/**
 * Script to manage documentation preview comments on pull requests.
 */

const path = require("path");

const MARKER = "<!-- documentation preview -->";

/**
 * Check if a URL is accessible
 * @param {string} url - URL to check
 * @returns {Promise<boolean|undefined>} True if the URL is accessible (200 or 3xx), false otherwise; undefined if an error occurs
 */
async function isUrlAccessible(url) {
  try {
    const res = await fetch(url, { method: "GET", redirect: "manual" });
    // treat 200 and 3xx as "accessible", 404 as "missing"
    return res.ok || (res.status >= 300 && res.status < 400);
  } catch (e) {
    console.error(`Error checking accessibility for ${url}:`, e);
    return undefined;
  }
}

/**
 * Fetch changed files from a pull request
 * @param {object} params - Parameters object
 * @param {object} params.github - GitHub API client
 * @param {string} params.owner - Repository owner
 * @param {string} params.repo - Repository name
 * @param {string} params.pullNumber - Pull request number
 * @returns {Promise<Array<{filename: string, status: string}>>} Array of changed file objects with filename and status
 */
async function fetchChangedFiles({ github, owner, repo, pullNumber }) {
  const iterator = github.paginate.iterator(github.rest.pulls.listFiles, {
    owner,
    repo,
    pull_number: pullNumber,
    per_page: 100,
  });

  const changedFiles = [];
  for await (const { data } of iterator) {
    changedFiles.push(...data.map(({ filename, status }) => ({ filename, status })));
  }

  return changedFiles;
}

/**
 * Get changed documentation pages from the list of changed files
 * @param {Array<{filename: string, status: string}>} changedFiles - Array of changed file objects
 * @returns {Array<{page: string, status: string}>} Array of documentation page objects with page path and status, sorted alphabetically by page path
 */
function getChangedDocPages(changedFiles) {
  const DOCS_DIR = "docs/docs/";
  const changedPages = [];

  for (const { filename, status } of changedFiles) {
    const ext = path.extname(filename);
    if (ext !== ".md" && ext !== ".mdx") continue;
    if (!filename.startsWith(DOCS_DIR)) continue;

    const relativePath = path.relative(DOCS_DIR, filename);
    const { dir, name, base } = path.parse(relativePath);

    let pagePath;
    if (base === "index.mdx") {
      pagePath = dir;
    } else {
      pagePath = path.join(dir, name);
    }

    // Adjust classic-ml/ to ml/
    pagePath = pagePath.replace(/^classic-ml/, "ml");

    // Ensure forward slashes for web paths
    pagePath = pagePath.split(path.sep).join("/");

    changedPages.push({ page: pagePath, status });
  }

  // Sort alphabetically by page path for easier lookup
  changedPages.sort((a, b) => a.page.localeCompare(b.page));

  return changedPages;
}

/**
 * Create or update a PR comment with documentation preview information
 * @param {object} params - Parameters object
 * @param {object} params.github - GitHub API client
 * @param {string} params.owner - Repository owner
 * @param {string} params.repo - Repository name
 * @param {string} params.pullNumber - Pull request number
 * @param {string} params.commentBody - Comment body content
 */
async function upsertComment({ github, owner, repo, pullNumber, commentBody }) {
  // Get existing comments on the PR
  const { data: comments } = await github.rest.issues.listComments({
    owner,
    repo,
    issue_number: pullNumber,
    per_page: 100,
  });

  // Find existing preview docs comment
  const existingComment = comments.find((comment) => comment.body.includes(MARKER));
  const commentBodyWithMarker = `${MARKER}\n\n${commentBody}`;

  if (!existingComment) {
    console.log("Creating comment");
    await github.rest.issues.createComment({
      owner,
      repo,
      issue_number: pullNumber,
      body: commentBodyWithMarker,
    });
  } else {
    console.log("Updating comment");
    await github.rest.issues.updateComment({
      owner,
      repo,
      comment_id: existingComment.id,
      body: commentBodyWithMarker,
    });
  }
}

