import { writeAudit } from './audit'
import type { DB } from './db'
import { createDraft, issueDocument } from './repos-documents'
import { getClientModule } from './repos-modules'
import { outstandingPaise } from './repos-payments'
import { CADENCE_KIND, getRecurringPlan } from './repos-recurring'
import { getNumberSetting, getSetting, resolveSchedule, setReminderStatus, upsertReminder } from './repos-reminders'
import { sendReminder, type SendReminderDeps } from './send-reminder'

/**
 * Daily scan — pure w.r.t. the clock: `today` (YYYY-MM-DD) is injected, so tests
 * are deterministic. Every reminder is created through upsertReminder (INSERT OR
 * IGNORE on the idempotency key), which makes re-runs and catch-up after downtime
 * safe with no extra bookkeeping. The four detection rules all land in the manual
 * queue; recurring generation is transactional (claim + generate + advance next_run
 * all-or-nothing) with the auto-send strictly after commit — at most once per period.
 */

export type ScanDeps = SendReminderDeps

export interface ScanResult {
  today: string
  created: Record<string, number>
  autoSent: number
  autoFailed: number
}

/** ISO date arithmetic on YYYY-MM-DD (UTC), lexical-compare safe. */
export function addDaysIso(dateIso: string, days: number): string {
  const [y, m, d] = dateIso.split('-').map(Number)
  return new Date(Date.UTC(y!, m! - 1, d! + days)).toISOString().slice(0, 10)
}

/** Whole days from `fromIso` to `toIso` (UTC midnights; negative when from > to). */
export function daysBetweenIso(fromIso: string, toIso: string): number {
  const at = (s: string): number => {
    const [y, m, d] = s.split('-').map(Number)
    return Date.UTC(y!, m! - 1, d!)
  }
  return Math.round((at(toIso) - at(fromIso)) / 86_400_000)
}

/** Advance a YYYY-MM-DD anchor by one cadence (UTC; month/day overflow normalizes). */
export function addCadence(dateIso: string, cadence: 'monthly' | 'yearly'): string {
  const [y, m, d] = dateIso.split('-').map(Number)
  const ms = cadence === 'yearly' ? Date.UTC(y! + 1, m! - 1, d!) : Date.UTC(y!, m!, d!)
  return new Date(ms).toISOString().slice(0, 10)
}

function bump(created: Record<string, number>, kind: string): void {
  created[kind] = (created[kind] ?? 0) + 1
}

type ClaimResult = 'done' | { created: boolean; auto: boolean; reminderId: string }

/** One period for one plan, atomically. Callers wrap in db.transaction. */
function claimAndGenerate(db: DB, planId: string, today: string, now: string): ClaimResult {
  const plan = getRecurringPlan(db, planId)
  if (plan === null || !plan.active || plan.nextRun > today) return 'done'
  const duePeriod = plan.nextRun
  const up = upsertReminder(db, {
    ruleKind: 'recurring_generated', subjectId: plan.id, duePeriod,
    clientId: plan.clientId, policyApplied: plan.policy, now,
  })
  const nextRun = addCadence(plan.nextRun, plan.cadence)
  if (!up.created) {
    // Defensive: the period's reminder already exists but next_run wasn't advanced.
    // Only reachable if generation were ever non-transactional; advance, never regenerate.
    db.prepare(`UPDATE recurring_plan SET next_run=? WHERE id=?`).run(nextRun, planId)
    return { created: false, auto: false, reminderId: up.id }
  }
  if (plan.clientModuleId === null) throw new Error(`recurring_plan ${plan.id}: client_module required to generate`)
  const cm = getClientModule(db, plan.clientModuleId)
  if (cm === null) throw new Error(`recurring_plan ${plan.id}: client_module not found`)
  const kind = CADENCE_KIND[plan.cadence]
  const draft = createDraft(db, 'system', {
    docType: 'INVOICE', clientId: plan.clientId,
    lines: [{
      moduleId: cm.moduleId, qty: 1, kind, edition: cm.edition,
      ...(plan.amountPaise !== null ? { unitPricePaise: plan.amountPaise } : {}),
    }],
  })
  const inv = issueDocument(db, 'system', draft.id)
  db.prepare(`UPDATE reminder SET doc_id=? WHERE id=?`).run(inv.id, up.id)
  db.prepare(`UPDATE recurring_plan SET next_run=? WHERE id=?`).run(nextRun, planId)
  writeAudit(db, 'system', 'generate', 'recurring_plan', plan.id, { nextRun: plan.nextRun }, { nextRun, invoiceId: inv.id })
  return { created: true, auto: plan.policy === 'auto', reminderId: up.id }
}

