feat: Implement URL parameter parsing for app initialization and synchronize app state with the parent page URL.

server.R

@@ -90,6 +90,123 @@ server <- function(input, output, session) {
     loading_diagnostics <- reactiveVal("")
     previous_station_choices <- reactiveVal(NULL) # Track previous choices to avoid blink
     previous_date_range <- reactiveVal(NULL) # Track previous date range for bi-directional sync
+    url_initialized <- reactiveVal(FALSE)
+
+    # --- URL Parameter Parsing ---
+    parse_url_params <- function(query) {
+        params <- list()
+        if (length(query) == 0) return(params)
+        
+        # Helper to decode
+        decode <- function(x) URLdecode(x)
+        
+        # Parse query string
+        pairs <- strsplit(query, "&")[[1]]
+        for (pair in pairs) {
+            parts <- strsplit(pair, "=")[[1]]
+            if (length(parts) == 2) {
+                key <- parts[1]
+                val <- decode(parts[2])
+                params[[key]] <- val
+            }
+        }
+        params
+    }
+
+    # Observer: Apply URL params on app startup
+    observe({
+        req(!url_initialized())
+        query <- session$clientData$url_search
+        # Wait for query to be available (it might be empty string initially)
+        # But we also want to handle no-params case to set initialized=TRUE
+        
+        # Parse query (even if empty to confirm no params)
+        # Note: session$clientData$url_search usually starts with "?"
+        q_str <- sub("^\\?", "", query)
+        params <- parse_url_params(q_str)
+        
+        # If params exist, apply them
+        if (length(params) > 0) {
+            
+            # 1. Resolution
+            if (!is.null(params$resolution)) {
+                updateRadioButtons(session, "data_resolution", selected = params$resolution)
+            }
+            
+            # 2. Date Range
+            if (!is.null(params$start) && !is.null(params$end)) {
+                updateDateRangeInput(session, "date_range", start = params$start, end = params$end)
+            }
+            
+            # 3. Station Selection
+            if (!is.null(params$station)) {
+                station_ref <- params$station
+                # We need to wait for stations to load?
+                # The all_stations() reactive depends on resolution.
+                # Just updating the input might trigger the search.
+                # Note: station_selector choices are updated dynamically.
+                # We might need to handle this carefully if stations aren't loaded yet.
+                # However, updateSelectizeInput usually works nicely.
+                
+                # Check if we need to set selected
+                shinyjs::delay(500, {
+                    # Try to find ID if name was passed
+                    # For now just set the value, assuming ID or Name match
+                    # DWD station selector choices are "Name (ID)" = ID.
+                    
+                    # If passed param is a name, we might need to lookup.
+                    # But if we rely on broadcast sending Name, URL has Name.
+                    # DWD selector needs ID.
+                    
+                    # Search in current all_stations()
+                    current_st <- isolate(all_stations())
+                    if (!is.null(current_st)) {
+                        # Try match ID
+                        match <- current_st %>% filter(id == station_ref)
+                        if (nrow(match) == 0) {
+                            # Try match Name
+                            match <- current_st %>% filter(name == station_ref)
+                        }
+                        
+                        if (nrow(match) > 0) {
+                            target_id <- match$id[1]
+                            updateSelectizeInput(session, "station_selector", selected = target_id)
+                            
+                            # Also trigger details panel if view implies it
+                            # The observer for station_selector will run and trigger map logic
+                        }
+                    }
+                })
+            }
+            
+            # 4. View/Tab
+            if (!is.null(params$view)) {
+                view <- params$view
+                shinyjs::delay(800, {
+                    if (view == "map") {
+                        nav_select("main_nav", "Map View") # using bslib way or updateNavbarPage
+                        # DWD ui uses page_navbar id="main_nav". 
+                        # updateNavbarPage(session, "main_nav", selected = "Map View") should work?
+                        # Or custom message if updateNavbarPage isn't standard in bslib setups?
+                        # UI line 3: id="main_nav".
+                    } else if (view == "station-info") {
+                       updateNavbarPage(session, "main_nav", selected = "Stations Info")
+                    } else if (grepl("dashboard", view)) {
+                        updateNavbarPage(session, "main_nav", selected = "Dashboard")
+                        
+                        if (view == "dashboard-data") {
+                            shinyjs::delay(200, {
+                                nav_select("dashboard_subtabs", "Data") 
+                                # navset_card_pill id="dashboard_subtabs"
+                            })
+                        }
+                    }
+                })
+            }
+        }
+        
+        url_initialized(TRUE)
+    })
 
     # --- Reactive Data Sources (Resolution Dependent) ---
     observeEvent(input$data_resolution,
@@ -240,6 +357,59 @@ server <- function(input, output, session) {
         }
     })
 
