// Package attendance fetches attendance CSV exports from Google Sheets.
// No auth required — the sheet must be publicly readable.
package attendance

import (
	"context"
	"encoding/csv"
	"fmt"
	"io"
	"net/http"
	"strings"
)

const exportBase = "https://docs.google.com/spreadsheets/d"

// Client fetches attendance CSV exports from a public Google Spreadsheet.
type Client struct {
	http      *http.Client
	sheetID   string
	adultGID  string
	juniorGID string
}

// New returns a Client for the given spreadsheet.
// adultGID is typically "0"; juniorGID is the GID of the junior tab.
func New(httpClient *http.Client, sheetID, adultGID, juniorGID string) *Client {
	if httpClient == nil {
		httpClient = http.DefaultClient
	}
	return &Client{http: httpClient, sheetID: sheetID, adultGID: adultGID, juniorGID: juniorGID}
}

// FetchAdults returns the adult attendance tab as raw CSV rows.
func (c *Client) FetchAdults(ctx context.Context) ([][]string, error) {
	return c.fetch(ctx, c.adultGID)
}

// FetchJuniors returns the junior attendance tab as raw CSV rows.
func (c *Client) FetchJuniors(ctx context.Context) ([][]string, error) {
	return c.fetch(ctx, c.juniorGID)
}

func (c *Client) fetch(ctx context.Context, gid string) ([][]string, error) {
	url := fmt.Sprintf("%s/%s/export?format=csv&gid=%s", exportBase, c.sheetID, gid)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, err
	}
	resp, err := c.http.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("attendance fetch: HTTP %d for gid=%s", resp.StatusCode, gid)
	}
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, err
	}
	r := csv.NewReader(strings.NewReader(string(body)))
	r.FieldsPerRecord = -1 // rows may have different lengths
	return r.ReadAll()
}