use std::vec::IntoIter;

use derive_builder_core::BuildMethod;

use darling::util::{Flag, PathList};
use darling::{self, FromMeta};
use proc_macro2::Span;
use syn::{self, Attribute, Generics, Ident, Path, Visibility};

use derive_builder_core::{
    Bindings, Builder, BuilderField, BuilderPattern, DeprecationNotes, Initializer, Setter,
};
use options::DefaultExpression;

/// `derive_builder` uses separate sibling keywords to represent
/// mutually-exclusive visibility states. This trait requires implementers to
/// expose those flags and provides a method to compute any explicit visibility
/// bounds.
trait FlagVisibility {
    fn public(&self) -> &Flag;
    fn private(&self) -> &Flag;

    /// Get the explicitly-expressed visibility preference from the attribute.
    /// This returns `None` if the input didn't include either keyword.
    ///
    /// # Panics
    /// This method panics if the input specifies both `public` and `private`.
    fn as_expressed_vis(&self) -> Option<Visibility> {
        match (self.public().is_some(), self.private().is_some()) {
            (true, true) => panic!("A field cannot be both public and private"),
            (true, false) => Some(syn::parse_str("pub").unwrap()),
            (false, true) => Some(Visibility::Inherited),
            (false, false) => None,
        }
    }
}

/// Options for the `build_fn` property in struct-level builder options.
/// There is no inheritance for these settings from struct-level to field-level,
/// so we don't bother using `Option` for values in this struct.
#[derive(Debug, Clone, FromMeta)]
#[darling(default)]
pub struct BuildFn {
    skip: bool,
    name: Ident,
    validate: Option<Path>,
    public: Flag,
    private: Flag,
}

impl Default for BuildFn {
    fn default() -> Self {
        BuildFn {
            skip: false,
            name: Ident::new("build", Span::call_site()),
            validate: None,
            public: Default::default(),
            private: Default::default(),
        }
    }
}

impl FlagVisibility for BuildFn {
    fn public(&self) -> &Flag {
        &self.public
    }

    fn private(&self) -> &Flag {
        &self.private
    }
}

/// Contents of the `field` meta in `builder` attributes.
#[derive(Debug, Clone, Default, FromMeta)]
#[darling(default)]
pub struct FieldMeta {
    public: Flag,
    private: Flag,
}

impl FlagVisibility for FieldMeta {
    fn public(&self) -> &Flag {
        &self.public
    }

    fn private(&self) -> &Flag {
        &self.private
    }
}

#[derive(Debug, Clone, Default, FromMeta)]
#[darling(default)]
pub struct StructLevelSetter {
    prefix: Option<Ident>,
    into: Option<bool>,
    strip_option: Option<bool>,
    skip: Option<bool>,
}

impl StructLevelSetter {
    /// Check if setters are explicitly enabled or disabled at
    /// the struct level.
    pub fn enabled(&self) -> Option<bool> {
        self.skip.map(|x| !x)
    }
}

/// The `setter` meta item on fields in the input type.
/// Unlike the `setter` meta item at the struct level, this allows specific
/// name overrides.
#[derive(Debug, Clone, Default, FromMeta)]
#[darling(default)]
pub struct FieldLevelSetter {
    prefix: Option<Ident>,
    name: Option<Ident>,
    into: Option<bool>,
    strip_option: Option<bool>,
    skip: Option<bool>,
    custom: Option<bool>,
}

impl FieldLevelSetter {
    /// Get whether the setter should be emitted. The rules are the same as
    /// for `field_enabled`, except we only skip the setter if `setter(custom)` is present.
    pub fn setter_enabled(&self) -> Option<bool> {
        if self.custom.is_some() {
            return self.custom.map(|x| !x);
        }

        self.field_enabled()
    }

    /// Get whether or not this field-level setter indicates a setter and
    /// field should be emitted. The setter shorthand rules are that the
    /// presence of a `setter` with _any_ properties set forces the setter
    /// to be emitted.
    pub fn field_enabled(&self) -> Option<bool> {
        if self.skip.is_some() {
            return self.skip.map(|x| !x);
        }

        if self.prefix.is_some()
            || self.name.is_some()
            || self.into.is_some()
            || self.strip_option.is_some()
        {
            return Some(true);
        }

