Implement RateProvider adapter

go.mod

@@ -2,4 +2,16 @@ module converter
 
 go 1.24.3
 
-require github.com/shopspring/decimal v1.4.0
+require (
+	github.com/go-resty/resty/v2 v2.16.5
+	github.com/shopspring/decimal v1.4.0
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/objx v0.5.2 // indirect
+	github.com/stretchr/testify v1.11.1 // indirect
+	golang.org/x/net v0.33.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

go.sum

@@ -1,2 +1,19 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-resty/resty/v2 v2.16.5 h1:hBKqmWrr7uRc3euHVqmh1HTHcKn99Smr7o5spptdhTM=
+github.com/go-resty/resty/v2 v2.16.5/go.mod h1:hkJtXbA2iKHzJheXYvQ8snQES5ZLGKMwQ07xAwp/fiA=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/shopspring/decimal v1.4.0 h1:bxl37RwXBklmTi0C79JfXCEBD1cqqHt0bbgBAGFp81k=
 github.com/shopspring/decimal v1.4.0/go.mod h1:gawqmDU56v4yIKSwfBSFip1HdCCXN8/+DMd9qYNcwME=
+github.com/stretchr/objx v0.5.2 h1:xuMeJ0Sdp5ZMRXx/aWO6RZxdr3beISkG5/G/aIRr3pY=
+github.com/stretchr/objx v0.5.2/go.mod h1:FRsXN1f5AsAjCGJKqEizvkpNtU+EGNCLh3NxZ/8L+MA=
+github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
+github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+golang.org/x/net v0.33.0 h1:74SYHlV8BIgHIFC/LrYkOGIwL19eTYXQ5wc6TBuO36I=
+golang.org/x/net v0.33.0/go.mod h1:HXLR5J+9DxmrqMwG9qjGCxZ+zKXxBru04zlTvWlWuN4=
+golang.org/x/time v0.6.0 h1:eTDhh4ZXt5Qf0augr54TN6suAUudPcawVZeIAPU7D4U=
+golang.org/x/time v0.6.0/go.mod h1:3BpzKBy/shNhVucY/MWOyx10tF3SFh9QdLuxbVysPQM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

