// Copyright 2022 Christian Ulrich
//
// This program 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.
//
// This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

use std::io;

pub struct Forest {
    trees: Vec<Vec<u8>>,
}

pub enum Direction {
    North,
    East,
    South,
    West,
}

pub struct Trees<'a> {
    forest: &'a Forest,
    direction: Direction,
    x: usize,
    y: usize,
}

impl Forest {
    pub fn from_stdin() -> Result<Forest, &'static str> {
        let mut trees = vec![];
        for line in io::stdin().lines() {
            let line = line.unwrap();
            if line.len() > 0 {
                trees.push(line.bytes().map(|b| b - '0' as u8).collect());
            }
        }
        Ok(Self { trees: trees })
    }

    pub fn dimensions(&self) -> (usize, usize) {
        (self.trees[0].len(), self.trees.len())
    }

    pub fn tree(&self, x: usize, y: usize) -> Option<u8> {
        Some(*self.trees.get(y)?.get(x)?)
    }

    pub fn view(&self, x: usize, y: usize, direction: Direction) -> Option<Trees> {
        let _ = self.tree(x, y)?;
        Some(Trees {
            forest: self,
            direction: direction,
            x: x,
            y: y,
        })
    }
}

impl Iterator for Trees<'_> {
    type Item = u8;

    fn next(&mut self) -> Option<Self::Item> {
        match self.direction {
            Direction::North => self.y = self.y.checked_sub(1)?,
            Direction::East => self.x = self.x.checked_add(1)?,
            Direction::South => self.y = self.y.checked_add(1)?,
            Direction::West => self.x = self.x.checked_sub(1)?,
        };
        self.forest.tree(self.x, self.y)
    }
}