// Copyright (C) Parity Technologies (UK) Ltd.

// This file is part of Polkadot.

// Polkadot 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.

// Polkadot 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 Polkadot.  If not, see <http://www.gnu.org/licenses/>.

//! XCM `Location` datatype.

use super::{traits::Reanchorable, Junction, Junctions};

use crate::{v3::MultiLocation as OldLocation, VersionedLocation};

use codec::{Decode, Encode, MaxEncodedLen};

use core::result;

use scale_info::TypeInfo;

/// A relative path between state-bearing consensus systems.

///

/// A location in a consensus system is defined as an *isolatable state machine* held within global

/// consensus. The location in question need not have a sophisticated consensus algorithm of its

/// own; a single account within Ethereum, for example, could be considered a location.

///

/// A very-much non-exhaustive list of types of location include:

/// - A (normal, layer-1) block chain, e.g. the Bitcoin mainnet or a parachain.

/// - A layer-0 super-chain, e.g. the Polkadot Relay chain.

/// - A layer-2 smart contract, e.g. an ERC-20 on Ethereum.

/// - A logical functional component of a chain, e.g. a single instance of a pallet on a Frame-based

///   Substrate chain.

/// - An account.

///

/// A `Location` is a *relative identifier*, meaning that it can only be used to define the

/// relative path between two locations, and cannot generally be used to refer to a location

/// universally. It is comprised of an integer number of parents specifying the number of times to

/// "escape" upwards into the containing consensus system and then a number of *junctions*, each

/// diving down and specifying some interior portion of state (which may be considered a

/// "sub-consensus" system).

///

/// This specific `Location` implementation uses a `Junctions` datatype which is a Rust `enum`

/// in order to make pattern matching easier. There are occasions where it is important to ensure

/// that a value is strictly an interior location, in those cases, `Junctions` may be used.

///

/// The `Location` value of `Null` simply refers to the interpreting consensus system.

#[derive(

	Clone,

	Decode,

	Encode,

	Eq,

	PartialEq,

	Ord,

	PartialOrd,

	Debug,

	serde::Serialize,

)]

pub struct Location {

	/// The number of parent junctions at the beginning of this `Location`.

	pub parents: u8,

	/// The interior (i.e. non-parent) junctions that this `Location` contains.

	pub interior: Junctions,

}

impl Default for Location {

}

/// A relative location which is constrained to be an interior location of the context.

///

/// See also `Location`.

pub type InteriorLocation = Junctions;

impl Location {

	/// Creates a new `Location` with the given number of parents and interior junctions.

	/// Consume `self` and return the equivalent `VersionedLocation` value.

	/// Creates a new `Location` with 0 parents and a `Here` interior.

	///

	/// The resulting `Location` can be interpreted as the "current consensus system".

	/// Creates a new `Location` which evaluates to the parent context.

	/// Creates a new `Location` with `parents` and an empty (`Here`) interior.

	/// Whether the `Location` has no parents and has a `Here` interior.

	/// Remove the `NetworkId` value in any interior `Junction`s.

	/// Return a reference to the interior field.

	/// Return a mutable reference to the interior field.

	/// Returns the number of `Parent` junctions at the beginning of `self`.

	/// Returns the parent count and the interior [`Junctions`] as a tuple.

	///

	/// To be used when pattern matching, for example:

	///

	/// ```rust

	/// # use staging_xcm::v4::{Junctions::*, Junction::*, Location};

	/// fn get_parachain_id(loc: &Location) -> Option<u32> {

	///     match loc.unpack() {

	///         (0, [Parachain(id)]) => Some(*id),

	///         _ => None

	///     }

	/// }

	/// ```

	/// Returns boolean indicating whether `self` contains only the specified amount of

	/// parents and no interior junctions.

	/// Returns the number of parents and junctions in `self`.

	/// Returns the first interior junction, or `None` if the location is empty or contains only

	/// parents.

	/// Returns last junction, or `None` if the location is empty or contains only parents.

	/// Splits off the first interior junction, returning the remaining suffix (first item in tuple)

	/// and the first element (second item in tuple) or `None` if it was empty.

	/// Splits off the last interior junction, returning the remaining prefix (first item in tuple)

	/// and the last element (second item in tuple) or `None` if it was empty or if `self` only

	/// contains parents.

	/// Mutates `self`, suffixing its interior junctions with `new`. Returns `Err` with `new` in

	/// case of overflow.

	/// Mutates `self`, prefixing its interior junctions with `new`. Returns `Err` with `new` in

	/// case of overflow.

	/// Consumes `self` and returns a `Location` suffixed with `new`, or an `Err` with

	/// the original value of `self` in case of overflow.

		}

	/// Consumes `self` and returns a `Location` prefixed with `new`, or an `Err` with the

	/// original value of `self` in case of overflow.

