/**
 * Detector automático de padrões sobre a BD `sessions` (Observabilidade Fase 6A).
 *
 * Seis detectores heurísticos em SQL puro (via better-sqlite3). Cada detector
 * devolve zero ou mais `Pattern` para a semana analisada. Pipeline:
 *   1. Correr detectores sobre intervalo [weekStart, weekEnd]
 *   2. Persistir via `upsertPattern` (idempotente por (week_iso, pattern_key))
 *   3. Calcular `consecutive_weeks` olhando para semanas anteriores
 */
import type Database from 'better-sqlite3'
import type { SessionsDb, PatternRecord } from './db.js'

export type Severity = 'info' | 'warning' | 'action'

export interface Pattern {
  pattern_key: string
  title: string
  description: string
  severity: Severity
  metric_value: number | null
  sample_session_ids: string[]
  affected_count: number
}

export interface DetectCtx {
  db: Database.Database
  weekStartIso: string
  weekEndIso: string
}

/** Converte Date para string ISO UTC. */
function iso(d: Date): string {
  return d.toISOString()
}

/**
 * Calcula intervalo [segunda 00:00:00 UTC, domingo 23:59:59.999 UTC] da semana
 * que contém `ref` (Regra 17 — semana começa à segunda).
 */
export function weekRange(ref: Date): { start: Date; end: Date; iso: string } {
  const d = new Date(Date.UTC(ref.getUTCFullYear(), ref.getUTCMonth(), ref.getUTCDate()))
  const dow = d.getUTCDay() // 0=Dom, 1=Seg
  const diffToMonday = dow === 0 ? -6 : 1 - dow
  const start = new Date(d)
  start.setUTCDate(d.getUTCDate() + diffToMonday)
  const end = new Date(start)
  end.setUTCDate(start.getUTCDate() + 6)
  end.setUTCHours(23, 59, 59, 999)
  return { start, end, iso: weekIso(start) }
}

/** Semana ISO 8601 (YYYY-Www) para segunda de referência. */
export function weekIso(monday: Date): string {
  // Usa algoritmo ISO: quinta da mesma semana determina o ano
  const thursday = new Date(monday)
  thursday.setUTCDate(monday.getUTCDate() + 3)
  const year = thursday.getUTCFullYear()
  const jan1 = new Date(Date.UTC(year, 0, 1))
  const week = Math.floor(
    ((thursday.getTime() - jan1.getTime()) / 86400000 + (jan1.getUTCDay() === 0 ? 6 : jan1.getUTCDay() - 1)) / 7
  ) + 1
  return `${year}-W${String(week).padStart(2, '0')}`
}

/** Helper: todos os session_ids no intervalo. */
function baseRows(ctx: DetectCtx) {
  return ctx.db.prepare(`
    SELECT session_id, project_slug, started_at, event_count, tool_calls, tools_used, skills_invoked, outcome, duration_sec
    FROM sessions
    WHERE started_at >= ? AND started_at <= ?
  `).all(ctx.weekStartIso, ctx.weekEndIso) as Array<{
    session_id: string
    project_slug: string
    started_at: string
    event_count: number
    tool_calls: number
    tools_used: string
    skills_invoked: string
    outcome: string
    duration_sec: number | null
  }>
}

/** 1. Skills com taxa elevada de erro/interrupção. */
export function detectSkillsHighErrorRate(ctx: DetectCtx): Pattern[] {
  const rows = baseRows(ctx)
  // Agregar por skill
  const bySkill = new Map<string, { total: number; fail: number; ids: string[] }>()
  for (const r of rows) {
    let skills: string[] = []
    try { skills = JSON.parse(r.skills_invoked) } catch {}
    for (const sk of skills) {
      const entry = bySkill.get(sk) ?? { total: 0, fail: 0, ids: [] }
      entry.total++
      if (r.outcome === 'error' || r.outcome === 'interrupted') {
        entry.fail++
        if (entry.ids.length < 5) entry.ids.push(r.session_id)
      }
      bySkill.set(sk, entry)
    }
  }
  const out: Pattern[] = []
  for (const [skill, v] of bySkill) {
    if (v.total < 3) continue
    const ratio = v.fail / v.total
    if (ratio <= 0.2) continue
    const severity: Severity = ratio > 0.4 ? 'action' : 'warning'
    out.push({
      pattern_key: `skill_error_rate:${skill}`,
      title: `Skill ${skill}: ${(ratio * 100).toFixed(0)}% das sessões falham`,
      description: `De ${v.total} sessões que invocaram ${skill}, ${v.fail} terminaram em erro/interrupção.`,
      severity,
      metric_value: Math.round(ratio * 1000) / 1000,
      sample_session_ids: v.ids,
      affected_count: v.fail,
    })
  }
  return out
}

