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// Copyright 2019-2020 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Substrate is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! Chain Spec extensions helpers.

use std::fmt::Debug;
use std::collections::BTreeMap;

use serde::{Serialize, Deserialize, de::DeserializeOwned};

/// A `ChainSpec` extension.
///
/// This trait is implemented automatically by `ChainSpecGroup` macro.
pub trait Group: Clone + Sized {
	/// An associated type containing fork definition.
	type Fork: Fork<Base=Self>;

	/// Convert to fork type.
	fn to_fork(self) -> Self::Fork;
}

/// A `ChainSpec` extension fork definition.
///
/// Basically should look the same as `Group`, but
/// all parameters are optional. This allows changing
/// only one parameter as part of the fork.
/// The forks can be combined (summed up) to specify
/// a complete set of parameters
pub trait Fork: Serialize + DeserializeOwned + Clone + Sized {
	/// A base `Group` type.
	type Base: Group<Fork=Self>;

	/// Combine with another struct.
	///
	/// All parameters set in `other` should override the
	/// ones in the current struct.
	fn combine_with(&mut self, other: Self);

	/// Attempt to convert to the base type if all parameters are set.
	fn to_base(self) -> Option<Self::Base>;
}

macro_rules! impl_trivial {
	() => {};
	($A : ty) => {
		impl_trivial!($A ,);
	};
	($A : ty , $( $B : ty ),*) => {
		impl_trivial!($( $B ),*);

		impl Group for $A {
			type Fork = $A;

			fn to_fork(self) -> Self::Fork {
				self
			}
		}

		impl Fork for $A {
			type Base = $A;

			fn combine_with(&mut self, other: Self) {
				*self = other;
			}

			fn to_base(self) -> Option<Self::Base> {
				Some(self)
			}
		}
	}
}

impl_trivial!((), u8, u16, u32, u64, usize, String, Vec<u8>);

impl<T: Group> Group for Option<T> {
	type Fork = Option<T::Fork>;

	fn to_fork(self) -> Self::Fork {
		self.map(|a| a.to_fork())
	}
}

impl<T: Fork> Fork for Option<T> {
	type Base = Option<T::Base>;

	fn combine_with(&mut self, other: Self) {
		*self = match (self.take(), other) {
			(Some(mut a), Some(b)) => {
				a.combine_with(b);
				Some(a)
			},
			(a, b) => a.or(b),
		};
	}

	fn to_base(self) -> Option<Self::Base> {
		self.map(|x| x.to_base())
	}
}

/// A collection of `ChainSpec` extensions.
///
/// This type can be passed around and allows the core
/// modules to request a strongly-typed, but optional configuration.
pub trait Extension: Serialize + DeserializeOwned + Clone {
	type Forks: IsForks;

	/// Get an extension of specific type.
	fn get<T: 'static>(&self) -> Option<&T>;

	/// Get forkable extensions of specific type.
	fn forks<BlockNumber, T>(&self) -> Option<Forks<BlockNumber, T>> where
		BlockNumber: Ord + Clone + 'static,
		T: Group + 'static,
		<Self::Forks as IsForks>::Extension: Extension,
		<<Self::Forks as IsForks>::Extension as Group>::Fork: Extension,
	{
		self.get::<Forks<BlockNumber, <Self::Forks as IsForks>::Extension>>()?
			.for_type()
	}
}

impl Extension for crate::NoExtension {
	type Forks = Self;

	fn get<T: 'static>(&self) -> Option<&T> { None }
}

pub trait IsForks {
	type BlockNumber: Ord + 'static;
	type Extension: Group + 'static;
}

impl IsForks for Option<()> {
	type BlockNumber = u64;
	type Extension = Self;
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
#[serde(deny_unknown_fields)]
pub struct Forks<BlockNumber: Ord, T: Group> {
	forks: BTreeMap<BlockNumber, T::Fork>,
	#[serde(flatten)]
	base: T,
}

impl<B: Ord, T: Group + Default> Default for Forks<B, T> {
	fn default() -> Self {
		Self {
			base: Default::default(),
			forks: Default::default(),
		}
	}
}

impl<B: Ord, T: Group> Forks<B, T> where
	T::Fork: Debug,
{
	/// Create new fork definition given the base and the forks.
	pub fn new(base: T, forks: BTreeMap<B, T::Fork>) -> Self {
		Self { base, forks }
	}

	/// Return a set of parameters for `Group` including all forks up to `block` (inclusive).
	pub fn at_block(&self, block: B) -> T {
		let mut start = self.base.clone().to_fork();

		for (_, fork) in self.forks.range(..=block) {
			start.combine_with(fork.clone());
		}

		start
			.to_base()
			.expect("We start from the `base` object, so it's always fully initialized; qed")
	}
}

impl<B, T> IsForks for Forks<B, T> where
	B: Ord + 'static,
	T: Group + 'static,
{
	type BlockNumber = B;
	type Extension = T;
}

impl<B: Ord + Clone, T: Group + Extension> Forks<B, T> where
	T::Fork: Extension,
{
	/// Get forks definition for a subset of this extension.
	///
	/// Returns the `Forks` struct, but limited to a particular type
	/// within the extension.
	pub fn for_type<X>(&self) -> Option<Forks<B, X>> where
		X: Group + 'static,
	{
		let base = self.base.get::<X>()?.clone();
		let forks = self.forks.iter().filter_map(|(k, v)| {
			Some((k.clone(), v.get::<Option<X::Fork>>()?.clone()?))
		}).collect();