		}

	/// Returns the junction at index `i`, or `None` if the location is a parent or if the location

	/// does not contain that many elements.

	/// Returns a mutable reference to the junction at index `i`, or `None` if the location is a

	/// parent or if it doesn't contain that many elements.

	/// Decrements the parent count by 1.

	/// Removes the first interior junction from `self`, returning it

	/// (or `None` if it was empty or if `self` contains only parents).

	/// Removes the last element from `interior`, returning it (or `None` if it was empty or if

	/// `self` only contains parents).

	/// Ensures that `self` has the same number of parents as `prefix`, its junctions begins with

	/// the junctions of `prefix` and that it has a single `Junction` item following.

	/// If so, returns a reference to this `Junction` item.

	///

	/// # Example

	/// ```rust

	/// # use staging_xcm::v4::{Junctions::*, Junction::*, Location};

	/// # fn main() {

	/// let mut m = Location::new(1, [PalletInstance(3), OnlyChild]);

	/// assert_eq!(

	///     m.match_and_split(&Location::new(1, [PalletInstance(3)])),

	///     Some(&OnlyChild),

	/// );

	/// assert_eq!(m.match_and_split(&Location::new(1, Here)), None);

	/// # }

	/// ```

	/// Mutate `self` so that it is suffixed with `suffix`.

	///

	/// Does not modify `self` and returns `Err` with `suffix` in case of overflow.

	///

	/// # Example

	/// ```rust

	/// # use staging_xcm::v4::{Junctions::*, Junction::*, Location, Parent};

	/// # fn main() {

	/// let mut m: Location = (Parent, Parachain(21), 69u64).into();

	/// assert_eq!(m.append_with((Parent, PalletInstance(3))), Ok(()));

	/// assert_eq!(m, Location::new(1, [Parachain(21), PalletInstance(3)]));

	/// # }

	/// ```

		}

	/// Consume `self` and return its value suffixed with `suffix`.

	///

	/// Returns `Err` with the original value of `self` and `suffix` in case of overflow.

	///

	/// # Example

	/// ```rust

	/// # use staging_xcm::v4::{Junctions::*, Junction::*, Location, Parent};

	/// # fn main() {

	/// let mut m: Location = (Parent, Parachain(21), 69u64).into();

	/// let r = m.appended_with((Parent, PalletInstance(3))).unwrap();

	/// assert_eq!(r, Location::new(1, [Parachain(21), PalletInstance(3)]));

	/// # }

	/// ```

		}

	/// Mutate `self` so that it is prefixed with `prefix`.

	///

	/// Does not modify `self` and returns `Err` with `prefix` in case of overflow.

	///

	/// # Example

	/// ```rust

	/// # use staging_xcm::v4::{Junctions::*, Junction::*, Location, Parent};

	/// # fn main() {

	/// let mut m: Location = (Parent, Parent, PalletInstance(3)).into();

	/// assert_eq!(m.prepend_with((Parent, Parachain(21), OnlyChild)), Ok(()));

	/// assert_eq!(m, Location::new(1, [PalletInstance(3)]));

	/// # }

	/// ```

		// cancel out the final item on the prefix interior for one of the suffix's parents.

		// now we have either removed all suffix's parents or prefix interior.

		// this means we can combine the prefix's and suffix's remaining parents/interior since

		// we know that with at least one empty, the overall order will be respected:

		//     prefix     self (suffix)

		// P .. P   (I)   p .. p i .. i => P + p .. (no I) i

		//  -- or --

		// P .. P I .. I    (p)  i .. i => P (no p) .. I + i

	/// Consume `self` and return its value prefixed with `prefix`.

	///

	/// Returns `Err` with the original value of `self` and `prefix` in case of overflow.

	///

	/// # Example

	/// ```rust

	/// # use staging_xcm::v4::{Junctions::*, Junction::*, Location, Parent};

	/// # fn main() {

	/// let m: Location = (Parent, Parent, PalletInstance(3)).into();

	/// let r = m.prepended_with((Parent, Parachain(21), OnlyChild)).unwrap();

	/// assert_eq!(r, Location::new(1, [PalletInstance(3)]));

	/// # }

	/// ```

		}

	/// Remove any unneeded parents/junctions in `self` based on the given context it will be

	/// interpreted in.

			// Not enough context

			}

		}

	/// Return the Location subsection identifying the chain that `self` points to.

		// start popping junctions until we reach chain identifier

				// return chain subsection

		}

}

impl Reanchorable for Location {

	type Error = Self;

	/// Mutate `self` so that it represents the same location from the point of view of `target`.

	/// The context of `self` is provided as `context`.

	///

	/// Does not modify `self` in case of overflow.

		// TODO: https://github.com/paritytech/polkadot/issues/4489 Optimize this.

		// 1. Use our `context` to figure out how the `target` would address us.

