package internal

import (
	"encoding/csv"
	"errors"
	"fmt"
	"io"
	"os"
	"strconv"
)

type Headings []string

func (h Headings) IndexOf(heading string) int {
	for i, value := range h {
		if value == heading {
			return i
		}
	}

	return -1
}

func ReadCsvRedirects(file string) (Redirects, error) {
	reader, err := os.Open(file)
	if err != nil {
		return nil, err
	}
	defer reader.Close()

	csvReader := csv.NewReader(reader)

	// Process headings
	textHeadings, err := csvReader.Read()
	if err != nil {
		return nil, err
	}
	headings := Headings(textHeadings)
	fromCol := headings.IndexOf("From")
	toCol := headings.IndexOf("To")
	statusCol := headings.IndexOf("Status Code")
	if fromCol == -1 || toCol == -1 || statusCol == -1 {
		return nil, errors.New("CSV must contain From, To, and Status Code headings")
	}

	// Read data
	redirects := Redirects{}

	for line := 2; ; line++ {
		row, err := csvReader.Read()
		if err != nil {
			if errors.Is(err, io.EOF) {
				break
			}
			return nil, err
		}

		statusCode, err := strconv.Atoi(row[statusCol])
		if err != nil {
			return nil, fmt.Errorf("line %d: status code %q is not a number", line, row[statusCol])
		}
		if statusCode < 300 || statusCode > 399 {
			return nil, fmt.Errorf("line %d: status code %d is not a redirect (must be 3xx)", line, statusCode)
		}

		redirects = append(redirects, &Redirect{
			From:       row[fromCol],
			To:         row[toCol],
			StatusCode: statusCode,
		})
	}

	return redirects, nil
}