/**
 * Timeline types + grouping.
 *
 * This is the contract between the future `GET /api/history` route and the
 * history page.
 *
 * ── Reference, don't duplicate ─────────────────────────────────────────
 * An entry is a *pointer* to a record plus an optional narrative override.
 * When the admin panel's "add to timeline" button fires on an event, it
 * writes a row holding the event's id and nothing else; title, logo and
 * date are read back from `events` at query time. Editing the event
 * therefore edits the timeline, and there is no second copy to drift.
 *
 * Hand-authored entries — "bylaws rewritten", "the gathering becomes
 * annual" — carry no ref and supply their own title and blurb. An entry
 * may also do both: reference an event but override its title, for when
 * the timeline wants to say something the event card doesn't.
 *
 * ── What the server resolves, and what it doesn't ──────────────────────
 * The server resolves *data*: title, date, logo filename, the members of
 * a referenced team. It does not resolve *routes* or *asset paths* —
 * those are presentation, and live in `timelineRefs.ts` so React Router
 * and the public/ layout stay the frontend's business.
 */

import type { OrgKind } from './hrefs.ts'

export type DatePrecision = 'year' | 'month' | 'day'

/** What an entry is about. Drives the marker and the body layout. */
export type TimelineKind =
  | 'milestone'      // free-standing narrative, no record behind it
  | 'event'
  | 'organization'
  | 'award'
  | 'people'         // a team forming, someone joining one

/** Tables an entry can point at. Mirrors the polymorphic owner_kind
 *  pattern already used by content_blocks and links. */
export type RefKind = 'event' | 'organization' | 'award' | 'person' | 'team'

export type TimelineRef = {
  kind: RefKind
  /** The row's TEXT primary key — an event id, org slug, team slug. */
  id: string
  /** Only on organizations: history.js copies v_timeline.org_kind. */
  orgKind?: OrgKind
}

/** Filename plus the table it came from; the directory is derived
 *  frontend-side, because asset layout is not database business. */
export type TimelineLogo = {
  file: string
  kind: RefKind
}

/** A person as they appear in a 'people' entry. Resolved server-side,
 *  whether the entry named a team or listed people directly. */
export type PersonRef = {
  id: string
  name: string
  /** people.photo — filename only. */
  photo?: string
  /** Their affiliation title at the time, if it's worth printing. */
  title?: string
}

export type TeamRef = {
  id: string
  name: string
  orgId?: string
  orgName?: string
  logo?: string
}

export type TimelineItem = {
  /** The timeline row's own id, not the referenced record's. */
  id: string
  /** "2014" | "2014-06" | "2014-06-12" */
  date: string
  /** How much of `date` is trustworthy. Authoritative — a backfilled row
   *  may hold a full date while only the year is actually known. */
  precision: DatePrecision
  kind: TimelineKind

  /** Falls back to the referenced record's own name when the row has no
   *  title of its own. Resolved server-side. */
  title: string
  blurb?: string
  /** Secondary line: host org, region, venue, recipient. */
  meta?: string
  featured?: boolean

  /** The record this points at. Absent for free-standing milestones. */
  ref?: TimelineRef
  /** Explicit link override. Absent → derived from `ref`. Every kind can
   *  carry one; event/organization/award fall back to their own page. */
  href?: string

  logo?: TimelineLogo

  /** kind === 'people': who the entry is about. Populated from the named
   *  team's current members, or from an explicit person list. */
  people?: PersonRef[]
  /** Set when the entry named a team rather than loose people. */
  team?: TeamRef
}

export type DecadeMeta = {
  /** 2010, 2020, … */
  decade: number
  title: string
  tagline: string
  blurb?: string
  /** Renders the ghosted treatment and the "before NGU" marker. */
  preProgram?: boolean
}

export type GroupedMonth = {
  month: number
  label: string
  items: TimelineItem[]
}

export type GroupedYear = {
  year: number
  featured: boolean
  count: number
  featuredItems: TimelineItem[]
  /** Year-precision items — known to be this year, month unknown. */
  undated: TimelineItem[]
  months: GroupedMonth[]
}

