using System.Data;
using System.Reflection;
using Dapper;
using JdeScoping.DataSync.Contracts;
using JdeScoping.DataSync.Exceptions;
using JdeScoping.DataSync.Models;

namespace JdeScoping.DataSync.Services;

/// <summary>
/// Validates data against database table schema.
/// </summary>
internal sealed class SchemaValidator : ISchemaValidator
{
    /// <inheritdoc />
    public async Task<IReadOnlyList<ColumnSchema>> GetTableSchemaAsync(
        IDbConnection connection,
        string tableName,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(connection);
        ArgumentException.ThrowIfNullOrWhiteSpace(tableName);

        // Parse schema and table name
        var (schemaName, table) = ParseTableName(tableName);

        const string sql = """
            SELECT
                COLUMN_NAME AS Name,
                DATA_TYPE AS DataType,
                CHARACTER_MAXIMUM_LENGTH AS MaxLength,
                NUMERIC_PRECISION AS [Precision],
                NUMERIC_SCALE AS Scale,
                CASE WHEN IS_NULLABLE = 'YES' THEN 1 ELSE 0 END AS IsNullable,
                ORDINAL_POSITION AS OrdinalPosition
            FROM INFORMATION_SCHEMA.COLUMNS
            WHERE TABLE_SCHEMA = @Schema AND TABLE_NAME = @Table
            ORDER BY ORDINAL_POSITION
            """;

        var columns = await connection.QueryAsync<ColumnSchema>(
            new CommandDefinition(
                sql,
                new { Schema = schemaName, Table = table },
                cancellationToken: cancellationToken));

        return columns.ToList();
    }

    /// <inheritdoc />
    public IReadOnlyList<ValidationError> ValidateBatch<T>(
        IReadOnlyList<T> data,
        IReadOnlyList<ColumnSchema> schema,
        int maxErrors = 100) where T : class
    {
        ArgumentNullException.ThrowIfNull(data);
        ArgumentNullException.ThrowIfNull(schema);

        if (data.Count == 0 || schema.Count == 0)
            return [];

        var errors = new List<ValidationError>();
        var schemaLookup = schema.ToDictionary(s => s.Name, StringComparer.OrdinalIgnoreCase);
        var properties = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance)
            .ToDictionary(p => p.Name, StringComparer.OrdinalIgnoreCase);

        for (int rowIndex = 0; rowIndex < data.Count; rowIndex++)
        {
            var row = data[rowIndex];
            if (row == null) continue;

            foreach (var column in schema)
            {
                if (!properties.TryGetValue(column.Name, out var property))
                    continue;

                var value = property.GetValue(row);
                var error = ValidateValue(rowIndex, column, value);

                if (error != null)
                {
                    errors.Add(error);

                    if (maxErrors > 0 && errors.Count >= maxErrors)
                        return errors;
                }
            }
        }

        return errors;
    }

    private static ValidationError? ValidateValue(int rowIndex, ColumnSchema column, object? value)
    {
        // Check nullability
        if (value == null || (value is string s && string.IsNullOrEmpty(s)))
        {
            if (!column.IsNullable && !IsIdentityOrComputed(column))
            {
                return new ValidationError(
                    rowIndex,
                    column.Name,
                    value,
                    $"Column '{column.Name}' does not allow null values.");
            }
            return null;
        }

        // Check string length
        if (column.MaxLength.HasValue && column.MaxLength.Value > 0)
        {
            var stringValue = value as string ?? value.ToString();
            if (stringValue != null && stringValue.Length > column.MaxLength.Value)
            {
                return new ValidationError(
                    rowIndex,
                    column.Name,
                    value,
                    $"Value for '{column.Name}' exceeds maximum length of {column.MaxLength}. Actual length: {stringValue.Length}.");
            }
        }

        // Check decimal precision/scale
        if (column.Precision.HasValue && column.Scale.HasValue && IsDecimalType(column.DataType))
        {
            if (value is decimal decimalValue)
            {
                var error = ValidateDecimal(rowIndex, column, decimalValue);
                if (error != null)
                    return error;
            }
            else if (value is double || value is float)
            {
                // Convert to decimal for validation
                try
                {
                    var decVal = Convert.ToDecimal(value);
                    var error = ValidateDecimal(rowIndex, column, decVal);
                    if (error != null)
                        return error;
                }
                catch
                {
                    return new ValidationError(
                        rowIndex,
                        column.Name,
                        value,
                        $"Value for '{column.Name}' cannot be converted to decimal.");
                }
            }
        }

        return null;
    }

    private static ValidationError? ValidateDecimal(int rowIndex, ColumnSchema column, decimal value)
    {
        // Calculate actual precision and scale
        var sqlString = value.ToString(System.Globalization.CultureInfo.InvariantCulture);
        var parts = sqlString.TrimStart('-').Split('.');
        var integerDigits = parts[0].TrimStart('0').Length;
        var decimalDigits = parts.Length > 1 ? parts[1].TrimEnd('0').Length : 0;

        // Handle zero case
        if (integerDigits == 0 && decimalDigits == 0)
            integerDigits = 1;

        var totalDigits = integerDigits + decimalDigits;
        var maxTotalDigits = column.Precision!.Value;
        var maxDecimalDigits = column.Scale!.Value;
        var maxIntegerDigits = maxTotalDigits - maxDecimalDigits;

        if (integerDigits > maxIntegerDigits)
        {
            return new ValidationError(
                rowIndex,
                column.Name,
                value,
                $"Value {value} for '{column.Name}' exceeds maximum integer digits. " +
                $"Maximum: {maxIntegerDigits}, Actual: {integerDigits}.");
        }

        // Note: We don't validate decimal digits as SQL Server will truncate/round them
        return null;
    }

    private static bool IsDecimalType(string dataType)
    {
        return dataType.Equals("decimal", StringComparison.OrdinalIgnoreCase) ||
               dataType.Equals("numeric", StringComparison.OrdinalIgnoreCase) ||
               dataType.Equals("money", StringComparison.OrdinalIgnoreCase) ||
               dataType.Equals("smallmoney", StringComparison.OrdinalIgnoreCase);
    }

    private static bool IsIdentityOrComputed(ColumnSchema column)
    {
        // Identity columns and computed columns can be null in the source data
        // This is a simple heuristic - actual identity check would require additional metadata
        return column.Name.Equals("Id", StringComparison.OrdinalIgnoreCase) ||
               column.Name.EndsWith("Id", StringComparison.OrdinalIgnoreCase);
    }

    private static (string Schema, string Table) ParseTableName(string tableName)
    {
        // Remove brackets if present
        var cleaned = tableName.Replace("[", "").Replace("]", "");

        // Check for temp table
        if (cleaned.StartsWith('#'))
        {
            return ("dbo", cleaned);
        }

        // Split by dot
        var parts = cleaned.Split('.');
        return parts.Length switch
        {
            1 => ("dbo", parts[0]),
            2 => (parts[0], parts[1]),
            _ => throw new ArgumentException($"Invalid table name format: {tableName}")
        };
    }
}