import { raw, type Platform, type RawQueryFragment } from '@mikro-orm/core';
import { SqlitePlatform } from '@mikro-orm/sql';
import { sql, type Expression } from 'kysely';

/**
 * The only place a repository may spell a database function.
 *
 * Every helper takes the MikroORM `Platform` the caller's EntityManager is
 * running on (`em.getPlatform()`) plus an already-qualified column reference
 * (`'t.created_at'`), and dispatches on that platform at runtime. TREK ships
 * one binary and the database is chosen by configuration, so the dialect is a
 * runtime property of the live connection, not a build-time swap: when the
 * Postgres driver arrives this file grows a second branch and no repository
 * changes. An unknown platform fails closed rather than guessing a spelling.
 *
 * Values are never interpolated — the day count in `dateAdd` is checked to be
 * an integer before it is spelled.
 */

function column(ref: string): string {
  if (!/^[a-z_][a-z0-9_]*(\.[a-z_][a-z0-9_]*)?$/i.test(ref)) {
    throw new Error(`sql-functions: not a column reference: ${ref}`);
  }
  return ref;
}

function unsupported(platform: Platform): never {
  throw new Error(`sql-functions: no implementation for platform ${platform.constructor.name}`);
}

/** The calendar date (`YYYY-MM-DD`) of a timestamp column. */
export function dateOf(platform: Platform, ref: string): RawQueryFragment {
  if (platform instanceof SqlitePlatform) return raw(`date(${column(ref)})`);
  return unsupported(platform);
}

/** The timestamp column shifted by whole days, as a calendar date. */
export function dateAdd(platform: Platform, ref: string, days: number): RawQueryFragment {
  if (!Number.isInteger(days)) throw new Error(`sql-functions: dateAdd needs an integer day count, got ${days}`);
  if (platform instanceof SqlitePlatform) {
    const sign = days < 0 ? '-' : '+';
    return raw(`date(${column(ref)}, '${sign}${Math.abs(days)} days')`);
  }
  return unsupported(platform);
}

/** The database clock, in the same text the column defaults produce. */
export function currentTimestamp(platform: Platform): RawQueryFragment {
  if (platform instanceof SqlitePlatform) return raw('CURRENT_TIMESTAMP');
  return unsupported(platform);
}

/**
 * A bare reference to another column of the same row, for a filter or update
 * value that must compare against or combine with a sibling column instead
 * of a bound parameter (e.g. `used_count < max_uses` — `InviteTokensRepository
 * .incrementUsedCount`'s capacity guard). Portable across dialects on its own,
 * but still routed through this file (not spelled with `raw()` in a
 * repository) so every escape hatch stays in one place ESLint's
 * `no-restricted-syntax` rule for `src/db/repositories/**` can enforce.
 */
export function columnRef(platform: Platform, ref: string): RawQueryFragment {
  if (platform instanceof SqlitePlatform) return raw(column(ref));
  return unsupported(platform);
}

/** A column shifted by a signed integer amount: `<col> + n` / `<col> - n`. */
export function columnIncrementedBy(platform: Platform, ref: string, amount: number): RawQueryFragment {
  if (!Number.isInteger(amount)) {
    throw new Error(`sql-functions: columnIncrementedBy needs an integer amount, got ${amount}`);
  }
  if (platform instanceof SqlitePlatform) {
    const sign = amount < 0 ? '-' : '+';
    return raw(`${column(ref)} ${sign} ${Math.abs(amount)}`);
  }
  return unsupported(platform);
}

/**
 * A case-insensitive column reference, for use as a filter's object key:
 * `{ [lower(platform, 'email')]: value.toLowerCase() }` produces
 * `WHERE LOWER(email) = ?`. This is the parity-preserving equivalent of the
 * legacy `LOWER(col) = LOWER(?)` sites (`AuthService`/`OidcService`/
 * `UserProfileService`'s username/email CI lookups): the caller lowercases
 * the bound value itself (every one of this migration's call sites already
 * does, via `String.prototype.toLowerCase`), so the comparison is between
 * two already-lowercased values either way — SQLite's `LOWER()` is ASCII-only
 * exactly like `toLowerCase()` is for the identifier characters these
 * columns hold (usernames/emails), so the two spellings agree on every
 * input this codebase stores.
 *
 * Typed `RawQueryFragment & symbol` (not the bare `RawQueryFragment` the
 * other helpers in this file return): TypeScript only accepts a
 * `string | number | symbol` as a computed property name, and a raw
 * fragment is only usable as an object key because `raw()`'s default
 * generic already brands it with a `[Symbol.toPrimitive]`. The other
 * helpers here are only ever used as VALUES, where that brand isn't needed.
 */
export function lower(platform: Platform, ref: string): RawQueryFragment & symbol {
  if (platform instanceof SqlitePlatform) return raw(`LOWER(${column(ref)})`);
  return unsupported(platform);
}

/**
 * `CURRENT_TIMESTAMP`, for a query built through `em.getKysely()` — the
 * escape hatch for a recursive CTE (`OauthTokensRepository.collectChainIds`)
 * or a join the QueryBuilder's relation metadata cannot express correctly
 * (`OauthTokensRepository.listActiveByUser`/`listAllActiveWithClientAndUser`
 * — `oauth_tokens.client_id` references `oauth_clients.client_id`, not its
 * primary key, and the generated entity's `client` relation has no
 * `referencedColumnNames` override, so a QueryBuilder `.innerJoin('ot.client',
 * …)` silently joins on the wrong column; see those methods' docstrings).
 * Kysely has its own expression system, entirely separate from MikroORM's
 * `raw()` — `currentTimestamp` above returns a value this file's OTHER
 * consumers (the QueryBuilder, `nativeUpdate`) accept, but a Kysely query
 * cannot use a `RawQueryFragment` as an operand. This is the one place a
 * repository may reach for the Kysely spelling of the same literal, kept
 * here rather than in a repository file so `no-restricted-syntax`'s ban on
 * spelling raw SQL directly in `src/db/repositories/**` still holds — this
 * file is exempt from that rule by design (it IS the one approved place).
 */
export function currentTimestampKysely(platform: Platform): Expression<string> {
  if (platform instanceof SqlitePlatform) return sql<string>`CURRENT_TIMESTAMP`;
  return unsupported(platform);
}