import type { Pool } from "pg"

export type PartitionKind = "day" | "week" | "month"

export interface PartitionSpec {
  parent: string
  kind: PartitionKind
  keepDays: number
}

/** Leaf-only: PG forbids storage params on partitioned parents (SQLSTATE 42809). */
const FACT_LEAF_STORAGE =
  "fillfactor = 70, autovacuum_vacuum_scale_factor = 0.05, autovacuum_vacuum_cost_limit = 2000"

const FACT_PARENTS = new Set(["flow_hour_facts", "flow_daily_facts"])

export const PARTITION_SPECS: PartitionSpec[] = [
  { parent: "flow_buckets", kind: "day", keepDays: 4 },
  { parent: "flow_minute_stats", kind: "day", keepDays: 4 },
  { parent: "flow_minute_dims", kind: "day", keepDays: 4 },
  { parent: "flow_daily_dims", kind: "month", keepDays: 420 },
  { parent: "flow_hour_facts", kind: "day", keepDays: 3 },
  { parent: "flow_daily_facts", kind: "month", keepDays: 420 },
  { parent: "traffic_samples", kind: "week", keepDays: 21 },
  { parent: "servers_rest_ping_samples", kind: "week", keepDays: 35 },
  { parent: "uptime_probe_samples", kind: "week", keepDays: 21 },
  { parent: "uptime_resource_samples", kind: "week", keepDays: 21 },
  { parent: "server_snapshots", kind: "week", keepDays: 21 },
  { parent: "internet_path_snapshots", kind: "week", keepDays: 21 },
]

const WEEK_SLACK_DAYS = 7

async function resolveKeepDays(pool: Pool): Promise<Map<string, number>> {
  const map = new Map(PARTITION_SPECS.map((s) => [s.parent, s.keepDays]))
  try {
    const traffic = await pool.query<{ retention_days: number }>(
      `SELECT retention_days FROM traffic_settings WHERE id = 1`,
    )
    const td = Number(traffic.rows[0]?.retention_days)
    if (Number.isFinite(td) && td > 0) map.set("traffic_samples", td + WEEK_SLACK_DAYS)

    const uptime = await pool.query<{ retention_days: number }>(
      `SELECT retention_days FROM uptime_settings WHERE id = 1`,
    )
    const ud = Number(uptime.rows[0]?.retention_days)
    if (Number.isFinite(ud) && ud > 0) {
      map.set("uptime_probe_samples", ud + WEEK_SLACK_DAYS)
      map.set("uptime_resource_samples", ud + WEEK_SLACK_DAYS)
    }

    const path = await pool.query<{ retention_days: number }>(
      `SELECT retention_days FROM internet_path_settings WHERE id = 1`,
    )
    const pd = Number(path.rows[0]?.retention_days)
    if (Number.isFinite(pd) && pd > 0) map.set("internet_path_snapshots", pd + WEEK_SLACK_DAYS)
  } catch {
    /* settings may be absent mid-migration */
  }
  return map
}

function utcDate(d: Date): Date {
  return new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate()))
}

function addUtcDays(d: Date, n: number): Date {
  const x = utcDate(d)
  x.setUTCDate(x.getUTCDate() + n)
  return x
}

function startOfWeekUtc(d: Date): Date {
  const x = utcDate(d)
  const day = x.getUTCDay() || 7
  x.setUTCDate(x.getUTCDate() - (day - 1))
  return x
}

function startOfMonthUtc(d: Date): Date {
  return new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), 1))
}

function fmtDay(d: Date): string {
  return d.toISOString().slice(0, 10)
}

function partName(parent: string, kind: PartitionKind, start: Date): string {
  if (kind === "day") return `${parent}_d_${fmtDay(start).replaceAll("-", "")}`
  if (kind === "week") return `${parent}_w_${fmtDay(start).replaceAll("-", "")}`
  return `${parent}_m_${start.getUTCFullYear()}${String(start.getUTCMonth() + 1).padStart(2, "0")}`
}

