# Get package host

## Overview

This vignette demonstrates how to use a set of R functions to programmatically retrieve the URL and code host package hosted on CRAN, Bioconductor and Github.

We will walk through each step, from checking if a package exists on CRAN to fetching its version history and constructing an appropriate download URL.

## CRAN

    library(DT)
    library(risk.assessr)

### Check if the Package Exists on CRAN

    risk.assessr:::check_cran_package("here")

### Parse Package Archive HTML from CRAN database

fetch information from “https://cran.r-project.org/src/contrib/Archive/here/”

    html <- risk.assessr:::parse_package_info("here")
    html

### Extract Version Information from the Archive Page

Create table with `package_name`, `package_version`, `link`, `date`, `size` from CRAN website

### Get All Versions and the Latest Version

    version_info <- risk.assessr:::get_versions(table, "here")
    version_info$last_version

### Get CRAN package URL source code

    url <- risk.assessr:::get_cran_package_url(
      package_name = "here",
      version = NULL,
      last_version = version_info$last_version,
      all_versions = version_info$all_versions
    )
    url

## Internal R package

`risk.assessr` can also provide similar information from Internal mirror

    result_intern <- risk.assessr:::get_internal_package_url("herald")

    result_intern$url

    result_intern$last_version

## Bioconductor package

Steps to get an R package stored on Bioconductor

    html_content <- fetch_bioconductor_releases()
    release_data <- parse_bioconductor_releases(html_content)
    result_bio <- get_bioconductor_package_url("flowCore", "2.18.0", release_data)

    result_bio$url

## Github repository

R packages stored on Github are assess by looking at BugReports or URL in DESCRIPTION file to find a owner. github link are then created such as below and used to request Github API.

    urls <- c(
      "https://github.com/tidyverse/ggplot2"
    )
    bug_reports <- c(
      "https://github.com/tidyverse/ggplot2/issues"
    )

    all_links <- c(urls, bug_reports)

    github_pattern <- "https://github.com/([^/]+)/([^/]+).*"
    matching_links <- grep(github_pattern, all_links, value = TRUE)
    owner_names <- sub(github_pattern, "\\1", matching_links)
    package_names_github <- sub(github_pattern, "\\2", matching_links)

    valid <- which(owner_names != "" & package_names_github != "")

      if (length(valid) > 0) {
        github_links <- unique(paste0("https://github.com/", owner_names[valid], "/", package_names_github[valid]))
      } else {
        github_links <- NULL
      }

    github_links

## Get R package source code

    tarball_path <- get_package_tarfile("dplyr", version = "1.0.0")