defmodule Lapis do
  @moduledoc """
  With `Lapis`, you can define schemas you can use to validate, transform, and reverse data.

  The core building block of `Lapis` is **schema**. Schema could **parse** data (possibly with errors), and it could **reverse** parsed data back to its input.
  `Lapis` allows collecting **multiple errors at once**, in `Lapis.Error`.

  You can compose schemas to build complex validators and transformers.
  `Lapis` provides many essential building blocks, all built on the same small core - `Lapis.Schema`.
  You can define your own too.

  Quick example:

      iex> person =
      ...>   Lapis.map(
      ...>     name: Lapis.string(),
      ...>     nickname: Lapis.string() |> Lapis.optional(),
      ...>     age: Lapis.integer() |> Lapis.positive()
      ...>   )
      iex> Lapis.parse(person, %{"name" => "Marcius", "age" => 2665})
      {:ok, %{name: "Marcius", age: 2665}}
      iex> {:error, err} = Lapis.parse(person, %{age: "fifteen"})
      iex> Enum.sort(err)
      [expected_integer: [:age], missing_key: [:name]]

  ## Examples

  ### Parse and reverse coordinates

  Parse a list of coordinates as tuples:

      iex> schema =
      ...>   Lapis.tuple({Lapis.number(), Lapis.number()})
      ...>   |> Lapis.pipe(fn {x, y} -> %{x: x, y: y} end)
      ...>   |> Lapis.list()
      iex> Lapis.parse(schema, [[1, 2], [3, 4]])
      {:ok, [%{x: 1, y: 2}, %{x: 3, y: 4}]}

  To reverse the output back, the second argument to `Lapis.pipe/2` could be used:

      iex> schema =
      ...>   Lapis.tuple({Lapis.number(), Lapis.number()})
      ...>   |> Lapis.pipe(fn {x, y} -> %{x: x, y: y} end, fn out -> {out.x, out.y} end)
      ...>   |> Lapis.list()
      iex> Lapis.reverse(schema, [%{x: 1, y: 2}, %{x: 3, y: 4}])
      [[1, 2], [3, 4]]

  ### Parse yes/no values

      iex> alias Lapis, as: L
      iex> schema =
      ...>   L.choice([
      ...>     L.literal(true),
      ...>     L.literal(false),
      ...>     L.literal(1) |> L.replace(true),
      ...>     L.literal(0) |> L.replace(false),
      ...>     L.literal("yes") |> L.replace(true),
      ...>     L.literal("no") |> L.replace(false),
      ...>   ])
      iex> L.parse(schema, "yes")
      {:ok, true}
      iex> L.parse(schema, "no")
      {:ok, false}
      iex> L.parse(schema, false)
      {:ok, false}
      iex> L.parse(schema, 1)
      {:ok, true}
      iex> {:error, _} = L.parse(schema, -1)

  ### Errors handling

  TODO

  ## Compile-Time Schemas

  All utilities in Lapis are compile-time-friendly. Meaning, they don't use function captures and
  therefore could be used in e.g. module attributes:

      defmodule CompTimeTest do
        alias Lapis, as: L

        @schema L.number() |> L.positive() |> L.list()

        def parse_num_list(data) do
          @schema
          |> L.parse(data)
        end
      end

  Internally, it is done by assigning data necessary to parse/reverse to schemas (see `Lapis.Schema.assign/2`),
  and by referencing parsers/reversers via "fully qualified specifiers" in the `Lapis.Internal` module (e.g. `Lapis.Internal.boolean_parse/1`).
  Same strategy could be used for user-specified custom schemas. Maybe there is a better way to do so in Elixir, but I haven't found it yet.

  ## Inspiration

  The key inspiration is the excelent TypeScript library [Zod](https://zod.dev).

  Additional credits to:

  - [`NimbleParsec`](https://hexdocs.pm/nimble_parsec/NimbleParsec.html)
  - [`Parameter`](https://hexdocs.pm/parameter/Parameter.html)
  - [`winnow`](https://docs.rs/winnow/0.7.13/winnow/index.html)
  """

  alias Lapis.Internal
  alias Lapis.Schema
  alias __MODULE__.Map, as: LMap

  @doc """
  Create a schema of a map. Shorthand for `Lapis.Map.new/2`.

