package blobscan

import (
	"context"
	"encoding/hex"
	"encoding/json"
	"fmt"
	log "log/slog"
	"net/http"

	"github.com/cerc-io/eth-blob-indexer/pkg/storage"
)

const (
	// Max number of objects returned per API call (same for blobs & blocks)
	BlobscanMaxResults = 25
)

var (
	BlobscanBlocksRangePath = "/blocks?sort=asc&startBlock=%d&endBlock=%d"
	BlobscanBlobsPath       = "/blobs/%s"
)

type BlobscanScraper struct {
	URL       string
	BlockStep uint64
}

func (bs *BlobscanScraper) Endpoint(path string, args ...any) string {
	return fmt.Sprintf(bs.URL+path, args...)
}

// ApiBlocksRange returns the API endpoint for fetching a (half-open) range of blocks
func (bs *BlobscanScraper) ApiBlocksRange(from, to uint64) string {
	return bs.Endpoint(BlobscanBlocksRangePath, from, to)
}

func (bs *BlobscanScraper) ScrapeBlobs(ctx context.Context, from, to uint64, db storage.KvStorage) error {
	for num := from; to == 0 || num <= to; num += bs.BlockStep {
		if ctx.Err() != nil {
			return ctx.Err()
		}
		end := min(to, num+bs.BlockStep)
		endpoint := bs.ApiBlocksRange(num, end)
		log.Debug("Fetching block", "endpoint", endpoint)
		blocks, err := fetchBlocks(ctx, endpoint)
		if err != nil {
			log.Error("Failed to fetch blocks", "block", num, "error", err)
			return err
		}

		for _, block := range blocks {
			log.Debug("Processing block", "block", block.Number)
			for _, tx := range block.Transactions {
				for _, txblob := range tx.Blobs {
					endpoint := bs.Endpoint(BlobscanBlobsPath, txblob.VersionedHash.String())
					log.Debug("Fetching blob", "endpoint", endpoint)
					blob, err := fetchBlob(ctx, endpoint)
					if err != nil {
						log.Error("Failed to fetch blob", "error", err, "endpoint", endpoint)
						return err
					}
					data, err := hex.DecodeString(blob.Data[2:])
					if err != nil {
						log.Error("Error decoding blob", "error", err)
						return err
					}
					if err := pushBlob(ctx, blob.VersionedHash, data, db); err != nil {
						return err
					}
				}
			}
		}
	}
	return nil
}

func httpGetJson[T any](ctx context.Context, endpoint string, ret *T) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return err
	}
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return err
	}
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("HTTP %d", resp.StatusCode)
	}
	defer resp.Body.Close()

	return json.NewDecoder(resp.Body).Decode(ret)
}

func fetchBlocks(ctx context.Context, endpoint string) ([]BlobscanBlock, error) {
	var ret struct {
		Blobs []BlobscanBlock `json:"blocks"`
	}
	return ret.Blobs, httpGetJson(ctx, endpoint, &ret)
}

func fetchBlob(ctx context.Context, endpoint string) (*BlobscanBlob, error) {
	var ret BlobscanBlob
	return &ret, httpGetJson(ctx, endpoint, &ret)
}

func pushBlob(ctx context.Context, vhash VersionedHash, data []byte, db storage.KvStorage) error {
	log.Info("Storing blob", "vhash", vhash)
	err := db.Set(ctx, storage.BlobKeyFromHash(vhash), data, 0)
	if err != nil {
		log.Error("Error storing blob", "error", err)
	}
	return err
}