using System.Text.RegularExpressions;

namespace CareFix.Api.Security;

/// <summary>Removes patient-identifying data before anything is sent to the AI or stored in query logs.</summary>
public sealed partial class PiiMasker
{
    public const string Mask = "[masked]";

    private static readonly string[] ColumnContains =
        ["MOBILE", "PHONE", "CONTACTNO", "AADHA", "ADHAR", "ABHA", "ADDRESS", "EMAIL", "PASSPORT", "PANCARD"];
    private static readonly string[] NameExact =
        ["PNAME", "FNAME", "MNAME", "LNAME", "PATNAME", "FIRSTNAME", "MIDDLENAME", "LASTNAME", "SURNAME"];
    private static readonly string[] NameSuffix =
        ["PATIENTNAME", "FIRSTNAME", "MIDDLENAME", "LASTNAME", "FATHERNAME", "MOTHERNAME", "HUSBANDNAME",
         "SPOUSENAME", "RELATIVENAME", "KINNAME", "GUARDIANNAME"];

    [GeneratedRegex(@"[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}")] private static partial Regex Email();
    [GeneratedRegex(@"(?<!\d)\d{2}-\d{4}-\d{4}-\d{4}(?!\d)")] private static partial Regex Abha();
    [GeneratedRegex(@"(?<!\d)\d{4}[\s-]?\d{4}[\s-]?\d{4}(?!\d)")] private static partial Regex Aadhaar();
    [GeneratedRegex(@"(?<!\d)(?:\+?91[\s-]?)?[6-9]\d{9}(?!\d)")] private static partial Regex Mobile();

    public bool IsPiiColumn(string column, ISet<string>? kbPiiColumns)
    {
        if (kbPiiColumns?.Contains(column) == true) return true;
        var n = column.Replace("_", "").ToUpperInvariant();
        return ColumnContains.Any(n.Contains) || NameExact.Contains(n) || NameSuffix.Any(n.EndsWith);
    }

    /// <summary>Masks phone, Aadhaar, ABHA and e-mail patterns inside free text.</summary>
    public string MaskText(string s)
    {
        var r = Email().Replace(s, Mask);
        r = Abha().Replace(r, Mask);
        r = Aadhaar().Replace(r, Mask);
        return Mobile().Replace(r, Mask);
    }

    public object? MaskValue(string column, object? value, ISet<string>? kbPiiColumns)
    {
        if (value is null) return null;
        if (IsPiiColumn(column, kbPiiColumns)) return Mask;
        // Pure numbers are usually IDs (bill no, UHID) that the AI needs; only free text is scanned.
        if (value is string s && s.Any(ch => char.IsLetter(ch) || ch == ' ')) return MaskText(s);
        return value;
    }
}