# Provider Sync Enhancements

> Status: Planned
> Tier: 3.5 (Business tools)

Small improvements to provider sync for better visibility and resilience. Not versioning products (overkill), just better audit trail and handling of edge cases.

---

## Overview

Three enhancements to the provider sync system:

1. **Detailed audit logging** — Field-level change tracking, not just "3 updated"
2. **Soft-delete for discontinued products** — Don't break carts/orders/links
3. **Variant-level availability** — Handle out of stock / discontinued variants
4. **Price change alerts** — Warn when margins might be affected

---

## 1. Detailed sync audit logging

Currently `sync.completed` logs "47 products, 3 updated" but doesn't capture *what* changed. Enhance to log field-level changes.

**Implementation:**
```elixir
# In product sync, before update
def sync_product(product, provider_data) do
  changes = diff_product(product, provider_data)

  if changes != %{} do
    ActivityLog.log_event("sync.product_updated",
      "#{product.title}: #{summarize_changes(changes)}",
      payload: %{product_id: product.id, changes: changes}
    )
  end

  update_product(product, provider_data)
end

defp diff_product(current, new) do
  fields = [:title, :description, :base_price, :status]
  Enum.reduce(fields, %{}, fn field, acc ->
    old_val = Map.get(current, field)
    new_val = Map.get(new, field)
    if old_val != new_val, do: Map.put(acc, field, {old_val, new_val}), else: acc
  end)
end

defp summarize_changes(changes) do
  changes
  |> Map.keys()
  |> Enum.map(&to_string/1)
  |> Enum.join(", ")
  # => "title, base_price"
end
```

**Activity log entries:**
- `sync.product_updated` — "Awesome T-Shirt: title, base_price changed"
- `sync.product_added` — "New product: Cool Hoodie"
- `sync.product_removed` — "Product removed: Old Mug" (if provider removes it)

---

## 2. Soft-delete for discontinued products

When a product disappears from the provider catalogue (sync returns 404 or product not in list), don't hard-delete it. Set `status: "discontinued"` instead.

**Why:**
- Existing carts might have this product
- Order history references it
- Links from external sites won't 404 immediately

**Implementation:**
```elixir
# products schema
field :status, :string, default: "active"  # "active", "discontinued", "draft"

# In sync
def handle_missing_product(product) do
  Products.update_product(product, %{status: "discontinued"})
  ActivityLog.log_event("sync.product_discontinued",
    "#{product.title} no longer available from provider",
    level: "warning",
    payload: %{product_id: product.id}
  )
end
```

**UI behaviour:**
- Discontinued products hidden from shop browse/search
- Product page shows "This product is no longer available"
- Cart shows warning if item is discontinued
- Admin can see discontinued products in a filtered view

---

## 2b. Variant-level availability

Variants can go out of stock or be discontinued independently of the product. This matters because:
- A customer may have "Blue / Large" in their cart when that specific variant becomes unavailable
- The product is still active, just that combination isn't

**Variant statuses:**
```elixir
# variants schema
field :availability, :string, default: "available"
# "available", "out_of_stock", "discontinued"
```

**Sync handling:**
```elixir
def sync_variant(variant, provider_data) do
  new_availability = case provider_data do
    %{is_available: false, is_enabled: false} -> "discontinued"
    %{is_available: false} -> "out_of_stock"
    %{is_available: true} -> "available"
  end

  if variant.availability != new_availability do
    Products.update_variant(variant, %{availability: new_availability})

    if new_availability in ["out_of_stock", "discontinued"] do
      ActivityLog.log_event("sync.variant_unavailable",
        "#{product.title} (#{variant.title}): now #{new_availability}",
        level: "warning",
        payload: %{variant_id: variant.id, product_id: variant.product_id}
      )
    end
  end
end
```

**Cart impact:**
- On cart load: check all variants still available
- If out of stock: show warning "This size/colour is currently out of stock"
- If discontinued: show warning "This option is no longer available"
- Prevent checkout if cart contains unavailable variants (or offer to remove them)

**Product page:**
- Out of stock variants: show crossed out or greyed, not selectable
- Discontinued variants: hide entirely from selector
- If all variants unavailable: show "Currently unavailable" on product

---

## 3. Price change alerts

Log a warning when a product's cost basis changes significantly (>5% or configurable threshold). Helps shop owner know when their margins might be affected.

**Implementation:**
```elixir
def check_price_change(product, new_cost) do
  old_cost = product.base_cost
  return if old_cost == nil or old_cost == 0

  change_pct = abs((new_cost - old_cost) / old_cost * 100)

  if change_pct > 5 do
    ActivityLog.log_event("sync.price_change",
      "#{product.title}: cost changed from £#{old_cost} to £#{new_cost} (#{round(change_pct)}%)",
      level: if(change_pct > 20, do: "warning", else: "info"),
      payload: %{product_id: product.id, old_cost: old_cost, new_cost: new_cost, change_pct: change_pct}
    )
  end
end
```

---

## Files to Modify

| File | Changes |
|------|---------|
| `lib/berrypod/products/product.ex` | Add `status` field if not present |
| `lib/berrypod/products/variant.ex` | Add `availability` field |
| `lib/berrypod/providers/printify.ex` | Add diff logic, price change check, soft-delete handling, variant availability sync |
| `lib/berrypod/providers/printful.ex` | Same as above |
| `lib/berrypod/products.ex` | Query helpers for discontinued products/variants |
| `lib/berrypod_web/live/shop/pages/product_page.ex` | Handle discontinued status, variant availability display |
| `lib/berrypod_web/components/shop_components/cart.ex` | Warn on discontinued/unavailable items |
| `lib/berrypod_web/components/shop_components/product.ex` | Grey out/hide unavailable variants in selector |

---

## Tasks

| # | Task | Est |
|---|------|-----|
| 1 | Add `status` field to products, `availability` field to variants | 30m |
| 2 | Product discontinued handling in sync (soft-delete) | 45m |
| 3 | Variant availability sync (out of stock / discontinued) | 45m |
| 4 | Detailed sync audit logging (field-level diff) | 1h |
| 5 | Price change alerts with threshold | 30m |
| 6 | Product page UI: discontinued products, variant availability display | 1h |
| 7 | Cart UI: warn on discontinued/unavailable items, prevent checkout | 1h |
| **Total** | | **5.5h** |

---

## Verification

1. Manually trigger a sync
2. Check activity log shows field-level changes
3. Remove a product from provider (or mock it) — verify soft-delete
4. Change a product's cost — verify price change alert appears
5. Try to add discontinued product to cart — verify warning
6. Mark a variant as out of stock — verify greyed out on product page
7. Mark a variant as discontinued — verify hidden from selector
8. Add item to cart, then mark its variant unavailable — verify cart warning
9. Try to checkout with unavailable variant — verify blocked or prompted to remove
