R/KorAPQuery.R - KorAP/RKorAPClient - Gitiles

 #' Class KorAPQuery
 #'
 #' This class provides methods to perform different kinds of queries on the KorAP API server.
 #' `KorAPQuery` objects, which are typically created by the [corpusQuery()] method,
 #' represent the current state of a query to a KorAP server.
 #'
 #' @include KorAPConnection.R
 #' @import httr
 #'
 #' @include RKorAPClient-package.R

 #' @export
 KorAPQuery <- setClass("KorAPQuery", slots = c(
   "korapConnection",
   "request",
   "vc",
   "totalResults",
   "nextStartIndex",
   "fields",
   "requestUrl",
   "webUIRequestUrl",
   "apiResponse",
   "collectedMatches",
   "hasMoreMatches"
 ))

 #' Method initialize
 #'
 #' @rdname KorAPQuery-class
 #' @param .Object …
 #' @param korapConnection KorAPConnection object
 #' @param request query part of the request URL
 #' @param vc definition of a virtual corpus
 #' @param totalResults number of hits the query has yielded
 #' @param nextStartIndex at what index to start the next fetch of query results
 #' @param fields what data / metadata fields should be collected
 #' @param requestUrl complete URL of the API request
 #' @param webUIRequestUrl URL of a web frontend request corresponding to the API request
 #' @param apiResponse data-frame representation of the JSON response of the API request
 #' @param hasMoreMatches logical that signals if more query results can be fetched
 #' @param collectedMatches matches already fetched from the KorAP-API-server
 #'
 #' @importFrom tibble tibble
 #' @export
 setMethod("initialize", "KorAPQuery",
           function(.Object, korapConnection = NULL, request = NULL, vc="", totalResults=0, nextStartIndex=0, fields=c("corpusSigle", "textSigle", "pubDate",  "pubPlace",
                                                                               "availability", "textClass", "snippet", "tokens"),
                    requestUrl="", webUIRequestUrl = "", apiResponse = NULL, hasMoreMatches= FALSE, collectedMatches = NULL) {
             .Object <- callNextMethod()
             .Object@korapConnection = korapConnection
             .Object@request = request
             .Object@vc = vc
             .Object@totalResults = totalResults
             .Object@nextStartIndex = nextStartIndex
             .Object@fields = fields
             .Object@requestUrl = requestUrl
             .Object@webUIRequestUrl = webUIRequestUrl
             .Object@apiResponse = apiResponse
             .Object@hasMoreMatches = hasMoreMatches
             .Object@collectedMatches = collectedMatches
             .Object
           })

 setGeneric("corpusQuery", function(kco, ...)  standardGeneric("corpusQuery") )
 setGeneric("fetchAll", function(kqo, ...)  standardGeneric("fetchAll") )
 setGeneric("fetchNext", function(kqo, ...)  standardGeneric("fetchNext") )
 setGeneric("fetchRest", function(kqo, ...)  standardGeneric("fetchRest") )
 setGeneric("frequencyQuery", function(kco, ...)  standardGeneric("frequencyQuery") )

 maxResultsPerPage <- 50

 ## quiets concerns of R CMD check re: the .'s that appear in pipelines
 if(getRversion() >= "2.15.1")  utils::globalVariables(c("."))

