use core::convert::TryFrom;
use core::fmt;
use core::ops::Deref;
use lang_c::ast;
use lang_c::span::Node;
use std::collections::{HashMap, HashSet};
use std::hash::Hash;
use thiserror::Error;

use itertools::izip;

use crate::ir::*;
use crate::some_or;

/// TODO(document)
#[derive(Debug, PartialEq, Error)]
pub enum DtypeError {
    /// For uncommon error
    #[error("{message}")]
    Misc {
        /// TODO(document)
        message: String,
    },
}

/// TODO(document)
pub trait HasDtype {
    /// TODO(document)
    fn dtype(&self) -> Dtype;
}

#[derive(Default)]
struct BaseDtype {
    scalar: Option<ast::TypeSpecifier>,
    size_modifiers: Vec<ast::TypeSpecifier>,
    signed_option: Option<ast::TypeSpecifier>,
    typedef_name: Option<String>,
    struct_type: Option<ast::StructType>,
    is_const: bool,
    is_typedef: bool,
}

/// TODO(document)
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
pub enum Dtype {
    /// TODO(document)
    Unit {
        /// TODO(document)
        is_const: bool,
    },
    /// TODO(document)
    Int {
        /// TODO(document)
        width: usize,

        /// TODO(document)
        is_signed: bool,

        /// TODO(document)
        is_const: bool,
    },
    /// TODO(document)
    Float {
        /// TODO(document)
        width: usize,

        /// TODO(document)
        is_const: bool,
    },
    /// TODO(document)
    Pointer {
        /// TODO(document)
        inner: Box<Dtype>,

        /// TODO(document)
        is_const: bool,
    },
    /// TODO(document)
    Array {
        /// TODO(document)
        inner: Box<Dtype>,

        /// TODO(document)
        size: usize,
    },
    /// TODO(document)
    Struct {
        /// TODO(document)
        name: Option<String>,

        /// TODO(document)
        fields: Option<Vec<Named<Dtype>>>,

        /// TODO(document)
        is_const: bool,

        /// TODO(document)
        size_align_offsets: Option<(usize, usize, Vec<usize>)>,
    },
    /// TODO(document)
    Function {
        /// TODO(document)
        ret: Box<Dtype>,

        /// TODO(document)
        params: Vec<Dtype>,
    },
    /// TODO(document)
    Typedef {
        /// TODO(document)
        name: String,

        /// TODO(document)
        is_const: bool,
    },
}

impl BaseDtype {
    /// Apply `StorageClassSpecifier` to `BaseDtype`
    ///
    /// let's say declaration is `typedef int i32_t;`, if `self` represents `int`
    /// and `type_qualifier` represents `typedef`, `self` is transformed to
    /// representing `typedef int` after function performs.
    ///
    /// # Arguments
    ///
    /// * `self` - Part that has been converted to 'BaseDtype' on the declaration
    /// * `storage_class` - storage class requiring apply to 'self' immediately
    ///
    #[inline]
    fn apply_storage_class(
        &mut self,
        storage_class: &ast::StorageClassSpecifier,
    ) -> Result<(), DtypeError> {
        match storage_class {
            ast::StorageClassSpecifier::Typedef => {
                // duplicate `typedef` is allowed
                self.is_typedef = true;
            }
            _ => panic!("unsupported storage class"),
        }

        Ok(())
    }

    /// Apply `TypeSpecifier` to `BaseDtype`
    ///
    /// let's say declaration is `const int a;`, if `self` represents `int`
    /// and `type_specifier` represents `const`, `self` is transformed to
    /// representing `const int` after function performs.
    ///
    /// # Arguments
    ///
    /// * `self` - Part that has been converted to 'BaseDtype' on the declaration
    /// * `type_qualifier` - type qualifiers requiring apply to 'self' immediately
    ///
    #[inline]
    fn apply_type_specifier(
        &mut self,
        type_specifier: &ast::TypeSpecifier,
    ) -> Result<(), DtypeError> {
        match type_specifier {
            ast::TypeSpecifier::Unsigned | ast::TypeSpecifier::Signed => {
                if self.signed_option.is_some() {
                    return Err(DtypeError::Misc {
                        message: "duplicate signed option".to_string(),
                    });
                }
                self.signed_option = Some(type_specifier.clone());
            }
            ast::TypeSpecifier::Void
            | ast::TypeSpecifier::Bool
            | ast::TypeSpecifier::Char
            | ast::TypeSpecifier::Int
            | ast::TypeSpecifier::Float
            | ast::TypeSpecifier::Double => {
                if self.scalar.is_some() {
                    return Err(DtypeError::Misc {
                        message: "two or more scalar types in declaration specifiers".to_string(),
                    });
                }
                self.scalar = Some(type_specifier.clone());
            }
            ast::TypeSpecifier::Short | ast::TypeSpecifier::Long => {
                self.size_modifiers.push(type_specifier.clone())
            }
            ast::TypeSpecifier::TypedefName(identifier) => {
                if self.typedef_name.is_some() {
                    return Err(DtypeError::Misc {
                        message: "two or more typedef names in declaration specifiers".to_string(),
                    });
                }
                self.typedef_name = Some(identifier.node.name.clone());
            }
            ast::TypeSpecifier::Struct(struct_type) => {
                if self.struct_type.is_some() {
                    return Err(DtypeError::Misc {
                        message: "two or more struct type in declaration specifiers".to_string(),
                    });
                }
                self.struct_type = Some(struct_type.node.clone());
            }
            _ => todo!("apply_type_specifier: support {:?}", type_specifier),
        }

