Fundamental file helpers

// Copyright 2020, Timothy J. Bruce
using System.Linq;

namespace Icod.TestRig {

    public static class FileHelper {

        #region fields
        public const System.Int32 EOL = -1;
        public const System.Int32 EOF = EOL;
        #endregion fields


        #region methods
        public static System.String PathCombine( System.String path, System.Char pathSeparator, System.String name ) {
            if ( System.String.IsNullOrEmpty( name ) ) {
                throw new System.ArgumentNullException( "name" );
            } else if ( System.String.IsNullOrEmpty( path ) ) {
                throw new System.ArgumentNullException( "path" );
            }
            var sep = pathSeparator.ToString();
            while ( path.EndsWith( sep ) ) {
                path = path.Substring( 0, path.Length - 1 );
            }
            while ( name.StartsWith( sep ) ) {
                name = name.Substring( 1 );
            }
            return path + sep + name;
        }

        public static System.String ReadLine( this System.IO.TextReader file, System.String recordSeparator, System.Char quoteChar ) {
            if ( System.String.IsNullOrEmpty( recordSeparator ) ) {
                throw new System.ArgumentNullException( "recordSeparator" );
            } else if ( null == file ) {
                throw new System.ArgumentNullException( "file" );
            } else if ( ( 1 == recordSeparator.Length ) && recordSeparator.Equals( quoteChar.ToString() ) ) {
                throw new System.InvalidOperationException( "Quote character and record separator cannot be the same." );
            } else if ( EOF == file.Peek() ) {
                return null;
            }

            var output = new System.Text.StringBuilder();
            var leLen = recordSeparator.Length;
            var lenStop = leLen - 1;
            System.Int32 i = 0;
            System.Char c;
            System.Boolean isPlaintext = true;
            System.Int32 p = file.Read();
            System.Char q;
            while ( EOL != p ) {
                c = System.Convert.ToChar( p );
                output = output.Append( c );
                if ( isPlaintext ) {
                    if ( quoteChar.Equals( c ) ) {
                        isPlaintext = false;
                    } else if ( ( leLen <= output.Length ) && ( recordSeparator[ i ].Equals( output[ ( output.Length - leLen ) - i ] ) ) ) {
                        if ( lenStop <= ++i ) {
                            output.Remove( output.Length - leLen, leLen );
                            break;
                        }
                    } else {
                        i = 0;
                    }
                } else {
                    if ( quoteChar.Equals( c ) ) {
                        p = file.Peek();
                        if ( EOL == p ) {
                            throw new System.IO.EndOfStreamException();
                        }
                        c = System.Convert.ToChar( p );
                        if ( quoteChar.Equals( c ) ) {
                            file.Read();
                            output = output.Append( c );
                        } else {
                            i = 0;
                            isPlaintext = true;
                        }
                    }
                }
                p = file.Read();
            }

            return output.ToString();
        }
        public static System.String ReadLine( this System.IO.TextReader file, System.String recordSeparator ) {
            if ( System.String.IsNullOrEmpty( recordSeparator ) ) {
                throw new System.ArgumentNullException( "recordSeparator" );
            } else if ( null == file ) {
                throw new System.ArgumentNullException( "file" );
            } else if ( EOF == file.Peek() ) {
                return null;
            }

            System.Boolean isReading = true;
            var rs = recordSeparator.ToCharArray();
            System.Int32 i = 0;
            var maxI = rs.Length;
            var line = new System.Text.StringBuilder();
            System.Int32 j = 0;
            System.Int32 c;
            System.Boolean isNull = true;
            do {
                c = file.Read();
                if ( -1 == c ) {
                    maxI = 0;
                    isReading = false;
                    break;
                }
                isNull = false;
                line.Append( System.Convert.ToChar( c ) );
                if ( line[ j ].Equals( rs[ i ] ) ) {
                    i++;
                } else {
                    i = 0;
                }
                if ( i == maxI ) {
                    isReading = false;
                    break;
                }
                j++;
            } while ( isReading );
            line.Remove( line.Length - maxI, maxI );
            return isNull ? null : line.ToString();
        }
        public static System.String ReadLine( this System.IO.StreamReader file, System.String recordSeparator, System.Char quoteChar ) {
            if ( System.String.IsNullOrEmpty( recordSeparator ) ) {
                throw new System.ArgumentNullException( "recordSeparator" );
            } else if ( null == file ) {
                throw new System.ArgumentNullException( "file" );
            } else if ( ( 1 == recordSeparator.Length ) && recordSeparator.Equals( quoteChar.ToString() ) ) {
                throw new System.InvalidOperationException( "Quote character and record separator cannot be the same." );
            } else if ( EOF == file.Peek() ) {
                return null;
            }

            var output = new System.Text.StringBuilder();
            var leLen = recordSeparator.Length;
            var lenStop = leLen - 1;
            System.Int32 i = 0;
            System.Char c;
            System.Boolean isPlaintext = true;
            System.Int32 p = file.Read();
            System.Char q;
            while ( EOL != p ) {
                c = System.Convert.ToChar( p );
                output = output.Append( c );
                if ( isPlaintext ) {
                    if ( quoteChar.Equals( c ) ) {
                        isPlaintext = false;
                    } else if ( ( leLen <= output.Length ) && ( recordSeparator[ i ].Equals( output[ ( output.Length - leLen ) - i ] ) ) ) {
                        if ( lenStop <= ++i ) {
                            output.Remove( output.Length - leLen, leLen );
                            break;
                        }
                    } else {
                        i = 0;
                    }
                } else {
                    if ( quoteChar.Equals( c ) ) {
                        p = file.Peek();
                        if ( EOL == p ) {
                            throw new System.IO.EndOfStreamException();
                        }
                        c = System.Convert.ToChar( p );
                        if ( quoteChar.Equals( c ) ) {
                            file.Read();
                            output = output.Append( c );
                        } else {
                            i = 0;
                            isPlaintext = true;
                        }
                    }
                }
                p = file.Read();
            }

            return output.ToString();
        }
        public static System.String ReadLine( this System.IO.StreamReader file, System.String recordSeparator ) {
            if ( System.String.IsNullOrEmpty( recordSeparator ) ) {
                throw new System.ArgumentNullException( "recordSeparator" );
            } else if ( null == file ) {
                throw new System.ArgumentNullException( "file" );
            } else if ( EOF == file.Peek() ) {
                return null;
            }

