export type ClassifierPromptInput = {
  emails: Array<{
    id: string
    subject: string
    sender: string
    snippet: string
    userLabels: string[]
    senderReputation: string
    recentSubjects: string[]
  }>
  emailHints: string
}

function compact(value: string, max = 300): string {
  return value.replace(/\s+/g, ' ').trim().slice(0, max)
}

export function buildClassifierPrompt(input: ClassifierPromptInput): string {
  const hints = input.emailHints.trim()
  const hintsBlock = hints.length > 0
    ? `User-defined email hints:\n${hints}\n\n`
    : ''

  const emails = input.emails.map(email => {
    const labels = email.userLabels.length > 0 ? email.userLabels.join(', ') : '(none)'
    const recent = email.recentSubjects.length > 0
      ? email.recentSubjects.map(s => `    - ${compact(s, 140)}`).join('\n')
      : '    - (none)'

    return `- id: ${email.id}
  from: ${compact(email.sender, 160)}
  subject: ${compact(email.subject, 220)}
  user_labels: ${labels}
  sender_reputation: ${email.senderReputation}
  recent_subject_pattern:
${recent}
  snippet: ${compact(email.snippet, 360)}`
  }).join('\n')

  return `${hintsBlock}You are scoring incoming email for a PhD researcher in Information Systems / trust in AI who is also building a venture.

Score each email for today's attention on a 1-5 importance scale:
1 = ignore or archive
2 = low priority, batch later
3 = useful but not urgent
4 = important and should be handled soon
5 = must-handle-today

Signals that raise importance:
- deadlines, meeting confirmations, schedule changes, calendar invites
- thesis advisor, committee, lab, university, fieldwork, publication, reviewer, or collaborator messages
- venture co-founder, investor, customer, partner, legal, contract, payment, or platform-risk messages
- personal notes from close people, actionable questions, unread replies in active threads

Signals that lower importance:
- newsletters, digests, mass mailing, marketing, promotions
- routine SaaS notifications, automated receipts without ambiguity
- lists or communities without direct action required

Treat user labels as high-signal user intent. Treat sender reputation as a prior, not a rule. Use recent subject pattern for thread context.

Output STRICT JSON array. One object per email in the same order. Keys:
  id - the email id I sent you
  importance - integer 1-5
  importance_reason - 5-12 words
  topic - optional, 1-3 words

NO prose, NO markdown fences. Just the JSON array.

Emails:
${emails}`
}