export type GroupedDecade = DecadeMeta & {
  years: GroupedYear[]
  count: number
}

export type SortDirection = 'desc' | 'asc'

export const MONTH_LABELS = [
  'January', 'February', 'March', 'April', 'May', 'June',
  'July', 'August', 'September', 'October', 'November', 'December',
]

export function decadeOf(year: number): number {
  return Math.floor(year / 10) * 10
}

export function decadeLabel(decade: number): string {
  return `${decade}s`
}

// ── dates ────────────────────────────────────────────────────────────

type DateParts = { year: number; month: number | null; day: number | null }

function parseDate(item: TimelineItem): DateParts {
  const [y, m, d] = item.date.split('-')
  const year = Number(y)
  if (!Number.isFinite(year)) {
    throw new Error(`Timeline item ${item.id} has an unparseable date: "${item.date}"`)
  }
  if (item.precision === 'year') return { year, month: null, day: null }
  const month = m ? Number(m) : null
  if (item.precision === 'month') return { year, month, day: null }
  return { year, month, day: d ? Number(d) : null }
}

const pad = (n: number) => String(n).padStart(2, '0')

/**
 * Start of the item's date window, as a sortable YYYY-MM-DD.
 *
 * A year-precision item resolves to 1 January, a month-precision one to
 * the 1st. That makes "is this still upcoming?" answerable for imprecise
 * dates in the one way that can't surprise anyone: an entry stops being
 * upcoming as soon as any part of its window has passed. A row dated
 * only "2027" is upcoming through the end of 2026 and no longer is on
 * 1 January 2027, even though its real date may be months away.
 */
export function windowStart(item: TimelineItem): string {
  const { year, month, day } = parseDate(item)
  return `${year}-${pad(month ?? 1)}-${pad(day ?? 1)}`
}

export function todayISO(now: Date = new Date()): string {
  return `${now.getFullYear()}-${pad(now.getMonth() + 1)}-${pad(now.getDate())}`
}

/**
 * Split upcoming from recorded, off the wall clock rather than a flag.
 * Nothing needs flipping when a date passes.
 */
export function partitionByDate(
  items: TimelineItem[],
  now: Date = new Date(),
): { upcoming: TimelineItem[]; past: TimelineItem[] } {
  const today = todayISO(now)
  const upcoming: TimelineItem[] = []
  const past: TimelineItem[] = []
  for (const item of items) {
    if (windowStart(item) > today) upcoming.push(item)
    else past.push(item)
  }
  return { upcoming, past }
}

// ── grouping ─────────────────────────────────────────────────────────

function byDay(dir: SortDirection) {
  return (a: TimelineItem, b: TimelineItem) => {
    const da = parseDate(a).day
    const db = parseDate(b).day
    if (da == null && db == null) return a.title.localeCompare(b.title)
    if (da == null) return 1
    if (db == null) return -1
    return dir === 'desc' ? db - da : da - db
  }
}

function byFeaturedThenDay(dir: SortDirection) {
  const day = byDay(dir)
  return (a: TimelineItem, b: TimelineItem) => {
    if (!!a.featured !== !!b.featured) return a.featured ? -1 : 1
    return day(a, b)
  }
}

export type GroupOptions = {
  direction?: SortDirection
  /**
   * Decades ending before this year get the pre-program treatment even
   * if the decade row doesn't say so. Lets the gap survive missing
   * metadata.
   */
  programStartYear?: number
  /**
   * Repeat featured items inside their month node as well as in the
   * featured block. Off by default — in a sparse year it just prints the
   * same line twice. A month left with nothing but featured items drops
   * out entirely.
   */
  featuredInMonths?: boolean
}