  See `Lapis.Map` module for tips and tricks.
  """
  def map(fields, opts \\ []) do
    LMap.new(fields, opts)
  end

  @doc """
  Mark map key as optional. Shorthand for `Lapis.Map.key_optional/1`.
  """
  def optional(schema) do
    LMap.key_optional(schema)
  end

  @doc """
  Mark map key as required. Shorthand for `Lapis.Map.key_required/1`.
  """
  def required(schema) do
    LMap.key_required(schema)
  end

  @doc """
  Provide a default value for a map entry if the key is absent in the input. Shorthand for `Lapis.Map.key_default/2`.
  """
  def default(schema, lazy) do
    LMap.key_default(schema, lazy)
  end

  @doc """
  Rename a map key. Shorthand for `Lapis.Map.key_rename/2`.
  """
  def rename(schema, name) do
    LMap.key_rename(schema, name)
  end

  @doc """
  Define a schema for a list.

  All elements of the list are parsed/reversed with the given schema.
  """
  def list(schema) do
    Schema.new(
      &Internal.list_parse/2,
      &Internal.list_reverse/2
    )
    |> Schema.assign(list: schema)
  end

  @doc """
  Define a schema for a tuple.

  Tuple is a fixed-length sequence of schemas. Schemas themselves may be either a tuple or a list.

  The *input* may be a tuple or a list. The length of input must match the length of the schemas.
  The *output* is always a tuple.

  Reverse conversion **always produces lists**. This is done in favor of JSON encoders and JSON format in general that does not have "tuples" but only arrays. (TODO: provide an option to reverse as a tuple?)

      iex> schema = Lapis.tuple({Lapis.string(), Lapis.number()})
      iex> Lapis.parse(schema, {"hey", 5}) # tuple input
      {:ok, {"hey", 5}}
      iex> Lapis.parse(schema, ["hey", 5]) # list input
      {:ok, {"hey", 5}}
      iex> {:error, _} = Lapis.parse(schema, ["hey", 5, 1])
      iex> Lapis.reverse(schema, {"reverse", 42})
      ["reverse", 42]
  """
  def tuple(schemas) when is_tuple(schemas) do
    tuple(Tuple.to_list(schemas))
  end

  def tuple(schemas) when is_list(schemas) do
    Schema.new(&Internal.tuple_parse/2, &Internal.tuple_reverse/2)
    |> Schema.assign(tuple: schemas)
  end

  @doc """
  Define a schema for a fixed set of allowable literals.

  This can be viewed as a convenience for using `Lapis.choice/2` with a set of `Lapis.literal/1`.
  However, **atoms are handled specially:** during _parsing_ they are checked against both atoms and their respective
  strings.

  A canonical example would be using a list of atoms:

      iex> fish = Lapis.enum([:salmon, :tuna, :trout])
      iex> Lapis.parse(fish, :salmon)
      {:ok, :salmon}
      iex> Lapis.parse(fish, "salmon")
      {:ok, :salmon}

  However, any values could be used:

      iex> schema = Lapis.enum(["yes", "no", true, false, 1, 0])
      iex> Lapis.parse(schema, "yes")
      {:ok, "yes"}
      iex> Lapis.parse(schema, "no")
      {:ok, "no"}
      iex> Lapis.parse(schema, 1)
      {:ok, 1}
      iex> {:error, _} = Lapis.parse(schema, 2)
  """
  def enum(vars) do
    map =
      vars
      |> Enum.reduce(%{}, fn var, acc ->
        acc = Map.put_new(acc, var, var)

        if is_atom(var) do
          Map.put_new(acc, Atom.to_string(var), var)
        else
          acc
        end
      end)

    Schema.new(&Internal.enum_parse/2)
    |> Schema.assign(enum: {map, vars})
  end

  @doc """
  Define a schema for a value that must strictly match (`===/2`).

      iex> Lapis.literal("La-pi-su") |> Lapis.parse("La-pi-su")
      {:ok, "La-pi-su"}
  """
  def literal(lit) do
    Schema.new(&Internal.literal_parse/2)
    |> Schema.assign(literal: lit)
  end

  @doc """
  Define a schema for a string (`is_binary/1`).

