/**
 * Pure archivist record placement topology (ADR 0048 / 0065 / dossier-topology).
 * No SessionManager / pi-coding-agent — cold public-bin and ledger discovery
 * may import this without pulling open-session runtime into the graph.
 *
 * Navigator work-subject is the sole book-top subject partition (#852):
 * books/<book>/navigator/<work-subject-digest>/. Callers must not re-hash
 * subject or re-join book/navigator/digest themselves.
 */
import { createHash } from "node:crypto";
import { join } from "node:path";

import { resolveBookKeyFromGit } from "./activation-ledger-git.ts";
import {
  activationBookDirectory,
  resolveActivationLedgerHome,
  tryHomeFromAkRolesPath,
} from "./activation-ledger-topology.ts";

/** Book-top partition for cross-ticket navigator route-memory (dossier-topology). */
export const NAVIGATOR_RECORD_KIND = "navigator" as const;

/** One resolved navigator work-subject placement — ledger root and nest together. */
export type NavigatorWorkSubjectPlacement = {
  readonly ledgerHome: string;
  readonly sessionDir: string;
};

/**
 * Sole navigator work-subject placement under the ledger book.
 * Returns ledgerHome and nest once so createRecordSessionOpen does not re-branch
 * parent/home. Work-subject key shape is sha256(subject) hex truncated to 32
 * (#852 out of scope — shape unchanged).
 *
 * parentSessionFile contributes home only when tryHomeFromAkRolesPath succeeds;
 * otherwise the explicit home (from HostContext.runDirectory) is kept. Never
 * invents a second home via passwd/env fallback from a foreign parent path.
 */
export function resolveNavigatorWorkSubjectPlacement(input: {
  readonly cwd: string;
  readonly subject: string;
  /** Parent session file — home path-derives from it only under .ak-roles. */
  readonly parentSessionFile?: string;
  /** Explicit process home when no ledger parent path is available. */
  readonly home?: string;
}): NavigatorWorkSubjectPlacement {
  let ledgerHome: string | undefined;
  if (input.parentSessionFile !== undefined && input.parentSessionFile.length > 0) {
    const fromParent = tryHomeFromAkRolesPath(input.parentSessionFile);
    if (fromParent !== undefined && fromParent.length > 0) {
      ledgerHome = resolveActivationLedgerHome(fromParent);
    }
  }
  ledgerHome ??= resolveActivationLedgerHome(input.home);
  const digest = createHash("sha256").update(input.subject).digest("hex").slice(0, 32);
  return {
    ledgerHome,
    sessionDir: join(
      activationBookDirectory(ledgerHome, resolveBookKeyFromGit(input.cwd)),
      NAVIGATOR_RECORD_KIND,
      digest,
    ),
  };
}