/**
 * Generate the comment template for documentation preview
 * @param {object} params - Parameters object
 * @param {string} params.commitSha - Git commit SHA
 * @param {string} params.workflowRunLink - Link to the workflow run
 * @param {string} params.docsWorkflowRunUrl - Link to the docs workflow run
 * @param {string} params.mainMessage - Main message content
 * @param {Array<{link: string, status: string, isAccessible?: boolean}>} params.changedPages - Array of changed documentation page objects with link, status, and optional accessibility flag
 * @returns {string} Comment template
 */
function getCommentTemplate({
  commitSha,
  workflowRunLink,
  docsWorkflowRunUrl,
  mainMessage,
  changedPages,
}) {
  let changedPagesSection = "";

  if (changedPages && changedPages.length > 0) {
    const pageLinks = changedPages
      .map(({ link, status, isAccessible }) => {
        let statusText = status;
        // Add warning or success indicator for removed and renamed files
        if (status === "removed" || status === "renamed") {
          if (isAccessible === true) {
            statusText = `${status}, ✅ redirect exists`;
          } else if (isAccessible === false) {
            statusText = `${status}, ❌ add a redirect`;
          } else {
            // If accessibility check failed
            statusText = `${status}, ⚠️ failed to check`;
          }
        }
        return `- ${link} (${statusText})`;
      })
      .join("\n");

    // Only collapse if there are more than 5 changed pages
    if (changedPages.length > 5) {
      changedPagesSection = `

<details>
<summary>Changed Pages (${changedPages.length})</summary>

${pageLinks}

</details>
`;
    } else {
      changedPagesSection = `

**Changed Pages (${changedPages.length})**

${pageLinks}
`;
    }
  }

  return `
Documentation preview for ${commitSha} ${mainMessage}
${changedPagesSection}
<details>
<summary>More info</summary>

- Ignore this comment if this PR does not change the documentation.
- The preview is updated when a new commit is pushed to this PR.
- This comment was created by [this workflow run](${workflowRunLink}).
- The documentation was built by [this workflow run](${docsWorkflowRunUrl}).

</details>
`;
}

/**
 * Main function to handle documentation preview comments
 * @param {object} params - Parameters object containing context and github
 * @param {object} params.github - GitHub API client
 * @param {object} params.context - GitHub context
 * @param {object} params.env - Environment variables
 */
module.exports = async ({ github, context, env }) => {
  const commitSha = env.COMMIT_SHA;
  const pullNumber = env.PULL_NUMBER;
  const workflowRunId = env.WORKFLOW_RUN_ID;
  const stage = env.STAGE;
  const netlifyUrl = env.NETLIFY_URL;
  const docsWorkflowRunUrl = env.DOCS_WORKFLOW_RUN_URL;

  // Validate required parameters
  if (!commitSha || !pullNumber || !workflowRunId || !stage || !docsWorkflowRunUrl) {
    throw new Error(
      "Missing required parameters: commit-sha, pull-number, workflow-run-id, stage, docs-workflow-run-url"
    );
  }

  if (!["completed", "failed"].includes(stage)) {
    throw new Error("Stage must be either 'completed' or 'failed'");
  }

  if (stage === "completed" && !netlifyUrl) {
    throw new Error("netlify-url is required for completed stage");
  }

  const { owner, repo } = context.repo;
  const workflowRunLink = `https://github.com/${owner}/${repo}/actions/runs/${workflowRunId}`;

  let mainMessage;
  let changedPages = [];

  if (stage === "completed") {
    mainMessage = `is available at:\n\n- ${netlifyUrl}`;

    // Fetch changed files and get documentation pages
    try {
      const changedFiles = await fetchChangedFiles({ github, owner, repo, pullNumber });
      const docPages = getChangedDocPages(changedFiles);

      // Convert to clickable links with status if we have changed pages
      if (docPages.length > 0) {
        changedPages = await Promise.all(
          docPages.map(async ({ page, status }) => {
            const pageUrl = `${netlifyUrl}/${page}`;
            const link = `[${page}](${pageUrl})`;

            // Check accessibility for removed or renamed pages
            let isAccessible;
            if (status === "removed" || status === "renamed") {
              isAccessible = await isUrlAccessible(pageUrl);
            }

            return {
              link,
              status,
              isAccessible,
            };
          })
        );
      }
    } catch (error) {
      console.error("Error fetching changed files:", error);
      // Continue without changed pages list
    }
  } else if (stage === "failed") {
    mainMessage = "failed to build or deploy.";
  }

  const commentBody = getCommentTemplate({
    commitSha,
    workflowRunLink,
    docsWorkflowRunUrl,
    mainMessage,
    changedPages,
  });
  await upsertComment({ github, owner, repo, pullNumber, commentBody });
};