read config from env (#6)

src/env.zig

@@ -0,0 +1,23 @@
+const std = @import("std");
+const util = @import("./util.zig");
+const string = util.string;
+
+const env_prefix = "SHIMAKAZE_";
+
+const AppEnv = struct {
+    token: string,
+};
+
+pub fn getEnv() !AppEnv {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+
+    const env_map: *std.process.EnvMap = try arena.allocator().create(std.process.EnvMap);
+    env_map.* = try std.process.getEnvMap(arena.allocator());
+
+    const env_token = env_map.get(env_prefix + "TOKEN") orelse return error.BAD_ENV_TOKEN;
+
+    return AppEnv{
+        .token = env_token,
+    };
+}