/* SPDX-License-Identifier: Apache-2.0
 *
 * The documentation reader.
 *
 * Renders the project's Markdown in the site's own theme, so the docs can be
 * read without leaving the page and without a build step. No dependency: the
 * parser below handles exactly what docs/ actually uses -- headings, fenced
 * code, tables, lists, quotes, and inline marks. Pulling in a 40 KB Markdown
 * library to render 29 files would outweigh every other asset here combined.
 *
 * Everything is escaped before any tag is emitted. The only HTML that reaches
 * the page is HTML this file wrote.
 */
(function () {
  "use strict";

  /* ---- the index ---------------------------------------------------- */

  var DOCS = [
    { group: "Start here", items: [
      ["README.md",                   "Overview"],
      ["plan/1.0.md",                 "The 1.0 definition"],
      ["licensing.md",                "Licensing"]
    ]},
    { group: "Architecture", items: [
      ["architecture/README.md",      "The system, layer by layer"],
      ["architecture/boot.md",        "Boot"],
      ["architecture/kernel.md",      "Kernel"],
      ["architecture/syscalls.md",    "Syscalls"],
      ["architecture/filesystem.md",  "The VFS"],
      ["architecture/schfs.md",       "SchFS"],
      ["architecture/terminals.md",   "Virtual terminals"],
      ["architecture/devices.md",     "Device model"],
      ["architecture/usb.md",         "USB"],
      ["architecture/graphics.md",    "Graphics"],
      ["architecture/networking.md",  "Networking"],
      ["architecture/init.md",        "init"]
    ]},
    { group: "Guides", items: [
      ["guides/building.md",          "Building"],
      ["guides/testing.md",           "Testing"],
      ["guides/layout.md",            "Tree layout"],
      ["guides/adding-a-driver.md",   "Adding a driver"]
    ]},
    { group: "Plan", items: [
      ["plan/README.md",              "What plan/ is for"],
      ["plan/roadmap.md",             "Roadmap"],
      ["plan/foundations.md",         "Foundations"],
      ["plan/init.md",                "schinit"],
      ["plan/wayland.md",             "Wayland"],
      ["plan/hybrid.md",              "Hybrid kernel"],
      ["plan/schapi.md",              "SchAPI"]
    ]},
    { group: "History", items: [
      ["history/README.md",           "Why history/ exists"],
      ["history/kernel.md",           "Kernel"],
      ["history/schfs.md",            "SchFS"],
      ["history/moving-to-linux.md",  "Moving to Linux"]
    ]},
    { group: "Branding", items: [
      ["branding/README.md",          "The three marks"]
    ]}
  ];

  /* ---- helpers ------------------------------------------------------- */

  function esc(s) {
    return s.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
  }

  /* Resolve a doc-relative link against the doc it appeared in, so
     "../history/schfs.md" inside architecture/ lands on history/schfs.md. */
  function resolve(from, href) {
    var base = from.split("/").slice(0, -1);
    var parts = href.split("/");
    for (var i = 0; i < parts.length; i++) {
      if (parts[i] === "." || parts[i] === "") continue;
      if (parts[i] === "..") base.pop();
      else base.push(parts[i]);
    }
    return base.join("/");
  }

  /* encodeURIComponent turns every "/" into %2F, which works but makes a
     shared link unreadable. Slashes are legal in a query value, so keep them. */
  function docHref(p) {
    return "?doc=" + encodeURIComponent(p).replace(/%2F/g, "/");
  }

  function slug(s) {
    return s.toLowerCase().replace(/[^\w\s-]/g, "").trim().replace(/\s+/g, "-");
  }

  /* ---- inline marks --------------------------------------------------- */

  /* U+0001 as the placeholder sentinel: it cannot occur in a Markdown source
     file, so a code span lifted out here can never be confused with document
     text when it is put back. */
  var SENTINEL = "\u0001";

  function inline(s, from) {
    /* Code spans come out first and go back last, so nothing inside a backtick
       pair is mistaken for emphasis or for a link. */
    var spans = [];
    s = s.replace(/`([^`]+)`/g, function (_, code) {
      spans.push("<code>" + esc(code) + "</code>");
      return SENTINEL + (spans.length - 1) + SENTINEL;
    });

    s = esc(s);

    s = s.replace(/!\[([^\]]*)\]\(([^)\s]+)[^)]*\)/g, function (_, alt, src) {
      return '<img src="' + encodeURI(src) + '" alt="' + alt + '">';
    });