        None
    }
}

/// `derive_builder` allows the calling code to use `setter` as a word to enable
/// setters when they've been disabled at the struct level.
/// `darling` doesn't provide that out of the box, so we read the user input
/// into this enum then convert it into the `FieldLevelSetter`.
#[derive(Debug, Clone)]
enum FieldSetterMeta {
    /// The keyword in isolation.
    /// This is equivalent to `setter(skip = false)`.
    Shorthand,
    Longhand(FieldLevelSetter),
}

impl From<FieldSetterMeta> for FieldLevelSetter {
    fn from(v: FieldSetterMeta) -> Self {
        match v {
            FieldSetterMeta::Shorthand => FieldLevelSetter {
                skip: Some(false),
                ..Default::default()
            },
            FieldSetterMeta::Longhand(val) => val,
        }
    }
}

impl FromMeta for FieldSetterMeta {
    fn from_word() -> darling::Result<Self> {
        Ok(FieldSetterMeta::Shorthand)
    }

    fn from_meta(value: &syn::Meta) -> darling::Result<Self> {
        if let syn::Meta::Path(_) = *value {
            FieldSetterMeta::from_word()
        } else {
            FieldLevelSetter::from_meta(value).map(FieldSetterMeta::Longhand)
        }
    }
}

/// Data extracted from the fields of the input struct.
#[derive(Debug, Clone, FromField)]
#[darling(attributes(builder), forward_attrs(doc, cfg, allow))]
pub struct Field {
    ident: Option<Ident>,
    attrs: Vec<Attribute>,
    vis: syn::Visibility,
    ty: syn::Type,
    /// Field-level override for builder pattern.
    /// Note that setting this may force the builder to derive `Clone`.
    #[darling(default)]
    pattern: Option<BuilderPattern>,
    #[darling(default)]
    public: Flag,
    #[darling(default)]
    private: Flag,
    // See the documentation for `FieldSetterMeta` to understand how `darling`
    // is interpreting this field.
    #[darling(default, map = "FieldSetterMeta::into")]
    setter: FieldLevelSetter,
    /// The value for this field if the setter is never invoked.
    ///
    /// A field can get its default one of three ways:
    ///
    /// 1. An explicit `default = "..."` expression
    /// 2. An explicit `default` word, in which case the field type's `Default::default()`
    ///    value is used
    /// 3. Inherited from the field's value in the struct's `default` value.
    ///
    /// This property only captures the first two, the third is computed in `FieldWithDefaults`.
    #[darling(default)]
    default: Option<DefaultExpression>,
    #[darling(default)]
    try_setter: Flag,
    #[darling(default)]
    field: FieldMeta,
}

impl FlagVisibility for Field {
    fn public(&self) -> &Flag {
        &self.public
    }

    fn private(&self) -> &Flag {
        &self.private
    }
}

#[derive(Debug, Clone, FromDeriveInput)]
#[darling(
    attributes(builder),
    forward_attrs(doc, cfg, allow),
    supports(struct_named)
)]
pub struct Options {
    ident: Ident,

    attrs: Vec<Attribute>,

    vis: Visibility,

    generics: Generics,

    /// The name of the generated builder. Defaults to `#{ident}Builder`.
    #[darling(default)]
    name: Option<Ident>,

    #[darling(default)]
    pattern: BuilderPattern,

    #[darling(default)]
    build_fn: BuildFn,

    /// Additional traits to derive on the builder.
    #[darling(default)]
    derive: PathList,

    /// Setter options applied to all field setters in the struct.
    #[darling(default)]
    setter: StructLevelSetter,

    /// Struct-level value to use in place of any unfilled fields
    #[darling(default)]
    default: Option<DefaultExpression>,

    #[darling(default)]
    public: Flag,

    #[darling(default)]
    private: Flag,

    /// The parsed body of the derived struct.
    data: darling::ast::Data<darling::util::Ignored, Field>,

    #[darling(default)]
    no_std: Flag,

    /// When present, emit additional fallible setters alongside each regular
    /// setter.
    #[darling(default)]
    try_setter: Flag,