/** 2. Tools com baixa eficiência (tool_calls/event_count elevado). */
export function detectToolsLowEfficiency(ctx: DetectCtx): Pattern[] {
  const rows = baseRows(ctx)
  const byTool = new Map<string, { sum: number; count: number; ids: string[] }>()
  for (const r of rows) {
    if (!r.event_count || r.event_count === 0) continue
    const ratio = r.tool_calls / r.event_count
    let tools: string[] = []
    try { tools = JSON.parse(r.tools_used) } catch {}
    for (const t of tools) {
      const e = byTool.get(t) ?? { sum: 0, count: 0, ids: [] }
      e.sum += ratio
      e.count++
      if (e.ids.length < 5) e.ids.push(r.session_id)
      byTool.set(t, e)
    }
  }
  const out: Pattern[] = []
  for (const [tool, v] of byTool) {
    if (v.count < 5) continue
    const avg = v.sum / v.count
    if (avg <= 0.5) continue
    out.push({
      pattern_key: `tool_low_efficiency:${tool}`,
      title: `Tool ${tool}: rácio tool_calls/event_count médio ${avg.toFixed(2)}`,
      description: `Em ${v.count} sessões, ${tool} domina o event_count. Indício de uso ineficiente ou looping.`,
      severity: 'info',
      metric_value: Math.round(avg * 1000) / 1000,
      sample_session_ids: v.ids,
      affected_count: v.count,
    })
  }
  return out
}

/** 3. Pares (skill, tool) mais frequentes. */
export function detectSkillToolPairs(ctx: DetectCtx): Pattern[] {
  const rows = baseRows(ctx)
  const byPair = new Map<string, { count: number; ids: string[] }>()
  for (const r of rows) {
    let skills: string[] = []
    let tools: string[] = []
    try { skills = JSON.parse(r.skills_invoked) } catch {}
    try { tools = JSON.parse(r.tools_used) } catch {}
    for (const s of skills) {
      for (const t of tools) {
        const key = `${s}::${t}`
        const e = byPair.get(key) ?? { count: 0, ids: [] }
        e.count++
        if (e.ids.length < 5) e.ids.push(r.session_id)
        byPair.set(key, e)
      }
    }
  }
  const sorted = [...byPair.entries()].filter(([, v]) => v.count >= 5).sort((a, b) => b[1].count - a[1].count).slice(0, 5)
  return sorted.map(([key, v]) => ({
    pattern_key: `skill_tool_pair:${key}`,
    title: `Par frequente: ${key.replace('::', ' + ')}`,
    description: `Skill e tool co-ocorreram em ${v.count} sessões esta semana.`,
    severity: 'info' as Severity,
    metric_value: v.count,
    sample_session_ids: v.ids,
    affected_count: v.count,
  }))
}

/** 4. Duration outliers: sessões > p95 por projecto com outcome != completed. */
export function detectDurationOutliers(ctx: DetectCtx): Pattern[] {
  const rows = baseRows(ctx).filter((r) => r.duration_sec != null && r.duration_sec > 0)
  const byProject = new Map<string, Array<typeof rows[number]>>()
  for (const r of rows) {
    const arr = byProject.get(r.project_slug) ?? []
    arr.push(r)
    byProject.set(r.project_slug, arr)
  }
  const out: Pattern[] = []
  for (const [proj, arr] of byProject) {
    if (arr.length < 4) continue
    const durations = arr.map((r) => r.duration_sec as number).sort((a, b) => a - b)
    const p95Idx = Math.max(0, Math.floor(durations.length * 0.95) - 1)
    const p95 = durations[p95Idx]
    const outliers = arr.filter((r) => (r.duration_sec as number) > p95 && r.outcome !== 'completed')
    if (outliers.length < 3) continue
    out.push({
      pattern_key: `duration_outliers:${proj}`,
      title: `Projecto ${proj}: ${outliers.length} sessões longas não concluídas`,
      description: `Sessões com duração acima do p95 (${p95}s) e outcome != completed. Sinal de sessões penduradas.`,
      severity: 'warning',
      metric_value: p95,
      sample_session_ids: outliers.slice(0, 5).map((r) => r.session_id),
      affected_count: outliers.length,
    })
  }
  return out
}

