from mkdocs.structure.pages import Page
from mkdocs.structure.files import Files
from mkdocs.exceptions import PluginError
import os
from mkdocs.utils import write_file

REDIRECTS = dict()

def on_pre_build(config):
    REDIRECTS.clear()

def on_page_markdown(markdown, page: Page, config, files: Files):
    if not (redirects := page.meta.get("redirects")):
        return

    for redirect in redirects:
        if files.get_file_from_path(redirect):
            raise PluginError(f"Cannnot redirect to {page.url}, source {redirect} already exists")

        if redirect in REDIRECTS:
            raise PluginError(f"Redirect from {redirect} already exists: {REDIRECTS[redirect]}")

        REDIRECTS[redirect] = f"/{page.url}"


def on_post_build(config):
    redirect_file = os.path.join(config["site_dir"], ".config", "redirects.txt")

    redirects = "\n".join(
        f"{src}\t{dest};"
        for src, dest in REDIRECTS.items()
    )

    write_file(redirects.encode(), redirect_file)