fixture <- local({

  get_test_data <- function(expr) {
    code <- enc2utf8(paste0(deparse(expr, backtick = TRUE), collapse = "\n"))
    hash <- cli::hash_md5(code)
    snap <- getOption("testthat.snapshotter")
    list(
      root = testthat::test_path(),
      expr = expr,
      code = code,
      hash = hash,
      file = snap$file,
      test = snap$test,
      seen = snap$test_file_seen
    )
  }

  mkdirp <- function(dir) {
    s <- vlapply(dir, dir.create, recursive = TRUE, showWarnings = FALSE)
    invisible(s)
  }

  find_test_file <- function(ctx, root) {
    ptn <- paste0("^test[-_]", ctx, "[.][Rr]")
    file <- grep(ptn, dir(root), value = TRUE)[1]
    as.character(file)
  }

  context_name <- function(filename) {
    # Remove test- prefix
    filename <- sub("^test[-_]", "", filename)
    # Remove terminal extension
    filename <- sub("[.][Rr]$", "", filename)
    filename
  }

  rstudio_tickle <- function() {
    if (!requireNamespace("rstudioapi", quietly = TRUE)) {
      return()
    }

    if (!asNamespace("rstudioapi")$hasFun("executeCommand")) {
      return()
    }

    asNamespace("rstudioapi")$executeCommand("vcsRefresh")
    asNamespace("rstudioapi")$executeCommand("refreshFiles")
  }

  read_lines <- function(path, n = -1L, encoding = "UTF-8") {
    base::readLines(path, n = n, encoding = encoding, warn = FALSE)
  }

  write_lines <- function(text, path) {
    base::writeLines(enc2utf8(text), path, useBytes = TRUE)
  }

  fix_to_md <- function(data) {
    h2 <- paste0("# ", names(data), "\n\n")
    code_block <- function(x) paste0(indent_add(x), collapse = "\n\n---\n\n")
    data <- vapply(data, code_block, character(1))

    paste0(h2, data, "\n\n", collapse = "")
  }

  indent_add <- function(x, prefix = "    ") {
    paste0(prefix, gsub("\n", paste0("\n", prefix), x, fixed = TRUE))
  }

  indent_del <- function(x, prefix = "    ") {
    x <- gsub(paste0("^", prefix), "", x)
    x <- gsub(paste0("\n", prefix), "\n", x)
    x
  }

  compact <- function(x) {
    x[lengths(x) > 0]
  }

  new_fixture_reporter <- function(data) {
    FixtureReporter <- R6::R6Class(
      "FixtureReporter",
      inherit = testthat::Reporter,
      public = list(
        fix_dir = "_fixtures",
        file = NULL,
        test = NULL,
        cur_fixs = NULL,
        files_seen = NULL,
        hashes_seen = NULL,

        initialize = function(files_seen = character()) {
          self$files_seen <- files_seen
        },

        start_file = function(path, test = NULL) {
          self$files_seen <- c(self$files_seen, path)
          self$file <- context_name(path)
          self$cur_fixs <- list()
          if (!is.null(test)) {
            self$start_test(NULL, test)
          }
        },

        start_test = function(context, test) {
          self$test <- test

          if (length(self$cur_fixs[[test]]) > 0) {
            warning("Duplicate test, discarding previous fixtures")
          }
          self$cur_fixs[[test]] <- list()
        },

        add_fixture = function(hash, code) {
          value <- paste(collapse = "\n", c(
            "Hash", paste0("  ", hash),
            "Code", paste0("  ", strsplit(code, "\n", fixed = TRUE)[[1]])
          ))
          self$hashes_seen <- c(self$hashes_seen, hash)
          self$cur_fixs <- self$fix_append(self$cur_fixs, value)
        },

        end_file = function() {
          dir.create(self$fix_dir, showWarnings = FALSE)
          self$fixs_write(self$cur_fixs)
        },

        end_reporter = function() {
          tests <- testthat::find_test_scripts(".", full.names = FALSE)
          if (all(tests %in% self$files_seen)) {
            rds <- dir(self$fix_dir, pattern = "[.]rds$")
            seen <- paste0(self$hashes_seen, ".rds")
            unused <- setdiff(rds, seen)
            if (length(unused) > 0) {
              message("Deleting unused fixtures: ", unused)
              unlink(file.path(self$fix_dir, unused))
            }
          }
          if (length(dir(self$fix_dir)) == 0) {
            unlink(self$fix_dir, recursive = TRUE)
          }
          rstudio_tickle()
        },

        fix_append = function(data, fix) {
          data[[self$test]] <- c(data[[self$test]], list(fix))
          data
        },

