/*******************************************************************************
 * You may amend and distribute as you like, but don't remove this header!
 *
 * EPPlus provides server-side generation of Excel 2007/2010 spreadsheets.
 * See http://www.codeplex.com/EPPlus for details.
 *
 * Copyright (C) 2011  Jan Källman
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.

 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Lesser General Public License for more details.
 *
 * The GNU Lesser General Public License can be viewed at http://www.opensource.org/licenses/lgpl-license.php
 * If you unfamiliar with this license or have questions about it, here is an http://www.gnu.org/licenses/gpl-faq.html
 *
 * All code and executables are provided "as is" with no warranty either express or implied.
 * The author accepts no liability for any damage or loss of business that this product may cause.
 *
 * Code change notes:
 *
 * Author							Change						Date
 * ******************************************************************************
 * Mats Alm   		                Added       		        2013-03-01 (Prior file history on https://github.com/swmal/ExcelFormulaParser)
 *******************************************************************************/

using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.Text.RegularExpressions;

namespace EpplusFormulaParser;

internal static partial class SourceCodeTokenizer {
  public static List<Token> Tokenize(string input) {
    if (string.IsNullOrEmpty(input)) {
      return [];
    }
    // MA 1401: Ignore leading plus in formula.
    input = input.TrimStart('+');
    var context = new TokenizerContext(input);

    var isSingleQuoteString = false;
    for (var i = 0; i < context.Formula.Length; i++) {
      var c = context.Formula[i];
      if (CharIsTokenSeparator(c, out var tokenSeparator)) {
        if (context.IsInString) {
          if (IsDoubleQuote(tokenSeparator, i, context)) {
            i++;
            context.AppendToCurrentToken(c);
            continue;
          }
          if (tokenSeparator.TokenType != TokenType.String) {
            context.AppendToCurrentToken(c);
            continue;
          }
          // CHANGE 2
          if ((isSingleQuoteString && c != '\'') || (!isSingleQuoteString && c != '"')) {
            context.AppendToCurrentToken(c);
            continue;
          }
        }
        if (tokenSeparator.TokenType == TokenType.OpeningBracket) {
          context.AppendToCurrentToken(c);
          context.BracketCount++;
          continue;
        }
        if (tokenSeparator.TokenType == TokenType.ClosingBracket) {
          context.AppendToCurrentToken(c);
          context.BracketCount--;
          continue;
        }
        if (context.BracketCount > 0) {
          context.AppendToCurrentToken(c);
          continue;
        }
        // two operators in sequence could be "<=" or ">="
        if (IsPartOfMultipleCharSeparator(context, c)) {
          var sOp = context.LastToken!.Value + c.ToString(CultureInfo.InvariantCulture);
          var op = TokenSeparatorProvider.Tokens[sOp];
          context.ReplaceLastToken(op);
          context.NewToken();
          continue;
        }
        if (tokenSeparator.TokenType == TokenType.String) {
          // CHANGE3 :
          isSingleQuoteString = c == '\'';
          if (context.LastToken is { TokenType: TokenType.OpeningEnumerable }) {
            // context.AppendToCurrentToken(c);  // Praveen's change of 10/28/2015
            context.ToggleIsInString();
            continue;
          }
          if (context.LastToken is { TokenType: TokenType.String }) {
            context.AddToken(
                !context.CurrentTokenHasValue
                    ? new(string.Empty, TokenType.StringContent)
                    : new Token(context.CurrentToken, TokenType.StringContent));
          }
          context.AddToken(new("\"", TokenType.String));
          context.ToggleIsInString();
          context.NewToken();
          continue;
        }
        if (context.CurrentTokenHasValue) {
          if (StringRegex().IsMatch(context.CurrentToken)) {
            context.AddToken(new(context.CurrentToken, TokenType.StringContent));
          } else {
            context.AddToken(CreateToken(context));
          }

          //If the next token is an opening parantheses and the previous token is interpeted as an address or name, then the current token is a function
          if (tokenSeparator.TokenType == TokenType.OpeningParenthesis
              && context.LastToken?.TokenType is TokenType.ExcelAddress or TokenType.NameValue) {
            context.LastToken.TokenType = TokenType.Function;
          }
        }
        if (tokenSeparator.Value == "-") {
          if (TokenIsNegator(context)) {
            context.AddToken(new("-", TokenType.Negator));
            continue;
          }
        }
        context.AddToken(tokenSeparator);
        context.NewToken();
        continue;
      }
      context.AppendToCurrentToken(c);
    }
    if (context.CurrentTokenHasValue) {
      context.AddToken(CreateToken(context));
    }

