"""The page constructs the generator writes, in the syntax of the site engine.

Every block that is not plain Markdown (a callout, a collapsible block, OS
tabs, a button, a card grid) is written through one of these functions, so
the generator holds no engine syntax of its own. Bodies are passed without
indentation: the function indents them as the engine reads them.

The site is built with Astro Starlight. The MkDocs Material syntax the site
was first written in stays as one thing only: the yardstick of the size
budgets that split long pages (system pages, platform sections). Those
budgets were set on that Markdown, and measuring it keeps every page cut
at the same file, so no card changes address.
"""

from __future__ import annotations

import html
import re
from collections.abc import Iterator
from contextlib import contextmanager

ENGINES = ("mkdocs", "starlight")
_engine = "starlight"

# Material's callout kinds, by the role Starlight gives them.
ASIDE_ROLES = {
    "note": "note", "info": "note", "abstract": "note", "example": "note",
    "question": "note", "quote": "note", "tip": "tip", "success": "tip",
    "warning": "caution", "failure": "danger", "danger": "danger", "bug": "danger",
}

# The attribute that keeps an element out of the site search.
SEARCH_EXCLUDE = {"mkdocs": "data-search-exclude", "starlight": "data-pagefind-ignore"}


def set_engine(name: str) -> None:
    global _engine
    if name not in ENGINES:
        raise ValueError(f"unknown site engine {name!r}, expected one of {ENGINES}")
    _engine = name


def engine() -> str:
    return _engine


@contextmanager
def using(name: str) -> Iterator[None]:
    """Write in another syntax for a while: a page split by size is
    measured in the MkDocs Markdown its budgets were set on."""
    previous = _engine
    set_engine(name)
    try:
        yield
    finally:
        set_engine(previous)


def starlight() -> bool:
    return _engine == "starlight"


def search_exclude() -> str:
    return SEARCH_EXCLUDE[_engine]


def inline_html(text: str) -> str:
    """Inline Markdown (code, bold, links) for text placed inside raw HTML,
    where Markdown is not read."""
    parts = re.split(r"(`[^`]+`)", text)
    out = []
    for part in parts:
        if part.startswith("`") and part.endswith("`") and len(part) > 1:
            out.append(f"<code>{html.escape(part[1:-1], quote=False)}</code>")
            continue
        part = html.escape(part, quote=False)
        part = re.sub(r"\*\*([^*]+)\*\*", r"<strong>\1</strong>", part)
        part = re.sub(r"\[([^\]]+)\]\(([^)\s]+)\)", r'<a href="\2">\1</a>', part)
        out.append(part)
    return "".join(out)


def _indented(lines: list[str], pad: str) -> list[str]:
    return [f"{pad}{line}" if line.strip() else "" for line in lines]


def _trim(lines: list[str]) -> list[str]:
    start, end = 0, len(lines)
    while start < end and not lines[start].strip():
        start += 1
    while end > start and not lines[end - 1].strip():
        end -= 1
    return list(lines[start:end])


def aside(kind: str, title: str, body: list[str], indent: str = "") -> list[str]:
    """A callout that is always open."""
    body = _trim(body)
    if _engine == "mkdocs":
        return [f'{indent}!!! {kind} "{title}"', "", *_indented(body, indent + "    "), ""]
    label = title.replace("[", "\\[").replace("]", "\\]")
    fence = "::::" if any(line.lstrip().startswith(":::") for line in body) else ":::"
    return [f"{indent}{fence}{ASIDE_ROLES.get(kind, 'note')}[{label}]",
            *_indented(body, indent), f"{indent}{fence}", ""]


def details(kind: str, title: str, body: list[str], indent: str = "", opened: bool = False) -> list[str]:
    """A collapsible block, closed unless *opened*."""
    body = _trim(body)
    if _engine == "mkdocs":
        marker = "???+" if opened else "???"
        return [f'{indent}{marker} {kind} "{title}"', "", *_indented(body, indent + "    "), ""]
    role = ASIDE_ROLES.get(kind, "note")
    state = " open" if opened else ""
    return [
        f'{indent}<details class="rb-details rb-details-{role}"{state}>',
        f"{indent}<summary>{inline_html(title)}</summary>",
        "",
        *_indented(body, indent),
        "",
        f"{indent}</details>",
        "",
    ]


