From 51e5228145cb3239a84c635286de9f39121ef54d Mon Sep 17 00:00:00 2001
From: Pavel Lutskov <pavel.lutskov@gmail.com>
Date: Sun, 14 Nov 2021 14:42:53 +0100
Subject: [PATCH] Implement basic Piece infrastructure

And the Pawn class
---
 rs/src/main.rs | 166 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 164 insertions(+), 2 deletions(-)

diff --git a/rs/src/main.rs b/rs/src/main.rs
index e7a11a9..e46caf2 100644
--- a/rs/src/main.rs
+++ b/rs/src/main.rs
@@ -1,3 +1,165 @@
-fn main() {
-    println!("Hello, world!");
+use std::marker::PhantomData;
+enum Color {
+    Black,
+    White,
 }
+
+struct Position {
+    row: Row,
+    column: Column,
+}
+
+impl Position {
+    fn delta(&self, delta_row_column: (i8, i8)) -> Result<Position, ()> {
+        let (delta_row, delta_column) = delta_row_column;
+        Ok(Position {
+            row: self.row.delta(delta_row)?,
+            column: self.column.delta(delta_column)?,
+        })
+    }
+}
+
+#[derive(PartialEq, Clone, Copy)]
+enum Row {
+    _1,
+    _2,
+    _3,
+    _4,
+    _5,
+    _6,
+    _7,
+    _8,
+}
+
+#[derive(PartialEq, Clone, Copy)]
+enum Column {
+    A,
+    B,
+    C,
+    D,
+    E,
+    F,
+    G,
+    H,
+}
+
+trait GridAxis
+where
+    Self: Sized,
+    Self: Clone,
+{
+    const ALL_VALUES: [Self; 8];
+    fn new(index: u8) -> Result<Self, ()> {
+        return Ok(
+            Self::ALL_VALUES[Self::validate_index(index)? as usize].clone()
+        );
+    }
+    fn validate_index(index: u8) -> Result<u8, ()> {
+        if index as usize >= Self::ALL_VALUES.len() {
+            Err(())
+        } else {
+            Ok(index)
+        }
+    }
+    fn get_index(&self) -> u8;
+    fn delta(&self, delta: i8) -> Result<Self, ()> {
+        let highest = Self::ALL_VALUES.len() as i8 - 1;
+        if delta > highest
+            || delta < -highest
+            || (delta < 0 && self.get_index() < delta.abs() as u8)
+            || (delta > 0 && self.get_index() + delta as u8 > highest as u8)
+        {
+            Err(())
+        } else {
+            Ok(Self::new(((self.get_index() as i8) + delta) as u8)?)
+        }
+    }
+}
+
+impl GridAxis for Row {
+    const ALL_VALUES: [Row; 8] = [
+        Row::_1,
+        Row::_2,
+        Row::_3,
+        Row::_4,
+        Row::_5,
+        Row::_6,
+        Row::_7,
+        Row::_8,
+    ];
+    fn get_index(&self) -> u8 {
+        *self as u8
+    }
+}
+
+impl GridAxis for Column {
+    const ALL_VALUES: [Column; 8] = [
+        Column::A,
+        Column::B,
+        Column::C,
+        Column::D,
+        Column::E,
+        Column::F,
+        Column::G,
+        Column::H,
+    ];
+    fn get_index(&self) -> u8 {
+        *self as u8
+    }
+}
+
+struct Piece<T> {
+    position: Position,
+    color: Color,
+    piece_type: PhantomData<T>,
+}
+
+trait Movement {
+    fn get_moves(&self) -> Vec<Position>;
+    fn get_captures(&self) -> Vec<Position>;
+}
+
+struct Pawn {}
+
+impl<T> Piece<T> {
+    fn deltas_to_valid_positions(
+        &self,
+        deltas: &Vec<(i8, i8)>,
+    ) -> Vec<Position> {
+        deltas
+            .iter()
+            .filter_map(|&delta_row_column| {
+                self.position.delta(delta_row_column).ok()
+            })
+            .collect()
+    }
+}
+
+impl Piece<Pawn> {
+    fn get_home_row_direction(&self) -> (Row, i8) {
+        match self.color {
+            Color::Black => (Row::_7, -1),
+            Color::White => (Row::_2, 1),
+        }
+    }
+}
+
+impl Movement for Piece<Pawn> {
+    fn get_moves(&self) -> Vec<Position> {
+        let (home_row, direction) = self.get_home_row_direction();
+        let deltas: Vec<(i8, i8)> = if self.position.row == home_row {
+            vec![(1 * direction, 0), (2 * direction, 0)]
+        } else {
+            vec![(1 * direction, 0)]
+        };
+        self.deltas_to_valid_positions(&deltas)
+    }
+    fn get_captures(&self) -> Vec<Position> {
+        let (_, direction) = self.get_home_row_direction();
+        let deltas: Vec<(i8, i8)> =
+            vec![(1 * direction, 1), (1 * direction, -1)];
+        self.deltas_to_valid_positions(&deltas)
+    }
+}
+
+fn main() {}