/**
 * 配方数据源展开 —— **纯函数,零 IO**。
 *
 * 嵌套**两层封顶**:两层(某几颗料 × 该类型的参数字段)是已知业务的上限;
 * 超出就别 auto —— 退回模型,或者把那一段切出去。
 */
import type { AutoExpr, AutoSource } from '@contracts';
import { evalExpr, rowsAt, type ExprCtx, type Row } from './auto-expr.ts';

export type ExpandedRow = { readonly row: Row; readonly outer?: Row | undefined };

/** where 是等值过滤;比值按字符串(台账里数字与文本混着存) */
function matches(
  row: Row,
  where: Readonly<Record<string, AutoExpr>> | undefined,
  ctx: ExprCtx,
  outer?: Row | undefined,
): boolean {
  if (where === undefined) return true;
  return Object.entries(where).every(([column, valueExpr]) => {
    const want = evalExpr(valueExpr, { ...ctx, row, ...(outer === undefined ? {} : { outer }) });
    const got = row[column];
    return (got === null || got === undefined ? '' : String(got)) === (want === null || want === undefined ? '' : String(want));
  });
}

export function expandSource(source: AutoSource, ctx: ExprCtx): readonly ExpandedRow[] {
  if ('once' in source) return [{ row: {} }];

  if ('rows' in source) {
    return source.rows.map((literal) => {
      const row: Record<string, unknown> = {};
      for (const [name, expr] of Object.entries(literal)) row[name] = evalExpr(expr, { ...ctx, row });
      return { row };
    });
  }

  const outers = rowsAt(ctx.scope, source.each).filter((row) => matches(row, source.where, ctx));
  if (source.then === undefined) return outers.map((row) => ({ row }));

  const inner = source.then;
  const out: ExpandedRow[] = [];
  for (const outer of outers) {
    for (const row of rowsAt(ctx.scope, inner.each)) {
      if (matches(row, inner.where, ctx, outer)) out.push({ row, outer });
    }
  }
  return out;
}