using System;
using System.IO;
using System.Collections.Generic;
using System.Text;
using ln.templates.streams;
using ln.templates.elements;

namespace ln.templates
{
    public class Template
    {
        public TemplateProvider Provider { get; private set; }
        public String SourceFilename { get; private set; }
        public String PseudoFilename { get; private set; }
        public DateTime SourceTimeStamp { get; private set; }

        public Element RootElement { get; private set; }

        public Expression FrameExpression { get; private set; }

        public Template(String sourceFilename)
        {
            SourceFilename = sourceFilename;
            PseudoFilename = sourceFilename;

            LoadSource(null);
        }

        public Template(String sourceFilename, TemplateProvider provider)
        {
            Provider = provider;
            SourceFilename = sourceFilename;
            PseudoFilename = sourceFilename;

            LoadSource(null);
        }

        public Template(String source,String pseudoFilename,TemplateProvider provider)
        {
            Provider = provider;
            PseudoFilename = pseudoFilename;

            LoadSource(source);
        }

        private void LoadSource(String source)
        {
            if (source == null)
            {
                using (FileStream fileStream = new FileStream(SourceFilename, FileMode.Open))
                {
                    byte[] loadBuffer = new byte[fileStream.Length];
                    fileStream.Read(loadBuffer, 0, loadBuffer.Length);
                    fileStream.Close();
                    source = Encoding.UTF8.GetString(loadBuffer);

                    SourceTimeStamp = File.GetLastWriteTimeUtc(SourceFilename);
                }
            }

            TemplateReader templateReader = new TemplateReader(source);

            RootElement = templateReader.RootElement;
            FrameExpression = templateReader.FrameExpression;
        }

        public String Generate()
        {
            return Generate(false);
        }
        public String Generate(bool unframed)
        {
            Context context = new Context(this);
            return Generate(context);
        }
        public String Generate(Context context)
        {
            return Generate(context, false);
        }
        public String Generate(Context context,bool unframed)
        {
            if (SourceFilename != null)
            {
                DateTime ts = File.GetLastWriteTimeUtc(SourceFilename);
                if (ts > SourceTimeStamp)
                    LoadSource(null);
            }

            StringWriter writer = new StringWriter();
            RootElement.Generate(writer, context);

            if (!unframed && (FrameExpression != null))
            {
                Template frame = context.Provider.FindTemplate(FrameExpression.Evaluate(context.ExpressionContext) as string);
                if (frame == null)
                {
                    throw new NullReferenceException(String.Format("FindTemplate() returned null for {0}",FrameExpression.Source));
                }
                return frame.Generate(new Context(context, writer.ToString()));
            }

            return writer.ToString();
        }


        public class Context
        {
            public Context Parent { get; }
            public Template Template { get; }
            public TemplateProvider Provider => Template.Provider;

            public String FramedContent { get; }
            public Expression.Context ExpressionContext { get; }

            public Context(Template template)
            {
                Template = template;
                ExpressionContext = new Expression.Context(null, null);
                ExpressionContext.AddMappedValue("__template__", template.SourceFilename);
                ExpressionContext.AddMappedValue("__provider__", template.Provider);
            }
            public Context(Context parent,String framedContent)
            {
                Parent = parent;
                Template = parent.Template;
                FramedContent = framedContent;
                ExpressionContext = new Expression.Context(parent.ExpressionContext);
                if (framedContent != null)
                    ExpressionContext.SetMappedValue("__frame__", framedContent);
            }
        }

    }
}