#' regexplain gadget
#'
#' @import miniUI
#' @import shiny
#' @param text Text to explore in gadget (editable using interface)
#' @param start_page Open gadget to this tab, one of `"Text"`, `"Regex"`,
#'   `"Output"`, or `"Help"`
#' @export
regex_gadget <- function(text = NULL,
                         start_page = if (is.null(text)) "Text" else "Regex") {
  stopifnot(requireNamespace("miniUI"), requireNamespace("shiny"))

  # ---- UI ----
  ui <- miniPage(
    shiny::includeCSS(system.file("styles", "style.css", package = "regexplain")),
    shiny::includeCSS(system.file("styles", "gadget.css", package = "regexplain")),
    gadgetTitleBar(
      "regexplain",
      right = miniTitleBarButton("done", "Send Regex To Console", TRUE)
    ),
    miniTabstripPanel(
      selected = match.arg(start_page, c("Text", "Regex", "Output", "Help")),
      # --- UI - Tab - Text ----
      miniTabPanel(
        "Text", icon = icon('file-text-o'),
        miniContentPanel(
          fillCol(
            textAreaInputAlt('text',
                             label = "Text to search or parse",
                             value = paste(text, collapse = "\n"),
                             resize = "both",
                             width = "100%",
                             height="90%",
                             placeholder = "Paste, enter, or edit your sample text here.")
          )
        )
      ),
      # ---- UI - Tab - Regex ----
      miniTabPanel(
        "Regex", icon = icon('terminal'),
        miniContentPanel(
          fillCol(
            flex = c(1, 3),
            fillCol(
              flex = c(1, 1),
              textInputCode('pattern', 'Regex', width = "100%",
                            placeholder = "Enter regex, single \\ okay"),
              checkboxGroupInput(
                'regex_options',
                label = "",
                inline = TRUE,
                width = "90%",
                choices = c("Break Lines" = "text_break_lines",
                            "Ignore Case" = "ignore.case",
                            "Perl Style" = "perl",
                            "Fixed" = "fixed",
                            "Use Bytes" = "useBytes"
                            # , "Invert" = "invert"
                ),
                selected = c('text_break_lines')
              )
            ),
            tags$div(
              class = "gadget-result",
              style = "overflow-y: scroll; height: 100%;",
              htmlOutput('result')
            )
          )
        )
      ),
      # ---- UI - Tab - Output ----
      miniTabPanel(
        "Output", icon = icon("table"),
        miniContentPanel(
          fillCol(
            flex = c(1, 3),
            inputPanel(
              width = "100%;",
              selectInput('regexFn', label = 'Apply Function',
                          choices = regexFn_choices),
              uiOutput("output_sub")
            ),
            # verbatimTextOutput('output_result', placeholder = TRUE)
            tags$pre(
              id = "output_result",
              class = "shiny-text-output",
              style = "overflow-y: scroll; height: 100%;"
            )
          )
        )
      ),
      # ---- UI - Tab - Help ----
      miniTabPanel(
        "Help", icon = icon("support"),
        help_ui("help")
      )
    )
  )

  # ---- Server ----
  server <- function(input, output, session) {
    # ---- Server - Global ----
    rtext <- reactive({
      x <- if ('text_break_lines' %in% input$regex_options) {
        strsplit(input$text, "\n")[[1]]
      } else input$text
      x
    })

    pattern <- reactive({
      sanitize_text_input(input$pattern)
    })

    alert_result <- function(msg, type = "danger") {
      msg <- gsub("\n", "<br>", msg)
      msg <- gsub("\t", "&nbsp;&nbsp;", msg)
      paste0("<pre class='alert alert-", type, "' ",
             "style='padding: 4px; margin-top: 1px; margin-bottom: 4px;'>",
             paste(msg, collapse = "<br>"),
             "</pre>")
    }

