#!/usr/bin/env python
# coding: utf-8

# In[1]:


import numpy as np
from copy import deepcopy
from scipy.spatial.distance import cdist
from scipy.special import expit
from scipy.optimize import minimize
from sklearn.datasets import load_iris
from sklearn.linear_model import LogisticRegression as skLogisticRegression
from sklearn.multiclass import OutputCodeClassifier as skOutputCodeClassifier


# In[2]:


class OutputCodeClassifier():
    def __init__(self, estimator,
                 code_size=1.5, random_state=0):
        self.estimator = estimator
        self.code_size = code_size
        self.random_state = random_state

    def fit(self, X, y):
        self.classes_, y_enc = np.unique(y, return_inverse=True)
        code_size_ = int(len(self.classes_) * self.code_size)
        rng = np.random.RandomState(self.random_state)
        self.code_book_ = rng.random_sample((len(self.classes_), code_size_))
        self.code_book_[self.code_book_ > 0.5] = 1
        self.code_book_[self.code_book_ != 1] = -1
        y_train = self.code_book_[y_enc]
        self.estimators_ = []
        for i in range(y_train.shape[1]):
            cur_y = y_train[:, i]
            clf = deepcopy(self.estimator)
            clf.fit(X, cur_y)
            self.estimators_.append(clf)
        return self

    def predict(self, X):
        scores = np.zeros((X.shape[0], len(self.estimators_)))
        for i, est in enumerate(self.estimators_):
            scores[:, i] = est.decision_function(X)
        pred = cdist(scores, self.code_book_).argmin(axis=1)
        return self.classes_[pred]


# In[3]:


# Simplified version of LogisticRegression, only work for binary classification
class BinaryLogisticRegression():
    def __init__(self, C=1.0):
        self.C = C

    @staticmethod
    def _cost_grad(w, X, y, alpha):
        def _log_logistic(x):
            if x > 0:
                return -np.log(1 + np.exp(-x))
            else:
                return x - np.log(1 + np.exp(x))
        yz = y * (np.dot(X, w[:-1]) + w[-1])
        cost = -np.sum(np.vectorize(_log_logistic)(yz)) + 0.5 * alpha * np.dot(w[:-1], w[:-1])
        grad = np.zeros(len(w))
        t = (expit(yz) - 1) * y
        grad[:-1] = np.dot(X.T, t) + alpha * w[:-1]
        grad[-1] = np.sum(t)
        return cost, grad

    def _solve_lbfgs(self, X, y):
        y_train = np.full(X.shape[0], -1)
        y_train[y == 1] = 1
        w0 = np.zeros(X.shape[1] + 1)
        res = minimize(fun=self._cost_grad, jac=True, x0=w0,
                       args=(X, y_train, 1 / self.C), method='L-BFGS-B')
        return res.x[:-1], res.x[-1]

    def fit(self, X, y):
        self.coef_, self.intercept_ = self._solve_lbfgs(X, y)
        return self

    def decision_function(self, X):
        scores = np.dot(X, self.coef_) + self.intercept_
        return scores

    def predict(self, X):
        scores = self.decision_function(X)
        indices = (scores > 0).astype(int)
        return indices


# In[4]:


for C in [0.1, 1, 10, np.inf]:
    X, y = load_iris(return_X_y=True)
    clf1 = OutputCodeClassifier(BinaryLogisticRegression(C=C)).fit(X, y)
    clf2 = skOutputCodeClassifier(skLogisticRegression(C=C, multi_class="ovr", solver="lbfgs",
                                                       # keep consisent with scipy default
                                                       tol=1e-5, max_iter=15000),
                                  random_state=0).fit(X, y)
    pred1 = clf1.predict(X)
    pred2 = clf2.predict(X)
    assert np.array_equal(pred1, pred2)