"""FormInput — a Provider that collects structured input from the user.

Define a Pydantic model for the data you need, and ``FormInput``
generates a form UI. The user fills it out, the submission is
validated, and an optional callback processes the result.

Requires ``fastmcp[apps]`` (prefab-ui).

Usage::

    from pydantic import BaseModel
    from fastmcp import FastMCP
    from fastmcp.apps.form import FormInput

    class ShippingAddress(BaseModel):
        street: str
        city: str
        state: str
        zip_code: str

    mcp = FastMCP("My Server")
    mcp.add_provider(FormInput(model=ShippingAddress))
"""

from __future__ import annotations

import json
from collections.abc import Callable
from typing import Any

from packaging.version import InvalidVersion, Version

try:
    import prefab_ui
    from prefab_ui.actions import SetState
    from prefab_ui.actions.mcp import CallTool, SendMessage
    from prefab_ui.app import PrefabApp
    from prefab_ui.components import (
        H3,
        Card,
        CardContent,
        CardFooter,
        CardHeader,
        Column,
        Form,
        Muted,
    )
    from prefab_ui.components.control_flow import If
    from prefab_ui.rx import RESULT, STATE
except ImportError as _exc:
    raise ImportError(
        "FormInput requires prefab-ui. Install with: pip install 'fastmcp[apps]'"
    ) from _exc

# `defaults` kwarg on Form.from_model was added in prefab-ui 0.19.1. Gate on
# version so that older prefab-ui keeps working — `default` silently no-ops.
try:
    _FORM_SUPPORTS_DEFAULTS = Version(prefab_ui.__version__) >= Version("0.19.1")
except InvalidVersion:
    _FORM_SUPPORTS_DEFAULTS = False

import pydantic

from fastmcp.apps.app import FastMCPApp


def _backfill_boolean_defaults(
    model: type[pydantic.BaseModel],
    data: dict[str, Any],
) -> dict[str, Any]:
    """Fill in missing boolean fields with their model defaults.

    HTML checkboxes omit the field entirely when unchecked, so the
    submitted data dict won't contain a key for ``False`` booleans.
    This backfills those missing keys so Pydantic validation succeeds.
    """
    for name, field_info in model.model_fields.items():
        if name in data:
            continue
        if field_info.annotation is bool:
            if field_info.default is not pydantic.fields.PydanticUndefined:
                data[name] = field_info.default
            else:
                data[name] = False
    return data


class FormInput(FastMCPApp):
    """A Provider that collects structured input via a Pydantic model.

    Define a model for the data you need, and ``FormInput`` generates
    a form from it using ``Form.from_model()``. Field types, labels,
    descriptions, and validation are all derived from the model.

    Optionally provide an ``on_submit`` callback to process the
    validated data. The callback receives a model instance and returns
    a string that goes back to the LLM. Without a callback, the
    validated JSON is sent directly.

    Example::

        from pydantic import BaseModel
        from fastmcp import FastMCP
        from fastmcp.apps.form import FormInput

        class Contact(BaseModel):
            name: str
            email: str

        mcp = FastMCP("My Server")
        mcp.add_provider(FormInput(model=Contact))

    With a callback::

        def save_contact(contact: Contact) -> str:
            db.insert(contact.model_dump())
            return f"Saved {contact.name}"

        mcp.add_provider(FormInput(model=Contact, on_submit=save_contact))
    """

    def __init__(
        self,
        model: type[pydantic.BaseModel],
        *,
        name: str | None = None,
        title: str | None = None,
        submit_text: str = "Submit",
        tool_name: str | None = None,
        on_submit: Callable[..., str] | None = None,
        send_message: bool = False,
    ) -> None:
        app_name = name or model.__name__
        super().__init__(app_name)
        self._model = model
        self._title = title or model.__name__
        self._submit_text = submit_text
        self._tool_name = tool_name or f"collect_{model.__name__.lower()}"
        self._on_submit = on_submit
        self._send_message = send_message
        self._register_tools()

    def __repr__(self) -> str:
        return f"FormInput({self._model.__name__!r})"

    def _register_tools(self) -> None:
        provider = self
        model = self._model

        @self.tool()
        def submit_form(data: dict[str, Any] | None = None) -> str:
            """Validate and process form submission."""
            if data is None:
                data = {}
            data = _backfill_boolean_defaults(model, data)
            validated = model.model_validate(data)
            if provider._on_submit is not None:
                return provider._on_submit(validated)
            return json.dumps(validated.model_dump(mode="json"))

        @self.ui(
            name=provider._tool_name,
            description=(
                f"Collect {model.__name__} information from the user via a form. "
                f"Call this tool when you need the user to provide "
                f"{model.__name__} data. The user will see a validated form. "
                f"After calling this tool, STOP and wait for the user to submit."
            ),
        )
        def collect_input(
            prompt: str,
            title: str | None = None,
            submit_text: str | None = None,
            default: dict[str, Any] | None = None,
        ) -> PrefabApp:
            """Collect structured input from the user.

            Args:
                prompt: Tell the user what you need and why.
                title: Optional heading for the form card.
                submit_text: Optional label for the submit button.
                default: Optional suggested response — a partial dict of form
                    field values keyed by field name. The form renders with
                    those values pre-filled so the user can confirm or edit
                    rather than start from a blank form. Use this when you
                    already know (or can infer) what the answer should be.
                    Requires prefab-ui>=0.19.1; silently ignored on older
                    versions.
            """
            _title = title or provider._title
            _submit = submit_text or provider._submit_text

            with Card(css_class="max-w-lg mx-auto") as view:
                with CardHeader():
                    H3(_title)

                with CardContent(), Column(gap=4):
                    Muted(prompt)

                    on_success_actions: list[Any] = [
                        SetState("submitted", True),
                    ]
                    if provider._send_message:
                        on_success_actions.insert(
                            0,
                            SendMessage(RESULT),
                        )

                    from_model_kwargs: dict[str, Any] = {
                        "submit_label": _submit,
                        "on_submit": [
                            CallTool(
                                "submit_form",
                                on_success=on_success_actions,
                            ),
                        ],
                    }
                    if default and _FORM_SUPPORTS_DEFAULTS:
                        from_model_kwargs["defaults"] = default

                    Form.from_model(model, **from_model_kwargs)

                with CardFooter(), If(STATE.submitted):
                    Muted("Submitted.")

            return PrefabApp(
                view=view,
                state={"submitted": False},
            )
