import type { RecordUsage } from "@/types/usage";

import { apiGet, apiPost, apiPatch, apiDelete } from "@/api/client";

/** A lesson: a transferable insight, retrievable by the SITUATION it applies
 *  to rather than by its topic.
 *
 *  The fields mirror what the backend composes and reads back
 *  (`services/lessons.py::lesson_to_dict`), not the stored row. `title` and
 *  `body` are DERIVED — the service builds them from `what`, `when_to_apply`
 *  and `insight` — so an editor sends the three parts and never the document.
 *  That is the whole design: the trigger ends up in the title and again at the
 *  head of the body, which is what makes a lesson rank on when it applies. */
export interface Lesson {
  id: number;
  /** The composed document title, `{what} — {when_to_apply}`. Read-only. */
  title: string;
  /** The composed body. Read-only — edit `insight` instead. */
  body: string;
  /** The claim itself, as you would say it. */
  what: string;
  /** WHEN this applies — the situation, in the words it presents itself in.
   *  The entire retrieval story: a lesson without one saves, reads correctly
   *  and never surfaces, so both doors refuse an empty one. */
  when_to_apply: string;
  /** The body with the composed lines stripped — what an edit form binds to,
   *  so saving doesn't accumulate a copy of the trigger line per save. */
  insight: string;
  /** Ids of the records that taught this — issues, tasks or notes. */
  learned_from: number[];
  /** The same sources RESOLVED, sent by the detail route only. A bare "#4181"
   *  on a page tells a reader nothing about whether it is worth opening, and
   *  the provenance is the point of a lesson — one that loses its incidents
   *  loses its evidence. A source that has been deleted drops out rather than
   *  rendering a link to nothing. */
  learned_from_records?: {
    id: number;
    title: string;
    note_type: string;
    is_task: boolean;
    task_kind: string | null;
    status: string | null;
  }[];
  tags: string[];
  note_type: string;
  /** Where it was LEARNED. Kept as a fact, but not a limit on where it can be
   *  found: a lesson is retrievable from every project (milestone 385 step 3). */
  project_id: number | null;
  permission?: string;
  created_at: string | null;
  updated_at: string | null;
  systems?: { id: number; name: string }[];
  usage?: RecordUsage;
  /** Set when another user owns this record. */
  shared?: boolean;
  owner?: string | null;
}

/** A row in the browse listing — the trigger travels with it, because a list
 *  of lessons without their triggers is a list of claims with the half that
 *  says when each one matters left off. */
export interface LessonListRow {
  id: number;
  title: string;
  tags: string[];
  when_to_apply?: string;
  snippet?: string;
  shared?: boolean;
  owner?: string | null;
}

export interface LessonListResponse {
  lessons: LessonListRow[];
  total: number;
}

/** What the create/update forms send. `what` and `when_to_apply` are required
 *  on create; every field is optional on update, and the service re-composes
 *  the whole document from the merged set — so a partial save can never leave
 *  the title and body disagreeing about the trigger. */
export interface LessonPayload {
  what?: string;
  when_to_apply?: string;
  insight?: string;
  learned_from?: number[];
  tags?: string[];
  project_id?: number | null;
  system_ids?: number[];
  /** Deliberate override of the near-duplicate gate, once the writer has seen
   *  the warning. Two lessons under one trigger compete for one reserved slot,
   *  so a duplicate displaces rather than merely clutters. */
  force?: boolean;
}

export function listLessons(params: {
  q?: string;
  tag?: string;
  project_id?: number;
  limit?: number;
  offset?: number;
} = {}): Promise<LessonListResponse> {
  const qs = new URLSearchParams();
  if (params.q) qs.set("q", params.q);
  if (params.tag) qs.set("tag", params.tag);
  if (params.project_id) qs.set("project_id", String(params.project_id));
  if (params.limit != null) qs.set("limit", String(params.limit));
  if (params.offset != null) qs.set("offset", String(params.offset));
  const suffix = qs.toString() ? `?${qs}` : "";
  return apiGet<LessonListResponse>(`/api/lessons${suffix}`);
}

export function getLesson(id: number): Promise<Lesson> {
  return apiGet<Lesson>(`/api/lessons/${id}`);
}

export function createLesson(payload: LessonPayload): Promise<Lesson> {
  return apiPost<Lesson>("/api/lessons", payload);
}

export function updateLesson(
  id: number,
  payload: LessonPayload,
): Promise<Lesson> {
  return apiPatch<Lesson>(`/api/lessons/${id}`, payload);
}

/** Trash, not erase — recoverable. `apiDelete` discards the body, which is the
 *  established shape here (snippets delete the same way): the batch id is in
 *  the response, but no caller has needed it and inventing a second delete
 *  helper to carry it would be the duplication, not the feature. */
export function deleteLesson(id: number): Promise<void> {
  return apiDelete(`/api/lessons/${id}`);
}

/** The lessons drawn FROM one record — the reverse of `learned_from`.
 *
 *  The direction that gets forgotten, and arguably the more useful one: a
 *  reader opening an old issue wants to know what was learned from it, and
 *  without this the relation is only navigable from the lesson's side. */
export function lessonsTaughtBy(
  recordId: number,
): Promise<{ lessons: Lesson[]; taught_by: number }> {
  return apiGet<{ lessons: Lesson[]; taught_by: number }>(
    `/api/lessons/taught-by/${recordId}`,
  );
}