// Package explorer implements the read-only queries used by GL's web explorer.
package explorer

import (
	"context"
	"errors"
	"fmt"
	"sort"
	"strings"
	"time"

	"gl/domain/ledger"
)

const (
	recentJournalLimit  = 12
	transactionPageSize = 20
	topAssetLimit       = 5
	topHoldersPerAsset  = 5
)

type Stats struct {
	JournalCount   int64
	EntryCount     int64
	AccountCount   int64
	LastRecordedAt time.Time
}

type Holder struct {
	Rank      int64
	OwnerType string
	OwnerID   string
	AssetID   int64
	Balance   ledger.Amount
}

type HolderReference struct {
	OwnerType string
	OwnerID   string
	AssetID   int64
}

type Repository interface {
	Stats(context.Context) (Stats, error)
	List(context.Context, ledger.JournalFilter) ([]ledger.Journal, error)
	GetByTransactionHash(context.Context, string) ([]ledger.Journal, error)
	GetByID(context.Context, string) (ledger.Journal, error)
	Balance(context.Context, ledger.AccountReference, time.Time) (ledger.Amount, error)
	TopHolders(context.Context, int, int) ([]Holder, error)
}

type Service struct {
	repository Repository
}

type Dashboard struct {
	Stats    Stats
	Journals []ledger.Journal
}

type Assets struct {
	TopHolders []Holder
}

type TransactionListing struct {
	Journals    []ledger.Journal
	Filter      TransactionFilter
	HasPrevious bool
	HasNext     bool
}

type TransactionFilter struct {
	Page       int
	Wallet     string
	EffectKind string
}

type Account struct {
	Reference ledger.AccountReference
	Balance   ledger.Amount
	Journals  []ledger.Journal
}

type HolderAccount struct {
	Reference HolderReference
	Balance   ledger.Amount
	Journals  []ledger.Journal
}

func NewService(repository Repository) *Service {
	return &Service{repository: repository}
}

func (s *Service) Dashboard(ctx context.Context) (Dashboard, error) {
	stats, err := s.repository.Stats(ctx)
	if err != nil {
		return Dashboard{}, fmt.Errorf("read explorer stats: %w", err)
	}
	journals, err := s.repository.List(ctx, ledger.JournalFilter{Limit: recentJournalLimit})
	if err != nil {
		return Dashboard{}, fmt.Errorf("read recent journals: %w", err)
	}
	return Dashboard{Stats: stats, Journals: journals}, nil
}

func (s *Service) Assets(ctx context.Context) (Assets, error) {
	holders, err := s.repository.TopHolders(ctx, topAssetLimit, topHoldersPerAsset)
	if err != nil {
		return Assets{}, fmt.Errorf("read top asset holders: %w", err)
	}
	return Assets{TopHolders: holders}, nil
}

func (s *Service) Transactions(ctx context.Context, filter TransactionFilter) (TransactionListing, error) {
	filter.Wallet = strings.TrimSpace(filter.Wallet)
	filter.EffectKind = strings.TrimSpace(filter.EffectKind)
	if filter.Page < 1 {
		filter.Page = 1
	}
	if filter.Page > 1_000_000 {
		return TransactionListing{}, fmt.Errorf("transaction page is too large")
	}
	if len(filter.Wallet) > 256 || len(filter.EffectKind) > 128 {
		return TransactionListing{}, fmt.Errorf("transaction filter is too long")
	}
	repositoryFilter := ledger.JournalFilter{
		Limit:  transactionPageSize + 1,
		Offset: (filter.Page - 1) * transactionPageSize,
	}
	if filter.Wallet != "" {
		repositoryFilter.OwnerID = &filter.Wallet
	}
	if filter.EffectKind != "" {
		repositoryFilter.EffectKind = &filter.EffectKind
	}
	journals, err := s.repository.List(ctx, repositoryFilter)
	if err != nil {
		return TransactionListing{}, fmt.Errorf("read transaction page: %w", err)
	}
	listing := TransactionListing{Journals: journals, Filter: filter, HasPrevious: filter.Page > 1}
	if len(listing.Journals) > transactionPageSize {
		listing.HasNext = true
		listing.Journals = listing.Journals[:transactionPageSize]
	}
	return listing, nil
}

