/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

// A remark plugin that fills fenced code blocks from real example files, so the
// snippets shown in the docs are slices of code that CI actually compiles and
// runs. Usage in markdown:
//
//   ```rust file=core/examples/getting-started/src/main.rs region=quickstart
//   ```
//
// `file` is resolved from the repository root. `region` (optional) extracts the
// lines between `ANCHOR: <name>` and `ANCHOR_END: <name>` markers in the file —
// language-agnostic, so it works with //, #, --, etc. Without a region, the
// whole file is used with any leading license-header comment block stripped.

const fs = require("fs");
const path = require("path");

// website/plugins -> website -> repository root.
const ROOT = path.resolve(__dirname, "..", "..");

function parseMeta(meta) {
  const out = {};
  for (const m of meta.matchAll(/(\w+)=("[^"]*"|\S+)/g)) {
    out[m[1]] = m[2].replace(/^"|"$/g, "");
  }
  return out;
}

function dedent(lines) {
  const indents = lines
    .filter((l) => l.trim().length > 0)
    .map((l) => l.match(/^[ \t]*/)[0].length);
  const min = indents.length ? Math.min(...indents) : 0;
  return lines.map((l) => l.slice(min));
}

function extractRegion(content, region, file) {
  const lines = content.split("\n");
  const start = new RegExp(`ANCHOR:\\s*${region}\\b`);
  const end = new RegExp(`ANCHOR_END:\\s*${region}\\b`);
  let from = -1;
  let to = -1;
  for (let i = 0; i < lines.length; i++) {
    if (from === -1 && start.test(lines[i])) {
      from = i + 1;
    } else if (from !== -1 && end.test(lines[i])) {
      to = i;
      break;
    }
  }
  if (from === -1 || to === -1) {
    throw new Error(`remark-include-code: region "${region}" not found in ${file}`);
  }
  return dedent(lines.slice(from, to)).join("\n").replace(/^\n+|\s+$/g, "");
}

function stripLicenseHeader(content) {
  // Drop a leading block of comment/blank lines (the ASF header) so it does not
  // show up in the rendered snippet.
  const lines = content.split("\n");
  let i = 0;
  while (
    i < lines.length &&
    (lines[i].trim() === "" || /^\s*(\/\/|#|--|\/\*|\*)/.test(lines[i]))
  ) {
    i++;
  }
  return lines.slice(i).join("\n").replace(/^\n+|\s+$/g, "");
}

function transform(node) {
  if (
    node.type === "code" &&
    typeof node.meta === "string" &&
    /(^|\s)file=/.test(node.meta)
  ) {
    const opts = parseMeta(node.meta);
    const abs = path.resolve(ROOT, opts.file);
    const content = fs.readFileSync(abs, "utf8");
    node.value = opts.region
      ? extractRegion(content, opts.region, opts.file)
      : stripLicenseHeader(content);
    const meta = node.meta
      .replace(/\s*file=("[^"]*"|\S+)/, "")
      .replace(/\s*region=("[^"]*"|\S+)/, "")
      .trim();
    node.meta = meta.length ? meta : null;
  }
  if (Array.isArray(node.children)) {
    node.children.forEach(transform);
  }
}

module.exports = function remarkIncludeCode() {
  return (tree) => {
    transform(tree);
  };
};