        # File management ----------------------------------------------------------

        fixs_write = function(data, suffix = "") {
          data <- compact(data)
          if (length(data) > 0) {
            out <- fix_to_md(data)
            # trim off last line since write_lines() adds one
            out <- gsub("\n$", "", out)
            write_lines(out, self$fix_path(suffix))
          } else {
            self$fixs_delete(suffix)
          }
        },

        fixs_delete = function(suffix = "") {
          unlink(self$fix_path(suffix))
        },

        fix_path = function(suffix = "") {
          file.path(self$fix_dir, paste0(self$file, suffix, ".md"))
        }
      )
    )

    fixer <- FixtureReporter$new(data$seen)

    fixer
  }

  setup_reporter <- function(data) {
    rep <- testthat::get_reporter()
    if (!isTRUE(rep$capabilities$fixture_setup)) {
      rep$capabilities$fixture_setup <- TRUE
      if (class(rep)[1] != "MultiReporter") return()
      fixer <- new_fixture_reporter(data)
      file <- find_test_file(data$file, data$root)
      if (is.na(file)) stop("Cannot determine test file for fixtures")
      fixer$start_file(file, data$test)
      rep$reporters <- c(rep$reporters, list(fixer))
    }
    wfix <- sapply(rep$reporters, inherits, "FixtureReporter")
    if (sum(wfix) != 1) stop("Must be exactly one FixtureReporter")
    fixer <- rep$reporters[[which(wfix)]]
    fixer$add_fixture(data$hash, data$code)
  }

  get <- function(expr, envir = parent.frame()) {
    expr <- substitute(expr)
    data <- get_test_data(expr)
    if (!is.null(data$file)) setup_reporter(data)
    fxfile <- paste0(data$hash, ".rds")
    fxpath <- file.path(data$root, "_fixtures", fxfile)
    upd <- isTRUE(getOption("fixtures.update"))
    upd1 <- isTRUE(getOption("fixtures.update1"))
    if (upd || upd1) {
      if (upd1) options(fixtures.update1 = NULL)
      value <- eval(expr, envir = envir)
      mkdirp(dirname(fxpath))
      saveRDS(value, fxpath, version = 2L)
      value

    } else {
      tryCatch(
        suppressWarnings(readRDS(fxpath)),
        error = function(err) {
          stop("Cannot read fixture file `", fxpath, "`")
        }
      )
    }
  }

  update <- function(files = NULL, ...) {
    opt <- options(fixtures.update = TRUE)
    on.exit(options(opt), add = TRUE)
    testthat::test_local(filter = files, ...)
  }

  update_next <- function() {
    options(fixtures.update1 = TRUE)
  }

  snap_from_md <- function(lines) {
    lines <- gsub("\r", "", lines, fixed = TRUE)

    h2 <- grepl("^# ", lines)
    tests_group <- cumsum(h2)
    tests <- split(lines[!h2], tests_group[!h2])
    names(tests) <- gsub("^# ", "", lines[h2])

    split_tests <- function(lines) {
      sep <- grepl("^-{3, }", lines)
      case_group <- cumsum(sep)

      # Remove first line and last line, separator, line above and line below
      sep_loc <- which(sep)
      drop <- c(1, sep_loc, sep_loc + 1, sep_loc - 1, length(lines))

      cases <- unname(split(lines[-drop], case_group[-drop]))
      code_unblock <- function(x) paste0(indent_del(x), collapse = "\n")
      vapply(cases, code_unblock, character(1))
    }

    lapply(tests, split_tests)
  }

  read_hashes <- function(path) {
    lines <- readLines(path)
    fixes <- snap_from_md(lines)
    hashes <- sub("^Hash\n[ ]+([a-f0-9]+)\n.*$", "\\1", unlist(fixes))
    unique(sort(unname(hashes)))
  }

  read_all_hashes <- function(root, reports) {
    unique(sort(unlist(lapply(file.path(root, reports), read_hashes))))
  }

  cleanup <- function(force = FALSE) {
    root <- testthat::test_path()
    fixroot <- file.path(root, "_fixtures")
    reports <- dir(fixroot, pattern = "[.]md$")
    tests <- testthat::find_test_scripts(root, full.names = FALSE)
    tests_used <- vcapply(sub("[.]md$", "", reports), find_test_file, root)
    old <- names(tests_used)[which(is.na(tests_used))]
    old <- setdiff(old, "_other")
    if (length(old) > 0) {
      old <- paste0(old, ".md")
      message("Unused test fixture reports: ", paste(old, collapse = ", "))
      reports <- setdiff(reports, old)
    }

    allfix <- dir(fixroot, pattern = "[.]rds$")
    usedfix <- paste0(read_all_hashes(fixroot, reports), ".rds")

    old2 <- setdiff(allfix, usedfix)
    if (length(old2) > 0) {
      message("Unused test fixture files: ", paste(old2, collapse = ", "))
    }

    if (length(old) > 0 || length(old2) > 0) {
      if (!force) {
        message("Call with `force = TRUE` to remove these files")
      } else {
        message("Removing them.")
        unlink(file.path(fixroot, old))
        unlink(file.path(fixroot, old2))
      }
    }
  }

  list(
    get = get,
    update = update,
    update_next = update_next,
    cleanup = cleanup,
    .internal = environment()
  )
})