source("funs/scraper.R")
source("funs/map_helpers.R")
source("funs/plot_weather_jma.R")

server <- function(input, output, session) {
    selected_station <- reactiveVal(NULL)
    station_data <- reactiveVal(NULL) # Store loaded data for display
    prev_dates <- reactiveVal(NULL) # Track previous date inputs for specific difference detection
    url_initialized <- reactiveVal(FALSE) # Track if URL params have been applied

    # MapLibre Reactive Values
    style_change_trigger <- reactiveVal(0) # Trigger station re-render after style change
    map_initialized <- reactiveVal(FALSE) # Track if map bounds have been set
    stations_before_id <- reactiveVal(NULL) # Layer ID for station ordering
    current_raster_layers <- reactiveVal(character(0)) # Track dynamically added raster layers

    # Helper: Parse URL query string
    parse_url_params <- function(query_string) {
        if (is.null(query_string) || query_string == "" || query_string == "?") {
            return(list())
        }
        # Remove leading "?"
        qs <- sub("^\\?", "", query_string)
        if (qs == "") {
            return(list())
        }

        pairs <- strsplit(qs, "&")[[1]]
        params <- list()
        for (pair in pairs) {
            kv <- strsplit(pair, "=")[[1]]
            if (length(kv) == 2) {
                params[[kv[1]]] <- URLdecode(kv[2])
            }
        }
        params
    }

    # Helper: Broadcast current state to parent page
    broadcast_state <- function(view_override = NULL) {
        st <- selected_station()
        # Extract scalar values from tibble row
        station_id <- if (!is.null(st) && nrow(st) > 0) as.character(st$ID[[1]]) else NULL
        station_name <- if (!is.null(st) && nrow(st) > 0) as.character(st$DisplayName[[1]]) else NULL
        prefecture <- if (!is.null(st) && nrow(st) > 0 && !is.na(st$PrecName[[1]])) as.character(st$PrecName[[1]]) else NULL
        resolution <- input$data_resolution

        # Determine current view
        main_tab <- input$main_nav
        view <- if (!is.null(view_override)) {
            view_override
        } else if (!is.null(main_tab)) {
            if (main_tab == "Map View") {
                "map"
            } else if (main_tab == "Station Info") {
                "station-info"
            } else if (main_tab == "Dashboard") {
                subtab <- input$dashboard_subtabs
                if (!is.null(subtab) && subtab == "Data") {
                    "dashboard-data"
                } else {
                    "dashboard-plots"
                }
            } else {
                "map"
            }
        } else {
            "map"
        }

        start_date <- if (!is.null(input$date_range)) as.character(input$date_range[1]) else NULL
        end_date <- if (!is.null(input$date_range)) as.character(input$date_range[2]) else NULL

        session$sendCustomMessage("updateParentURL", list(
            station = station_id,
            stationName = station_name,
            prefecture = prefecture,
            resolution = resolution,
            view = view,
            start = start_date,
            end = end_date
        ))
    }

    # Observer: Apply URL params on app startup
    observe({
        req(!url_initialized())

        query <- session$clientData$url_search
        params <- parse_url_params(query)

        if (length(params) == 0) {
            url_initialized(TRUE)
            return()
        }

        # Apply resolution
        if (!is.null(params$resolution) && params$resolution %in% c("10 Minutes", "Hourly", "Daily", "Monthly")) {
            updateRadioButtons(session, "data_resolution", selected = params$resolution)
        }

        # Apply date range
        if (!is.null(params$start) && !is.null(params$end)) {
            start_date <- tryCatch(as.Date(params$start), error = function(e) NULL)
            end_date <- tryCatch(as.Date(params$end), error = function(e) NULL)
            if (!is.null(start_date) && !is.null(end_date)) {
                updateDateRangeInput(session, "date_range", start = start_date, end = end_date)
                prev_dates(c(start_date, end_date))
            }
        }

        # Apply station selection (deferred to allow inputs to update)
        if (!is.null(params$station)) {
            station_id <- params$station
            # Find station by ID or DisplayName
            st <- stations %>%
                filter(ID == station_id | DisplayName == station_id) %>%
                head(1)
            if (nrow(st) > 0) {
                selected_station(st)
                updateSelectizeInput(session, "station_selector", selected = st$DisplayName)
                # Trigger download after a short delay to let other inputs settle
                shinyjs::delay(500, {
                    start_download(st)
                })
            }
        }

        # Apply view/tab navigation (deferred)
        if (!is.null(params$view)) {
            view <- params$view
            shinyjs::delay(600, {
                if (view == "map") {
                    session$sendCustomMessage("switchTab", list(tabId = "Map View"))
                } else if (view == "station-info") {
                    session$sendCustomMessage("switchTab", list(tabId = "Station Info"))
                } else if (view %in% c("dashboard-plots", "dashboard-data")) {
                    session$sendCustomMessage("switchTab", list(tabId = "Dashboard"))
                    if (view == "dashboard-data") {
                        shinyjs::delay(800, {
                            # Click the tab directly; assumes id="dashboard_subtabs" -> li a[data-value="Data"]
                            # Use robust JS to switch tab as updateNavsetCardPill might fail during init
                            shinyjs::runjs("$('a[data-value=\"Data\"]').tab('show');")
                        })
                    }
                }
            })
        }

        url_initialized(TRUE)
    })

