using System;
using System.Collections.Generic;
using System.Linq;

namespace Swan.Parsers {
  /// <summary>
  /// Represents a generic tokenizer.
  /// </summary>
  public abstract class Tokenizer {
    private const Char PeriodChar = '.';
    private const Char CommaChar = ',';
    private const Char StringQuotedChar = '"';
    private const Char OpenFuncChar = '(';
    private const Char CloseFuncChar = ')';
    private const Char NegativeChar = '-';

    private const String OpenFuncStr = "(";

    private readonly List<Operator> _operators = new List<Operator>();

    /// <summary>
    /// Initializes a new instance of the <see cref="Tokenizer"/> class.
    /// This constructor will use the following default operators:
    ///
    /// <list type="table">
    ///     <listheader>
    ///     <term>Operator</term>
    ///     <description>Precedence</description>
    ///     </listheader>
    /// <item>
    /// <term>=</term>
    /// <description>1</description>
    /// </item>
    /// <item>
    /// <term>!=</term>
    /// <description>1</description>
    /// </item>
    /// <item>
    /// <term>&gt;</term>
    /// <description>2</description>
    /// </item>
    /// <item>
    /// <term>&lt;</term>
    /// <description>2</description>
    /// </item>
    /// <item>
    /// <term>&gt;=</term>
    /// <description>2</description>
    /// </item>
    /// <item>
    /// <term>&lt;=</term>
    /// <description>2</description>
    /// </item>
    /// <item>
    /// <term>+</term>
    /// <description>3</description>
    /// </item>
    /// <item>
    /// <term>&amp;</term>
    /// <description>3</description>
    /// </item>
    /// <item>
    /// <term>-</term>
    /// <description>3</description>
    /// </item>
    /// <item>
    /// <term>*</term>
    /// <description>4</description>
    /// </item>
    /// <item>
    /// <term>(backslash)</term>
    /// <description>4</description>
    /// </item>
    /// <item>
    /// <term>/</term>
    /// <description>4</description>
    /// </item>
    /// <item>
    /// <term>^</term>
    /// <description>4</description>
    /// </item>
    /// </list>
    /// </summary>
    /// <param name="input">The input.</param>
    protected Tokenizer(String input) {
      this._operators.AddRange(this.GetDefaultOperators());
      this.Tokenize(input);
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="Tokenizer" /> class.
    /// </summary>
    /// <param name="input">The input.</param>
    /// <param name="operators">The operators to use.</param>
    protected Tokenizer(String input, IEnumerable<Operator> operators) {
      this._operators.AddRange(operators);
      this.Tokenize(input);
    }

    /// <summary>
    /// Gets the tokens.
    /// </summary>
    /// <value>
    /// The tokens.
    /// </value>
    public List<Token> Tokens { get; } = new List<Token>();

    /// <summary>
    /// Validates the input and return the start index for tokenizer.
    /// </summary>
    /// <param name="input">The input.</param>
    /// <param name="startIndex">The start index.</param>
    /// <returns><c>true</c> if the input is valid, otherwise <c>false</c>.</returns>
    public abstract Boolean ValidateInput(String input, out Int32 startIndex);

    /// <summary>
    /// Resolves the type of the function or member.
    /// </summary>
    /// <param name="input">The input.</param>
    /// <returns>The token type.</returns>
    public abstract TokenType ResolveFunctionOrMemberType(String input);

    /// <summary>
    /// Evaluates the function or member.
    /// </summary>
    /// <param name="input">The input.</param>
    /// <param name="position">The position.</param>
    /// <returns><c>true</c> if the input is a valid function or variable, otherwise <c>false</c>.</returns>
    public virtual Boolean EvaluateFunctionOrMember(String input, Int32 position) => false;

    /// <summary>
    /// Gets the default operators.
    /// </summary>
    /// <returns>An array with the operators to use for the tokenizer.</returns>
    public virtual Operator[] GetDefaultOperators() => new[]
    {
            new Operator {Name = "=", Precedence = 1},
            new Operator {Name = "!=", Precedence = 1},
            new Operator {Name = ">", Precedence = 2},
            new Operator {Name = "<", Precedence = 2},
            new Operator {Name = ">=", Precedence = 2},
            new Operator {Name = "<=", Precedence = 2},
            new Operator {Name = "+", Precedence = 3},
            new Operator {Name = "&", Precedence = 3},
            new Operator {Name = "-", Precedence = 3},
            new Operator {Name = "*", Precedence = 4},
            new Operator {Name = "/", Precedence = 4},
            new Operator {Name = "\\", Precedence = 4},
            new Operator {Name = "^", Precedence = 4},
        };