        Ok(())
    }

    /// Apply `Typequalifier` to `BaseDtype`
    ///
    /// let's say declaration is `const int a;`, if `self` represents `int`
    /// and `type_qualifier` represents `const`, `self` is transformed to
    /// representing `const int` after function performs.
    ///
    /// # Arguments
    ///
    /// * `self` - Part that has been converted to 'BaseDtype' on the declaration
    /// * `type_qualifier` - type qualifiers requiring apply to 'self' immediately
    ///
    #[inline]
    fn apply_type_qualifier(
        &mut self,
        type_qualifier: &ast::TypeQualifier,
    ) -> Result<(), DtypeError> {
        match type_qualifier {
            ast::TypeQualifier::Const => {
                // duplicate `const` is allowed
                self.is_const = true;
            }
            _ => panic!("type qualifier is unsupported except `const`"),
        }

        Ok(())
    }

    pub fn apply_specifier_qualifier(
        &mut self,
        typename_specifier: &ast::SpecifierQualifier,
    ) -> Result<(), DtypeError> {
        match typename_specifier {
            ast::SpecifierQualifier::TypeSpecifier(type_specifier) => {
                self.apply_type_specifier(&type_specifier.node)?
            }
            ast::SpecifierQualifier::TypeQualifier(type_qualifier) => {
                self.apply_type_qualifier(&type_qualifier.node)?
            }
            ast::SpecifierQualifier::Extension(_) => panic!("unsupported specifier qualifier"),
        }

        Ok(())
    }

    pub fn apply_declaration_specifier(
        &mut self,
        declaration_specifier: &ast::DeclarationSpecifier,
    ) -> Result<(), DtypeError> {
        match declaration_specifier {
            ast::DeclarationSpecifier::StorageClass(storage_class) => {
                self.apply_storage_class(&storage_class.node)?
            }
            ast::DeclarationSpecifier::TypeSpecifier(type_specifier) => {
                self.apply_type_specifier(&type_specifier.node)?
            }
            ast::DeclarationSpecifier::TypeQualifier(type_qualifier) => {
                self.apply_type_qualifier(&type_qualifier.node)?
            }
            _ => panic!("is_unsupported"),
        }

        Ok(())
    }

    /// Apply `PointerQualifier` to `BaseDtype`
    ///
    /// let's say pointer declarator is `* const` of `const int * const a;`.
    /// If `self` represents nothing, and `pointer_qualifier` represents `const`
    /// between first and second asterisk, `self` is transformed to
    /// representing `const` after function performs. This information is used later
    /// when generating `Dtype`.
    ///
    /// # Arguments
    ///
    /// * `self` - Part that has been converted to 'BaseDtype' on the pointer declarator
    /// * `pointer_qualifier` - Pointer qualifiers requiring apply to 'BaseDtype' immediately
    ///
    pub fn apply_pointer_qualifier(
        &mut self,
        pointer_qualifier: &ast::PointerQualifier,
    ) -> Result<(), DtypeError> {
        match pointer_qualifier {
            ast::PointerQualifier::TypeQualifier(type_qualifier) => {
                self.apply_type_qualifier(&type_qualifier.node)?;
            }
            ast::PointerQualifier::Extension(_) => {
                panic!("ast::PointerQualifier::Extension is unsupported")
            }
        }

        Ok(())
    }

    pub fn apply_specifier_qualifiers(
        &mut self,
        typename_specifiers: &[Node<ast::SpecifierQualifier>],
    ) -> Result<(), DtypeError> {
        for ast_spec in typename_specifiers {
            self.apply_specifier_qualifier(&ast_spec.node)?;
        }

        Ok(())
    }

    pub fn apply_declaration_specifiers(
        &mut self,
        declaration_specifiers: &[Node<ast::DeclarationSpecifier>],
    ) -> Result<(), DtypeError> {
        for ast_spec in declaration_specifiers {
            self.apply_declaration_specifier(&ast_spec.node)?;
        }

        Ok(())
    }
}

impl TryFrom<BaseDtype> for Dtype {
    type Error = DtypeError;

    /// Derive a data type containing scalar type from specifiers.
    ///
    /// # Example
    ///
    /// For declaration is `const unsigned int * p`, `specifiers` is `const unsigned int`,
    /// and the result is `Dtype::Int{ width: 4, is_signed: false, is_const: ture }`
    fn try_from(spec: BaseDtype) -> Result<Self, DtypeError> {
        assert!(
            !(spec.scalar.is_none()
                && spec.size_modifiers.is_empty()
                && spec.signed_option.is_none()
                && spec.typedef_name.is_none()
                && spec.struct_type.is_none()
                && !spec.is_const),
            "BaseDtype is empty"
        );

        if let Some(name) = spec.typedef_name {
            if !(spec.scalar.is_none()
                && spec.size_modifiers.is_empty()
                && spec.signed_option.is_none()
                && spec.struct_type.is_none())
            {
                return Err(DtypeError::Misc {
                    message: "`typedef` can only be used with `const`".to_string(),
                });
            }

            let dtype = Self::typedef(name).set_const(spec.is_const);

            return Ok(dtype);
        }

        if let Some(struct_type) = spec.struct_type {
            if !(spec.scalar.is_none()
                && spec.size_modifiers.is_empty()
                && spec.signed_option.is_none()
                && spec.typedef_name.is_none())
            {
                return Err(DtypeError::Misc {
                    message: "`struct` can only be used with `const`".to_string(),
                });
            }

            assert!(struct_type.identifier.is_some() || struct_type.declarations.is_some());
            assert_eq!(struct_type.kind.node, ast::StructKind::Struct);
            let struct_name = struct_type.identifier.map(|i| i.node.name);
            let fields = if let Some(declarations) = struct_type.declarations {
                let fields = declarations
                    .iter()
                    .map(|d| Self::try_from_ast_struct_declaration(&d.node))
                    .collect::<Result<Vec<_>, _>>()?
                    .concat();