    # ---- Server - Tab - Regex ----
    output$result <- renderUI({
      if (is.null(rtext())) return(NULL)
      if (pattern() == "") {
        return(toHTML(paste('<p class="results">', escape_html(rtext()), "</p>", collapse = "")))
      }
      res <- NULL
      error_message <- NULL
      warning_message <- NULL
      tryCatch({
        res <- paste(
          view_regex(
            rtext(),
            pattern(),
            ignore.case = 'ignore.case' %in% input$regex_options,
            perl = 'perl' %in% input$regex_options,
            fixed = 'fixed' %in% input$regex_options,
            useBytes = 'useBytes' %in% input$regex_options,
            # invert = 'invert' %in% input$regex_options,
            render = FALSE,
            escape = TRUE,
            exact  = FALSE),
          collapse = ""
        )
      },
      error = function(e) {
        error_message <<- alert_result(e$message, "danger")
      },
      warning = function(w) {
        warning_message <<- alert_result(w$message, "warning")
      })

      if (is.null(res)) res <- toHTML(
        paste('<p class="results">', escape_html(rtext()), "</p>", collapse = "")
      )

      toHTML(paste(error_message, warning_message, res))
    })

    # ---- Server - Tab - Output ----
    regexFn_replacement_val <- NULL

    output$output_sub <- renderUI({
      req(input$regexFn)
      if (!input$regexFn %in% regexFn_substitute) return(NULL)
      textInputCode('regexFn_replacement', 'Subsitution',
                    value = regexFn_replacement_val,
                    placeholder = "Replacement Text")
    })

    replacement <- reactive({
      req(input$regexFn)
      if (!input$regexFn %in% regexFn_substitute) {
        NULL
      } else {
        regexFn_replacement_val <<- input$regexFn_replacement
        sanitize_text_input(input$regexFn_replacement)
      }
    })

    output$output_result <- renderPrint({
      req(input$regexFn)
      regexPkg <- get_pkg_namespace(input$regexFn)
      regexFn <- getFromNamespace(input$regexFn, regexPkg)
      req_sub_arg <- input$regexFn %in% regexFn_substitute
      x <- if (regexPkg == "base") {
        if (req_sub_arg) {
          req(replacement())
          regexFn(pattern(), replacement(), rtext())
        } else {
          regexFn(pattern(), rtext())
        }
      } else if (regexPkg == "stringr") {
        if (req_sub_arg) {
          req(replacement())
          regexFn(rtext(), pattern(), replacement())
        } else {
          regexFn(rtext(), pattern())
        }
      } else {
        "Um. Not sure how I got here."
      }
      print(x)
    })

    # ---- Server - Tab - Help ----
    help_text <- callModule(help_server, "help")

    # ---- Server - Tab - Exit ----
    observeEvent(input$done, {
      # browser()
      if (pattern() != "") {
        pattern <- paste0('pattern <- "', escape_backslash(pattern()), '"')
        rstudioapi::sendToConsole(pattern, FALSE)
      }
      stopApp()
    })

    observeEvent(input$cancel, {
      stopApp()
    })
  }

  viewer <- shiny::paneViewer(700)
  runGadget(ui, server, viewer = viewer)
}

# ---- Gadget Helper Functions and Variables ----

sanitize_text_input <- function(x) {
  if (is.null(x) || !nchar(x)) return(x)
  if (grepl("\\u|\\x|\\N|\\a|\\o", x)) {
    try({
      y <- stringi::stri_unescape_unicode(x)
    }, silent = TRUE)
    if (!is.na(y)) x <- y
  }
  # x <- gsub("\u201C|\u201D", '"', x)
  # x <- gsub("\u2018|\u2019", "'", x)
  x
}

toHTML <- function(...) {
  x <- paste(..., collapse = "")
  x <- gsub("\n", "\\\\n", x)
  x <- gsub("\t", "\\\\t", x)
  x <- gsub("\r", "\\\\r", x)
  HTML(x)
}

regexFn_choices <- list(
  "Choose a function" = "",
  base = c(
    "grep",
    "grepl",
    "sub",  #<<
    "gsub", #<<
    "regexpr",
    "gregexpr",
    "regexec"
  ),
  stringr = c(
    "str_detect",
    "str_locate",
    "str_locate_all",
    "str_extract",
    "str_extract_all",
    "str_match",
    "str_match_all",
    "str_replace",     #<<
    "str_replace_all", #<<
    "str_split"
  )
)

regexFn_substitute <- c(
  paste0(c("", "g"), "sub"),
  paste0("str_replace", c("", "_all"))
)

get_pkg_namespace <- function(fn) {
  x <- names(purrr::keep(regexFn_choices, ~ (fn %in% .)))
  if (length(x) > 1) warning(fn, " matches multiple functions in regexFn_choices, please review.")
  x
}