    s = s.replace(/\[([^\]]+)\]\(([^)\s]+)[^)]*\)/g, function (_, text, href) {
      if (/^https?:/.test(href))
        return '<a href="' + encodeURI(href) + '" target="_blank" rel="noopener">' + text + "</a>";
      if (href.charAt(0) === "#")
        return '<a href="' + encodeURI(href) + '">' + text + "</a>";
      if (/\.md($|#)/.test(href)) {
        var cut  = href.indexOf("#");
        var hash = cut >= 0 ? href.slice(cut) : "";
        var path = cut >= 0 ? href.slice(0, cut) : href;
        return '<a href="' + docHref(resolve(from, path)) + hash + '">' + text + "</a>";
      }
      /* Anything else is a file in the repo rather than a document. Link at it
         relative to docs/, which is where this page's ../ points. */
      return '<a href="../' + encodeURI(resolve(from, href)) + '">' + text + "</a>";
    });

    s = s.replace(/\*\*([^*]+)\*\*/g, "<strong>$1</strong>");
    s = s.replace(/(^|[^*])\*([^*\n]+)\*/g, "$1<em>$2</em>");

    var restore = new RegExp(SENTINEL + "(\\d+)" + SENTINEL, "g");
    return s.replace(restore, function (_, n) { return spans[+n]; });
  }

  /* ---- blocks --------------------------------------------------------- */

  function render(md, from, headings) {
    md = md.replace(/\r\n?/g, "\n").replace(/<!--[\s\S]*?-->/g, "");
    var L = md.split("\n"), out = [], i = 0, m;

    function listBlock(ordered) {
      var tag = ordered ? "ol" : "ul", items = [];
      while (i < L.length) {
        var li = L[i].match(ordered ? /^\s*\d+\.\s+(.*)$/ : /^\s*[-*+]\s+(.*)$/);
        if (!li) {
          /* an indented continuation line belongs to the item above it */
          if (items.length && /^\s+\S/.test(L[i])) {
            items[items.length - 1] += " " + L[i].trim();
            i++;
            continue;
          }
          break;
        }
        items.push(li[1]);
        i++;
      }
      out.push("<" + tag + ">");
      items.forEach(function (t) { out.push("<li>" + inline(t, from) + "</li>"); });
      out.push("</" + tag + ">");
    }

    function cells(row) {
      return row.replace(/^\s*\|/, "").replace(/\|\s*$/, "").split("|")
                .map(function (c) { return c.trim(); });
    }

    while (i < L.length) {
      var line = L[i];

      if (!line.trim()) { i++; continue; }

      /* fenced code */
      if (/^\s*```/.test(line)) {
        var lang = line.replace(/^\s*```/, "").trim(), buf = [];
        i++;
        while (i < L.length && !/^\s*```/.test(L[i])) buf.push(L[i++]);
        i++;
        out.push('<pre class="code"' + (lang ? ' data-lang="' + esc(lang) + '"' : "") +
                 "><code>" + esc(buf.join("\n")) + "</code></pre>");
        continue;
      }

      /* table: a pipe row followed by a separator row */
      if (/^\s*\|/.test(line) && /^\s*\|?[\s:|-]+$/.test(L[i + 1] || "") && /-/.test(L[i + 1] || "")) {
        var head = cells(line);
        i += 2;
        out.push('<div class="tablewrap"><table><thead><tr>');
        head.forEach(function (c) { out.push("<th>" + inline(c, from) + "</th>"); });
        out.push("</tr></thead><tbody>");
        while (i < L.length && /^\s*\|/.test(L[i])) {
          out.push("<tr>");
          cells(L[i++]).forEach(function (c) { out.push("<td>" + inline(c, from) + "</td>"); });
          out.push("</tr>");
        }
        out.push("</tbody></table></div>");
        continue;
      }

      /* heading */
      if ((m = line.match(/^(#{1,6})\s+(.*?)\s*#*$/))) {
        var lvl = m[1].length, text = m[2], id = slug(text);
        if (lvl <= 3) headings.push({ level: lvl, text: text, id: id });
        out.push("<h" + lvl + ' id="' + id + '">' + inline(text, from) + "</h" + lvl + ">");
        i++;
        continue;
      }

      /* rule */
      if (/^\s*(-{3,}|\*{3,}|_{3,})\s*$/.test(line)) { out.push("<hr>"); i++; continue; }

      /* blockquote */
      if (/^\s*>/.test(line)) {
        var q = [];
        while (i < L.length && /^\s*>/.test(L[i])) q.push(L[i++].replace(/^\s*>\s?/, ""));
        out.push("<blockquote>" + render(q.join("\n"), from, []) + "</blockquote>");
        continue;
      }

      if (/^\s*[-*+]\s+/.test(line)) { listBlock(false); continue; }
      if (/^\s*\d+\.\s+/.test(line)) { listBlock(true);  continue; }

      /* paragraph: runs to the next blank line or block opener */
      var para = [];
      while (i < L.length && L[i].trim() &&
             !/^\s*(```|>|#{1,6}\s|[-*+]\s|\d+\.\s|\|)/.test(L[i]) &&
             !/^\s*(-{3,}|\*{3,}|_{3,})\s*$/.test(L[i])) {
        para.push(L[i++]);
      }
      if (para.length) out.push("<p>" + inline(para.join(" "), from) + "</p>");
      else i++;   /* a block opener we do not handle: never spin on it */
    }
    return out.join("\n");
  }

