Add variable related functions and helper class

Author: lambdalisue

mod.ts

@@ -1,2 +1,3 @@
 export * from "./autocmd.ts";
 export * from "./execute.ts";
+export * from "./variable.ts";

variable.ts

@@ -0,0 +1,67 @@
+import { Denops } from "./deps.ts";
+
+/**
+ * Vim variable groups
+ *
+ * g - Global variables
+ * b - Buffer local variables
+ * w - Window local variables
+ * t - Tab page local variables
+ * v - Vim's variables
+ * env - Environment variables
+ *
+ */
+export type VariableGroups = "g" | "b" | "w" | "t" | "v" | "env";
+
+export async function getVar<T = unknown>(
+  denops: Denops,
+  group: VariableGroups,
+  prop: string,
+): Promise<T> {
+  const name = group === "env" ? `\$${prop}` : `${group}:${prop}`;
+  // deno-lint-ignore no-explicit-any
+  return (await denops.eval(name)) as any;
+}
+
+export async function setVar<T = unknown>(
+  denops: Denops,
+  group: VariableGroups,
+  prop: string,
+  value: T,
+): Promise<void> {
+  const name = group === "env" ? `\$${prop}` : `${group}:${prop}`;
+  await denops.cmd(`let ${name} = value`, {
+    value,
+  });
+}
+
+export async function removeVar(
+  denops: Denops,
+  group: VariableGroups,
+  prop: string,
+): Promise<void> {
+  const name = group === "env" ? `\$${prop}` : `${group}:${prop}`;
+  await denops.cmd(`unlet ${name}`);
+}
+
+export class VariableHelper {
+  #denops: Denops;
+  #group: VariableGroups;
+
+  constructor(denops: Denops, group: VariableGroups) {
+    this.#denops = denops;
+    this.#group = group;
+  }
+
+  async get<T = unknown>(prop: string): Promise<T> {
+    return await getVar(this.#denops, this.#group, prop);
+  }
+
+  async set<T = unknown>(prop: string, value: T): Promise<void> {
+    await setVar(this.#denops, this.#group, prop, value);
+  }
+
+  async remove(prop: string): Promise<void> {
+    await removeVar(this.#denops, this.#group, prop);
+  }
+}