#
# In this global.R field, we create all objects and run all code
# that we only want to run once when we start our app and that we
# want accessible to all parts of our app. This includes database
# queries (in this case at least), API keys, etc.
#
# First, we load and attach packages. A package must be installed before
# loading; for example, to install RPostgreSQL, we simply type
# install.packages("RPostgreSQL").
#
# RPostgreSQL allows us to connect to our database.
library(RPostgreSQL)

# sf (Simple Features) is our spatial package of choice. It uses Simple
# Features lists to store geometries. SF is a standard storage model
# maintained by the Open Geospatial Consortium (OGS) and the
# International Organization for Standardization (ISO), so it's like
# reaaaal offish. Incidentally, PostGIS also implements Simple Features,
# so SF plays very nicely with SF.
library(sf)

# Shiny is a web application Framework for R that provides both
# server-side scripting and a browser user interface API.
library(shiny)

# Mapdeck is an R interface for MapboxGL and Deck.gl; this is the library
# that we'll be using to build our map.
library(mapdeck)

# Here, we create and initialize a PostgreSQL client.
# We could also write driver <- dbDriver('PostgreSQL')
# I discovered digging into the docs that dbDriver methods are deprecated,
# meaning that users are encouraged to instead use database-specific
# functions to initialize drivers.
driver <- PostgreSQL()

# Here, we initiate a connection to our database using parameters that
# should by now look pretty familiar!
con <- dbConnect(driver,
                 dbname='class521_s19',
                 host='cronpgsql.mit.edu',
                 user='',
                 password='')

# Storing a SQL query as a character string.
evic_rate_q <- "SELECT
  t.geoid10,
  t.geom,
  e.eviction_rate,
  e.year
FROM
  somerville.gb_bg_2010 AS t
    INNER JOIN somerville.evic_bg AS e ON t.geoid10 = e.geoid10;"


# st_read comes from the SF package, and allows us to read a file or
# query a database whose results are stored as a data frame with a
# simple feature column. The ST_ prefix should look familiar from our
# PostGIS work! It stands for Spatial Type.
evic_rate <- st_read(dsn = con, query = evic_rate_q)

# We now disconnect our database instance to ensure that we don't open
# multiple unnecessary connections to our database (this is especially
# relevant in development, as you'll likely be stopping and starting
# your application frequently).
dbDisconnect(con)

# This is your Mapbox API key (or 'token'), available on the dashboard of your account.
mb_token = ''