feat: add usage command for premium request billing

Adds `gh models usage` command that shows premium request usage
statistics from the GitHub billing API, with breakdown by model.

Features:
- Shows requests, gross cost, and net cost per model
- Supports --today, --year, --month, --day flags
- Sorted by gross amount descending
- Color-coded discount/cost summary
- Full test coverage with httptest mock server

Closes #81

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: marcelsafin

cmd/root.go

@@ -12,6 +12,7 @@ import (
 	"github.com/github/gh-models/cmd/generate"
 	"github.com/github/gh-models/cmd/list"
 	"github.com/github/gh-models/cmd/run"
+	"github.com/github/gh-models/cmd/usage"
 	"github.com/github/gh-models/cmd/view"
 	"github.com/github/gh-models/internal/azuremodels"
 	"github.com/github/gh-models/pkg/command"
@@ -54,11 +55,12 @@ func NewRootCommand() *cobra.Command {
 		}
 	}
 
-	cfg := command.NewConfigWithTerminal(terminal, client)
+	cfg := command.NewConfigWithTerminal(terminal, client, token)
 
 	cmd.AddCommand(eval.NewEvalCommand(cfg))
 	cmd.AddCommand(list.NewListCommand(cfg))
 	cmd.AddCommand(run.NewRunCommand(cfg))
+	cmd.AddCommand(usage.NewUsageCommand(cfg))
 	cmd.AddCommand(view.NewViewCommand(cfg))
 	cmd.AddCommand(generate.NewGenerateCommand(cfg))
 

