// Derives META_REQUEST/JSON_SCHEMA_REQUEST field metadata from seed data itself,
// so every table/view/query gets working metadata without hand-authoring it —
// datasource init won't complete without a non-empty FIELD array (see README).

import type { FieldMetadata, Row } from '../types.ts';

// Numeric fields scan EVERY row, not just the first non-null value: a column
// like PRICE is DOUBLE if any row holds a fractional value, even when row one
// happens to land on a whole number. A column whose values are all whole
// numbers still infers as LONG — if it's semantically a DOUBLE, say so via
// the fieldTypes override (see README).
function inferFieldType(name: string, rows: Row[], sample: unknown): string {
  if (typeof sample === 'number') {
    const anyFractional = rows.some(
      (row) => typeof row[name] === 'number' && !Number.isInteger(row[name]),
    );
    return anyFractional ? 'DOUBLE' : 'LONG';
  }
  if (typeof sample === 'boolean') return 'BOOLEAN';
  return 'STRING';
}

/** rows: array of plain row objects. Returns a FIELD array covering every key seen. */
export function deriveFields(rows: Row[], overrides: Record<string, string> = {}): FieldMetadata[] {
  const fieldNames: string[] = [];
  const seen = new Set<string>();
  for (const row of rows) {
    for (const key of Object.keys(row)) {
      if (!seen.has(key)) {
        seen.add(key);
        fieldNames.push(key);
      }
    }
  }

  return fieldNames.map((name) => {
    const sampleRow = rows.find((row) => row[name] !== undefined && row[name] !== null);
    const type =
      overrides[name] ?? (sampleRow ? inferFieldType(name, rows, sampleRow[name]) : 'STRING');
    return { NAME: name, TYPE: type };
  });
}