// Copyright (c) 2021 Soni L.
// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT license.
// Documentation and comments licensed under CC BY-SA 4.0.

//! Argument processing.

use ::std::future::Future;
use ::std::pin::Pin;

use crate::strcursor::StringReader;
use crate::suggestion::Suggestions;
use crate::suggestion::SuggestionsBuilder;

// FIXME delete when implemented
pub struct CommandContext<'a, T>(::std::marker::PhantomData<(&'a str, T)>);

/// An argument parser.
///
/// # Type params
///
/// - `'i`: Lifetime of the input.
/// - `R`: The reader accepted by this argument type.
/// - `S`: The source type accepted by this argument type.
/// - `E`: The error type accepted by this argument type.
///
/// # Examples
///
/// A very basic `bool` argument type:
///
/// ```
/// use ::iosonism::args::ArgumentType;
/// use ::iosonism::strcursor::{ReadError, StringReader};
///
/// struct BoolArgumentType;
///
/// impl<'i, R, S, E> ArgumentType<'i, R, S, E> for BoolArgumentType
/// where R: StringReader<'i>, E: ReadError<'i, R> {
///     type Result = bool;
///     fn parse(&self, reader: &mut R) -> Result<bool, E> {
///         reader.read_bool()
///     }
/// }
/// ```
pub trait ArgumentType<'i, T: StringReader<'i>, S, E> {
    /// The parsed type of the argument.
    type Result: Sized + 'static + ::std::any::Any;

    /// Parses an argument of this type, returning the parsed argument.
    fn parse(&self, reader: &mut T) -> Result<Self::Result, E>;

    /// Creates suggestions for this argument.
    // The hope here is that S is lightweight enough for one to clone into the
    // closure. Unfortunately making it borrowable would be a pain.
    // FIXME: this API doesn't look great, can we make it better somehow?
    fn list_suggestions(
        &self,
        context: &CommandContext<'i, S>,
        builder: SuggestionsBuilder<'i>,
    ) -> Pin<Box<dyn Future<Output=Suggestions> + Send + 'i>> {
        let _ = context;
        let _ = builder;
        todo!()
    }

    /// Returns examples for this argument.
    fn get_examples(&self) -> Vec<&str> {
        Vec::new()
    }
}