import requests
from datetime import date, timedelta, datetime
import time
import pandas as pd
from os.path import exists
import streamlit as st

@st.cache(persist=True)
def create_assets(total_coins=50):
  '''
  A function to retrieve info about the largest total_coins number of
  cryptocurrencies, ranked by market cap, generated by a call to coincap assets
  api.
  '''
  url = "https://api.coincap.io/v2/assets"

  # N.B. here adampt the params dict to only request what you need
  payload={'limit': total_coins}
  headers = {}

  assets_json = requests.request("GET", url, params=payload, headers=headers).json()
  return assets_json

@st.cache(persist=True)
def gen_symbols(assets_json):
  '''
  Function to generate three lists: symbols, names and ids, from the result of
  a call to the coincap assets api, assets_json.
  '''
  symbols_list = []
  names_list = []
  ids_list =[]
  for dict in assets_json['data']:
    symbols_list.append(dict['symbol'])
    names_list.append(dict['name'])
    ids_list.append(dict['id'])
  return symbols_list, names_list, ids_list

@st.cache(persist=True, show_spinner=False)
def create_market_cap_dict(assets_json):
  market_cap_dict = {}
  for asset_dict in assets_json['data']:
    market_cap_dict[asset_dict['id']] = int(float(asset_dict['marketCapUsd']))
  return market_cap_dict

def load_histories(coin_ids, start, end):
  '''
  Function to load daily historic prices for all crypto currencies in the
  coin_ids list within the time period defined by the interval [start, end].
  '''
  url = "http://api.coincap.io/v2/assets/{}/history"

  payload={'interval':'d1', 'start':start, 'end':end}
  headers = {}

  histories_dict = {}
  for id in coin_ids:
    response_histories = requests.request("GET", url.format(id), headers=headers, params=payload)
    histories_json = response_histories.json()
    histories_dict[id] = histories_json['data']
  return histories_dict

@st.cache(persist=True, show_spinner=False)
def date_conv(date):
  '''
  Function to convert string to datetime.date.
  '''
  return datetime.strptime(date, '%Y-%m-%d').date()

@st.cache(persist=True)
def create_unix_dates(today=date.today(), lookback_years = 5):
  '''
  A function to create start_unix and end_unix times in UNIX time in milliseconds
  '''
  start_datetime = today-timedelta(365*lookback_years)
  start_unix = int(time.mktime(start_datetime.timetuple()) * 1000)
  end_unix = int(time.mktime(date.today().timetuple()) * 1000)
  return start_unix, end_unix

@st.cache(persist=True, show_spinner=False)
def create_histories_df(coin_ids, start_unix, end_unix):
  '''
  A function to create a dataframe of historical prices for all of the
  crypto currencies in the coin_ids=ids list, over a period defined by the
  interval [start_unix, end_unix].
  N.B. This code uses the data for bitcoin as the first dataframe on which
  other temp_df are outer joined from the right. This is because bitcoin
  has the longest history.
  '''
  print('Downloading data from coincap.io, may take several minutes...')

  # download histories from coincap.io
  with st.spinner("You're the first user today so asset histories are being updated. May take several minutes."):
    histories_dict = load_histories(coin_ids, start_unix, end_unix)

  # convert all dates in histories_dict to python datetime.date objects and remove 'time' key
  for id in coin_ids:
    for dict in histories_dict[id]:
      dict.pop('time')
      dict['priceUsd']=float(dict['priceUsd'])
      dict['date'] = date_conv(dict['date'][0:10])

  # convert histories_dict to pd.DataFrame
  histories_df = pd.json_normalize(histories_dict['bitcoin'])
  histories_df = histories_df.set_index('date', drop=True)
  for id in [x for x in coin_ids if x != "bitcoin"]:
    temp_df = pd.json_normalize(histories_dict[id])
    temp_df = temp_df.set_index('date', drop=True)
    histories_df = histories_df.merge(temp_df, how='outer',  left_index=True, right_index=True)

  histories_df.columns = coin_ids
  return histories_df

# N.B. allow_output_mutation set to True because in create_rebased_df I am
# deliberately chaning the value returns_df[start_date:start_date] to 0
# however I want the cahced value to remain unchanged so that if I rebase to a
# different start_date we go back to the orrignal returns_df.
@st.cache(persist=True, show_spinner=False, allow_output_mutation=True)
def create_returns_df(histories_df):
  return histories_df.pct_change(1)

@st.cache(persist=True, show_spinner=False)
def create_rebased_df(returns_df, start_date, end_date):
  returns_df[start_date:start_date]=0
  return (1 + returns_df[start_date:end_date]).cumprod()

@st.cache(persist=True, show_spinner=False)
def date_range(end_date, lookback_years):
  return [end_date - timedelta(x) for x in range(365 * lookback_years)][::-1]

@st.cache(persist=True, show_spinner=False)
def ids2names_dict(coin_ids, names):
  ids2names_dict={}
  for i, id in enumerate(coin_ids):
    ids2names_dict[id] = names[i]
  return ids2names_dict

@st.cache(persist=True, show_spinner=False)
def names2ids_dict(names, coin_ids):
  names2ids_dict={}
  for i, name in enumerate(names):
    names2ids_dict[name] = coin_ids[i]
  return names2ids_dict

@st.cache(persist=True, show_spinner=False)
def gen_rebased_df(histories_df, ids_with_histories, start_date, end_date):
  returns_df = histories_df[ids_with_histories].pct_change(1)
  returns_df[start_date:start_date]=0
  return (1 + returns_df[start_date:end_date]).cumprod()