/** 5. Sessões abandonadas (event_count < 3 AND outcome=unknown). */
export function detectAbandonedSessions(ctx: DetectCtx): Pattern[] {
  const rows = ctx.db.prepare(`
    SELECT session_id FROM sessions
    WHERE started_at >= ? AND started_at <= ?
      AND event_count < 3 AND outcome = 'unknown'
  `).all(ctx.weekStartIso, ctx.weekEndIso) as Array<{ session_id: string }>
  if (rows.length < 5) return []
  return [{
    pattern_key: 'abandoned_sessions',
    title: `${rows.length} sessões abandonadas esta semana`,
    description: `Sessões com menos de 3 eventos e outcome=unknown — tipicamente abertas e descartadas.`,
    severity: 'info',
    metric_value: rows.length,
    sample_session_ids: rows.slice(0, 5).map((r) => r.session_id),
    affected_count: rows.length,
  }]
}

/** 6. Crescimento de complexidade: avg(tool_calls) actual vs semana anterior. */
export function detectGrowingComplexity(ctx: DetectCtx, prevWeekStartIso: string, prevWeekEndIso: string): Pattern[] {
  const curRows = baseRows(ctx)
  const prevRows = ctx.db.prepare(`
    SELECT skills_invoked, tool_calls FROM sessions
    WHERE started_at >= ? AND started_at <= ?
  `).all(prevWeekStartIso, prevWeekEndIso) as Array<{ skills_invoked: string; tool_calls: number }>

  const curBySkill = new Map<string, { sum: number; count: number; ids: string[] }>()
  for (const r of curRows) {
    let sk: string[] = []
    try { sk = JSON.parse(r.skills_invoked) } catch {}
    for (const s of sk) {
      const e = curBySkill.get(s) ?? { sum: 0, count: 0, ids: [] }
      e.sum += r.tool_calls
      e.count++
      if (e.ids.length < 5) e.ids.push(r.session_id)
      curBySkill.set(s, e)
    }
  }
  const prevBySkill = new Map<string, { sum: number; count: number }>()
  for (const r of prevRows) {
    let sk: string[] = []
    try { sk = JSON.parse(r.skills_invoked) } catch {}
    for (const s of sk) {
      const e = prevBySkill.get(s) ?? { sum: 0, count: 0 }
      e.sum += r.tool_calls
      e.count++
      prevBySkill.set(s, e)
    }
  }
  const out: Pattern[] = []
  for (const [skill, cur] of curBySkill) {
    if (cur.count < 5) continue
    const curAvg = cur.sum / cur.count
    const prev = prevBySkill.get(skill)
    if (!prev || prev.count < 3) continue
    const prevAvg = prev.sum / prev.count
    if (prevAvg === 0 || curAvg <= prevAvg * 1.3) continue
    out.push({
      pattern_key: `growing_complexity:${skill}`,
      title: `Skill ${skill}: tool_calls médio +${Math.round((curAvg / prevAvg - 1) * 100)}% vs semana anterior`,
      description: `Média de tool_calls/sessão subiu de ${prevAvg.toFixed(1)} para ${curAvg.toFixed(1)}.`,
      severity: 'warning',
      metric_value: Math.round(curAvg * 10) / 10,
      sample_session_ids: cur.ids,
      affected_count: cur.count,
    })
  }
  return out
}

/** Orquestra todos os detectores para a semana indicada. */
export function detectPatterns(
  dbWrapper: SessionsDb,
  weekStart: Date,
  weekEnd: Date,
): Pattern[] {
  const db = dbWrapper.rawDb()
  const ctx: DetectCtx = {
    db,
    weekStartIso: iso(weekStart),
    weekEndIso: iso(weekEnd),
  }
  const prevStart = new Date(weekStart); prevStart.setUTCDate(prevStart.getUTCDate() - 7)
  const prevEnd = new Date(weekEnd); prevEnd.setUTCDate(prevEnd.getUTCDate() - 7)
  return [
    ...detectSkillsHighErrorRate(ctx),
    ...detectToolsLowEfficiency(ctx),
    ...detectSkillToolPairs(ctx),
    ...detectDurationOutliers(ctx),
    ...detectAbandonedSessions(ctx),
    ...detectGrowingComplexity(ctx, iso(prevStart), iso(prevEnd)),
  ]
}

/** Converte Pattern + contexto em PatternRecord pronto a persistir. */
export function toPatternRecord(p: Pattern, weekIso: string, consecutiveWeeks: number): PatternRecord {
  return {
    detected_at: new Date().toISOString(),
    week_iso: weekIso,
    pattern_key: p.pattern_key,
    title: p.title,
    description: p.description,
    severity: p.severity,
    metric_value: p.metric_value,
    sample_session_ids: p.sample_session_ids,
    affected_count: p.affected_count,
    consecutive_weeks: consecutiveWeeks,
  }
}