/** Generate every due period for every active plan; collect auto reminders to send. */
function generateRecurring(db: DB, today: string, now: string, created: Record<string, number>): string[] {
  const plans = db.prepare(
    `SELECT id FROM recurring_plan WHERE active=1 AND next_run <= ?`,
  ).all(today) as { id: string }[]
  const autoQueue: string[] = []
  for (const { id } of plans) {
    let guard = 0
    for (;;) {
      if (guard++ > 240) break // safety cap: ~20 years of monthly against a corrupt next_run
      const claim = db.transaction(() => claimAndGenerate(db, id, today, now))()
      if (claim === 'done') break
      if (claim.created) {
        bump(created, 'recurring_generated')
        if (claim.auto) autoQueue.push(claim.reminderId)
      }
    }
  }
  return autoQueue
}

export async function runDailyScan(db: DB, deps: ScanDeps, today: string): Promise<ScanResult> {
  const now = deps.now?.() ?? new Date().toISOString()
  const created: Record<string, number> = {}

  // --- invoice_overdue (dN day-past-issue milestones from the dated schedule; spec §8) ---
  // A7: there is no due-date column — age anchors on doc_date (the issue date).
  // Catch-up guard (F7): only the HIGHEST crossed milestone enqueues per scan, so a
  // scan gap (or the old monthly→dN cutover) nudges once, never the whole ladder;
  // under daily scans each milestone still fires exactly once as it is crossed.
  const invOffsets = resolveSchedule(db, 'invoice_overdue', today).dayOffsets // ascending
  const overdueCutoff = addDaysIso(today, -invOffsets[0]!)
  const overdue = db.prepare(
    `SELECT id, client_id, doc_date FROM document
     WHERE doc_type='INVOICE' AND doc_no IS NOT NULL
       AND status NOT IN ('paid','cancelled','lost') AND doc_date <= ?`,
  ).all(overdueCutoff) as { id: string; client_id: string; doc_date: string }[]
  for (const inv of overdue) {
    if (outstandingPaise(db, inv.id) <= 0) continue
    const age = daysBetweenIso(inv.doc_date, today)
    const crossed = invOffsets.filter((d) => age >= d)
    if (crossed.length === 0) continue
    const highest = crossed[crossed.length - 1]!
    if (upsertReminder(db, { ruleKind: 'invoice_overdue', subjectId: inv.id, duePeriod: `d${highest}`, clientId: inv.client_id, docId: inv.id, now }).created) {
      bump(created, 'invoice_overdue')
    }
  }

  // --- renewal_due ---
  const renewalDays = getNumberSetting(db, 'reminders.renewal_days', 15)
  const renewalHorizon = addDaysIso(today, renewalDays)
  const renewals = db.prepare(
    `SELECT id, client_id, next_renewal FROM client_module
     WHERE active=1 AND next_renewal IS NOT NULL AND next_renewal >= ? AND next_renewal <= ?`,
  ).all(today, renewalHorizon) as { id: string; client_id: string; next_renewal: string }[]
  for (const cm of renewals) {
    if (upsertReminder(db, { ruleKind: 'renewal_due', subjectId: cm.id, duePeriod: cm.next_renewal, clientId: cm.client_id, now }).created) {
      bump(created, 'renewal_due')
    }
  }

  // --- amc_expiring (per-contract window) ---
  const amcs = db.prepare(
    `SELECT id, client_id, period_to, renewal_reminder_days FROM amc_contract WHERE active=1`,
  ).all() as { id: string; client_id: string; period_to: string; renewal_reminder_days: number }[]
  for (const a of amcs) {
    const horizon = addDaysIso(today, a.renewal_reminder_days)
    if (a.period_to < today || a.period_to > horizon) continue
    if (upsertReminder(db, { ruleKind: 'amc_expiring', subjectId: a.id, duePeriod: a.period_to, clientId: a.client_id, now }).created) {
      bump(created, 'amc_expiring')
    }
  }

