diff options
author | Julien Dessaux | 2021-12-07 14:26:36 +0100 |
---|---|---|
committer | Julien Dessaux | 2021-12-07 14:26:36 +0100 |
commit | 6ed18289c89eaff3557907df63cf58bd2009b3ee (patch) | |
tree | 903d730030c18ab25c212938794c1c03f65f800f /2021/05/line/line.go | |
parent | Initial import (diff) | |
download | advent-of-code-6ed18289c89eaff3557907df63cf58bd2009b3ee.tar.gz advent-of-code-6ed18289c89eaff3557907df63cf58bd2009b3ee.tar.bz2 advent-of-code-6ed18289c89eaff3557907df63cf58bd2009b3ee.zip |
Added the first days
Diffstat (limited to '')
-rw-r--r-- | 2021/05/line/line.go | 239 |
1 files changed, 239 insertions, 0 deletions
diff --git a/2021/05/line/line.go b/2021/05/line/line.go new file mode 100644 index 0000000..aedf455 --- /dev/null +++ b/2021/05/line/line.go @@ -0,0 +1,239 @@ +package line + +import ( + "bufio" + "bytes" + "fmt" + "io" + "strconv" +) + +type Line struct { + X1, Y1, X2, Y2 int +} + +// Token represents a lexical token. +type Token int + +const ( + // Special tokens + ILLEGAL Token = iota + EOF + WHITESPACE + + // Literals + INT // integers + + // Misc characters + COMMA // , + ARROW // -> +) + +func isWhitespace(ch rune) bool { + return ch == ' ' || ch == '\t' || ch == '\n' +} + +func isDigit(ch rune) bool { + return (ch >= '0' && ch <= '9') +} + +var eof = rune(0) + +// Scanner represents a lexical scanner. +type Scanner struct { + r *bufio.Reader +} + +// NewScanner returns a new instance of Scanner. +func NewScanner(r io.Reader) *Scanner { + return &Scanner{r: bufio.NewReader(r)} +} + +// read reads the next rune from the bufferred reader. +// Returns the rune(0) if an error occurs (or io.EOF is returned). +func (s *Scanner) read() rune { + ch, _, err := s.r.ReadRune() + if err != nil { + return eof + } + return ch +} + +// unread places the previously read rune back on the reader. +func (s *Scanner) unread() { _ = s.r.UnreadRune() } + +// Scan returns the next token and literal value. +func (s *Scanner) Scan() (tok Token, lit string) { + // Read the next rune. + ch := s.read() + + // If we see whitespace then consume all contiguous whitespace. + // If we see a digit then consume as an int. + if isWhitespace(ch) { + return s.scanWhitespace(ch) + } else if isDigit(ch) { + return s.scanInt(ch) + } + + // Otherwise read the individual character. + switch ch { + case eof: + return EOF, "" + case ',': + return COMMA, string(ch) + case '-': + return s.scanArrow(ch) + } + + return ILLEGAL, string(ch) +} + +// scanWhitespace consumes the current rune and all contiguous whitespace. +func (s *Scanner) scanWhitespace(read rune) (tok Token, lit string) { + // Create a buffer and read the current character into it. + var buf bytes.Buffer + buf.WriteRune(read) + + // Read every subsequent whitespace character into the buffer. + // Non-whitespace characters and EOF will cause the loop to exit. + for { + if ch := s.read(); ch == eof { + break + } else if !isWhitespace(ch) { + s.unread() + break + } else { + buf.WriteRune(ch) + } + } + + return WHITESPACE, buf.String() +} + +// scanInt consumes the current rune and all contiguous digit runes. +func (s *Scanner) scanInt(read rune) (tok Token, lit string) { + // Create a buffer and read the current character into it. + var buf bytes.Buffer + buf.WriteRune(read) + + // Read every subsequent ident character into the buffer. + // Non-ident characters and EOF will cause the loop to exit. + for { + if ch := s.read(); ch == eof { + break + } else if !isDigit(ch) { + s.unread() + break + } else { + _, _ = buf.WriteRune(ch) + } + } + + // Otherwise return as a regular identifier. + return INT, buf.String() +} + +func (s *Scanner) scanArrow(read rune) (tok Token, lit string) { + // Create a buffer and read the current character into it. + var buf bytes.Buffer + buf.WriteRune(read) + + // Read every subsequent ident character into the buffer. + // Non-ident characters and EOF will cause the loop to exit. + for { + if ch := s.read(); ch == eof { + break + } else if ch == '>' { + _, _ = buf.WriteRune(ch) + return ARROW, buf.String() + } else { + _, _ = buf.WriteRune(ch) + break + } + } + + // Otherwise return as a regular identifier. + return ILLEGAL, buf.String() +} + +// Parser represents a parser. +type Parser struct { + s *Scanner + buf struct { + tok Token // last read token + lit string // last read literal + n int // buffer size (max=1) + } +} + +// NewParser returns a new instance of Parser. +func NewParser(r io.Reader) *Parser { + return &Parser{s: NewScanner(r)} +} + +// scan returns the next token from the underlying scanner. +// If a token has been unscanned then read that instead. +func (p *Parser) scan() (tok Token, lit string) { + // If we have a token on the buffer, then return it. + if p.buf.n != 0 { + p.buf.n = 0 + return p.buf.tok, p.buf.lit + } + + // Otherwise read the next token from the scanner. + tok, lit = p.s.Scan() + + // Save it to the buffer in case we unscan later. + p.buf.tok, p.buf.lit = tok, lit + + return +} + +// unscan pushes the previously read token back onto the buffer. +func (p *Parser) unscan() { p.buf.n = 1 } + +// scanIgnoreWhitespace scans the next non-whitespace token. +func (p *Parser) scanIgnoreWhitespace() (tok Token, lit string) { + tok, lit = p.scan() + if tok == WHITESPACE { + tok, lit = p.scan() + } + return +} + +func (p *Parser) Parse() (*Line, error) { + l := &Line{} + if tok, lit := p.scanIgnoreWhitespace(); tok != INT { + return nil, fmt.Errorf("found %q, expected INT", lit) + } else { + l.X1, _ = strconv.Atoi(lit) + } + if tok, lit := p.scanIgnoreWhitespace(); tok != COMMA { + return nil, fmt.Errorf("found %q, expected COMMA", lit) + } + if tok, lit := p.scanIgnoreWhitespace(); tok != INT { + return nil, fmt.Errorf("found %q, expected INT", lit) + } else { + l.Y1, _ = strconv.Atoi(lit) + } + if tok, lit := p.scanIgnoreWhitespace(); tok != ARROW { + return nil, fmt.Errorf("found %q, expected ARROW", lit) + } + if tok, lit := p.scanIgnoreWhitespace(); tok != INT { + return nil, fmt.Errorf("found %q, expected INT", lit) + } else { + l.X2, _ = strconv.Atoi(lit) + } + if tok, lit := p.scanIgnoreWhitespace(); tok != COMMA { + return nil, fmt.Errorf("found %q, expected COMMA", lit) + } + if tok, lit := p.scanIgnoreWhitespace(); tok != INT { + return nil, fmt.Errorf("found %q, expected INT", lit) + } else { + l.Y2, _ = strconv.Atoi(lit) + } + if tok, lit := p.scan(); tok != WHITESPACE { + return nil, fmt.Errorf("found %q, expected WHITESPACE", lit) + } + return l, nil +} |