    # helper for rich label similar to DWD
    generate_label <- function(name, id, type, start, end, vars) {
        paste0(
            "<div style='font-size:14px; min-width: 200px;'>",
            "<b>", htmltools::htmlEscape(name), "</b> (", id, ")<br>",
            "Type: ", type, "<br>",
            "Period: ", start, " - ", end, "<br>",
            "<div style='margin-top:5px; font-size:12px; color:#555;'>",
            "Vars: ", substring(vars, 1, 50), "...",
            "</div>",
            "</div>"
        )
    }

    add_resolution_period <- function(df, resolution) {
        df %>%
            mutate(
                ResolutionStart = case_when(
                    resolution == "Daily" ~ Start_Daily,
                    resolution == "Hourly" ~ Start_Hourly,
                    resolution == "10 Minutes" ~ Start_10min,
                    resolution == "Monthly" ~ Start_Monthly,
                    TRUE ~ NA_real_
                ),
                ResolutionEnd = case_when(
                    resolution == "Daily" ~ End_Daily,
                    resolution == "Hourly" ~ End_Hourly,
                    resolution == "10 Minutes" ~ End_10min,
                    resolution == "Monthly" ~ End_Monthly,
                    TRUE ~ NA_real_
                )
            )
    }

    get_resolution_period <- function(st, resolution) {
        start_val <- switch(resolution,
            "Daily" = st$Start_Daily,
            "Hourly" = st$Start_Hourly,
            "10 Minutes" = st$Start_10min,
            "Monthly" = st$Start_Monthly,
            NA_real_
        )
        end_val <- switch(resolution,
            "Daily" = st$End_Daily,
            "Hourly" = st$End_Hourly,
            "10 Minutes" = st$End_10min,
            "Monthly" = st$End_Monthly,
            NA_real_
        )
        list(start = start_val, end = end_val)
    }

    format_period_labels <- function(start, end, current_year = NULL) {
        start_label <- ifelse(is.na(start), "Unknown", start)
        if (is.null(current_year)) {
            end_label <- ifelse(is.na(end), "Present", end)
        } else {
            end_label <- ifelse(is.na(end) | end == current_year, "Present", end)
        }
        list(start = start_label, end = end_label)
    }

    filtered_stations <- reactive({
        res <- stations

        # 1. Filter by Name if selected
        # 1. Filter by Name if selected - REMOVED to prevent loop and allow map context
        # if (input$station_selector != "All") {
        #     res <- res %>% filter(DisplayName == input$station_selector)
        # }

        # 2. Filter by Resolution and Date Range
        if (!is.null(input$date_range) && !is.null(input$data_resolution)) {
            start_yr <- as.numeric(format(input$date_range[1], "%Y"))
            end_yr <- as.numeric(format(input$date_range[2], "%Y"))
            resolution <- input$data_resolution

            # Get the start year for the selected resolution
            res <- res %>%
                add_resolution_period(resolution) %>%
                # Filter: Station must have data for this resolution AND overlap with date range
                filter(
                    !is.na(ResolutionStart) & # Must have data for this resolution
                        ResolutionStart <= end_yr & # Started before or in the end year
                        (is.na(ResolutionEnd) | ResolutionEnd >= start_yr) # Still active or ended after start
                ) %>%
                select(-ResolutionStart, -ResolutionEnd)
        }

        res
    })


    output$visible_count <- renderText({
        count <- nrow(filtered_stations())
        sprintf("Visible Stations: %d", count)
    })

    # Server-side selectize for performance
    observe({
        # Update choices based on filtered stations OR all stations?
        # DWD uses all stations usually, but if we filter by resolution, maybe strictly filtered?
        # Let's use filtered for consistency with the map.
        df <- filtered_stations()

        # We need a named vector or just names.
        # choices are DisplayName, values are DisplayName (or ID? existing logic uses DisplayName)
        # Existing logic uses DisplayName for lookup.

        updateSelectizeInput(session, "station_selector",
            choices = c("All", sort(df$DisplayName)),
            server = TRUE
        )
    })

    output$map <- renderMaplibre({
        maplibre(
            style = "https://basemaps.cartocdn.com/gl/positron-gl-style/style.json",
            center = c(138, 36),
            zoom = 4
        ) %>%
            add_navigation_control(show_compass = FALSE, visualize_pitch = FALSE, position = "top-left")
    })

    # Initialize map bounds only once
    observe({
        req(!map_initialized())
        req(input$map_zoom) # Wait for map to be ready

        # Initial bounds set by renderMaplibre, just mark initialized
        map_initialized(TRUE)
    })

    # Zoom to extent of all filtered stations
    observeEvent(input$zoom_home, {
        df <- filtered_stations()
        req(df)
        if (nrow(df) > 0) {
            # Calculate bounds
            lons <- range(df$Lon, na.rm = TRUE)
            lats <- range(df$Lat, na.rm = TRUE)

            # If only one station, zoom to it with a small buffer
            if (nrow(df) == 1) {
                maplibre_proxy("map") %>%
                    fly_to(center = c(df$Lon[1], df$Lat[1]), zoom = 12)
            } else {
                maplibre_proxy("map") %>%
                    fit_bounds(c(lons[1], lats[1], lons[2], lats[2]), animate = TRUE)
            }
        }
    })

    # Fix Map Rendering on Tab Switch
    observeEvent(input$main_nav, {
        if (input$main_nav == "Map View") {
            # Slight delay to ensure tab is visible - MapLibre handles resize automatically
            shinyjs::runjs("
                setTimeout(function() {
                    var map = document.getElementById('map');
                    if (map && map.__mapgl) {
                        map.__mapgl.resize();
                    }
                }, 200);
            ")
        }
    })

    # --- Basemap Switching ---
    observeEvent(input$basemap, {
        proxy <- maplibre_proxy("map")

        # Explicitly remove any previously added raster layers
        old_layers <- isolate(current_raster_layers())
        if (length(old_layers) > 0) {
            for (layer_id in old_layers) {
                proxy %>% clear_layer(layer_id)
            }
            current_raster_layers(character(0))
        }

        if (input$basemap %in% c("carto_positron", "carto_voyager")) {
            # VECTOR LOGIC (Carto-based styles)
            style_url <- switch(input$basemap,
                "carto_positron" = "https://basemaps.cartocdn.com/gl/positron-gl-style/style.json",
                "carto_voyager" = "https://basemaps.cartocdn.com/gl/voyager-gl-style/style.json"
            )

            proxy %>%
                set_style(style_url)