func (s *Service) Transaction(ctx context.Context, reference string) ([]ledger.Journal, error) {
	reference = strings.TrimSpace(reference)
	if reference == "" {
		return nil, fmt.Errorf("transaction reference is required")
	}
	if len(reference) > 256 {
		return nil, fmt.Errorf("transaction reference is too long")
	}
	journals, err := s.repository.GetByTransactionHash(ctx, reference)
	if err != nil {
		return nil, fmt.Errorf("read transaction: %w", err)
	}
	if len(journals) != 0 {
		return journals, nil
	}
	if !isJournalID(reference) {
		return nil, ledger.ErrNotFound
	}
	journal, err := s.repository.GetByID(ctx, reference)
	if err != nil {
		if errors.Is(err, ledger.ErrNotFound) {
			return nil, ledger.ErrNotFound
		}
		return nil, fmt.Errorf("read internal transaction: %w", err)
	}
	return []ledger.Journal{journal}, nil
}

func isJournalID(value string) bool {
	if len(value) != 36 {
		return false
	}
	for index, character := range value {
		switch index {
		case 8, 13, 18, 23:
			if character != '-' {
				return false
			}
		default:
			if !((character >= '0' && character <= '9') || (character >= 'a' && character <= 'f') || (character >= 'A' && character <= 'F')) {
				return false
			}
		}
	}
	return true
}

func (s *Service) Account(ctx context.Context, reference ledger.AccountReference) (Account, error) {
	if err := reference.Validate(); err != nil {
		return Account{}, fmt.Errorf("invalid account: %w", err)
	}
	balance, err := s.repository.Balance(ctx, reference, time.Time{})
	if err != nil {
		return Account{}, fmt.Errorf("read account balance: %w", err)
	}
	journals, err := s.repository.List(ctx, ledger.JournalFilter{
		Account: &reference,
		AssetID: &reference.AssetID,
		Limit:   50,
	})
	if err != nil {
		return Account{}, fmt.Errorf("read account journals: %w", err)
	}
	return Account{Reference: reference, Balance: balance, Journals: journals}, nil
}

func (s *Service) Holder(ctx context.Context, reference HolderReference) (HolderAccount, error) {
	if strings.TrimSpace(reference.OwnerType) == "" || strings.TrimSpace(reference.OwnerID) == "" || reference.AssetID <= 0 {
		return HolderAccount{}, fmt.Errorf("invalid holder reference")
	}

	result := HolderAccount{Reference: reference}
	seen := make(map[string]struct{})
	for _, class := range []ledger.AccountClass{ledger.AccountClassUserAvailable, ledger.AccountClassUserFrozen} {
		account := ledger.AccountReference{Class: class, OwnerType: reference.OwnerType, OwnerID: reference.OwnerID, AssetID: reference.AssetID}
		balance, err := s.repository.Balance(ctx, account, time.Time{})
		if err != nil {
			return HolderAccount{}, fmt.Errorf("read holder balance: %w", err)
		}
		result.Balance = result.Balance.Add(balance)

		journals, err := s.repository.List(ctx, ledger.JournalFilter{Account: &account, AssetID: &reference.AssetID, Limit: 50})
		if err != nil {
			return HolderAccount{}, fmt.Errorf("read holder journals: %w", err)
		}
		for _, journal := range journals {
			if _, exists := seen[journal.ID]; exists {
				continue
			}
			seen[journal.ID] = struct{}{}
			result.Journals = append(result.Journals, journal)
		}
	}
	sort.Slice(result.Journals, func(left, right int) bool {
		if result.Journals[left].RecordedAt.Equal(result.Journals[right].RecordedAt) {
			return result.Journals[left].ID > result.Journals[right].ID
		}
		return result.Journals[left].RecordedAt.After(result.Journals[right].RecordedAt)
	})
	if len(result.Journals) > 50 {
		result.Journals = result.Journals[:50]
	}
	return result, nil
}

func IsNotFound(err error) bool {
	return errors.Is(err, ledger.ErrNotFound)
}