"""Local backend process skeleton (U-007, extended in U-022): pure stdlib
`http.server`, no third-party deps (05 §5.7) -- this process is also where
the Graph Engine scheduler will live later (05 §5.4.1), but that's a
different Unit.

MVP scope: process start/stop, `c_pick_folder` (03-C §3.-1, now all three
platforms -- U-007 shipped macOS only via `osascript`; U-022 adds Windows
via a `powershell` FolderBrowserDialog script and Linux via `zenity`/
`kdialog`, whichever is installed), `c_project_create` (03-C §3.0, wired to
the U-002 `project_scaffold.create_project()` function that had no HTTP
route until now) for `v_project_setup`'s submit flow, and serving the U-008
frontend shell as static files (no build step, 05 §5.7: whitelisted by exact
path, not a generic directory walker, so there's no path-traversal surface
to reason about).
"""

import json
import os
import platform
import subprocess
import threading
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer

from src import paths, project_scaffold, schema

_FRONTEND_DIR = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "frontend")

# U-008: exact-path whitelist, not a generic static-file server -- the
# frontend is 3 fixed files until PH3 adds real pages.
_STATIC_FILES = {
    "/": ("index.html", "text/html; charset=utf-8"),
    "/index.html": ("index.html", "text/html; charset=utf-8"),
    "/app.js": ("app.js", "text/javascript; charset=utf-8"),
    "/style.css": ("style.css", "text/css; charset=utf-8"),
}


class DialogUnavailableError(Exception):
    """DIALOG_UNAVAILABLE -- 03-C §3.-1: no native-dialog capability here."""


def pick_folder():
    """c_pick_folder (03-C §3.-1), all three platforms. Returns
    {"selected_path": str} on success, {"selected_path": None} on user
    cancel (not an error). Raises DialogUnavailableError if the platform's
    native dialog tool itself fails or isn't installed."""
    system = platform.system()
    if system == "Darwin":
        return _pick_folder_macos()
    if system == "Windows":
        return _pick_folder_windows()
    return _pick_folder_linux()


def _pick_folder_macos():
    script = 'POSIX path of (choose folder with prompt "Select a graphlemon project folder")'
    result = subprocess.run(["osascript", "-e", script], capture_output=True, text=True)
    if result.returncode != 0:
        if "User canceled" in result.stderr or "(-128)" in result.stderr:
            return {"selected_path": None}
        raise DialogUnavailableError(result.stderr.strip())
    return {"selected_path": result.stdout.strip()}


def _pick_folder_windows():
    # .NET FolderBrowserDialog via a one-shot PowerShell script -- no
    # cancel-vs-error signal other than empty stdout on a clean exit.
    script = (
        "Add-Type -AssemblyName System.Windows.Forms; "
        "$f = New-Object System.Windows.Forms.FolderBrowserDialog; "
        "if ($f.ShowDialog() -eq [System.Windows.Forms.DialogResult]::OK) { Write-Output $f.SelectedPath }"
    )
    try:
        result = subprocess.run(
            ["powershell", "-NoProfile", "-NonInteractive", "-Command", script],
            capture_output=True, text=True,
        )
    except FileNotFoundError as e:
        raise DialogUnavailableError(str(e))
    if result.returncode != 0:
        raise DialogUnavailableError(result.stderr.strip())
    return {"selected_path": result.stdout.strip() or None}


def _pick_folder_linux():
    # zenity (GNOME) and kdialog (KDE) are the two dialogs actually present
    # across mainstream Linux desktops; try whichever exists. Both exit
    # non-zero on user cancel, indistinguishable here from "no folder
    # chosen" -- both cases map to selected_path=None, not an error.
    for cmd in (
        ["zenity", "--file-selection", "--directory"],
        ["kdialog", "--getexistingdirectory", os.path.expanduser("~")],
    ):
        try:
            result = subprocess.run(cmd, capture_output=True, text=True)
        except FileNotFoundError:
            continue
        if result.returncode != 0:
            return {"selected_path": None}
        return {"selected_path": result.stdout.strip()}
    raise DialogUnavailableError("neither zenity nor kdialog is installed")


class _Handler(BaseHTTPRequestHandler):
    def do_GET(self):
        entry = _STATIC_FILES.get(self.path)
        if entry is None:
            self._send_json(404, {"error": "NOT_FOUND"})
            return
        filename, content_type = entry
        with open(os.path.join(_FRONTEND_DIR, filename), "rb") as f:
            body = f.read()
        self.send_response(200)
        self.send_header("Content-Type", content_type)
        self.send_header("Content-Length", str(len(body)))
        self.end_headers()
        self.wfile.write(body)

    def do_POST(self):
        if self.path == "/api/system/pick-folder":
            self._handle_pick_folder()
        elif self.path == "/api/projects":
            self._handle_project_create()
        else:
            self._send_json(404, {"error": "NOT_FOUND"})

    def _handle_pick_folder(self):
        try:
            self._send_json(200, pick_folder())
        except DialogUnavailableError as e:
            self._send_json(422, {"error": "DIALOG_UNAVAILABLE", "detail": str(e)})

    def _handle_project_create(self):
        length = int(self.headers.get("Content-Length", 0))
        try:
            payload = json.loads(self.rfile.read(length) or b"{}")
        except json.JSONDecodeError:
            self._send_json(400, {"error": "INVALID_INPUT", "detail": "body is not valid JSON"})
            return
        target_folder_path = payload.get("target_folder_path")
        if not target_folder_path:
            self._send_json(400, {"error": "INVALID_INPUT", "detail": "target_folder_path is required"})
            return
        try:
            with self.server.conn_lock:
                result = project_scaffold.create_project(
                    self.server.conn,
                    target_folder_path,
                    name=payload.get("name"),
                    init_git_if_missing=bool(payload.get("init_git_if_missing", False)),
                )
        except project_scaffold.PathNotFoundError as e:
            self._send_json(404, {"error": "PATH_NOT_FOUND", "detail": str(e)})
        except project_scaffold.PathNotWritableError as e:
            self._send_json(403, {"error": "PATH_NOT_WRITABLE", "detail": str(e)})
        except project_scaffold.GitInitDeclinedError as e:
            self._send_json(409, {"error": "GIT_INIT_DECLINED", "detail": str(e)})
        else:
            self._send_json(200, result)

    def _send_json(self, status, obj):
        body = json.dumps(obj).encode("utf-8")
        self.send_response(status)
        self.send_header("Content-Type", "application/json")
        self.send_header("Content-Length", str(len(body)))
        self.end_headers()
        self.wfile.write(body)

    def log_message(self, format, *args):
        pass  # quiets test output; real request logging is a later Unit's concern


def _ensure_schema(conn):
    exists = conn.execute(
        "SELECT 1 FROM sqlite_master WHERE type = 'table' AND name = 'project'"
    ).fetchone()
    if exists is None:
        schema.create_schema(conn)


class _Server(ThreadingHTTPServer):
    def server_close(self):
        super().server_close()
        self.conn.close()


def create_server(host="127.0.0.1", port=0, db_path=None):
    """port=0 lets the OS assign a free port -- avoids collisions in tests
    and lets multiple graphlemon instances run side by side if ever needed.

    db_path defaults to paths.db_path() (U-003's platform_home, so it never
    lives inside a target project's own repo); tests pass ":memory:" or a
    tempfile so runs don't touch the real developer's ~/.graphlemon/."""
    conn = schema.connect(db_path if db_path is not None else paths.db_path(), check_same_thread=False)
    _ensure_schema(conn)
    server = _Server((host, port), _Handler)
    server.conn = conn
    server.conn_lock = threading.Lock()
    return server