feat: add PR diff, PR review, and structured error handling commands

cmd/errors.go

@@ -0,0 +1,76 @@
+package cmd
+
+import (
+	"encoding/json"
+	"errors"
+	"os"
+
+	"codeberg.org/romaintb/fgj/internal/api"
+)
+
+// Error codes for structured error output.
+const (
+	ErrAuthRequired       = "auth_required"
+	ErrNotFound           = "not_found"
+	ErrAPIError           = "api_error"
+	ErrInvalidInput       = "invalid_input"
+	ErrGitDetectionFailed = "git_detection_failed"
+	ErrNetworkError       = "network_error"
+)
+
+// CLIError is a structured error type for machine-readable output.
+type CLIError struct {
+	Code    string `json:"code"`
+	Message string `json:"message"`
+	Detail  string `json:"detail,omitempty"`
+	Status  int    `json:"status,omitempty"`
+}
+
+func (e *CLIError) Error() string {
+	return e.Message
+}
+
+// NewCLIError creates a new CLIError with the given code and message.
+func NewCLIError(code, message string) *CLIError {
+	return &CLIError{Code: code, Message: message}
+}
+
+// NewAPIError creates a CLIError from an HTTP status and message.
+func NewAPIError(status int, message string) *CLIError {
+	return &CLIError{Code: ErrAPIError, Message: message, Status: status}
+}
+
+// writeJSONError writes a structured JSON error to stderr.
+// It attempts to extract structured info from known error types.
+// WriteJSONError writes a structured JSON error to stderr.
+// It is exported for use from main.go.
+func WriteJSONError(err error) {
+	cliErr := &CLIError{
+		Code:    ErrAPIError,
+		Message: err.Error(),
+	}
+
+	// Try to extract structured info from the error chain.
+	var apiErr *api.APIError
+	var cErr *CLIError
+
+	switch {
+	case errors.As(err, &cErr):
+		cliErr = cErr
+	case errors.As(err, &apiErr):
+		cliErr.Status = apiErr.StatusCode
+		cliErr.Detail = apiErr.Body
+		switch {
+		case apiErr.StatusCode == 401 || apiErr.StatusCode == 403:
+			cliErr.Code = ErrAuthRequired
+		case apiErr.StatusCode == 404:
+			cliErr.Code = ErrNotFound
+		default:
+			cliErr.Code = ErrAPIError
+		}
+	}
+
+	enc := json.NewEncoder(os.Stderr)
+	enc.SetIndent("", "  ")
+	_ = enc.Encode(cliErr)
+}