            # For vector sandwich, we want stations below labels
            stations_before_id("watername_ocean")
            style_change_trigger(isolate(style_change_trigger()) + 1)
        } else if (input$basemap == "esri_imagery") {
            # Esri Imagery (Raster + Styles?) - DWD implementation uses Voyager style base + Raster layer
            proxy %>%
                set_style("https://basemaps.cartocdn.com/gl/voyager-gl-style/style.json")

            stations_before_id("watername_ocean")

            current_session <- shiny::getDefaultReactiveDomain()
            selected_basemap <- input$basemap

            later::later(function() {
                shiny::withReactiveDomain(current_session, {
                    # Race condition check
                    current_basemap <- isolate(input$basemap)
                    if (current_basemap != selected_basemap) {
                        return()
                    }

                    unique_suffix <- as.numeric(Sys.time()) * 1000
                    source_id <- paste0("esri_imagery_source_", unique_suffix)
                    layer_id <- paste0("esri_imagery_layer_", unique_suffix)

                    esri_url <- "https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}"

                    maplibre_proxy("map") %>%
                        add_raster_source(id = source_id, tiles = c(esri_url), tileSize = 256) %>%
                        add_layer(
                            id = layer_id,
                            type = "raster",
                            source = source_id,
                            paint = list("raster-opacity" = 1),
                            before_id = "watername_ocean"
                        )

                    current_raster_layers(c(layer_id))
                    style_change_trigger(isolate(style_change_trigger()) + 1)
                })
            }, delay = 0.5)
        } else {
            # RASTER LOGIC (Esri Topo, OSM)
            tile_url <- if (input$basemap %in% c("osm", "osm_gray")) {
                "https://tile.openstreetmap.org/{z}/{x}/{y}.png"
            } else {
                "https://server.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer/tile/{z}/{y}/{x}"
            }

            attribution_text <- if (input$basemap %in% c("osm", "osm_gray")) {
                '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'
            } else {
                "Tiles &copy; Esri"
            }

            paint_props <- list("raster-opacity" = 1)
            if (input$basemap == "osm_gray") {
                paint_props[["raster-saturation"]] <- -0.9
                paint_props[["raster-contrast"]] <- 0.3
            }

            # Use blank style + raster layer
            blank_style <- list(
                version = 8,
                sources = list(),
                layers = list(),
                metadata = list(timestamp = as.numeric(Sys.time()))
            )
            json_blank <- jsonlite::toJSON(blank_style, auto_unbox = TRUE)
            blank_uri <- paste0("data:application/json,", URLencode(as.character(json_blank), reserved = TRUE))

            proxy %>%
                set_style(blank_uri)

            current_session <- shiny::getDefaultReactiveDomain()
            selected_basemap <- input$basemap

            later::later(function() {
                shiny::withReactiveDomain(current_session, {
                    current_basemap <- isolate(input$basemap)
                    if (current_basemap != selected_basemap) {
                        return()
                    }

                    unique_suffix <- as.numeric(Sys.time()) * 1000
                    source_id <- paste0("raster_source_", unique_suffix)
                    layer_id <- paste0("raster_layer_", unique_suffix)

                    maplibre_proxy("map") %>%
                        add_raster_source(id = source_id, tiles = c(tile_url), tileSize = 256, attribution = attribution_text) %>%
                        add_layer(
                            id = layer_id,
                            type = "raster",
                            source = source_id,
                            paint = paint_props
                        )

                    stations_before_id(NULL)
                    current_raster_layers(c(layer_id))
                    style_change_trigger(isolate(style_change_trigger()) + 1)
                })
            }, delay = 0.5)
        }
    })

    # Toggle Labels visibility
    observeEvent(input$show_labels,
        {
            visibility <- if (input$show_labels) "visible" else "none"

            label_layers <- c(
                "place_villages", "place_town", "place_country_2", "place_country_1",
                "place_state", "place_continent",
                "place_city_r6", "place_city_r5", "place_city_dot_r7", "place_city_dot_r4",
                "place_city_dot_r2", "place_city_dot_z7",
                "place_capital_dot_z7", "place_capital",
                "roadname_minor", "roadname_sec", "roadname_pri", "roadname_major",
                "motorway_name",
                "watername_ocean", "watername_sea", "watername_lake", "watername_lake_line",
                "poi_stadium", "poi_park", "poi_zoo",
                "airport_label",
                "country-label", "state-label", "settlement-major-label", "settlement-minor-label",
                "settlement-subdivision-label", "road-label", "waterway-label", "natural-point-label",
                "poi-label", "airport-label"
            )

            proxy <- maplibre_proxy("map")

            for (layer_id in label_layers) {
                tryCatch(
                    {
                        proxy <- proxy %>% set_layout_property(layer_id, "visibility", visibility)
                    },
                    error = function(e) {
                        # Layer may not exist in current style, ignore silently
                    }
                )
            }
        },
        ignoreInit = TRUE
    )

    # Update Markers
    observe({
        # Wait for map to be ready before adding markers
        req(map_initialized())

        # Dependency on style change
        style_change_trigger()

        # Use system date for default link
        current_year <- as.numeric(format(Sys.Date(), "%Y"))
        resolution <- input$data_resolution

        # Prepare data with labels for hover
        data <- filtered_stations() %>%
            add_resolution_period(resolution) %>%
            mutate(
                station_label = DisplayName,
                station_type_label = ifelse(station_type == "a", "AMeDAS", "Manned station"),
                period_start_label = ifelse(is.na(ResolutionStart), "Unknown", ResolutionStart),
                period_end_label = ifelse(is.na(ResolutionEnd) | ResolutionEnd == current_year, "Present", ResolutionEnd),
                period_label = ifelse(is.na(ResolutionStart), "Unknown", paste0(ResolutionStart, " - ", period_end_label)),
                hover_content = generate_label(DisplayName, ID, station_type_label, period_start_label, period_end_label, ObservedVariables)
            )

        if (nrow(data) > 0) {
            # Convert to sf for MapLibre
            map_data <- st_as_sf(data, coords = c("Lon", "Lat"), crs = 4326)

            maplibre_proxy("map") %>%
                clear_layer("stations") %>%
                add_circle_layer(
                    id = "stations",
                    source = map_data,
                    circle_color = "navy",
                    circle_radius = 6,
                    circle_stroke_color = "#00000000",
                    circle_stroke_width = 0,
                    circle_opacity = 0.7,
                    tooltip = "hover_content",
                    before_id = stations_before_id()
                )
        } else {
            maplibre_proxy("map") %>% clear_layer("stations")
        }

