using System.Text;

namespace Strata.SqlTools.SqlServer.Exceptions;

/// <summary>
/// Exception thrown when SQL parsing fails.
/// Provides detailed context about the parse failure including position and surrounding text.
/// </summary>
public class SqlParseException : Exception
{
    /// <summary>
    /// Gets the position in the SQL string where the parse error occurred.
    /// </summary>
    public int Position { get; }

    /// <summary>
    /// Gets the SQL statement that failed to parse.
    /// </summary>
    public string Sql { get; }

    /// <summary>
    /// Gets the text near the error position (up to 40 characters).
    /// </summary>
    public string NearText { get; }

    /// <summary>
    /// Initializes a new instance of the <see cref="SqlParseException"/> class.
    /// </summary>
    /// <param name="message">The error message describing the parse failure.</param>
    /// <param name="sql">The SQL statement that failed to parse.</param>
    /// <param name="position">The position in the SQL where the error occurred.</param>
    /// <example>
    /// <code>
    /// throw new SqlParseException(
    ///     "Unexpected token 'FROM'",
    ///     "SELECT * FRM users",
    ///     10
    /// );
    /// // Message will include:
    /// // - Error description
    /// // - Position: 10
    /// // - Near: "* FRM users"
    /// // - Full SQL statement
    /// </code>
    /// </example>
    public SqlParseException(string message, string sql, int position)
        : base(FormatMessage(message, sql, position))
    {
        Position = position;
        Sql = sql ?? string.Empty;
        NearText = ExtractNearText(Sql, position);
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="SqlParseException"/> class with an inner exception.
    /// </summary>
    /// <param name="message">The error message describing the parse failure.</param>
    /// <param name="sql">The SQL statement that failed to parse.</param>
    /// <param name="position">The position in the SQL where the error occurred.</param>
    /// <param name="innerException">The exception that caused this parse failure.</param>
    public SqlParseException(string message, string sql, int position, Exception innerException)
        : base(FormatMessage(message, sql, position), innerException)
    {
        Position = position;
        Sql = sql ?? string.Empty;
        NearText = ExtractNearText(Sql, position);
    }

    private static string FormatMessage(string message, string sql, int position)
    {
        if (string.IsNullOrEmpty(sql))
        {
            return $"{message}\nSQL statement is empty or null.";
        }

        var nearText = ExtractNearText(sql, position);
        var sb = new StringBuilder();

        sb.AppendLine(message);
        sb.AppendLine($"Position: {position}");
        sb.AppendLine($"Near: '{nearText}'");

        // Show full SQL for short statements, truncated for long ones
        if (sql.Length <= 200)
        {
            sb.AppendLine($"Full SQL: {sql}");
        }
        else
        {
            sb.AppendLine($"SQL (truncated): {sql.Substring(0, 197)}...");
        }

        return sb.ToString();
    }

    private static string ExtractNearText(string sql, int position)
    {
        if (string.IsNullOrEmpty(sql))
        {
            return string.Empty;
        }

        // Clamp position to valid range
        position = Math.Max(0, Math.Min(position, sql.Length));

        // Extract up to 20 chars before and 20 chars after the position
        var start = Math.Max(0, position - 20);
        var length = Math.Min(40, sql.Length - start);

        var nearText = sql.Substring(start, length);

        // Add ellipsis if truncated
        if (start > 0)
        {
            nearText = "..." + nearText;
        }
        if (start + length < sql.Length)
        {
            nearText = nearText + "...";
        }

        return nearText;
    }
}