use proc_macro::TokenStream;
use proc_macro2::Span;
use quote::{format_ident, quote};
use syn::{
    parse_macro_input, FnArg, ItemFn, PatType, ReturnType,
    Visibility,
};

/**
* wrap webtest annotated functions in an async Pin<Box>
**/
pub fn webtest_impl(_args: TokenStream, input: TokenStream) -> TokenStream {
    let input_fn = parse_macro_input!(input as ItemFn);

    if let Err(err) = validate_function(&input_fn) {
        return syn::Error::new(Span::call_site(), err)
            .to_compile_error()
            .into();
    }

    let fn_name = &input_fn.sig.ident;
    let fn_name_str = fn_name.to_string();
    let vis = &input_fn.vis;
    let attrs = &input_fn.attrs;
    let fn_block = &input_fn.block;
    let fn_inputs = &input_fn.sig.inputs;
    let fn_output = &input_fn.sig.output;
    let fn_generics = &input_fn.sig.generics;
    let fn_asyncness = &input_fn.sig.asyncness;

    let original_fn_name = format_ident!("{}_original", fn_name);

    let expanded = quote! {
        #(#attrs)*
        #vis #fn_asyncness fn #original_fn_name #fn_generics(#fn_inputs) #fn_output #fn_block

        fn #fn_name #fn_generics(
            driver: &::thirtyfour::WebDriver
        ) -> ::std::pin::Pin<Box<dyn ::std::future::Future<Output = crate::TestResult> + Send + '_>> {
            Box::pin(async move {
                #original_fn_name(driver).await
            })
        }

        ::inventory::submit! {
            crate::TestFunction {
                name: #fn_name_str,
                func: #fn_name,
            }
        }
    };

    TokenStream::from(expanded)
}

fn validate_function(func: &ItemFn) -> Result<(), String> {
    is_async(func)?;
    is_visible(func)?;
    matches_arguments(&["WebDriver"], func)?;
    matches_return_type("TestResult", func)?;

    Ok(())
}

fn is_async(func: &ItemFn) -> Result<(), String> {
    if func.sig.asyncness.is_none() {
        Err("Test functions must be async".to_string())
    } else { Ok(()) }
}

fn is_visible(func: &ItemFn) -> Result<(), String> {
    match func.vis {
        Visibility::Inherited | Visibility::Public(_) => {
            Ok(())
        }
        _ => {
            Err("Test functions should be pub or have default visibility".to_string())
        }
    }
}

fn matches_arguments(types: &[&str], func: &ItemFn) -> Result<(), String> {
    let args = matches_argument_count(types.len(), func)?;
    for index in 0..args.len() {
        matches_argument_type(types.get(index).unwrap(), args.get(index).unwrap())?;
    }
    Ok(())
}

fn matches_argument_count(expected: usize, func: &ItemFn) -> Result<Vec<&FnArg>, String> {
    let inputs: Vec<_> = func.sig.inputs.iter().collect();
    if inputs.len() != expected {
        Err(format!("Test functions must take exactly {} parameters", expected))
    } else { Ok(inputs) }
}

fn matches_argument_type(expected: &str, arg: &FnArg) -> Result<(), String> {
    match arg {
        FnArg::Receiver(_) => {
            Err("Test functions cannot be methods (no self parameter)".to_string())
        }
        FnArg::Typed(PatType { ty, .. }) => {
            let type_str = quote!(#ty).to_string();
            if !type_str.contains(expected) {
                Err("First parameter must be &WebDriver".to_string())
            } else { Ok(()) }
        }
    }
}

fn matches_return_type(expected: &str, func: &ItemFn) -> Result<(), String> {
    match &func.sig.output {
        ReturnType::Default => {
            Err("Test functions must return TestResult".to_string())
        }
        ReturnType::Type(_, ty) => {
            let type_str = quote!(#ty).to_string();
            if !type_str.contains(expected) && !type_str.contains("Result") {
                Err("Test functions must return TestResult".to_string())
            } else { Ok(()) }
        }
    }
}