        # Re-apply highlight if a station is selected
        st <- isolate(selected_station())
        if (!is.null(st)) {
            # Re-gen label for consistency
            period <- get_resolution_period(st, resolution)
            period_labels <- format_period_labels(period$start, period$end, current_year)
            lbl <- generate_label(
                st$DisplayName, st$ID,
                ifelse(st$station_type == "a", "AMeDAS", "Manned station"),
                period_labels$start, period_labels$end,
                st$ObservedVariables
            )
            highlight_selected_station(maplibre_proxy("map"), st$Lon, st$Lat, lbl)
        }
    })

    # Observe marker clicks (MapLibre Feature Click)
    observeEvent(input$map_feature_click, {
        click <- input$map_feature_click

        # Check if the click was on the "stations" layer
        if (!is.null(click) && (isTRUE(click$layer_id == "stations") || isTRUE(click$layer == "stations"))) {
            # The properties are available directly
            props <- click$properties
            # Note: simple feature properties might be lowercased or preserved depending on driver,
            # usually they are preserved but let's check keys if issues arise.
            # We passed `data` which had ID, DisplayName etc.

            id_val <- props$ID # Assuming column name is preserved

            if (!is.null(id_val)) {
                # Use layerId (station ID)
                closest <- stations %>%
                    filter(ID == id_val) %>%
                    head(1)

                selected_station(closest)

                # Highlight & Zoom
                current_year <- as.numeric(format(Sys.Date(), "%Y"))
                period <- get_resolution_period(closest, input$data_resolution)
                period_labels <- format_period_labels(period$start, period$end, current_year = current_year)
                lbl <- generate_label(
                    closest$DisplayName, closest$ID,
                    ifelse(closest$station_type == "a", "AMeDAS", "Manned station"),
                    period_labels$start, period_labels$end,
                    closest$ObservedVariables
                )
                highlight_selected_station(maplibre_proxy("map"), closest$Lon, closest$Lat, lbl)

                # Sync sidebar filter
                updateSelectizeInput(session, "station_selector", selected = closest$DisplayName)

                # Start download directly
                start_download(closest)

                # Broadcast state to parent page for SEO URL sync
                broadcast_state()
            }
        }
    })

    # Helper to calculate and enforce limits
    # Returns a list(start=Date, end=Date, limited=FALSE) to be applied
    check_and_limit_dates <- function(start, end, resolution, anchor = "end") {
        limit_days <- Inf
        limit_msg <- ""

        if (resolution %in% c("Hourly", "10 Minutes")) {
            limit_days <- 93 # ~3 months
            limit_msg <- "3 months"
        } else if (resolution == "Daily") {
            limit_days <- 366 # 1 year
            limit_msg <- "1 year"
        } else if (resolution == "Monthly") {
            limit_days <- 1826 # ~5 years
            limit_msg <- "5 years"
        }

        diff <- as.numeric(end - start)
        if (diff > limit_days) {
            new_start <- start
            new_end <- end

            if (anchor == "start") {
                # Start is fixed, adjust end
                new_end <- start + limit_days
            } else {
                # End is fixed (default), adjust start
                new_start <- end - limit_days
            }
            return(list(start = new_start, end = new_end, limited = TRUE, msg = limit_msg))
        }
        return(list(start = start, end = end, limited = FALSE))
    }

    # Auto-refetch when resolution changes
    observeEvent(input$data_resolution, {
        st <- selected_station()
        req(st)
        req(input$date_range)

        start <- as.Date(input$date_range[1])
        end <- as.Date(input$date_range[2])

        # When changing resolution, usually we want to keep the End date and adjust Start if needed
        res_val <- input$data_resolution

        if (res_val == "Monthly") {
            # Special rule for Monthly: Always default to 3 years back
            new_start <- end - 365 * 3
            res <- list(start = new_start, end = end, limited = TRUE, msg = "3 years")
        } else {
            res <- check_and_limit_dates(start, end, res_val, anchor = "end")
        }

        if (res$limited) {
            updateDateRangeInput(session, "date_range", start = res$start, end = res$end)
            showNotification(paste0("Range adjusted to ", res$msg, " for ", input$data_resolution, " resolution."), type = "warning")
            # Update prev dates so we don't trigger the other observer unnecessarily
            prev_dates(c(res$start, res$end))
        }

        # Trigger download
        start_download(st, override_start = res$start, override_end = res$end)
    })

    # Auto-refetch and Smart Limit when Date Range Changes
    observeEvent(input$date_range, {
        st <- selected_station()
        req(input$date_range)

        current_dates <- input$date_range
        current_start <- as.Date(current_dates[1])
        current_end <- as.Date(current_dates[2])

        last_dates <- prev_dates()

        # Logic to determine anchor
        anchor <- "end" # Default

        if (!is.null(last_dates)) {
            last_start <- as.Date(last_dates[1])
            last_end <- as.Date(last_dates[2])

            # If Start changed, anchor Start. If End changed, anchor End.
            if (current_start != last_start) {
                anchor <- "start"
            }
            # If both changed (rare in picker?) or just End, default to End anchor
        }

        # Check Limits
        res <- check_and_limit_dates(current_start, current_end, input$data_resolution, anchor = anchor)

        if (res$limited) {
            # Update UI (this will trigger observer again, but logic should stabilize)
            updateDateRangeInput(session, "date_range", start = res$start, end = res$end)
            showNotification(paste0("Limit exceeded. Adjusted to ", res$msg, "."), type = "warning")
            prev_dates(c(res$start, res$end))

