"""
dev.py
======
This script acts as a local development orchestrator.
It performs three main actions sequentially:
1. Executes `roi.py` to fetch the latest market data and generate the frontend JSON files.
2. Executes the `bun run build` command to compile the TypeScript frontend into browser-ready JavaScript.
3. Spawns a local Python HTTP server pointing to the `www/` directory so you can view the changes in your browser.
"""

import os           # Required for changing working directories and checking paths.
import subprocess   # Required for spawning external processes (like 'bun' and other python scripts).
import sys          # Required to grab the current Python executable path.
import http.server  # Required to run the local web server.
import socketserver # Required to bind the HTTP handler to a specific port.

def main() -> None:
    """
    Main execution function for the local development server orchestrator.
    """
    # -------------------------------------------------------------------------
    # STEP 1: GENERATE BACKEND DATA
    # -------------------------------------------------------------------------
    # We first need to ensure that the JSON data files that the frontend consumes
    # actually exist and are up to date. We do this by calling the existing `roi.py` script.
    print(">>> [1/3] Running roi.py to generate updated JSON data...")
    try:
        # sys.executable ensures we use the exact same Python interpreter currently running this script.
        # check=True ensures that if roi.py crashes, this script will also halt and raise a CalledProcessError.
        subprocess.run([sys.executable, "roi.py"], check=True)
    except subprocess.CalledProcessError as e:
        # If roi.py fails, we catch the error, print a helpful message, and exit the program gracefully
        # instead of spitting out a massive unhandled stack trace.
        sys.exit(f"!!! Error: Failed to execute roi.py. Process exited with code {e.returncode}")

    # -------------------------------------------------------------------------
    # STEP 2: BUILD THE FRONTEND
    # -------------------------------------------------------------------------
    # The frontend is written in TypeScript (inside the ts/ folder). Browsers cannot natively
    # execute TypeScript in the way this project is structured. As outlined in `package.json`,
    # 'bun' is used as the bundler to compile these files into the 'www/' directory.
    print(">>> [2/3] Building the TypeScript frontend using Bun...")
    try:
        # We invoke the 'build' script defined in package.json.
        # This corresponds to: "bun build ts/buy.ts ... --outdir www --target browser --sourcemap=external"
        subprocess.run(["bun", "run", "build"], check=True)
    except FileNotFoundError:
        # If 'bun' is not installed or not in the system's PATH, a FileNotFoundError is raised.
        # We must alert the user that this system dependency is missing.
        sys.exit("!!! Error: 'bun' command not found. Please ensure Bun is installed (https://bun.sh/) and in your PATH.")
    except subprocess.CalledProcessError as e:
        # Catch compilation errors in the TypeScript code itself.
        sys.exit(f"!!! Error: Frontend build failed. Bun exited with code {e.returncode}")

    # -------------------------------------------------------------------------
    # STEP 3: SERVE THE FRONTEND LOCALLY
    # -------------------------------------------------------------------------
    # We must serve the compiled files via an HTTP server because opening local HTML files
    # directly (via file:// protocol) often causes CORS (Cross-Origin Resource Sharing) errors
    # when the JavaScript attempts to fetch the local JSON files generated in Step 1.
    print(">>> [3/3] Starting local development server...")
    
    # Define the port we want to host the site on. 8000 is a standard web development port.
    PORT = 8000
    # Define the directory we want to serve. The bun build step outputs to 'www'.
    WEB_DIR = "www"

    # We must ensure the 'www' directory exists before attempting to switch into it.
    if not os.path.isdir(WEB_DIR):
        sys.exit(f"!!! Error: Directory '{WEB_DIR}' does not exist. The build step may have failed silently.")

    # Change the current working directory to 'www'. This ensures the HTTP server roots itself here,
    # making the index.html inside 'www' the default page, and allowing relative path resolutions to work.
    os.chdir(WEB_DIR)

    # http.server.SimpleHTTPRequestHandler is a built-in handler that serves files from the current directory.
    Handler = http.server.SimpleHTTPRequestHandler

    # socketserver.TCPServer creates a TCP server that listens on the specified port and binds our handler to it.
    # We use a 'with' block to ensure the network socket is properly released and cleaned up when the server stops.
    with socketserver.TCPServer(("", PORT), Handler) as httpd:
        print(f">>> Serving at http://localhost:{PORT}")
        print(">>> Press Ctrl+C to stop the server.")
        try:
            # serve_forever() puts the script into an infinite loop, constantly listening for and fulfilling HTTP requests.
            httpd.serve_forever()
        except KeyboardInterrupt:
            # Catch the Ctrl+C command from the user to gracefully shut down the server.
            print("\n>>> Shutting down development server gracefully. Goodbye!")

if __name__ == '__main__':
    # This standard Python idiom ensures that the main() function is only called if this script
    # is executed directly from the command line (e.g., `python dev.py`), rather than imported as a module.
    main()