"""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 engine is Astro Starlight. MkDocs Material is kept while the two builds
are compared page by page, selected with set_engine("mkdocs").
"""

from __future__ import annotations

import html
import re
from contextlib import contextmanager

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

# 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):
    """Write in another engine's syntax for a while. A page split by size
    is measured in the MkDocs Markdown its budgets were tuned on, so both
    engines cut the same pages at the same files."""
    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}"