    CleanupTokens(context);

    return context.Result;
  }

  private static bool IsDoubleQuote(
      Token tokenSeparator,
      int formulaCharIndex,
      TokenizerContext context) {
    return tokenSeparator.TokenType == TokenType.String
        && formulaCharIndex + 1 < context.Formula.Length
        && context.Formula[formulaCharIndex + 1] == '\"';
  }

  private static void CleanupTokens(TokenizerContext context) {
    for (var i = 0; i < context.Result.Count; i++) {
      var token = context.Result[i];
      if (token.TokenType == TokenType.Unrecognized) {
        if (i < context.Result.Count - 1) {
          if (context.Result[i + 1].TokenType == TokenType.OpeningParenthesis) {
            token.TokenType = TokenType.Function;
          } else {
            token.TokenType = TokenType.NameValue;
          }
        } else {
          token.TokenType = TokenType.NameValue;
        }
      } else if (token.TokenType == TokenType.Function) {
        if (i < context.Result.Count - 1) {
          if (context.Result[i + 1].TokenType == TokenType.OpeningParenthesis) {
            token.TokenType = TokenType.Function;
          } else {
            token.TokenType = TokenType.Unrecognized;
          }
        } else {
          token.TokenType = TokenType.Unrecognized;
        }
      } else if ((token.TokenType == TokenType.Operator || token.TokenType == TokenType.Negator)
          && i < context.Result.Count - 1
          && (token.Value == "+" || token.Value == "-")) {
        if (i > 0
            && token.Value
                == "+") //Remove any + with an opening parenthesis before.
        {
          if (context.Result[i - 1].TokenType == TokenType.OpeningParenthesis) {
            context.Result.RemoveAt(i);
            SetNegatorOperator(context, i);
            i--;
            continue;
          }
        }

        var nextToken = context.Result[i + 1];
        if (nextToken.TokenType == TokenType.Operator || nextToken.TokenType == TokenType.Negator) {
          if (token.Value == "+" && (nextToken.Value == "+" || nextToken.Value == "-")) {
            //Remove first
            context.Result.RemoveAt(i);
            SetNegatorOperator(context, i);
            i--;
          } else if (token.Value == "-" && nextToken.Value == "+") {
            //Remove second
            context.Result.RemoveAt(i + 1);
            SetNegatorOperator(context, i);
            i--;
          } else if (token.Value == "-" && nextToken.Value == "-") {
            //Remove first and set operator to +
            context.Result.RemoveAt(i);
            if (i == 0) {
              context.Result.RemoveAt(i + 1);
              i += 2;
            } else {
              //context.Result[i].TokenType = TokenType.Operator;
              //context.Result[i].Value = "+";
              context.Result[i] = TokenSeparatorProvider.Tokens["+"];
              SetNegatorOperator(context, i);
              i--;
            }
          }
        }
      }
    }
  }

  private static void SetNegatorOperator(TokenizerContext context, int i) {
    if (context.Result[i].Value == "-"
        && i > 0
        && (context.Result[i].TokenType == TokenType.Operator
                || context.Result[i].TokenType == TokenType.Negator)) {
      if (TokenIsNegator(context.Result[i - 1])) {
        context.Result[i] = new("-", TokenType.Negator);
      } else {
        context.Result[i] = TokenSeparatorProvider.Tokens["-"];
      }
    }
  }

  private static bool TokenIsNegator(TokenizerContext context) {
    return TokenIsNegator(context.LastToken);
  }

  private static bool TokenIsNegator(Token? t) {
    return t == null
        || t.TokenType == TokenType.Operator
        || t.TokenType == TokenType.OpeningParenthesis
        || t.TokenType == TokenType.Comma
        || t.TokenType == TokenType.SemiColon
        || t.TokenType == TokenType.OpeningEnumerable;
  }

  private static bool IsPartOfMultipleCharSeparator(TokenizerContext context, char c) {
    var lastToken = context.LastToken != null ? context.LastToken.Value : string.Empty;
    return TokenSeparatorProvider.IsOperator(lastToken)
        && TokenSeparatorProvider.IsPossibleLastPartOfMultipleCharOperator(
            c.ToString(CultureInfo.InvariantCulture))
        && !context.CurrentTokenHasValue;
  }

  private static Token CreateToken(TokenizerContext context) {
    if (context is { CurrentToken: "-", LastToken: null }) {
      throw new NullReferenceException();
    }
    return TokenFactory.Create(context.Result, context.CurrentToken);
  }

  private static bool CharIsTokenSeparator(char c, [NotNullWhen(true)] out Token? token) {
    return TokenSeparatorProvider.Tokens.TryGetValue(c.ToString(), out token);
  }

  [GeneratedRegex("^\"*$")]
  private static partial Regex StringRegex();
}