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use std::{iter::Zip, ops::Range};
use arrayvec::ArrayVec;
use crate::{
data::TeamSeed,
simulate::{SwissSystem, TeamSet},
};
/// Different representations of seeded matchups.
#[derive(Debug)]
enum Matchups {
Range(Zip<Range<TeamSeed>, Range<TeamSeed>>),
Vec {
matchups: ArrayVec<(TeamSeed, TeamSeed), 8>,
index: usize,
},
Iterative {
teams: ArrayVec<TeamSeed, 16>,
matchups: ArrayVec<(TeamSeed, TeamSeed), 8>,
team_index: usize,
matchup_index: usize,
},
}
/// Struct to iterate seeded matchups.
#[derive(Debug)]
pub struct MatchupGenerator {
matchups: Matchups,
opponents: [TeamSet; 16],
diffs: [i8; 16],
}
impl MatchupGenerator {
/// Pre-determined matchup priority for a group size of 4.
const MATCHUP_PRIORITY_4: [[(usize, usize); 2]; 3] = [
[(0, 3), (1, 2)], // first priority
[(0, 2), (1, 3)],
[(0, 1), (2, 3)],
];
/// Pre-determined matchup priority for a group size of 6.
///
/// 0 -> lowest seeded team in the group, 5 -> highest seeded team in the group
///
/// [Rules and Regs - Swiss Bracket](https://github.com/ValveSoftware/counter-strike_rules_and_regs/blob/main/major-supplemental-rulebook.md#swiss-bracket)
const MATCHUP_PRIORITY_6: [[(usize, usize); 3]; 15] = [
[(0, 5), (1, 4), (2, 3)], // first priority
[(0, 5), (1, 3), (2, 4)],
[(0, 4), (1, 5), (2, 3)],
[(0, 4), (1, 3), (2, 5)],
[(0, 3), (1, 5), (2, 4)],
[(0, 3), (1, 4), (2, 5)],
[(0, 5), (1, 2), (3, 4)],
[(0, 4), (1, 2), (3, 5)],
[(0, 2), (1, 5), (3, 4)],
[(0, 2), (1, 4), (3, 5)],
[(0, 3), (1, 2), (4, 5)],
[(0, 2), (1, 3), (4, 5)],
[(0, 1), (2, 5), (3, 4)],
[(0, 1), (2, 4), (3, 5)],
[(0, 1), (2, 3), (4, 5)], // last priority
];
/// Pre-determined matchup priority for a group size of 8.
///
/// Determined by matching highest seed teams first with lowest seed teams.
/// No need to explore every permutation, only the first 3 options for each team.
const MATCHUP_PRIORITY_8: [[(usize, usize); 4]; 7] = [
[(0, 7), (1, 6), (2, 5), (3, 4)], // first priority
[(0, 6), (1, 7), (2, 5), (3, 4)],
[(0, 5), (1, 7), (2, 6), (3, 4)],
[(0, 7), (1, 5), (2, 6), (3, 4)],
[(0, 7), (1, 4), (2, 6), (3, 5)],
[(0, 7), (1, 6), (2, 4), (3, 5)],
[(0, 7), (1, 6), (2, 3), (4, 5)], // last priority
];
/// Pre-determined matchups for second round.
/// Highest vs. lowest mid-stage seed for each group, groups being 0-7 and 8-15
const SECOND_ROUND_MATCHUPS: [(usize, usize); 8] = [
(0, 7),
(1, 6),
(2, 5),
(3, 4),
(8, 15),
(9, 14),
(10, 13),
(11, 12),
];
pub fn new(ss: &SwissSystem) -> Self {
Self {
matchups: match ss.rounds_complete {
// First round is matched up differently (1-9, 2-10, 3-11 etc.)
0 => Matchups::Range((0..8).zip(8..16)),
// Second round is trivial to match
1 => {
let teams = ss.seed_teams();
let mut matchups = ArrayVec::new();
for (ia, ib) in Self::SECOND_ROUND_MATCHUPS {
matchups.push((teams[ia], teams[ib]));
}
Matchups::Vec { matchups, index: 0 }
}
_ => Matchups::Iterative {
teams: ss.seed_teams(),
matchups: ArrayVec::new(),
team_index: 0,
matchup_index: 0,
},
},
opponents: ss.opponents,
diffs: ss.diffs,
}
}
/// Apply a matchup priority lookup table to a group and return an iterator of matchups.
fn apply_priority<const N: usize, const M: usize>(
opponents: &[TeamSet],
priority: [[(usize, usize); M]; N],
group: &[TeamSeed],
) -> ArrayVec<(TeamSeed, TeamSeed), 8> {
'outer: for indices in priority {
for (ia, ib) in indices {
if opponents[group[ia] as usize].contains(&group[ib]) {
continue 'outer;
}
}
let mut matchups = ArrayVec::new();
for (ia, ib) in indices {
matchups.push((group[ia], group[ib]));
}
return matchups;
}
unreachable!("matchups without rematch not possible")
}
}
impl Iterator for MatchupGenerator {
type Item = (TeamSeed, TeamSeed);
/// Group team indices by record and arrange matchups, highest seed vs lowest seed.
///
/// Rearrange to avoid rematches:
/// - in rounds 2 and 3 (group sizes of 4 or 8), the highest seeded team faces the lowest seeded team that doesn't result in a rematch
/// - in rounds 4 and 5 (group sizes of 6), follow pre-determined highest priority matchup that doesn't result in a rematch
///
/// [Rules and Regs - Swiss Bracket](https://github.com/ValveSoftware/counter-strike_rules_and_regs/blob/main/major-supplemental-rulebook.md#swiss-bracket)
fn next(&mut self) -> Option<Self::Item> {
match &mut self.matchups {
Matchups::Range(range) => range.next(),
Matchups::Vec { matchups, index } => {
if *index < matchups.len() {
let next = matchups[*index];
*index += 1;
Some(next)
} else {
None
}
}
Matchups::Iterative {
teams,
matchups,
team_index,
matchup_index,
} => loop {
if *matchup_index < matchups.len() {
let next = matchups[*matchup_index];
*matchup_index += 1;
return Some(next);
} else if *team_index < teams.len() {
*matchup_index = 0;
// Chunk into groups of win-loss diff.
let start = *team_index;
let group_diff = self.diffs[teams[start] as usize];
*team_index += 1;
while *team_index < teams.len()
&& self.diffs[teams[*team_index] as usize] == group_diff
{
*team_index += 1;
}
// Apply matchup priority to group and extend matchups.
match *team_index - start {
4 => {
*matchups = Self::apply_priority(
&self.opponents,
Self::MATCHUP_PRIORITY_4,
&teams[start..*team_index],
)
}
6 => {
*matchups = Self::apply_priority(
&self.opponents,
Self::MATCHUP_PRIORITY_6,
&teams[start..*team_index],
)
}
8 => {
*matchups = Self::apply_priority(
&self.opponents,
Self::MATCHUP_PRIORITY_8,
&teams[start..*team_index],
)
}
_ => unreachable!("malformed group"),
}
} else {
return None;
}
},
}
}
}