timetracker/common/components/core.py

"""Node layer: the lazy component tree, its renderer, and media collection.

A FastHTML-style model. Everything renderable is a :class:`Node`. The single
:class:`Element` class represents *any* HTML element (tag + attrs + children);
named builders like ``Div`` / ``Span`` are generated from a whitelist rather
than hand-written per tag (see ``primitives.py``). Higher-level, behaviour- or
media-bearing components subclass :class:`BaseComponent` and implement
``render()`` returning a node subtree.

Nodes are *lazy*: they hold structure and render to HTML only when asked
(``str(node)`` / ``node.__html__()`` / :func:`render`). This is what lets
``Page()`` walk a finished tree and collect every component's declared JS
(:class:`Media`) instead of each view threading ``scripts=`` by hand.

Backwards compatibility: the legacy ``Component(tag_name=...)`` function still
returns a ``SafeText`` string, so existing string-based call sites keep working
during the migration. Its child handling is Node-aware, so a tree mixing old
(string-returning) and new (node-returning) components renders correctly.
"""

import hashlib
from functools import lru_cache

from django.utils.html import escape
from django.utils.safestring import SafeText, mark_safe


HTMLAttribute = tuple[str, str | int | bool]


HTMLTag = str


# ── Media: declarative JS dependencies ──────────────────────────────────────


def _dedup(*sequences: tuple[str, ...]) -> tuple[str, ...]:
    """First-seen dedup that preserves declaration order across sequences."""
    seen: dict[str, None] = {}
    for sequence in sequences:
        for item in sequence:
            seen.setdefault(item, None)
    return tuple(seen)


class Media:
    """A component's JS dependencies, modelled on ``django.forms.Media``.

    ``js`` are static ES-module filenames (rendered as ``ModuleScript``);
    ``js_external`` are vendored UMD / classic bundles (rendered as
    ``StaticScript``). Addition merges with first-seen, order-preserving dedup,
    so a page that uses a component many times emits each script once.
    """

    __slots__ = ("js", "js_external")

    def __init__(
        self,
        js: tuple[str, ...] | list[str] = (),
        js_external: tuple[str, ...] | list[str] = (),
    ) -> None:
        self.js = tuple(js)
        self.js_external = tuple(js_external)

    def __add__(self, other: "Media | None") -> "Media":
        if not other:
            return self
        return Media(
            _dedup(self.js, other.js),
            _dedup(self.js_external, other.js_external),
        )

    def __radd__(self, other: "Media | None") -> "Media":
        # Supports ``sum(medias, Media())`` and ``0 + media``.
        if not other or other == 0:
            return self
        return other.__add__(self)

    def __bool__(self) -> bool:
        return bool(self.js or self.js_external)

    def __eq__(self, other: object) -> bool:
        return (
            isinstance(other, Media)
            and self.js == other.js
            and self.js_external == other.js_external
        )

    def __hash__(self) -> int:
        return hash((self.js, self.js_external))

    def __repr__(self) -> str:
        return f"Media(js={self.js!r}, js_external={self.js_external!r})"


# ── Node tree ────────────────────────────────────────────────────────────────


class Node:
    """Base class for everything renderable to HTML."""

    # Declared dependencies. Class-level default is shared and empty; concrete
    # components override with their own ``Media(...)``.
    media: Media = Media()

    def _render(self) -> str:
        raise NotImplementedError

    def collect_media(self) -> Media:
        """Total media of this node and its subtree."""
        return self.media

    # `__html__` marks the value HTML-safe for Django (conditional_escape).
    # `__str__` lets f-strings, ``str()`` and ``"".join(str(...))`` render the
    # node — the bridge that keeps most existing composition working.
    def __html__(self) -> str:
        return self._render()

    def __str__(self) -> str:
        return self._render()


def _child_key(child: object) -> tuple[str, bool]:
    """Normalise a child to a ``(text, is_safe)`` pair.

    Nodes render to safe HTML; ``SafeText`` (and anything exposing ``__html__``)
    is already safe; plain strings are escaped. ``is_safe`` is part of the
    render cache key so a safe ``"<b>"`` and an unsafe ``"<b>"`` never collide.
    """
    if isinstance(child, Node):
        return (child._render(), True)
    if isinstance(child, str):
        return (child, isinstance(child, SafeText))
    if hasattr(child, "__html__"):
        return (child.__html__(), True)
    return (str(child), False)


@lru_cache(maxsize=4096)
def _render_element(
    tag_name: str,
    attrs_key: tuple[tuple[str, str], ...],
    children_key: tuple[tuple[str, bool], ...],
) -> str:
    """Pure, memoized HTML builder. Identical (tag, attrs, children) render once.

