hi.zig

const std  = @import("std");
const warn = std.debug.warn;

pub fn main() void {
    var arg_it = std.process.args();

    const name = arg_it.inner.next();
    const text = arg_it.inner.next();

    if (text) |value| {
        filterStdIn(value) catch |err| {
            return;
        };
    } else {
        warn("usage: {} text\n", name);
        return;
    }

    return;
}

fn filterStdIn(text: []const u8) !void {
    var buf: [1024 * 4]u8 = undefined;

    while (true) {
        const line = std.io.readLineSlice(buf[0..]) catch |err| {
            return err;
        };

        try filter(line, text);
    }
    
}

fn filter(line: []u8, text: []const u8) !void {
    var stdout = try std.io.getStdOut();    

    if (strstr(line, text)) {
        try stdout.write(line);
        try stdout.write("\n");
    }
}

fn strstr(str: []const u8, s: []const u8) bool {
    if (s.len == 0) {
        return false;
    }

    outer: for (str) |c, i| {
        if (i + s.len > str.len) {
            break;
        }

        for (s) |sc, si| {
            if (sc != str[i + si]) {
                continue :outer;
            }
        }
        return true;
    }

    return false;
}