// The reads and the actions, one function per contract operation. Plain async functions plus plain
// option objects: the query layer is React's, and `src/api/` stays free of React so that the seam
// can be tested and replaced without a renderer.
//
// Every read goes through the same two steps in the same order — follow the cursor to the end of
// the collection, then narrow the vocabularies, then let the revision guard drop a stale answer.

import { replaceEqualDeep } from '@tanstack/react-query';

import { request, requestAll } from './client';
import { narrow } from './contract';
import { bookStatus } from './vocabulary';
import type {
  Bank,
  BankDecision,
  BookDetail,
  BookStatus,
  ChapterList,
  Id,
  Library,
  NoteList,
  Run,
  RunOptions,
  UnitList,
  Usage,
} from './contract';
import type { components } from './schema';

type Schemas = components['schemas'];

/**
 * Discarding a stale read is the CLIENT's duty (contract, `Revision`), and this is where it is done
 * — against what the application HAS, not against a copy of it.
 *
 * The counter is per book, and the stream carries the same counter: a frame raises the revision of
 * the cache entry it patches, so a read prepared before that frame and delivered after it arrives
 * with a LOWER number and is dropped here. Comparing against a private copy of the last read
 * instead — which is what this code did first — never saw the frame at all, and the interface
 * rolled progress backwards on every refetch on focus. The query layer already holds the previous
 * value; a second store of it was both a leak and a lie.
 */
export function freshest<T extends { revision: number }>(previous: T | undefined, next: T): T {
  return previous !== undefined && next.revision < previous.revision ? previous : next;
}

// Applied by the query layer to every read below.
//
// ⚠ COMPOSED with the library's own structural sharing, not substituted for it. `structuralSharing`
// is a single slot: a function there REPLACES `replaceEqualDeep`, and every read rebuilds its rows
// (`rows.map(narrow.*)`), so an ordinary refetch would hand the cache a wholly new object graph.
// The lists this feeds are the 2284-chapter tree and the 1200-term bank, which rebuild their whole
// collection on a new identity — a full rebuild on every window focus, where the library would have
// produced no render at all.
const dropStaleReads = {
  structuralSharing: (previous: unknown, next: unknown) => {
    const kept = freshest(
      previous as { revision: number } | undefined,
      next as { revision: number },
    );
    return kept === next ? replaceEqualDeep(previous, next) : kept;
  },
};

/**
 * How often a book still in intake is asked about again, in milliseconds.
 *
 * ⚠ POLLING, and it is the contract's shape that forces it rather than a shortcut: the live channel
 * belongs to a RUN (`/runs/{runId}/events`), and a book being uploaded or parsed has no run — so
 * nothing pushes "the parsing is over". Without asking again, a book stays `parsing` on the screen
 * until something else happens to invalidate the read. The interval is deliberately unhurried: this
 * is a step that takes minutes on a real book, and the answer is a small JSON. It stops the moment
 * the book leaves intake — a poll that never stops is the thing to be afraid of here (BACKLOG Ф-56:
 * an event for the end of the intake is a question for the contract's owner).
 */
export const intakePollMs = 3000;

/** Whether a book is still arriving. The answer is a property of the STATUS and lives with it. */
export const inIntake = (status: BookStatus | null | undefined) =>
  status !== undefined && bookStatus.describe(status).intake === true;

export const keys = {
  library: () => ['library'] as const,
  book: (bookId: Id) => ['book', bookId] as const,
  chapters: (bookId: Id) => ['chapters', bookId] as const,
  units: (bookId: Id, chapterId: Id) => ['units', bookId, chapterId] as const,
  /** The text of EVERY chapter of one book — the scope a stage boundary makes stale. */
  bookUnits: (bookId: Id) => ['units', bookId] as const,
  notes: (bookId: Id) => ['notes', bookId] as const,
  bank: (bookId: Id) => ['bank', bookId] as const,
  usage: () => ['usage'] as const,
  runOptions: (bookId: Id) => ['run-options', bookId] as const,
};

/**
 * Everything read ABOUT one book. The book id stands second in every book-scoped key and nowhere
 * else, so a resync can throw away one book's world without touching the library, the usage or a
 * second book — which a keyless `invalidateQueries()` did.
 */
export const bookScope = (bookId: Id) => ({
  predicate: (query: { queryKey: readonly unknown[] }) => query.queryKey[1] === bookId,
});

export async function readLibrary(): Promise<Library> {
  const { page, rows } = await requestAll<Schemas['Book'], Schemas['Library']>(
    '/books',
    (body) => body.books,
  );
  return { ...page, books: rows.map(narrow.book) };
}

export async function readBook(bookId: Id): Promise<BookDetail> {
  const wire = await request<Schemas['BookDetail']>(`/books/${encodeURIComponent(bookId)}`);
  return { ...wire, book: narrow.book(wire.book), run: wire.run ? narrow.run(wire.run) : wire.run };
}

