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//! `glsl-lang-quote` offers proc-macros to quote GLSL syntax in Rust, using the [glsl_lang] crate.
//!
//! # Usage
//!
//! ```
//! use glsl_lang_quote::glsl;
//!
//! // Parse a translation unit at compile time
//! let ast = glsl! {
//!     void main() {
//!         gl_FragColor = vec4(1., 0., 0., 1.);
//!     }
//! };
//!
//! // There is exactly one external declaration
//! assert_eq!(ast.0.len(), 1);
//! ```
//!
//! # Parsing expressions
//!
//! This crate offers a set of features `quote-expr`, `quote-preprocessor`, and `quote-statement`.
//! Enabling those features enable the respective `parser-expr`, `parser-preprocessor` and
//! `parser-statement` in [glsl_lang], which creates dedicated parsers for those types of GLSL
//! fragments of the language grammar.
//!
//! This is the most efficient option for parsing lots of expressions and statements at
//! compile-time, however this will slow down the initial compilation of `glsl-lang-quote` since
//! the generated parser file in [glsl_lang] will be much larger.
//!
//! This is why by default, this crate enables the `quote-parsable` feature, which uses
//! [glsl_lang]'s [glsl_lang::parse::Parsable] trait, whose limitations apply. Whichever method you
//! chose, the following code will work:
//!
//! ```
//! use glsl_lang_quote::glsl_expr;
//!
//! // Parse an expression
//! let ast = glsl_expr! {
//!     a = vec4(1., 0., 0., 1.)
//! };
//! ```
//!
//! # Quoting and stateful lexers
//!
//! Since [glsl_lang]'s parser has a stateful lexer (to handle the fact that GLSL's grammar is not
//! context-free), declaring a type (a `struct` for example) and using it must happen in the same
//! macro invocation, otherwise the parser will *forget* about the previously declared types. The
//! best is to only parse whole translation units ([glsl!] macro), or parse unambiguous fragments
//! (such as expressions, but not statements).
//!
//! ```ignore
//! use glsl_lang_quote::{glsl, glsl_statement};
//!
//! // This is ok:
//! let ast = glsl! {
//!     struct PointLight {
//!         vec3 pos;
//!         vec3 color;
//!     }
//!
//!     PointLight p;
//! };
//!
//! // This will not compile, PointLight can't be parsed as a type name without extra state
//! let statement = glsl_expr! {
//!     PointLight p;
//! };

#![deny(missing_docs)]

use glsl_lang::{
    ast,
    parse::{Parsable, ParseOptions},
};
use proc_macro2::TokenStream;

use crate::tokenize::Tokenize;

mod quoted;
mod tokenize;

fn glsl_internal<F>(input: proc_macro::TokenStream) -> proc_macro::TokenStream
where
    F: Parsable + Tokenize + std::fmt::Debug,
{
    let s = format!("{}", &input);
    let opts = ParseOptions {
        allow_rs_ident: true,
        ..Default::default()
    }
    .build();
    let parsed: Result<(F, _), _> = Parsable::parse_with_options(&s, &opts);

    if let Ok((tu, _)) = parsed {
        // create the stream and return it
        let mut stream = TokenStream::new();
        tu.tokenize(&mut stream);

        stream.into()
    } else {
        panic!("GLSL error: {:?}", parsed);
    }
}

/// Parse a translation unit at compile time
#[proc_macro]
pub fn glsl(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    glsl_internal::<ast::TranslationUnit>(input)
}

/// Parse a statement at compile time
#[cfg(any(feature = "quote-statement", feature = "quote-parsable"))]
#[proc_macro]
pub fn glsl_statement(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    glsl_internal::<ast::Statement>(input)
}

/// Parse an expression at compile time
#[cfg(any(feature = "quote-expr", feature = "quote-parsable"))]
#[proc_macro]
pub fn glsl_expr(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    glsl_internal::<ast::Expr>(input)
}