import { createHmac, timingSafeEqual } from 'node:crypto';
import {
  DevLink,
  DevLinkKind,
  DevLinkState,
} from '@task-stream/api/tracker/domain';

export type GitProvider = 'github' | 'gitea' | 'gitlab';

/** Code the host told us about, and the text where ticket keys may appear. */
export interface GitMention {
  text: string;
  link: DevLink;
}

type Json = Record<string, any>; // eslint-disable-line @typescript-eslint/no-explicit-any

/** Which host sent it, from its event header. */
export function gitProviderOf(
  headers: Record<string, string | undefined>,
): { provider: GitProvider; event: string } | null {
  if (headers['x-gitea-event'])
    return { provider: 'gitea', event: headers['x-gitea-event'] };
  if (headers['x-github-event'])
    return { provider: 'github', event: headers['x-github-event'] };
  if (headers['x-gitlab-event'])
    return { provider: 'gitlab', event: headers['x-gitlab-event'] };
  return null;
}

const same = (a: string, b: string) =>
  a.length === b.length && timingSafeEqual(Buffer.from(a), Buffer.from(b));

/**
 * GitHub and Gitea sign the raw body (HMAC-SHA256, hex); GitLab sends the
 * secret itself as a token.
 */
export function verifyGitSignature(
  provider: GitProvider,
  headers: Record<string, string | undefined>,
  rawBody: Buffer | undefined,
  secret: string,
): boolean {
  if (provider === 'gitlab')
    return (
      !!headers['x-gitlab-token'] && same(headers['x-gitlab-token'], secret)
    );
  const received = (
    provider === 'github'
      ? headers['x-hub-signature-256']
      : headers['x-gitea-signature']
  )?.replace(/^sha256=/, '');
  if (!received || !rawBody) return false;
  return same(
    received,
    createHmac('sha256', secret).update(rawBody).digest('hex'),
  );
}

const branchOf = (ref: unknown) =>
  typeof ref === 'string' && ref.startsWith('refs/heads/')
    ? ref.slice('refs/heads/'.length)
    : null;

/** Commits of a push, and the branch they went to (all three hosts). */
function fromPush(
  provider: GitProvider,
  body: Json,
  repoUrl: string,
): GitMention[] {
  const mentions: GitMention[] = [];
  const branch = branchOf(body['ref']);
  for (const commit of (body['commits'] ?? []) as Json[]) {
    if (!commit?.['url'] || !commit['id']) continue;
    const message = String(commit['message'] ?? '');
    mentions.push({
      text: message,
      link: {
        kind: DevLinkKind.COMMIT,
        url: String(commit['url']),
        title: message,
        ref: String(commit['id']).slice(0, 8),
        state: null,
        provider,
        repository: null,
        author: commit['author']?.['name'] ?? null,
        at: String(commit['timestamp'] ?? new Date().toISOString()),
      },
    });
  }
  if (branch && repoUrl) {
    const path =
      provider === 'gitlab'
        ? '/-/tree/'
        : provider === 'gitea'
          ? '/src/branch/'
          : '/tree/';
    mentions.push({
      text: branch,
      link: {
        kind: DevLinkKind.BRANCH,
        url: `${repoUrl}${path}${branch}`,
        title: branch,
        ref: branch,
        state: null,
        provider,
        repository: null,
        author:
          body['pusher']?.['name'] ??
          body['pusher']?.['login'] ??
          body['user_name'] ??
          null,
        at: new Date().toISOString(),
      },
    });
  }
  return mentions;
}

function prState(merged: boolean, state: string): DevLinkState {
  if (merged || state === 'merged') return DevLinkState.MERGED;
  return state === 'closed' ? DevLinkState.CLOSED : DevLinkState.OPEN;
}

/**
 * What a webhook delivery is about: commits and branches of a push, or a
 * pull/merge request. Anything else (pings, tags, issues…) is nothing.
 */
export function gitMentionsOf(
  provider: GitProvider,
  event: string,
  body: Json,
): GitMention[] {
  const repoUrl = String(
    body['repository']?.['html_url'] ?? body['project']?.['web_url'] ?? '',
  ).replace(/\/$/, '');
  if (event === 'push' || event === 'Push Hook')
    return fromPush(provider, body, repoUrl);
  if (provider !== 'gitlab' && event === 'pull_request') {
    const pr = body['pull_request'] as Json | undefined;
    if (!pr?.['html_url']) return [];
    const title = String(pr['title'] ?? '');
    return [
      {
        text: `${title} ${pr['head']?.['ref'] ?? ''} ${pr['body'] ?? ''}`,
        link: {
          kind: DevLinkKind.PULL_REQUEST,
          url: String(pr['html_url']),
          title,
          ref: `#${pr['number'] ?? ''}`,
          state: prState(!!pr['merged'], String(pr['state'] ?? 'open')),
          provider,
          repository: null,
          author: pr['user']?.['login'] ?? null,
          at: String(pr['updated_at'] ?? new Date().toISOString()),
        },
      },
    ];
  }
  if (provider === 'gitlab' && event === 'Merge Request Hook') {
    const mr = body['object_attributes'] as Json | undefined;
    if (!mr?.['url']) return [];
    const title = String(mr['title'] ?? '');
    return [
      {
        text: `${title} ${mr['source_branch'] ?? ''} ${mr['description'] ?? ''}`,
        link: {
          kind: DevLinkKind.PULL_REQUEST,
          url: String(mr['url']),
          title,
          ref: `!${mr['iid'] ?? ''}`,
          state: prState(false, String(mr['state'] ?? 'opened')),
          provider,
          repository: null,
          author: body['user']?.['username'] ?? null,
          at: String(mr['updated_at'] ?? new Date().toISOString()),
        },
      },
    ];
  }
  return [];
}