                Some(fields)
            } else {
                None
            };

            if let Some(fields) = &fields {
                let mut field_names = HashSet::new();
                if !check_no_duplicate_field(fields, &mut field_names) {
                    return Err(DtypeError::Misc {
                        message: "struct has duplicate field name".to_string(),
                    });
                }
            }

            let dtype = Self::structure(struct_name, fields).set_const(spec.is_const);

            return Ok(dtype);
        }

        // Creates `dtype` from scalar.
        let mut dtype = if let Some(t) = spec.scalar {
            match t {
                ast::TypeSpecifier::Void => Self::unit(),
                ast::TypeSpecifier::Bool => Self::BOOL,
                ast::TypeSpecifier::Char => Self::CHAR,
                ast::TypeSpecifier::Int => Self::INT,
                ast::TypeSpecifier::Float => Self::FLOAT,
                ast::TypeSpecifier::Double => Self::DOUBLE,
                _ => panic!("Dtype::try_from::<BaseDtype>: {:?} is not a scalar type", t),
            }
        } else {
            Self::default()
        };

        let number_of_modifier = spec.size_modifiers.len();
        dtype = match number_of_modifier {
            0 => dtype,
            1 => match spec.size_modifiers[0] {
                ast::TypeSpecifier::Short => Self::SHORT,
                ast::TypeSpecifier::Long => Self::LONG,
                _ => panic!(
                    "Dtype::try_from::<BaseDtype>: {:?} is not a size modifiers",
                    spec.size_modifiers
                ),
            },
            2 => {
                if spec.size_modifiers[0] != ast::TypeSpecifier::Long
                    || spec.size_modifiers[1] != ast::TypeSpecifier::Long
                {
                    return Err(DtypeError::Misc {
                        message: "two or more size modifiers in declaration specifiers".to_string(),
                    });
                }
                Self::LONGLONG
            }
            _ => {
                return Err(DtypeError::Misc {
                    message: "two or more size modifiers in declaration specifiers".to_string(),
                })
            }
        };

        // Applies signedness.
        if let Some(signed_option) = spec.signed_option {
            let is_signed = match signed_option {
                ast::TypeSpecifier::Signed => true,
                ast::TypeSpecifier::Unsigned => false,
                _ => panic!(
                    "Dtype::try_from::<BaseDtype>: {:?} is not a signed option",
                    signed_option
                ),
            };

            if dtype.get_int_width().is_none() {
                return Err(DtypeError::Misc {
                    message: "`signed` and `unsigned` only be applied to `Dtype::Int`".to_string(),
                });
            }

            dtype = dtype.set_signed(is_signed);
        }

        dtype = dtype.set_const(spec.is_const);

        Ok(dtype)
    }
}

impl TryFrom<&ast::TypeName> for Dtype {
    type Error = DtypeError;

    /// Derive a data type from typename.
    fn try_from(type_name: &ast::TypeName) -> Result<Self, Self::Error> {
        let mut spec = BaseDtype::default();
        BaseDtype::apply_specifier_qualifiers(&mut spec, &type_name.specifiers)?;
        let mut dtype = Self::try_from(spec)?;

        if let Some(declarator) = &type_name.declarator {
            dtype = dtype.with_ast_declarator(&declarator.node)?.deref().clone();
        }
        Ok(dtype)
    }
}

impl TryFrom<&ast::ParameterDeclaration> for Dtype {
    type Error = DtypeError;

    /// Generate `Dtype` based on parameter declaration
    fn try_from(parameter_decl: &ast::ParameterDeclaration) -> Result<Self, Self::Error> {
        let mut spec = BaseDtype::default();
        BaseDtype::apply_declaration_specifiers(&mut spec, &parameter_decl.specifiers)?;
        let mut dtype = Self::try_from(spec)?;

        if let Some(declarator) = &parameter_decl.declarator {
            dtype = dtype.with_ast_declarator(&declarator.node)?.deref().clone();

            // A function call with an array argument performs array-to-pointer conversion.
            // For this reason, when `declarator` is from function parameter declaration
            // and `base_dtype` is `Dtype::Array`, `base_dtype` is transformed to pointer type.
            // https://www.eskimo.com/~scs/cclass/notes/sx10f.html
            if let Some(inner) = dtype.get_array_inner() {
                dtype = Self::pointer(inner.clone());
            }
        }
        Ok(dtype)
    }
}

impl Dtype {
    /// TODO(document)
    pub const BITS_OF_BYTE: usize = 8;

    /// TODO(document)
    pub const SIZE_OF_BYTE: usize = 1;

    /// TODO(document)
    // TODO: consider architecture dependency (current: 64-bit architecture)
    pub const SIZE_OF_POINTER: usize = 8;

    /// TODO(document)
    pub const SIZE_OF_CHAR: usize = 1;

    /// TODO(document)
    pub const SIZE_OF_SHORT: usize = 2;

    /// TODO(document)
    pub const SIZE_OF_INT: usize = 4;

