Dashboard Refactor: Flow-based Metrics + Unified Data Model (#4)

# Dashboard Refactor: Flow-based Metrics + Unified Data Model

## Summary

This MR transforms the dashboard into a **flow-driven, backend-powered analytics system** with a significantly cleaner architecture and improved UX.

## Overview

This MR introduces a **major refactor of the dashboard and report data model**, transitioning from separate `expense/income` handling to a unified **flow-based (`outflows` / `inflows`) system** backed by a single `metric` structure.

It simplifies data handling, improves UI consistency, and enables better extensibility for future analytics.

---

## Key Changes

### 1. Data Model Simplification

* Replaced:

  * `expenses` / `incomes`
* With:

  * `metric`

```ts
ReportPeriod {
  start: string;
  end: string;
  metric: {
    sum: number;
    count: number;
    transactions: Transaction[];
  }
}
```

* Eliminates duplication across logic paths
* Flow is now controlled at query level instead of data shape

---

### 2. Flow-based System (Core Change)

* Introduced:

  ```ts
  type DashboardFlow = "outflows" | "inflows";
  ```

* Replaced all references of:

  * `expense` → `outflows`
  * `income` → `inflows`

* Flow is now:

  * Controlled at **Dashboard level**
  * Propagated to **API query (`useReport`)**

---

### 3. API Changes

#### `useReport`

* Removed legacy params:

  * `group_by`, `rolling`, `include_transactions`, etc.

* New structure:

```ts
useReport({
  periods: ["daily", "weekly", "monthly", "all"],
  flow,
  payee,
  tags
})
```

* Backend now handles:

  * Flow filtering
  * Aggregation

---

### 4. Period System Update

* Removed:

  * yearly, fyly, full

* Added:

  * `daily`
  * `all`

```ts
type PeriodType = "daily" | "weekly" | "monthly" | "all";
```

* Updated helpers:

  * `periodIdToKey`
  * `buildPeriodId`
  * `buildLabel`

---

### 5. React Query UX Improvement

* Added:

```ts
placeholderData: keepPreviousData
```

* Prevents UI flicker on filter/flow changes
* Enables smooth transitions

---

### 6. Dashboard State Refactor

#### Before

```ts
mode: "expense" | "income"
```

#### After

```ts
flow: "outflows" | "inflows"
```

* Introduced `onFlowChange` callback
* Lifted flow state to parent (`Dashboard.tsx`)
* Flow change triggers API refetch

---

### 7. UI Improvements

#### Flow Toggle

* Replaced mode toggle with:

  * Outflows / Inflows switch

#### Loading State Handling

* Added `isFetching` across components
* UI behavior during fetch:

  * Reduced opacity
  * Disabled interactions

#### Drill-down UX

* Added:

  * "Clear Drill-down" button

---

### 8. New Components

#### TopPayees

* New analytics card

* Shows top payees based on:

  * Selected period
  * Drill-down filters

* Supports:

  * Click-to-filter (drill-down)

---

### 9. Adapter Layer Simplification

#### Removed mode branching everywhere

Examples:

* `getAmount(period)` now uses:

  ```ts
  period.metric.sum
  ```

* `LatestItems`, `TopTags`, `HistoryChart`:

  * No longer split logic by expense/income
  * Work on unified transaction stream

---

### 10. GroupKey Generalization

#### Before

```ts
{
  payee?: string[];
  tags?: string[];
}
```

#### After

```ts
{
  [dimension: string]: string[];
}
```

* Enables future dimensions without refactor

---

## Behavioral Changes

* Flow selection now **controls backend query**
* All components consume **filtered data only**
* No client-side filtering for expense/income

---

## Benefits

* Single source of truth (`metric`)
* Cleaner adapters (no branching explosion)
* Easier feature additions (new dimensions, filters)
* Better UX (no flicker, smoother transitions)
* Backend-driven correctness

---

## Migration Notes

* Replace all `mode` usages with `flow`
* Update adapters to use `metric`
* Remove assumptions about:

  * `expenses`
  * `incomes`
* Ensure API supports:

  * `flow`
  * new period types

---

## Future Scope

* Add more dimensions (account, category hierarchy)
* Multi-flow comparison (inflows vs outflows together)
* Snapshot-based caching (already partially supported)

---

## Testing Notes

Verify:

* Flow toggle updates API calls
* No UI flicker on filter change
* Drill-down works across:

  * tags
  * payees
* Daily / Weekly / Monthly / All tabs behave correctly
* Loading state disables interaction properly