		// 2. Prepend `inverted_target` to `self` to get self's location from the perspective of

		// `target`.

		// 3. Given that we know some of `target` context, ensure that any parents in `self` are

		// strictly needed.

	/// Consume `self` and return a new value representing the same location from the point of view

	/// of `target`. The context of `self` is provided as `context`.

	///

	/// Returns the original `self` in case of overflow.

		}

}

impl TryFrom<OldLocation> for Option<Location> {

	type Error = ();

}

impl TryFrom<OldLocation> for Location {

	type Error = ();

}

/// A unit struct which can be converted into a `Location` of `parents` value 1.

#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]

pub struct Parent;

impl From<Parent> for Location {

}

/// A tuple struct which can be converted into a `Location` of `parents` value 1 with the inner

/// interior.

#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]

pub struct ParentThen(pub Junctions);

impl From<ParentThen> for Location {

}

/// A unit struct which can be converted into a `Location` of the inner `parents` value.

#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]

pub struct Ancestor(pub u8);

impl From<Ancestor> for Location {

}

/// A unit struct which can be converted into a `Location` of the inner `parents` value and the

/// inner interior.

#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]

pub struct AncestorThen<Interior>(pub u8, pub Interior);

impl<Interior: Into<Junctions>> From<AncestorThen<Interior>> for Location {

}

impl From<[u8; 32]> for Location {

}

#[cfg(test)]

mod tests {

	use crate::v4::prelude::*;

	use codec::{Decode, Encode};

	#[test]

	fn conversion_works() {

		let x: Location = Parent.into();

		assert_eq!(x, Location { parents: 1, interior: Here });

		//		let x: Location = (Parent,).into();

		//		assert_eq!(x, Location { parents: 1, interior: Here });

		//		let x: Location = (Parent, Parent).into();

		//		assert_eq!(x, Location { parents: 2, interior: Here });

		let x: Location = (Parent, Parent, OnlyChild).into();

		assert_eq!(x, Location { parents: 2, interior: OnlyChild.into() });

		let x: Location = OnlyChild.into();

		assert_eq!(x, Location { parents: 0, interior: OnlyChild.into() });

		let x: Location = (OnlyChild,).into();

		assert_eq!(x, Location { parents: 0, interior: OnlyChild.into() });

	}

	#[test]

	fn simplify_basic_works() {

		let mut location: Location =

			(Parent, Parent, Parachain(1000), PalletInstance(42), GeneralIndex(69)).into();

		let context = [Parachain(1000), PalletInstance(42)].into();

		let expected = GeneralIndex(69).into();

		location.simplify(&context);

		assert_eq!(location, expected);

		let mut location: Location = (Parent, PalletInstance(42), GeneralIndex(69)).into();

		let context = [PalletInstance(42)].into();

		let expected = GeneralIndex(69).into();

		location.simplify(&context);

		assert_eq!(location, expected);

		let mut location: Location = (Parent, PalletInstance(42), GeneralIndex(69)).into();

		let context = [Parachain(1000), PalletInstance(42)].into();

		let expected = GeneralIndex(69).into();

		location.simplify(&context);

		assert_eq!(location, expected);

		let mut location: Location =

			(Parent, Parent, Parachain(1000), PalletInstance(42), GeneralIndex(69)).into();

		let context = [OnlyChild, Parachain(1000), PalletInstance(42)].into();

		let expected = GeneralIndex(69).into();

		location.simplify(&context);

		assert_eq!(location, expected);

	}

	#[test]

	fn simplify_incompatible_location_fails() {

		let mut location: Location =

			(Parent, Parent, Parachain(1000), PalletInstance(42), GeneralIndex(69)).into();

		let context = [Parachain(1000), PalletInstance(42), GeneralIndex(42)].into();

		let expected =

			(Parent, Parent, Parachain(1000), PalletInstance(42), GeneralIndex(69)).into();

		location.simplify(&context);

		assert_eq!(location, expected);

		let mut location: Location =

			(Parent, Parent, Parachain(1000), PalletInstance(42), GeneralIndex(69)).into();

		let context = [Parachain(1000)].into();

		let expected =

			(Parent, Parent, Parachain(1000), PalletInstance(42), GeneralIndex(69)).into();

		location.simplify(&context);

		assert_eq!(location, expected);

	}

	#[test]

	fn reanchor_works() {

		let mut id: Location = (Parent, Parachain(1000), GeneralIndex(42)).into();

		let context = Parachain(2000).into();

		let target = (Parent, Parachain(1000)).into();

		let expected = GeneralIndex(42).into();

		id.reanchor(&target, &context).unwrap();

		assert_eq!(id, expected);