    /// TODO(document)
    pub const SIZE_OF_LONG: usize = 8;

    /// TODO(document)
    pub const SIZE_OF_LONGLONG: usize = 8;

    /// TODO(document)
    pub const SIZE_OF_FLOAT: usize = 4;

    /// TODO(document)
    pub const SIZE_OF_DOUBLE: usize = 8;

    /// TODO(document)
    // signed option cannot be applied to boolean value
    pub const BOOL: Self = Self::Int {
        width: 1,
        is_signed: false,
        is_const: false,
    };

    /// TODO(document)
    pub const CHAR: Self = Self::int(Self::SIZE_OF_CHAR * Self::BITS_OF_BYTE);

    /// TODO(document)
    pub const SHORT: Self = Self::int(Self::SIZE_OF_SHORT * Self::BITS_OF_BYTE);

    /// TODO(document)
    pub const INT: Self = Self::int(Self::SIZE_OF_INT * Self::BITS_OF_BYTE);

    /// TODO(document)
    pub const LONG: Self = Self::int(Self::SIZE_OF_LONG * Self::BITS_OF_BYTE);

    /// TODO(document)
    pub const LONGLONG: Self = Self::int(Self::SIZE_OF_LONGLONG * Self::BITS_OF_BYTE);

    /// TODO(document)
    pub const FLOAT: Self = Self::float(Self::SIZE_OF_FLOAT * Self::BITS_OF_BYTE);

    /// TODO(document)
    pub const DOUBLE: Self = Self::float(Self::SIZE_OF_DOUBLE * Self::BITS_OF_BYTE);

    /// TODO(document)
    #[inline]
    pub const fn unit() -> Self {
        Self::Unit { is_const: false }
    }

    /// TODO(document)
    #[inline]
    pub const fn int(width: usize) -> Self {
        Self::Int {
            width,
            is_signed: true,
            is_const: false,
        }
    }

    /// TODO(document)
    #[inline]
    pub const fn float(width: usize) -> Self {
        Self::Float {
            width,
            is_const: false,
        }
    }

    /// TODO(document)
    #[inline]
    pub fn pointer(inner: Dtype) -> Self {
        Self::Pointer {
            inner: Box::new(inner),
            is_const: false,
        }
    }

    /// TODO(document)
    ///
    /// # Examples
    ///
    /// Suppose the C declaration is `int *a[2][3]`. Then `a`'s `ir::Dtype` should be `[2 x [3 x
    /// int*]]`.  But in the AST, it is parsed as `Array(3, Array(2, Pointer(int)))`, reversing the
    /// order of `2` and `3`.  In the recursive translation of declaration into Dtype, we need to
    /// insert `3` inside `[2 * int*]`.
    pub fn array(base_dtype: Dtype, size: usize) -> Self {
        match base_dtype {
            Self::Array {
                inner,
                size: old_size,
            } => {
                let inner = inner.deref().clone();
                let inner = Self::array(inner, size);
                Self::Array {
                    inner: Box::new(inner),
                    size: old_size,
                }
            }
            Self::Function { .. } => panic!("array size cannot be applied to function type"),
            inner => Self::Array {
                inner: Box::new(inner),
                size,
            },
        }
    }

    /// TODO(document)
    #[inline]
    pub fn structure(name: Option<String>, fields: Option<Vec<Named<Self>>>) -> Self {
        Self::Struct {
            name,
            fields,
            is_const: false,
            size_align_offsets: None,
        }
    }

    pub fn fill_size_align_offsets_of_struct(
        self,
        structs: &HashMap<String, Option<Dtype>>,
    ) -> Result<Self, DtypeError> {
        if let Self::Struct {
            name,
            fields,
            is_const,
            size_align_offsets,
        } = self
        {
            assert!(
                name.is_some() && fields.is_some() && !is_const && size_align_offsets.is_none()
            );

            let fields = fields.unwrap();
            if fields.is_empty() {
                return Ok(Self::Struct {
                    name,
                    fields: Some(fields),
                    is_const,
                    size_align_offsets: Some((0, 1, Vec::new())),
                });
            }

            let align_of = fields
                .iter()
                .map(|f| f.deref().size_align_of(structs))
                .collect::<Result<Vec<_>, _>>()?
                .iter()
                .map(|(_, a)| *a)
                .max()
                .unwrap_or(0);

            let mut offsets = Vec::new();
            let mut offset = 0;
            for field in &fields {
                let (size_of_dtype, align_of_dtype) = field.deref().size_align_of(structs)?;

                let pad = if (offset % align_of_dtype) != 0 {
                    align_of_dtype - (offset % align_of_dtype)
                } else {
                    0
                };

                offset += pad;
                offsets.push(offset);

                offset += size_of_dtype;
            }

            let size_of = ((offset - 1) / align_of + 1) * align_of;

            Ok(Self::Struct {
                name,
                fields: Some(fields),
                is_const,
                size_align_offsets: Some((size_of, align_of, offsets)),
            })
        } else {
            panic!("struct type is needed")
        }
    }

    #[inline]
    pub fn function(ret: Dtype, params: Vec<Dtype>) -> Self {
        Self::Function {
            ret: Box::new(ret),
            params,
        }
    }

    #[inline]
    pub fn typedef(name: String) -> Self {
        Self::Typedef {
            name,
            is_const: false,
        }
    }

    #[inline]
    pub fn get_int_width(&self) -> Option<usize> {
        if let Self::Int { width, .. } = self {
            Some(*width)
        } else {
            None
        }
    }

