wallet.go

// Package wallet defines a domain of the wallet functionality and entities.
// The layout is heavily inspired by Ben Johnson's https://github.com/benbjohnson/wtf.
package wallet

import (
	"context"

	"github.com/cockroachdb/apd"
)

const (
	// DecimalMaxDigits is a decimal precision (defaults to 28 as in Python).
	DecimalMaxDigits = 28
	// DecimalPlaces defines how many decimal places are used to quantize a number.
	DecimalPlaces = 2
)

// Transfer is a customer request to send money.
type Transfer struct {
	// ID is a random string generated by a client for duplicate suppression.
	ID string `json:"request_id"`
	// From which account to send money.
	From   string      `json:"from"`
	Amount apd.Decimal `json:"amount"`
	// To is a transfer recipient account.
	To string `json:"to"`
	// Partition is a number of a partition where the transfer request was stored.
	Partition int32 `json:"-"`
	// SequenceID is ID assigned internally. For example, in Kafka it is an offset of the message.
	SequenceID int64 `json:"-"`
}

// Payment is an instruction that affects account balance.
// For example, outgoing 0.5 payment from Alice's account.
type Payment struct {
	// RequestID is a client request ID from Transfer entity for duplicate suppression.
	RequestID string `json:"request_id"`
	// Account where the payment belongs to.
	Account string `json:"account"`
	// Direction defines whether payment is incoming or outgoing.
	Direction string      `json:"direction"`
	Amount    apd.Decimal `json:"amount"`
	// Partition is a number of a partition where the payment was stored.
	Partition int32 `json:"-"`
	// SequenceID is ID assigned internally. For example, in Kafka it is an offset of the message.
	SequenceID int64 `json:"-"`
}

// TransferService represents a service to store transfer requests.
type TransferService interface {
	CreateTransfer(ctx context.Context, t *Transfer) error
	FromOffset(ctx context.Context, partition int32, offset int64) (<-chan *Transfer, <-chan error)
}

// PaymentService represents a service to store payments which are created based on
// transfer requests.
type PaymentService interface {
	CreatePayment(ctx context.Context, p *Payment) error
	FromOffset(ctx context.Context, partition int32, offset int64) (<-chan *Payment, <-chan error)
}

// DedupService is responsible for requests deduplication.
type DedupService interface {
	HasSeen(requestID string) (bool, error)
	Save(requestID string) error
}