feat: adds fetch_codebase (#24)

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# Content
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Author: jayhack

docs/building-with-codegen/parsing-codebases.mdx

@@ -7,9 +7,9 @@ iconType: "solid"
 
 The primary entrypoint to programs leveraging Codegen is the [Codebase](../api-reference/core/Codebase) class.
 
-Construct a Codebase by passing in a path to a local `git` repository.
-
+## Local Codebases
 
+Construct a Codebase by passing in a path to a local `git` repository.
 
 ```python
 from codegen import Codebase
@@ -20,13 +20,46 @@ codebase = Codebase("path/to/repository")
 # Parse from current directory
 codebase = Codebase("./")
 ```
-<Note>This will automatically infer the programming language of the codebase and parse all files in the codebase.</Note>
 
-<Tip>The initial parse may take a few minutes for large codebases. This pre-computation enables constant-time operations afterward. [Learn more here.](/introduction/how-it-works)</Tip>
+<Note>
+  This will automatically infer the programming language of the codebase and
+  parse all files in the codebase.
+</Note>
+
+<Tip>
+  The initial parse may take a few minutes for large codebases. This
+  pre-computation enables constant-time operations afterward. [Learn more
+  here.](/introduction/how-it-works)
+</Tip>
+
+## Remote Repositories
+
+To fetch and parse a repository directly from GitHub, use the `fetch_codebase` function.
+
+```python
+import codegen
+
+# Fetch and parse a repository (defaults to /tmp/codegen/{repo_name})
+codebase = codegen.fetch_codebase('fastapi/fastapi')
+
+# Customize temp directory, clone depth, or specific commit
+codebase = codegen.fetch_codebase(
+    'fastapi/fastapi',
+    tmp_dir='/custom/temp/dir',  # Optional: custom temp directory
+    shallow=False,  # Optional: full clone instead of shallow
+    commit_hash='fe513719ea98abade167d8a89e92f600d9d8f0e5'  # Optional: specific commit
+)
+```
+
+<Note>
+  Remote repositories are cloned to the `/tmp/codegen/{repo_name}` directory by
+  default. The clone is shallow by default for better performance.
+</Note>
 
 ## Supported Languages
 
 Codegen currently supports:
+
 - [Python](/api-reference/python)
 - [TypeScript/JavaScript](/api-reference/javascript)
 - [React/JSX](/building-with-codegen/react-and-jsx)

src/graph_sitter/fetch_codebase.py

@@ -0,0 +1,75 @@
+import logging
+import os
+
+from codegen_git.repo_operator.local_repo_operator import LocalRepoOperator
+from graph_sitter.codebase.config import DefaultConfig, ProjectConfig
+from graph_sitter.core.codebase import Codebase
+from graph_sitter.utils import determine_project_language
+
+logger = logging.getLogger(__name__)
+
+DEFAULT_CODEGEN_DIR = "/tmp/codegen"
+
+
+def fetch_codebase(repo_name: str, *, tmp_dir: str | None = None, shallow: bool = True, commit_hash: str | None = None) -> Codebase:
+    """Fetches a codebase from GitHub and returns a Codebase instance.
+
+    Args:
+        repo_name (str): The name of the repository in format "owner/repo"
+        tmp_dir (Optional[str]): The directory to clone the repo into. Defaults to /tmp/codegen
+        shallow (bool): Whether to do a shallow clone. Defaults to True
+        commit_hash (Optional[str]): The specific commit hash to clone. Defaults to HEAD
+    Returns:
+        Codebase: A Codebase instance initialized with the cloned repository
+    Example:
+        ```python
+        import graph_sitter
+        import logging
+        # Enable logging to see progress
+        logging.basicConfig(level=logging.INFO)
+        # Clone a repository to default location (/tmp/codegen)
+        codebase = graph_sitter.fetch_codebase('facebook/react')
+        # Or specify a custom directory
+        codebase = graph_sitter.fetch_codebase('facebook/react', tmp_dir='~/my_repos')
+        # Or clone a specific commit
+        codebase = graph_sitter.fetch_codebase('facebook/react', commit_hash='abc123')
+        ```
+    """
+    logger.info(f"Fetching codebase for {repo_name}")
+
+    # Parse repo name
+    if "/" not in repo_name:
+        raise ValueError("repo_name must be in format 'owner/repo'")
+    owner, repo = repo_name.split("/")
+
+    # Setup temp directory
+    if tmp_dir is None:
+        tmp_dir = DEFAULT_CODEGEN_DIR
+    os.makedirs(tmp_dir, exist_ok=True)
+    logger.info(f"Using directory: {tmp_dir}")
+
+    # Setup repo path and URL
+    repo_path = os.path.join(tmp_dir, repo)
+    repo_url = f"https://github.com/{repo_name}.git"
+    logger.info(f"Will clone {repo_url} to {repo_path}")
+
+    try:
+        # Use LocalRepoOperator to fetch the repository
+        logger.info("Cloning repository...")
+        repo_operator = LocalRepoOperator.create_from_commit(
+            repo_path=repo_path,
+            default_branch="main",  # We'll get the actual default branch after clone
+            commit=commit_hash or "HEAD",
+            url=repo_url,
+        )
+        logger.info("Clone completed successfully")
+
+        # Initialize and return codebase with proper context
+        logger.info("Initializing Codebase...")
+        project = ProjectConfig(repo_operator=repo_operator, programming_language=determine_project_language(repo_path))
+        codebase = Codebase(projects=[project], config=DefaultConfig)
+        logger.info("Codebase initialization complete")
+        return codebase
+    except Exception as e:
+        logger.error(f"Failed to initialize codebase: {e}")
+        raise