# `MishkaGervaz.Errors`
[🔗](https://github.com/mishka-group/mishka_gervaz/blob/v0.0.2/lib/mishka_gervaz/errors.ex#L1)

Splode-based error handling for MishkaGervaz.

## Error Classes

- `:data`   - Data loading, query, and fetch errors
- `:action` - Action execution errors (destroy, update, etc.)

## Usage

    # Raise an error
    raise MishkaGervaz.Errors.Data.LoadFailed, resource: MyResource, reason: :timeout

    # Create error without raising
    error = MishkaGervaz.Errors.Data.LoadFailed.exception(resource: MyResource, reason: :timeout)

    # Convert any value into a Splode error (unrecognized values become `Errors.Unknown`)
    MishkaGervaz.Errors.to_error(error)

    # Format error for flash message
    MishkaGervaz.Errors.format_flash_message(error)

## Translation

Every word these functions return goes through the Gettext backend
`MishkaGervaz.Messages.gettext_backend/0` names, in the locale of the calling process:

- MishkaGervaz's own words and templates in the `"mishka_gervaz"` domain.
- An error's own message, such as Ash's `"is required"`, in the `"errors"` domain, with
  `dngettext` when its vars hold an integer `:count`. Its `%{key}` placeholders are filled from
  the error's vars after it is translated.
- A field's name from the label the resource declares for it: its form field's `ui` label, else
  its table column's label. A field with neither is named by its humanized name in the
  `"mishka_gervaz"` domain.

A message whose last character ends a sentence (`.` `!` `?` `…` `؟` `۔` `。` and the like, before
any closing quote or bracket) is shown as written. Any other message is joined to its field's name
through the `"%{field} %{message}"` template.

A reason that is not a validation error is worded too: `:not_found`, and an
`Ash.Error.Query.NotFound` with no primary key, as `"This record is no longer here."`; an
`Ash.Error.Forbidden` by its policy's `custom_message`, else as `"You are not allowed to do
this."`; any other exception by its own message.

# `class`

```elixir
@type class() :: %{
  :__struct__ => class_module(),
  :__exception__ => true,
  :errors => [t()],
  :class => error_class(),
  :bread_crumbs => [String.t()],
  :vars => Keyword.t(),
  :stacktrace => Splode.Stacktrace.t() | nil,
  :context => map(),
  optional(atom()) => any()
}
```

# `class_module`

```elixir
@type class_module() ::
  MishkaGervaz.Errors.Action | MishkaGervaz.Errors.Data | Splode.Error.Unknown
```

# `error_class`

```elixir
@type error_class() :: :action | :data | :unknown
```

# `t`

```elixir
@type t() :: %{
  :__struct__ => module(),
  :__exception__ => true,
  :class => error_class(),
  :bread_crumbs => [String.t()],
  :vars => Keyword.t(),
  :stacktrace => Splode.Stacktrace.t() | nil,
  :context => map(),
  optional(atom()) => any()
}
```

# `extract_error_message`

```elixir
@spec extract_error_message(any(), module() | nil) :: String.t()
```

Extracts a human-readable message from various error formats.

`resource` is the resource whose declared labels name the error's field. An Ash error AshPhoenix
can show on a form (`AshPhoenix.FormData.Error`) is read the way the form reads it; one the form
shows on no field is read by its own message. An error class holding several errors, such as
`Ash.Error.Invalid`, joins the message of each, a repeated message once.

## Examples

    iex> MishkaGervaz.Errors.extract_error_message(%{message: "Invalid email"})
    "Invalid email"

    iex> MishkaGervaz.Errors.extract_error_message(%{field: :email, message: "is invalid"})
    "Email is invalid"

    iex> MishkaGervaz.Errors.extract_error_message(%{field: :tag_id, message: "That tag is archived."})
    "That tag is archived."

    iex> MishkaGervaz.Errors.extract_error_message(%{field: :title, message: "must be at least %{min}", vars: [min: 3]})
    "Title must be at least 3"

# `field_message`

```elixir
@spec field_message(
  String.t() | nil,
  keyword() | map() | nil,
  atom() | String.t() | nil,
  module() | nil
) :: String.t()
```

An error message about `field`, as a person reads it.

`message` is translated with `translate_error/2`. A translated message that ends a sentence is
returned as written; any other is joined to the field's name through the `"%{field} %{message}"`
template. `field` is named by the label `resource` declares for it, else by its humanized name.
A `nil` field, or AshPhoenix's `:_form` for the whole form, returns the message alone.

# `format_flash_message`

```elixir
@spec format_flash_message(any(), module() | nil) :: String.t()
```

Formats an error into a human-readable flash message.

Handles MishkaGervaz errors, Ash errors, and generic errors. `resource` names the fields of an
error that has no resource of its own; an `Action.Failed` or `Data.LoadFailed` uses its own
`:resource` when `resource` is `nil`.

An `Action.Failed` names its action by its `:label` (a string or a zero-arity function), else by
its humanized `:action`.

## Examples

    iex> error = MishkaGervaz.Errors.Action.Failed.exception(action: :archive, reason: "forbidden")
    iex> MishkaGervaz.Errors.format_flash_message(error)
    "Archive failed: forbidden"

    iex> error = MishkaGervaz.Errors.Action.Failed.exception(action: :archive, label: "Delete", reason: "forbidden")
    iex> MishkaGervaz.Errors.format_flash_message(error)
    "Delete failed: forbidden"

# `splode_error?`

# `translate_error`

```elixir
@spec translate_error(String.t(), keyword() | map() | nil) :: String.t()
```

Translates an error's own message in the `"errors"` domain and fills its `%{key}` placeholders
from `vars`.

Uses `dngettext` when `vars` holds an integer `:count`. A list var is joined with `", "`, and a
value `String.Chars` cannot print is inspected. A message with a `%{key}` placeholder `vars` does
not fill is returned as written.

## Examples

    iex> MishkaGervaz.Errors.translate_error("must be at least %{min}", min: 3)
    "must be at least 3"

# `traverse_errors`

Traverses errors, calling `fun` for each leaf error, and returns a nested
map of results grouped by each error's `path`.

See `Splode.traverse_errors/2` for full documentation.

## Example

    iex> Elixir.MishkaGervaz.Errors.traverse_errors(error, fn error ->
    ...>   Exception.message(error)
    ...> end)
    %{name: ["name is required"]}

# `unwrap!`

Raises an error if the result is an error, otherwise returns the result

Alternatively, you can use the `defsplode` macro, which does this automatically.

### Options

- `:error_opts` - Options to pass to `to_error/2` when converting the returned error
- `:unknown_error_opts` - Options to pass to the unknown error if the function returns only `:error`.
  not necessary if your function always returns `{:error, error}`.

### Examples

  def function(arg) do
    case do_something(arg) do
      :success -> :ok
      {:success, result} -> {:ok, result}
      {:error, error} -> {:error, error}
    end
  end

  def function!(arg) do
    YourErrors.unwrap!(function(arg))
  end

---

*Consult [api-reference.md](api-reference.md) for complete listing*