      iex> Lapis.string() |> Lapis.parse("Lapis")
      {:ok, "Lapis"}
  """
  def string() do
    Schema.new(&Internal.string_parse/1)
  end

  @doc """
  Define a schema for a boolean (`is_boolean/1`).

      iex> Lapis.boolean() |> Lapis.parse(false)
      {:ok, false}
  """
  def boolean() do
    Schema.new(&Internal.boolean_parse/1)
  end

  @doc """
  Define a schema for any number, be it an integer or a floating-point number (`is_number/1`).

      iex> Lapis.number() |> Lapis.parse(1)
      {:ok, 1}
      iex> Lapis.number() |> Lapis.parse(1.52)
      {:ok, 1.52}

  See also:

  - `Lapis.integer/0`
  """
  def number() do
    Schema.new(&Internal.number_parse/1)
  end

  @doc """
  Define a schema for an integer (`is_integer/1`).

      iex> Lapis.integer() |> Lapis.parse(1)
      {:ok, 1}
      iex> {:error, _} = Lapis.integer() |> Lapis.parse(1.52)
  """
  def integer() do
    Schema.new(&Internal.integer_parse/1)
  end

  # TODO: float()

  @doc """
  Validate that a number is positive.
  """
  def positive(schema) do
    schema
    |> refine(&Internal.refine_num_cmp/2, cmp: {:gt, 0})
  end

  @doc """
  Validate that a number is non-negative.
  """
  def nonnegative(schema) do
    schema
    |> refine(&Internal.refine_num_cmp/2, cmp: {:gte, 0})
  end

  @doc """
  Validate that a number is non-positive.
  """
  def nonpositive(schema) do
    schema
    |> refine(&Internal.refine_num_cmp/2, cmp: {:lte, 0})
  end

  @doc """
  Validate that a number is negative.
  """
  def negative(schema) do
    schema
    |> refine(&Internal.refine_num_cmp/2, cmp: {:lt, 0})
  end

  @doc """
  Pipe a schema into another schema.

  During **parsing**, data is first parsed with the _inner_ schema, then with the _outer_.
  During **reversing**, data is first reversed with the _outer_ schema, then with the _inner_.

      iex> str_sep = Lapis.Schema.new(&String.split(&1, " "), &Enum.join(&1, " "))
      iex> two_str = Lapis.tuple({Lapis.string(), Lapis.string()})
      iex> schema = Lapis.string() |> Lapis.pipe(str_sep) |> Lapis.pipe(two_str)
      iex> Lapis.parse(schema, "1 2")
      {:ok, {"1", "2"}}
      iex> Lapis.reverse(schema, {"1", "2"})
      "1 2"
      iex> {:error, _} = Lapis.parse(schema, "1 2 3")

  Piping holds the [associative property](https://en.wikipedia.org/wiki/Associative_property),
  i.e. `(A |> B) |> C` equals to `A |> (B |> C)`:

      iex> a = Lapis.string()
      iex> b = Lapis.Schema.new(&String.length/1)
      iex> c = Lapis.number()
      iex> a |> Lapis.pipe(b) |> Lapis.pipe(c) |> Lapis.parse("hello")
      {:ok, 5}
      iex> a |> Lapis.pipe(b |> Lapis.pipe(c)) |> Lapis.parse("hello")
      {:ok, 5}
     
  """
  def pipe(%Schema{} = inner, %Schema{} = outer) do
    Schema.new(&Internal.pipe_parse/2, &Internal.pipe_reverse/2)
    |> Schema.assign(pipe: {inner, outer})
  end

  @doc """
  Pipe a schema into a pair of parse/reverse functions.

      iex> schema = Lapis.string() |> Lapis.pipe(&String.split(&1, " "))
      iex> Lapis.parse(schema, "1 2 3")
      {:ok, ["1", "2", "3"]}

  See `Lapis.pipe/2` for more details.
  """
  def pipe(%Schema{} = inner, parse, reverse \\ &Function.identity/1) do
    pipe(inner, Schema.new(parse, reverse))
  end

  @doc ~S"""
  Refine a schema with a custom validation. Shorthand for `Lapis.Schema.refine/3`.

