/**
 * Topic issues and their problem sub-issues: the ONE reading of "is this topic
 * finished", shared by close-topics.ts (closes the topic issue) and
 * release-topics.ts (publishes the topic's timever release) so the two can
 * never disagree about when a topic was done.
 *
 * Rule: a topic is finished when it has a core set (`set:core` sub-issues) and
 * every one of them is closed. Optional and deferred problems are extra credit
 * and never hold a topic open. A topic with no core sub-issues is never
 * finished — that would be indistinguishable from a mis-labelled problem set.
 *
 * Library: side-effect-free on import; every call takes the caller's github().
 */
import type { GitHub } from "./github.ts";

/** One problem sub-issue, narrowed from the sub_issues payload. */
export interface Problem {
  number: number;
  /** `LC <num> · <Name>`. */
  title: string;
  /** ISO instant the issue closed; null while it is open. */
  closedAt: string | null;
  labels: string[];
}

export interface Core {
  /** Core sub-issues, closed and open alike, lowest number first. */
  all: number[];
  /** The core sub-issues still open — non-empty means the topic stays open. */
  pending: number[];
  /** When the last core sub-issue closed; null until the topic is finished. */
  finishedAt: string | null;
}

/**
 * Every sub-issue of a topic. The sub_issues payload carries the full issue
 * objects (state + labels), so no per-problem follow-up request is needed.
 */
export async function readProblems(gh: GitHub, topic: number): Promise<Problem[]> {
  const problems: Problem[] = [];
  for await (const raw of gh.list(`/repos/${gh.repo}/issues/${topic}/sub_issues`)) {
    if (!raw || typeof raw !== "object") continue;
    if (!("number" in raw) || typeof raw.number !== "number") continue;
    if (!("title" in raw) || typeof raw.title !== "string") continue;
    if (!("state" in raw) || typeof raw.state !== "string") continue;
    if (!("labels" in raw) || !Array.isArray(raw.labels)) continue;
    const closedAt =
      raw.state === "closed" && "closed_at" in raw && typeof raw.closed_at === "string"
        ? raw.closed_at
        : null;
    const labels = raw.labels.flatMap((label: unknown) =>
      label && typeof label === "object" && "name" in label && typeof label.name === "string"
        ? [label.name]
        : [],
    );
    problems.push({ number: raw.number, title: raw.title, closedAt, labels });
  }
  return problems.sort((a, b) => a.number - b.number);
}

/** The value of a `prefix:value` label (`set:` → `core`), if the problem has one. */
export function labelValue(problem: Problem, prefix: string): string | undefined {
  return problem.labels.find((l) => l.startsWith(prefix))?.slice(prefix.length);
}

export function coreSet(problems: Problem[]): Core {
  const core = problems.filter((p) => labelValue(p, "set:") === "core");
  const pending = core.filter((p) => !p.closedAt).map((p) => p.number);
  // ISO instants from the API share one format, so string order is time order.
  const finishedAt =
    core.length && !pending.length
      ? core.map((p) => p.closedAt!).reduce((a, b) => (a > b ? a : b))
      : null;
  return { all: core.map((p) => p.number), pending, finishedAt };
}