            # Download with CORRECTED dates
            if (!is.null(st)) {
                start_download(st, override_start = res$start, override_end = res$end)
            }
        } else {
            # No limit applied, just update state
            prev_dates(current_dates)
            # Download with CURRENT dates
            if (!is.null(st)) {
                # Only download if effectively changed (checking prev might be good, but safe to call)
                if (tab_down_trigger_check(current_dates, last_dates)) {
                    start_download(st, override_start = current_start, override_end = current_end)
                }
            }
        }
    })

    # Helper to avoid double downloads if dates haven't materially changed
    tab_down_trigger_check <- function(curr, last) {
        if (is.null(last)) {
            return(TRUE)
        }
        if (curr[1] != last[1] || curr[2] != last[2]) {
            return(TRUE)
        }
        return(FALSE)
    }

    # --- Async Fetch State Machine ---

    # State Variables
    fetch_stage <- reactiveVal(0) # 0=Idle, 1=Init, 2=Next, 4=Download/Parse, 6=Merge
    fetch_queue <- reactiveVal(list())
    fetch_queue_idx <- reactiveVal(0)
    parsed_data_list <- reactiveVal(list())
    fetch_current_token <- reactiveVal(NULL)
    final_data_path <- reactiveVal(NULL) # Path to the ready-to-download file

    reset_fetch <- function() {
        fetch_stage(0)
        fetch_current_token(as.numeric(Sys.time()))
        # Unfreeze UI
        session$sendCustomMessage("unfreezeUI", list())
        # We don't need to enable buttons since we depend on click
    }

    # Handle Cancel
    observeEvent(input$cancel_loading, {
        reset_fetch()
        showNotification("Loading cancelled by user.", type = "warning")
    })

    start_download <- function(st, override_start = NULL, override_end = NULL) {
        req(input$date_range)

        # Clear existing data instantly to indicate refresh
        station_data(NULL)

        if (!is.null(override_start)) {
            start_date <- as.Date(override_start)
        } else {
            start_date <- as.Date(input$date_range[1])
        }

        if (!is.null(override_end)) {
            end_date <- as.Date(override_end)
        } else {
            end_date <- as.Date(input$date_range[2])
        }

        # --- Enforce Date Range Limits (Safety Check only) ---
        # Note: The smart observers should handle UI updates and overrides.
        # This block remains just to clamp wildly invalid args if they bypass observers.
        # For simplicity, we trust overrides or input, assuming observers are working.
        # ---------------------------------

        # UI Setup
        # shinyjs calls removed or replaced by freezeUI
        msg <- paste0("Initializing fetch for ", st$DisplayName, "...")
        session$sendCustomMessage("freezeUI", list(text = msg, station = st$DisplayName))

        # Generate Queue based on resolution
        resolution <- input$data_resolution

        if (resolution %in% c("Daily", "Monthly")) {
            # Daily/Monthly: iterate months
            seq_start <- as.Date(format(start_date, format = "%Y-%m-01"))
            seq_end <- as.Date(format(end_date, format = "%Y-%m-01"))

            # Clamp to current month to avoid future requests
            current_month_start <- as.Date(format(Sys.Date(), "%Y-%m-01"))
            if (seq_end > current_month_start) {
                seq_end <- current_month_start
            }

            dates <- seq(seq_start, seq_end, by = "month")

            if (length(dates) == 0) {
                showNotification("Invalid date range.", type = "error")
                reset_fetch()
                return()
            }

            # Create queue items (month-level)
            q <- list()
            for (i in seq_along(dates)) {
                d <- dates[i]
                yr <- as.numeric(format(d, format = "%Y"))
                mo <- as.numeric(format(d, format = "%m"))
                q[[length(q) + 1]] <- list(year = yr, month = mo, day = NULL)
            }
        } else {
            # Hourly/10-min: iterate days
            # Clamp end_date to today to avoid future requests
            today <- Sys.Date()
            if (end_date > today) {
                end_date <- today
            }

            dates <- seq(start_date, end_date, by = "day")

            if (length(dates) == 0) {
                showNotification("Invalid date range.", type = "error")
                reset_fetch()
                return()
            }

            # Create queue items (day-level)
            q <- list()
            for (i in seq_along(dates)) {
                d <- as.Date(dates[i], origin = "1970-01-01")
                yr <- as.numeric(format(d, format = "%Y"))
                mo <- as.numeric(format(d, format = "%m"))
                dy <- as.numeric(format(d, format = "%d"))
                q[[length(q) + 1]] <- list(year = yr, month = mo, day = dy)
            }
        }


        fetch_queue(q)
        fetch_queue_idx(1)
        parsed_data_list(list())
        fetch_current_token(as.numeric(Sys.time()))

        fetch_stage(2) # Go to Next
    }

    # Stage 2: Next File
    observe({
        req(fetch_stage() == 2)
        idx <- fetch_queue_idx()
        q <- fetch_queue()

        if (idx > length(q)) {
            fetch_stage(6) # Merge
        } else {
            # UI Update
            item <- q[[idx]]
            if (is.null(item$day)) {
                msg <- paste0(
                    "Fetching data for ", item$year, "-", sprintf("%02d", item$month),
                    " (", idx, "/", length(q), ")..."
                )
            } else {
                msg <- paste0(
                    "Fetching data for ", item$year, "-", sprintf("%02d", item$month), "-", sprintf("%02d", item$day),
                    " (", idx, "/", length(q), ")..."
                )
            }
            session$sendCustomMessage("freezeUI", list(text = msg))
            fetch_stage(4) # Go to Download/Parse
        }
    })

    # Stage 4: Download & Parse (Async Yield)
    observe({
        req(fetch_stage() == 4)
        token <- fetch_current_token()

        later::later(function() {
            if (!identical(isolate(fetch_current_token()), token)) {
                return()
            }

            isolate({
                idx <- fetch_queue_idx()
                q <- fetch_queue()
                item <- q[[idx]]
                st <- selected_station()