 #' Corpus query
 #'
 #' **`corpusQuery`** performs a corpus query via a connection to a KorAP-API-server
 #'
 #' @rdname KorAPQuery-class
 #' @aliases corpusQuery
 #'
 #' @importFrom urltools url_encode
 #' @importFrom purrr pmap
 #' @importFrom dplyr bind_rows
 #'
 #' @param kco [KorAPConnection()] object (obtained e.g. from `new("KorAPConnection")`
 #' @param query string that contains the corpus query. The query language depends on the `ql` parameter. Either `query` must be provided or `KorAPUrl`.
 #' @param vc string describing the virtual corpus in which the query should be performed. An empty string (default) means the whole corpus, as far as it is license-wise accessible.
 #' @param KorAPUrl instead of providing the query and vc string parameters, you can also simply copy a KorAP query URL from your browser and use it here (and in `KorAPConnection`) to provide all necessary information for the query.
 #' @param metadataOnly logical that determines whether queries should return only metadata without any snippets. This can also be useful to prevent access rewrites. Note that the default value is TRUE.
 #'    If you want your corpus queries to return not only metadata, but also KWICS, you need to authorize
 #'    your RKorAPClient application as explained in the
 #'   [authorization section](https://github.com/KorAP/RKorAPClient#authorization)
 #'   of the RKorAPClient Readme on GitHub and set the `metadataOnly` parameter to
 #'   `FALSE`.
 #' @param ql string to choose the query language (see [section on Query Parameters](https://github.com/KorAP/Kustvakt/wiki/Service:-Search-GET#user-content-parameters) in the Kustvakt-Wiki for possible values.
 #' @param fields (meta)data fields that will be fetched for every match.
 #' @param accessRewriteFatal abort if query or given vc had to be rewritten due to insufficient rights (not yet implemented).
 #' @param verbose print some info
 #' @param as.df return result as data frame instead of as S4 object?
 #' @param expand logical that decides if `query` and `vc` parameters are expanded to all of their combinations
 #' @param context string that specifies the size of the left and the right context returned in `snippet`
 #'        (provided that `metadataOnly` is set to `false` and that the necessary access right are  met).
 #'        The format of the context size specifcation (e.g. `3-token,3-token`) is described in the [Service: Search GET documentation of the Kustvakt Wiki](https://github.com/KorAP/Kustvakt/wiki/Service:-Search-GET).
 #'        If the parameter is not set, the default context size secification of the KorAP server instance will be used.
 #'        Note that you cannot overrule the maximum context size set in the KorAP server instance,
 #'        as this is typically legally motivated.
 #' @return Depending on the `as.df` parameter, a table or a [KorAPQuery()] object that, among other information, contains the total number of results in `@totalResults`. The resulting object can be used to fetch all query results (with [fetchAll()]) or the next page of results (with [fetchNext()]).
 #' A corresponding URL to be used within a web browser is contained in `@webUIRequestUrl`
 #' Please make sure to check `$collection$rewrites` to see if any unforeseen access rewrites of the query's virtual corpus had to be performed.
 #'
 #' @examples
 #' \dontrun{
 #'
 #' # Fetch metadata of every query hit for "Ameisenplage" and show a summary
 #' new("KorAPConnection") %>% corpusQuery("Ameisenplage") %>% fetchAll()
 #' }
 #'
 #' \dontrun{
 #'
 #' # Use the copy of a KorAP-web-frontend URL for an API query of "Ameise" in a virtual corpus
 #' # and show the number of query hits (but don't fetch them).
 #'
 #' new("KorAPConnection", verbose = TRUE) %>%
 #'  corpusQuery(KorAPUrl =
 #'    "https://korap.ids-mannheim.de/?q=Ameise&cq=pubDate+since+2017&ql=poliqarp")
 #' }
 #'
 #' \dontrun{
 #'
 #' # Plot the time/frequency curve of "Ameisenplage"
 #' new("KorAPConnection", verbose=TRUE) %>%
 #'   { . ->> kco } %>%
 #'   corpusQuery("Ameisenplage") %>%
 #'   fetchAll() %>%
 #'   slot("collectedMatches") %>%
 #'   mutate(year = lubridate::year(pubDate)) %>%
 #'   dplyr::select(year) %>%
 #'   group_by(year) %>%
 #'   summarise(Count = dplyr::n()) %>%
 #'   mutate(Freq = mapply(function(f, y)
 #'     f / corpusStats(kco, paste("pubDate in", y))@tokens, Count, year)) %>%
 #'   dplyr::select(-Count) %>%
 #'   complete(year = min(year):max(year), fill = list(Freq = 0)) %>%
 #'   plot(type = "l")
 #' }
 #' @seealso [KorAPConnection()], [fetchNext()], [fetchRest()], [fetchAll()], [corpusStats()]
 #'
 #' @references
 #' <https://ids-pub.bsz-bw.de/frontdoor/index/index/docId/9026>
 #'
 #' @export
 setMethod("corpusQuery", "KorAPConnection",
           function(kco,
                    query = if (missing(KorAPUrl))
                      stop("At least one of the parameters query and KorAPUrl must be specified.", call. = FALSE)
                    else
                      httr::parse_url(KorAPUrl)$query$q,
                    vc = if (missing(KorAPUrl)) "" else httr::parse_url(KorAPUrl)$query$cq,
                    KorAPUrl,
                    metadataOnly = TRUE,
                    ql = if (missing(KorAPUrl)) "poliqarp" else httr::parse_url(KorAPUrl)$query$ql,
                    fields = c(
                      "corpusSigle",
                      "textSigle",
                      "pubDate",
                      "pubPlace",
                      "availability",
                      "textClass",
                      "snippet",
                      "tokens"
                    ),
                    accessRewriteFatal = TRUE,
                    verbose = kco@verbose,
                    expand = length(vc) != length(query),
           as.df = FALSE,
           context = NULL) {
   if (length(query) > 1 || length(vc) > 1) {
     grid <- if (expand) expand_grid(query=query, vc=vc) else tibble(query=query, vc=vc)
     purrr::pmap(grid, function(query, vc, ...)
       corpusQuery(kco, query=query, vc=vc, ql=ql, verbose=verbose, as.df = TRUE)) %>%
       bind_rows()
   } else {
       contentFields <- c("snippet", "tokens")
       if (metadataOnly) {
         fields <- fields[!fields %in% contentFields]
       }
       request <-
         paste0('?q=',
                url_encode(enc2utf8(query)),
                ifelse (!metadataOnly && ! is.null(context) && context !=  '', paste0('&context=', url_encode(enc2utf8(context))), ''),
                ifelse (vc != '', paste0('&cq=', url_encode(enc2utf8(vc))), ''),
                ifelse (!metadataOnly, '&show-tokens=true', ''),
                '&ql=', ql)
       webUIRequestUrl <- paste0(kco@KorAPUrl, request)
       requestUrl <- paste0(
         kco@apiUrl,
         'search',
         request,
         '&fields=',
         paste(fields, collapse = ","),
         if (metadataOnly) '&access-rewrite-disabled=true' else ''
       )
       log_info(verbose, "Searching \"", query, "\" in \"", vc, "\"", sep =
                  "")
       res = apiCall(kco, paste0(requestUrl, '&count=0'))
       if (is.null(res)) {
         log_info(verbose, " [failed]\n")
         message("API call failed.")
         totalResults <- 0
       } else {
         totalResults <-res$meta$totalResults
         log_info(verbose, ": ", totalResults, " hits")
         if(!is.null(res$meta$cached))
           log_info(verbose, " [cached]\n")
         else
           log_info(verbose, ", took ", res$meta$benchmark, "\n", sep = "")
       }
       if (as.df)
         data.frame(
           query = query,
           totalResults = totalResults,
           vc = vc,
           webUIRequestUrl = webUIRequestUrl,
           stringsAsFactors = FALSE
         )
       else
         KorAPQuery(
           korapConnection = kco,
           nextStartIndex = 0,
           fields = fields,
           requestUrl = requestUrl,
           request = request,
           totalResults = totalResults,
           vc = vc,
           apiResponse = res,
           webUIRequestUrl = webUIRequestUrl,
           hasMoreMatches = (totalResults > 0),
         )
     }
   })

