using System;
using System.IO;
using System.Text;

namespace Assignment_1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓");
            Console.WriteLine("┃  159.341 2021 Semester 1, Assignment 1   ┃");
            Console.WriteLine("┃  Submitted by Brychan Dempsey, 14299890  ┃");
            Console.WriteLine("┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛");
            MemoryStream sourceStream = new MemoryStream(1024); // Creates a memory stream to retain source while being interpreted.
            Parser parser = new Parser();
            bool dynamicInput = false;
            // From https://stackoverflow.com/questions/3453220/how-to-detect-if-console-in-stdin-has-been-redirected
            // Reading from pipes is equivalent to reading user input, though the input is redirected
            if (Console.IsInputRedirected)
            {
                sourceStream.Write(Encoding.UTF8.GetBytes(Console.In.ReadToEnd()));
                sourceStream.Position = 0;
            }
            else
            {
                sourceStream.Write(Encoding.UTF8.GetBytes("{\r\n"));
                sourceStream.Position = 0;
                dynamicInput = true;
            }
            parser.FindProgram(sourceStream, dynamicInput);
        }
        public class Parser
        {
            public int FindProgram(Stream sourceStream, bool dynamicInput = false)
            {
                if (sourceStream.ReadByte() == '{')
                {
                    FindStatement();
                }
                else return -1; // Could not find the start of the program
            }

            void Command_Exit()
            {
                Environment.Exit(0);
            }

            int FindStatement(Stream s)
            {
                string statement;
                if (dynamicInput)
                {
                    Console.Write("Enter a \'Statement\': ");
                    statement = Console.ReadLine();
                }
                else
                {
                    statement = GetNextLine(s);
                }

                int wordBound = 0;
                string nextWord = GetNextWord(statement, out wordBound);
                switch (nextWord)
                {
                    case "append":
                        FindIdentifier();
                        FindExpression();
                        break;
                    case "list":
                        break;
                    case "exit":
                        Environment.Exit(0);
                        break;
                    case "print":
                        break;
                    case "printlength":
                        break;
                    case "printwords":
                        break;
                    case "printwordcount":
                        break;
                    case "set":
                        break;
                    case "reverse":
                        break;
                    default:
                        break;
                }

                // Look for further elements
                return 1;
            }

            int FindIdentifier(Stream s)
            {

            }
        }
        


        /// <summary>
        /// Reads the memory stream as a UTF-8 encoded string until the next occurance of '\n' or '\r\n' (consuming, and excluded)
        /// </summary>
        /// <param name="s"></param>
        /// <returns></returns>
        static string GetNextLine(Stream s)
        {
            long start = s.Position;
            StringBuilder sb = new StringBuilder();
            bool newLineFound = false;
            while (!newLineFound)
            {
                // As UTF-8 allows codepoints to span multiple bytes, reading a single byte as a character will not always give the expected
                // value. 
                // Fortunately, the standard ASCII table is 7-bits long. The 8th bit is used to determine the character size
                int readAmount = 0;
                int firstChar = s.ReadByte();
                if ((firstChar >> 3) == 0x1E) // 11110xxx implies a 4-byte length character
                {
                    readAmount = 3;
                }
                else if((firstChar >> 4) == 0xE) // 1110xxxx, 3-byte
                {
                    readAmount = 2;
                }
                else if ((firstChar >> 5) == 0x6) // 110xxxxx, 2-byte
                {
                    readAmount = 1;
                }

                byte[] charBytes = new byte[readAmount + 1];
                charBytes[0] = (byte)firstChar;
                for (int i = 1; i < readAmount; i++)
                {
                    int nextChar = s.ReadByte();
                    if (nextChar >> 6 != 2) throw new Exception("Character is not a valid UTF-8 code point!");
                    charBytes[i] = (byte)nextChar;
                }
                string converted = Encoding.UTF8.GetString(charBytes);
                if (converted == "\r" || converted == "\n")
                {
                    if (s.ReadByte() != '\n') s.Position--; // Return the position if the next character isn't a new line
                    newLineFound = true;
                }
                else
                {
                    sb.Append(converted);
                }
            }
            return sb.ToString();
        }

        static string GetNextWord(string s, out int wordEndPos)
        {
            // remove whitespace from the start
            int wordStart = 0;
            if (char.IsWhiteSpace(s[0]))
            {
                for (int i = 0; i < s.Length; i++)
                {
                    if (char.IsWhiteSpace(s[i])) break;
                    wordStart = i;
                }
            }
            int wordEnd = wordStart;
            for (int i = wordEnd; i < s.Length; i++)
            {
                if (char.IsWhiteSpace(s[i])) break;
                wordEnd = i;
            }
            wordEndPos = wordEnd;
            return s.Substring(wordStart, wordEnd);
        }
    }
}