import { Encoding, PageType } from './constants.js'
import { deserializeTCompactProtocol } from './thrift.js'

/**
 * Read parquet header from a buffer.
 *
 * @typedef {import("./types.d.ts").DataReader} DataReader
 * @typedef {import("./types.d.ts").PageHeader} PageHeader
 * @param {DataReader} reader - parquet file reader
 * @returns {PageHeader} metadata object and bytes read
 */
export function parquetHeader(reader) {
  const header = deserializeTCompactProtocol(reader)

  // Parse parquet header from thrift data
  const type = PageType[header.field_1]
  const uncompressed_page_size = header.field_2
  const compressed_page_size = header.field_3
  const crc = header.field_4
  const data_page_header = header.field_5 && {
    num_values: header.field_5.field_1,
    encoding: Encoding[header.field_5.field_2],
    definition_level_encoding: Encoding[header.field_5.field_3],
    repetition_level_encoding: Encoding[header.field_5.field_4],
    statistics: header.field_5.field_5 && {
      max: header.field_5.field_5.field_1,
      min: header.field_5.field_5.field_2,
      null_count: header.field_5.field_5.field_3,
      distinct_count: header.field_5.field_5.field_4,
      max_value: header.field_5.field_5.field_5,
      min_value: header.field_5.field_5.field_6,
    },
  }
  const index_page_header = header.field_6
  const dictionary_page_header = header.field_7 && {
    num_values: header.field_7.field_1,
    encoding: Encoding[header.field_7.field_2],
    is_sorted: header.field_7.field_3,
  }
  const data_page_header_v2 = header.field_8 && {
    num_values: header.field_8.field_1,
    num_nulls: header.field_8.field_2,
    num_rows: header.field_8.field_3,
    encoding: Encoding[header.field_8.field_4],
    definition_levels_byte_length: header.field_8.field_5,
    repetition_levels_byte_length: header.field_8.field_6,
    is_compressed: header.field_8.field_7 === undefined ? true : header.field_8.field_7, // default true
    statistics: header.field_8.field_8,
  }

  return {
    type,
    uncompressed_page_size,
    compressed_page_size,
    crc,
    data_page_header,
    index_page_header,
    dictionary_page_header,
    data_page_header_v2,
  }
}