GraphQL ফান্ডামেন্টাল

import json

# ---------- আসল ডেটা (এখানে একটি in-memory "ডেটাবেস") ----------
users_db = {
    1: {"id": 1, "name": "Farhana Akter", "email": "farhana@example.com", "posts": [101, 102]},
    2: {"id": 2, "name": "Kamal Hossain", "email": "kamal@example.com", "posts": [103]},
}
posts_db = {
    101: {"id": 101, "title": "GraphQL শেখা শুরু", "body": "প্রথম পোস্ট...", "author_id": 1},
    102: {"id": 102, "title": "REST বনাম GraphQL", "body": "দ্বিতীয় পোস্ট...", "author_id": 1},
    103: {"id": 103, "title": "WebSocket পরিচিতি", "body": "তৃতীয় পোস্ট...", "author_id": 2},
}

# ---------- SCHEMA -- প্রতিটি ফিল্ডের জন্য একটি resolver + তার রিটার্ন-টাইপ ----------
SCHEMA = {
    "Query": {
        "user": {"resolve": lambda root, args: users_db.get(args.get("id")), "type": "User"},
    },
    "User": {
        "id":    {"resolve": lambda obj, args: obj["id"], "type": "scalar"},
        "name":  {"resolve": lambda obj, args: obj["name"], "type": "scalar"},
        "email": {"resolve": lambda obj, args: obj["email"], "type": "scalar"},
        "posts": {"resolve": lambda obj, args: [posts_db[pid] for pid in obj["posts"]], "type": "Post_list"},
    },
    "Post": {
        "id":        {"resolve": lambda obj, args: obj["id"], "type": "scalar"},
        "title":     {"resolve": lambda obj, args: obj["title"], "type": "scalar"},
        "body":      {"resolve": lambda obj, args: obj["body"], "type": "scalar"},
        "author_id": {"resolve": lambda obj, args: obj["author_id"], "type": "scalar"},
    },
}


# ---------- EXECUTE -- একটি query-শেপ রিকার্সিভভাবে ওয়াক করে সঠিক resolver কল করে ----------
def execute(query_shape, root, type_name):
    result = {}
    for field_name, sub in query_shape.items():
        field_def = SCHEMA[type_name][field_name]
        args = sub.get("_args", {})
        value = field_def["resolve"](root, args)
        field_type = field_def["type"]

        if field_type == "scalar":
            result[field_name] = value

        elif field_type.endswith("_list"):
            child_type = field_type[:-len("_list")]
            select = sub.get("_select", [])
            items = []
            for item in value:
                item_result = {f: SCHEMA[child_type][f]["resolve"](item, {}) for f in select}
                nested_keys = [k for k in sub if k not in ("_args", "_select") and k not in select]
                for nk in nested_keys:
                    item_result[nk] = execute({nk: sub[nk]}, item, child_type)[nk]
                items.append(item_result)
            result[field_name] = items

        else:
            child_type = field_type
            select = sub.get("_select", [])
            obj_result = {f: SCHEMA[child_type][f]["resolve"](value, {}) for f in select}
            nested_keys = [k for k in sub if k not in ("_args", "_select") and k not in select]
            for nk in nested_keys:
                obj_result[nk] = execute({nk: sub[nk]}, value, child_type)[nk]
            result[field_name] = obj_result

    return result


# ---------- একটি concrete কোয়েরি -- শুধু name, email, ও posts.title চাওয়া হচ্ছে ----------
query = {
    "user": {
        "_args": {"id": 1},
        "_select": ["name", "email"],
        "posts": {"_select": ["title"]},
    }
}

result = execute(query, root=None, type_name="Query")

print("কোয়েরি-শেপ (ক্লায়েন্ট যা চেয়েছে):")
print(json.dumps(query, ensure_ascii=False, indent=2))

print("\nচূড়ান্ত ফলাফল (resolver-রা প্রকৃতভাবে হিসাব করে দিয়েছে):")
print(json.dumps(result, ensure_ascii=False, indent=2))