  /* ---- the page ------------------------------------------------------- */

  var nav     = document.getElementById("docnav");
  var article = document.getElementById("doc");
  var tocEl   = document.getElementById("toc");

  function buildNav() {
    DOCS.forEach(function (g) {
      var h = document.createElement("p");
      h.className = "navgroup";
      h.textContent = g.group;
      nav.appendChild(h);
      var ul = document.createElement("ul");
      g.items.forEach(function (it) {
        var li = document.createElement("li");
        var a = document.createElement("a");
        a.href = docHref(it[0]);
        a.textContent = it[1];
        a.dataset.path = it[0];
        li.appendChild(a);
        ul.appendChild(li);
      });
      nav.appendChild(ul);
    });
  }

  function markCurrent(path) {
    Array.prototype.forEach.call(nav.querySelectorAll("a"), function (a) {
      a.classList.toggle("on", a.dataset.path === path);
    });
  }

  function buildToc(headings) {
    tocEl.innerHTML = "";
    var real = headings.filter(function (h) { return h.level >= 2; });
    if (real.length < 2) { tocEl.hidden = true; return; }
    tocEl.hidden = false;
    var t = document.createElement("p");
    t.className = "navgroup";
    t.textContent = "On this page";
    tocEl.appendChild(t);
    var ul = document.createElement("ul");
    real.forEach(function (h) {
      var li = document.createElement("li");
      li.className = "lvl" + h.level;
      var a = document.createElement("a");
      a.href = "#" + h.id;
      a.textContent = h.text;
      li.appendChild(a);
      ul.appendChild(li);
    });
    tocEl.appendChild(ul);
  }

  function fail(title, body) {
    article.innerHTML = "<h1>" + title + "</h1>" + body;
    tocEl.hidden = true;
  }

  function load(path) {
    markCurrent(path);
    document.title = "Docs — SchOS";
    article.setAttribute("aria-busy", "true");

    fetch("../" + path).then(function (r) {
      if (!r.ok) throw new Error(r.status + " " + r.statusText);
      return r.text();
    }).then(function (text) {
      var headings = [];
      article.innerHTML = render(text, path, headings);
      buildToc(headings);
      article.removeAttribute("aria-busy");
      if (headings.length) document.title = headings[0].text + " — SchOS docs";
      var hash = location.hash.slice(1);
      var target = hash && document.getElementById(hash);
      if (target) target.scrollIntoView();
      else window.scrollTo(0, 0);
    }).catch(function (e) {
      article.removeAttribute("aria-busy");
      /* The common case, and worth naming precisely: browsers refuse fetch()
         on file:// for the same reason they refuse it cross-origin, so this
         one page needs a server even though nothing here is dynamic. */
      if (location.protocol === "file:") {
        fail("This page needs a local server",
             "<p>Browsers block <code>fetch()</code> on <code>file://</code> URLs, so the " +
             "reader cannot load the Markdown. The rest of the site works from a file; " +
             "this page does not. Serve the repository root:</p>" +
             '<pre class="code"><code>cd /home/nexoniarz/Dokumenty/Projects/SchOS\n' +
             "python3 -m http.server 8000</code></pre>" +
             "<p>Then open <code>http://localhost:8000/docs/Website/docs.html</code>.</p>" +
             '<p>Or read this one directly: <a href="../' + esc(path) + '">' + esc(path) + "</a></p>");
      } else {
        fail("Could not load that document",
             "<p><code>" + esc(path) + "</code> — " + esc(e.message) + "</p>" +
             '<p><a href="?doc=README.md">Back to the overview</a></p>');
      }
    });
  }

  function pathFromUrl() {
    var m = /[?&]doc=([^&#]+)/.exec(location.search);
    var p = m ? decodeURIComponent(m[1]) : "README.md";
    /* Only ever load something that is in the index above. */
    var known = DOCS.some(function (g) {
      return g.items.some(function (it) { return it[0] === p; });
    });
    return known ? p : "README.md";
  }

  buildNav();
  load(pathFromUrl());

  /* Intercept in-page navigation so the reader does not reload its own shell. */
  document.addEventListener("click", function (ev) {
    var a = ev.target.closest ? ev.target.closest("a") : null;
    if (!a || ev.metaKey || ev.ctrlKey || ev.shiftKey || a.target) return;
    var href = a.getAttribute("href") || "";
    if (href.indexOf("?doc=") !== 0) return;
    ev.preventDefault();
    history.pushState(null, "", href);
    load(pathFromUrl());
  });

  window.addEventListener("popstate", function () { load(pathFromUrl()); });
})();