 #' Fetch the next bunch of results of a KorAP query.
 #'
 #' **`fetchNext`** fetches the next bunch of results of a KorAP query.
 #'
 #' @param kqo object obtained from [corpusQuery()]
 #' @param offset start offset for query results to fetch
 #' @param maxFetch maximum number of query results to fetch
 #' @param verbose print progress information if true
 #' @param randomizePageOrder fetch result pages in pseudo random order if true. Use [set.seed()] to set seed for reproducible results.
 #' @return The `kqo` input object with updated slots `collectedMatches`, `apiResponse`, `nextStartIndex`, `hasMoreMatches`
 #'
 #' @examples
 #' \dontrun{
 #'
 #' q <- new("KorAPConnection") %>% corpusQuery("Ameisenplage") %>% fetchNext()
 #' q@collectedMatches
 #' }
 #'
 #' @references
 #' <https://ids-pub.bsz-bw.de/frontdoor/index/index/docId/9026>
 #'
 #' @aliases fetchNext
 #' @rdname KorAPQuery-class
 #' @importFrom dplyr rowwise bind_rows select summarise n
 #' @export
 setMethod("fetchNext", "KorAPQuery", function(kqo,
                                               offset = kqo@nextStartIndex,
                                               maxFetch = maxResultsPerPage,
                                               verbose = kqo@korapConnection@verbose,
                                               randomizePageOrder = FALSE) {
   if (kqo@totalResults == 0 || offset >= kqo@totalResults) {
     return(kqo)
   }

   page <- kqo@nextStartIndex / maxResultsPerPage + 1
   results <- 0
   pubDate <- NULL # https://stackoverflow.com/questions/8096313/no-visible-binding-for-global-variable-note-in-r-cmd-check
   collectedMatches <- kqo@collectedMatches

   if (randomizePageOrder) {
     pages <- head(sample.int(ceiling(kqo@totalResults / maxResultsPerPage)), maxFetch) - 1
   }

   repeat {
     page = length(collectedMatches[,1]) %/% maxResultsPerPage + 1
     currentOffset = ifelse(randomizePageOrder, pages[page],  page - 1) * maxResultsPerPage
     query <- paste0(kqo@requestUrl, '&count=', min(if (!is.na(maxFetch)) maxFetch - results else maxResultsPerPage, maxResultsPerPage) ,'&offset=', currentOffset, '&cutoff=true')
     res <- apiCall(kqo@korapConnection, query)
     if (length(res$matches) == 0) {
       break
     }

     for (field in kqo@fields) {
       if (!field %in% colnames(res$matches)) {
         res$matches[, field] <- NA
       }
     }
     currentMatches <-
       res$matches %>%
       dplyr::select(kqo@fields)
     if (!is.list(collectedMatches)) {
       collectedMatches <- currentMatches
     } else {
       collectedMatches <- bind_rows(collectedMatches, currentMatches)
     }
     if (verbose) {
       cat(paste0(
         "Retrieved page ",
         ceiling(length(collectedMatches[, 1]) / res$meta$itemsPerPage),
         "/",
         if (!is.na(maxFetch) && maxFetch < kqo@totalResults)
           sprintf("%d (%d)", ceiling(maxFetch / res$meta$itemsPerPage), ceiling(kqo@totalResults / res$meta$itemsPerPage))
         else
           sprintf("%d", ceiling(kqo@totalResults / res$meta$itemsPerPage)),
         ' in ',
         res$meta$benchmark,
         '\n'
       ))
     }
     page <- page + 1
     results <- results + res$meta$itemsPerPage
     if (length(collectedMatches[,1]) >= kqo@totalResults || (!is.na(maxFetch) && results >= maxFetch)) {
       break
     }
   }
   nextStartIndex <- min(res$meta$startIndex + res$meta$itemsPerPage, kqo@totalResults)
   KorAPQuery(nextStartIndex = nextStartIndex,
     korapConnection = kqo@korapConnection,
     fields = kqo@fields,
     requestUrl = kqo@requestUrl,
     request = kqo@request,
     totalResults = kqo@totalResults,
     vc = kqo@vc,
     webUIRequestUrl = kqo@webUIRequestUrl,
     hasMoreMatches = (kqo@totalResults > nextStartIndex),
     apiResponse = res,
     collectedMatches = collectedMatches)
 })

