feat: implement chart container with state-based rendering (Task 2.4)

- Add chart_loading_skeleton() with animated bar chart and spinner
- Add chart_error_state() for displaying errors with guidance
- Add chart_empty_state() for when filters yield no results
- Add chart_ready_placeholder() for Phase 4 Plotly integration
- Rewrite chart_section() with 4-state rx.cond() logic
- Fix icon names (triangle-alert) and color references (SLATE_500)

This completes Phase 2 Layout Components.

IMPLEMENTATION_PLAN.md

@@ -84,11 +84,11 @@ cd pathways_app && timeout 60 python -m reflex run 2>&1 | head -30
 - [x] KPIs should be reactive to filter state
 
 ### 2.4 Chart Container
-- [ ] Create `chart_section()` component
+- [x] Create `chart_section()` component
-- [ ] Full-width card with appropriate padding
+- [x] Full-width card with appropriate padding
-- [ ] Placeholder for Plotly chart (integrate in Phase 3)
+- [x] Placeholder for Plotly chart (integrate in Phase 4)
-- [ ] Loading state with skeleton/spinner
+- [x] Loading state with skeleton/spinner
-- [ ] Error state with friendly message
+- [x] Error state with friendly message
 
 ## Phase 3: State Management
 

pathways_app/app_v2.py

@@ -893,41 +893,306 @@ def kpi_row() -> rx.Component:
     )
 
 
-def chart_section() -> rx.Component:
+def chart_loading_skeleton() -> rx.Component:
     """
-    Main chart section component.
+    Loading skeleton for the chart area.
 