    #[inline]
    pub fn get_float_width(&self) -> Option<usize> {
        if let Self::Float { width, .. } = self {
            Some(*width)
        } else {
            None
        }
    }

    #[inline]
    pub fn get_pointer_inner(&self) -> Option<&Self> {
        if let Self::Pointer { inner, .. } = self {
            Some(inner.deref())
        } else {
            None
        }
    }

    #[inline]
    pub fn get_array_inner(&self) -> Option<&Self> {
        if let Self::Array { inner, .. } = self {
            Some(inner.deref())
        } else {
            None
        }
    }

    #[inline]
    pub fn get_struct_name(&self) -> Option<&Option<String>> {
        if let Self::Struct { name, .. } = self {
            Some(name)
        } else {
            None
        }
    }

    #[inline]
    pub fn get_struct_fields(&self) -> Option<&Option<Vec<Named<Self>>>> {
        if let Self::Struct { fields, .. } = self {
            Some(fields)
        } else {
            None
        }
    }

    #[inline]
    pub fn get_struct_size_align_offsets(&self) -> Option<&Option<(usize, usize, Vec<usize>)>> {
        if let Self::Struct {
            size_align_offsets, ..
        } = self
        {
            Some(size_align_offsets)
        } else {
            None
        }
    }

    #[inline]
    pub fn get_function_inner(&self) -> Option<(&Self, &Vec<Self>)> {
        if let Self::Function { ret, params } = self {
            Some((ret.deref(), params))
        } else {
            None
        }
    }

    #[inline]
    pub fn is_scalar(&self) -> bool {
        match self {
            Self::Unit { .. } => todo!(),
            Self::Int { .. } => true,
            Self::Float { .. } => true,
            Self::Pointer { .. } => true,
            _ => false,
        }
    }

    #[inline]
    pub fn is_int_signed(&self) -> bool {
        match self {
            Self::Int { is_signed, .. } => *is_signed,
            _ => panic!("only `Dtype::Int` can be judged whether it is sigend"),
        }
    }

    pub fn is_const(&self) -> bool {
        match self {
            Self::Unit { is_const } => *is_const,
            Self::Int { is_const, .. } => *is_const,
            Self::Float { is_const, .. } => *is_const,
            Self::Pointer { is_const, .. } => *is_const,
            Self::Array { .. } => true,
            Self::Struct { is_const, .. } => *is_const,
            Self::Function { .. } => true,
            Self::Typedef { is_const, .. } => *is_const,
        }
    }

    #[inline]
    /// Check if `Dtype` is constant. if it is constant, the variable of `Dtype` is not assignable.
    pub fn is_immutable(&self, structs: &HashMap<String, Option<Dtype>>) -> bool {
        match self {
            Self::Unit { is_const } => *is_const,
            Self::Int { is_const, .. } => *is_const,
            Self::Float { is_const, .. } => *is_const,
            Self::Pointer { is_const, .. } => *is_const,
            Self::Array { .. } => true,
            Self::Struct { name, is_const, .. } => {
                let name = name.as_ref().expect("`name` must be exist");
                let struct_type = structs
                    .get(name)
                    .expect("struct type matched with `name` must exist")
                    .as_ref()
                    .expect("`struct_type` must have its definition");
                let fields = struct_type
                    .get_struct_fields()
                    .expect("`struct_type` must be struct type")
                    .as_ref()
                    .expect("`fields` must be `Some`");

                *is_const
                    // If any of the fields in the structure type is constant, return `true`.
                    || fields
                        .iter()
                        .any(|f| {
                        // If an array is wrapped in a struct and the array's inner type is not 
                        // constant, it is assignable to another object of the same struct type.
                        if let Self::Array { inner, .. } = f.deref() {
                            inner.is_immutable_for_array_struct_field_inner(structs)
                        } else {
                            f.deref().is_immutable(structs)
                        }
                    })
            }
            Self::Function { .. } => true,
            Self::Typedef { .. } => panic!("typedef should be replaced by real dtype"),
        }
    }

    fn is_immutable_for_array_struct_field_inner(
        &self,
        structs: &HashMap<String, Option<Dtype>>,
    ) -> bool {
        if let Self::Array { inner, .. } = self {
            inner.is_immutable_for_array_struct_field_inner(structs)
        } else {
            self.is_immutable(structs)
        }
    }

    #[must_use]
    pub fn set_const(self, is_const: bool) -> Self {
        match self {
            Self::Unit { .. } => Self::Unit { is_const },
            Self::Int {
                width, is_signed, ..
            } => Self::Int {
                width,
                is_signed,
                is_const,
            },
            Self::Float { width, .. } => Self::Float { width, is_const },
            Self::Pointer { inner, .. } => Self::Pointer { inner, is_const },
            Self::Array { .. } => self,
            Self::Struct {
                name,
                fields,
                size_align_offsets,
                ..
            } => Self::Struct {
                name,
                fields,
                is_const,
                size_align_offsets,
            },
            Self::Function { .. } => self,
            Self::Typedef { name, .. } => Self::Typedef { name, is_const },
        }
    }

    pub fn size_align_of(
        &self,
        structs: &HashMap<String, Option<Dtype>>,
    ) -> Result<(usize, usize), DtypeError> {
        match self {
            Self::Unit { .. } => Ok((0, 1)),
            Self::Int { width, .. } | Self::Float { width, .. } => {
                let size_of = (*width + Self::BITS_OF_BYTE - 1) / Self::BITS_OF_BYTE;
                let align_of = size_of;