 #' Fetch all results of a KorAP query.
 #'
 #' **`fetchAll`** fetches all results of a KorAP query.
 #'
 #' @examples
 #' \dontrun{
 #'
 #' q <- new("KorAPConnection") %>% corpusQuery("Ameisenplage") %>% fetchAll()
 #' q@collectedMatches
 #' }
 #'
 #' @aliases fetchAll
 #' @rdname KorAPQuery-class
 #' @export
 setMethod("fetchAll", "KorAPQuery", function(kqo, verbose = kqo@korapConnection@verbose, ...) {
   return(fetchNext(kqo, offset = 0, maxFetch = NA, verbose = verbose, ...))
 })

 #' Fetches the remaining results of a KorAP query.
 #'
 #' @examples
 #' \dontrun{
 #'
 #' q <- new("KorAPConnection") %>% corpusQuery("Ameisenplage") %>% fetchRest()
 #' q@collectedMatches
 #' }
 #'
 #' @aliases fetchRest
 #' @rdname KorAPQuery-class
 #' @export
 setMethod("fetchRest", "KorAPQuery", function(kqo, verbose = kqo@korapConnection@verbose, ...) {
   return(fetchNext(kqo, maxFetch = NA, verbose = verbose, ...))
 })

 #' Query relative frequency of search term(s)
 #'
 #' **`frequencyQuery`** combines [corpusQuery()], [corpusStats()] and
 #' [ci()] to compute a table with the relative frequencies and
 #' confidence intervals of one ore multiple search terms across one or multiple
 #' virtual corpora.
 #'
 #' @aliases frequencyQuery
 #' @rdname KorAPQuery-class
 #' @examples
 #' \dontrun{
 #'
 #' new("KorAPConnection", verbose = TRUE) %>%
 #'   frequencyQuery(c("Mücke", "Schnake"), paste0("pubDate in ", 2000:2003))
 #' }
 #'
 #' @param kco [KorAPConnection()] object (obtained e.g. from `new("KorAPConnection")`
 #' @param query string that contains the corpus query. The query language depends on the `ql` parameter. Either `query` must be provided or `KorAPUrl`.
 #' @param conf.level confidence level of the returned confidence interval (passed through [ci()]  to [prop.test()]).
 #' @param as.alternatives LOGICAL that specifies if the query terms should be treated as alternatives. If `as.alternatives` is TRUE, the sum over all query hits, instead of the respective vc token sizes is used as total for the calculation of relative frequencies.
 #' @export
 setMethod("frequencyQuery", "KorAPConnection",
   function(kco, query, vc = "", conf.level = 0.95, as.alternatives = FALSE, ...) {
       (if (as.alternatives) {
         corpusQuery(kco, query, vc, metadataOnly = TRUE, as.df = TRUE, ...) %>%
         group_by(vc) %>%
         mutate(total = sum(totalResults))
       } else {
         corpusQuery(kco, query, vc, metadataOnly = TRUE, as.df = TRUE, ...) %>%
         mutate(total = corpusStats(kco, vc=vc, as.df=TRUE)$tokens)
       } ) %>%
       ci(conf.level = conf.level)
 })


 #' buildWebUIRequestUrl
 #'
 #' @rdname KorAPQuery-class
 #' @importFrom urltools url_encode
 #' @export
 buildWebUIRequestUrl <- function(kco,
                                  query = if (missing(KorAPUrl))
                                    stop("At least one of the parameters query and KorAPUrl must be specified.", call. = FALSE)
                                  else
                                    httr::parse_url(KorAPUrl)$query$q,
                                  vc = if (missing(KorAPUrl)) "" else httr::parse_url(KorAPUrl)$query$cq,
                                  KorAPUrl,
                                  metadataOnly = TRUE,
                                  ql = if (missing(KorAPUrl)) "poliqarp" else httr::parse_url(KorAPUrl)$query$ql,
                                  fields = c(
                                    "corpusSigle",
                                    "textSigle",
                                    "pubDate",
                                    "pubPlace",
                                    "availability",
                                    "textClass",
                                    "snippet",
                                    "tokens"
                                  ),
                                  accessRewriteFatal = TRUE) {
   request <-
     paste0(
       '?q=',
       urltools::url_encode(enc2utf8(as.character(query))),
       ifelse(vc != '',
         paste0('&cq=', urltools::url_encode(enc2utf8(vc))),
         ''),
       '&ql=',
       ql
     )
   webUIRequestUrl <- paste0(kco@KorAPUrl, request)
   requestUrl <- paste0(
     kco@apiUrl,
     'search',
     request,
     '&fields=',
     paste(fields, collapse = ","),
     if (metadataOnly)
       '&access-rewrite-disabled=true'
     else
       ''
   )
   webUIRequestUrl
 }

 #´ format()
 #' @rdname KorAPQuery-class
 #' @param x KorAPQuery object
 #' @param ... further arguments passed to or from other methods
 #' @export
 format.KorAPQuery <- function(x, ...) {
   cat("<KorAPQuery>\n")
   q <- x
   aurl = parse_url(q@request)
   cat("           Query: ", aurl$query$q, "\n")
   if (!is.null(aurl$query$cq) && aurl$query$cq != "") {
     cat("  Virtual corpus: ", aurl$query$cq, "\n")
   }
   if (!is.null(q@collectedMatches)) {
     cat("==============================================================================================================", "\n")
     print(summary(q@collectedMatches))
     cat("==============================================================================================================", "\n")
   }
   cat("   Total results: ", q@totalResults, "\n")
   cat(" Fetched results: ", q@nextStartIndex, "\n")
 }