    #[darling(default)]
    field: FieldMeta,

    #[darling(skip, default)]
    deprecation_notes: DeprecationNotes,
}

impl FlagVisibility for Options {
    fn public(&self) -> &Flag {
        &self.public
    }

    fn private(&self) -> &Flag {
        &self.private
    }
}

/// Accessors for parsed properties.
impl Options {
    pub fn builder_ident(&self) -> Ident {
        if let Some(ref custom) = self.name {
            return custom.clone();
        }

        syn::parse_str(&format!("{}Builder", self.ident))
            .expect("Struct name with Builder suffix should be an ident")
    }

    /// The visibility of the builder struct.
    /// If a visibility was declared in attributes, that will be used;
    /// otherwise the struct's own visibility will be used.
    pub fn builder_vis(&self) -> Visibility {
        self.as_expressed_vis().unwrap_or_else(|| self.vis.clone())
    }

    /// Get the visibility of the emitted `build` method.
    /// This defaults to the visibility of the parent builder, but can be overridden.
    pub fn build_method_vis(&self) -> Visibility {
        self.build_fn
            .as_expressed_vis()
            .unwrap_or_else(|| self.builder_vis())
    }

    pub fn raw_fields<'a>(&'a self) -> Vec<&'a Field> {
        self.data
            .as_ref()
            .take_struct()
            .expect("Only structs supported")
            .fields
    }

    /// A builder requires `Clone` to be derived if its build method or any of its setters
    /// use the mutable or immutable pattern.
    pub fn requires_clone(&self) -> bool {
        self.pattern.requires_clone() || self.fields().any(|f| f.pattern().requires_clone())
    }

    /// Get an iterator over the input struct's fields which pulls fallback
    /// values from struct-level settings.
    pub fn fields<'a>(&'a self) -> FieldIter<'a> {
        FieldIter(self, self.raw_fields().into_iter())
    }

    pub fn field_count(&self) -> usize {
        self.raw_fields().len()
    }

    fn bindings(&self) -> Bindings {
        Bindings {
            no_std: self.no_std.is_some(),
        }
    }
}

/// Converters to codegen structs
impl Options {
    pub fn as_builder<'a>(&'a self) -> Builder<'a> {
        Builder {
            enabled: true,
            ident: self.builder_ident(),
            pattern: self.pattern,
            derives: &self.derive,
            generics: Some(&self.generics),
            visibility: self.builder_vis(),
            fields: Vec::with_capacity(self.field_count()),
            functions: Vec::with_capacity(self.field_count()),
            must_derive_clone: self.requires_clone(),
            doc_comment: None,
            deprecation_notes: Default::default(),
            bindings: self.bindings(),
        }
    }

    pub fn as_build_method<'a>(&'a self) -> BuildMethod<'a> {
        let (_, ty_generics, _) = self.generics.split_for_impl();
        BuildMethod {
            enabled: !self.build_fn.skip,
            ident: &self.build_fn.name,
            visibility: self.build_method_vis(),
            pattern: self.pattern,
            target_ty: &self.ident,
            target_ty_generics: Some(ty_generics),
            initializers: Vec::with_capacity(self.field_count()),
            doc_comment: None,
            bindings: self.bindings(),
            default_struct: self
                .default
                .as_ref()
                .map(|x| x.parse_block(self.no_std.into())),
            validate_fn: self.build_fn.validate.as_ref(),
        }
    }
}

/// Accessor for field data which can pull through options from the parent
/// struct.
pub struct FieldWithDefaults<'a> {
    parent: &'a Options,
    field: &'a Field,
}

/// Accessors for parsed properties, with transparent pull-through from the
/// parent struct's configuration.
impl<'a> FieldWithDefaults<'a> {
    /// Check if this field should emit a setter.
    pub fn setter_enabled(&self) -> bool {
        self.field
            .setter
            .setter_enabled()
            .or(self.parent.setter.enabled())
            .unwrap_or(true)
    }

    pub fn field_enabled(&self) -> bool {
        self.field
            .setter
            .field_enabled()
            .or(self.parent.setter.enabled())
            .unwrap_or(true)
    }

    /// Check if this field should emit a fallible setter.
    /// This depends on the `TryFrom` trait, which hasn't yet stabilized.
    pub fn try_setter(&self) -> bool {
        self.field.try_setter.is_some() || self.parent.try_setter.is_some()
    }

