Add validation for Old and New URL in both the interface and CSV import

[GeekInTheNorth]

See #174

Add validation to ensure Old Url and New Url are valid absolute or relative Uris
Updated the CSV import functionality to skip entries where either the Old or New Url is not a valid absolute or relative Uri.

[gemini-code-assist]

Summary of Changes

Hello @GeekInTheNorth, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the robustness of URL handling within the redirect management system. It introduces comprehensive validation for both user-entered and CSV-imported redirect URLs, ensuring that only well-formed absolute or relative URIs are accepted. This prevents the creation of broken redirects and enhances data integrity across the application.

Highlights

• UI Validation for Redirects: I've added client-side validation to the RedirectModel by implementing IValidatableObject. This ensures that when users manually create or edit redirects via the admin interface, both the 'Old Url' and 'New Url' fields are validated to be well-formed absolute or relative URIs before submission. This prevents invalid URLs from being saved.
• CSV Import Validation and Skipping: I've enhanced the CSV import functionality to include validation for 'Old Url' and 'New Url' entries. During the import process, each row is now checked for valid URI formats. If either URL in a CSV entry is not a well-formed absolute or relative URI, that specific entry will be skipped, and a warning will be logged, preventing malformed redirects from being imported into the system.

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[gemini-code-assist]

Code Review

The pull request successfully adds URL validation for OldUrl and NewUrl in both the admin interface model (RedirectModel.cs) and the CSV import process (RedirectsCsvParser.cs). The validation ensures that these URLs are well-formed, either as relative or absolute URIs. The CSV import now correctly skips and logs entries with invalid URLs. The changes are clear and address the stated objectives. A minor suggestion is provided to potentially centralize the URL validation logic for improved long-term maintainability if this pattern is expected to proliferate.

[gemini-code-assist]

The URL validation logic Uri.IsWellFormedUriString(url, UriKind.RelativeOrAbsolute) is also used in RedirectModel.Validate. While not a major issue with only two occurrences, consider centralizing this logic into a shared static utility method if this validation pattern is expected to be used elsewhere or might evolve. This would improve maintainability by ensuring a single source of truth for what constitutes a valid redirect URL string.

For example, you could have a utility class:

public static class UrlValidationHelper
{
    public static bool IsValidRedirectUri(string uriString)
    {
        return Uri.IsWellFormedUriString(uriString, UriKind.RelativeOrAbsolute);
    }
}

Then, both RedirectModel.Validate and this IsValidRedirect method could call UrlValidationHelper.IsValidRedirectUri().

[GeekInTheNorth]

@valdisiljuconoks Assuming you're okay with the initial approach, I can refactor the model validation into an extension method. I can also then apply this to the TXT and XML imports as well.