//! Generator for [`Register`].
//! The entry point is [`reg_type_def`].

use heck::{ToShoutySnekCase, ToSnakeCase};
use itertools::Itertools;
use proc_macro2::{Ident, TokenStream};
use quote::quote;

use crate::types::{DataType, Field, MultipleParams, Register};

use super::{
    util::{self, RustUxTypes},
    CodeGenError,
};

/// Generate underlying `T` and its implementation for `RegisterSpec`.
///
/// # Returns
/// tuple of
/// - code of `T` definition and its impls
/// - [`Ident`] of `T`
/// - [`Ident`] of `Ux`
///
/// # Cases
/// - `T` == `Ux` => [`reg_type_def_simple`]
/// - `T` is masked `Ux` => [`reg_type_def_masked`]
/// - `T` has 1+ fields => [`reg_type_def_with_field`]
pub(super) fn reg_type_def(
    reg: &Register,
    upper_camel_name: &Ident,
) -> Result<(TokenStream, Ident, Ident), CodeGenError> {
    Ok(match reg.elements.is_empty() {
        true => match reg.mask {
            Some(mask) => reg_type_def_masked(&reg.r#type, mask, upper_camel_name),
            None => reg_type_def_simple(&reg.r#type),
        },
        false => reg_type_def_with_field(&reg.r#type, &reg.elements, upper_camel_name)?,
    })
}

/// Where `T` == `Ux`.
///
/// No `T` def nor impl are required.
///
/// # Returns
/// same as [`reg_type_def`]
fn reg_type_def_simple(basetype: &DataType) -> (TokenStream, Ident, Ident) {
    let type_t_ux = {
        let x: RustUxTypes = basetype.into();
        x.to_rust_type_token()
    };

    let out = quote! {};
    (out, type_t_ux.clone(), type_t_ux)
}

/// Where `T` is masked `Ux`.
///
/// `T` is a one-length "tuple struct" `T(pub Ux)`.
/// `impl TryFrom<Ux> for T` and `impl From<T> for Ux` are included,
/// but without `impl T`.
///
/// # Returns
/// same as [`reg_type_def`]
fn reg_type_def_masked(
    basetype: &DataType,
    mask: u32,
    upper_camel_name: &Ident,
) -> (TokenStream, Ident, Ident) {
    let type_ux = {
        let x: RustUxTypes = basetype.into();
        x.to_rust_type_token()
    };

    let out = quote! {
        #[derive(Debug, Clone, Copy, Default)]
        pub struct #upper_camel_name(pub #type_ux);
        impl TryFrom<#type_ux> for #upper_camel_name {
            type Error = DataConversionError<#type_ux, Self>;

            fn try_from(value: #type_ux) -> Result<Self, Self::Error> {
                let mask = #mask;
                Ok(SlId(value & mask))
            }
        }
        impl From<#upper_camel_name> for #type_ux {
            fn from(value: #upper_camel_name) -> Self {
                value.0
            }
        }

    };

    (out, upper_camel_name.clone(), type_ux)
}

/// Where `T` has fields.
///
/// `T` is a "struct struct" which has a single field `inner: Ux`.
/// Also, a bunch of "mask" constants and getter/setter are defined for each fields.
///
/// # Returns
/// same as [`reg_type_def`]
///
/// # Field generation
/// This function calls [`generate_field`] for each [`Field`] entries to generate field definitions.
/// See the doc of `generate_field` for more detail
fn reg_type_def_with_field(
    basetype: &DataType,
    fields: &[Field],
    upper_camel_name: &Ident,
) -> Result<(TokenStream, Ident, Ident), CodeGenError> {
    let type_ux = {
        let x: RustUxTypes = basetype.into();
        x.to_rust_type_token()
    };

    let (code_masks, code_getters, code_setters): (
        Vec<TokenStream>,
        Vec<TokenStream>,
        Vec<TokenStream>,
    ) = fields
        .iter()
        .map(|field| generate_field(field, basetype))
        .process_results(|iter| iter.multiunzip())?;

    let out = quote! {
        #(#code_masks)*

        #[derive(Debug, Clone, Copy, Default)]
        pub struct #upper_camel_name {
            inner: #type_ux,
        }

        impl GtyDelayBank123 {
            #(#code_getters)*

            #(#code_setters)*
        }
        impl TryFrom<#type_ux> for #upper_camel_name {
            type Error = DataConversionError<#type_ux, Self>;

            fn try_from(value: #type_ux) -> Result<Self, Self::Error> {
                Ok(Self { inner: value })
            }
        }
        impl From<GtyDelayBank123> for u32 {
            fn from(value: #upper_camel_name) -> Self {
                value.inner
            }
        }
    };