 #' show()
 #'
 #' @rdname KorAPQuery-class
 #' @param object KorAPQuery object
 #' @export
 setMethod("show", "KorAPQuery", function(object) {
   format(object)
 })
	#' Class KorAPQuery
	#'
	#' This class provides methods to perform different kinds of queries on the KorAP API server.
	#' `KorAPQuery` objects, which are typically created by the [corpusQuery()] method,
	#' represent the current state of a query to a KorAP server.
	#'
	#' @include KorAPConnection.R
	#' @import httr
	#'
	#' @include RKorAPClient-package.R

	#' @export
	KorAPQuery <- setClass("KorAPQuery", slots = c(
	"korapConnection",
	"request",
	"vc",
	"totalResults",
	"nextStartIndex",
	"fields",
	"requestUrl",
	"webUIRequestUrl",
	"apiResponse",
	"collectedMatches",
	"hasMoreMatches"
	))

	#' Method initialize
	#'
	#' @rdname KorAPQuery-class
	#' @param .Object …
	#' @param korapConnection KorAPConnection object
	#' @param request query part of the request URL
	#' @param vc definition of a virtual corpus
	#' @param totalResults number of hits the query has yielded
	#' @param nextStartIndex at what index to start the next fetch of query results
	#' @param fields what data / metadata fields should be collected
	#' @param requestUrl complete URL of the API request
	#' @param webUIRequestUrl URL of a web frontend request corresponding to the API request
	#' @param apiResponse data-frame representation of the JSON response of the API request
	#' @param hasMoreMatches logical that signals if more query results can be fetched
	#' @param collectedMatches matches already fetched from the KorAP-API-server
	#'
	#' @importFrom tibble tibble
	#' @export
	setMethod("initialize", "KorAPQuery",
	function(.Object, korapConnection = NULL, request = NULL, vc="", totalResults=0, nextStartIndex=0, fields=c("corpusSigle", "textSigle", "pubDate", "pubPlace",
	"availability", "textClass", "snippet", "tokens"),
	requestUrl="", webUIRequestUrl = "", apiResponse = NULL, hasMoreMatches= FALSE, collectedMatches = NULL) {
	.Object <- callNextMethod()
	.Object@korapConnection = korapConnection
	.Object@request = request
	.Object@vc = vc
	.Object@totalResults = totalResults
	.Object@nextStartIndex = nextStartIndex
	.Object@fields = fields
	.Object@requestUrl = requestUrl
	.Object@webUIRequestUrl = webUIRequestUrl
	.Object@apiResponse = apiResponse
	.Object@hasMoreMatches = hasMoreMatches
	.Object@collectedMatches = collectedMatches
	.Object
	})

	setGeneric("corpusQuery", function(kco, ...) standardGeneric("corpusQuery") )
	setGeneric("fetchAll", function(kqo, ...) standardGeneric("fetchAll") )
	setGeneric("fetchNext", function(kqo, ...) standardGeneric("fetchNext") )
	setGeneric("fetchRest", function(kqo, ...) standardGeneric("fetchRest") )
	setGeneric("frequencyQuery", function(kco, ...) standardGeneric("frequencyQuery") )

	maxResultsPerPage <- 50

	## quiets concerns of R CMD check re: the .'s that appear in pipelines
	if(getRversion() >= "2.15.1") utils::globalVariables(c("."))

