Initial implementation of SVG path parser

py/hexagram/path.py

@@ -1,13 +1,131 @@
 from typing import Iterable
 
+import enum
 import cairo
 
+class State(enum.Enum):
+    NONE    = 0
+    COMMAND = 1
+    INT     = 2
+    FLOAT   = 3
+
+class ParseError(Exception):
+    pass
+
+class PathCommand():
+    __slots__ = 'command', 'args', 'arg',
+
+    def __init__(self):
+        self.command = None
+        self.args    = list()
+        self.arg     = ''
+
+    def set_command(self, command: str):
+        self.command = command
+
+    def arg_addch(self, ch: str):
+        self.arg += ch
+
+    def arg_next(self, ch: str):
+        if len(self.arg) == 0:
+            return
+
+        self.arg += ch
+        self.args.append(self.arg)
+        self.arg = ''
+
+    def arg_finish(self):
+        if len(self.arg) > 0:
+            self.args.append(self.arg)
+
+        self.arg = ''
+
+    def finish(self):
+        if len(self.arg) > 0:
+            self.args.append(self.arg)
+
+        ret = [self.command, self.args]
+
+        self.command = None
+        self.args    = list()
+        self.arg     = ''
+
+        return ret
+
 class Path():
     __slots__ = 'commands',
 
     def __init__(self, commands: Iterable):
         self.commands = commands
 
+    def is_command(c):
+        return (c >= ord('a') and c <= ord('z')) or (c >= ord('A') and c <= ord('Z'))
+
+    def is_number(c):
+        return (c >= ord('0') and c <= ord('9'))
+
+    def parse(text: str) -> list:
+        commands = list()
+        command  = PathCommand()
+        state    = State.NONE
+
+        for ch in text:
+            c = ord(ch)
+
+            if state is State.NONE:
+                if Path.is_command(c):
+                    command.set_command(ch)
+                    state = State.COMMAND
+                elif ch == ' ':
+                    continue
+                else:
+                    raise ParseError()
+            elif state is State.COMMAND:
+                if Path.is_command(c):
+                    commands.append(command.finish())
+                    command.set_command(ch)
+                elif Path.is_number(c) or ch == '-':
+                    state = State.INT
+                    command.arg_addch(ch)
+                elif ch == '.':
+                    state = State.FLOAT
+                    command.arg_addch(ch)
+                elif ch == ' ':
+                    continue
+                else:
+                    raise ParseError()
+            elif state is State.INT:
+                if Path.is_command(c):
+                    commands.append(command.finish())
+                    command.set_command(ch)
+                elif Path.is_number(c):
+                    command.arg_addch(ch)
+                elif ch == '.':
+                    command.arg_addch(ch)
+                    state = State.FLOAT
+                elif ch == '-':
+                    command.arg_next(ch)
+                elif ch == ' ' or ch == ',':
+                    command.arg_finish()
+                else:
+                    raise ParseError()
+            elif state is State.FLOAT:
+                if Path.is_command(c):
+                    commands.append(command.finish())
+                    command.set_command(ch)
+                elif Path.is_number(c):
+                    command.arg_addch(ch)
+                elif ch == ' ' or ch == ',':
+                    state = State.INT
+                    command.arg_finish()
+                else:
+                    raise ParseError(ch)
+
+        if command.command is not None:
+            commands.append(command.finish())
+
+        return commands
+
     def horiz_to(self, cr: cairo.Context, x2: float):
         _, y = cr.get_current_point()