package runner

import (
	"errors"
	"fmt"
	"regexp"
	"strings"
)

var (
	variableNamePattern = regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*$`)
	// Matches $Name or ${Name}; only known names in the vars map are replaced.
	dollarVarPattern = regexp.MustCompile(`\$\{([A-Za-z_][A-Za-z0-9_]*)\}|\$([A-Za-z_][A-Za-z0-9_]*)`)
)

// ValidateVariableName checks that name is a valid run-scoped variable identifier.
func ValidateVariableName(name string) error {
	trimmed := strings.TrimSpace(name)
	if trimmed == "" {
		return errors.New("variable name is required")
	}
	if trimmed != name {
		return errors.New("variable name must not have leading or trailing spaces")
	}
	if !variableNamePattern.MatchString(trimmed) {
		return fmt.Errorf("invalid variable name %q", name)
	}
	return nil
}

// ExpandDollarVars replaces $Name and ${Name} when Name exists in vars.
// Unknown identifiers are left unchanged for the remote shell.
func ExpandDollarVars(text string, vars map[string]string) string {
	if vars == nil || len(vars) == 0 || text == "" {
		return text
	}
	return dollarVarPattern.ReplaceAllStringFunc(text, func(match string) string {
		submatches := dollarVarPattern.FindStringSubmatch(match)
		if len(submatches) < 3 {
			return match
		}
		name := submatches[1]
		if name == "" {
			name = submatches[2]
		}
		value, ok := vars[name]
		if !ok {
			return match
		}
		return value
	})
}