def tabs(items: list[tuple[str, list[str]]], indent: str = "", sync: str = "os") -> list[str]:
    """Content tabs. Tabs that share a label share the reader's choice
    across pages."""
    lines: list[str] = []
    if _engine == "mkdocs":
        for label, body in items:
            lines += [f'{indent}=== "{label}"', "", *_indented(_trim(body), indent + "    "), ""]
        return lines
    lines.append(f'{indent}<Tabs syncKey="{sync}">')
    for label, body in items:
        lines += [f'{indent}<TabItem label="{html.escape(label)}">', "",
                  *_indented(_trim(body), indent), "", f"{indent}</TabItem>"]
    return [*lines, f"{indent}</Tabs>", ""]


def button(text: str, target: str, primary: bool = False) -> str:
    """A link drawn as a button."""
    if _engine == "mkdocs":
        classes = ".md-button .md-button--primary" if primary else ".md-button"
        return f"[{text}]({target}){{ {classes} }}"
    classes = "rb-button rb-button-primary" if primary else "rb-button"
    return f'<a class="{classes}" href="{html.escape(target)}">{inline_html(text)}</a>'


def image(alt: str, src: str, **attributes: str) -> str:
    """An image with HTML attributes (width, align)."""
    if _engine == "mkdocs":
        attrs = " ".join(f"{key}={value}" for key, value in attributes.items())
        return f"![{alt}]({src}){{ {attrs} }}"
    attrs = "".join(f' {key}="{html.escape(str(value))}"' for key, value in attributes.items())
    return f'<img src="{html.escape(src)}" alt="{html.escape(alt)}"{attrs}>'


def hash_value(value: object) -> str:
    """A hash printed whole, in the hash style. One element under Starlight:
    a span around a code span was 1,400 extra elements on a page of cards."""
    text = str(value).replace("`", "'")
    if _engine == "mkdocs":
        return f'<span class="rb-hash">`{text}`</span>'
    return f'<code class="rb-hash">{html.escape(text, quote=False)}</code>'


def block_open(tag: str, attributes: str = "") -> str:
    """The opening tag of an HTML block whose content is Markdown."""
    attributes = f" {attributes.strip()}" if attributes.strip() else ""
    if _engine == "mkdocs":
        return f"<{tag}{attributes} markdown>"
    return f"<{tag}{attributes}>"


def card_grid(cards: list[tuple[str, list[str]]]) -> list[str]:
    """Cards in a grid: a bold title line and a body each."""
    lines = [block_open("div", 'class="grid cards"' if _engine == "mkdocs" else 'class="rb-cards"'), ""]
    for title, body in cards:
        if _engine == "mkdocs":
            lines += [f"-   **{title}**", "", *_indented(_trim(body), "    "), ""]
        else:
            lines += ['<div class="rb-card">', "", f"**{title}**", "", *_trim(body), "", "</div>", ""]
    return [*lines, "</div>", ""]


def steps(items: list[str]) -> list[str]:
    """An ordered list drawn as numbered steps."""
    return [block_open("div", 'class="rb-steps"'), "",
            *(f"{number}. {item}" for number, item in enumerate(items, 1)), "", "</div>", ""]


def heading_attributes(anchor: str = "", classes: str = "", search: bool = True) -> str:
    """The attribute block of a heading: its id, classes, and whether the
    search reads it."""
    parts = [f"#{anchor}" if anchor else "", *(f".{c}" for c in classes.split())]
    if not search:
        parts.append(search_exclude())
    parts = [part for part in parts if part]
    return f" {{ {' '.join(parts)} }}" if parts else ""


def site_href(path: str) -> str:
    """A link to a site address written in raw HTML (``files/?sha1=...``),
    which no Markdown resolution reaches: rooted at the site under Starlight,
    relative to a page two levels deep under MkDocs."""
    if _engine == "mkdocs":
        return f"../../{path}"
    return f"/retrobios/{path}"