import type { ProductWorkspaceStore } from './store'
import type { BacklogPbi, BacklogStory, BacklogTask, TaskDetail } from './types'

// G1: stable EMPTY-references zodat selectors geen nieuwe array per call retourneren.
const EMPTY_PBIS: BacklogPbi[] = []
const EMPTY_STORIES: BacklogStory[] = []
const EMPTY_TASKS: (BacklogTask | TaskDetail)[] = []

/**
 * Lijst-selector. Vereist `useShallow` in componenten (G2) — anders re-rendert
 * elke ongerelateerde store-mutatie het component.
 */
export function selectVisiblePbis(s: ProductWorkspaceStore): BacklogPbi[] {
  if (s.relations.pbiIds.length === 0) return EMPTY_PBIS
  const out: BacklogPbi[] = []
  for (const id of s.relations.pbiIds) {
    const pbi = s.entities.pbisById[id]
    if (pbi) out.push(pbi)
  }
  return out.length === 0 ? EMPTY_PBIS : out
}

/**
 * Lijst-selector. Vereist `useShallow` in componenten (G2).
 */
export function selectStoriesForActivePbi(s: ProductWorkspaceStore): BacklogStory[] {
  const pbiId = s.context.activePbiId
  if (!pbiId) return EMPTY_STORIES
  const ids = s.relations.storyIdsByPbi[pbiId]
  if (!ids || ids.length === 0) return EMPTY_STORIES
  const out: BacklogStory[] = []
  for (const id of ids) {
    const story = s.entities.storiesById[id]
    if (story) out.push(story)
  }
  return out.length === 0 ? EMPTY_STORIES : out
}

/**
 * Lijst-selector. Vereist `useShallow` in componenten (G2).
 */
export function selectTasksForActiveStory(
  s: ProductWorkspaceStore,
): (BacklogTask | TaskDetail)[] {
  const storyId = s.context.activeStoryId
  if (!storyId) return EMPTY_TASKS
  const ids = s.relations.taskIdsByStory[storyId]
  if (!ids || ids.length === 0) return EMPTY_TASKS
  const out: (BacklogTask | TaskDetail)[] = []
  for (const id of ids) {
    const task = s.entities.tasksById[id]
    if (task) out.push(task)
  }
  return out.length === 0 ? EMPTY_TASKS : out
}

/**
 * Single-value selector. `useShallow` niet vereist — retourneert stable
 * entity-reference (zelfde object zolang entity ongewijzigd).
 */
export function selectActivePbi(s: ProductWorkspaceStore): BacklogPbi | null {
  const id = s.context.activePbiId
  if (!id) return null
  return s.entities.pbisById[id] ?? null
}

/**
 * Single-value selector. `useShallow` niet vereist.
 */
export function selectActiveStory(s: ProductWorkspaceStore): BacklogStory | null {
  const id = s.context.activeStoryId
  if (!id) return null
  return s.entities.storiesById[id] ?? null
}

/**
 * Single-value selector. `useShallow` niet vereist.
 */
export function selectActiveTask(
  s: ProductWorkspaceStore,
): BacklogTask | TaskDetail | null {
  const id = s.context.activeTaskId
  if (!id) return null
  return s.entities.tasksById[id] ?? null
}

/**
 * Single-value selector voor stories binnen een specifiek PBI (niet per se actief).
 */
export function selectStoriesForPbi(
  s: ProductWorkspaceStore,
  pbiId: string,
): BacklogStory[] {
  const ids = s.relations.storyIdsByPbi[pbiId]
  if (!ids || ids.length === 0) return EMPTY_STORIES
  const out: BacklogStory[] = []
  for (const id of ids) {
    const story = s.entities.storiesById[id]
    if (story) out.push(story)
  }
  return out.length === 0 ? EMPTY_STORIES : out
}