any2anexoj/internal/report.go

package internal

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"time"

	"github.com/shopspring/decimal"
)

type Record interface {
	Symbol() string
	Nature() Nature
	BrokerCountry() int64
	AssetCountry() int64
	Kind() Kind
	Price() decimal.Decimal
	Quantity() decimal.Decimal
	Timestamp() time.Time
	Fees() decimal.Decimal
	Taxes() decimal.Decimal
}

type RecordReader interface {
	// ReadRecord should return Records until an error is found.
	ReadRecord(context.Context) (Record, error)
}

type ReportItem struct {
	Symbol        string
	Nature        Nature
	BrokerCountry int64
	AssetCountry  int64
	BuyValue      decimal.Decimal
	BuyTimestamp  time.Time
	SellValue     decimal.Decimal
	SellTimestamp time.Time
	Fees          decimal.Decimal
	Taxes         decimal.Decimal
}

func (ri ReportItem) RealisedPnL() decimal.Decimal {
	return ri.SellValue.Sub(ri.BuyValue)
}

type ReportWriter interface {
	// ReportWriter writes report items
	Write(context.Context, ReportItem) error
}

type optionals struct {
	selector Selector
	store    Store
}

func applyOptions(defaults optionals, opts []Option) optionals {
	for _, opt := range opts {
		opt(&defaults)
	}
	return defaults
}

type Option func(*optionals)

// Selector returns true if a record should be selected for processing, false otherwise.
type Selector func(Record) bool

func WithSelector(s Selector) Option {
	return func(o *optionals) {
		o.selector = s
	}
}

type Store interface {
	Load(context.Context) (map[string]*FillerQueue, error)
	Save(context.Context, map[string]*FillerQueue) error
}

func WithStore(s Store) Option {
	return func(o *optionals) {
		o.store = s
	}
}

// BuildReport reads records from a RecordReader and, if the record passes the Selector, it is
// processed into the ReportWriter.
func BuildReport(ctx context.Context, reader RecordReader, writer ReportWriter, options ...Option) error {
	optionals := applyOptions(optionals{
		selector: Any(),
		store:    EphemeralStore{},
	}, options)

	buys, err := optionals.store.Load(ctx)
	if err != nil {
		return fmt.Errorf("loading state: %w", err)
	}

	var (
		recordsCount  int64
		lastTimestamp time.Time
		progTicker    = time.NewTicker(10 * time.Second)
	)
	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-progTicker.C:
			slog.InfoContext(
				ctx, "Progress update",
				slog.Int64("records_count", recordsCount),
				slog.Time("last_record_timestamp", lastTimestamp),
			)
		default:
			rec, err := reader.ReadRecord(ctx)
			if err != nil {
				if errors.Is(err, io.EOF) {
					err = optionals.store.Save(ctx, buys)
					if err != nil {
						return fmt.Errorf("saving state: %w", err)
					}

					return nil
				}
				return err
			}

			if !rec.Kind().Valid() {
				return fmt.Errorf("found invalid Kind(%d)", rec.Kind())
			}

			lastTimestamp = rec.Timestamp()
			recordsCount++

			buyQueue, ok := buys[rec.Symbol()]
			if !ok {
				buyQueue = new(FillerQueue)
				buys[rec.Symbol()] = buyQueue
			}

			err = processRecord(ctx, buyQueue, rec, optionals.selector, writer)
			if err != nil {
				return fmt.Errorf("processing record: %w", err)
			}
		}
	}
}

// processRecord either adds buys to the queue or consumes buys from the queue when processing a
// sell record.
func processRecord(ctx context.Context, q *FillerQueue, rec Record, sel Selector, writer ReportWriter) error {
	slog.Debug(
		"Report: processing record",
		slog.String("symbol", rec.Symbol()),
		slog.String("side", rec.Kind().String()),
	)

	switch rec.Kind() {
	case KindBuy:
		// Selectors are only applied when processing sell records for performance reasons. It's much
		// cheaper to just accumulate buys and only actually inspect any records once a sell happens. This
		// avoids potential network requests to for every single record.
		q.Push(NewFiller(rec))

	case KindSell:
		if !sel(rec) {
			slog.Debug(
				"Report: skipping record",
				slog.String("symbol", rec.Symbol()),
				slog.String("side", rec.Kind().String()),
			)
			return nil
		}

		unmatchedQty := rec.Quantity()

		for unmatchedQty.IsPositive() {
			buy, ok := q.Peek()
			if !ok {
				return ErrInsufficientBoughtVolume
			}

			matchedQty, filled := buy.Fill(unmatchedQty)

			if filled {
				_, ok := q.Pop()
				if !ok {
					return fmt.Errorf("pop empty filler queue")
				}
			}

			unmatchedQty = unmatchedQty.Sub(matchedQty)

			buyValue := matchedQty.Mul(buy.Price())
			sellValue := matchedQty.Mul(rec.Price())

			err := writer.Write(ctx, ReportItem{
				Symbol:        rec.Symbol(),
				BrokerCountry: rec.BrokerCountry(),
				AssetCountry:  rec.AssetCountry(),
				BuyValue:      buyValue,
				BuyTimestamp:  buy.Timestamp(),
				SellValue:     sellValue,
				SellTimestamp: rec.Timestamp(),
				Fees:          buy.Fees().Add(rec.Fees()),
				Taxes:         buy.Taxes().Add(rec.Taxes()),
				Nature:        buy.Nature(),
			})
			if err != nil {
				return fmt.Errorf("write report item: %w", err)
			}
		}

	case KindSplit:
		q.AdjustForSplit(rec.Quantity())

	default:
		return fmt.Errorf("unknown side: %v", rec.Kind())
	}

	return nil
}