infrastructure/coinmarketcap/client.go

@@ -0,0 +1,138 @@
+package coinmarketcap
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/go-resty/resty/v2"
+)
+
+// CoinMarketCap specific errors
+var (
+	ErrUnknownSymbol   = errors.New("unknown symbol")
+	ErrInvalidConvert  = errors.New("invalid convert currency")
+	ErrAPIError        = errors.New("coinmarketcap api error")
+	ErrInvalidResponse = errors.New("invalid response format")
+)
+
+const (
+	baseURL    = "https://pro-api.coinmarketcap.com"
+	quotesPath = "/v1/cryptocurrency/quotes/latest"
+)
+
+// Client implements the RateProvider interface for CoinMarketCap API
+type Client struct {
+	httpClient *resty.Client
+	apiKey     string
+}
+
+// NewClient creates a new CoinMarketCap API client
+func NewClient(apiKey string) *Client {
+	client := resty.New().
+		SetBaseURL(baseURL).
+		SetHeader("Accept", "application/json").
+		SetHeader("X-CMC_PRO_API_KEY", apiKey)
+
+	return &Client{
+		httpClient: client,
+		apiKey:     apiKey,
+	}
+}
+
+// GetRate fetches exchange rate from CoinMarketCap API
+func (c *Client) GetRate(ctx context.Context, fromCode, toCode string) (RateDTO, error) {
+	// Try direct conversion first
+	rateDTO, err := c.tryGetRate(ctx, fromCode, toCode)
+	if err == nil {
+		return rateDTO, nil
+	}
+
+	// If empty result but no other error, try reverse
+	if err == ErrUnknownSymbol {
+		reverseDTO, reverseErr := c.tryGetRate(ctx, toCode, fromCode)
+		if reverseErr == nil {
+			return reverseDTO, nil
+		}
+
+		// If reverse request failed with invalid convert, that confirms the original
+		// "from" currency is indeed unknown (it's now the "convert" parameter)
+		if reverseErr == ErrInvalidConvert {
+			return RateDTO{}, err // Return original unknown symbol error
+		}
+
+		// Any other error from reverse request (network, auth, etc) should be surfaced
+		return RateDTO{}, reverseErr
+	}
+
+	// Return original error (either non-unknown-symbol error or first currency not in crypto database)
+	return RateDTO{}, err
+}
+
+// tryGetRate attempts to get rate in specified direction
+func (c *Client) tryGetRate(ctx context.Context, fromCode, toCode string) (RateDTO, error) {
+	var response APIResponse
+
+	// Make API request
+	resp, err := c.httpClient.R().
+		SetContext(ctx).
+		SetQueryParam("symbol", fromCode).
+		SetQueryParam("convert", toCode).
+		SetResult(&response).
+		Get(quotesPath)
+
+	if err != nil {
+		return RateDTO{}, fmt.Errorf("%w: %v", ErrAPIError, err)
+	}
+
+	// Check HTTP status first
+	if resp.StatusCode() != 200 {
+		switch resp.StatusCode() {
+		case 400:
+			return RateDTO{}, fmt.Errorf("%w: %s", ErrInvalidConvert, toCode)
+		case 401:
+			return RateDTO{}, fmt.Errorf("%w: unauthorized - bad or missing API key", ErrAPIError)
+		default:
+			return RateDTO{}, fmt.Errorf("%w: HTTP %d", ErrAPIError, resp.StatusCode())
+		}
+	}
+
+	// Check if data is empty - invalid currency
+	if len(response.Data) == 0 {
+		return RateDTO{}, fmt.Errorf("%w: %s", ErrUnknownSymbol, fromCode)
+	}
+
+	// Extract rate from response
+	rateDTO, err := c.extractRateDTO(response, fromCode, toCode)
+	if err != nil {
+		return RateDTO{}, err
+	}
+
+	return rateDTO, nil
+}
+
+
+// extractRateDTO converts API response to RateDTO
+func (c *Client) extractRateDTO(response APIResponse, fromCode, toCode string) (RateDTO, error) {
+	// Get crypto data for the from currency
+	cryptoData, exists := response.Data[fromCode]
+	if !exists {
+		return RateDTO{}, ErrInvalidResponse
+	}
+
+	// Get quote for the to currency
+	quote, exists := cryptoData.Quote[toCode]
+	if !exists {
+		return RateDTO{}, ErrInvalidResponse
+	}
+
+	// Return the rate exactly as API provided it
+	return RateDTO{
+		FromCode: fromCode,
+		ToCode:   toCode,
+		FromName: cryptoData.Name,
+		ToName:   toCode,
+		Price:    quote.Price,
+		Source:   "coinmarketcap",
+	}, nil
+}

infrastructure/coinmarketcap/models.go

@@ -0,0 +1,34 @@
+package coinmarketcap
+
+// APIResponse represents the top-level CoinMarketCap API response
+type APIResponse struct {
+	Status Status                 `json:"status"`
+	Data   map[string]CryptoQuote `json:"data"`
+}
+
+// Status represents the API response status
+type Status struct {
+	ErrorCode    int     `json:"error_code"`
+	ErrorMessage *string `json:"error_message"`
+}
+
+// CryptoQuote represents cryptocurrency data with quotes
+type CryptoQuote struct {
+	Name  string                   `json:"name"`
+	Quote map[string]CurrencyQuote `json:"quote"`
+}
+
+// CurrencyQuote represents price quote in a specific currency
+type CurrencyQuote struct {
+	Price float64 `json:"price"`
+}
+
+// RateDTO represents exchange rate data from infrastructure layer
+type RateDTO struct {
+	FromCode string
+	ToCode   string
+	FromName string
+	ToName   string
+	Price    float64
+	Source   string
+}