// Package rates holds the Data-Source client stub for ds:per-diem-rates.
// Current state: skeleton — no HTTP transport, no Session-Scope-Token
// acquisition. The intent is to document the eventual signature and let
// the calc package compile against it.
package rates

import (
	"errors"
	"time"
)

// Client exposes the one operation the calculator needs: fetch the applicable
// rate for a country+date. The real implementation will call
// ds:per-diem-rates /rates with a Session-Scope-Token and return the single
// applicable rate (filtering by city if provided).
type Client struct {
	// BaseURL, HTTPClient, ScopeTokenFetcher — intentionally omitted in skeleton
}

// RateFor is a stub that always returns a helpful error so tests that need a
// real provider substitute their own.
func (c *Client) RateFor(country string, day time.Time) (interface{}, error) {
	return nil, errors.New("rates.Client is a skeleton; substitute a test or real provider")
}