import logging
import csv
import os
from .base import TaskProcessor


class CSVTaskProcessor(TaskProcessor):

    def _extract(self):
        input_path = self.global_config.source_filepath
        output_path = self.output_filepath
        encoding = self.global_config.encoding_type

        logging.info(f"Reading source CSV file at '{input_path}'")

        # Open both input & output at once for streaming row-by-row
        temp_output = output_path + ".tmp"
        with open(input_path, newline="", encoding=encoding) as inf, open(
            temp_output, newline="", encoding=encoding, mode="w"
        ) as outf:

            reader = csv.reader(inf)
            writer = csv.writer(outf, quoting=csv.QUOTE_ALL)

            # Read and parse the header
            headers = next(reader)

            # Build the list of headers to keep + their new names
            headers_to_keep = [old for _, old in self.csv_entries]
            headers_rename = [new for new, _ in self.csv_entries]

            # Check if all specified headers exist in the input file
            missing = [h for h in headers_to_keep if h not in headers]
            if missing:
                raise ValueError(
                    f"The following headers are not in the input CSV: {missing}"
                )

            # Determine the indices of the headers to keep
            indices = [headers.index(old) for old in headers_to_keep]

            # Write the renamed header
            writer.writerow(headers_rename)

            # Stream through every data row and write out the filtered columns
            for row in reader:
                filtered = [row[i] for i in indices]
                writer.writerow(filtered)

        # Atomically replace the old file
        os.replace(temp_output, output_path)
        logging.info(f"Core data written to CSV file at '{output_path}'")