import { PREVIEW_ROWS } from "./limits";
import { transformRows } from "./transform";
import type { ColumnSchema, MappingInput } from "./types";

export type PreviewContract = {
  preview: true;
  columns: { name: string; required: boolean }[];
  rows: string[][];
  rowCount: number;
  truncated: boolean;
};

export function buildPreview(
  modelColumns: ColumnSchema[],
  sourceHeaders: string[],
  dataRows: string[][],
  mappings: MappingInput[],
): PreviewContract {
  const ordered = modelColumns.map((column) => column.name);
  const all = transformRows(ordered, sourceHeaders, dataRows, mappings);
  return {
    preview: true,
    columns: modelColumns.map((column) => ({ name: column.name, required: column.required })),
    rows: all.slice(0, PREVIEW_ROWS),
    rowCount: all.length,
    truncated: all.length > PREVIEW_ROWS,
  };
}