                # Call Scraper
                df <- tryCatch(
                    get_jma_data(
                        block_no = st$ID,
                        year = item$year,
                        month = item$month,
                        day = item$day,
                        prec_no = st$prec_no,
                        type = paste0(st$station_type, "1"),
                        resolution = input$data_resolution
                    ),
                    error = function(e) NULL
                )

                if (!is.null(df)) {
                    if ("Day" %in% names(df)) {
                        df <- df %>%
                            mutate(Date = as.Date(sprintf("%04d-%02d-%02d", Year, Month, Day)))
                    }
                    plist <- parsed_data_list()
                    plist[[length(plist) + 1]] <- df
                    parsed_data_list(plist)
                }

                fetch_queue_idx(idx + 1)
                fetch_stage(2)
            })
        }, 0.5)
        fetch_stage(-1)
    })

    # Stage 6: Merge & Finalize
    observe({
        req(fetch_stage() == 6)
        token <- fetch_current_token()
        msg <- "Merging data..."
        session$sendCustomMessage("freezeUI", list(text = msg))

        later::later(function() {
            if (!identical(isolate(fetch_current_token()), token)) {
                return()
            }

            isolate({
                plist <- parsed_data_list()

                if (length(plist) == 0) {
                    showNotification("No data found for the selected range.", type = "warning", session = session)
                    reset_fetch()
                    return()
                }

                # Merge
                final_df <- bind_rows(plist)

                # Filter precise range
                start_date <- input$date_range[1]
                end_date <- input$date_range[2]

                if ("Date" %in% names(final_df)) {
                    final_df <- final_df %>%
                        filter(Date >= start_date & Date <= end_date) %>%
                        select(-Date)
                }

                if (nrow(final_df) == 0) {
                    showNotification("No data in exact range.", type = "warning", session = session)
                    reset_fetch()
                    return()
                }

                # Save to temp file for downloadHandler
                tmp <- tempfile(fileext = ".xlsx")
                write_xlsx(final_df, path = tmp)
                final_data_path(tmp)

                # Update reactive for display
                station_data(final_df)

                # Success UI
                reset_fetch()

                # Switch to "Dashboard" tab
                if (is.null(input$main_nav) || input$main_nav != "Dashboard") {
                    session$sendCustomMessage("switchTab", list(tabId = "Dashboard"))
                }
                showNotification(paste("Successfully loaded", nrow(final_df), "rows."), type = "message", session = session)
            })
        }, 0.1)
        fetch_stage(-1)
    })

    # Output: Station Ready (Controls Dashboard Visibility)
    output$station_ready <- reactive({
        !is.null(station_data())
    })
    outputOptions(output, "station_ready", suspendWhenHidden = FALSE)

    # Output: Station Info Header (Dashboard Card)
    output$station_info_header <- renderUI({
        st <- selected_station()
        if (is.null(st)) {
            return(NULL)
        }

        # Determine Resolution Badge
        res_label <- input$data_resolution
        res_class <- if (res_label == "Hourly") "bg-primary" else "bg-success"

        # Data Range Text
        df <- station_data()
        if (is.null(df) || nrow(df) == 0) {
            dates_text <- "No data loaded"
        } else {
            # Assumes 'Date' column exists for Daily, or constructing from Year/Month/Day
            if ("Date" %in% names(df)) {
                d_range <- range(df$Date, na.rm = TRUE)
                dates_text <- paste(d_range[1], "to", d_range[2])
            } else if ("Year" %in% names(df) && "Month" %in% names(df) && "Day" %in% names(df)) {
                # Hourly/10min
                # Construct dates just for display
                start_d <- as.Date(paste(df$Year[1], df$Month[1], df$Day[1], sep = "-"))
                n <- nrow(df)
                end_d <- as.Date(paste(df$Year[n], df$Month[n], df$Day[n], sep = "-"))
                dates_text <- paste(start_d, "to", end_d)
            } else {
                dates_text <- "Loaded"
            }
        }

        # Render Card
        card(
            style = "margin-bottom: 20px; border-left: 5px solid #007bff;",
            card_body(
                padding = 15,
                layout_columns(
                    fill = FALSE,
                    # Col 1: Station
                    div(
                        strong("Station"), br(),
                        span(st$DisplayName, style = "font-size: 1.1rem;"), br(),
                        tags$small(class = "text-muted", paste("ID:", st$ID))
                    ),
                    # Col 2: Location
                    div(
                        strong("Location"), br(),
                        span(paste0(st$Lat, "°N, ", st$Lon, "°E")), br(),
                        tags$small(class = "text-muted", st$PrecLabel)
                    ),
                    # Col 3: Technical
                    div(
                        strong("Technical"), br(),
                        span(paste0(st$Elevation, " m")), br(),
                        span(class = paste("badge", res_class), res_label)
                    ),
                    # Col 4: Period
                    div(
                        strong("Data Selection"), br(),
                        span(dates_text)
                    ),
                    # Col 5: Actions
                    div(
                        class = "d-flex align-items-center justify-content-end",
                        downloadButton(
                            "downloadData",
                            label = "Export Excel",
                            class = "btn-sm btn-primary",
                            icon = icon("file-excel")
                        )
                    )
                )
            )
        )
    })

    # Download Handler
    output$downloadData <- downloadHandler(
        filename = function() {
            req(selected_station())
            st <- selected_station()
            res <- if (!is.null(input$data_resolution)) tolower(input$data_resolution) else "data"
            sprintf("jma_%s_%s_%s.xlsx", st$ID, res, format(Sys.Date(), "%Y%m%d"))
        },
        content = function(file) {
            req(final_data_path())
            file.copy(final_data_path(), file)
        }
    )

    # Render Table
    # --- Dashboard Logic ---

    # 1. Update Variable Choices when data changes


    # 2. Render Plot
    # --- Dynamic Plot Rendering ---

    # 1. Determine available variables and render UI
    output$jma_plots_container <- renderUI({
        df <- station_data()
        req(df)