function rangeFor(kind: PartitionKind, ts: Date): { start: Date; end: Date } {
  if (kind === "day") {
    const start = utcDate(ts)
    return { start, end: addUtcDays(start, 1) }
  }
  if (kind === "week") {
    const start = startOfWeekUtc(ts)
    return { start, end: addUtcDays(start, 7) }
  }
  const start = startOfMonthUtc(ts)
  const end = new Date(Date.UTC(start.getUTCFullYear(), start.getUTCMonth() + 1, 1))
  return { start, end }
}

export async function ensurePartitionFor(
  pool: Pool,
  parent: string,
  kind: PartitionKind,
  ts: Date,
): Promise<string> {
  const { start, end } = rangeFor(kind, ts)
  const name = partName(parent, kind, start)
  const from = fmtDay(start)
  const to = fmtDay(end)
  await pool.query(
    `CREATE TABLE IF NOT EXISTS ${name} PARTITION OF ${parent} FOR VALUES FROM ('${from}') TO ('${to}')`,
  )
  if (FACT_PARENTS.has(parent)) {
    await pool.query(`ALTER TABLE ${name} SET (${FACT_LEAF_STORAGE})`)
  }
  return name
}

export async function ensurePartitionsBetween(
  pool: Pool,
  parent: string,
  kind: PartitionKind,
  from: Date,
  to: Date,
): Promise<void> {
  const start = from.getTime() <= to.getTime() ? from : to
  const end = from.getTime() <= to.getTime() ? to : from
  for (let t = new Date(start.getTime()); t <= end; ) {
    await ensurePartitionFor(pool, parent, kind, t)
    if (kind === "day") t = addUtcDays(t, 1)
    else if (kind === "week") t = addUtcDays(t, 7)
    else t = new Date(Date.UTC(t.getUTCFullYear(), t.getUTCMonth() + 1, 1))
  }
}

export async function ensurePartitionsAround(pool: Pool, around = new Date()): Promise<void> {
  const keepDays = await resolveKeepDays(pool)
  for (const spec of PARTITION_SPECS) {
    const keep = keepDays.get(spec.parent) ?? spec.keepDays
    const daysAhead = spec.kind === "month" ? 40 : spec.kind === "week" ? 21 : 8
    const start = addUtcDays(around, -keep)
    const end = addUtcDays(around, daysAhead)
    for (let t = new Date(start.getTime()); t < end; ) {
      await ensurePartitionFor(pool, spec.parent, spec.kind, t)
      if (spec.kind === "day") t = addUtcDays(t, 1)
      else if (spec.kind === "week") t = addUtcDays(t, 7)
      else t = new Date(Date.UTC(t.getUTCFullYear(), t.getUTCMonth() + 1, 1))
    }
  }
}

export async function dropExpiredPartitions(pool: Pool, around = new Date()): Promise<void> {
  const keepDays = await resolveKeepDays(pool)
  for (const spec of PARTITION_SPECS) {
    const keep = keepDays.get(spec.parent) ?? spec.keepDays
    const cutoff = addUtcDays(around, -keep)
    const { rows } = await pool.query<{ relname: string }>(
      `SELECT c.relname
       FROM pg_inherits i
       JOIN pg_class c ON c.oid = i.inhrelid
       JOIN pg_class p ON p.oid = i.inhparent
       WHERE p.relname = $1`,
      [spec.parent],
    )
    for (const row of rows) {
      const m = row.relname.match(/_([dwm])_(\d{8}|\d{6})$/)
      if (!m) continue
      const stamp = m[2]
      let start: Date
      if (stamp.length === 6) {
        start = new Date(Date.UTC(Number(stamp.slice(0, 4)), Number(stamp.slice(4, 6)) - 1, 1))
      } else {
        start = new Date(`${stamp.slice(0, 4)}-${stamp.slice(4, 6)}-${stamp.slice(6, 8)}T00:00:00Z`)
      }
      if (start < cutoff) {
        await pool.query(`DROP TABLE IF EXISTS ${row.relname}`)
      }
    }
  }
}

export function specForParent(parent: string): PartitionSpec | undefined {
  return PARTITION_SPECS.find((s) => s.parent === parent)
}