93 lines
3.3 KiB
Python
93 lines
3.3 KiB
Python
from __future__ import print_function
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from random import Random
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MAXIMUM_TRIES = 100000
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class CoinSelector:
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def __init__(self, coins, target, cost_of_change, seed=None, debug=False):
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self.coins = coins
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self.target = target
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self.cost_of_change = cost_of_change
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self.exact_match = False
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self.tries = 0
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self.available = sum(c.effective_amount for c in self.coins)
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self.debug = debug
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self.random = Random(seed)
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debug and print(target)
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debug and print([c.effective_amount for c in self.coins])
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def select(self):
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if not self.coins:
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return
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if self.target > self.available:
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return
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return self.branch_and_bound() or self.single_random_draw()
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def branch_and_bound(self):
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# see bitcoin implementation for more info:
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# https://github.com/bitcoin/bitcoin/blob/master/src/wallet/coinselection.cpp
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self.coins.sort(reverse=True)
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current_value = 0
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current_available_value = self.available
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current_selection = []
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best_waste = self.cost_of_change
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best_selection = []
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while self.tries < MAXIMUM_TRIES:
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self.tries += 1
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backtrack = False
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if current_value + current_available_value < self.target or \
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current_value > self.target + self.cost_of_change:
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backtrack = True
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elif current_value >= self.target:
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new_waste = current_value - self.target
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if new_waste <= best_waste:
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best_waste = new_waste
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best_selection = current_selection[:]
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backtrack = True
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if backtrack:
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while current_selection and not current_selection[-1]:
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current_selection.pop()
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current_available_value += self.coins[len(current_selection)].effective_amount
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if not current_selection:
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break
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current_selection[-1] = False
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utxo = self.coins[len(current_selection)-1]
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current_value -= utxo.effective_amount
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else:
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utxo = self.coins[len(current_selection)]
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current_available_value -= utxo.effective_amount
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previous_utxo = self.coins[len(current_selection)-1] if current_selection else None
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if current_selection and not current_selection[-1] and \
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utxo.effective_amount == previous_utxo.effective_amount and \
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utxo.fee == previous_utxo.fee:
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current_selection.append(False)
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else:
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current_selection.append(True)
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current_value += utxo.effective_amount
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self.debug and print(current_selection)
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if best_selection:
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self.exact_match = True
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return [
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self.coins[i] for i, include in enumerate(best_selection) if include
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]
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def single_random_draw(self):
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self.random.shuffle(self.coins)
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selection = []
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amount = 0
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for coin in self.coins:
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selection.append(coin)
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amount += coin.effective_amount
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if amount >= self.target+self.cost_of_change:
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return selection
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