export interface PrWebhookEvent {
  kind: 'pr'
  issueNumber: number | undefined
  action: string
  pr: string
  branch: string
  htmlUrl: string
  title: string
  body: string
  raw: unknown
}

export interface IssueWebhookEvent {
  kind: 'issue'
  action: string
  issueNumber: number
  title: string
  body: string
  htmlUrl: string
  raw: unknown
}

export interface IssueCommentWebhookEvent {
  kind: 'issue_comment'
  action: string
  issueNumber: number
  prNumber: number | undefined
  commentBody: string
  commentAuthor: string
  commentHtmlUrl: string
  raw: unknown
}

export interface PushWebhookEvent {
  kind: 'push'
  branch: string
  raw: unknown
}

export type WebhookEvent = PrWebhookEvent | IssueWebhookEvent | IssueCommentWebhookEvent | PushWebhookEvent

export function parseEvent(
  eventHeader: string,
  issueNumber: number | undefined,
  raw: unknown,
): WebhookEvent | null {
  if (!raw || typeof raw !== 'object')
    return null
  const obj = raw as {
    action?: unknown
    pull_request?: unknown
    issue?: unknown
    comment?: unknown
    ref?: unknown
    sender?: unknown
  }

  if (eventHeader === 'push') {
    // gitea push 事件无 `action`，顶层带 `ref: "refs/heads/<branch>"`。
    if (typeof obj.ref !== 'string')
      return null
    const branch = obj.ref.replace(/^refs\/heads\//, '')
    if (!branch)
      return null
    return { kind: 'push', branch, raw }
  }

  if (typeof obj.action !== 'string')
    return null

  if (eventHeader === 'issue_comment') {
    const issue = obj.issue
    const comment = obj.comment
    if (!issue || typeof issue !== 'object')
      return null
    if (!comment || typeof comment !== 'object')
      return null
    const issueObj = issue as {
      number?: unknown
      pull_request?: unknown
    }
    const commentObj = comment as {
      body?: unknown
      html_url?: unknown
      user?: unknown
    }
    const num = typeof issueObj.number === 'number' ? issueObj.number : Number(issueObj.number)
    if (!Number.isFinite(num))
      return null
    // gitea sets issue.pull_request (non-null object) when the issue is a PR.
    const prNumber = issueObj.pull_request && typeof issueObj.pull_request === 'object'
      ? num
      : undefined
    const commentBody = typeof commentObj.body === 'string' ? commentObj.body : ''
    const commentHtmlUrl = typeof commentObj.html_url === 'string' ? commentObj.html_url : ''
    const commentUser = commentObj.user as { login?: unknown, username?: unknown } | undefined
    const sender = obj.sender as { login?: unknown, username?: unknown } | undefined
    const commentAuthor = (typeof commentUser?.login === 'string' && commentUser.login)
      || (typeof commentUser?.username === 'string' && commentUser.username)
      || (typeof sender?.login === 'string' && sender.login)
      || (typeof sender?.username === 'string' && sender.username)
      || ''
    return {
      kind: 'issue_comment',
      action: obj.action,
      issueNumber: num,
      prNumber,
      commentAuthor,
      commentBody,
      commentHtmlUrl,
      raw,
    }
  }

  if (eventHeader === 'issues') {
    const issue = obj.issue
    if (!issue || typeof issue !== 'object')
      return null
    const issueObj = issue as {
      number?: unknown
      html_url?: unknown
      title?: unknown
      body?: unknown
    }
    const num = typeof issueObj.number === 'number' ? issueObj.number : Number(issueObj.number)
    if (!Number.isFinite(num))
      return null
    const htmlUrl = typeof issueObj.html_url === 'string' ? issueObj.html_url : ''
    const title = typeof issueObj.title === 'string' ? issueObj.title : ''
    const body = typeof issueObj.body === 'string' ? issueObj.body : ''
    return {
      kind: 'issue',
      action: obj.action,
      issueNumber: num,
      title,
      body,
      htmlUrl,
      raw,
    }
  }

  // Default path: pull_request payload (preserves legacy behaviour for any
  // event header value, since gitea historically may not set the header).
  const pr = obj.pull_request
  if (!pr || typeof pr !== 'object')
    return null
  const prObj = pr as {
    number?: unknown
    html_url?: unknown
    head?: unknown
    title?: unknown
    body?: unknown
  }
  const num = typeof prObj.number === 'number' ? prObj.number : Number(prObj.number)
  if (!Number.isFinite(num))
    return null
  const htmlUrl = typeof prObj.html_url === 'string' ? prObj.html_url : ''
  const head = prObj.head as { ref?: unknown } | undefined
  const branch = head && typeof head.ref === 'string' ? head.ref : ''
  const title = typeof prObj.title === 'string' ? prObj.title : ''
  const body = typeof prObj.body === 'string' ? prObj.body : ''

  if (!branch || !htmlUrl)
    return null

  return {
    kind: 'pr',
    issueNumber,
    action: obj.action,
    pr: String(num),
    branch,
    htmlUrl,
    title,
    body,
    raw,
  }
}