    /// <summary>
    /// Shunting the yard.
    /// </summary>
    /// <param name="includeFunctionStopper">if set to <c>true</c> [include function stopper] (Token type <c>Wall</c>).</param>
    /// <returns>
    /// Enumerable of the token in in.
    /// </returns>
    /// <exception cref="InvalidOperationException">
    /// Wrong token
    /// or
    /// Mismatched parenthesis.
    /// </exception>
    public virtual IEnumerable<Token> ShuntingYard(Boolean includeFunctionStopper = true) {
      Stack<Token> stack = new Stack<Token>();

      foreach(Token tok in this.Tokens) {
        switch(tok.Type) {
          case TokenType.Number:
          case TokenType.Variable:
          case TokenType.String:
            yield return tok;
            break;
          case TokenType.Function:
            stack.Push(tok);
            break;
          case TokenType.Operator:
            while(stack.Any() && stack.Peek().Type == TokenType.Operator && this.CompareOperators(tok.Value, stack.Peek().Value)) {
              yield return stack.Pop();
            }

            stack.Push(tok);
            break;
          case TokenType.Comma:
            while(stack.Any() && stack.Peek().Type != TokenType.Comma && stack.Peek().Type != TokenType.Parenthesis) {
              yield return stack.Pop();
            }

            break;
          case TokenType.Parenthesis:
            if(tok.Value == OpenFuncStr) {
              if(stack.Any() && stack.Peek().Type == TokenType.Function) {
                if(includeFunctionStopper) {
                  yield return new Token(TokenType.Wall, tok.Value);
                }
              }

              stack.Push(tok);
            } else {
              while(stack.Peek().Value != OpenFuncStr) {
                yield return stack.Pop();
              }

              _ = stack.Pop();

              if(stack.Any() && stack.Peek().Type == TokenType.Function) {
                yield return stack.Pop();
              }
            }

            break;
          default:
            throw new InvalidOperationException("Wrong token");
        }
      }

      while(stack.Any()) {
        Token tok = stack.Pop();
        if(tok.Type == TokenType.Parenthesis) {
          throw new InvalidOperationException("Mismatched parenthesis");
        }

        yield return tok;
      }
    }

    private static Boolean CompareOperators(Operator op1, Operator op2) => op1.RightAssociative ? op1.Precedence < op2.Precedence : op1.Precedence <= op2.Precedence;

    private void Tokenize(String input) {
      if(!this.ValidateInput(input, out Int32 startIndex)) {
        return;
      }

      for(Int32 i = startIndex; i < input.Length; i++) {
        if(Char.IsWhiteSpace(input, i)) {
          continue;
        }

        if(input[i] == CommaChar) {
          this.Tokens.Add(new Token(TokenType.Comma, new String(new[] { input[i] })));
          continue;
        }

        if(input[i] == StringQuotedChar) {
          i = this.ExtractString(input, i);
          continue;
        }

        if(Char.IsLetter(input, i) || this.EvaluateFunctionOrMember(input, i)) {
          i = this.ExtractFunctionOrMember(input, i);

          continue;
        }

        if(Char.IsNumber(input, i) || input[i] == NegativeChar && (this.Tokens.Any() && this.Tokens.Last().Type != TokenType.Number || !this.Tokens.Any())) {
          i = this.ExtractNumber(input, i);
          continue;
        }

        if(input[i] == OpenFuncChar || input[i] == CloseFuncChar) {
          this.Tokens.Add(new Token(TokenType.Parenthesis, new String(new[] { input[i] })));
          continue;
        }

        i = this.ExtractOperator(input, i);
      }
    }

    private Int32 ExtractData(String input, Int32 i, Func<String, TokenType> tokenTypeEvaluation, Func<Char, Boolean> evaluation, Int32 right = 0, Int32 left = -1) {
      Int32 charCount = 0;
      for(Int32 j = i + right; j < input.Length; j++) {
        if(evaluation(input[j])) {
          break;
        }

        charCount++;
      }

      // Extract and set the value
      String value = input.SliceLength(i + right, charCount);
      this.Tokens.Add(new Token(tokenTypeEvaluation(value), value));

      i += charCount + left;
      return i;
    }

    private Int32 ExtractOperator(String input, Int32 i) => this.ExtractData(input, i, x => TokenType.Operator, x => x == OpenFuncChar || x == CommaChar || x == PeriodChar || x == StringQuotedChar || Char.IsWhiteSpace(x) || Char.IsNumber(x));

    private Int32 ExtractFunctionOrMember(String input, Int32 i) => this.ExtractData(input, i, this.ResolveFunctionOrMemberType, x => x == OpenFuncChar || x == CloseFuncChar || x == CommaChar || Char.IsWhiteSpace(x));

    private Int32 ExtractNumber(String input, Int32 i) => this.ExtractData(input, i, x => TokenType.Number, x => !Char.IsNumber(x) && x != PeriodChar && x != NegativeChar);

    private Int32 ExtractString(String input, Int32 i) {
      Int32 length = this.ExtractData(input, i, x => TokenType.String, x => x == StringQuotedChar, 1, 1);

      // open string, report issue
      if(length == input.Length && input[length - 1] != StringQuotedChar) {
        throw new FormatException($"Parser error (Position {i}): Expected '\"' but got '{input[length - 1]}'.");
      }

      return length;
    }

    private Boolean CompareOperators(String op1, String op2) => CompareOperators(this.GetOperatorOrDefault(op1), this.GetOperatorOrDefault(op2));

    private Operator GetOperatorOrDefault(String op) => this._operators.FirstOrDefault(x => x.Name == op) ?? new Operator { Name = op, Precedence = 0 };
  }
}