using System;
using System.Globalization;

namespace FrameworkBLL.GOP.Transform
{
    // ============================================================
    // ITransformExpression — extension point for mapping node transforms.
    //
    // Each implementation handles one transform key (e.g. "UPPER", "ROUND").
    // The Key property is matched case-insensitively against the
    // MMAPPINGNODE.TRANSFORMEXPRESSION column value.
    //
    // Expression syntax:
    //   "UPPER"            → Key="UPPER", argument=null
    //   "ROUND:2"          → Key="ROUND", argument="2"
    //   "FORMAT_DATE:yyyy-MM-dd" → Key="FORMAT_DATE", argument="yyyy-MM-dd"
    //
    // Registration (Program.cs in any SL project):
    //   services.AddTransformExpression<UpperTransform>();
    //   services.AddTransformExpression<CustomTransform>();
    // ============================================================
    public interface ITransformExpression
    {
        /// <summary>
        /// The transform key matched against MMAPPINGNODE.TRANSFORMEXPRESSION.
        /// Comparison is case-insensitive.
        /// </summary>
        string Key { get; }

        /// <summary>
        /// Apply the transform to <paramref name="value"/>.
        /// </summary>
        /// <param name="value">The raw string value extracted from the source path.</param>
        /// <param name="argument">
        /// The part of the expression after the first colon, or null if none.
        /// Example: for "ROUND:2" the argument is "2".
        /// </param>
        /// <returns>The transformed string value, or the original if transformation cannot be applied.</returns>
        string Transform(string value, string? argument);
    }

    // ──────────────────────────────────────────────────────────────
    // Built-in implementations
    // ──────────────────────────────────────────────────────────────

    /// <summary>Converts the value to upper-case.</summary>
    public sealed class UpperTransform : ITransformExpression
    {
        public string Key => "UPPER";
        public string Transform(string value, string? argument) => value.ToUpperInvariant();
    }

    /// <summary>Converts the value to lower-case.</summary>
    public sealed class LowerTransform : ITransformExpression
    {
        public string Key => "LOWER";
        public string Transform(string value, string? argument) => value.ToLowerInvariant();
    }

    /// <summary>Trims leading and trailing whitespace.</summary>
    public sealed class TrimTransform : ITransformExpression
    {
        public string Key => "TRIM";
        public string Transform(string value, string? argument) => value.Trim();
    }

    /// <summary>Returns an empty string if the value is null or whitespace.</summary>
    public sealed class NullToEmptyTransform : ITransformExpression
    {
        public string Key => "NULL_TO_EMPTY";
        public string Transform(string value, string? argument)
            => string.IsNullOrWhiteSpace(value) ? string.Empty : value;
    }

    /// <summary>
    /// Ignores the resolved source value entirely and returns the fixed literal
    /// supplied as the argument. Lets a mapping node populate a target field with
    /// a constant (e.g. a default status code) regardless of what SourcePath resolves to.
    /// Expression: "CONST:Active" (argument = "Active").
    /// </summary>
    public sealed class ConstTransform : ITransformExpression
    {
        public string Key => "CONST";
        public string Transform(string value, string? argument) => argument ?? string.Empty;
    }

    /// <summary>
    /// Rounds a decimal value to N decimal places.
    /// Expression: "ROUND:2"  (argument = "2").
    /// Falls through unchanged if the value is not a valid decimal or argument is invalid.
    /// </summary>
    public sealed class RoundTransform : ITransformExpression
    {
        public string Key => "ROUND";

        public string Transform(string value, string? argument)
        {
            if (!decimal.TryParse(value, NumberStyles.Any, CultureInfo.InvariantCulture, out var d))
                return value;

            if (!int.TryParse(argument, out int places) || places < 0 || places > 28)
                return value;

            return Math.Round(d, places, MidpointRounding.AwayFromZero)
                       .ToString(CultureInfo.InvariantCulture);
        }
    }

    /// <summary>
    /// Formats a date/time value using the supplied format string.
    /// Expression: "FORMAT_DATE:yyyy-MM-dd"  (argument = "yyyy-MM-dd").
    /// Falls through unchanged if the value cannot be parsed as a DateTime.
    /// </summary>
    public sealed class FormatDateTransform : ITransformExpression
    {
        public string Key => "FORMAT_DATE";

        public string Transform(string value, string? argument)
        {
            if (string.IsNullOrWhiteSpace(argument)) return value;
            if (!DateTime.TryParse(value, CultureInfo.InvariantCulture,
                    DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal, out var dt))
                return value;

            return dt.ToString(argument, CultureInfo.InvariantCulture);
        }
    }

    /// <summary>
    /// Parses the value as a decimal and returns it in invariant-culture numeric format
    /// (removes currency symbols, thousand separators, normalises locale decimal point).
    /// Falls through unchanged if the value cannot be parsed.
    /// </summary>
    public sealed class ToNumberTransform : ITransformExpression
    {
        public string Key => "TO_NUMBER";

        public string Transform(string value, string? argument)
        {
            if (!decimal.TryParse(value, NumberStyles.Any, CultureInfo.InvariantCulture, out var d))
                return value;

            return d.ToString(CultureInfo.InvariantCulture);
        }
    }

    /// <summary>
    /// Parses the value as a DateTime and returns it in ISO 8601 UTC format (yyyy-MM-ddTHH:mm:ssZ).
    /// Falls through unchanged if the value cannot be parsed.
    /// </summary>
    public sealed class ToDateTimeTransform : ITransformExpression
    {
        public string Key => "TO_DATETIME";

        public string Transform(string value, string? argument)
        {
            if (!DateTime.TryParse(value, CultureInfo.InvariantCulture,
                    DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal, out var dt))
                return value;

            return dt.ToString("yyyy-MM-ddTHH:mm:ssZ", CultureInfo.InvariantCulture);
        }
    }
}