using System;
using System.Linq;
using System.Text;
using Sprache;
using XNeedle.Formats;
using XNeedle.Parser;
using XNeedle.Parser.Elements;
using System.Xml.Linq;
using System.Xml.XPath;

namespace XNeedle.Transformation
{
    public class ContextFunctions
    {
        public static string hexlit(Context ctx, double value)
        {
            uint v = (uint)value;
            return $"#x{v:x8}";
        }

        public static string lower(Context ctx, string text)
        {
            return text.ToLower();
        }

        public static string upper(Context ctx, string text)
        {
            return text.ToUpper();
        }

        public static double GetLevel(Context ctx)
        {
            int level = 0;
            XElement? n = ctx.Node;
            while (null != (n = n?.Parent))
                level++;
            return level;
        }

        private static uint ComputeCrc32(byte[] data, uint poly, uint init, uint xorOut, bool reflected)
        {
            uint crc = init;
            uint polyReflected = ReflectBits(poly, 32);
            foreach (byte b in data)
            {
                if (reflected)
                {
                    crc ^= b;
                    for (int i = 0; i < 8; i++)
                        crc = (crc & 1) != 0 ? (crc >> 1) ^ polyReflected : crc >> 1;
                }
                else
                {
                    crc ^= (uint)b << 24;
                    for (int i = 0; i < 8; i++)
                        crc = (crc & 0x80000000u) != 0 ? (crc << 1) ^ poly : crc << 1;
                }
            }
            return crc ^ xorOut;
        }

        private static uint ReflectBits(uint value, int bits)
        {
            uint reflected = 0;
            for (int i = 0; i < bits; i++)
            {
                if ((value & (1u << i)) != 0)
                    reflected |= 1u << (bits - 1 - i);
            }
            return reflected;
        }

        public static double crc32(Context ctx, int poly = 0x04C11DB7, int init = 0, int xorOut = 0, bool reflected = false)
        {
            if (ctx.Node is null)
                return 0;

            // Step 1: Render the element to a string, preserving source style
            var (writer, buffer) = XmlRoundtripWriter.CreateToString(ctx.SLoc.FilePath, ctx.SLoc.Encoding);
            ctx.Node.WriteTo(writer);
            writer.Flush();
            string xml = buffer.ToString();
            
            // Step 2: Extract all text after the opening tag through and including the closing tag
            string tagName = ctx.Node.Name.LocalName;
            string data = XmlFragParser.ChecksumData(tagName).Parse(xml);
            //byte[] fragBytes = ctx.SLoc.Encoding.GetBytes(data);
            byte[] fragBytes = Encoding.UTF8.GetBytes(data);

            // Step 3: Digest into CRC32 using parameterized CRC32 - by default MPEG-2
            return (double)ComputeCrc32(fragBytes, (uint)poly, (uint)init, (uint)xorOut, reflected);
        }

        public static string text(Context ctx)
        {
            if (ctx.Node is null) return "";
            return ctx.Node.Value;
        }

        public static string text(Context ctx, string txt)
        {
            if (ctx.Node is null) return "";
            ctx.Node.SetValue(txt);
            return txt;
        }

        public static string cdata(Context ctx)
        {
            if (ctx.Node is null) return "";
            var cdataNode = ctx.Node.Nodes().OfType<System.Xml.Linq.XCData>().FirstOrDefault();
            return cdataNode?.Value ?? "";
        }

        public static string cdata(Context ctx, string txt)
        {
            if (ctx.Node is null) return "";
            var cdataNode = ctx.Node.Nodes().OfType<System.Xml.Linq.XCData>().FirstOrDefault();
            if (cdataNode != null)
            {
                cdataNode.Value = txt;
            }
            else
            {
                ctx.Node.Add(new System.Xml.Linq.XCData(txt));
            }
            return txt;
        }

        public static string attr(Context ctx, string name, string value)
        {
            if (ctx.Node is null) return "";
            var attr = ctx.Node.Attribute(name);
            if (attr != null)
            {
                attr.Value = value;
            }
            else
            {
                ctx.Node.SetAttributeValue(name, value);
            }
            return "";
        }

        public static string attr(Context ctx, string name)
        {
            var attr = ctx.Node?.Attribute(name);
            if (attr != null)
            {
                return attr.Value;
            }
            return "";
        }

        public static string swap(Context ctx, string a_select, string b_select)
        {
            if (ctx.Node == null)
            {
                throw new ArgumentNullException("!swap needs a reachable node");
            }
            
            var a_node = ctx.Node.XPathSelectElement(a_select);
            var b_node = ctx.Node.XPathSelectElement(b_select);

            if (a_node == null || b_node == null)
            {
                throw new InvalidOperationException($"!swap could not find nodes for \"{a_select}\" and/or \"{b_select}\".");
            }
            
            var placeholder = new XElement("__placeholder__");
            a_node.ReplaceWith(placeholder);
            b_node.ReplaceWith(a_node);
            placeholder.ReplaceWith(b_node);

            return "";
        }

        public static string remove(Context ctx, string select)
        {
            if (ctx.Node == null)
            {
                throw new ArgumentNullException("!remove needs a reachable node");
            }
            
            // Use ToList to make the lazy/generator enumeration concrete before applying operations
            var nodes = ctx.Node.XPathSelectElements(select).ToList();

            foreach (var node in nodes)
            {
                node.Remove();
            }

            return "";
        } 

        public static string rename(Context ctx, string newName)
        {
            if (ctx.Node is null) return "";
            var replacement = new XElement(newName, ctx.Node.Attributes(), ctx.Node.Nodes());
            ctx.Node.ReplaceWith(replacement);
            ctx.Node = replacement;   // update context to point to new element
            return "";
        }

        public static string rename(Context ctx, string select, string newName)
        {
            if (ctx.Node is null) return "";

            int atIdx = select.IndexOf('@');
            if (atIdx >= 0)
            {
                // "Node@Attr" — rename an attribute
                var elementSelect = select[..atIdx].TrimEnd();
                var attrName = select[(atIdx + 1)..].TrimStart();
                var target = string.IsNullOrEmpty(elementSelect)
                    ? ctx.Node
                    : ctx.Node.XPathSelectElement(elementSelect);
                var attr = target?.Attribute(attrName);
                if (attr is null) return "";
                attr.Remove();
                target!.SetAttributeValue(newName, attr.Value);
            }
            else
            {
                // plain XPath select — rename element
                var target = ctx.Node.XPathSelectElement(select);
                if (target is null) return "";
                var replacement = new XElement(newName, target.Attributes(), target.Nodes());
                target.ReplaceWith(replacement);
            }
            return "";
        }

        public static string require(Context ctx, string message = "Required node not present")
        {
            if (ctx.Node == null)
            {
                throw new RequireException{SLoc=ctx.SLoc, UserMessage=message};
            }
            else
            {
                Console.WriteLine(ctx.Node.ToString());
            }
            return "";
        }
    }
}