magpie: Make API endpoint wrappers with ease

magpie.R

endpoint <- function(verb, url, body = (verb %in% c("POST", "PUT")), encode = "json", query, headers, dots = TRUE, class) {
  f <- function() {}
  if (body) {
    if (dots) {
      if (missing(headers)) {
        if (missing(query)) {
          formals(f) <- alist(body = , ... = )
          body(f)[[2]] <- as.call(list(verb, url, quote(...), body = quote(body), encode = encode))
        } else {
          formals(f) <- alist(body = , ... = )
          body(f)[[2]] <- as.call(list(verb, url, quote(...), body = quote(body), encode = encode))
        }
      } else {
        if (missing(query)) {
          formals(f) <- alist(body = , ... = )
          body(f)[[2]] <- as.call(list(verb, url, quote(...), body = quote(body), encode = encode))
        } else {
          formals(f) <- alist(body = , ... = )
          body(f)[[2]] <- as.call(list(verb, url, quote(...), body = quote(body), encode = encode))
        }
      }
    } else {
      if (missing(headers)) {
        if (missing(query)) {
          formals(f) <- alist(body = )
          body(f)[[2]] <- as.call(list(verb, url, body = quote(body), encode = encode))
        } else {
          formals(f) <- alist(body = )
          body(f)[[2]] <- as.call(list(verb, url, body = quote(body), encode = encode))
        }
      } else {
        if (missing(query)) {
          formals(f) <- alist(body = )
          body(f)[[2]] <- as.call(list(verb, url, body = quote(body), encode = encode))
        } else {
          formals(f) <- alist(body = )
          body(f)[[2]] <- as.call(list(verb, url, body = quote(body), encode = encode))
        }
      }
    }
  } else {
    if (dots) {
      if (missing(headers)) {
        if (missing(query)) {
          formals(f) <- alist(... = )
          body(f)[[2]] <- as.call(list(verb, url, quote(...)))
        } else {
          formals(f) <- alist(... = )
          body(f)[[2]] <- as.call(list(verb, url, quote(...)))
        }
      } else {
        if (missing(query)) {
          formals(f) <- alist(... = )
          body(f)[[2]] <- as.call(list(verb, url, quote(...)))
        } else {
          formals(f) <- alist(... = )
          body(f)[[2]] <- as.call(list(verb, url, quote(...)))
        }
      }
    } else {
      if (missing(headers)) {
        if (missing(query)) {
          body(f)[[2]] <- as.call(list(verb, url))
        } else {
          body(f)[[2]] <- as.call(list(verb, url))
        }
      } else {
        if (missing(query)) {
          body(f)[[2]] <- as.call(list(verb, url))
        } else {
          body(f)[[2]] <- as.call(list(verb, url))
        }
      }
    }
  }
  body(f)[[3]] <- call("structure", class = quote(class))
  return(f)
}

# quick tests
# endpoint("GET", "http://www.example.com", query = list("arg1", "arg2"))

# useful notes: http://stackoverflow.com/questions/12982528/how-to-create-an-r-function-programmatically