    Ok((out, upper_camel_name.clone(), type_ux))
}

/// Generate code for each field, which consists of these three.
/// 1. mask definition
/// 2. getter method
/// 3. setter method
///
/// # Cases
/// This function is separated into two cases.
/// See each function docs for more detail.
///
/// 1. field is not "multiple" => [`generate_single_field`]
/// 2. field is "multiple" => [`generate_multiple_field`]
fn generate_field(
    field: &Field,
    basetype: &DataType,
) -> Result<(TokenStream, TokenStream, TokenStream), CodeGenError> {
    let mask_name = util::parse_to_ident(&format!("{}_MASK", field.name.TO_SHOUTY_SNEK_CASE()))?;
    let base_type = util::RustUxTypes::from(basetype).to_rust_type_token();

    let snake_case_name = util::parse_to_ident(&field.name.to_snake_case())?;
    let field_type = util::RustUxTypes::from_mask(field.mask);

    let (code_mask, code_getter, code_setter) = match &field.multiple {
        Some(multiple_params) => generate_multiple_field(
            mask_name,
            base_type,
            field.mask,
            field_type,
            snake_case_name,
            multiple_params,
        ),
        None => generate_single_field(
            mask_name,
            base_type,
            field.mask,
            field_type,
            snake_case_name,
        ),
    };

    Ok((code_mask, code_getter, code_setter))
}

/// Generate "single" field definition (mask, getter, setter).
///
/// # Cases
/// This function is separated into two cases.
///
/// - field is `bool` => [`generate_single_bool_field`]
/// - field is `u8`/`u16`/`u32` => [`generate_single_ux_field`]
///
/// For the details of types of register/field, see [`DataType`].
/// Note that in both cases, mask definitions are the same.
fn generate_single_field(
    mask_name: Ident,
    base_type: Ident,
    mask_val: u32,
    field_type: RustUxTypes,
    snake_case_name: Ident,
) -> (TokenStream, TokenStream, TokenStream) {
    let mask_val = util::parse_to_literal(&format!("0x{:x}", mask_val)).unwrap();
    let code_mask = quote! {
        const #mask_name: #base_type = #mask_val;
    };
    let (code_getter, code_setter) = match field_type {
        RustUxTypes::Bool => generate_single_bool_field(mask_name, snake_case_name),
        RustUxTypes::U8 | RustUxTypes::U16 | RustUxTypes::U32 => {
            generate_single_ux_field(mask_name, base_type, snake_case_name, field_type)
        }
    };

    (code_mask, code_getter, code_setter)
}

/// Generate bool "single" field definition (getter, setter).
fn generate_single_bool_field(
    mask_name: Ident,
    snake_case_name: Ident,
) -> (TokenStream, TokenStream) {
    let setter_name = util::parse_to_ident(&format!("set_{}", snake_case_name)).unwrap();
    let code_getter = quote! {
        pub fn #snake_case_name(&self) -> bool {
            (self.inner & #mask_name) == #mask_name
        }
    };
    let code_setter = quote! {
        pub fn #setter_name(self, val: bool) -> Self {
            let mut inner = self.inner;
            if val {
                inner |= #mask_name
            } else {
                inner &= !#mask_name
            };
            Self { inner }
        }
    };
    (code_getter, code_setter)
}

/// Generate u8/u16/u32 "single" field definition (getter, setter).
fn generate_single_ux_field(
    mask_name: Ident,
    base_type: Ident,
    snake_case_name: Ident,
    field_type: RustUxTypes,
) -> (TokenStream, TokenStream) {
    let field_type = field_type.to_rust_type_token();
    let setter_name = util::parse_to_ident(&format!("set_{}", snake_case_name)).unwrap();

    let code_getter = quote! {
        pub fn #snake_case_name(&self) -> #field_type {
            const RIGHT_SHIFT: #base_type = #mask_name.trailing_zeros();
            ((self.inner & #mask_name) >> RIGHT_SHIFT)
                .try_into()
                .unwrap()
        }
    };
    let code_setter = quote! {
        pub fn #setter_name(&self, val: #field_type) -> Self {
            let update: #base_type = val & #mask_name;
            let mut inner = self.inner;
            inner &= !mask;
            inner |= update;
            Self { inner }
        }
    };
    (code_getter, code_setter)
}