                Ok((size_of, align_of))
            }
            Self::Pointer { .. } => Ok((Self::SIZE_OF_POINTER, Self::SIZE_OF_POINTER)),
            Self::Array { inner, size, .. } => {
                let (size_of_inner, align_of_inner) = inner.size_align_of(structs)?;

                Ok((
                    size * std::cmp::max(size_of_inner, align_of_inner),
                    align_of_inner,
                ))
            }
            Self::Struct { name, .. } => {
                let name = name.as_ref().expect("`name` must be exist");
                let struct_type = structs
                    .get(name)
                    .ok_or_else(|| DtypeError::Misc {
                        message: format!("unknown struct name `{}`", name),
                    })?
                    .as_ref()
                    .expect("`struct_type` must have its definition");
                let (size_of, align_of, _) = struct_type
                    .get_struct_size_align_offsets()
                    .expect("`struct_type` must be stcut type")
                    .as_ref()
                    .unwrap();

                Ok((*size_of, *align_of))
            }
            Self::Function { .. } => Ok((0, 1)),
            Self::Typedef { .. } => panic!("typedef should be replaced by real dtype"),
        }
    }

    pub fn get_offset_struct_field(
        &self,
        field_name: &str,
        structs: &HashMap<String, Option<Dtype>>,
    ) -> Option<(usize, Self)> {
        if let Self::Struct { name, .. } = self {
            let struct_name = name.as_ref().expect("`self` must have its name");
            let struct_type = structs
                .get(struct_name)
                .expect("`structs` must have value matched with `struct_name`")
                .as_ref()
                .expect("`struct_type` must have its definition");
            let fields = struct_type
                .get_struct_fields()
                .expect("`struct_type` must be struct type")
                .as_ref()
                .expect("`fields` must be `Some`");
            let (_, _, offsets) = struct_type
                .get_struct_size_align_offsets()
                .expect("`struct_type` must be struct type")
                .as_ref()
                .expect("`offsets` must be `Some`");

            assert_eq!(fields.len(), offsets.len());
            for (field, offset) in izip!(fields, offsets) {
                if let Some(name) = field.name() {
                    if name == field_name {
                        return Some((*offset, field.deref().clone()));
                    }
                } else {
                    let field_dtype = field.deref();
                    let (offset_inner, dtype) = some_or!(
                        field_dtype.get_offset_struct_field(field_name, structs),
                        continue
                    );
                    return Some((*offset + offset_inner, dtype));
                }
            }

            None
        } else {
            None
        }
    }

    #[must_use]
    pub fn set_signed(self, is_signed: bool) -> Self {
        match self {
            Self::Int {
                width, is_const, ..
            } => Self::Int {
                width,
                is_signed,
                is_const,
            },
            _ => panic!("`signed` and `unsigned` only be applied to `Dtype::Int`"),
        }
    }

    /// Derive a data type from declaration specifiers.
    pub fn try_from_ast_declaration_specifiers(
        specifiers: &[Node<ast::DeclarationSpecifier>],
    ) -> Result<(Self, bool), DtypeError> {
        let mut spec = BaseDtype::default();
        BaseDtype::apply_declaration_specifiers(&mut spec, specifiers)?;
        let is_typedef = spec.is_typedef;
        let dtype = Self::try_from(spec)?;

        Ok((dtype, is_typedef))
    }

    /// Derive a data type and its name from struct declaration
    pub fn try_from_ast_struct_declaration(
        declaration: &ast::StructDeclaration,
    ) -> Result<Vec<Named<Self>>, DtypeError> {
        let field_decl = if let ast::StructDeclaration::Field(field_decl) = declaration {
            &field_decl.node
        } else {
            panic!("ast::StructDeclaration::StaticAssert is unsupported")
        };

        let mut spec = BaseDtype::default();
        BaseDtype::apply_specifier_qualifiers(&mut spec, &field_decl.specifiers)?;
        let dtype = Self::try_from(spec)?;

        let fields = field_decl
            .declarators
            .iter()
            .map(|d| {
                dtype
                    .clone()
                    .with_ast_declarator(&d.node.declarator.as_ref().unwrap().node)
            })
            .collect::<Result<Vec<_>, _>>()?;

        if fields.is_empty() {
            // If anonymous field is `Dtype::Struct`, structure type of this field
            // can use this field's field as its field.
            // For exampe, let's `struct A { struct { int f; }} t;`, `t.f` is valid.
            if let Self::Struct { name, .. } = &dtype {
                if name.is_none() {
                    // Note that `const` qualifier has no effect in this time.
                    return Ok(vec![Named::new(None, dtype.set_const(false))]);
                }
            }

            Err(DtypeError::Misc {
                message: "declaration does not declare anything".to_string(),
            })
        } else {
            Ok(fields)
        }
    }

