"""Jinja2-based attribute templating with ``..`` / ``...`` parent access.

Syntax inside ``{{ }}`` expressions:
  - ``..``       → immediate parent      (alias ``p1``)
  - ``...``      → parent of parent      (alias ``p2``)
  - ``....``     → great-grandparent     (alias ``p3``)
  - ``service``  → the Service instance
  - ``index``    → 0-based index within a ``quantity`` loop

Example::

    attrs:
      name: "rtr-{{ service.tenant.slug }}-{{ index + 1 }}"
      site: "{{ ..site.pk }}"          # parent device's site PK
      notes: "{{ ...region.slug }}"     # grandparent region slug
"""

import re

from jinja2.sandbox import SandboxedEnvironment

_DOT_RE = re.compile(r"(?<![.\w])\.{2,}")

_env = SandboxedEnvironment(
    variable_start_string="{{",
    variable_end_string="}}",
    autoescape=False,
)


def preprocess_dots(s):
    """Replace ``..`` → ``p1.``, ``...`` → ``p2.``, etc.

    Runs of 2+ dots not preceded by a word char or dot are replaced.
    This preserves single dots (attribute access, IP addresses like
    ``10.0.0.1``) and literal strings without ``{{ }}``.
    """
    def replacer(m):
        depth = len(m.group(0)) - 1
        return f"p{depth}."

    return _DOT_RE.sub(replacer, s)


def _build_jinja_ctx(service, ancestors, index):
    ctx = {"service": service, "index": index}
    for i, obj in enumerate(ancestors):
        ctx[f"p{i + 1}"] = obj
    return ctx


def render_value(value, service, ancestors, index):
    """Render a single attribute value.

    Strings are preprocessed (``..`` → ``p1.``) then Jinja2-rendered.
    Non-strings (int, bool, list, dict) are returned as-is.
    """
    if not isinstance(value, str):
        return value

    if "{{" not in value:
        return value

    processed = preprocess_dots(value)
    template = _env.from_string(processed)
    return template.render(**_build_jinja_ctx(service, ancestors, index))


def render_attrs(attrs, service, ancestors, index):
    """Render all values in an attrs dict.

    *ancestors* is a list where ``ancestors[0]`` is the immediate parent,
    ``ancestors[1]`` is the grandparent, etc.
    """
    if not attrs:
        return {}
    return {
        key: render_value(val, service, ancestors, index)
        for key, val in attrs.items()
    }