/// Generate "multiple" field definition (mask, getter, setter).
///
/// # Cases
/// As "single" field cases, this function is separated into two cases;
///
/// - fields are `bool` => [`generate_multiple_bool_field`]
/// - fields are `u8`/`u16`/`u32` => todo
fn generate_multiple_field(
    mask_name: Ident,
    base_type: Ident,
    single_mask_val: u32,
    single_field_type: RustUxTypes,
    snake_case_name: Ident,
    multiple_params: &MultipleParams,
) -> (TokenStream, TokenStream, TokenStream) {
    let num_multiple = multiple_params.multiple;
    let id_num_multiple = util::parse_to_ident(&num_multiple.to_string()).unwrap();
    let id_field_type = single_field_type.to_rust_type_token();
    let masks: Vec<_> = (0..multiple_params.multiple)
        .map(|x| x * multiple_params.offset)
        .map(|offset| single_mask_val << offset)
        .map(|mask| util::parse_to_ident(&format!("0x{mask:x}")).unwrap())
        .collect();
    debug_assert_eq!(masks.len(), num_multiple.try_into().unwrap());
    let code_mask = quote! {
        const #mask_name: [#id_field_type; #id_num_multiple] = [#(#masks),*];
    };

    let (code_getter, code_setter) = match single_field_type {
        RustUxTypes::Bool => {
            generate_multiple_bool_field(mask_name, base_type, snake_case_name, masks.clone())
        }
        RustUxTypes::U8 | RustUxTypes::U16 | RustUxTypes::U32 => generate_multiple_ux_field(
            mask_name,
            base_type,
            snake_case_name,
            single_field_type,
            masks,
        ),
    };

    (code_mask, code_getter, code_setter)
}

/// Generate bool "multiple" field definition (getter, setter).
fn generate_multiple_bool_field(
    mask_name: Ident,
    base_type: Ident,
    snake_case_name: Ident,
    masks: Vec<Ident>,
) -> (TokenStream, TokenStream) {
    let num_multiple = masks.len();
    let elem_getter = masks.iter().enumerate().map(|(i, _mask)| {
        quote! {
            (self.inner & #mask_name[#i]) == #mask_name[#i]
        }
    });
    let code_getter = quote! {
        pub fn #snake_case_name(&self) -> [bool; #num_multiple] {
            [
                #(#elem_getter),*
            ]
        }
    };

    let setter_name = util::parse_to_ident(&format!("set_{}", snake_case_name)).unwrap();
    let code_setter = quote! {
        pub fn #setter_name(self, val: [bool; #num_multiple]) -> Self {
            let mask: #base_type = #mask_name.iter().sum();
            let update: #base_type = BANK121_GTY_CHANNEL_MASK
                .iter()
                .zip(val)
                .filter_map(|(mask, val)| val.then_some(mask))
                .sum();
            let mut inner = self.inner;
            inner &= !mask;
            inner |= update;
            Self { inner }
        }
    };

    (code_getter, code_setter)
}

/// Generate u8/u16/u32 "multiple" field definition (getter, setter).
fn generate_multiple_ux_field(
    mask_name: Ident,
    base_type: Ident,
    snake_case_name: Ident,
    single_field_type: RustUxTypes,
    masks: Vec<Ident>,
) -> (TokenStream, TokenStream) {
    let field_type = single_field_type.to_rust_type_token();
    let num_multiple = masks.len();
    let elem_getter = masks.iter().enumerate().map(|(i, _mask)| {
        quote! {
            ((self.inner & #mask_name[#i])
                >> (#mask_name[#i].trailing_zeros()))
            .try_into()
            .unwrap()
        }
    });
    let code_getter = quote! {
        pub fn #snake_case_name(&self) -> [#field_type; #num_multiple] {
            [
                #(#elem_getter),*
            ]
        }
    };

    let setter_name = util::parse_to_ident(&format!("set_{}", snake_case_name)).unwrap();
    let code_setter = quote! {
        pub fn #setter_name(&self, val: [#field_type; #num_multiple]) -> Self {
            let mask: #base_type = #mask_name.iter().sum();
            let update: #base_type = #mask_name
                .iter()
                .zip(val)
                .map(|(mask, val)| (#base_type::from(val)) << (mask.trailing_zeros()))
                .sum();
            let mut inner = self.inner;
            inner &= !mask;
            inner |= update;
            Self { inner }
        }
    };

    (code_getter, code_setter)
}