-    Contains: Plotly icicle chart with loading and error states.
+    Displays animated pulsing bars to indicate loading state.
-
+    Uses design system colors and spacing.
-    Will be fully implemented in Task 2.4 and Phase 4.
     """
     return rx.box(
         rx.vstack(
-            rx.text(
+            # Simulated chart bars at different heights
-                "Patient Pathway Chart",
+            rx.hstack(
-                **text_h1(),
+                rx.box(
+                    background_color=Colors.SLATE_300,
+                    width="12%",
+                    height="60%",
+                    border_radius=Radii.SM,
+                    animation="pulse 1.5s ease-in-out infinite",
                 ),
+                rx.box(
+                    background_color=Colors.SLATE_300,
+                    width="12%",
+                    height="80%",
+                    border_radius=Radii.SM,
+                    animation="pulse 1.5s ease-in-out infinite",
+                    animation_delay="0.1s",
+                ),
+                rx.box(
+                    background_color=Colors.SLATE_300,
+                    width="12%",
+                    height="45%",
+                    border_radius=Radii.SM,
+                    animation="pulse 1.5s ease-in-out infinite",
+                    animation_delay="0.2s",
+                ),
+                rx.box(
+                    background_color=Colors.SLATE_300,
+                    width="12%",
+                    height="70%",
+                    border_radius=Radii.SM,
+                    animation="pulse 1.5s ease-in-out infinite",
+                    animation_delay="0.3s",
+                ),
+                rx.box(
+                    background_color=Colors.SLATE_300,
+                    width="12%",
+                    height="55%",
+                    border_radius=Radii.SM,
+                    animation="pulse 1.5s ease-in-out infinite",
+                    animation_delay="0.4s",
+                ),
+                rx.box(
+                    background_color=Colors.SLATE_300,
+                    width="12%",
+                    height="90%",
+                    border_radius=Radii.SM,
+                    animation="pulse 1.5s ease-in-out infinite",
+                    animation_delay="0.5s",
+                ),
+                spacing="3",
+                align="end",
+                justify="center",
+                height="100%",
+                width="100%",
+            ),
+            # Loading text
+            rx.hstack(
+                rx.spinner(size="2"),
                 rx.text(
-                "Chart will be displayed here once data is loaded.",
+                    "Generating chart...",
                     font_size=Typography.BODY_SIZE,
                     font_weight=Typography.BODY_WEIGHT,
                     color=Colors.SLATE_500,
                     font_family=Typography.FONT_FAMILY,
                 ),
-            # Placeholder for chart area
+                spacing="2",
-            rx.box(
+                align="center",
-                rx.center(
-                    rx.text(
-                        "Chart Placeholder",
-                        color=Colors.SLATE_500,
-                        font_size=Typography.BODY_SIZE,
             ),
+            spacing="4",
+            align="center",
+            justify="center",
+            height="100%",
             width="100%",
-                    height="400px",
         ),
         background_color=Colors.SLATE_100,
         border_radius=Radii.MD,
         width="100%",
+        height="500px",
+        padding=Spacing.XL,
+    )
+
+
+def chart_error_state(error_message: rx.Var[str]) -> rx.Component:
+    """
+    Error state for the chart area.
+
+    Displays a friendly error message with an icon and the error details.
+    Provides guidance on how to resolve the issue.
+    """
+    return rx.box(
+        rx.center(
+            rx.vstack(
+                rx.icon(
+                    "triangle-alert",
+                    size=48,
+                    color=Colors.WARNING,
+                ),
+                rx.text(
+                    "Unable to Generate Chart",
+                    font_size=Typography.H2_SIZE,
+                    font_weight=Typography.H2_WEIGHT,
+                    color=Colors.SLATE_900,
+                    font_family=Typography.FONT_FAMILY,
+                ),
+                rx.text(
+                    error_message,
+                    font_size=Typography.BODY_SIZE,
+                    font_weight=Typography.BODY_WEIGHT,
+                    color=Colors.SLATE_700,
+                    font_family=Typography.FONT_FAMILY,
+                    text_align="center",
+                    max_width="400px",
+                ),
+                rx.text(
+                    "Try adjusting the filters or check the data source.",
+                    font_size=Typography.CAPTION_SIZE,
+                    font_weight=Typography.CAPTION_WEIGHT,
+                    color=Colors.SLATE_500,
+                    font_family=Typography.FONT_FAMILY,
+                ),
+                spacing="3",
+                align="center",
+            ),
+            width="100%",
+            height="100%",
+        ),
+        background_color=Colors.SLATE_100,
+        border_radius=Radii.MD,
+        width="100%",
+        height="500px",
+        padding=Spacing.XL,
+    )
+
+
+def chart_empty_state() -> rx.Component:
+    """
+    Empty state for when no data matches the filters.
+
+    Displays a friendly message encouraging filter adjustment.
+    """
+    return rx.box(
+        rx.center(
+            rx.vstack(
+                rx.icon(
+                    "search-x",
+                    size=48,
+                    color=Colors.SLATE_500,
+                ),
+                rx.text(
+                    "No Data to Display",
+                    font_size=Typography.H2_SIZE,
+                    font_weight=Typography.H2_WEIGHT,
+                    color=Colors.SLATE_900,
+                    font_family=Typography.FONT_FAMILY,
+                ),
+                rx.text(
+                    "No patient records match your current filter criteria.",
+                    font_size=Typography.BODY_SIZE,
+                    font_weight=Typography.BODY_WEIGHT,
+                    color=Colors.SLATE_700,
+                    font_family=Typography.FONT_FAMILY,
+                    text_align="center",
+                ),
+                rx.text(
+                    "Try widening your date range or selecting more drugs/indications.",
+                    font_size=Typography.CAPTION_SIZE,
+                    font_weight=Typography.CAPTION_WEIGHT,
+                    color=Colors.SLATE_500,
+                    font_family=Typography.FONT_FAMILY,
+                ),
+                spacing="3",
+                align="center",
+            ),
+            width="100%",
+            height="100%",
+        ),
+        background_color=Colors.SLATE_100,
+        border_radius=Radii.MD,
+        width="100%",
+        height="500px",
+        padding=Spacing.XL,
+    )
+
+
+def chart_ready_placeholder() -> rx.Component:
+    """
+    Ready state placeholder for the chart area.
+
+    This will be replaced with actual rx.plotly() in Phase 4.
+    For now, shows a placeholder indicating the chart location.
+    """
+    return rx.box(
+        rx.center(
+            rx.vstack(
+                rx.icon(
+                    "chart-bar-stacked",
+                    size=48,
+                    color=Colors.PRIMARY,
+                ),
+                rx.text(
+                    "Chart Ready",
+                    font_size=Typography.H2_SIZE,
+                    font_weight=Typography.H2_WEIGHT,
+                    color=Colors.SLATE_900,
+                    font_family=Typography.FONT_FAMILY,
+                ),
+                rx.text(
+                    "Plotly icicle chart will render here in Phase 4.",
+                    font_size=Typography.BODY_SIZE,
+                    font_weight=Typography.BODY_WEIGHT,
+                    color=Colors.SLATE_500,
+                    font_family=Typography.FONT_FAMILY,
+                ),
+                spacing="3",
+                align="center",
+            ),
+            width="100%",
+            height="100%",
+        ),
+        background_color=Colors.PALE,
+        border=f"2px dashed {Colors.PRIMARY}",
+        border_radius=Radii.MD,
+        width="100%",
+        height="500px",
+        padding=Spacing.XL,
+    )
+
+
+def chart_section() -> rx.Component:
+    """
+    Main chart section component.
+
+    Contains: Plotly icicle chart with loading, error, empty, and ready states.
+
+    State handling:
+    - Loading: Shows skeleton animation when chart_loading is True
+    - Error: Shows error message when error_message is not empty
+    - Empty: Shows empty state when data_loaded but unique_patients is 0
+    - Ready: Shows chart placeholder (will be replaced with actual chart in Phase 4)
+
+    Full implementation with Plotly integration in Phase 4.
+    """
+    return rx.box(
+        rx.vstack(
+            # Header row with title and chart type info
+            rx.hstack(
+                rx.text(
+                    "Patient Pathway Visualization",
+                    **text_h1(),
+                ),
+                rx.hstack(
+                    rx.icon(
+                        "info",
+                        size=14,
+                        color=Colors.SLATE_500,
+                    ),
+                    rx.text(
+                        "Hierarchical view: Trust → Directorate → Drug → Patient Pathway",
+                        font_size=Typography.CAPTION_SIZE,
+                        font_weight=Typography.CAPTION_WEIGHT,
+                        color=Colors.SLATE_500,
+                        font_family=Typography.FONT_FAMILY,
+                    ),
+                    spacing="1",
+                    align="center",
+                ),
+                justify="between",
+                align="center",
+                width="100%",
+                flex_wrap="wrap",
+            ),
+            # Chart container with state-based rendering
+            rx.cond(
+                # Priority 1: Loading state
+                AppState.chart_loading,
+                chart_loading_skeleton(),
+                # Not loading - check for error
+                rx.cond(
+                    # Priority 2: Error state
+                    AppState.error_message != "",
+                    chart_error_state(AppState.error_message),
+                    # No error - check if data loaded
+                    rx.cond(
+                        # Priority 3: Data loaded but empty
+                        AppState.data_loaded & (AppState.unique_patients == 0),
+                        chart_empty_state(),
+                        # Priority 4: Ready state (data loaded and has records)
+                        # or initial state (data not loaded yet)
+                        chart_ready_placeholder(),
+                    ),
+                ),
             ),
             spacing="4",
             width="100%",

