use std::rc::Rc;

use crate::{
    controls::{
        BuiltControlData, ControlBuilder, ControlData, FieldFn, ParseFn, UnparseFn, ValidationFn,
        VanityControlBuilder, VanityControlData,
    },
    styles::FormStyle,
};
use leptos::{
    create_rw_signal, create_signal, IntoSignal, IntoView, RwSignal, SignalGet, SignalSet,
    SignalUpdate, View,
};

pub struct Validator<FD: FormData> {
    validations: Vec<Rc<dyn ValidationFn<FD>>>,
}

impl<FD: FormData> Validator<FD> {
    pub fn validate(&self, form_data: &FD) -> Result<(), String> {
        for v in self.validations.iter() {
            (*v)(form_data)?;
        }
        Ok(())
    }
}

/// A constructed form object.
///
/// With this, you can render the form, get the form data, or get
/// a validator for the data.
pub struct Form<FD: FormData> {
    pub fd: RwSignal<FD>,
    validations: Vec<Rc<dyn ValidationFn<FD>>>,
    view: View,
}

impl<FD: FormData> Form<FD> {
    pub fn validator(self) -> Validator<FD> {
        Validator {
            validations: self.validations,
        }
    }

    pub fn validate(&self, form_data: &FD) -> Result<(), String> {
        for v in self.validations.iter() {
            (*v)(form_data)?;
        }
        Ok(())
    }

    pub fn view(&self) -> View {
        self.view.clone()
    }

    pub fn to_parts(self) -> (RwSignal<FD>, Validator<FD>, View) {
        (
            self.fd,
            Validator {
                validations: self.validations,
            },
            self.view,
        )
    }
}

impl<FD: FormData> IntoView for Form<FD> {
    fn into_view(self) -> View {
        self.view()
    }
}

/// A version of the [`FormBuilder`] that contains all the data
/// needed for full building of a [`Form`].
struct FullFormBuilder<FD: FormData, FS: FormStyle> {
    fd: RwSignal<FD>,
    fs: FS,
    validations: Vec<Rc<dyn ValidationFn<FD>>>,
    views: Vec<View>,
}
/// The internal type for building forms
///
/// This allows us to build either the full form
/// with views, validation and data. Or we can just
/// build the validation functions.
///
/// This is useful in the context of a server that
/// cannot or should not render the form. You can
/// still get all the validation functions from the
/// form data.
enum FormBuilderInner<FD: FormData, FS: FormStyle> {
    /// For building the form with views
    FullBuilder(FullFormBuilder<FD, FS>),
    /// For building only the validations for the form
    ValidationBuilder {
        validations: Vec<Rc<dyn ValidationFn<FD>>>,
    },
}

pub struct FormBuilder<FD: FormData, FS: FormStyle> {
    inner: FormBuilderInner<FD, FS>,
}

impl<FD: FormData, FS: FormStyle> FormBuilder<FD, FS> {
    // TODO: remove the Default trait bound and bind it to this function only
    fn new_full_builder(form_style: FS) -> FormBuilder<FD, FS> {
        let fd = create_rw_signal(FD::default());
        FormBuilder {
            inner: FormBuilderInner::FullBuilder(FullFormBuilder {
                fd,
                fs: form_style,
                validations: Vec::new(),
                views: Vec::new(),
            }),
        }
    }

    fn new_full_builder_with(starting_data: FD, form_style: FS) -> FormBuilder<FD, FS> {
        let fd = create_rw_signal(starting_data);
        FormBuilder {
            inner: FormBuilderInner::FullBuilder(FullFormBuilder {
                fd,
                fs: form_style,
                validations: Vec::new(),
                views: Vec::new(),
            }),
        }
    }

    fn new_validation_builder() -> FormBuilder<FD, FS> {
        FormBuilder {
            inner: FormBuilderInner::ValidationBuilder {
                validations: Vec::new(),
            },
        }
    }

    pub(crate) fn new_vanity<C: VanityControlData + Default>(
        mut self,
        builder: impl Fn(VanityControlBuilder<FS, C>) -> VanityControlBuilder<FS, C>,
    ) -> Self {
        let vanity_builder = VanityControlBuilder::new(C::default());
        let control = builder(vanity_builder);
        self.add_vanity(control);
        self
    }

    pub(crate) fn new_control<C: ControlData + Default, FDT: 'static>(
        mut self,
        builder: impl Fn(ControlBuilder<FD, FS, C, FDT>) -> ControlBuilder<FD, FS, C, FDT>,
    ) -> Self {
        let control_builder = ControlBuilder::new(C::default());
        let control = builder(control_builder);
        self.add_control(control);
        self
    }

    fn add_vanity<C: VanityControlData>(&mut self, vanity_control: VanityControlBuilder<FS, C>) {
        let builder = match &mut self.inner {
            FormBuilderInner::FullBuilder(fb) => fb,
            FormBuilderInner::ValidationBuilder { validations: _ } => return,
        };

        let render_data = vanity_control.build();
        let view = VanityControlData::build_control(&builder.fs, render_data);
        builder.views.push(view);
    }

