import crypto from "node:crypto";
import { readRegularFile } from "../infra/fs-safe.js";
import type { MigrationItem, MigrationPlan } from "../plugins/types.js";

export const MAX_MEMORY_MIGRATION_FILE_BYTES = 64 * 1024 * 1024;

/** Bind copyable memory items to the exact source bytes reviewed by an embedded migration UI. */
export async function bindMemoryMigrationPlanSources(
  plan: MigrationPlan,
  opts: { includeConflicts?: boolean } = {},
): Promise<MigrationPlan> {
  const items: MigrationItem[] = [];
  for (const item of plan.items) {
    if (
      item.kind !== "memory" ||
      item.action !== "copy" ||
      (item.status !== "planned" && !(opts.includeConflicts && item.status === "conflict")) ||
      !item.source
    ) {
      items.push(item);
      continue;
    }
    const { buffer } = await readRegularFile({
      filePath: item.source,
      maxBytes: MAX_MEMORY_MIGRATION_FILE_BYTES,
    });
    items.push({
      ...item,
      sourceRevision: {
        algorithm: "sha256",
        digest: crypto.createHash("sha256").update(buffer).digest("hex"),
      },
    });
  }
  return { ...plan, items };
}

/** Reject source bytes that differ from an embedded migration's reviewed plan. */
export function assertMemoryMigrationSourceRevision(
  item: MigrationItem,
  sourceBuffer: Buffer,
): void {
  const expectedSourceSha256 = item.sourceRevision?.digest;
  if (
    item.sourceRevision?.algorithm === "sha256" &&
    typeof expectedSourceSha256 === "string" &&
    crypto.createHash("sha256").update(sourceBuffer).digest("hex") !== expectedSourceSha256
  ) {
    throw new Error("memory migration source changed; refresh the plan before importing");
  }
}