	#' Corpus query
	#'
	#' `corpusQuery` performs a corpus query via a connection to a KorAP-API-server
	#'
	#' @rdname KorAPQuery-class
	#' @aliases corpusQuery
	#'
	#' @importFrom urltools url_encode
	#' @importFrom purrr pmap
	#' @importFrom dplyr bind_rows
	#'
	#' @param kco [KorAPConnection()] object (obtained e.g. from `new("KorAPConnection")`
	#' @param query string that contains the corpus query. The query language depends on the `ql` parameter. Either `query` must be provided or `KorAPUrl`.
	#' @param vc string describing the virtual corpus in which the query should be performed. An empty string (default) means the whole corpus, as far as it is license-wise accessible.
	#' @param KorAPUrl instead of providing the query and vc string parameters, you can also simply copy a KorAP query URL from your browser and use it here (and in `KorAPConnection`) to provide all necessary information for the query.
	#' @param metadataOnly logical that determines whether queries should return only metadata without any snippets. This can also be useful to prevent access rewrites. Note that the default value is TRUE.
	#' If you want your corpus queries to return not only metadata, but also KWICS, you need to authorize
	#' your RKorAPClient application as explained in the
	#' [authorization section](https://github.com/KorAP/RKorAPClient#authorization)
	#' of the RKorAPClient Readme on GitHub and set the `metadataOnly` parameter to
	#' `FALSE`.
	#' @param ql string to choose the query language (see [section on Query Parameters](https://github.com/KorAP/Kustvakt/wiki/Service:-Search-GET#user-content-parameters) in the Kustvakt-Wiki for possible values.
	#' @param fields (meta)data fields that will be fetched for every match.
	#' @param accessRewriteFatal abort if query or given vc had to be rewritten due to insufficient rights (not yet implemented).
	#' @param verbose print some info
	#' @param as.df return result as data frame instead of as S4 object?
	#' @param expand logical that decides if `query` and `vc` parameters are expanded to all of their combinations
	#' @param context string that specifies the size of the left and the right context returned in `snippet`
	#' (provided that `metadataOnly` is set to `false` and that the necessary access right are met).
	#' The format of the context size specifcation (e.g. `3-token,3-token`) is described in the [Service: Search GET documentation of the Kustvakt Wiki](https://github.com/KorAP/Kustvakt/wiki/Service:-Search-GET).
	#' If the parameter is not set, the default context size secification of the KorAP server instance will be used.
	#' Note that you cannot overrule the maximum context size set in the KorAP server instance,
	#' as this is typically legally motivated.
	#' @return Depending on the `as.df` parameter, a table or a [KorAPQuery()] object that, among other information, contains the total number of results in `@totalResults`. The resulting object can be used to fetch all query results (with [fetchAll()]) or the next page of results (with [fetchNext()]).
	#' A corresponding URL to be used within a web browser is contained in `@webUIRequestUrl`
	#' Please make sure to check `$collection$rewrites` to see if any unforeseen access rewrites of the query's virtual corpus had to be performed.
	#'
	#' @examples
	#' \dontrun{
	#'
	#' # Fetch metadata of every query hit for "Ameisenplage" and show a summary
	#' new("KorAPConnection") %>% corpusQuery("Ameisenplage") %>% fetchAll()
	#' }
	#'
	#' \dontrun{
	#'
	#' # Use the copy of a KorAP-web-frontend URL for an API query of "Ameise" in a virtual corpus
	#' # and show the number of query hits (but don't fetch them).
	#'
	#' new("KorAPConnection", verbose = TRUE) %>%
	#' corpusQuery(KorAPUrl =
	#' "https://korap.ids-mannheim.de/?q=Ameise&cq=pubDate+since+2017&ql=poliqarp")
	#' }
	#'
	#' \dontrun{
	#'
	#' # Plot the time/frequency curve of "Ameisenplage"
	#' new("KorAPConnection", verbose=TRUE) %>%
	#' { . ->> kco } %>%
	#' corpusQuery("Ameisenplage") %>%
	#' fetchAll() %>%
	#' slot("collectedMatches") %>%
	#' mutate(year = lubridate::year(pubDate)) %>%
	#' dplyr::select(year) %>%
	#' group_by(year) %>%
	#' summarise(Count = dplyr::n()) %>%
	#' mutate(Freq = mapply(function(f, y)
	#' f / corpusStats(kco, paste("pubDate in", y))@tokens, Count, year)) %>%
	#' dplyr::select(-Count) %>%
	#' complete(year = min(year):max(year), fill = list(Freq = 0)) %>%
	#' plot(type = "l")
	#' }
	#' @seealso [KorAPConnection()], [fetchNext()], [fetchRest()], [fetchAll()], [corpusStats()]
	#'
	#' @references
	#' <https://ids-pub.bsz-bw.de/frontdoor/index/index/docId/9026>
	#'
	#' @export
	setMethod("corpusQuery", "KorAPConnection",
	function(kco,
	query = if (missing(KorAPUrl))
	stop("At least one of the parameters query and KorAPUrl must be specified.", call. = FALSE)
	else
	httr::parse_url(KorAPUrl)$query$q,
	vc = if (missing(KorAPUrl)) "" else httr::parse_url(KorAPUrl)$query$cq,
	KorAPUrl,
	metadataOnly = TRUE,
	ql = if (missing(KorAPUrl)) "poliqarp" else httr::parse_url(KorAPUrl)$query$ql,
	fields = c(
	"corpusSigle",
	"textSigle",
	"pubDate",
	"pubPlace",
	"availability",
	"textClass",
	"snippet",
	"tokens"
	),
	accessRewriteFatal = TRUE,
	verbose = kco@verbose,
	expand = length(vc) != length(query),
	as.df = FALSE,
	context = NULL) {
	if (length(query) > 1 \|\| length(vc) > 1) {
	grid <- if (expand) expand_grid(query=query, vc=vc) else tibble(query=query, vc=vc)
	purrr::pmap(grid, function(query, vc, ...)
	corpusQuery(kco, query=query, vc=vc, ql=ql, verbose=verbose, as.df = TRUE)) %>%
	bind_rows()
	} else {
	contentFields <- c("snippet", "tokens")
	if (metadataOnly) {
	fields <- fields[!fields %in% contentFields]
	}
	request <-
	paste0('?q=',
	url_encode(enc2utf8(query)),
	ifelse (!metadataOnly && ! is.null(context) && context != '', paste0('&context=', url_encode(enc2utf8(context))), ''),
	ifelse (vc != '', paste0('&cq=', url_encode(enc2utf8(vc))), ''),
	ifelse (!metadataOnly, '&show-tokens=true', ''),
	'&ql=', ql)
	webUIRequestUrl <- paste0(kco@KorAPUrl, request)
	requestUrl <- paste0(
	kco@apiUrl,
	'search',
	request,
	'&fields=',
	paste(fields, collapse = ","),
	if (metadataOnly) '&access-rewrite-disabled=true' else ''
	)
	log_info(verbose, "Searching \"", query, "\" in \"", vc, "\"", sep =
	"")
	res = apiCall(kco, paste0(requestUrl, '&count=0'))
	if (is.null(res)) {
	log_info(verbose, " [failed]\n")
	message("API call failed.")
	totalResults <- 0
	} else {
	totalResults <-res$meta$totalResults
	log_info(verbose, ": ", totalResults, " hits")
	if(!is.null(res$meta$cached))
	log_info(verbose, " [cached]\n")
	else
	log_info(verbose, ", took ", res$meta$benchmark, "\n", sep = "")
	}
	if (as.df)
	data.frame(
	query = query,
	totalResults = totalResults,
	vc = vc,
	webUIRequestUrl = webUIRequestUrl,
	stringsAsFactors = FALSE
	)
	else
	KorAPQuery(
	korapConnection = kco,
	nextStartIndex = 0,
	fields = fields,
	requestUrl = requestUrl,
	request = request,
	totalResults = totalResults,
	vc = vc,
	apiResponse = res,
	webUIRequestUrl = webUIRequestUrl,
	hasMoreMatches = (totalResults > 0),
	)
	}
	})

