using System;
using System.Collections.Generic;
using ln.templates.elements;
using System.IO;
using System.Text;
namespace ln.templates
{
    public class TemplateReader
    {
        public ContainerElement RootElement { get; private set; } = new ContainerElement(null);
        public ContainerElement CurrentElement { get; private set; }

        public Expression FrameExpression { get; private set; }

        public String Source { get; private set; }

        public TemplateReader(String source)
        {
            Source = source;
            Parse();
        }

        private void Parse()
        {
            CurrentElement = RootElement;

            while (Source.Length > 0)
            {
                String t, op;
                int i, j;

                i = Source.IndexOf("<%");
                if (i == -1)
                {
                    t = Source;
                    op = null;
                    Source = "";
                }
                else
                {
                    t = Source.Substring(0, i);
                    j = Source.IndexOf("%>", i + 1);
                    if (j == -1)
                    {
                        throw new FormatException(String.Format("missing '%>' in {0}", Source.Substring(i, 64)));
                    }
                    op = Source.Substring(i + 2, j - i - 2);
                    Source = Source.Substring(j + 2);
                }

                new TextElement(CurrentElement, t);
                if (op != null)
                    ParseOP(op);
            }
        }

        private void ParseOP(String op)
        {
            StringReader reader = new StringReader(op);
            String opkey;

            if (reader.Peek() == '=')
            {
                reader.Read();
                opkey = "=";
            }
            else
            {
                opkey = reader.PopWord();
            }

            switch (opkey)
            {
                case "=":
                    new ExpressionElement(CurrentElement, new Expression(reader.ReadToEnd()));
                    break;
                case "frame":
                    FrameExpression = new Expression(reader.ReadToEnd());
                    break;
                case "iterate":
                    String iterName = reader.PopWord();
                    CurrentElement = new IteratorElement(CurrentElement, iterName, new Expression(reader.ReadToEnd()));
                    break;
                case "if":
                    CurrentElement = new ConditionalElement(CurrentElement, new Expression(reader.ReadToEnd()));
                    break;
                case "else":
                    if (CurrentElement is ConditionalElement)
                    {
                        ConditionalElement ce = CurrentElement as ConditionalElement;
                        CurrentElement = ce.AlternativeContainer;
                    }
                    break;
                case "elseif":
                    if (CurrentElement is ConditionalElement)
                    {
                        ConditionalElement ce = CurrentElement as ConditionalElement;
                        CurrentElement = new ConditionalElement(null, new Expression(reader.ReadToEnd()));
                        ce.AlternativeContainer = CurrentElement;
                    }
                    break;

                case "include":
                    new IncludeElement(CurrentElement, new Expression(reader.ReadToEnd()));
                    break;

                case "set":
                    String setName = reader.PopWord();
                    new SetElement(CurrentElement, setName, new Expression(reader.ReadToEnd()));
                    break;

                case "end":
                    CurrentElement = CurrentElement.Container;
                    break;
                default:
                    throw new NotImplementedException(opkey);
            }
        }
    }

    static class StringHelper
    {
        public static int IndexOf(this String s,Func<char,bool> predicate)
        {
            for (int i=0;i<s.Length;i++)
            {
                if (predicate(s[i]))
                    return i;
            }
            return -1;
        }

        public static void SkipWhiteSpace(this TextReader reader)
        {
            while (char.IsWhiteSpace((char)reader.Peek()))
            {
                reader.Read();
            }
        }
        public static String PopWord(this TextReader reader)
        {
            StringBuilder stringBuilder = new StringBuilder();
            while ((reader.Peek()!=-1) && !char.IsWhiteSpace((char)reader.Peek()))
            {
                stringBuilder.Append((char)reader.Read());
            }
            reader.SkipWhiteSpace();
            return stringBuilder.ToString();
        }
    }
}