using Core.Notes;

namespace Core.Parsers;

/// <summary>
/// Builds a starter CSV for <c>/students/import</c> with roster columns plus leftover note fields.
/// </summary>
public static class StudentImportCsvTemplate
{
    public static readonly string[] RosterHeaders =
    [
        "Student Name",
        "Grade",
        "TSA year",
        "State ID",
        "Regional ID",
        "National ID"
    ];

    /// <summary>
    /// Returns a CSV with a header row and one example data row.
    /// </summary>
    public static string Build(IEnumerable<string>? leftoverFieldNames = null)
    {
        List<string> leftovers = leftoverFieldNames?
            .Where(name => !string.IsNullOrWhiteSpace(name))
            .Select(name => name.Trim())
            .Where(name => !StudentNotesFieldParser.IsReservedHeader(name))
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .ToList() ?? [];

        if (leftovers.Count == 0)
            leftovers = [.. StudentNoteFieldDefaults.IndexColumns];

        var headers = RosterHeaders.Concat(leftovers).ToArray();
        var values = headers.Select(ExampleValue).ToArray();
        return $"{ToCsvRow(headers)}{Environment.NewLine}{ToCsvRow(values)}{Environment.NewLine}";
    }

    private static string ExampleValue(string header) => header switch
    {
        "Student Name" => "Last, First",
        "Grade" => "9",
        "TSA year" => "1st",
        "Interview Time" => "3:20-3:35",
        _ when ContainsIgnoreCase(header, "Application")
               || ContainsIgnoreCase(header, "Permission") => "x",
        _ => string.Empty
    };

    private static bool ContainsIgnoreCase(string value, string part) =>
        value.Contains(part, StringComparison.OrdinalIgnoreCase);

    private static string ToCsvRow(IEnumerable<string> cells) =>
        string.Join(",", cells.Select(EscapeCsv));

    private static string EscapeCsv(string value)
    {
        if (value.Contains(',') || value.Contains('"') || value.Contains('\n'))
            return $"\"{value.Replace("\"", "\"\"")}\"";
        return value;
    }
}