using System.Text;

namespace LehrerApp.Core.Importing;

internal sealed record DelimitedRecord(int LineNumber, IReadOnlyList<string> Fields);

internal static class DelimitedTextParser
{
    public static bool TryParse(
        string text,
        char delimiter,
        out List<DelimitedRecord> records,
        out string? error)
    {
        records = [];
        error = null;
        var fields = new List<string>();
        var field = new StringBuilder();
        var inQuotes = false;
        var line = 1;
        var recordStartLine = 1;

        for (var index = 0; index < text.Length; index++)
        {
            var current = text[index];
            if (current == '"')
            {
                if (inQuotes && index + 1 < text.Length && text[index + 1] == '"')
                {
                    field.Append('"');
                    index++;
                }
                else
                {
                    inQuotes = !inQuotes;
                }
                continue;
            }

            if (current == delimiter && !inQuotes)
            {
                fields.Add(field.ToString());
                field.Clear();
                continue;
            }

            if ((current == '\r' || current == '\n') && !inQuotes)
            {
                if (current == '\r' && index + 1 < text.Length && text[index + 1] == '\n')
                    index++;
                fields.Add(field.ToString());
                field.Clear();
                records.Add(new DelimitedRecord(recordStartLine, fields.ToList()));
                fields.Clear();
                line++;
                recordStartLine = line;
                continue;
            }

            if (current == '\n') line++;
            field.Append(current);
        }

        if (inQuotes)
        {
            error = $"Ein Textfeld ab Zeile {recordStartLine} besitzt kein schließendes Anführungszeichen.";
            return false;
        }

        if (field.Length > 0 || fields.Count > 0)
        {
            fields.Add(field.ToString());
            records.Add(new DelimitedRecord(recordStartLine, fields.ToList()));
        }
        return true;
    }
}