export async function readChapters(bookId: Id): Promise<ChapterList> {
  const { page, rows } = await requestAll<Schemas['Chapter'], Schemas['ChapterList']>(
    `/books/${encodeURIComponent(bookId)}/chapters`,
    (body) => body.chapters,
  );
  return { ...page, chapters: rows };
}

export async function readUnits(bookId: Id, chapterId: Id): Promise<UnitList> {
  const { page, rows } = await requestAll<Schemas['Unit'], Schemas['UnitList']>(
    `/books/${encodeURIComponent(bookId)}/chapters/${encodeURIComponent(chapterId)}/units`,
    (body) => body.units,
  );
  return { ...page, units: rows.map(narrow.unit) };
}

export async function readNotes(bookId: Id): Promise<NoteList> {
  const { page, rows } = await requestAll<Schemas['Note'], Schemas['NoteList']>(
    `/books/${encodeURIComponent(bookId)}/notes`,
    (body) => body.notes,
  );
  return { ...page, notes: rows.map(narrow.note) };
}

export async function readBank(bookId: Id): Promise<Bank> {
  let counts = { total: 0, signed: 0 };
  const { page, rows } = await requestAll<Schemas['BankTerm'], Schemas['Bank']>(
    `/books/${encodeURIComponent(bookId)}/bank`,
    (body) => {
      // Both counts are of the whole bank, not of the page, so the last page's numbers are the
      // book's numbers — a sum across pages would multiply them.
      counts = { total: body.total, signed: body.signed };
      return body.terms;
    },
  );
  return { ...page, ...counts, terms: rows.map(narrow.term) };
}

export async function readUsage(): Promise<Usage> {
  return narrow.usage(await request<Schemas['Usage']>('/usage'));
}

export async function readRunOptions(bookId: Id): Promise<RunOptions> {
  return request<RunOptions>(`/books/${encodeURIComponent(bookId)}/run-options`);
}

/**
 * Option objects for the query layer. Plain data, so the screen writes `useQuery(libraryQuery())`
 * and the key never gets paired with the wrong function in two different screens.
 */
export const libraryQuery = () => ({
  queryKey: keys.library(),
  queryFn: readLibrary,
  ...dropStaleReads,
  refetchInterval: ({ state }: { state: { data?: Library } }) =>
    state.data?.books.some((book) => inIntake(book.status)) === true ? intakePollMs : false,
});
export const bookQuery = (bookId: Id) => ({
  queryKey: keys.book(bookId),
  queryFn: () => readBook(bookId),
  ...dropStaleReads,
  refetchInterval: ({ state }: { state: { data?: BookDetail } }) =>
    inIntake(state.data?.book.status) ? intakePollMs : false,
});
export const chaptersQuery = (bookId: Id) => ({
  queryKey: keys.chapters(bookId),
  queryFn: () => readChapters(bookId),
  ...dropStaleReads,
});
export const unitsQuery = (bookId: Id, chapterId: Id) => ({
  queryKey: keys.units(bookId, chapterId),
  queryFn: () => readUnits(bookId, chapterId),
  ...dropStaleReads,
});
export const notesQuery = (bookId: Id) => ({
  queryKey: keys.notes(bookId),
  queryFn: () => readNotes(bookId),
  ...dropStaleReads,
});
export const bankQuery = (bookId: Id) => ({
  queryKey: keys.bank(bookId),
  queryFn: () => readBank(bookId),
  ...dropStaleReads,
});
export const usageQuery = () => ({ queryKey: keys.usage(), queryFn: readUsage });
export const runOptionsQuery = (bookId: Id) => ({
  queryKey: keys.runOptions(bookId),
  queryFn: () => readRunOptions(bookId),
  // ⚠ NEVER fresh from the cache, against the client's own 15-second default: the whole reason
  // these bounds are a resource of their own is that the maximum belongs to the ACCOUNT and moves
  // while the book does not (contract, `run-options`). Re-opening the form within the window
  // otherwise showed a scale read before somebody else's hold was taken.
  staleTime: 0,
});

// Actions. Unsafe methods, so every one of them carries `X-TM-Client` — the client half of the
// CSRF rule, applied by `request()` and not by each caller.

export async function startRun(bookId: Id, body: Schemas['RunRequest']): Promise<Run> {
  return narrow.run(
    await request<Schemas['Run']>(`/books/${encodeURIComponent(bookId)}/runs`, {
      method: 'POST',
      body,
    }),
  );
}

export async function stopRun(runId: Id): Promise<Run> {
  return narrow.run(
    await request<Schemas['Run']>(`/runs/${encodeURIComponent(runId)}/stop`, { method: 'POST' }),
  );
}

export async function resumeRun(runId: Id): Promise<Run> {
  return narrow.run(
    await request<Schemas['Run']>(`/runs/${encodeURIComponent(runId)}/resume`, { method: 'POST' }),
  );
}

export async function submitBankDecisions(
  bookId: Id,
  decisions: BankDecision[],
): Promise<Schemas['BankDecisionsResult']> {
  return request<Schemas['BankDecisionsResult']>(
    `/books/${encodeURIComponent(bookId)}/bank/decisions`,
    { method: 'POST', body: { decisions } },
  );
}