import pickle

class Ledger():
    def __init__(self) -> None:
        self.data = []
        self.indexes = {} # ID: Index
    
    def readLedger(self, ID):
        data = None
        index = self.indexes.get(ID, None)
        if index is not None:
            data = self.data[index]
        return data
    
    def writeLedger(self, ID, data):
        oldData = self.readLedger(ID)
        if oldData is not None:
            data = self.updateLedger(data, oldData)
            index = self.indexes[ID]
            self.data[index] = data
        else:
            self.data.append(data)
            index = len(self.data) - 1
            self.indexes.update({ID: index})
        
        self.saveLedger()
    
    def updateLedger(self, data, newData):
        return data