page.js

const regLayout = /<!-- #layout \b(\w+)\b -->\n([\s\S]*)/;
const regMixin = /<!-- #mixin \b(\w+)\b -->\n([\s\S]*)/;
const regPage0 = /<!-- #page -->\n([\s\S]*)/;
const regPage = /<!-- #page \b(\w+)\b -->\n([\s\S]*)/;
const regPage2 = /<!-- #page \b(\w+)\b \b(\w+)\b -->\n([\s\S]*)/;
const regPageContent = /<!-- #content \b(\w+)\b -->\n?([\s\S]*)/;
const regPageContentNonGreedy = /<!-- #content \b\w+\b -->\n?[\s\S]*?(?=<!-- #content|$)/g;
const regPageContentRest = /([\s\S]*?)(?=<!-- #content|$)/;
const regPageContentRestOptionalNl = /([\s\S]*?)(?=\n?<!-- #content|$)/;

function jener(defs) {
  let layouts = {},
      mixins = {},
      ctx = {
    layouts,
    mixins
  },
      res = [];
  let pages = [];

  for (let i = 0; i < defs.length; i += 2) {
    let filename = defs[i],
        content = defs[i + 1];
    let match;

    if (match = content.match(regPage)) {
      pages.push(filename);
      pages.push(page(match[2], match[1]));
    } else if (match = content.match(regPage0)) {
      pages.push(filename);
      pages.push(page(match[1]));
    } else if (match = content.match(regPage2)) {
      pages.push(filename);
      pages.push(page(match[3], match[1], match[2]));
    } else if (match = content.match(regLayout)) {
      layouts[match[1]] = layout(match[2]);
    } else if (match = content.match(regMixin)) {
      mixins[match[1]] = mixin(match[2]);
    }
  }

  for (let i = 0; i < pages.length; i += 2) {
    res.push(pages[i], genFromPage(ctx, pages[i + 1]));
  }

  return res;
}

function genFromPage(ctx, fsPage) {
  let res = {
    res: ``,
    replace: {}
  };
  fsPage.forEach(f => {
    f(ctx, res);
  });
  return res.res;
}

function layout(layout) {
  let res = [];
  let prematch = layout.match(regPageContentRest);
  res.push(fappend(prematch[1]));
  let matchs = layout.match(regPageContentNonGreedy);
  matchs.forEach(match => {
    let [_, name, text] = match.match(regPageContent);
    res.push(fcontent(name));
    res.push(fappend(text));
  });
  return res;
}

function mixin(mixin) {
  return mixin;
}

function page(page, layout, replace) {
  if (!layout) {
    return [fappend(page)];
  }

  let innerMatch;
  let res = [];

  if (replace) {
    let match = page.match(regPageContentRestOptionalNl);
    res.push(freplace(replace, match[1]));
  }

  let matchs = page.match(regPageContentNonGreedy);

  if (matchs) {
    matchs.forEach(match => {
      let [_, name, body] = match.match(regPageContent);
      res.push(freplace(name, body));
    });
  }

  res.push(flayout(layout));
  return res;
}

function freplace(content, body) {
  return (ctx, res) => {
    res.replace[content] = body;
  };
}

function fappend(body) {
  return (ctx, res) => {
    let {
      mixins
    } = ctx;

    for (let mixin in mixins) {
      let regexStr = `<!-- #include ${mixin} -->\n?`;
      body = body.replace(new RegExp(regexStr), mixins[mixin]);
    }

    res.res += body;
  };
}

function flayout(layout) {
  return (ctx, res) => {
    let {
      layouts
    } = ctx;
    layout = layouts[layout];
    layout.forEach(f => {
      f(ctx, res);
    });
  };
}

function fcontent(name) {
  return (ctx, res) => {
    fappend(res.replace[name])(ctx, res);
  };
}

module.exports = jener;