import { z } from "zod";

/** Sort directions accepted by the LLM. */
export type SortDirection = "asc" | "desc";

export interface Sort {
  field: string;
  direction: SortDirection;
}

/**
 * Carte-author-declared shape: which built-in sort fields a query may expose,
 * and (optionally) which directions are allowed for each. Typically supplied
 * via `defineParams({ sorts: ... })`. Used by `parsePlan` (to reject
 * LLM-emitted sorts that don't fit) and `generatePrompt` (to teach the LLM
 * what's available).
 */
export interface AllowedSort {
  /**
   * Permitted directions for this field. Default `["asc", "desc"]` (both).
   * Set to a single direction for fields where only one ordering makes
   * semantic sense (e.g. `createdAt: ["desc"]` for recent-first feeds).
   */
  directions?: SortDirection[];
  /** Optional human-readable description shown in the prompt. */
  description?: string;
}

export type AllowedSorts = Record<string, AllowedSort>;

// ─── Zod schemas ────────────────────────────────────────────────────────────

const sortDirectionSchema = z.enum(["asc", "desc"]);

export const sortSchema: z.ZodType<Sort> = z.object({
  field: z.string().min(1),
  direction: sortDirectionSchema,
});

/**
 * Sugar for `z.array(sortSchema)`. `defineParams({ sorts: ... })` adds this
 * automatically for built-in sort support. You can still use it directly in a
 * plain params schema when you want to own sort semantics yourself.
 */
export const sortsParamSchema = z.array(sortSchema);

export const allowedSortSchema: z.ZodType<AllowedSort> = z.object({
  directions: z.array(sortDirectionSchema).min(1).optional(),
  description: z.string().optional(),
});

// ─── Pure validation helper (no drizzle dep) ─────────────────────────────────

const DEFAULT_DIRECTIONS: SortDirection[] = ["asc", "desc"];

/**
 * Returns a human-readable error message if `sort` is not allowed under
 * `allowed`, or `undefined` if it passes. Used by `validatePlan` and
 * `applyDrizzleSort`.
 */
export function checkSort(sort: Sort, allowed: AllowedSorts): string | undefined {
  const def = allowed[sort.field];
  if (!def) {
    return `field "${sort.field}" is not an allowed sort field`;
  }
  const directions = def.directions ?? DEFAULT_DIRECTIONS;
  if (!directions.includes(sort.direction)) {
    return `direction "${sort.direction}" is not allowed for field "${sort.field}" (allowed: ${directions.join(", ")})`;
  }
  return undefined;
}