		Some(Forks {
			base,
			forks,
		})
	}
}

impl<B, E> Extension for Forks<B, E> where
	B: Serialize + DeserializeOwned + Ord + Clone + 'static,
	E: Extension + Group + 'static,
{
	type Forks = Self;

	fn get<T: 'static>(&self) -> Option<&T> {
		use std::any::{TypeId, Any};

		match TypeId::of::<T>() {
			x if x == TypeId::of::<E>() => Any::downcast_ref(&self.base),
			_ => self.base.get(),
		}
	}

	fn forks<BlockNumber, T>(&self) -> Option<Forks<BlockNumber, T>> where
		BlockNumber: Ord + Clone + 'static,
		T: Group + 'static,
		<Self::Forks as IsForks>::Extension: Extension,
		<<Self::Forks as IsForks>::Extension as Group>::Fork: Extension,
	{
		use std::any::{TypeId, Any};

		if TypeId::of::<BlockNumber>() == TypeId::of::<B>() {
			Any::downcast_ref(&self.for_type::<T>()?).cloned()
		} else {
			self.get::<Forks<BlockNumber, <Self::Forks as IsForks>::Extension>>()?
				.for_type()
		}
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use sc_chain_spec_derive::{ChainSpecGroup, ChainSpecExtension};
	// Make the proc macro work for tests and doc tests.
	use crate as sc_chain_spec;

	#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, ChainSpecGroup)]
	#[serde(deny_unknown_fields)]
	pub struct Extension1 {
		pub test: u64,
	}

	#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, ChainSpecGroup)]
	#[serde(deny_unknown_fields)]
	pub struct Extension2 {
		pub test: u8,
	}

	#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, ChainSpecGroup, ChainSpecExtension)]
	#[serde(deny_unknown_fields)]
	pub struct Extensions {
		pub ext1: Extension1,
		pub ext2: Extension2,
	}

	#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, ChainSpecExtension)]
	#[serde(deny_unknown_fields)]
	pub struct Ext2 {
		#[serde(flatten)]
		ext1: Extension1,
		#[forks]
		forkable: Forks<u64, Extensions>,
	}

	#[test]
	fn forks_should_work_correctly() {
		use super::Extension as _ ;

		// We first need to deserialize into a `Value` because of the following bug:
		// https://github.com/serde-rs/json/issues/505
		let ext_val: serde_json::Value = serde_json::from_str(r#"
{
	"test": 11,
	"forkable": {
		"ext1": {
			"test": 15
		},
		"ext2": {
			"test": 123
		},
		"forks": {
			"1": {
				"ext1": { "test": 5 }
			},
			"2": {
				"ext2": { "test": 5 }
			},
			"5": {
				"ext2": { "test": 1 }
			}
		}
	}
}
		"#).unwrap();

		let ext: Ext2 = serde_json::from_value(ext_val).unwrap();

		assert_eq!(ext.get::<Extension1>(), Some(&Extension1 {
			test: 11
		}));

		// get forks definition
		let forks = ext.get::<Forks<u64, Extensions>>().unwrap();
		assert_eq!(forks.at_block(0), Extensions {
			ext1: Extension1 { test: 15 },
			ext2: Extension2 { test: 123 },
		});
		assert_eq!(forks.at_block(1), Extensions {
			ext1: Extension1 { test: 5 },
			ext2: Extension2 { test: 123 },
		});
		assert_eq!(forks.at_block(2), Extensions {
			ext1: Extension1 { test: 5 },
			ext2: Extension2 { test: 5 },
		});
		assert_eq!(forks.at_block(4), Extensions {
			ext1: Extension1 { test: 5 },
			ext2: Extension2 { test: 5 },
		});
		assert_eq!(forks.at_block(5), Extensions {
			ext1: Extension1 { test: 5 },
			ext2: Extension2 { test: 1 },
		});
		assert_eq!(forks.at_block(10), Extensions {
			ext1: Extension1 { test: 5 },
			ext2: Extension2 { test: 1 },
		});
		assert!(forks.at_block(10).get::<Extension2>().is_some());

		// filter forks for `Extension2`
		let ext2 = forks.for_type::<Extension2>().unwrap();
		assert_eq!(ext2.at_block(0), Extension2 { test: 123 });
		assert_eq!(ext2.at_block(2), Extension2 { test: 5 });
		assert_eq!(ext2.at_block(10), Extension2 { test: 1 });

		// make sure that it can return forks correctly
		let ext2_2 = forks.forks::<u64, Extension2>().unwrap();
		assert_eq!(ext2, ext2_2);

		// also ext should be able to return forks correctly:
		let ext2_3 = ext.forks::<u64, Extension2>().unwrap();
		assert_eq!(ext2_2, ext2_3);
	}
}