extern crate proc_macro;
extern crate proc_macro2;

use std::convert::{TryFrom, TryInto};
use std::mem;

use failure::Error;

use proc_macro2::{Span, TokenStream};
use quote::{quote, quote_spanned};
use syn::parse::{Parse, ParseStream, Parser};
use syn::spanned::Spanned;
use syn::Ident;
use syn::{parenthesized, Token};

use crate::util::{JSONObject, JSONValue, SimpleIdent};

/// The main `Schema` type.
///
/// We have 2 fixed keys: `type` and `description`. The remaining keys depend on the `type`.
/// Generally, we create the following mapping:
///
/// ```text
/// {
///     type: Object,
///     description: "text",
///     foo: bar, // "unknown", will be added as a builder-pattern method
///     properties: { ... }
/// }
/// ```
///
/// to:
///
/// ```text
/// {
///     ObjectSchema::new("text", &[ ... ]).foo(bar)
/// }
/// ```
struct Schema {
    span: Span,

    /// Common in all schema entry types:
    description: Option<syn::LitStr>,

    /// The specific schema type (Object, String, ...)
    item: SchemaItem,

    /// The remaining key-value pairs the `SchemaItem` parser did not extract will be appended as
    /// builder-pattern method calls to this schema.
    properties: Vec<(Ident, syn::Expr)>,
}

/// We parse this in 2 steps: first we parse a `JSONValue`, then we "parse" that further.
impl Parse for Schema {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let obj: JSONObject = input.parse()?;
        Self::try_from(obj)
    }
}

/// Shortcut:
impl TryFrom<JSONValue> for Schema {
    type Error = syn::Error;

    fn try_from(value: JSONValue) -> Result<Self, syn::Error> {
        Self::try_from(value.into_object("a schema definition")?)
    }
}

/// To go from a `JSONObject` to a `Schema` we first extract the description, as it is a common
/// element in all schema entries, then we parse the specific `SchemaItem`, and collect all the
/// remaining "unused" keys as "constraints"/"properties" which will be appended as builder-pattern
/// method calls when translating the object to a schema definition.
impl TryFrom<JSONObject> for Schema {
    type Error = syn::Error;

    fn try_from(mut obj: JSONObject) -> Result<Self, syn::Error> {
        let description = obj
            .remove("description")
            .map(|v| v.try_into())
            .transpose()?;

        Ok(Self {
            span: obj.brace_token.span,
            description,
            item: SchemaItem::try_extract_from(&mut obj)?,
            properties: obj.into_iter().try_fold(
                Vec::new(),
                |mut properties, (key, value)| -> Result<_, syn::Error> {
                    properties.push((Ident::from(key), value.try_into()?));
                    Ok(properties)
                },
            )?,
        })
    }
}

impl Schema {
    fn to_schema(&self, ts: &mut TokenStream) -> Result<(), Error> {
        // First defer to the SchemaItem's `.to_schema()` method:
        let description = self
            .description
            .as_ref()
            .ok_or_else(|| format_err!(self.span, "missing description"))?;

        self.item.to_schema(ts, description)?;

        // Then append all the remaining builder-pattern properties:
        for prop in self.properties.iter() {
            let key = &prop.0;
            let value = &prop.1;
            ts.extend(quote! { .#key(#value) });
        }

        Ok(())
    }
}

enum SchemaItem {
    Null,
    Boolean,
    Integer,
    String,
    Object(SchemaObject),
    Array(SchemaArray),
}

impl SchemaItem {
    /// If there's a `type` specified, parse it as that type. Otherwise check for keys which
    /// uniqueply identify the type, such as "properties" for type `Object`.
    fn try_extract_from(obj: &mut JSONObject) -> Result<Self, syn::Error> {
        let ty = obj.remove("type").map(SimpleIdent::try_from).transpose()?;
        let ty = match &ty {
            Some(ty) => ty.as_str(),
            None => {
                if obj.contains_key("properties") {
                    "Object"
                } else if obj.contains_key("items") {
                    "Array"
                } else {
                    bail!(obj.span(), "failed to guess 'type' in schema definition");
                }
            }
        };
        match ty {
            "Null" => Ok(SchemaItem::Null),
            "Boolean" => Ok(SchemaItem::Boolean),
            "Integer" => Ok(SchemaItem::Integer),
            "String" => Ok(SchemaItem::String),
            "Object" => Ok(SchemaItem::Object(SchemaObject::try_extract_from(obj)?)),
            "Array" => Ok(SchemaItem::Array(SchemaArray::try_extract_from(obj)?)),
            ty => bail!(obj.span(), "unknown type name '{}'", ty),
        }
    }