	#' Fetch the next bunch of results of a KorAP query.
	#'
	#' `fetchNext` fetches the next bunch of results of a KorAP query.
	#'
	#' @param kqo object obtained from [corpusQuery()]
	#' @param offset start offset for query results to fetch
	#' @param maxFetch maximum number of query results to fetch
	#' @param verbose print progress information if true
	#' @param randomizePageOrder fetch result pages in pseudo random order if true. Use [set.seed()] to set seed for reproducible results.
	#' @return The `kqo` input object with updated slots `collectedMatches`, `apiResponse`, `nextStartIndex`, `hasMoreMatches`
	#'
	#' @examples
	#' \dontrun{
	#'
	#' q <- new("KorAPConnection") %>% corpusQuery("Ameisenplage") %>% fetchNext()
	#' q@collectedMatches
	#' }
	#'
	#' @references
	#' <https://ids-pub.bsz-bw.de/frontdoor/index/index/docId/9026>
	#'
	#' @aliases fetchNext
	#' @rdname KorAPQuery-class
	#' @importFrom dplyr rowwise bind_rows select summarise n
	#' @export
	setMethod("fetchNext", "KorAPQuery", function(kqo,
	offset = kqo@nextStartIndex,
	maxFetch = maxResultsPerPage,
	verbose = kqo@korapConnection@verbose,
	randomizePageOrder = FALSE) {
	if (kqo@totalResults == 0 \|\| offset >= kqo@totalResults) {
	return(kqo)
	}

	page <- kqo@nextStartIndex / maxResultsPerPage + 1
	results <- 0
	pubDate <- NULL # https://stackoverflow.com/questions/8096313/no-visible-binding-for-global-variable-note-in-r-cmd-check
	collectedMatches <- kqo@collectedMatches

	if (randomizePageOrder) {
	pages <- head(sample.int(ceiling(kqo@totalResults / maxResultsPerPage)), maxFetch) - 1
	}

	repeat {
	page = length(collectedMatches[,1]) %/% maxResultsPerPage + 1
	currentOffset = ifelse(randomizePageOrder, pages[page], page - 1) * maxResultsPerPage
	query <- paste0(kqo@requestUrl, '&count=', min(if (!is.na(maxFetch)) maxFetch - results else maxResultsPerPage, maxResultsPerPage) ,'&offset=', currentOffset, '&cutoff=true')
	res <- apiCall(kqo@korapConnection, query)
	if (length(res$matches) == 0) {
	break
	}

	for (field in kqo@fields) {
	if (!field %in% colnames(res$matches)) {
	res$matches[, field] <- NA
	}
	}
	currentMatches <-
	res$matches %>%
	dplyr::select(kqo@fields)
	if (!is.list(collectedMatches)) {
	collectedMatches <- currentMatches
	} else {
	collectedMatches <- bind_rows(collectedMatches, currentMatches)
	}
	if (verbose) {
	cat(paste0(
	"Retrieved page ",
	ceiling(length(collectedMatches[, 1]) / res$meta$itemsPerPage),
	"/",
	if (!is.na(maxFetch) && maxFetch < kqo@totalResults)
	sprintf("%d (%d)", ceiling(maxFetch / res$meta$itemsPerPage), ceiling(kqo@totalResults / res$meta$itemsPerPage))
	else
	sprintf("%d", ceiling(kqo@totalResults / res$meta$itemsPerPage)),
	' in ',
	res$meta$benchmark,
	'\n'
	))
	}
	page <- page + 1
	results <- results + res$meta$itemsPerPage
	if (length(collectedMatches[,1]) >= kqo@totalResults \|\| (!is.na(maxFetch) && results >= maxFetch)) {
	break
	}
	}
	nextStartIndex <- min(res$meta$startIndex + res$meta$itemsPerPage, kqo@totalResults)
	KorAPQuery(nextStartIndex = nextStartIndex,
	korapConnection = kqo@korapConnection,
	fields = kqo@fields,
	requestUrl = kqo@requestUrl,
	request = kqo@request,
	totalResults = kqo@totalResults,
	vc = kqo@vc,
	webUIRequestUrl = kqo@webUIRequestUrl,
	hasMoreMatches = (kqo@totalResults > nextStartIndex),
	apiResponse = res,
	collectedMatches = collectedMatches)
	})

