use proc_macro2::TokenStream;
use quote::{format_ident, quote};
use syn::{
  parse::Parser, punctuated::Punctuated, FnArg, Ident, ItemFn, Meta, NestedMeta, Pat, Path,
  ReturnType, Token, Type,
};

pub fn generate_command(attrs: Vec<NestedMeta>, function: ItemFn) -> TokenStream {
  // Check if "with_manager" attr was passed to macro
  let uses_manager = attrs.iter().any(|a| {
    if let NestedMeta::Meta(Meta::Path(path)) = a {
      path
        .get_ident()
        .map(|i| *i == "with_manager")
        .unwrap_or(false)
    } else {
      false
    }
  });

  let fn_name = function.sig.ident.clone();
  let fn_name_str = fn_name.to_string();
  let fn_wrapper = format_ident!("{}_wrapper", fn_name);
  let returns_result = match function.sig.output {
    ReturnType::Type(_, ref ty) => match &**ty {
      Type::Path(type_path) => {
        type_path
          .path
          .segments
          .first()
          .map(|seg| seg.ident.to_string())
          == Some("Result".to_string())
      }
      _ => false,
    },
    ReturnType::Default => false,
  };

  // Split function args into names and types
  let (mut names, mut types): (Vec<Ident>, Vec<Path>) = function
    .sig
    .inputs
    .iter()
    .map(|param| {
      let mut arg_name = None;
      let mut arg_type = None;
      if let FnArg::Typed(arg) = param {
        if let Pat::Ident(ident) = arg.pat.as_ref() {
          arg_name = Some(ident.ident.clone());
        }
        if let Type::Path(path) = arg.ty.as_ref() {
          arg_type = Some(path.path.clone());
        }
      }
      (
        arg_name.clone().unwrap(),
        arg_type.unwrap_or_else(|| panic!("Invalid type for arg \"{}\"", arg_name.unwrap())),
      )
    })
    .unzip();

  // If function doesn't take the webview manager, wrapper just takes webview manager generically and ignores it
  // Otherwise the wrapper uses the specific type from the original function declaration
  let mut manager_arg_type = quote!(::tauri::WebviewManager<A>);
  let mut application_ext_generic = quote!(<A: ::tauri::ApplicationExt>);
  let manager_arg_maybe = match types.first() {
    Some(first_type) if uses_manager => {
      // Give wrapper specific type
      manager_arg_type = quote!(#first_type);
      // Generic is no longer needed
      application_ext_generic = quote!();
      // Remove webview manager arg from list so it isn't expected as arg from JS
      types.drain(0..1);
      names.drain(0..1);
      // Tell wrapper to pass webview manager to original function
      quote!(_manager,)
    }
    // Tell wrapper not to pass webview manager to original function
    _ => quote!(),
  };
  let await_maybe = if function.sig.asyncness.is_some() {
    quote!(.await)
  } else {
    quote!()
  };

  // if the command handler returns a Result,
  // we just map the values to the ones expected by Tauri
  // otherwise we wrap it with an `Ok()`, converting the return value to tauri::InvokeResponse
  // note that all types must implement `serde::Serialize`.
  let return_value = if returns_result {
    quote! {
      match #fn_name(#manager_arg_maybe #(parsed_args.#names),*)#await_maybe {
        Ok(value) => ::core::result::Result::Ok(value.into()),
        Err(e) => ::core::result::Result::Err(tauri::Error::Command(::serde_json::to_value(e)?)),
      }
    }
  } else {
    quote! { ::core::result::Result::Ok(#fn_name(#manager_arg_maybe #(parsed_args.#names),*)#await_maybe.into()) }
  };

  quote! {
    #function
    pub async fn #fn_wrapper #application_ext_generic(_manager: #manager_arg_type, arg: ::serde_json::Value) -> ::tauri::Result<::tauri::InvokeResponse> {
      #[derive(::serde::Deserialize)]
      #[serde(rename_all = "camelCase")]
      struct ParsedArgs {
        #(#names: #types),*
      }
      let parsed_args: ParsedArgs = ::serde_json::from_value(arg).map_err(|e| ::tauri::Error::InvalidArgs(#fn_name_str, e))?;
      #return_value
    }
  }
}

pub fn generate_handler(item: proc_macro::TokenStream) -> TokenStream {
  // Get paths of functions passed to macro
  let paths = <Punctuated<Path, Token![,]>>::parse_terminated
    .parse(item)
    .expect("generate_handler!: Failed to parse list of command functions");

  // Get names of functions, used for match statement
  let fn_names = paths
    .iter()
    .map(|p| p.segments.last().unwrap().ident.clone());

  // Get paths to wrapper functions
  let fn_wrappers = paths.iter().map(|func| {
    let mut func = func.clone();
    let mut last_segment = func.segments.last_mut().unwrap();
    last_segment.ident = format_ident!("{}_wrapper", last_segment.ident);
    func
  });

  quote! {
    |webview_manager, arg| async move {
      let dispatch: ::std::result::Result<::tauri::DispatchInstructions, ::serde_json::Error> =
      ::serde_json::from_str(&arg);
      match dispatch {
        Err(e) => Err(e.into()),
        Ok(dispatch) => {
          match dispatch.cmd.as_str() {
            #(stringify!(#fn_names) => #fn_wrappers(webview_manager, dispatch.args).await,)*
            _ => Err(tauri::Error::UnknownApi(None)),
          }
        }
      }
    }
  }
}