            System.Boolean isReading = true;
            var rs = recordSeparator.ToCharArray();
            System.Int32 i = 0;
            var maxI = rs.Length;
            var line = new System.Text.StringBuilder();
            System.Int32 j = 0;
            System.Int32 c;
            System.Boolean isNull = true;
            do {
                c = file.Read();
                if ( -1 == c ) {
                    maxI = 0;
                    isReading = false;
                    break;
                }
                isNull = false;
                line.Append( System.Convert.ToChar( c ) );
                if ( line[ j ].Equals( rs[ i ] ) ) {
                    i++;
                } else {
                    i = 0;
                }
                if ( i == maxI ) {
                    isReading = false;
                    break;
                }
                j++;
            } while ( isReading );
            line.Remove( line.Length - maxI, maxI );
            return isNull ? null : line.ToString();
        }


        public static System.Collections.Generic.IEnumerable<System.String> ReadRecord(
            this System.IO.TextReader file, System.String recordSeparator,
            System.Char quoteChar, System.Char fieldSeparator
        ) {
            if ( null == file ) {
                throw new System.ArgumentNullException( "file" );
            } else if ( System.String.IsNullOrEmpty( recordSeparator ) ) {
                throw new System.InvalidOperationException();
            }

            var line = file.ReadLine( recordSeparator, quoteChar );
            if ( null == line ) {
                yield break;
            }
            using ( var reader = new System.IO.StringReader( line ) ) {
                System.Int32 i;
                System.Char c;
                System.String column;
                var reading = true;
                System.Nullable<System.Char> ec = null;
                var qc = quoteChar;
                do {
                    i = reader.Peek();
                    if ( -1 == i ) {
                        reading = false;
                        break;
                    }
                    c = System.Convert.ToChar( i );
                    if ( qc.Equals( c ) ) {
                        reader.Read();
                        column = ReadColumn( reader, quoteChar, true );
                        yield return column;
                    } else {
                        column = ReadColumn( reader, fieldSeparator, false );
                        yield return column;
                    }
                } while ( reading );
            }
        }
        public static System.Collections.Generic.IEnumerable<System.String> ReadRecord(
            this System.IO.StreamReader file, System.String recordSeparator,
            System.Char quoteChar, System.Char fieldSeparator
        ) {
            if ( null == file ) {
                throw new System.ArgumentNullException( "file" );
            } else if ( file.EndOfStream ) {
                yield break;
            } else if ( System.String.IsNullOrEmpty( recordSeparator ) ) {
                throw new System.InvalidOperationException();
            }

            var line = file.ReadLine( recordSeparator, quoteChar );
            if ( null == line ) {
                yield break;
            }
            using ( var reader = new System.IO.StringReader( line ) ) {
                System.Int32 i;
                System.Char c;
                System.String column;
                var reading = true;
                System.Nullable<System.Char> ec = null;
                var qc = quoteChar;
                do {
                    i = reader.Peek();
                    if ( -1 == i ) {
                        reading = false;
                        break;
                    }
                    c = System.Convert.ToChar( i );
                    if ( qc.Equals( c ) ) {
                        reader.Read();
                        column = ReadColumn( reader, quoteChar, true );
                        yield return column;
                    } else {
                        column = ReadColumn( reader, fieldSeparator, false );
                        yield return column;
                    }
                } while ( reading );
            }
        }
        public static System.String ReadColumn(
            this System.IO.StringReader reader, System.Char @break, System.Boolean readNextOnBreak
        ) {
            if ( null == reader ) {
                throw new System.ArgumentNullException( "reader" );
            }
            var sb = new System.Text.StringBuilder( 128 );
            System.Nullable<System.Char> ch;
            var reading = true;
            do {
                ch = ReadChar( reader, @break, readNextOnBreak );
                if ( ch.HasValue ) {
                    sb = sb.Append( ch.Value );
                } else {
                    reading = false;
                    break;
                }
            } while ( reading );
            return sb.ToString().TrimToNull();
        }
        public static System.Nullable<System.Char> ReadChar(
            this System.IO.StringReader reader, System.Char @break, System.Boolean readNextOnBreak
        ) {
            if ( null == reader ) {
                throw new System.ArgumentNullException( "reader" );
            }

            var p = reader.Peek();
            if ( -1 == p ) {
                return null;
            }
            var c = System.Convert.ToChar( reader.Read() );
            if ( @break.Equals( c ) ) {
                if ( readNextOnBreak ) {
                    p = reader.Peek();
                    if ( -1 == p ) {
                        return null;
                    } else if ( @break.Equals( System.Convert.ToChar( p ) ) ) {
                        return System.Convert.ToChar( reader.Read() );
                    } else {
                        reader.Read();
                    }
                }
                return null;
            }
            return c;
        }
        #endregion methods

    }

}