	#' Fetch all results of a KorAP query.
	#'
	#' `fetchAll` fetches all results of a KorAP query.
	#'
	#' @examples
	#' \dontrun{
	#'
	#' q <- new("KorAPConnection") %>% corpusQuery("Ameisenplage") %>% fetchAll()
	#' q@collectedMatches
	#' }
	#'
	#' @aliases fetchAll
	#' @rdname KorAPQuery-class
	#' @export
	setMethod("fetchAll", "KorAPQuery", function(kqo, verbose = kqo@korapConnection@verbose, ...) {
	return(fetchNext(kqo, offset = 0, maxFetch = NA, verbose = verbose, ...))
	})

	#' Fetches the remaining results of a KorAP query.
	#'
	#' @examples
	#' \dontrun{
	#'
	#' q <- new("KorAPConnection") %>% corpusQuery("Ameisenplage") %>% fetchRest()
	#' q@collectedMatches
	#' }
	#'
	#' @aliases fetchRest
	#' @rdname KorAPQuery-class
	#' @export
	setMethod("fetchRest", "KorAPQuery", function(kqo, verbose = kqo@korapConnection@verbose, ...) {
	return(fetchNext(kqo, maxFetch = NA, verbose = verbose, ...))
	})

	#' Query relative frequency of search term(s)
	#'
	#' `frequencyQuery` combines [corpusQuery()], [corpusStats()] and
	#' [ci()] to compute a table with the relative frequencies and
	#' confidence intervals of one ore multiple search terms across one or multiple
	#' virtual corpora.
	#'
	#' @aliases frequencyQuery
	#' @rdname KorAPQuery-class
	#' @examples
	#' \dontrun{
	#'
	#' new("KorAPConnection", verbose = TRUE) %>%
	#' frequencyQuery(c("Mücke", "Schnake"), paste0("pubDate in ", 2000:2003))
	#' }
	#'
	#' @param kco [KorAPConnection()] object (obtained e.g. from `new("KorAPConnection")`
	#' @param query string that contains the corpus query. The query language depends on the `ql` parameter. Either `query` must be provided or `KorAPUrl`.
	#' @param conf.level confidence level of the returned confidence interval (passed through [ci()] to [prop.test()]).
	#' @param as.alternatives LOGICAL that specifies if the query terms should be treated as alternatives. If `as.alternatives` is TRUE, the sum over all query hits, instead of the respective vc token sizes is used as total for the calculation of relative frequencies.
	#' @export
	setMethod("frequencyQuery", "KorAPConnection",
	function(kco, query, vc = "", conf.level = 0.95, as.alternatives = FALSE, ...) {
	(if (as.alternatives) {
	corpusQuery(kco, query, vc, metadataOnly = TRUE, as.df = TRUE, ...) %>%
	group_by(vc) %>%
	mutate(total = sum(totalResults))
	} else {
	corpusQuery(kco, query, vc, metadataOnly = TRUE, as.df = TRUE, ...) %>%
	mutate(total = corpusStats(kco, vc=vc, as.df=TRUE)$tokens)
	} ) %>%
	ci(conf.level = conf.level)
	})


	#' buildWebUIRequestUrl
	#'
	#' @rdname KorAPQuery-class
	#' @importFrom urltools url_encode
	#' @export
	buildWebUIRequestUrl <- function(kco,
	query = if (missing(KorAPUrl))
	stop("At least one of the parameters query and KorAPUrl must be specified.", call. = FALSE)
	else
	httr::parse_url(KorAPUrl)$query$q,
	vc = if (missing(KorAPUrl)) "" else httr::parse_url(KorAPUrl)$query$cq,
	KorAPUrl,
	metadataOnly = TRUE,
	ql = if (missing(KorAPUrl)) "poliqarp" else httr::parse_url(KorAPUrl)$query$ql,
	fields = c(
	"corpusSigle",
	"textSigle",
	"pubDate",
	"pubPlace",
	"availability",
	"textClass",
	"snippet",
	"tokens"
	),
	accessRewriteFatal = TRUE) {
	request <-
	paste0(
	'?q=',
	urltools::url_encode(enc2utf8(as.character(query))),
	ifelse(vc != '',
	paste0('&cq=', urltools::url_encode(enc2utf8(vc))),
	''),
	'&ql=',
	ql
	)
	webUIRequestUrl <- paste0(kco@KorAPUrl, request)
	requestUrl <- paste0(
	kco@apiUrl,
	'search',
	request,
	'&fields=',
	paste(fields, collapse = ","),
	if (metadataOnly)
	'&access-rewrite-disabled=true'
	else
	''
	)
	webUIRequestUrl
	}

	#´ format()
	#' @rdname KorAPQuery-class
	#' @param x KorAPQuery object
	#' @param ... further arguments passed to or from other methods
	#' @export
	format.KorAPQuery <- function(x, ...) {
	cat("<KorAPQuery>\n")
	q <- x
	aurl = parse_url(q@request)
	cat(" Query: ", aurl$query$q, "\n")
	if (!is.null(aurl$query$cq) && aurl$query$cq != "") {
	cat(" Virtual corpus: ", aurl$query$cq, "\n")
	}
	if (!is.null(q@collectedMatches)) {
	cat("==============================================================================================================", "\n")
	print(summary(q@collectedMatches))
	cat("==============================================================================================================", "\n")
	}
	cat(" Total results: ", q@totalResults, "\n")
	cat(" Fetched results: ", q@nextStartIndex, "\n")
	}

	#' show()
	#'
	#' @rdname KorAPQuery-class
	#' @param object KorAPQuery object
	#' @export
	setMethod("show", "KorAPQuery", function(object) {
	format(object)
	})