    /// Generate `Dtype` based on declarator and `self` which has scalar type.
    ///
    /// let's say declaration is `const int * const * const a;`.
    /// In general `self` start with `const int` which has scalar type and
    /// `declarator` represents `* const * const` with `ast::Declarator`
    ///
    /// # Arguments
    ///
    /// * `declarator` - Parts requiring conversion to 'Dtype' on the declaration
    /// * `decl_spec`  - Containing information that should be referenced
    ///                  when creating `Dtype` from `Declarator`.
    ///
    pub fn with_ast_declarator(
        mut self,
        declarator: &ast::Declarator,
    ) -> Result<Named<Self>, DtypeError> {
        for derived_decl in &declarator.derived {
            self = match &derived_decl.node {
                ast::DerivedDeclarator::Pointer(pointer_qualifiers) => {
                    let mut specifier = BaseDtype::default();
                    for qualifier in pointer_qualifiers {
                        specifier.apply_pointer_qualifier(&qualifier.node)?;
                    }
                    Self::pointer(self).set_const(specifier.is_const)
                }
                ast::DerivedDeclarator::Array(array_decl) => {
                    assert!(array_decl.node.qualifiers.is_empty());
                    self.with_ast_array_size(&array_decl.node.size)?
                }
                ast::DerivedDeclarator::Function(func_decl) => {
                    let mut params = func_decl
                        .node
                        .parameters
                        .iter()
                        .map(|p| Self::try_from(&p.node))
                        .collect::<Result<Vec<_>, _>>()?;

                    // If function parameter is (void), remove it
                    if params.len() == 1 && params[0] == Dtype::unit() {
                        let _ = params.pop();
                    }

                    Self::function(self, params)
                }
                ast::DerivedDeclarator::KRFunction(kr_func_decl) => {
                    // K&R function is allowed only when it has no parameter
                    assert!(kr_func_decl.is_empty());
                    Self::function(self, Vec::new())
                }
            };
        }

        let declarator_kind = &declarator.kind;
        match &declarator_kind.node {
            ast::DeclaratorKind::Abstract => Ok(Named::new(None, self)),
            ast::DeclaratorKind::Identifier(identifier) => {
                Ok(Named::new(Some(identifier.node.name.clone()), self))
            }
            ast::DeclaratorKind::Declarator(declarator) => {
                self.with_ast_declarator(&declarator.node)
            }
        }
    }

    /// Generates `Dtype` based on declarator and `self` which has scalar type.
    ///
    /// Let's say the AST declaration is `int a[2][3]`; `self` represents `int [2]`; and
    /// `array_size` is `[3]`. Then this function should return `int [2][3]`.
    ///
    /// # Arguments
    ///
    /// * `array_size` - the array size to add to the dtype `self`
    ///
    pub fn with_ast_array_size(self, array_size: &ast::ArraySize) -> Result<Self, DtypeError> {
        let expr = if let ast::ArraySize::VariableExpression(expr) = array_size {
            &expr.node
        } else {
            panic!("`ArraySize` is unsupported except `ArraySize::VariableExpression`")
        };

        let constant = Constant::try_from(expr)
            .expect("expression of `ArraySize::VariableExpression` must be constant value");

        let (value, _, is_signed) = constant.get_int().ok_or_else(|| DtypeError::Misc {
            message: "expression is not an integer constant expression".to_string(),
        })?;

        if is_signed && (value as i128) < 0 {
            return Err(DtypeError::Misc {
                message: "declared as an array with a negative size".to_string(),
            });
        }

        Ok(Self::array(self, value as usize))
    }

    pub fn resolve_typedefs(
        self,
        typedefs: &HashMap<String, Dtype>,
        structs: &HashMap<String, Option<Dtype>>,
    ) -> Result<Self, DtypeError> {
        let dtype = match &self {
            Self::Unit { .. } | Self::Int { .. } | Self::Float { .. } => self,
            Self::Pointer { inner, is_const } => {
                let inner = inner.deref().clone().resolve_typedefs(typedefs, structs)?;
                Self::pointer(inner).set_const(*is_const)
            }
            Self::Array { inner, size } => {
                let inner = inner.deref().clone().resolve_typedefs(typedefs, structs)?;
                Self::Array {
                    inner: Box::new(inner),
                    size: *size,
                }
            }
            Self::Struct {
                name,
                fields,
                is_const,
                ..
            } => {
                if let Some(fields) = fields {
                    let resolved_dtypes = fields
                        .iter()
                        .map(|f| f.deref().clone().resolve_typedefs(typedefs, structs))
                        .collect::<Result<Vec<_>, _>>()?;

                    assert_eq!(fields.len(), resolved_dtypes.len());
                    let fields = izip!(fields, resolved_dtypes)
                        .map(|(f, d)| Named::new(f.name().cloned(), d))
                        .collect::<Vec<_>>();

                    Self::structure(name.clone(), Some(fields)).set_const(*is_const)
                } else {
                    assert!(name.is_some());
                    self
                }
            }
            Self::Function { ret, params } => {
                let ret = ret.deref().clone().resolve_typedefs(typedefs, structs)?;
                let params = params
                    .iter()
                    .map(|p| p.clone().resolve_typedefs(typedefs, structs))
                    .collect::<Result<Vec<_>, _>>()?;

                Self::function(ret, params)
            }
            Self::Typedef { name, is_const } => {
                let dtype = typedefs
                    .get(name)
                    .ok_or_else(|| DtypeError::Misc {
                        message: format!("unknown type name `{}`", name),
                    })?
                    .clone();
                let is_const = dtype.is_const() || *is_const;

                dtype.set_const(is_const)
            }
        };

        Ok(dtype)
    }

    /// If the struct type has a definition, it is saved to the struct table
    /// and transformed to a struct type with no definition.
    pub fn resolve_structs(
        self,
        structs: &mut HashMap<String, Option<Dtype>>,
        tempid_counter: &mut usize,
    ) -> Result<Self, DtypeError> {
        let dtype = match &self {
            Self::Unit { .. } | Self::Int { .. } | Self::Float { .. } => self,
            Self::Pointer { inner, is_const } => {
                let inner = inner.deref();