	}

	#[test]

	fn encode_and_decode_works() {

		let m = Location {

			parents: 1,

			interior: [Parachain(42), AccountIndex64 { network: None, index: 23 }].into(),

		};

		let encoded = m.encode();

		assert_eq!(encoded, [1, 2, 0, 168, 2, 0, 92].to_vec());

		let decoded = Location::decode(&mut &encoded[..]);

		assert_eq!(decoded, Ok(m));

	}

	#[test]

	fn match_and_split_works() {

		let m = Location {

			parents: 1,

			interior: [Parachain(42), AccountIndex64 { network: None, index: 23 }].into(),

		};

		assert_eq!(m.match_and_split(&Location { parents: 1, interior: Here }), None);

		assert_eq!(

			m.match_and_split(&Location { parents: 1, interior: [Parachain(42)].into() }),

			Some(&AccountIndex64 { network: None, index: 23 })

		);

		assert_eq!(m.match_and_split(&m), None);

	}

	#[test]

	fn append_with_works() {

		let acc = AccountIndex64 { network: None, index: 23 };

		let mut m = Location { parents: 1, interior: [Parachain(42)].into() };

		assert_eq!(m.append_with([PalletInstance(3), acc]), Ok(()));

		assert_eq!(

			m,

			Location { parents: 1, interior: [Parachain(42), PalletInstance(3), acc].into() }

		);

		// cannot append to create overly long location

		let acc = AccountIndex64 { network: None, index: 23 };

		let m = Location {

			parents: 254,

			interior: [Parachain(42), OnlyChild, OnlyChild, OnlyChild, OnlyChild].into(),

		};

		let suffix: Location = (PalletInstance(3), acc, OnlyChild, OnlyChild).into();

		assert_eq!(m.clone().append_with(suffix.clone()), Err(suffix));

	}

	#[test]

	fn prepend_with_works() {

		let mut m = Location {

			parents: 1,

			interior: [Parachain(42), AccountIndex64 { network: None, index: 23 }].into(),

		};

		assert_eq!(m.prepend_with(Location { parents: 1, interior: [OnlyChild].into() }), Ok(()));

		assert_eq!(

			m,

			Location {

				parents: 1,

				interior: [Parachain(42), AccountIndex64 { network: None, index: 23 }].into()

			}

		);

		// cannot prepend to create overly long location

		let mut m = Location { parents: 254, interior: [Parachain(42)].into() };

		let prefix = Location { parents: 2, interior: Here };

		assert_eq!(m.prepend_with(prefix.clone()), Err(prefix));

		let prefix = Location { parents: 1, interior: Here };

		assert_eq!(m.prepend_with(prefix.clone()), Ok(()));

		assert_eq!(m, Location { parents: 255, interior: [Parachain(42)].into() });

	}

	#[test]

	fn double_ended_ref_iteration_works() {

		let m: Junctions = [Parachain(1000), Parachain(3), PalletInstance(5)].into();

		let mut iter = m.iter();

		let first = iter.next().unwrap();

		assert_eq!(first, &Parachain(1000));

		let third = iter.next_back().unwrap();

		assert_eq!(third, &PalletInstance(5));

		let second = iter.next_back().unwrap();

		assert_eq!(iter.next(), None);

		assert_eq!(iter.next_back(), None);

		assert_eq!(second, &Parachain(3));

		let res = Here

			.pushed_with(*first)

			.unwrap()

			.pushed_with(*second)

			.unwrap()

			.pushed_with(*third)

			.unwrap();

		assert_eq!(m, res);

		// make sure there's no funny business with the 0 indexing

		let m = Here;

		let mut iter = m.iter();

		assert_eq!(iter.next(), None);

		assert_eq!(iter.next_back(), None);

	}

	#[test]

	fn conversion_from_other_types_works() {

		use crate::v3;

		fn takes_location<Arg: Into<Location>>(_arg: Arg) {}

		takes_location(Parent);

		takes_location(Here);

		takes_location([Parachain(42)]);

		takes_location((Ancestor(255), PalletInstance(8)));

		takes_location((Ancestor(5), Parachain(1), PalletInstance(3)));

		takes_location((Ancestor(2), Here));

		takes_location(AncestorThen(

			3,

			[Parachain(43), AccountIndex64 { network: None, index: 155 }],

		));

		takes_location((Parent, AccountId32 { network: None, id: [0; 32] }));

		takes_location((Parent, Here));

		takes_location(ParentThen([Parachain(75)].into()));

		takes_location([Parachain(100), PalletInstance(3)]);

		assert_eq!(v3::Location::from(v3::Junctions::Here).try_into(), Ok(Location::here()));

		assert_eq!(v3::Location::from(v3::Parent).try_into(), Ok(Location::parent()));

		assert_eq!(

			v3::Location::from((v3::Parent, v3::Parent, v3::Junction::GeneralIndex(42u128),))

				.try_into(),

			Ok(Location { parents: 2, interior: [GeneralIndex(42u128)].into() }),

		);

	}

}