    fn to_schema(&self, ts: &mut TokenStream, description: &syn::LitStr) -> Result<(), Error> {
        ts.extend(quote! { ::proxmox::api::schema });
        match self {
            SchemaItem::Null => ts.extend(quote! { ::NullSchema::new(#description) }),
            SchemaItem::Boolean => ts.extend(quote! { ::BooleanSchema::new(#description) }),
            SchemaItem::Integer => ts.extend(quote! { ::IntegerSchema::new(#description) }),
            SchemaItem::String => ts.extend(quote! { ::StringSchema::new(#description) }),
            SchemaItem::Object(obj) => {
                let mut elems = TokenStream::new();
                obj.to_schema_inner(&mut elems)?;
                ts.extend(quote! { ::ObjectSchema::new(#description, &[#elems]) })
            }
            SchemaItem::Array(array) => {
                let mut items = TokenStream::new();
                array.to_schema_inner(&mut items)?;
                ts.extend(quote! { ::ArraySchema::new(#description, &#items.schema()) })
            }
        }
        Ok(())
    }
}

/// Contains a sorted list of properties:
struct SchemaObject {
    properties: Vec<(String, bool, Schema)>,
}

impl SchemaObject {
    fn try_extract_from(obj: &mut JSONObject) -> Result<Self, syn::Error> {
        Ok(Self {
            properties: obj
                .remove_required_element("properties")?
                .into_object("object field definition")?
                .into_iter()
                .try_fold(
                    Vec::new(),
                    |mut properties, (key, value)| -> Result<_, syn::Error> {
                        let mut schema: JSONObject =
                            value.into_object("schema definition for field")?;
                        let optional: bool = schema
                            .remove("optional")
                            .map(|opt| -> Result<bool, syn::Error> {
                                let v: syn::LitBool = opt.try_into()?;
                                Ok(v.value)
                            })
                            .transpose()?
                            .unwrap_or(false);
                        properties.push((key.to_string(), optional, schema.try_into()?));
                        Ok(properties)
                    },
                )
                // This must be kept sorted!
                .map(|mut properties| {
                    properties.sort_by(|a, b| (a.0).cmp(&b.0));
                    properties
                })?,
        })
    }

    fn to_schema_inner(&self, ts: &mut TokenStream) -> Result<(), Error> {
        for element in self.properties.iter() {
            let key = &element.0;
            let optional = element.1;
            let mut schema = TokenStream::new();
            element.2.to_schema(&mut schema)?;
            ts.extend(quote! { (#key, #optional, &#schema.schema()), });
        }
        Ok(())
    }
}

struct SchemaArray {
    item: Box<Schema>,
}

impl SchemaArray {
    fn try_extract_from(obj: &mut JSONObject) -> Result<Self, syn::Error> {
        Ok(Self {
            item: Box::new(obj.remove_required_element("items")?.try_into()?),
        })
    }

    fn to_schema_inner(&self, ts: &mut TokenStream) -> Result<(), Error> {
        self.item.to_schema(ts)
    }
}

/// We get macro attributes like `#[input(THIS)]` with the parenthesis around `THIS` included.
struct Parenthesized<T: Parse> {
    pub token: syn::token::Paren,
    pub content: T,
}

impl<T: Parse> Parse for Parenthesized<T> {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let content;
        Ok(Self {
            token: parenthesized!(content in input),
            content: content.parse()?,
        })
    }
}

/// We get macro attributes like `#[doc = "TEXT"]` with the `=` included.
struct BareAssignment<T: Parse> {
    pub token: Token![=],
    pub content: T,
}

impl<T: Parse> Parse for BareAssignment<T> {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        Ok(Self {
            token: input.parse()?,
            content: input.parse()?,
        })
    }
}

