package config

import (
	"fmt"
	"path/filepath"
	"regexp"
	"strings"
	"time"
)

var windowsAbsPathRE = regexp.MustCompile(`^[A-Za-z]:[\\/].*`)
var envVarNameRE = regexp.MustCompile(`^[A-Za-z_][A-Za-z0-9_]*$`)

func validateEnvVarNameField(fieldName, value string) error {
	trimmed := strings.TrimSpace(value)
	if trimmed == "" {
		return fmt.Errorf("%s must be non-empty", fieldName)
	}
	if !envVarNameRE.MatchString(trimmed) {
		return fmt.Errorf("%s must be a valid environment variable name", fieldName)
	}
	return nil
}

func validateRelativeSafePath(fieldName, value string) error {
	trimmed := strings.TrimSpace(value)
	if trimmed == "" {
		return fmt.Errorf("%s must be non-empty", fieldName)
	}
	if filepath.IsAbs(trimmed) || strings.HasPrefix(trimmed, "/") || strings.HasPrefix(trimmed, "\\") || windowsAbsPathRE.MatchString(trimmed) {
		return fmt.Errorf("%s must be a relative path", fieldName)
	}

	normalized := strings.ReplaceAll(trimmed, "\\", "/")
	for _, segment := range strings.Split(normalized, "/") {
		if segment == ".." {
			return fmt.Errorf("%s must not contain path traversal", fieldName)
		}
	}
	return nil
}

func validatePathWithinRoot(fieldName, value, root string) error {
	normalizedValue := filepath.ToSlash(filepath.Clean(strings.TrimSpace(value)))
	normalizedRoot := filepath.ToSlash(filepath.Clean(strings.TrimSpace(root)))
	if normalizedValue == normalizedRoot {
		return nil
	}
	if strings.HasPrefix(normalizedValue, normalizedRoot+"/") {
		return nil
	}
	return fmt.Errorf("%s must be under %s/", fieldName, normalizedRoot)
}

func validateDuration(fieldName, value string) error {
	trimmed := strings.TrimSpace(value)
	if trimmed == "" {
		return nil
	}

	duration, err := time.ParseDuration(trimmed)
	if err != nil {
		return fmt.Errorf("%s must be a valid duration: %w", fieldName, err)
	}
	if duration <= 0 {
		return fmt.Errorf("%s must be positive", fieldName)
	}

	return nil
}