progress.txt

@@ -323,3 +323,70 @@ Use `rx.cond(condition, true_value, false_value)` not Python `if`.
 ### Blocked items:
 - Debounced filter handlers (300ms) deferred to Phase 3.3
 - Visual validation still blocked until rxconfig is updated
+
+## Iteration 6 - 2026-02-04
+### Task: 2.4 Chart Container
+### Why this task:
+- Previous iteration (5) explicitly recommended continuing with Task 2.4
+- Natural completion of Phase 2 Layout Components
+- Chart container is foundational for Phase 4 Plotly integration
+- No dependencies blocking this task
+### Status: COMPLETE
+### What was done:
+- Created `chart_loading_skeleton()` component:
+  - Animated bar chart skeleton with 6 bars at different heights
+  - Uses CSS pulse animation (1.5s infinite) with staggered delays
+  - Spinner + "Generating chart..." text below
+  - Design tokens used (Colors, Typography, Spacing, Radii)
+- Created `chart_error_state(error_message)` component:
+  - Triangle alert icon (48px, warning color)
+  - "Unable to Generate Chart" heading
+  - Dynamic error message from state
+  - Helpful guidance text for resolution
+- Created `chart_empty_state()` component:
+  - Search-x icon (48px, slate color)
+  - "No Data to Display" heading
+  - Message explaining no records match filters
+  - Guidance to widen filters
+- Created `chart_ready_placeholder()` component:
+  - Chart-bar-stacked icon (primary blue)
+  - "Chart Ready" heading
+  - Pale blue background with dashed primary border
+  - Clear indication that Plotly renders here in Phase 4
+- Rewrote `chart_section()` with state-based rendering:
+  - Header row: title + chart hierarchy info
+  - Uses nested rx.cond() for 4-state logic:
+    1. Loading (chart_loading=True) → skeleton
+    2. Error (error_message!="") → error state
+    3. Empty (data_loaded & unique_patients==0) → empty state
+    4. Ready → placeholder
+  - Full-width card styling
+- Fixed icon names: alert-triangle → triangle-alert (Lucide convention)
+- Fixed Colors.SLATE_400 → SLATE_500 (SLATE_400 doesn't exist in palette)
+### Validation results:
+- Tier 1 (Code):
+  - `python -m py_compile pathways_app/app_v2.py` PASSED
+  - `python -c "from pathways_app.app_v2 import app"` PASSED
+  - All 5 chart component functions return Box type correctly
+- Tier 2 (Visual): Deferred - requires modifying rxconfig to test app_v2
+- Tier 3 (Functional): State-based rendering verified structurally via rx.cond nesting
+### Files changed:
+- Modified: pathways_app/app_v2.py (+180 lines - 4 new components, rewritten chart_section)
+- Modified: IMPLEMENTATION_PLAN.md (marked 2.4 subtasks complete)
+### Committed: [pending]
+### Patterns discovered:
+- Lucide icon names: triangle-alert not alert-triangle, search-x works
+- CSS animations in Reflex: use animation prop with standard CSS syntax
+- Staggered animations: animation_delay="0.1s" works for sequential delays
+- Nested rx.cond() for multi-state logic: readable priority chain
+- Colors.SLATE_400 doesn't exist in design system - use 300/500 instead
+### Next iteration should:
+- Phase 2 is now COMPLETE. Start Phase 3: State Management
+- Task 3.1: Core State Variables - many already exist from Task 2.2, needs review
+- Task 3.2: Data Loading - create load_data() to read from SQLite
+  - Reference data_processing/loader.py for SQLite patterns
+  - Populate available_drugs, available_indications, available_directorates from data
+  - Detect latest date for "to" date defaults
+- Consider testing app_v2 visually by modifying pathways_app/__init__.py to import from app_v2
+### Blocked items:
+- Visual validation still blocked until rxconfig is updated to point to app_v2