using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;
using Cosmos.Assembler;

namespace XSharp.Compiler {
  // This class performs the translation from X# source code into a target
  // assembly language. At current time the only supported assembler syntax is NASM.

  public class AsmGenerator {
    protected TokenPatterns mPatterns = new TokenPatterns();

    /// <summary>Should we keep the user comments in the generated target assembly program ?</summary>
    public bool EmitUserComments = false;
    protected int mLineNo = 0;
    protected string mPathname = "";

    /// <summary>Invoke this method when end of source code file is reached to make sure the last
    /// function or interrupt handler has well balanced opening/closing curly braces.</summary>
    private void AssertLastFunctionComplete() {
      if (!mPatterns.InFunctionBody) {
        return;
      }
      throw new Exception("The last function or interrupt handler from source code file is missing a curly brace.");
    }

    /// <summary>Parse the input X# source code file and generate the matching target assembly
    /// language.</summary>
    /// <param name="aReader">X# source code reader.</param>
    /// <returns>The resulting target assembler content. The returned object contains
    /// a code and a data block.</returns>
    public Assembler Generate(TextReader aReader)
    {
      if (aReader == null)
      {
        throw new ArgumentNullException(nameof(aReader));
      }
      mPatterns.EmitUserComments = EmitUserComments;
      mLineNo = 0;
      var xResult = new Assembler();
      try
      {
        // Read one X# source code line at a time and process it.
        while (true)
        {
          mLineNo++;
          string xLine = aReader.ReadLine();
          if (xLine == null)
          {
            break;
          }

          ProcessLine(xLine, mLineNo);
        }
        AssertLastFunctionComplete();
        return xResult;
      }
      finally
      {
        Assembler.ClearCurrentInstance();
      }
    }

    /// <summary>Parse the input X# source code file and generate the matching target assembly
    /// language.</summary>
    /// <param name="aSrcPathname">X# source code file.</param>
    /// <returns>The resulting target assembler content. The returned object contains
    /// a code and a data block.</returns>
    public Assembler Generate(string aSrcPathname)
    {
      try
      {
        using (var xInput = new StreamReader(aSrcPathname))
        {
          return Generate(xInput);
        }
      }
      catch (Exception E)
      {
        throw new Exception("Error while generating output for file " + Path.GetFileName(aSrcPathname), E);
      }
    }

    /// <summary>Parse the input X# source code file and generate two new files with target
    /// assembly language. The two generated files contain target assembler source and target
    /// assembler data respectively.</summary>
    /// <param name="aSrcPathname">X# source code file.</param>
    public void GenerateToFiles(string aSrcPathname) {
      mPathname = Path.GetFileName(aSrcPathname);
      new Assembler(false);
      try
      {
        using (var xInput = new StreamReader(aSrcPathname))
        {
          using (var xOutput = new StreamWriter(Path.ChangeExtension(aSrcPathname, ".asm")))
          {
            xOutput.WriteLine("; Generated at {0}", DateTime.Now.ToString(new CultureInfo("en-US")));

            Generate(xInput, xOutput);
          }
        }
      }
      finally
      {
        Assembler.ClearCurrentInstance();
      }
    }

    /// <summary>Parse the input X# source code from the given reader and write both target
    /// assembler code and target assembler data in their respective writers.</summary>
    /// <param name="aInput">A reader to acquire X# source code from.</param>
    /// <param name="aOutputData">A writer that will receive target assembler data.</param>
    /// <param name="aOutputCode">A writer that will receive target assembler code.</param>
    public void Generate(TextReader aInput, TextWriter aOutput) {
      mPatterns.EmitUserComments = EmitUserComments;
      mLineNo = 0;
      // Read one X# source code line at a time and process it.
      while (true) {
        mLineNo++;
        string xLine = aInput.ReadLine();
        if (xLine == null) {
          break;
        }

        ProcessLine(xLine, mLineNo);

      }
      Assembler.CurrentInstance.FlushText(aOutput);
      AssertLastFunctionComplete();
    }

    /// <summary>Process a single X# source code line and translate it into the target
    /// assembler syntax.</summary>
    /// <param name="aLine">The processed X# source code line.</param>
    /// <param name="lineNumber">Line number for debugging and diagnostic messages.</param>
    /// <returns>The resulting target assembler content. The returned object contains
    /// a code and a data block.</returns>
    protected void ProcessLine(string aLine, int lineNumber) {
      aLine = aLine.Trim();
      if (String.IsNullOrEmpty(aLine) || aLine == "//") {
        return;
      }

      // Currently we use a new assembler for every line.
      // If we dont it could create a really large in memory object.
      if (!mPatterns.GetCode(aLine, lineNumber)) {
        var xMsg = new StringBuilder();
        if (mPathname != "") {
          xMsg.Append("File " + mPathname + ", ");
        }
        xMsg.Append("Line " + mLineNo + ", ");
        xMsg.Append("Parsing error: " + aLine);
        throw new Exception(xMsg.ToString());
      }
    }
  }
}