/// Parse `#[input()]`, `#[returns()]` and `#[protected]` attributes out of an function annotated
/// with an `#[api]` attribute and produce a `const ApiMethod` named after the function.
///
/// See the top level macro documentation for a complete example.
pub(crate) fn api(attr: TokenStream, item: TokenStream) -> Result<TokenStream, Error> {
    let mut attribs = JSONObject::parse_inner.parse2(attr)?;
    let mut func: syn::ItemFn = syn::parse2(item)?;

    let mut input_schema: Schema = attribs
        .remove_required_element("input")?
        .into_object("input schema definition")?
        .try_into()?;

    let mut returns_schema: Schema = attribs
        .remove_required_element("returns")?
        .into_object("return schema definition")?
        .try_into()?;

    let protected: bool = attribs
        .remove("protected")
        .map(TryFrom::try_from)
        .transpose()?
        .unwrap_or(false);

    api_function_attributes(&mut input_schema, &mut returns_schema, &mut func.attrs)?;

    handle_function_signature(&mut input_schema, &mut returns_schema, &mut func)?;

    let input_schema = {
        let mut ts = TokenStream::new();
        input_schema.to_schema(&mut ts)?;
        ts
    };

    let returns_schema = {
        let mut ts = TokenStream::new();
        returns_schema.to_schema(&mut ts)?;
        ts
    };

    let vis = &func.vis;
    let func_name = &func.sig.ident;
    let api_method_name = Ident::new(
        &format!("API_METHOD_{}", func_name.to_string().to_uppercase()),
        func.sig.ident.span(),
    );

    Ok(quote_spanned! { func.sig.span() =>
        #vis const #api_method_name: ::proxmox::api::ApiMethod =
            ::proxmox::api::ApiMethod::new(
                &::proxmox::api::ApiHandler::Sync(&#func_name),
                &#input_schema,
            )
            .returns(& #returns_schema .schema())
            .protected(#protected);
        #func
    })
    //Ok(quote::quote!(#func))
}

fn api_function_attributes(
    input_schema: &mut Schema,
    returns_schema: &mut Schema,
    attrs: &mut Vec<syn::Attribute>,
) -> Result<(), Error> {
    let mut doc_comment = String::new();
    let doc_span = Span::call_site(); // FIXME: set to first doc comment

    for attr in mem::replace(attrs, Vec::new()) {
        // don't mess with #![...]
        if let syn::AttrStyle::Inner(_) = &attr.style {
            attrs.push(attr);
            continue;
        }

        if attr.path.is_ident("doc") {
            let doc: BareAssignment<syn::LitStr> = syn::parse2(attr.tokens.clone())?;
            if !doc_comment.is_empty() {
                doc_comment.push_str("\n");
            }
            doc_comment.push_str(doc.content.value().trim());
            attrs.push(attr);
        } else {
            attrs.push(attr);
        }
    }

    derive_descriptions(input_schema, returns_schema, &doc_comment, doc_span)
}

fn derive_descriptions(
    input_schema: &mut Schema,
    returns_schema: &mut Schema,
    doc_comment: &str,
    doc_span: Span,
) -> Result<(), Error> {
    // If we have a doc comment, allow automatically inferring the description for the input and
    // output objects:
    if doc_comment.is_empty() {
        return Ok(());
    }

    let mut parts = doc_comment.split("\nReturns:");

    if let Some(first) = parts.next() {
        if input_schema.description.is_none() {
            input_schema.description = Some(syn::LitStr::new(first.trim(), doc_span));
        }
    }

    if let Some(second) = parts.next() {
        if returns_schema.description.is_none() {
            returns_schema.description = Some(syn::LitStr::new(second.trim(), doc_span));
        }
    }

    if parts.next().is_some() {
        bail!(
            doc_span,
            "multiple 'Returns:' sections found in doc comment!"
        );
    }

    Ok(())
}

fn handle_function_signature(
    _input_schema: &mut Schema,
    _returns_schema: &mut Schema,
    func: &mut syn::ItemFn,
) -> Result<(), Error> {
    let sig = &func.sig;

    if sig.asyncness.is_some() {
        bail!(sig => "async fn is currently not supported");
    }

    Ok(())
}