    fn add_control<C: ControlData, FDT: 'static>(
        &mut self,
        control: ControlBuilder<FD, FS, C, FDT>,
    ) {
        let BuiltControlData {
            render_data,
            field_fn,
            parse_fn,
            unparse_fn,
            validation_fn,
        } = match control.build() {
            Ok(c) => c,
            Err(e) => panic!("Invalid Component: {}", e),
        };

        let builder = match &mut self.inner {
            FormBuilderInner::FullBuilder(fb) => fb,
            FormBuilderInner::ValidationBuilder {
                ref mut validations,
            } => {
                if let Some(validation_fn) = validation_fn {
                    validations.push(validation_fn);
                }
                return;
            }
        };
        if let Some(ref validation_fn) = validation_fn {
            builder.validations.push(validation_fn.clone());
        }

        let view = Self::build_control_view(
            builder,
            field_fn,
            unparse_fn,
            parse_fn,
            validation_fn,
            render_data,
        );

        builder.views.push(view);
    }

    fn build_control_view<C: ControlData, FDT: 'static>(
        builder: &FullFormBuilder<FD, FS>,
        field_fn: Rc<dyn FieldFn<FD, FDT>>,
        unparse_fn: Box<dyn UnparseFn<<C as ControlData>::ReturnType, FDT>>,
        parse_fn: Box<dyn ParseFn<<C as ControlData>::ReturnType, FDT>>,
        validation_fn: Option<Rc<dyn ValidationFn<FD>>>,
        render_data: crate::controls::ControlRenderData<FS, C>,
    ) -> View {
        let (validation_signal, validation_signal_set) = create_signal(Ok(()));
        // TODO: The on-submit triggering a validation could be done here with a create_effect
        let field_fn2 = field_fn.clone();
        let fd_getter = builder.fd.read_only();
        let value_getter = move || {
            // TODO: ideally, this should not be borrowed. If we get a clone when we call `.get` we should pass in the clone, not borrow this clone
            let mut fd = fd_getter.get();
            let field = field_fn2(&mut fd);
            (unparse_fn)(field)
        };
        let value_getter = value_getter.into_signal();

        let fd = builder.fd.clone();
        let value_setter = move |value| {
            // TODO: also do this on a submit somehow
            let parsed = match parse_fn(value) {
                Ok(p) => p,
                Err(e) => {
                    validation_signal_set.set(Err(e));
                    return;
                }
            };

            // parse succeeded, update value and validate
            let field_fn = field_fn.clone(); // move
            let validation_fn = validation_fn.clone(); // move

            // TODO: change this to a get then set, so that if the validation fails,
            //       The value is not actually updated
            fd.update(move |fd| {
                let field = field_fn(fd);
                *field = parsed;

                if let Some(ref validation_fn) = validation_fn {
                    let validation_result = (validation_fn)(fd);
                    validation_signal_set.set(validation_result);
                }
            });
        };
        let value_setter = Box::new(value_setter);
        // TODO: add a signal that triggers on submit to refresh the validation on_submit

        C::build_control(
            &builder.fs,
            render_data,
            value_getter,
            value_setter,
            validation_signal.into(),
        )
    }

    fn build(self) -> Option<Form<FD>> {
        let builder = match self.inner {
            FormBuilderInner::FullBuilder(fb) => fb,
            FormBuilderInner::ValidationBuilder { validations: _ } => return None,
        };
        let view = builder.fs.form_frame(builder.views.into_view());

        Some(Form {
            fd: builder.fd,
            validations: builder.validations,
            view,
        })
    }

    fn validator(self) -> Validator<FD> {
        let validations = match self.inner {
            FormBuilderInner::FullBuilder(fb) => fb.validations,
            FormBuilderInner::ValidationBuilder { validations } => validations,
        };
        Validator { validations }
    }
}

/// A trait allowing a form to be built around its containing data.
///
/// This trait defines a function that can be used to build all the data needed
/// to physically lay out a form, and how that data should be parsed and validated.
pub trait FormData: Default + Clone + 'static {
    type Style: FormStyle;

    /// Defines how the form should be layed out and how the data should be parsed and validated.
    ///
    /// To construct a [`From`] object, use one of the [`get_form`()] methods.
    ///
    /// Uses the given form builder to specify what fields should be present
    /// in the form, what properties those fields should have, and how that
    /// data should be parsed and checked.
    fn build_form(fb: FormBuilder<Self, Self::Style>) -> FormBuilder<Self, Self::Style>;

    /// Constructs a [`Form`] for this FormData type.
    ///
    /// The [`Form`] provides the way to render the form.
    fn get_form(style: Self::Style) -> Form<Self> {
        let builder = FormBuilder::new_full_builder(style);
        let builder = Self::build_form(builder);
        builder.build().expect("builder should be full builder")
    }

    fn get_form_with_starting_data(self, style: Self::Style) -> Form<Self> {
        let builder = FormBuilder::new_full_builder_with(self, style);
        let builder = Self::build_form(builder);
        builder.build().expect("builder should be full builder")
    }

    fn get_validator() -> Validator<Self> {
        let builder = FormBuilder::new_validation_builder();
        let builder = Self::build_form(builder);
        builder.validator()
    }
}