docs: Add Services reference (#1548)

docs/content/references/services/classes/InventoryService.md

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+# Class: InventoryService
+
+## Hierarchy
+
+- `"medusa-interfaces"`
+
+  ↳ **`InventoryService`**
+
+## Constructors
+
+### constructor
+
+• **new InventoryService**(`__namedParameters`)
+
+#### Parameters
+
+| Name | Type |
+| :------ | :------ |
+| `__namedParameters` | `Object` |
+
+#### Overrides
+
+BaseService.constructor
+
+#### Defined in
+
+[services/inventory.js:5](https://github.com/medusajs/medusa/blob/2d3e404f/packages/medusa/src/services/inventory.js#L5)
+
+## Methods
+
+### adjustInventory
+
+▸ **adjustInventory**(`variantId`, `adjustment`): `Promise`<`any`\>
+
+Updates the inventory of a variant based on a given adjustment.
+
+#### Parameters
+
+| Name | Type | Description |
+| :------ | :------ | :------ |
+| `variantId` | `string` | the id of the variant to update |
+| `adjustment` | `number` | the number to adjust the inventory quantity by |
+
+#### Returns
+
+`Promise`<`any`\>
+
+resolves to the update result.
+
+#### Defined in
+
+[services/inventory.js:36](https://github.com/medusajs/medusa/blob/2d3e404f/packages/medusa/src/services/inventory.js#L36)
+
+___
+
+### confirmInventory
+
+▸ **confirmInventory**(`variantId`, `quantity`): `Promise`<`boolean`\>
+
+Checks if the inventory of a variant can cover a given quantity. Will
+return true if the variant doesn't have managed inventory or if the variant
+allows backorders or if the inventory quantity is greater than `quantity`.
+
+#### Parameters
+
+| Name | Type | Description |
+| :------ | :------ | :------ |
+| `variantId` | `string` | the id of the variant to check |
+| `quantity` | `number` | the number of units to check availability for |
+
+#### Returns
+
+`Promise`<`boolean`\>
+
+true if the inventory covers the quantity
+
+#### Defined in
+
+[services/inventory.js:62](https://github.com/medusajs/medusa/blob/2d3e404f/packages/medusa/src/services/inventory.js#L62)
+
+___
+
+### withTransaction
+
+▸ **withTransaction**(`transactionManager`): [`InventoryService`](InventoryService.md)
+
+#### Parameters
+
+| Name | Type |
+| :------ | :------ |
+| `transactionManager` | `any` |
+
+#### Returns
+
+[`InventoryService`](InventoryService.md)
+
+#### Defined in
+
+[services/inventory.js:15](https://github.com/medusajs/medusa/blob/2d3e404f/packages/medusa/src/services/inventory.js#L15)