/**
 * lib/entity-columns.ts — THE definition of « which columns an index may name ».
 *
 * scaffold-entity/validate.ts owned this set alone (`knownIndexColumns`), and
 * it was a hard ERROR there: a typo'd `**Index**` column emitted a HasIndex over
 * a phantom property and failed the .NET build. That check ran SIX phases too
 * late — after the BA readiness GO, inside /ba-develop Phase 2. DM-023 moves it
 * left, and the two sides must never drift on what counts as a column: both
 * import this function, and the test pins the set.
 *
 * A known column is:
 *   - a declared field (the attribute table);
 *   - a SYNTHESISED foreign-key column — the FK named on an OWNING relation
 *     (`*→1` / `1→1`); the skeleton never lists FK columns in the table;
 *   - `code` on a coded entity (the engine-owned column of `**Code pattern**`);
 *   - a data-scope ownership column (scaffold side only — the BA model has no
 *     such notion, the scaffolder passes them explicitly);
 *   - the technical columns the base class + tenancy add: `TenantId`,
 *     `CreatedAt`. (`Id`, `UpdatedAt`, `DeletedAt` exist too, but an index on
 *     them is nonsense the scaffolder never accepted — kept out on purpose.)
 *
 * Comparison is case-insensitive: the corpus writes `TenantId`, `tenantId`
 * and `code` alike.
 */

/** Technical columns every generated entity carries and an index may name. */
export const TECHNICAL_INDEX_COLUMNS: readonly string[] = ['TenantId', 'CreatedAt']

export interface KnownColumnsInput {
  /** Declared field / attribute names. */
  fields: readonly string[]
  /** FK column names of the OWNING relations (`ClientId`, …). */
  owningFks: readonly string[]
  /** Extra columns the caller synthesises (data-scope ownership columns). */
  extra?: readonly string[]
  /** The entity carries a `**Code pattern**` → the engine adds `Code`. */
  coded: boolean
}

/** Lower-cased set of every column an `**Index**` declaration may reference. */
export function knownIndexColumns(input: KnownColumnsInput): Set<string> {
  const out = new Set<string>()
  const add = (n: string): void => {
    const v = n.trim().toLowerCase()
    if (v !== '') out.add(v)
  }
  for (const f of input.fields) add(f)
  for (const fk of input.owningFks) add(fk)
  for (const x of input.extra ?? []) add(x)
  if (input.coded) add('code')
  for (const t of TECHNICAL_INDEX_COLUMNS) add(t)
  return out
}

/** True when `column` is the tenant discriminator (any casing). */
export function isTenantColumn(column: string): boolean {
  return column.trim().toLowerCase() === 'tenantid'
}