  // --- follow_up (internal) ---
  const followUps = db.prepare(
    `SELECT id, client_id, follow_up_on FROM interaction
     WHERE follow_up_on IS NOT NULL AND follow_up_on <= ?`,
  ).all(today) as { id: string; client_id: string; follow_up_on: string }[]
  for (const f of followUps) {
    if (upsertReminder(db, { ruleKind: 'follow_up', subjectId: f.id, duePeriod: f.follow_up_on, clientId: f.client_id, now }).created) {
      bump(created, 'follow_up')
    }
  }

  // --- quote_followup (escalating chase on sent quotations — spec §7) ---
  // Age anchors on the FIRST 'sent' event (F15). The dated schedule (rule 3) yields
  // the day offsets; send policy is a flat operational setting, default manual.
  const followupSchedule = resolveSchedule(db, 'quote_followup', today)
  const followupPolicy: 'auto' | 'manual' =
    getSetting(db, 'quote.followup.policy') === 'auto' ? 'auto' : 'manual'
  // A lost client is dead pipeline — never chase (their queued rows can be dismissed
  // by hand). NOT EXISTS covers quotes converted before status-flip-on-convert landed:
  // a live forward child means the sale moved on, whatever the quote row still says.
  const sentQuotes = db.prepare(
    `SELECT d.id, d.client_id,
            (SELECT MIN(e.at_wall) FROM document_event e
              WHERE e.document_id = d.id AND e.kind = 'sent') AS first_sent
     FROM document d JOIN client c ON c.id = d.client_id
     WHERE d.doc_type='QUOTATION' AND d.status='sent'
       AND c.status != 'lost'
       AND NOT EXISTS (SELECT 1 FROM document ch
                        WHERE ch.ref_doc_id = d.id AND ch.status != 'cancelled')`,
  ).all() as { id: string; client_id: string; first_sent: string | null }[]
  const followupAuto: string[] = []
  for (const q of sentQuotes) {
    if (q.first_sent === null) continue
    const age = Math.floor((Date.parse(today) - Date.parse(q.first_sent.slice(0, 10))) / 86_400_000)
    const crossed = followupSchedule.dayOffsets.filter((o) => age >= o)
    if (crossed.length === 0) continue
    // Catch-up burst guard (F7): enqueue ONLY the single highest crossed milestone —
    // a quote already past several offsets gets one nudge, never the whole ladder.
    // Milestones consumed on their own day stay consumed (threshold-day bucket in the
    // unique key), so daily operation still fires each interval exactly once.
    const highest = crossed[crossed.length - 1]!
    const up = upsertReminder(db, {
      ruleKind: 'quote_followup', subjectId: q.id, duePeriod: `d${highest}`,
      clientId: q.client_id, docId: q.id, policyApplied: followupPolicy, now,
    })
    if (up.created) {
      bump(created, 'quote_followup')
      if (followupPolicy === 'auto') followupAuto.push(up.id)
    }
  }

  // --- recurring_generated (transactional generation, then async auto-send) ---
  const autoQueue = [...followupAuto, ...generateRecurring(db, today, now, created)]
  let autoSent = 0
  let autoFailed = 0
  for (const reminderId of autoQueue) {
    // Send outside the generation transaction: a failed send never rolls back the
    // (already-issued) invoice or the advanced schedule — it just parks the reminder.
    try {
      const out = await sendReminder(db, deps, reminderId, 'system')
      if (out.ok) autoSent += 1
      else autoFailed += 1
    } catch (err) {
      // A hard guard (no recipient email, share.base_url unset) must not kill the
      // drain: park THIS reminder as failed — loudly, with the reason — and keep going.
      setReminderStatus(db, 'system', reminderId, 'failed', {
        error: err instanceof Error ? err.message : String(err),
      })
      autoFailed += 1
    }
  }

  return { today, created, autoSent, autoFailed }
}