cmd/usage/usage.go

@@ -0,0 +1,291 @@
+// Package usage provides a gh command to show GitHub Models and Copilot usage information.
+package usage
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+
+	"github.com/MakeNowJust/heredoc"
+	"github.com/cli/go-gh/v2/pkg/tableprinter"
+	"github.com/github/gh-models/pkg/command"
+	"github.com/mgutz/ansi"
+	"github.com/spf13/cobra"
+)
+
+var githubAPIBase = "https://api.github.com"
+
+// setAPIBase overrides the API base URL (used in tests).
+func setAPIBase(url string) {
+	githubAPIBase = url
+}
+
+var (
+	headerColor = ansi.ColorFunc("white+du")
+	greenColor  = ansi.ColorFunc("green")
+	yellowColor = ansi.ColorFunc("yellow")
+)
+
+// premiumRequestUsageResponse represents the API response for premium request usage.
+type premiumRequestUsageResponse struct {
+	TimePeriod timePeriod  `json:"timePeriod"`
+	User       string      `json:"user"`
+	UsageItems []usageItem `json:"usageItems"`
+}
+
+type timePeriod struct {
+	Year  int `json:"year"`
+	Month int `json:"month"`
+	Day   int `json:"day,omitempty"`
+}
+
+type usageItem struct {
+	Product          string  `json:"product"`
+	SKU              string  `json:"sku"`
+	Model            string  `json:"model"`
+	UnitType         string  `json:"unitType"`
+	PricePerUnit     float64 `json:"pricePerUnit"`
+	GrossQuantity    float64 `json:"grossQuantity"`
+	GrossAmount      float64 `json:"grossAmount"`
+	DiscountQuantity float64 `json:"discountQuantity"`
+	DiscountAmount   float64 `json:"discountAmount"`
+	NetQuantity      float64 `json:"netQuantity"`
+	NetAmount        float64 `json:"netAmount"`
+}
+
+// NewUsageCommand returns a new command to show model usage information.
+func NewUsageCommand(cfg *command.Config) *cobra.Command {
+	var (
+		flagMonth int
+		flagYear  int
+		flagDay   int
+		flagToday bool
+	)
+
+	cmd := &cobra.Command{
+		Use:   "usage",
+		Short: "Show premium request usage and costs",
+		Long: heredoc.Docf(`
+			Display premium request usage statistics for GitHub Models and Copilot.
+
+			Shows a breakdown of requests by model, with gross and net costs.
+			By default, shows usage for the current billing period (month).
+
+			Use %[1]s--today%[1]s to see only today's usage, or %[1]s--month%[1]s and
+			%[1]s--year%[1]s to query a specific billing period.
+
+			Requires the %[1]suser%[1]s scope on your GitHub token. If you get a 404 error,
+			run: %[1]sgh auth refresh -h github.com -s user%[1]s
+		`, "`"),
+		Example: heredoc.Doc(`
+			# Show current month's usage
+			$ gh models usage
+
+			# Show today's usage
+			$ gh models usage --today
+
+			# Show usage for a specific month
+			$ gh models usage --year 2026 --month 2
+
+			# Show usage for a specific day
+			$ gh models usage --year 2026 --month 3 --day 15
+		`),
+		Args: cobra.NoArgs,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			token := cfg.Token
+			if token == "" {
+				return fmt.Errorf("no GitHub token found. Please run 'gh auth login' to authenticate")
+			}
+
+			ctx := cmd.Context()
+
+			// Resolve time period
+			now := time.Now().UTC()
+			year := flagYear
+			month := flagMonth
+			day := flagDay
+
+			if flagToday {
+				year = now.Year()
+				month = int(now.Month())
+				day = now.Day()
+			}
+
+			if year == 0 {
+				year = now.Year()
+			}
+			if month == 0 {
+				month = int(now.Month())
+			}
+
+			// Get username
+			username, err := getUsername(ctx, token)
+			if err != nil {
+				return fmt.Errorf("failed to get username: %w", err)
+			}
+
+			// Build query params
+			query := fmt.Sprintf("?year=%d&month=%d", year, month)
+			if day > 0 {
+				query += fmt.Sprintf("&day=%d", day)
+			}
+
+			// Fetch usage
+			data, err := fetchPremiumRequestUsage(ctx, token, username, query)
+			if err != nil {
+				return err
+			}
+
+			// Format period string
+			periodStr := fmt.Sprintf("%d-%02d", data.TimePeriod.Year, data.TimePeriod.Month)
+			if data.TimePeriod.Day > 0 {
+				periodStr += fmt.Sprintf("-%02d", data.TimePeriod.Day)
+			}
+
+			if len(data.UsageItems) == 0 {
+				cfg.WriteToOut(fmt.Sprintf("\nNo usage found for %s\n\n", periodStr))
+				return nil
+			}
+
+			// Sort by gross amount descending (simple bubble sort for small data)
+			items := data.UsageItems
+			for i := 0; i < len(items); i++ {
+				for j := i + 1; j < len(items); j++ {
+					if items[j].GrossAmount > items[i].GrossAmount {
+						items[i], items[j] = items[j], items[i]
+					}
+				}
+			}
+
+			// Calculate totals
+			var totalReqs, totalGross, totalNet float64
+			for _, item := range items {
+				totalReqs += item.GrossQuantity
+				totalGross += item.GrossAmount
+				totalNet += item.NetAmount
+			}
+
+			// Print header
+			if cfg.IsTerminalOutput {
+				cfg.WriteToOut("\n")
+				if flagToday {
+					cfg.WriteToOut(fmt.Sprintf("Premium request usage for %s (%s, today)\n", username, periodStr))
+				} else {
+					cfg.WriteToOut(fmt.Sprintf("Premium request usage for %s (%s)\n", username, periodStr))
+				}
+				cfg.WriteToOut("\n")
+			}
+
+			// Print table
+			printer := cfg.NewTablePrinter()
+
+			printer.AddHeader([]string{"PRODUCT", "MODEL", "REQUESTS", "GROSS", "NET"}, tableprinter.WithColor(headerColor))
+			printer.EndRow()
+
+			for _, item := range items {
+				if item.GrossQuantity == 0 {
+					continue
+				}
+				printer.AddField(item.Product)
+				printer.AddField(item.Model)
+				printer.AddField(fmt.Sprintf("%.1f", item.GrossQuantity))
+				printer.AddField(fmt.Sprintf("$%.2f", item.GrossAmount))
+				printer.AddField(fmt.Sprintf("$%.2f", item.NetAmount))
+				printer.EndRow()
+			}
+
+			if err := printer.Render(); err != nil {
+				return err
+			}
+
+			// Print summary
+			if cfg.IsTerminalOutput {
+				cfg.WriteToOut("\n")
+				cfg.WriteToOut(fmt.Sprintf("Total: %.0f requests, $%.2f gross, $%.2f net\n", totalReqs, totalGross, totalNet))
+
+				if totalGross > 0 && totalNet == 0 {
+					cfg.WriteToOut(greenColor("All usage included in your plan (100% discount)") + "\n")
+				} else if totalNet > 0 {
+					pct := (totalNet / totalGross) * 100
+					cfg.WriteToOut(yellowColor(fmt.Sprintf("Net cost: $%.2f (%.0f%% of gross)", totalNet, pct)) + "\n")
+				}
+				cfg.WriteToOut("\n")
+			}
+
+			return nil
+		},
+	}
+
+	cmd.Flags().IntVar(&flagYear, "year", 0, "Filter by year (default: current year)")
+	cmd.Flags().IntVar(&flagMonth, "month", 0, "Filter by month (default: current month)")
+	cmd.Flags().IntVar(&flagDay, "day", 0, "Filter by specific day")
+	cmd.Flags().BoolVar(&flagToday, "today", false, "Show only today's usage")
+
+	return cmd
+}
+
+func getUsername(ctx context.Context, token string) (string, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, githubAPIBase+"/user", nil)
+	if err != nil {
+		return "", err
+	}
+	req.Header.Set("Authorization", "Bearer "+token)
+	req.Header.Set("Accept", "application/vnd.github+json")
+	req.Header.Set("X-GitHub-Api-Version", "2022-11-28")
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("failed to get user info: HTTP %d", resp.StatusCode)
+	}
+
+	var user struct {
+		Login string `json:"login"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&user); err != nil {
+		return "", err
+	}
+	return user.Login, nil
+}
+
+func fetchPremiumRequestUsage(ctx context.Context, token, username, query string) (*premiumRequestUsageResponse, error) {
+	url := fmt.Sprintf("%s/users/%s/settings/billing/premium_request/usage%s", githubAPIBase, username, query)
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Authorization", "Bearer "+token)
+	req.Header.Set("Accept", "application/vnd.github+json")
+	req.Header.Set("X-GitHub-Api-Version", "2022-11-28")
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode == http.StatusNotFound {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("usage data not available (HTTP 404). You may need the 'user' scope.\nRun: gh auth refresh -h github.com -s user\n\nResponse: %s", string(body))
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("failed to fetch usage data: HTTP %d\n%s", resp.StatusCode, string(body))
+	}
+
+	var data premiumRequestUsageResponse
+	if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
+		return nil, fmt.Errorf("failed to parse usage response: %w", err)
+	}
+
+	return &data, nil
+}