int) error {
	status, err := b.Status(statusID)
	if err != nil {
		return fmt.Errorf("unable to retrieve the status from the database; %w", err)
	}

	if len(status.CardIds) > 0 {
		return StatusNotEmptyError{ID: statusID}
	}

	if err := db.Delete(b.db, db.StatusBucket, statusID); err != nil {
		return fmt.Errorf("unable to delete the status from the database; %w", err)
	}

	if err := b.normaliseStatusesPositionValuesFromDatabase(); err != nil {
		return fmt.Errorf("unable to normalise the statuses position values; %w", err)
	}

	return nil
}

// RepositionStatus re-positions a Status value on a slice of Statuses.
func (b *Board) RepositionStatus(currentIndex, targetIndex int) error {
	statuses, err := b.StatusList()
	if err != nil {
		return fmt.Errorf("unable to get the list of statuses; %w", err)
	}

	statuses = shuffle(statuses, currentIndex, targetIndex)

	if err := b.normaliseStatusesPositionValues(statuses); err != nil {
		return fmt.Errorf("unable to normalise the statuses position values; %w", err)
	}

	return nil
}

// normaliseStatusesPositionValuesFromDatabase retrieves the ordered list of statuses from the database and sets
// each status' positional value based on its position in the list before saving the updates to the database.
func (b *Board) normaliseStatusesPositionValuesFromDatabase() error {
	statuses, err := b.StatusList()
	if err != nil {
		return fmt.Errorf("unable to get the list of statuses; %w", err)
	}

	return b.normaliseStatusesPositionValues(statuses)
}

// normaliseStatusesPositionValues takes a list of statuses and sets
// each status' positional value based on its position in the list before
// saving the updates to the database.
func (b *Board) normaliseStatusesPositionValues(statuses []Status) error {
	for i, status := range statuses {
		updateArgs := UpdateStatusArgs{
			StatusID: status.ID,
			StatusArgs: StatusArgs{
				Name:     "",
				Position: i + 1,
			},
		}

		if err := b.UpdateStatus(updateArgs); err != nil {
			return fmt.Errorf("unable to update the status %q; %w", status.Name, err)
		}
	}

	return nil
}

// MoveToStatusArgs is an argument type for moving a card between statuses.
type MoveToStatusArgs struct {
	CardID          int
	CurrentStatusID int
	NextStatusID    int
}

// MoveToStatus moves a card between statuses.
func (b *Board) MoveToStatus(args MoveToStatusArgs) error {
	currentStatus, err := b.Status(args.CurrentStatusID)
	if err != nil {
		return fmt.Errorf("unable to get the card's current status [%d], %w", args.CurrentStatusID, err)
	}

	nextStatus, err := b.Status(args.NextStatusID)
	if err != nil {
		return fmt.Errorf("unable to get the card's next status [%d], %w", args.NextStatusID, err)
	}

	nextStatus.AddCardID(args.CardID)
	currentStatus.RemoveCardID(args.CardID)

	boltItems := []db.BoltItem{&currentStatus, &nextStatus}

	if _, err := db.Write(b.db, db.WriteModeUpdate, db.StatusBucket, boltItems); err != nil {
		return fmt.Errorf("unable to update the statuses in the db. %w", err)
	}

	return nil
}

// CardArgs is an argument type for creating or updating cards.
type CardArgs struct {
	NewTitle       string
	NewDescription string
}

// CreateCard creates a card in the database.
func (b *Board) CreateCard(args CardArgs) (int, error) {
	timestamp := time.Now().Format(time.DateTime)

	statusList, err := b.StatusList()
	if err != nil {
		return 0, fmt.Errorf("unable to read the status list, %w", err)
	}

	if len(statusList) == 0 {
		return 0, StatusListEmptyError{}
	}

	boltItems := []db.BoltItem{
		&Card{
			Identity:    Identity{ID: -1},
			Title:       args.NewTitle,
			Description: args.NewDescription,
			Created:     timestamp,
		},
	}

	cardIDs, err := db.Write(b.db, db.WriteModeCreate, db.CardBucket, boltItems)
	if err != nil {
		return 0, fmt.Errorf("unable to write card to the db. %w", err)
	}

	if len(cardIDs) != 1 {
		return 0, fmt.Errorf("unexpected number of card IDs returned after writing the card to the database; want: 1, got %d", len(cardIDs))
	}

	cardID := cardIDs[0]

	statusInFirstPos := statusList[0]

	statusInFirstPos.AddCardID(cardID)

	_, err = db.Write(b.db, db.WriteModeUpdate, db.StatusBucket, []db.BoltItem{&statusInFirstPos})
	if err != nil {
		return 0, fmt.Errorf("unable to write the %s status to the db. %w", statusInFirstPos.Name, err)
	}

	return cardID, nil
}

// Card returns a Card value from the database.
func (b *Board) Card(cardID int) (Card, error) {
	data, err := db.Read(b.db, db.CardBucket, cardID)
	if err != nil {
		return Card{}, fmt.Errorf("unable to read card [%d] from the db. %w", cardID, err)
	}

	if data == nil {
		return Card{}, CardNotExistError{ID: cardID}
	}

	var card Card

	buf := bytes.NewBuffer(data)

	decoder := gob.NewDecoder(buf)

	if err := decoder.Decode(&card); err != nil {
		return Card{}, fmt.Errorf("unable to decode data, %w", err)
	}

	return card, nil
}

// CardList returns a list of Card values from the db.
func (b *Board) CardList(ids []int) ([]Card, error) {
	data, err := db.ReadMany(b.db, db.CardBucket, ids)
	if err != nil {
		return nil, fmt.Errorf("unable to read card list from the db. %w", err)
	}

	cards := make([]Card, len(data))

	for ind, d := range data {
		buf := bytes.NewBuffer(d)

		decoder := gob.NewDecoder(buf)

		var card Card

		if err := decoder.Decode(&card); err != nil {
			return nil, fmt.Errorf("unable to decode data, %w", err)
		}

		cards[ind] = card
	}

	return cards, nil
}

// UpdateCardArgs is an argument type for updating a card.
type UpdateCardArgs struct {
	CardID int
	CardArgs
}

// UpdateCard modifies an existing card in the database.
func (b *Board) UpdateCard(args UpdateCardArgs) error {
	card, err := b.Card(args.CardID)
	if err != nil {
		return err
	}

	if len(args.NewTitle) > 0 {
		card.Title = args.NewTitle
	}

	if len(args.NewDescription) > 0 {
		card.Description = args.NewDescription
	}

	if _, err := db.Write(b.db, db.WriteModeUpdate, db.CardBucket, []db.BoltItem{&card}); err != nil {
		return fmt.Errorf("unable to write the card to the database; %w", err)
	}

	return nil
}

// DeleteCardArgs is an argument type for deleting a card.
type DeleteCardArgs struct {
	CardID   int
	StatusID int
}

// DeleteCard deletes a card from the database.
func (b *Board) DeleteCard(args DeleteCardArgs) error {
	if err := db.Delete(b.db, db.CardBucket, args.CardID); err != nil {
		return fmt.Errorf("unable to delete the card from the database; %w", err)
	}

	status, err := b.Status(args.StatusID)
	if err != nil {
		return fmt.Errorf("unable to read Status '%d' from the database; %w", args.StatusID, err)
	}

	status.RemoveCardID(args.CardID)

	if _, err := db.Write(b.db, db.WriteModeUpdate, db.StatusBucket, []db.BoltItem{&status}); err != nil {
		return fmt.Errorf("unable to update the status in the database; %w", err)
	}

	return nil
}