import { NextResponse } from "next/server";

export type ParseResult<T> =
  | { ok: true; value: T }
  | { ok: false; field: string };

interface PositiveIntOptions {
  field: string;
  defaultValue: number;
  min: number;
  max?: number;
}

function parseInteger(raw: string | null, field: string): ParseResult<number | undefined> {
  if (raw === null || raw === "") return { ok: true, value: undefined };
  if (!/^-?\d+$/.test(raw)) return { ok: false, field };

  const value = Number(raw);
  if (!Number.isSafeInteger(value)) return { ok: false, field };
  return { ok: true, value };
}

export function parseOptionalInt(raw: string | null, field: string): ParseResult<number | undefined> {
  const parsed = parseInteger(raw, field);
  if (!parsed.ok || parsed.value === undefined) return parsed;
  if (parsed.value < 0) return { ok: false, field };
  return parsed;
}

export function parsePositiveInt(raw: string | null, options: PositiveIntOptions): ParseResult<number> {
  const parsed = parseInteger(raw, options.field);
  if (!parsed.ok) return parsed;

  let value = parsed.value ?? options.defaultValue;
  if (value < 0) return { ok: false, field: options.field };
  if (value < options.min) value = options.min;
  if (options.max !== undefined && value > options.max) value = options.max;
  return { ok: true, value };
}

export function parseTimestampRange(
  searchParams: URLSearchParams
): ParseResult<{ startTs?: number; endTs?: number }> {
  const start = parseOptionalInt(searchParams.get("start"), "start");
  if (!start.ok) return start;

  const end = parseOptionalInt(searchParams.get("end"), "end");
  if (!end.ok) return end;

  if (start.value !== undefined && end.value !== undefined && start.value > end.value) {
    return { ok: false, field: "range" };
  }

  return { ok: true, value: { startTs: start.value, endTs: end.value } };
}

export function jsonError(field?: string, status = 400) {
  const body = field
    ? { error: "Invalid query parameter", field }
    : { error: "Internal server error" };
  return NextResponse.json(body, { status });
}