        # Identify available data
        # We check columns availability

        plot_list <- tagList()

        # Temperature
        has_temp <- any(c("Temperature", "Temp_Mean", "Temp_Max", "Temp_Min") %in% names(df) & !all(is.na(df[[if ("Temperature" %in% names(df)) "Temperature" else "Temp_Mean"]])))
        if (has_temp) {
            plot_list <- tagList(plot_list, div(class = "col-12 col-lg-6", plotlyOutput("plot_temp", height = "350px")))
        }

        # Precipitation
        if ("Precipitation" %in% names(df) && !all(is.na(df$Precipitation))) {
            plot_list <- tagList(plot_list, div(class = "col-12 col-lg-6", plotlyOutput("plot_precip", height = "300px")))
        }

        # Wind
        if ("Wind_Speed" %in% names(df) && !all(is.na(df$Wind_Speed))) {
            plot_list <- tagList(plot_list, div(class = "col-12 col-lg-6", plotlyOutput("plot_wind", height = "350px")))
        }

        # Humidity
        if ("Humidity" %in% names(df) && !all(is.na(df$Humidity))) {
            plot_list <- tagList(plot_list, div(class = "col-12 col-lg-6", plotlyOutput("plot_humidity", height = "350px")))
        }

        # Pressure
        if ("Pressure" %in% names(df) && !all(is.na(df$Pressure))) {
            plot_list <- tagList(plot_list, div(class = "col-12 col-lg-6", plotlyOutput("plot_pressure", height = "300px")))
        }

        # Sunshine
        has_sun <- any(c("Sunshine_Hours", "Sunshine_Minutes") %in% names(df) & !all(is.na(df[[if ("Sunshine_Hours" %in% names(df)) "Sunshine_Hours" else "Sunshine_Minutes"]])))
        if (has_sun) {
            plot_list <- tagList(plot_list, div(class = "col-12 col-lg-6", plotlyOutput("plot_sunshine", height = "300px")))
        }

        # Solar
        if ("Solar_Radiation" %in% names(df) && !all(is.na(df$Solar_Radiation))) {
            plot_list <- tagList(plot_list, div(class = "col-12 col-lg-6", plotlyOutput("plot_solar", height = "300px")))
        }

        # Snow
        has_snow <- any(c("Snow_Depth", "Snowfall") %in% names(df) & !all(is.na(df[[if ("Snow_Depth" %in% names(df)) "Snow_Depth" else "Snowfall"]])))
        if (has_snow) {
            plot_list <- tagList(plot_list, div(class = "col-12 col-lg-6", plotlyOutput("plot_snow", height = "300px")))
        }

        if (length(plot_list) == 0) {
            return(div(class = "alert alert-warning", "No plottable weather data found for this period."))
        }

        # Wrap in grid container (2 columns)
        div(
            class = "row g-3",
            style = "padding: 10px;",
            plot_list
        )
    })

    # 2. Render individual plots
    # We use observer to ensure data is fresh, although standard renderPlotly also works if outputs are defined.
    # We define all possible outputs throughout. Even if they are not in UI, it's fine.

    # Helper to prepare data with DateTime
    get_plot_df <- reactive({
        df <- station_data()
        req(df)
        res <- input$data_resolution

        if (res == "Monthly") {
            df$DateTime <- as.Date(paste(df$Year, df$Month, "01", sep = "-"))
        } else if (res == "Daily") {
            df$DateTime <- as.Date(paste(df$Year, df$Month, df$Day, sep = "-"))
        } else if (res == "Hourly") {
            df$DateTime <- as.POSIXct(paste0(df$Year, "-", df$Month, "-", df$Day, " ", df$Hour, ":00"), format = "%Y-%m-%d %H:%M")
        } else { # 10 Minutes
            df$DateTime <- as.POSIXct(paste0(df$Year, "-", df$Month, "-", df$Day, " ", df$Time), format = "%Y-%m-%d %H:%M")
        }
        df
    })

    output$plot_temp <- renderPlotly({
        df <- get_plot_df()
        create_temperature_plot_jma(df, input$data_resolution)
    })

    output$plot_precip <- renderPlotly({
        df <- get_plot_df()
        create_precipitation_plot_jma(df, input$data_resolution)
    })

    output$plot_wind <- renderPlotly({
        df <- get_plot_df()
        resolution <- input$data_resolution
        if (resolution == "Hourly") {
            create_wind_rose_jma(df, resolution)
        } else {
            create_wind_plot_jma(df, resolution)
        }
    })

    output$plot_humidity <- renderPlotly({
        df <- get_plot_df()
        create_humidity_plot_jma(df, input$data_resolution)
    })

    output$plot_pressure <- renderPlotly({
        df <- get_plot_df()
        create_pressure_plot_jma(df, input$data_resolution)
    })

    output$plot_sunshine <- renderPlotly({
        df <- get_plot_df()
        create_sunshine_plot_jma(df, input$data_resolution)
    })

    output$plot_solar <- renderPlotly({
        df <- get_plot_df()
        create_solar_plot_jma(df, input$data_resolution)
    })

    output$plot_snow <- renderPlotly({
        df <- get_plot_df()
        create_snow_plot_jma(df, input$data_resolution)
    })

    # --- Data Table Renderer ---
    output$daily_data <- DT::renderDataTable({
        req(station_data())
        df <- station_data()