                // the pointer type can have undeclared struct type as inner.
                // For example, let's `struct A { struct B *p }`, even if `struct B` has not been
                // declared before, it can be used as inner type of the pointer.
                if let Self::Struct { name, fields, .. } = inner {
                    if fields.is_none() {
                        let name = name.as_ref().expect("`name` must be `Some`");
                        let _ = structs.entry(name.to_string()).or_insert(None);
                        return Ok(self.clone());
                    }
                }

                let resolved_inner = inner.clone().resolve_structs(structs, tempid_counter)?;
                Self::pointer(resolved_inner).set_const(*is_const)
            }
            Self::Array { inner, size } => {
                let inner = inner
                    .deref()
                    .clone()
                    .resolve_structs(structs, tempid_counter)?;
                Self::Array {
                    inner: Box::new(inner),
                    size: *size,
                }
            }
            Self::Struct {
                name,
                fields,
                is_const,
                ..
            } => {
                if let Some(fields) = fields {
                    let resolved_dtypes = fields
                        .iter()
                        .map(|f| f.deref().clone().resolve_structs(structs, tempid_counter))
                        .collect::<Result<Vec<_>, _>>()?;

                    assert_eq!(fields.len(), resolved_dtypes.len());
                    let fields = izip!(fields, resolved_dtypes)
                        .map(|(f, d)| Named::new(f.name().cloned(), d))
                        .collect::<Vec<_>>();

                    let name = if let Some(name) = name {
                        name.clone()
                    } else {
                        let tempid = *tempid_counter;
                        *tempid_counter += 1;
                        format!("%t{}", tempid)
                    };
                    let resolved_struct = Self::structure(Some(name.clone()), Some(fields));
                    let filled_struct =
                        resolved_struct.fill_size_align_offsets_of_struct(structs)?;

                    let prev_dtype = structs.insert(name.clone(), Some(filled_struct));
                    if let Some(prev_dtype) = prev_dtype {
                        if prev_dtype.is_some() {
                            return Err(DtypeError::Misc {
                                message: format!("redefinition of {}", name),
                            });
                        }
                    }

                    Self::structure(Some(name), None).set_const(*is_const)
                } else {
                    let name = name.as_ref().expect("`name` must be exist");
                    let struct_type = structs.get(name).ok_or_else(|| DtypeError::Misc {
                        message: format!("unknown struct name `{}`", name),
                    })?;
                    if struct_type.is_none() {
                        return Err(DtypeError::Misc {
                            message: format!("variable has incomplete type 'struct {}'", name),
                        });
                    }

                    self
                }
            }
            Self::Function { ret, params } => {
                let ret = ret
                    .deref()
                    .clone()
                    .resolve_structs(structs, tempid_counter)?;
                let params = params
                    .iter()
                    .map(|p| p.clone().resolve_structs(structs, tempid_counter))
                    .collect::<Result<Vec<_>, _>>()?;

                Self::function(ret, params)
            }
            Self::Typedef { .. } => panic!("typedef should be replaced by real dtype"),
        };

        Ok(dtype)
    }
}

impl fmt::Display for Dtype {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Unit { is_const } => write!(f, "{}unit", if *is_const { "const " } else { "" }),
            Self::Int {
                width,
                is_signed,
                is_const,
            } => write!(
                f,
                "{}{}{}",
                if *is_const { "const " } else { "" },
                if *is_signed { "i" } else { "u" },
                width
            ),
            Self::Float { width, is_const } => {
                write!(f, "{}f{}", if *is_const { "const " } else { "" }, width)
            }
            Self::Pointer { inner, is_const } => {
                write!(f, "{}*{}", inner, if *is_const { "const" } else { "" })
            }
            Self::Array { inner, size, .. } => write!(f, "[{} x {}]", size, inner,),
            Self::Struct {
                name,
                fields,
                is_const,
                ..
            } => {
                let fields = if let Some(fields) = fields {
                    let fields = fields.iter().format_with(", ", |field, f| {
                        f(&format_args!(
                            "{}:{}",
                            if let Some(name) = field.name() {
                                name
                            } else {
                                "%anon"
                            },
                            field.deref()
                        ))
                    });
                    format!(":<{}>", fields)
                } else {
                    "".to_string()
                };
                write!(
                    f,
                    "{}struct {}{}",
                    if *is_const { "const " } else { "" },
                    if let Some(name) = name { name } else { "%anon" },
                    fields
                )
            }
            Self::Function { ret, params } => {
                write!(f, "[ret:{} params:({})]", ret, params.iter().format(", "))
            }
            Self::Typedef { name, is_const } => {
                write!(f, "{}{}", if *is_const { "const " } else { "" }, name)
            }
        }
    }
}

impl Default for Dtype {
    fn default() -> Self {
        // default dtype is `int`(i32)
        Self::INT
    }
}

#[inline]
fn check_no_duplicate_field(fields: &[Named<Dtype>], field_names: &mut HashSet<String>) -> bool {
    for field in fields {
        if let Some(name) = field.name() {
            if !field_names.insert(name.clone()) {
                return false;
            }
        } else {
            let field_dtype = field.deref();
            let fields = field_dtype
                .get_struct_fields()
                .expect("`field_dtype` must be struct type")
                .as_ref()
                .expect("struct type must have its definition");
            if !check_no_duplicate_field(fields, field_names) {
                return false;
            }
        }
    }

    true
}