---

Reviewed-on: #4
Co-authored-by: Vishesh 'ironeagle' Bangotra <aetoskia@gmail.com>
Co-committed-by: Vishesh 'ironeagle' Bangotra <aetoskia@gmail.com>

src/components/Dashboard/Dashboard.view.tsx

@@ -5,7 +5,8 @@ import {
   Grid,
   Typography,
   ToggleButton,
-  ToggleButtonGroup
+  ToggleButtonGroup,
+  Button
 } from "@mui/material";
 import { useTheme, alpha } from "@mui/material/styles";
 import { GroupKey } from "../../features/report";
@@ -14,7 +15,7 @@ import { DashboardProps, DashboardState } from "./Dashboard.models";
 interface ViewProps extends DashboardProps {
   state: DashboardState;
   setState: React.Dispatch<React.SetStateAction<DashboardState>>;
-  toggleMode: () => void;
+  toggleFlow: (event: React.MouseEvent<HTMLElement>, newFlow: "outflows" | "inflows" | null) => void;
   togglePeriodType: () => void;
   setSelectedPeriodId: (id: string | null) => void;
   setSelectedGroupKey: (groupKey: GroupKey | null) => void;
@@ -26,7 +27,7 @@ export default function DashboardView({
   data,
   state,
   setState,
-  toggleMode,
+  toggleFlow,
   togglePeriodType,
   toggleComparison,
   setSelectedPeriodId,
@@ -34,11 +35,11 @@ export default function DashboardView({
 }: ViewProps) {
   const theme = useTheme();
   const themeMode = theme.palette.mode;
-  const { mode, periodType, comparison, selectedPeriodId, selectedGroupKey } = state;
+  const { flow, periodType, comparison, selectedPeriodId, selectedGroupKey } = state;
 
   // Resolve colors with fallbacks
   const colors = React.useMemo(() => {
-    const palette = config.style?.palette?.[mode];
+    const palette = config.style?.palette?.[flow];
     const modeColors = palette ? palette[themeMode] : null;
 
     if (modeColors) {
@@ -50,13 +51,13 @@ export default function DashboardView({
     }
 
     // Fallback to standard theme colors
-    const themeColor = mode === 'expense' ? theme.palette.error : theme.palette.success;
+    const themeColor = flow === 'outflows' ? theme.palette.error : theme.palette.success;
     return {
       primary: themeColor.main,
       light: alpha(themeColor.main, themeMode === 'light' ? 0.08 : 0.15),
       text: themeColor.main
     };
-  }, [config.style?.palette, mode, themeMode, theme.palette]);
+  }, [config.style?.palette, flow, themeMode, theme.palette]);
 
   return (
     <Container
@@ -69,11 +70,11 @@ export default function DashboardView({
         transition: 'background 0.3s ease'
       }}
     >
-      <Box sx={{ display: "flex", justifyContent: "center", mb: 3 }}>
+      <Box sx={{ display: "flex", flexDirection: "column", alignItems: "center", mb: 3 }}>
         <ToggleButtonGroup
-          value={mode}
+          value={flow}
           exclusive
-          onChange={toggleMode}
+          onChange={toggleFlow}
           sx={{
             borderRadius: 3,
             overflow: "hidden",
@@ -89,9 +90,19 @@ export default function DashboardView({
             },
           }}
         >
-          <ToggleButton value="expense">Expenses</ToggleButton>
-          <ToggleButton value="income">Income</ToggleButton>
+          <ToggleButton value="outflows">Outflows</ToggleButton>
+          <ToggleButton value="inflows">Inflows</ToggleButton>
         </ToggleButtonGroup>
+
+        {selectedGroupKey && Object.keys(selectedGroupKey).length > 0 && (
+          <Button 
+            size="small" 
+            sx={{ mt: 1, textTransform: "none" }}
+            onClick={() => setSelectedGroupKey(null)}
+          >
+            Clear Drill-down
+          </Button>
+        )}
       </Box>
 
       <Grid container spacing={4}>
@@ -100,14 +111,6 @@ export default function DashboardView({
           
           return (
             <Grid key={section.id} size={section.style?.size || 12 as any}>
-              {section.title && !section.isList && (
-                <Box sx={{ mb: 2 }}>
-                  <Typography variant="h6" fontWeight={700}>
-                    {section.title}
-                  </Typography>
-                </Box>
-              )}
-
               <Component
                 {...section.settings}
                 header={section.title}
@@ -118,7 +121,7 @@ export default function DashboardView({
                 colorScheme={colors}
 
                 // State management
-                mode={mode}
+                flow={flow}
 
                 periodType={periodType}
                 comparison={comparison}
@@ -129,6 +132,7 @@ export default function DashboardView({
                 toggleComparison={toggleComparison}
                 setSelectedPeriodId={setSelectedPeriodId}
                 setSelectedGroupKey={setSelectedGroupKey}
+                isFetching={arguments[0].isFetching}
               />
             </Grid>
           );