bubba-macros 0.1.0

//! # `view!` Procedural Macro
//!
//! Transforms declarative JSX-like UI syntax into Rust [`Element`] builder calls.
//!
//! ## Input (what you write)
//! ```rust,ignore
//! view! {
//!     <h1 class="title">"Welcome to Bubba"</h1>
//!     <button class="primary-btn" onclick=alert("Tapped!")>
//!         "Tap me"
//!     </button>
//!     <input class="text-input" oninput=log("Typing...") />
//! }
//! ```
//!
//! ## Output (what it expands to)
//! ```rust,ignore
//! {
//!     use bubba_core::ui::Element;
//!     use bubba_core::events::EventHandler;
//!
//!     let mut __root = Element::div();
//!     __root = __root.child(
//!         Element::h1()
//!             .class("title")
//!             .text("Welcome to Bubba")
//!     );
//!     __root = __root.child(
//!         Element::button()
//!             .class("primary-btn")
//!             .text("Tap me")
//!             .on(EventHandler::onclick(|_| { alert("Tapped!") }))
//!     );
//!     __root = __root.child(
//!         Element::input()
//!             .class("text-input")
//!             .on(EventHandler::oninput(|_| { log("Typing...") }))
//!     );
//!     bubba_core::ui::Screen::new(__root)
//! }
//! ```

use proc_macro::TokenStream;
use proc_macro2::{Span, TokenStream as TokenStream2};
use quote::{quote, quote_spanned};
use syn::{
    parse::{Parse, ParseStream},
    parse_macro_input,
    spanned::Spanned,
    Expr, Ident, LitStr, Result, Token,
};

// ── Public macro entry point ──────────────────────────────────────────────────

/// Declare a screen's UI declaratively using JSX-like syntax.
///
/// # Supported Tags
/// `<h1>`, `<h2>`, `<h3>`, `<p>`, `<button>`, `<img>`, `<input>`,
/// `<div>`, `<span>`, `<a>`
///
/// # Supported Attributes
/// - `class="..."` — CSS class name(s)
/// - `src="..."`, `alt="..."`, `placeholder="..."`, `href="..."` — generic attrs
/// - `onclick=expr` — tap/click handler
/// - `oninput=expr` — input change handler  
/// - `onkeypress=expr` — key press handler
/// - `onfocus=expr` — focus handler
/// - `onblur=expr` — blur handler
///
/// # Built-in Event Expressions
/// - `alert("message")` — show native alert
/// - `log("message")` — log to console
/// - `navigate(ScreenName)` — navigate to a screen
#[proc_macro]
pub fn view(input: TokenStream) -> TokenStream {
    let nodes = parse_macro_input!(input as NodeList);
    let expanded = codegen_screen(nodes);
    TokenStream::from(expanded)
}

// ── AST types ─────────────────────────────────────────────────────────────────

/// A list of top-level nodes inside `view! { ... }`.
struct NodeList {
    nodes: Vec<Node>,
}

impl Parse for NodeList {
    fn parse(input: ParseStream) -> Result<Self> {
        let mut nodes = Vec::new();
        while !input.is_empty() {
            nodes.push(input.parse::<Node>()?);
        }
        Ok(NodeList { nodes })
    }
}

/// A single UI node — either a tag or a text literal.
enum Node {
    Element(ParsedElement),
    Text(LitStr),
}

impl Parse for Node {
    fn parse(input: ParseStream) -> Result<Self> {
        if input.peek(LitStr) {
            Ok(Node::Text(input.parse()?))
        } else {
            Ok(Node::Element(input.parse()?))
        }
    }
}

/// A parsed `<tag attr=val ...> children </tag>` or `<tag ... />`.
struct ParsedElement {
    span: Span,
    tag: Ident,
    attrs: Vec<ParsedAttr>,
    children: Vec<Node>,
}

impl Parse for ParsedElement {
    fn parse(input: ParseStream) -> Result<Self> {
        // `<`
        let lt: Token![<] = input.parse().map_err(|e| {
            syn::Error::new(e.span(), "Expected `<` to open a UI element.\n\nTip: every element starts with `<`, like `<button>` or `<h1>`.")
        })?;
        let span = lt.span();

        // tag name
        let tag: Ident = input.parse().map_err(|e| {
            syn::Error::new(e.span(), "Expected a tag name after `<`.\n\nSupported tags: h1, h2, h3, p, button, img, input, div, span, a")
        })?;

        // attributes
        let mut attrs = Vec::new();
        while !input.peek(Token![>]) && !input.peek(Token![/]) {
            attrs.push(input.parse::<ParsedAttr>()?);
        }

