const std = @import("std");

fn check(blocks: [6]u9, width: usize, height: usize, counts: [6]usize) bool {
    var totalBlocks: usize = 0;
    for (counts) |c| {
        totalBlocks += c;
    }

    if ((width / 3) * (height / 3) >= totalBlocks) {
        return true;
    }

    var totalUnits: usize = 0;
    for (counts, 0..) |c, i| {
        totalUnits += c * @popCount(blocks[i]);
    }
    if (width * height < totalUnits) {
        return false;
    }

    // more complex cases don't actually exist in the input data
    unreachable;
}

pub fn main() !void {
    const path: [:0]const u8 = std.mem.span(std.os.argv[1]);
    var file = try std.fs.cwd().openFile(path, .{});
    defer file.close();

    var buffer: [1024]u8 = undefined;
    var reader = file.reader(&buffer);

    var i: usize = 0;
    var blocks = [_]u9{0} ** 6;

    var part1: usize = 0;

    while (reader.interface.peekDelimiterExclusive('\n')) |line| {
        reader.interface.toss(line.len + 1);

        const j = i / 5;

        if (j < 6) {
            for (line) |c| {
                if (c == '#') {
                    blocks[j] <<= 1;
                    blocks[j] |= 1;
                } else if (c == '.') {
                    blocks[j] <<= 1;
                }
            }
        } else {
            var x1: usize = 0;
            var x2: usize = std.mem.indexOfScalar(u8, line, 'x').?;
            const width = try std.fmt.parseInt(usize, line[x1..x2], 10);

            x1 = x2 + 1;
            x2 = std.mem.indexOfScalar(u8, line, ':').?;
            const height = try std.fmt.parseInt(usize, line[x1..x2], 10);

            var counts = [_]usize{0} ** 6;
            x2 += 1;
            for (0..6) |k| {
                x1 = x2 + 1;
                x2 = x1 + (std.mem.indexOfScalar(u8, line[x1..], ' ') orelse (line.len - x1));
                counts[k] = try std.fmt.parseInt(usize, line[x1..x2], 10);
            }

            if (check(blocks, width, height, counts)) {
                part1 += 1;
            }
        }

        i += 1;
    } else |err| switch (err) {
        error.EndOfStream => {},
        else => |e| return e,
    }

    std.debug.print("part1: {}\n", .{part1});
}