        # Column Mapping
        col_map <- c(
            "Year" = "Year",
            "Month" = "Month",
            "Day" = "Day",
            "Hour" = "Hour",
            "Time" = "Time",
            "Pressure" = "Pressure [hPa]",
            "Pressure_Sea_Level" = "Sea Level Pressure [hPa]",
            "Precipitation" = "Precipitation [mm]",
            "Precipitation_Max_1h" = "Max 1h Precipitation [mm]",
            "Precipitation_Max_10min" = "Max 10m Precipitation [mm]",
            "Temp_Mean" = "Mean Temperature [°C]",
            "Temp_Max" = "Max Temperature [°C]",
            "Temp_Min" = "Min Temperature [°C]",
            "Temperature" = "Temperature [°C]",
            "Humidity" = "Humidity [%]",
            "Humidity_Min" = "Min Humidity [%]",
            "Wind_Speed" = "Wind Speed [m/s]",
            "Wind_Speed_Max" = "Max Wind Speed [m/s]",
            "Wind_Gust_Speed" = "Max Gust Speed [m/s]",
            "Wind_Direction" = "Wind Direction",
            "Wind_Direction_Deg" = "Wind Direction [Deg]",
            "Sunshine_Hours" = "Sunshine Duration [h]",
            "Sunshine_Minutes" = "Sunshine Duration [min]",
            "Solar_Radiation" = "Solar Radiation [MJ/m²]",
            "Snowfall" = "Snowfall [cm]",
            "Snow_Depth" = "Snow Depth [cm]",
            "Snow_Days" = "Snow Days",
            "Fog_Days" = "Fog Days",
            "Thunder_Days" = "Thunder Days",
            "Dew_Point" = "Dew Point [°C]",
            "Vapor_Pressure" = "Vapor Pressure [hPa]",
            "Cloud_Cover" = "Cloud Cover [1/10]",
            "Visibility" = "Visibility [km]"
        )

        # Rename columns that exist in the map
        current_names <- names(df)
        for (i in seq_along(current_names)) {
            cn <- current_names[i]
            if (cn %in% names(col_map)) {
                current_names[i] <- col_map[[cn]]
            }
        }
        names(df) <- current_names

        DT::datatable(df, options = list(pageLength = 15, scrollX = TRUE))
    })

    # Zoom to station if selected (sidebar)
    observeEvent(input$station_selector, {
        if (input$station_selector != "All") {
            closest <- stations %>%
                filter(DisplayName == input$station_selector) %>%
                head(1)
            if (nrow(closest) > 0) {
                selected_station(closest)

                # Highlight & Zoom
                period <- get_resolution_period(closest, input$data_resolution)
                period_labels <- format_period_labels(period$start, period$end, current_year = as.numeric(format(Sys.Date(), "%Y")))
                lbl <- generate_label(
                    closest$DisplayName, closest$ID,
                    ifelse(closest$station_type == "a", "AMeDAS", "Manned station"),
                    period_labels$start, period_labels$end,
                    closest$ObservedVariables
                )
                highlight_selected_station(maplibre_proxy("map"), closest$Lon, closest$Lat, lbl)

                # Start download
                start_download(closest)
            }
        }
    })

    # Station Info Table (Metadata for filtered stations)
    output$station_info_table <- DT::renderDataTable({
        df <- filtered_stations()
        req(df)

        # Select relevant columns based on resolution
        res <- input$data_resolution

        # Determine which start/end columns to show
        start_col <- switch(res,
            "Daily" = "Start_Daily",
            "Hourly" = "Start_Hourly",
            "10 Minutes" = "Start_10min",
            "Monthly" = "Start_Monthly"
        )
        end_col <- switch(res,
            "Daily" = "End_Daily",
            "Hourly" = "End_Hourly",
            "10 Minutes" = "End_10min",
            "Monthly" = "End_Monthly"
        )

        df_display <- df %>%
            select(
                ID,
                Name = DisplayName,
                Prefecture = PrecLabel,
                Lat,
                Lon,
                Elevation,
                Variables = ObservedVariables,
                !!sym(start_col),
                !!sym(end_col)
            )

        DT::datatable(df_display,
            selection = "none",
            rownames = FALSE,
            callback = DT::JS("
                table.on('dblclick', 'tr', function() {
                    var rowData = table.row(this).data();
                    if (rowData !== undefined && rowData !== null) {
                        var stationId = rowData[0];
                        Shiny.setInputValue('station_info_table_dblclick', stationId, {priority: 'event'});
                    }
                });
            "),
            options = list(
                pageLength = 20,
                scrollX = TRUE,
                searching = TRUE
            )
        )
    })

    # Selection from Table - Double Click
    observeEvent(input$station_info_table_dblclick, {
        id_val <- input$station_info_table_dblclick
        req(id_val)

        closest <- stations %>%
            filter(ID == id_val) %>%
            head(1)

        req(nrow(closest) > 0)

        selected_station(closest)

        # Highlight & Zoom
        period <- get_resolution_period(closest, input$data_resolution)
        period_labels <- format_period_labels(period$start, period$end, current_year = as.numeric(format(Sys.Date(), "%Y")))
        lbl <- generate_label(
            closest$DisplayName, closest$ID,
            ifelse(closest$station_type == "a", "AMeDAS", "Manned station"),
            period_labels$start, period_labels$end,
            closest$ObservedVariables
        )
        highlight_selected_station(maplibre_proxy("map"), closest$Lon, closest$Lat, lbl)

        # Start download
        start_download(closest)

        # Broadcast state to parent page for SEO URL sync
        broadcast_state()

        # Switch to Dashboard? The DWD app implies it ("view the dashboard").
        # The download will eventually auto-switch, but let's be explicit if needed.
        # Ideally the download logic (Stage 6) handles the switch.
        # But for UX, double-clicking implies "Go there".
    })

    # Observer: Broadcast state when main tab changes
    observeEvent(input$main_nav,
        {
            req(url_initialized())
            broadcast_state()
        },
        ignoreInit = TRUE
    )

    # Observer: Broadcast state when dashboard subtab changes
    observeEvent(input$dashboard_subtabs,
        {
            req(url_initialized())
            broadcast_state()
        },
        ignoreInit = TRUE
    )

    # Observer: Broadcast state when resolution changes
    observeEvent(input$data_resolution,
        {
            req(url_initialized())
            broadcast_state()
        },
        ignoreInit = TRUE
    )

    # Observer: Broadcast state when date range changes
    observeEvent(input$date_range,
        {
            req(url_initialized())
            broadcast_state()
        },
        ignoreInit = TRUE
    )
}