feat: add token index fetcher

internal/chain/token_index.go

@@ -0,0 +1,42 @@
+package chain
+
+import (
+	"context"
+	"math/big"
+
+	"github.com/celo-org/celo-blockchain/common"
+	"github.com/grassrootseconomics/w3-celo"
+	"github.com/grassrootseconomics/w3-celo/module/eth"
+	"github.com/grassrootseconomics/w3-celo/w3types"
+)
+
+var (
+	entryCountFunc = w3.MustNewFunc("entryCount()", "uint256")
+	entrySig       = w3.MustNewFunc("entry(uint256 _idx)", "address")
+)
+
+func (c *Chain) GetAllTokensFromTokenIndex(ctx context.Context, tokenIndex common.Address) ([]common.Address, error) {
+	var (
+		tokenIndexEntryCount big.Int
+	)
+
+	if err := c.provider.Client.CallCtx(
+		ctx,
+		eth.CallFunc(tokenIndex, entryCountFunc).Returns(&tokenIndexEntryCount),
+	); err != nil {
+		return nil, err
+	}
+
+	calls := make([]w3types.RPCCaller, tokenIndexEntryCount.Int64())
+	tokenAddresses := make([]common.Address, tokenIndexEntryCount.Int64())
+
+	for i := 0; i < int(tokenIndexEntryCount.Int64()); i++ {
+		calls[i] = eth.CallFunc(tokenIndex, entrySig, new(big.Int).SetInt64(int64(i))).Returns(&tokenAddresses[i])
+	}
+
+	if err := c.provider.Client.CallCtx(ctx, calls...); err != nil {
+		return nil, err
+	}
+
+	return tokenAddresses, nil
+}