        // self-closing `/>` → return immediately; open `>` → parse children
        if input.peek(Token![/]) {
            input.parse::<Token![/]>()?;
            input.parse::<Token![>]>()?;
            return Ok(ParsedElement { span, tag, attrs, children: vec![] });
        }
        input.parse::<Token![>]>()?;

        // children
        let mut children = Vec::new();
        loop {
            // closing tag `</tag>`
            if input.peek(Token![<]) && input.peek2(Token![/]) {
                input.parse::<Token![<]>()?;
                input.parse::<Token![/]>()?;
                let closing_tag: Ident = input.parse().map_err(|e| {
                    syn::Error::new(e.span(), "Expected closing tag name.")
                })?;
                input.parse::<Token![>]>()?;

                if closing_tag != tag {
                    return Err(syn::Error::new(
                        closing_tag.span(),
                        format!(
                            "Mismatched tags: opened `<{}>` but closed with `</{}>`.\n\nTip: every opening tag needs a matching closing tag.",
                            tag, closing_tag
                        ),
                    ));
                }
                break;
            }
            if input.is_empty() {
                return Err(syn::Error::new(
                    span,
                    format!("Unclosed `<{}>` — missing `</{}>`.\n\nTip: add `</{}>` after the children.", tag, tag, tag),
                ));
            }
            children.push(input.parse::<Node>()?);
        }

        Ok(ParsedElement { span, tag, attrs, children })
    }
}

/// A single attribute: `class="..."`, `onclick=expr`, `src="..."`, etc.
struct ParsedAttr {
    name: Ident,
    value: AttrValue,
}

/// The value side of an attribute.
enum AttrValue {
    /// A string literal: `class="title"`
    Str(LitStr),
    /// A Rust expression: `onclick=alert("hi")` or `onclick=navigate(Profile)`
    Expr(Expr),
}

impl Parse for ParsedAttr {
    fn parse(input: ParseStream) -> Result<Self> {
        let name: Ident = input.parse().map_err(|e| {
            syn::Error::new(e.span(), "Expected an attribute name (e.g. `class`, `onclick`, `src`).")
        })?;
        input.parse::<Token![=]>().map_err(|e| {
            syn::Error::new(e.span(), format!("Attribute `{}` needs a value: `{}=\"...\"` or `{}=expr`.", name, name, name))
        })?;

        let value = if input.peek(LitStr) {
            AttrValue::Str(input.parse()?)
        } else {
            // Parse a call expression like `alert("msg")`, `navigate(Screen)`,
            // `log("x")`, or a closure `|e| { ... }`.
            //
            // We deliberately do NOT call `input.parse::<Expr>()` because that
            // would greedily consume past the closing `>` into the tag's children.
            // Instead we parse just the function name / path, then optionally
            // a parenthesised argument list or a closure body.
            let expr = parse_event_expr(input).map_err(|e| {
                syn::Error::new(
                    e.span(),
                    format!(
                        "Could not parse value for `{}`.\n\nExamples:\n  {}=\"some-class\"\n  {}=alert(\"message\")\n  {}=navigate(ScreenName)",
                        name, name, name, name
                    ),
                )
            })?;
            AttrValue::Expr(expr)
        };

        Ok(ParsedAttr { name, value })
    }
}

/// Parse an event-handler expression that must NOT consume past `>` or `/>`.
///
/// Accepted forms:
///   `ident(args...)`          — function call: alert("hi"), navigate(Home)
///   `|pat| expr`              — closure
///   `|pat| { block }`         — closure with block
///   `ident`                   — bare function reference
fn parse_event_expr(input: ParseStream) -> Result<Expr> {
    // Closure: |pat| ...
    if input.peek(Token![|]) {
        return input.parse::<Expr>();
    }

    // Parse a path (possibly multi-segment: foo::bar)
    let path: syn::ExprPath = input.parse()?;

    // If followed by `(`, parse the argument list
    if input.peek(syn::token::Paren) {
        let args_content;
        let paren = syn::parenthesized!(args_content in input);
        let args: syn::punctuated::Punctuated<Expr, Token![,]> =
            args_content.parse_terminated(Expr::parse, Token![,])?;

        Ok(Expr::Call(syn::ExprCall {
            attrs: vec![],
            func: Box::new(Expr::Path(path)),
            paren_token: paren,
            args,
        }))
    } else {
        // Bare path / function reference
        Ok(Expr::Path(path))
    }
}