  Refines extend the schema without transforming data. Schema could have many refines,
  all of which run **after** the main parser. If any of them fail, entire parsing fails.

      iex> schema =
      ...>   Lapis.string()
      ...>   |> Lapis.refine(& if(&1 =~ ~r[lapis], do: :ok, else: {:error, "not lapis"}))
      ...>   |> Lapis.refine(& if(&1 =~ ~r[philosophorum], do: :ok, else: {:error, "not philosophorum"}))
      iex> Lapis.parse(schema, "lapis philosophorum")
      {:ok, "lapis philosophorum"}
      iex> {:error, error} = Lapis.parse(schema, "philosophorum")
      iex> Enum.to_list(error)
      [{"not lapis", []}]
      iex> {:error, error} = Lapis.parse(schema, "lapidarius")
      iex> Enum.sort(error)
      [{"not lapis", []}, {"not philosophorum", []}]

  Each refinement may have its own _assigns_, to enable reusability and compile-time schemas:

      iex> match_regex =
      ...>   fn input, %{regex: r} -> 
      ...>     if input =~ r do
      ...>       :ok
      ...>     else
      ...>       {:error, "does not match regex: #{inspect(r)}"}
      ...>     end
      ...>   end
      iex> schema =
      ...>   Lapis.string()
      ...>   |> Lapis.refine(match_regex, regex: ~r[lapis])
      ...>   |> Lapis.refine(match_regex, regex: ~r[philosophorum])
      iex> Lapis.parse(schema, "lapis philosophorum")
      {:ok, "lapis philosophorum"}
      iex> {:error, error} = Lapis.parse(schema, "philosophorum")
      iex> Enum.to_list(error)
      [{"does not match regex: ~r/lapis/", []}]

  Currently refinements have access only to its own assigns, not the schema's.
  """
  def refine(%Schema{} = schema, fun, assigns \\ []) when is_function(fun) do
    Schema.refine(schema, fun, assigns)
  end

  @doc """
  Pick the first successful parser.

  If all parsers fail, errors from all of them are collected.

      iex> schema = Lapis.choice([Lapis.string(), Lapis.number()])
      iex> Lapis.parse(schema, "5")
      {:ok, "5"}
      iex> Lapis.parse(schema, 51)
      {:ok, 51}
      iex> {:error, error} = Lapis.parse(schema, false)
      iex> [{{:all_choices_failed, %Lapis.Error{} = error}, []}] = Enum.to_list(error)
      iex> Enum.sort(error)
      [{:expected_number, []}, {:expected_string, []}]


  Reversing has no way of knowing which schema to use for that, therefore it must be provided manually.
  Default reverse simply returns its input.
  """
  def choice(choices, reverse \\ &Function.identity/1) when is_list(choices) do
    Schema.new(&Internal.choice_parse/2, reverse)
    |> Schema.assign(choice: choices)
  end

  @doc """
  Replace schema output with a value.

      iex> schema = Lapis.literal("yes") |> Lapis.replace(true)
      iex> Lapis.parse(schema, "yes")
      {:ok, true}

  Equivalent with `Lapis.pipe/2`:

      iex> schema = Lapis.literal("yes") |> Lapis.pipe(fn _ -> true end)
      iex> Lapis.parse(schema, "yes")
      {:ok, true}
  """
  def replace(schema, value) do
    pipe(schema, Schema.new(&Internal.replace_parse/2) |> Schema.assign(replace: value))
  end

  @doc """
  Validate that the input string matches the given regex.

  This is a _refine_ that expects an input to be a string.

      iex> schema = Lapis.string() |> Lapis.regex(~r[la])
      iex> {:ok, _} = Lapis.parse(schema, "lapis")
      iex> {:ok, _} = Lapis.parse(schema, "lazuli")
      iex> {:error, _} = Lapis.parse(schema, "lorem")
  """
  def regex(schema, %Regex{} = regex) do
    refine(schema, &Lapis.Internal.refine_regex/2, regex: regex)
  end

  @doc """
  Parse input with the given schema. Shorthand for `Lapis.Schema.parse/2`.
  """
  def parse(schema, input) do
    Schema.parse(schema, input)
  end

  @doc """
  Reverse the output back with the given schema. Shorthand for `Lapis.Schema.reverse/2`
  """
  def reverse(schema, output) do
    Schema.reverse(schema, output)
  end
end