1 files changed, 89 insertions, 0 deletions
diff --git a/lang/gjs/src/binding.ts b/lang/gjs/src/binding.ts
new file mode 100644
index 0000000..95d905f
--- /dev/null
+++ b/lang/gjs/src/binding.ts
@@ -0,0 +1,89 @@
+export const snakeify = (str: string) => str
+    .replace(/([a-z])([A-Z])/g, "$1_$2")
+    .replaceAll("-", "_")
+    .toLowerCase()
+
+export const kebabify = (str: string) => str
+    .replace(/([a-z])([A-Z])/g, "$1-$2")
+    .replaceAll("_", "-")
+    .toLowerCase()
+
+export interface Subscribable<T = unknown> {
+    subscribe(callback: (value: T) => void): () => void
+    get(): T
+    [key: string]: any
+}
+
+export interface Connectable {
+    connect(signal: string, callback: (...args: any[]) => unknown): number
+    disconnect(id: number): void
+    [key: string]: any
+}
+
+export default class Binding<Value> {
+    private transformFn = (v: any) => v
+
+    #emitter: Subscribable<Value> | Connectable
+    #prop?: string
+
+    static bind<
+        T extends Connectable,
+        P extends keyof T,
+    >(object: T, property: P): Binding<T[P]>
+
+    static bind<T>(object: Subscribable<T>): Binding<T>
+
+    static bind(emitter: Connectable | Subscribable, prop?: string) {
+        return new Binding(emitter, prop)
+    }
+
+    private constructor(emitter: Connectable | Subscribable<Value>, prop?: string) {
+        this.#emitter = emitter
+        this.#prop = prop && kebabify(prop)
+    }
+
+    toString() {
+        return `Binding<${this.#emitter}${this.#prop ? `, "${this.#prop}"` : ""}>`
+    }
+
+    as<T>(fn: (v: Value) => T): Binding<T> {
+        const bind = new Binding(this.#emitter, this.#prop)
+        bind.transformFn = (v: Value) => fn(this.transformFn(v))
+        return bind as unknown as Binding<T>
+    }
+
+    get(): Value {
+        if (typeof this.#emitter.get === "function")
+            return this.transformFn(this.#emitter.get())
+
+        if (typeof this.#prop === "string") {
+            const getter = `get_${snakeify(this.#prop)}`
+            if (typeof this.#emitter[getter] === "function")
+                return this.transformFn(this.#emitter[getter]())
+
+            return this.transformFn(this.#emitter[this.#prop])
+        }
+
+        throw Error("can not get value of binding")
+    }
+
+    subscribe(callback: (value: Value) => void): () => void {
+        if (typeof this.#emitter.subscribe === "function") {
+            return this.#emitter.subscribe(() => {
+                callback(this.get())
+            })
+        }
+        else if (typeof this.#emitter.connect === "function") {
+            const signal = `notify::${this.#prop}`
+            const id = this.#emitter.connect(signal, () => {
+                callback(this.get())
+            })
+            return () => {
+                (this.#emitter.disconnect as Connectable["disconnect"])(id)
+            }
+        }
+        throw Error(`${this.#emitter} is not bindable`)
+    }
+}
+
+export const { bind } = Binding