xiangting 5.0.5

A library for calculating the deficiency number (a.k.a. xiàngtīng number, 向聴数).
Documentation 
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// SPDX-FileCopyrightText: 2025 Apricot S.
// SPDX-License-Identifier: MIT
// This file is part of https://github.com/Apricot-S/xiangting

use crate::tile::{TileCounts, TileFlags};

fn parse_tile_indices(hand: &str) -> impl Iterator<Item = usize> + '_ {
    let mut current_color: Option<usize> = None;

    hand.chars()
        .rev()
        .map(move |c| match c {
            'm' => {
                current_color = Some(0);
                return None;
            }
            'p' => {
                current_color = Some(9);
                return None;
            }
            's' => {
                current_color = Some(18);
                return None;
            }
            'z' => {
                current_color = Some(27);
                return None;
            }
            _ => {
                let d = c.to_digit(10).expect("invalid digit") as usize;
                let base = current_color.expect("digit without type");
                if !(1..=9).contains(&d) {
                    panic!("tile number must be 1-9, got {}", d);
                }
                if base == 27 && d > 7 {
                    panic!("honor tile must be 1-7, got {}", d);
                }
                return Some(base + d - 1);
            }
        })
        .filter_map(|x| x)
}

pub trait FromTileCode: Sized {
    /// Converts a Tenhou-style tile string into `T`.
    fn from_code(hand: &str) -> Self;
    fn empty() -> Self;
    fn apply(self, idx: usize) -> Self;
}

impl FromTileCode for TileCounts {
    fn from_code(hand: &str) -> Self {
        let mut result = Self::empty();
        for idx in parse_tile_indices(hand) {
            result = result.apply(idx);
        }
        result
    }

    fn empty() -> Self {
        [0u8; 34]
    }

    fn apply(mut self, idx: usize) -> Self {
        self[idx] += 1;
        self
    }
}

impl FromTileCode for TileFlags {
    fn from_code(hand: &str) -> Self {
        let mut result = Self::empty();
        for idx in parse_tile_indices(hand) {
            result = result.apply(idx);
        }
        result
    }

    fn empty() -> Self {
        0u64
    }

    fn apply(self, idx: usize) -> Self {
        self | (1 << idx)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_from_code_tile_counts_normal() {
        let counts = TileCounts::from_code("123m456p789s12344z");
        let expected_counts: TileCounts = [
            1, 1, 1, 0, 0, 0, 0, 0, 0, // m
            0, 0, 0, 1, 1, 1, 0, 0, 0, // p
            0, 0, 0, 0, 0, 0, 1, 1, 1, // s
            1, 1, 1, 2, 0, 0, 0, // z
        ];
        assert_eq!(counts, expected_counts);
    }

    #[test]
    fn test_from_code_tile_counts_multiple_types() {
        let counts = TileCounts::from_code("11m22p33s44z11m2p7s");
        let expected_counts: TileCounts = [
            4, 0, 0, 0, 0, 0, 0, 0, 0, // m
            0, 3, 0, 0, 0, 0, 0, 0, 0, // p
            0, 0, 2, 0, 0, 0, 1, 0, 0, // s
            0, 0, 0, 2, 0, 0, 0, // z
        ];
        assert_eq!(counts, expected_counts);
    }

    #[test]
    fn test_from_code_tile_counts_empty() {
        let counts = TileCounts::from_code("");
        let expected_counts: TileCounts = [0u8; 34];
        assert_eq!(counts, expected_counts);
    }

    #[test]
    #[should_panic]
    fn test_from_code_tile_counts_no_type() {
        TileCounts::from_code("123456");
    }

    #[test]
    #[should_panic]
    fn test_from_code_tile_counts_offset_out_of_range_number() {
        // 0m does not exist
        TileCounts::from_code("0m");
    }

    #[test]
    #[should_panic]
    fn test_from_code_tile_counts_offset_out_of_range_z() {
        // 8z does not exist
        TileCounts::from_code("8z");
    }

    #[test]
    fn test_from_code_tile_flags_multiple_types() {
        let flags = TileFlags::from_code("11m22p33s44z11m2p7s");
        assert_eq!(flags, 0b0001000_001000100_000000010_000000001);
    }
}