/** Bucket a flat item list into years. Shared by the main rail and the
 *  upcoming block above it. */
export function groupYears(
  items: TimelineItem[],
  options: GroupOptions = {},
): GroupedYear[] {
  const direction = options.direction ?? 'desc'
  const featuredInMonths = options.featuredInMonths ?? false
  const sign = direction === 'desc' ? -1 : 1

  const yearBuckets = new Map<number, TimelineItem[]>()
  for (const item of items) {
    const { year } = parseDate(item)
    const bucket = yearBuckets.get(year)
    if (bucket) bucket.push(item)
    else yearBuckets.set(year, [item])
  }

  const years: GroupedYear[] = []

  for (const [year, yearItems] of yearBuckets) {
    const featuredItems: TimelineItem[] = []
    const undated: TimelineItem[] = []
    const monthMap = new Map<number, TimelineItem[]>()

    for (const item of yearItems) {
      if (item.featured) {
        featuredItems.push(item)
        if (!featuredInMonths) continue
      }
      const { month } = parseDate(item)
      if (month == null) {
        undated.push(item)
        continue
      }
      const bucket = monthMap.get(month)
      if (bucket) bucket.push(item)
      else monthMap.set(month, [item])
    }

    const months: GroupedMonth[] = [...monthMap.entries()]
      .sort((a, b) => sign * (a[0] - b[0]))
      .map(([month, monthItems]) => ({
        month,
        label: MONTH_LABELS[month - 1] ?? `Month ${month}`,
        items: monthItems.sort(byFeaturedThenDay(direction)),
      }))

    featuredItems.sort(byDay(direction))
    undated.sort((a, b) => a.title.localeCompare(b.title))

    years.push({
      year,
      featured: featuredItems.length > 0,
      count: yearItems.length,
      featuredItems,
      undated,
      months,
    })
  }

  return years.sort((a, b) => sign * (a.year - b.year))
}

export function groupTimeline(
  items: TimelineItem[],
  decades: DecadeMeta[],
  options: GroupOptions = {},
): GroupedDecade[] {
  const direction = options.direction ?? 'desc'
  const sign = direction === 'desc' ? -1 : 1
  const metaByDecade = new Map(decades.map((d) => [d.decade, d]))

  const decadeBuckets = new Map<number, GroupedYear[]>()
  for (const year of groupYears(items, options)) {
    const dec = decadeOf(year.year)
    const bucket = decadeBuckets.get(dec)
    if (bucket) bucket.push(year)
    else decadeBuckets.set(dec, [year])
  }

  // Include decades that have metadata but no items yet, so an authored
  // "before NGU" decade still renders its marker.
  for (const meta of decades) {
    if (!decadeBuckets.has(meta.decade)) decadeBuckets.set(meta.decade, [])
  }

  return [...decadeBuckets.entries()]
    .sort((a, b) => sign * (a[0] - b[0]))
    .map(([decade, years]) => {
      const meta = metaByDecade.get(decade)
      const inferredPreProgram =
        options.programStartYear != null && decade + 9 < options.programStartYear
      return {
        decade,
        title: meta?.title ?? decadeLabel(decade),
        tagline: meta?.tagline ?? '',
        blurb: meta?.blurb,
        preProgram: meta?.preProgram ?? inferredPreProgram,
        years: years.sort((a, b) => sign * (a.year - b.year)),
        count: years.reduce((sum, y) => sum + y.count, 0),
      }
    })
}

/**
 * Insert empty year nodes between the first and last year that actually
 * has data, so sparse decades read as gaps in the record rather than as
 * a shorter decade. Does not pad beyond the data.
 */
export function withGapYears(
  years: GroupedYear[],
  direction: SortDirection = 'desc',
): GroupedYear[] {
  if (years.length < 2) return years

  const present = new Map(years.map((y) => [y.year, y]))
  const all = years.map((y) => y.year)
  const min = Math.min(...all)
  const max = Math.max(...all)
  const filled: GroupedYear[] = []

  for (let year = min; year <= max; year += 1) {
    filled.push(
      present.get(year) ?? {
        year,
        featured: false,
        count: 0,
        featuredItems: [],
        undated: [],
        months: [],
      },
    )
  }

  return direction === 'desc' ? filled.reverse() : filled
}

/** Years that should start expanded: the most recent year with featured items. */
export function defaultOpenYears(decades: GroupedDecade[]): number[] {
  for (const decade of decades) {
    if (decade.preProgram) continue
    const hit = decade.years.find((y) => y.featured)
    if (hit) return [hit.year]
  }
  return []
}