import { ArgumentMetadata, Injectable, PipeTransform } from "@nestjs/common";
import { z, type ZodTypeAny } from "zod";
import { ApiError } from "../errors.js";

/**
 * Zod validation pipe.
 *
 *   @Body(ZodValidate(schema)) body
 *   @Query(ZodValidate(querySchema)) query
 *   @Params(ZodValidate(paramsSchema)) params
 *
 * Parses the raw input against the schema (with `.parse`) and returns the
 * transformed/validated object; failures throw VALIDATION_ERROR with
 * field-level details — handled by the global filter into the canonical
 * {error:{code:"VALIDATION_ERROR",details:[...]}} envelope.
 *
 * NOTE: constructed manually by the `ZodValidate` factory below — it is
 * `@Injectable()`-marked but NEVER provided to Nest DI, so its ctor takes
 * no `@Inject` (the schema is a value, not a DI token; TASK-0100 S0).
 */
@Injectable()
// Declared as `Promise<T>` because `transform` is `async` (it returns a
// promise). NestJS awaits pipe results at runtime (pipes-consumer), so the
// downstream handler still receives the resolved `T` — type-accurate, no
// behavioral change.
export class ZodValidationPipe<T = unknown> implements PipeTransform<unknown, Promise<T>> {
  constructor(private readonly schema: ZodTypeAny) {}

  async transform(value: unknown, _metadata: ArgumentMetadata): Promise<T> {
    const result = this.schema.safeParse(value);
    if (!result.success) {
      const details = result.error.issues.slice(0, 20).map((i) => ({
        field: i.path.join("."),
        issue: i.message
      }));
      throw ApiError.validation("Request validation failed.", details);
    }
    return result.data as T;
  }
}

/** Convenience factory: `ZodValidate(schema)`. */
export function ZodValidate(schema: ZodTypeAny): ZodValidationPipe {
  return new ZodValidationPipe(schema);
}

/**
 * Validate a plain query object (e.g. the result of parsePagination inputs)
 * against a schema — used by services for non-route validation.
 */
export function parseOrThrow<T>(schema: z.ZodType<T>, value: unknown): T {
  const r = schema.safeParse(value);
  if (!r.success) {
    const details = r.error.issues.slice(0, 20).map((i) => ({ field: i.path.join("."), issue: i.message }));
    throw ApiError.validation("Request validation failed.", details);
  }
  return r.data;
}