template_component.py

from django.template.loader import get_template


class ValidationError(Exception):
    pass


class Field:
    def __init__(self, default=None, required=False, allowed_type=None):
        self.allowed_type = allowed_type
        self.default = default
        self.required = required

    def clean(self, value=None):
        default = self.default() if callable(self.default) else self.default
        value = value or default
        self.validate(value)
        return value

    def validate(self, value=None):
        if self.allowed_type and not isinstance(value, self.allowed_type):
            msg = '{} has to be of type {}.'
            raise ValidationError(msg.format(value, self.allowed_type))

        if self.required and value is None:
            raise ValidationError('Field is required.')


class TemplateComponent:
    template_name = None

    def __init__(self, **data):
        assert self.template_name is not None
        self.fields = self.get_fields()
        self.context = {
            k: field.clean(data.get(k)) for k, field in self.fields.items()
        }

    def get_fields(self):
        return {
            k: getattr(self, k) for k in dir(self)
            if isinstance(getattr(self, k), Field)
        }

    def render_with_context(self, context):
        template = get_template(self.template_name)
        return template.render(context=context)

    def render(self):
        return self.render_with_context(self.context)

    def __str__(self):
        return self.render()


class TextBlock(TemplateComponent):
    """
    text_block.html':
    
    <p>{{ text }}</p>
    """
    template_name = 'text_block.html'

    text = Field(required=True)


class BulletList(TemplateComponent):
    """
    bullet_list.html':

    <ul>
        {% for li in list %}
            <li>{{ li }}</li>
        {% endif %}
    </ul>
    """
    template = 'bullet_list.html'

    list = Field(required=True, default=list)


class TestEmail(TemplateComponent):
    """
    emails/test-email.html:

    {{ my_list }}

    Bla

    {{ my_text }}
    """
    template_name = 'emails/test-email.html'

    my_list = Field(required=True, allowed_type=BulletList)
    my_text = Field(required=True, allowed_type=TextBlock)