import type { MentionMap } from "./mentions";

const NAME = "[A-Za-z0-9](?:[A-Za-z0-9-]{0,38})";
const REPO = "[A-Za-z0-9._-]{1,100}";
const TEAM = "[A-Za-z0-9][A-Za-z0-9_-]{0,99}";
const SHA = "[0-9a-f]{7,40}";
const SHORT_SHA = 7;

/** One pass over plain text so inserted anchors are never re-scanned by a later pattern. */
const REFERENCE = new RegExp(
  `(?<prefix>^|[\\s(])(?:${[
    `@(?<teamOrg>${NAME})\\/(?<team>${TEAM})`,
    `@(?<user>${NAME})`,
    `(?<issueOwner>${NAME})\\/(?<issueRepo>${REPO})#(?<issueNumber>\\d+)`,
    `(?<commitOwner>${NAME})\\/(?<commitRepo>${REPO})@(?<commitSha>${SHA})`,
    `#(?<localNumber>\\d+)`,
    `(?<localSha>${SHA})`,
  ].join("|")})\\b`,
  "g",
);

type Groups = Partial<Record<string, string>>;

function escapeHtml(value: string): string {
  return value.replace(/[&<>"']/g, (char) => `&#${char.charCodeAt(0)};`);
}

function anchor(href: string, text: string, kind: string, ref: string, className = ""): string {
  const classAttr = className ? ` class="${className}"` : "";
  return `<a href="${escapeHtml(href)}"${classAttr} data-hovercard="${kind}" data-ref="${escapeHtml(ref)}">${escapeHtml(text)}</a>`;
}

/**
 * Links `@user`, `@org/team`, `#123`, `owner/repo#123`, `owner/repo@sha` and bare commit SHAs in a text
 * segment of rendered HTML. Anchors carry `data-hovercard` so the client can show previews.
 */
export function linkTextReferences(
  text: string,
  context: { owner: string; repo: string } | null,
  mentions: MentionMap | null = null,
): string {
  let out = "";
  let last = 0;
  for (const match of text.matchAll(REFERENCE)) {
    const replacement = replaceReference(match.groups ?? {}, context, mentions);
    if (replacement === null) continue;
    out += text.slice(last, match.index) + (match.groups?.prefix ?? "") + replacement;
    last = match.index + match[0].length;
  }
  return out + text.slice(last);
}

/**
 * With a resolved `mentions` map, handles render under the account's current name (so renames carry over)
 * and handles that name nobody stay plain text. Without one, every handle links as written.
 */
function mentionName(handle: string, mentions: MentionMap | null): string | null {
  if (!mentions) return handle;
  return mentions.get(handle.toLowerCase())?.name ?? null;
}

function replaceReference(
  groups: Groups,
  context: { owner: string; repo: string } | null,
  mentions: MentionMap | null,
): string | null {
  const { teamOrg, team, user, issueOwner, issueRepo, issueNumber, commitOwner, commitRepo, commitSha } = groups;
  if (teamOrg && team) {
    const org = mentionName(teamOrg, mentions);
    return org ? anchor(`/${org}`, `@${org}/${team}`, "team", `${org}/${team}`, "mention") : null;
  }
  if (user) {
    const name = mentionName(user, mentions);
    return name ? anchor(`/${name}`, `@${name}`, "user", name, "mention") : null;
  }
  if (issueOwner && issueRepo && issueNumber) {
    const ref = `${issueOwner}/${issueRepo}#${issueNumber}`;
    return anchor(`/${issueOwner}/${issueRepo}/issues/${issueNumber}`, ref, "issue", ref);
  }
  if (commitOwner && commitRepo && commitSha)
    return anchor(
      `/${commitOwner}/${commitRepo}/commit/${commitSha}`,
      `${commitOwner}/${commitRepo}@${commitSha.slice(0, SHORT_SHA)}`,
      "commit",
      `${commitOwner}/${commitRepo}@${commitSha}`,
    );
  if (!context) return null;
  const { localNumber, localSha } = groups;
  if (localNumber)
    return anchor(
      `/${context.owner}/${context.repo}/issues/${localNumber}`,
      `#${localNumber}`,
      "issue",
      `${context.owner}/${context.repo}#${localNumber}`,
    );
  if (localSha && /[a-f]/.test(localSha) && /\d/.test(localSha))
    return anchor(
      `/${context.owner}/${context.repo}/commit/${localSha}`,
      localSha.slice(0, SHORT_SHA),
      "commit",
      `${context.owner}/${context.repo}@${localSha}`,
      "sha",
    );
  return null;
}