Validates that the given json follows the spec for ”links” and converts any child “links” to Alembic.Link.

In a most locations, "links" is optional, so it can be nil.

iex> Alembic.Links.from_json(
...>   nil,
...>   %Alembic.Error{
...>     source: %Alembic.Source{
...>       pointer: "/links"
...>     }
...>   }
...> )
{:ok, nil}

Links

The value of each links member MUST be an object (a “links object”).

— JSON API - Document Structure - Links

iex> Alembic.Links.from_json(
...>   ["http://example.com"],
...>   %Alembic.Error{
...>     source: %Alembic.Source{
...>       pointer: "/links"
...>     }
...>   }
...> )
{
  :error,
  %Alembic.Document{
    errors: [
      %Alembic.Error{
        detail: "`/links` type is not links object",
        meta: %{
          "type" => "links object"
        },
        source: %Alembic.Source{
          pointer: "/links"
        },
        status: "422",
        title: "Type is wrong"
      }
    ]
  }
}

Because the members of a “links object” are free-form, even an empty object is ok

iex> Alembic.Links.from_json(
...>   %{},
...>   %Alembic.Error{
...>     source: %Alembic.Source{
...>       pointer: "/links"
...>     }
...>   }
...> )
{:ok, %{}}

Link values

Each member of a links object is a “link”. A link MUST be represented as either:

• a string containing the link’s URL.
• an object (“link object”) which can contain the following members:
• href - a string containing the link’s URL.
• meta - a meta object containing non-standard meta-information about the link.

— JSON API - Document Structure - Links

iex> Alembic.Links.from_json(
...>   %{
...>     "string" => "http://example.com",
...>     "link_object" => %{
...>       "href" => "http://example.com",
...>       "meta" => %{
...>         "last_updated_on" => "2015-12-21"
...>       }
...>     }
...>   },
...>   %Alembic.Error{
...>     source: %Alembic.Source{
...>       pointer: "/links"
...>     }
...>   }
...> )
{
  :ok,
  %{
    "link_object" => %Alembic.Link{
      href: "http://example.com",
      meta: %{
        "last_updated_on" => "2015-12-21"
      }
    },
    "string" => "http://example.com"
  }
}

When any link has an error, then only errors will be returned, but errors from later links will be included

iex> Alembic.Links.from_json(
...>   %{
...>     "first_ok" => "http://example.com/first_ok",
...>     "first_error" => [],
...>     "second_ok" => "http://example.com/second_ok",
...>     "second_error" => []
...>   },
...>   %Alembic.Error{
...>     source: %Alembic.Source{
...>       pointer: "/links"
...>     }
...>   }
...> )
{
  :error,
  %Alembic.Document{
    errors: [
      %Alembic.Error{
        detail: "`/links/first_error` type is not link object",
        meta: %{
          "type" => "link object"
        },
        source: %Alembic.Source{
          pointer: "/links/first_error"
        },
        status: "422",
        title: "Type is wrong"
      },
      %Alembic.Error{
        detail: "`/links/second_error` type is not link object",
        meta: %{
          "type" => "link object"
        },
        source: %Alembic.Source{
          pointer: "/links/second_error"
        },
        status: "422",
        title: "Type is wrong"
      }
    ]
  }
}

Converts the links to Alembic.Pagination.t page fields

Single Page

When there is only one page, there will be a "first" and "last" link pointing to the same page, but no “next” or “prev” links.

iex> Alembic.Links.to_pagination(
...>   %{
...>     "first" => "https://example.com/api/v1/users?page%5Bnumber%5D=1&page%5Bsize%5D=10",
...>     "last" => "https://example.com/api/v1/users?page%5Bnumber%5D=1&page%5Bsize%5D=10"
...>   }
...> )
%Alembic.Pagination{
  first: %Alembic.Pagination.Page{
    number: 1,
    size: 10
  },
  last: %Alembic.Pagination.Page{
    number: 1,
    size: 10
  }
}

Multiple Pages

When there are multiple pages, every page will have a "first" and "last" link pointing to the respective, different pages.

On the first page, the "next" link will be set, but not the "prev" link.

iex> Alembic.Links.to_pagination(
...>   %{
...>     "first" => "https://example.com/api/v1/users?page%5Bnumber%5D=1&page%5Bsize%5D=10",
...>     "last" => "https://example.com/api/v1/users?page%5Bnumber%5D=3&page%5Bsize%5D=10",
...>     "next" => "https://example.com/api/v1/users?page%5Bnumber%5D=2&page%5Bsize%5D=10"
...>   }
...> )
%Alembic.Pagination{
  first: %Alembic.Pagination.Page{
    number: 1,
    size: 10
  },
  last: %Alembic.Pagination.Page{
    number: 3,
    size: 10
  },
  next: %Alembic.Pagination.Page{
    number: 2,
    size: 10
  }
}

On any middle page, both the "next" and "prev" links will be set.

iex> Alembic.Links.to_pagination(
...>   %{
...>     "first" => "https://example.com/api/v1/users?page%5Bnumber%5D=1&page%5Bsize%5D=10",
...>     "last" => "https://example.com/api/v1/users?page%5Bnumber%5D=3&page%5Bsize%5D=10",
...>     "next" => "https://example.com/api/v1/users?page%5Bnumber%5D=3&page%5Bsize%5D=10",
...>     "prev" => "https://example.com/api/v1/users?page%5Bnumber%5D=1&page%5Bsize%5D=10"
...>   }
...> )
%Alembic.Pagination{
  first: %Alembic.Pagination.Page{
    number: 1,
    size: 10
  },
  last: %Alembic.Pagination.Page{
    number: 3,
    size: 10
  },
  next: %Alembic.Pagination.Page{
    number: 3,
    size: 10
  },
  previous: %Alembic.Pagination.Page{
    number: 1,
    size: 10
  }
}

On the last page, the "prev" link will be set, but not the "next" link.

iex> Alembic.Links.to_pagination(
...>   %{
...>     "first" => "https://example.com/api/v1/users?page%5Bnumber%5D=1&page%5Bsize%5D=10",
...>     "last" => "https://example.com/api/v1/users?page%5Bnumber%5D=3&page%5Bsize%5D=10",
...>     "prev" => "https://example.com/api/v1/users?page%5Bnumber%5D=2&page%5Bsize%5D=10"
...>   }
...> )
%Alembic.Pagination{
  first: %Alembic.Pagination.Page{
    number: 1,
    size: 10
  },
  last: %Alembic.Pagination.Page{
    number: 3,
    size: 10
  },
  previous: %Alembic.Pagination.Page{
    number: 2,
    size: 10
  }
}

No Links

If there are no links, then nil will be returned

iex> Alembic.Links.to_pagination(nil)
nil

No pagination links

If there are links, but not for pagination, then nil will be returned

iex> Alembic.Links.to_pagination(%{ "about" => "https://example.com/about" })
nil