hateimparlament/scraping/fetch.R

source("../utils/helpers.R")
source("config.R")
library(rvest)
library(stringr)

mk_absolute_url <- function(path) paste0("https://www.bundestag.de", path)

mk_url <- function(offset) {
    mk_absolute_url %$% sprintf("/ajax/filterlist/de/services/opendata/543410-543410?offset=%d",
                                offset)
}

download_protocol <- function(path, name) {
    fp <- paste0(DOWNLOAD_DIR, name)
    try %$% download.file(mk_absolute_url(path), fp, quiet=T)
}

fetch_batch <- function(offset) {
    stopifnot("Offset must be numeric" = is.numeric(offset))
    mk_url(offset) %>%
        read_html() %>%
        as.character() %>%
        str_match_all("/resource/blob/.*?/([0-9]*-data\\.xml)") %>%
        `[[`(1) ->
        paths
    mapply(download_protocol, paths[,1], paths[,2])
    return(length(paths) > 0)
}

# TODO: error handling
# - what if: page not reachable
# - wrong format, etc.
fetch_all <- function() {
    offset <- 0
    while(fetch_batch(offset)) offset <- offset + 10
}