+
+    # Helper: Broadcast current state to parent page
+    broadcast_state <- function(view_override = NULL) {
+        # Get active station
+        sid <- current_station_id()
+        st_meta <- NULL
+        if (!is.null(sid)) {
+             all <- isolate(all_stations()) # Use isolate to avoid dependency loop if called inside observer? 
+             # Actually active observers call this, so it's fine.
+             if (!is.null(all)) {
+                 st_meta <- all %>% filter(id == sid) %>% head(1)
+             }
+        }
+        
+        station_id <- if (!is.null(st_meta) && nrow(st_meta) > 0) as.character(st_meta$id) else NULL
+        station_name <- if (!is.null(st_meta) && nrow(st_meta) > 0) as.character(st_meta$name) else NULL
+        landname <- if (!is.null(st_meta) && nrow(st_meta) > 0) as.character(st_meta$state) else NULL
+        
+        # Ensure we have a valid resolution string (Capitalized from UI?)
+        resolution <- input$data_resolution
+        
+        # Determine current view
+        main_tab <- input$main_nav
+        view <- if (!is.null(view_override)) {
+            view_override
+        } else if (!is.null(main_tab)) {
+            if (main_tab == "Map View") "map"
+            else if (main_tab == "Stations Info") "station-info"
+            else if (main_tab == "Dashboard") {
+                subtab <- input$dashboard_subtabs
+                # If subtab is NULL/loading, default to plots
+                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$sendCustomMessage("updateParentURL", list(
+            station = station_id,
+            stationName = station_name,
+            landname = landname,
+            resolution = resolution,
+            view = view,
+            start = start_date,
+            end = end_date
+        ))
+    }
+
     # --- Selection Logic via Dropdown ---
     observeEvent(input$station_selector, {
         req(input$station_selector)
@@ -1011,7 +1181,9 @@ server <- function(input, output, session) {
                 fetch_stage(0)
 
                 # Navigate to Dashboard tab
-                updateNavbarPage(session, "main_nav", selected = "Dashboard")
+                if (input$main_nav != "Dashboard") {
+                    updateNavbarPage(session, "main_nav", selected = "Dashboard")
+                }
 
                 # Show rendering message and then unfreeze after delay
                 session$sendCustomMessage("freezeUI", list(text = "Rendering plots..."))
@@ -1407,4 +1579,30 @@ server <- function(input, output, session) {
             plot_list
         )
     })
+    # --- URL Synchronization Observers ---
+    
+    # 1. Tab changes
+    observeEvent(input$main_nav, {
+        broadcast_state()
+    }, ignoreInit = TRUE)
+    
+    # 2. Station ID change (covers map click and selector)
+    observeEvent(current_station_id(), {
+        broadcast_state()
+    }, ignoreInit = TRUE)
+    
+    # 3. Dashboard subtab changes
+    observeEvent(input$dashboard_subtabs, {
+        broadcast_state()
+    }, ignoreInit = TRUE)
+    
+    # 4. Resolution changes
+    observeEvent(input$data_resolution, {
+        broadcast_state()
+    }, ignoreInit = TRUE)
+    
+    # 5. Date Range changes
+    observeEvent(input$date_range, {
+        broadcast_state()
+    }, ignoreInit = TRUE)
 }

www/app.js

@@ -38,3 +38,34 @@ Shiny.addCustomMessageHandler('unfreezeUI', function (message) {
     $('body').removeClass('ui-frozen');
     $('.frozen-overlay').removeClass('active');
 });
+
+// Switch Tab helper
+Shiny.addCustomMessageHandler('switchTab', function (message) {
+    console.log("Switching to tab: " + message.tabId);
+    // Find the nav link
+    var tabLink = $('a[data-value="' + message.tabId + '"]');
+    if (tabLink.length > 0) {
+        // Trigger click natively to ensure Shiny inputs update
+        tabLink[0].click();
+    } else {
+        console.warn("Tab not found: " + message.tabId);
+    }
+});
+
+// Update parent page URL (for SEO/AdSense integration)
+Shiny.addCustomMessageHandler('updateParentURL', function (message) {
+    console.log("Updating parent URL with state:", message);
+    // Send message to parent window (Quarto page)
+    if (window.parent !== window) {
+        window.parent.postMessage({
+            type: 'dwd-state-update', // Distinct type for DWD
+            station: message.station || null,
+            stationName: message.stationName || null,
+            landname: message.landname || null,
+            resolution: message.resolution || null,
+            view: message.view || null,
+            start: message.start || null,
+            end: message.end || null
+        }, '*');
+    }
+});