class RelationList():
    '''Relation list class.'''
    def __init__(self, lis=[], /):
        self.lis = lis
        self.relations = []
        self.elm = {}
        for i in range(len(lis)):
            self.elm[lis[i]] = 0
    def __str__(self):
        return str(self.lis)
    def __repr__(self):
        return repr((self.lis, self.relations, self.elm))
    def __iter__(self):
        a = []
        for i in range(len(self.lis)):
            a.append(self.lis[i], self.elm[lis[i]])
        return iter(a)
    def __len__(self):
        return len(self.lis)
    def __add__(self, other):
        # Note: this will discard all relations for both relation lists.
        return RelationList(self.lis+other.lis)
    @property
    def value(self):
        '''Returns the value of the list.'''
        return self.lis
    def relate(self, val1, val2, /, *, mode='break', assignment=None):
        '''Creates a relation between two elements.'''
        if val1 not in self.lis and val2 not in self.lis:
            raise ValueError(f"Values {val1} and {val2} not found.")
        elif val1 not in self.lis:
            raise ValueError(f"Value {val1} not found.")
        elif val2 not in self.lis:
            raise ValueError(f"Value {val2} not found.")
        if mode not in ('break', 'delete'):
            raise ValueError("Invaild mode.")
        if (val1, val2, mode, assignment) in self.relations:
            return
        self.relations.append((val1, val2, mode, assignment))
        self.elm[val1] += 1
        self.elm[val2] += 1
    def add(self, val, /, index=-1):
        '''Appends a new element to the assigned index in the list.'''
        if index == -1:
            self.lis.append(val)
        else:
            self.lis.insert(index, val)
        self.elm[val] = 0
    def delete(self, val, /, *, err="raise"):
        '''Deletes an element in the list.'''
        if val not in self.lis:
            if err == "raise":
                raise ValueError(f"Value {val} not found.")
            elif err == "ignore":
                return 
            elif err == "append":
                self.lis.add(val)
        else:
            if self.elm[val] == 0:
                self.lis.remove(val)
            else:
                for i in range(len(r := self.relations)):
                    if val in (r[i][0], r[i][1]):
                        y = r[i][1] if val == r[i][0] else r[i][0]
                        if r[i][2] == 'break': 
                            del r[i]
                            self.elm[y] -= 1
                            del self.elm[val]
                            self.lis.remove(val)
                        else:
                            del r[i]
                            self.lis.remove(y)
                            self.lis.remove(val)
                            del self.elm[val]
                            del self.elm[y]
    def relate_all(self, mode='break', assignments=None):
        '''Create relations between all elements.'''
        self.relatiosns.clear()
        for i in range(len(li := self.lis)-1):
            for j in range(i+1, len(li)-1):
                if not isinstance(assignments, (list, tuple)):
                    self.relate(li[i], li[j], mode, assignments)
                else:
                    try:
                        self.relate(li[i], li[j], mode, assignments[i])
                    except IndexError:
                        self.relate(li[i], li[j], mode, None)
    def get_relates(self, val, /):
        '''Returns all of the relations with the element.'''
        if val not in self.lis:
            raise ValueError(f"Value {val} not found.")
        a = []
        for i in range(len(r := self.relations)):
            if val in r[i]:
                a.append(r[i])
        return a
    def get_assignment(self, val1, val2):
        '''Returns the assignment assigned between two elements.'''
        for i in range(len(r := self.relations)):
            if val1 in r[i] and val2 in r[i]:
                return r[i][3]
        raise ValueError(f"Relation between {val1} and {val2} not found.")