package dyzurbot

import (
	"context"
	"log"
	"time"
)

// FetchFunc retrieves and parses the current rota from upstream (the Sheet).
type FetchFunc func(ctx context.Context) (Rota, error)

// Syncer refreshes a Store from an upstream fetch.
type Syncer struct {
	store *Store
	fetch FetchFunc
	now   func() time.Time
}

// NewSyncer wires a Store to a fetch function.
func NewSyncer(store *Store, fetch FetchFunc) *Syncer {
	return &Syncer{store: store, fetch: fetch, now: time.Now}
}

// Sync fetches once. On success it replaces the cache; on failure it logs a
// warning, leaves the last good cache in place, and returns the error so a
// caller (e.g. a manual /sync command) can report it.
func (sy *Syncer) Sync(ctx context.Context) error {
	rota, err := sy.fetch(ctx)
	if err != nil {
		log.Printf("sync: fetch failed, keeping cached data: %v", err)
		return err
	}
	return sy.store.Replace(rota, sy.now())
}

// Run polls Sync on the given interval until ctx is canceled.
func (sy *Syncer) Run(ctx context.Context, interval time.Duration) {
	ticker := time.NewTicker(interval)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			_ = sy.Sync(ctx)
		}
	}
}

// SheetFetcher builds a FetchFunc that reads the rota from Google Sheets.
func SheetFetcher(spreadsheetID, readRange string) FetchFunc {
	return func(ctx context.Context) (Rota, error) {
		rows, err := ReadSheet(ctx, spreadsheetID, readRange)
		if err != nil {
			return Rota{}, err
		}
		return ParseRota(rows), nil
	}
}