    /// Get the prefix that should be applied to the field name to produce
    /// the setter ident, if any.
    pub fn setter_prefix(&self) -> Option<&Ident> {
        self.field
            .setter
            .prefix
            .as_ref()
            .or(self.parent.setter.prefix.as_ref())
    }

    /// Get the ident of the emitted setter method
    pub fn setter_ident(&self) -> syn::Ident {
        if let Some(ref custom) = self.field.setter.name {
            return custom.clone();
        }

        let ident = &self.field.ident;

        if let Some(ref prefix) = self.setter_prefix() {
            return syn::parse_str(&format!("{}_{}", prefix, ident.as_ref().unwrap())).unwrap();
        }

        ident.clone().unwrap()
    }

    /// Checks if the emitted setter should be generic over types that impl
    /// `Into<FieldType>`.
    pub fn setter_into(&self) -> bool {
        self.field
            .setter
            .into
            .or(self.parent.setter.into)
            .unwrap_or_default()
    }

    /// Checks if the emitted setter should strip the wrapper Option over types that impl
    /// `Option<FieldType>`.
    pub fn setter_strip_option(&self) -> bool {
        self.field
            .setter
            .strip_option
            .or(self.parent.setter.strip_option)
            .unwrap_or_default()
    }

    /// Get the visibility of the emitted setter, if there will be one.
    pub fn setter_vis(&self) -> Visibility {
        self.field
            .as_expressed_vis()
            .or_else(|| self.parent.as_expressed_vis())
            .unwrap_or(syn::parse_str("pub").unwrap())
    }

    /// Get the ident of the input field. This is also used as the ident of the
    /// emitted field.
    pub fn field_ident(&self) -> &syn::Ident {
        self.field
            .ident
            .as_ref()
            .expect("Tuple structs are not supported")
    }

    pub fn field_vis(&self) -> Visibility {
        self.field
            .field
            .as_expressed_vis()
            .or_else(|| self.parent.field.as_expressed_vis())
            .unwrap_or(Visibility::Inherited)
    }

    pub fn pattern(&self) -> BuilderPattern {
        self.field.pattern.unwrap_or(self.parent.pattern)
    }

    pub fn use_parent_default(&self) -> bool {
        self.field.default.is_none() && self.parent.default.is_some()
    }

    pub fn deprecation_notes(&self) -> &DeprecationNotes {
        &self.parent.deprecation_notes
    }

    fn bindings(&self) -> Bindings {
        self.parent.bindings()
    }
}

/// Converters to codegen structs
impl<'a> FieldWithDefaults<'a> {
    /// Returns a `Setter` according to the options.
    pub fn as_setter(&'a self) -> Setter<'a> {
        Setter {
            setter_enabled: self.setter_enabled(),
            try_setter: self.try_setter(),
            visibility: self.setter_vis(),
            pattern: self.pattern(),
            attrs: &self.field.attrs,
            ident: self.setter_ident(),
            field_ident: &self.field_ident(),
            field_type: &self.field.ty,
            generic_into: self.setter_into(),
            strip_option: self.setter_strip_option(),
            deprecation_notes: self.deprecation_notes(),
            bindings: self.bindings(),
        }
    }

    /// Returns an `Initializer` according to the options.
    ///
    /// # Panics
    ///
    /// if `default_expression` can not be parsed as `Block`.
    pub fn as_initializer(&'a self) -> Initializer<'a> {
        Initializer {
            field_enabled: self.field_enabled(),
            field_ident: self.field_ident(),
            builder_pattern: self.pattern(),
            default_value: self
                .field
                .default
                .as_ref()
                .map(|x| x.parse_block(self.parent.no_std.into())),
            use_default_struct: self.use_parent_default(),
            bindings: self.bindings(),
        }
    }

    pub fn as_builder_field(&'a self) -> BuilderField<'a> {
        BuilderField {
            field_ident: self.field_ident(),
            field_type: &self.field.ty,
            field_enabled: self.field_enabled(),
            field_visibility: self.field_vis(),
            attrs: &self.field.attrs,
            bindings: self.bindings(),
        }
    }
}

pub struct FieldIter<'a>(&'a Options, IntoIter<&'a Field>);

impl<'a> Iterator for FieldIter<'a> {
    type Item = FieldWithDefaults<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        self.1.next().map(|field| FieldWithDefaults {
            parent: self.0,
            field,
        })
    }
}