    ``attrs_key`` is (name, stringified value) pairs (values always escaped);
    ``children_key`` is (text, is_safe) pairs (safe passes through, else escaped).
    """
    children_blob = "\n".join(
        child if is_safe else escape(child) for child, is_safe in children_key
    )
    if attrs_key:
        attributes_blob = " " + " ".join(
            f'{name}="{escape(value)}"' for name, value in attrs_key
        )
    else:
        attributes_blob = ""
    return f"<{tag_name}{attributes_blob}>{children_blob}</{tag_name}>"


class Element(Node):
    """Any HTML element: a tag name, attributes and children.

    Children may be other nodes, ``SafeText``, or plain strings (escaped).
    Rendering goes through the memoized :func:`_render_element`.
    """

    def __init__(
        self,
        tag_name: str,
        attributes: list[HTMLAttribute] | None = None,
        children: "list | Node | str | None" = None,
    ) -> None:
        if not tag_name:
            raise ValueError("tag_name is required.")
        self.tag_name = tag_name
        self.attributes = attributes or []
        if children is None:
            children = []
        elif isinstance(children, (str, Node)):
            children = [children]
        self.children = children

    def collect_media(self) -> Media:
        media = self.media
        for child in self.children:
            if isinstance(child, Node):
                media = media + child.collect_media()
        return media

    def _render(self) -> str:
        attrs_key = tuple((name, str(value)) for name, value in self.attributes)
        children_key = tuple(_child_key(child) for child in self.children)
        return _render_element(self.tag_name, attrs_key, children_key)


class Safe(Node):
    """A node wrapping pre-rendered, trusted HTML (the ``mark_safe`` analogue).

    Used as the migration bridge for components still built from f-strings:
    they return ``Safe(html)`` and declare their ``media`` explicitly rather
    than atomising their markup into a node tree up front.
    """

    def __init__(self, html: object, media: Media | None = None) -> None:
        self._html = str(html)
        if media is not None:
            self.media = media

    def _render(self) -> str:
        return self._html


class Fragment(Node):
    """An ordered group of children with no wrapping tag.

    Replaces ``mark_safe(str(a) + str(b))`` / ``"\\n".join(...)`` composition,
    so media still bubbles up from the grouped children.
    """

    def __init__(self, *children: object, separator: str = "") -> None:
        self.children = [c for c in children if c is not None and c != ""]
        self.separator = separator

    def collect_media(self) -> Media:
        media = Media()
        for child in self.children:
            if isinstance(child, Node):
                media = media + child.collect_media()
        return media

    def _render(self) -> str:
        parts = []
        for child in self.children:
            text, is_safe = _child_key(child)
            parts.append(text if is_safe else escape(text))
        return self.separator.join(parts)


class BaseComponent(Node):
    """Base for higher-level components: implement ``render()`` returning a node
    subtree and declare ``media`` (a :class:`Media`).

    ``render()`` is called once and memoized; ``collect_media()`` returns this
    component's own media merged with the rendered subtree's.
    """

    def render(self) -> Node:
        raise NotImplementedError

    def _tree(self) -> Node:
        cached = getattr(self, "_tree_cache", None)
        if cached is None:
            cached = self.render()
            self._tree_cache = cached
        return cached

    def _render(self) -> str:
        return self._tree()._render()

    def collect_media(self) -> Media:
        return self.media + self._tree().collect_media()


def render(node: "Node | str") -> SafeText:
    """Render a node (or pass a string through) to safe HTML."""
    if isinstance(node, Node):
        return mark_safe(node._render())
    return mark_safe(str(node))


def collect_media(node: "Node | str") -> Media:
    """Collect the media of a node tree (empty for a bare string)."""
    if isinstance(node, Node):
        return node.collect_media()
    return Media()


def Component(
    attributes: list[HTMLAttribute] | None = None,
    children: "list[HTMLTag] | HTMLTag | None" = None,
    tag_name: str = "",
) -> SafeText:
    """Legacy element builder: returns a ``SafeText`` string.

    Kept for backwards compatibility while call sites migrate to :class:`Element`
    and the generated tag builders. Child handling is Node-aware, so a tree that
    mixes string-returning and node-returning components still renders correctly.
    """
    return render(Element(tag_name, attributes, children))


def randomid(seed: str = "", content: str = "", length: int = 10) -> str:
    if not seed and not content:
        return seed
    hash_input = f"{seed}:{content}" if seed else content
    content_hash = hashlib.sha1(hash_input.encode()).hexdigest()
    base = (
        content_hash[:length]
        if not seed
        else content_hash[: max(0, length - len(seed))]
    )
    return seed + base