// ── Code generation ───────────────────────────────────────────────────────────

fn codegen_screen(nodes: NodeList) -> TokenStream2 {
    let element_stmts: Vec<TokenStream2> = nodes.nodes.iter().map(codegen_node_as_child).collect();
    quote! {
        {
            let mut __bubba_root = ::bubba_core::ui::Element::div();
            #(#element_stmts)*
            ::bubba_core::ui::Screen::new(__bubba_root)
        }
    }
}

fn codegen_node_as_child(node: &Node) -> TokenStream2 {
    match node {
        Node::Text(lit) => {
            quote! {
                __bubba_root = __bubba_root.child(
                    ::bubba_core::ui::Element::span().text(#lit)
                );
            }
        }
        Node::Element(el) => {
            let el_expr = codegen_element(el);
            quote! {
                __bubba_root = __bubba_root.child(#el_expr);
            }
        }
    }
}

fn codegen_element(el: &ParsedElement) -> TokenStream2 {
    let tag = &el.tag;
    let tag_str = tag.to_string();
    let span = el.span;

    // Start with the constructor
    let mut builder = quote_spanned! { span =>
        ::bubba_core::ui::Element::new(#tag_str)
    };

    // Process attributes
    for attr in &el.attrs {
        let attr_name = attr.name.to_string();
        match &attr.value {
            AttrValue::Str(s) => {
                match attr_name.as_str() {
                    "class" => {
                        builder = quote! { #builder.class(#s) };
                    }
                    _ => {
                        builder = quote! { #builder.attr(#attr_name, #s) };
                    }
                }
            }
            AttrValue::Expr(expr) => {
                let event_name = match attr_name.as_str() {
                    "onclick"    => Some("click"),
                    "oninput"    => Some("input"),
                    "onkeypress" => Some("keypress"),
                    "onfocus"    => Some("focus"),
                    "onblur"     => Some("blur"),
                    "onchange"   => Some("change"),
                    other => {
                        // Unknown event — emit a compile_error pointing at the attribute
                        let msg = format!(
                            "Unknown event attribute `{}`. Did you mean `onclick`, `oninput`, or `onkeypress`?",
                            other
                        );
                        builder = quote! {
                            #builder
                            compile_error!(#msg)
                        };
                        None
                    }
                };

                if let Some(ev) = event_name {
                    let handler_expr = codegen_event_expr(expr, ev);
                    builder = quote! { #builder.on(#handler_expr) };
                }
            }
        }
    }

    // Process children
    for child in &el.children {
        match child {
            Node::Text(lit) => {
                builder = quote! { #builder.text(#lit) };
            }
            Node::Element(child_el) => {
                let child_expr = codegen_element(child_el);
                builder = quote! { #builder.child(#child_expr) };
            }
        }
    }

    builder
}

/// Transform a Bubba event expression into a Rust EventHandler.
///
/// `alert("msg")`          → `EventHandler::new("click", |_| { alert("msg") })`
/// `log("msg")`            → `EventHandler::new("click", |_| { log_msg("msg") })`
/// `navigate(ScreenName)`  → `EventHandler::new("click", |_| { navigate_to(stringify!(ScreenName), ScreenName) })`
/// `my_custom_fn()`        → `EventHandler::new("click", |_| { my_custom_fn() })`
fn codegen_event_expr(expr: &Expr, event: &str) -> TokenStream2 {
    // Pattern-match Bubba built-ins, fall back to user expr
    match expr {
        Expr::Call(call) => {
            if let Expr::Path(path) = call.func.as_ref() {
                let name = path.path.segments.last().map(|s| s.ident.to_string());
                match name.as_deref() {
                    Some("alert") => {
                        let args = &call.args;
                        return quote! {
                            ::bubba_core::events::EventHandler::new(#event, move |_| {
                                ::bubba_core::runtime::alert(#args);
                            })
                        };
                    }
                    Some("log") => {
                        let args = &call.args;
                        return quote! {
                            ::bubba_core::events::EventHandler::new(#event, move |_| {
                                ::bubba_core::runtime::log_msg(#args);
                            })
                        };
                    }
                    Some("navigate") => {
                        // navigate(Profile) → navigate_to("Profile", Profile)
                        if let Some(screen_arg) = call.args.first() {
                            return quote! {
                                ::bubba_core::events::EventHandler::new(#event, move |_| {
                                    ::bubba_core::navigation::navigate_to(
                                        stringify!(#screen_arg),
                                        #screen_arg,
                                    );
                                })
                            };
                        }
                    }
                    _ => {}
                }
            }
            // Generic call expression
            quote! {
                ::bubba_core::events::EventHandler::new(#event, move |_| { #expr; })
            }
        }
        // Closure passed directly: onclick=|_| { ... }
        Expr::Closure(closure) => {
            quote! {
                ::bubba_core::events::EventHandler::new(#event, #closure)
            }
        }
        // Any other expression
        _ => {
            quote! {
                ::bubba_core::events::EventHandler::new(#event, move |_| { #expr; })
            }
        }
    }
}