<?php

declare(strict_types=1);

/**
 * The handbook as plain Markdown, one page per request.
 *
 *   llms.php                  index: every page with a summary and its size
 *   llms.php?doc=KEY          one chapter, as written
 *   llms.php?code=PATH        one source file
 *
 * Apache also answers llms.txt for the index, see .htaccess. That alias is a
 * convenience, not the canonical address: it needs mod_rewrite, and this file
 * has to work without it.
 *
 * This is the rendering meant for agents. It exists separately from index.php
 * so that a fetch costs only the page that was asked for: the index says what
 * each page contains and how large it is, and names the pages a given job
 * needs, so nothing has to be pulled in on the chance it might be relevant.
 */

require_once __DIR__ . "/inc/handbook.php";

$requestedDoc = isset($_GET["doc"]) ? (string) $_GET["doc"] : "";
$requestedCode = isset($_GET["code"]) ? (string) $_GET["code"] : "";

if ($requestedDoc === "" && $requestedCode === "") {
    handbookSendText(handbookRenderIndex());
}

$page = $requestedDoc !== ""
    ? handbookPage("doc", $requestedDoc)
    : handbookPage("code", $requestedCode);

if ($page === null) {
    http_response_code(404);
    handbookSendText(
        "# Not Found\n\n"
        . "This page doesn't exist. The index of every page is at\n"
        . handbookSelfUrl() . "/llms.php\n",
    );
}

// Chapters link each other by file name; inside this rendering the neighbour
// is another llms.php page, so a following request stays in plain Markdown.
handbookSendText(
    rtrim(handbookPageMarkdown($page, "llms.php")) . "\n\n"
    . "---\n\n"
    . "Index of every page: " . handbookSelfUrl() . "/llms.php\n"
    . "This page for humans: " . handbookPageUrl($page) . "\n",
);

/** Emits a Markdown document and ends the request. */
function handbookSendText(string $text): void
{
    header("Content-Type: text/plain; charset=utf-8");
    header("Content-Length: " . (string) strlen($text));
    header("X-Content-Type-Options: nosniff");
    // Cheap to rebuild, but an agent walking several pages should not pay for
    // a revalidation on each one.
    header("Cache-Control: public, max-age=300");

    echo $text;
    exit;
}

/**
 * The index: what exists, how big it is, and which pages a given job needs.
 */
function handbookRenderIndex(): string
{
    $self = handbookSelfUrl();
    $docs = handbookPagesOfKind("doc");
    $code = handbookPagesOfKind("code");

    $total = 0;
    foreach (handbookPages() as $page) {
        $total += $page["bytes"];
    }

    $out = [];
    $out[] = strtr(handbookRead(HANDBOOK_CONTENT_DIR . "/llms-intro.md"), [
        "{{SELF_URL}}" => $self,
        "{{BASE_URL}}" => handbookBaseUrl(),
        "{{PAGE_COUNT}}" => (string) count(handbookPages()),
        "{{TOTAL_SIZE}}" => handbookFormatBytes($total),
    ]);

    // ---- Recipes: the shortlist per job ------------------------------------
    $out[] = "## What Each Page Is For\n";
    foreach (handbookRecipes() as $recipe) {
        $lines = ["### " . $recipe["title"], "", $recipe["note"], ""];

        foreach ($recipe["pages"] as [$kind, $key]) {
            $page = handbookPage($kind, $key);
            if ($page === null) {
                continue;
            }
            $lines[] = "- " . handbookRawUrl($page) . " – " . $page["title"];
        }

        $out[] = implode("\n", $lines) . "\n";
    }

    // ---- Every page --------------------------------------------------------
    $out[] = handbookRenderList(
        "## Documentation",
        "Chapters in the recommended reading order.",
        $docs,
    );

    $out[] = "## Interface\n\n"
        . "- " . $self . "/openapi.php – OpenAPI 3.1 of the Manage server's four endpoints, "
        . "as JSON. Read together with the *Protocol v1* chapter for a custom client.\n"
        . "- " . $self . "/api.php – the same description in Swagger UI. A page for "
        . "humans, no use to a program.\n";

    $out[] = handbookRenderList(
        "## Source Code",
        "The complete client package, every file individually retrievable. Integrating it "
        . "needs the folder `manage-client/`; `examples/`, `docs/` and `scripts/` "
        . "are not part of that.",
        $code,
    );

    $vendored = handbookVendoredFiles();
    if ($vendored !== []) {
        $lines = ["## Not Reproduced Here", "", "Third-party libraries that are part of the "
            . "package but don't have a page here:", ""];
        foreach ($vendored as $relative => $bytes) {
            $lines[] = "- `client-package/" . $relative . "` (" . handbookFormatBytes($bytes) . ")";
        }
        $out[] = implode("\n", $lines) . "\n";
    }

    return implode("\n", $out);
}

/** @param array<string, array> $pages */
function handbookRenderList(string $heading, string $intro, array $pages): string
{
    $lines = [$heading, "", $intro, ""];

    foreach ($pages as $page) {
        $lines[] = "- " . handbookRawUrl($page)
            . " (" . handbookFormatBytes($page["bytes"]) . ")"
            . " – **" . $page["title"] . "**"
            . ($page["summary"] !== "" ? ". " . $page["summary"] : "");
    }

    return implode("\n", $lines) . "\n";
}