#![deny(warnings)]

extern crate proc_macro;
extern crate rand;
#[macro_use]
extern crate quote;
extern crate core;
extern crate proc_macro2;
#[macro_use]
extern crate syn;

use proc_macro2::Span;
use rand::Rng;
use rand::SeedableRng;
use std::collections::HashSet;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::time::{SystemTime, UNIX_EPOCH};
use syn::{
    parse, spanned::Spanned, AttrStyle, Attribute, FnArg, Ident, Item, ItemFn, ItemStatic,
    PathArguments, ReturnType, Stmt, Type, Visibility,
};

static CALL_COUNT: AtomicUsize = AtomicUsize::new(0);

use proc_macro::TokenStream;

/// Attribute to declare the entry point of the program
///
/// **IMPORTANT**: This attribute must appear exactly *once* in the dependency graph. Also, if you
/// are using Rust 1.30 the attribute must be used on a reachable item (i.e. there must be no
/// private modules between the item and the root of the crate); if the item is in the root of the
/// crate you'll be fine. This reachability restriction doesn't apply to Rust 1.31 and newer releases.
///
/// The specified function will be called by the reset handler *after* RAM has been initialized. In
/// the case of the `thumbv7em-none-eabihf` target the FPU will also be enabled before the function
/// is called.
///
/// The type of the specified function must be `[unsafe] fn() -> !` (never ending function)
///
/// # Properties
///
/// The entry point will be called by the reset handler. The program can't reference to the entry
/// point, much less invoke it.
///
/// `static mut` variables declared within the entry point are safe to access. The compiler can't
/// prove this is safe so the attribute will help by making a transformation to the source code: for
/// this reason a variable like `static mut FOO: u32` will become `let FOO: &'static mut u32;`. Note
/// that `&'static mut` references have move semantics.
///
/// # Examples
///
/// - Simple entry point
///
/// ``` no_run
/// # #![no_main]
/// # use cortex_m_rt_macros::entry;
/// #[entry]
/// fn main() -> ! {
///     loop {
///         /* .. */
///     }
/// }
/// ```
///
/// - `static mut` variables local to the entry point are safe to modify.
///
/// ``` no_run
/// # #![no_main]
/// # use cortex_m_rt_macros::entry;
/// #[entry]
/// fn main() -> ! {
///     static mut FOO: u32 = 0;
///
///     let foo: &'static mut u32 = FOO;
///     assert_eq!(*foo, 0);
///     *foo = 1;
///     assert_eq!(*foo, 1);
///
///     loop {
///         /* .. */
///     }
/// }
/// ```
#[proc_macro_attribute]
pub fn entry(args: TokenStream, input: TokenStream) -> TokenStream {
    let f = parse_macro_input!(input as ItemFn);

    // check the function signature
    let valid_signature = f.constness.is_none()
        && f.vis == Visibility::Inherited
        && f.abi.is_none()
        && f.decl.inputs.is_empty()
        && f.decl.generics.params.is_empty()
        && f.decl.generics.where_clause.is_none()
        && f.decl.variadic.is_none()
        && match f.decl.output {
            ReturnType::Default => false,
            ReturnType::Type(_, ref ty) => match **ty {
                Type::Never(_) => true,
                _ => false,
            },
        };

    if !valid_signature {
        return parse::Error::new(
            f.span(),
            "`#[entry]` function must have signature `[unsafe] fn() -> !`",
        )
        .to_compile_error()
        .into();
    }

    if !args.is_empty() {
        return parse::Error::new(Span::call_site(), "This attribute accepts no arguments")
            .to_compile_error()
            .into();
    }

    // XXX should we blacklist other attributes?
    let attrs = f.attrs;
    let unsafety = f.unsafety;
    let hash = random_ident();
    let (statics, stmts) = match extract_static_muts(f.block.stmts) {
        Err(e) => return e.to_compile_error().into(),
        Ok(x) => x,
    };

    let vars = statics
        .into_iter()
        .map(|var| {
            let (ref cfgs, ref attrs) = extract_cfgs(var.attrs);
            let ident = var.ident;
            let ty = var.ty;
            let expr = var.expr;

            quote!(
                #[allow(non_snake_case)]
                #(#cfgs)*
                let #ident: &'static mut #ty = unsafe {
                    #(#attrs)*
                    #(#cfgs)*
                    static mut #ident: #ty = #expr;

                    &mut #ident
                };
            )
        })
        .collect::<Vec<_>>();

    quote!(
        #[export_name = "main"]
        #(#attrs)*
        pub #unsafety fn #hash() -> ! {
            #(#vars)*

            #(#stmts)*
        }
    )
    .into()
}

/// Attribute to declare an exception handler
///
/// **IMPORTANT**: If you are using Rust 1.30 this attribute must be used on reachable items (i.e.
/// there must be no private modules between the item and the root of the crate); if the item is in
/// the root of the crate you'll be fine. This reachability restriction doesn't apply to Rust 1.31
/// and newer releases.
///
/// # Syntax
///
/// ```
/// # use cortex_m_rt_macros::exception;
/// #[exception]
/// fn SysTick() {
///     // ..
/// }
///
/// # fn main() {}
/// ```
///
/// where the name of the function must be one of:
///
/// - `DefaultHandler`
/// - `NonMaskableInt`
/// - `HardFault`
/// - `MemoryManagement` (a)
/// - `BusFault` (a)
/// - `UsageFault` (a)
/// - `SecureFault` (b)
/// - `SVCall`
/// - `DebugMonitor` (a)
/// - `PendSV`
/// - `SysTick`
///
/// (a) Not available on Cortex-M0 variants (`thumbv6m-none-eabi`)
///
/// (b) Only available on ARMv8-M
///
/// # Usage
///
/// `#[exception] fn HardFault(..` sets the hard fault handler. The handler must have signature
/// `[unsafe] fn(&ExceptionFrame) -> !`. This handler is not allowed to return as that can cause
/// undefined behavior.
///
/// `#[exception] fn DefaultHandler(..` sets the *default* handler. All exceptions which have not
/// been assigned a handler will be serviced by this handler. This handler must have signature
/// `[unsafe] fn(irqn: i16) [-> !]`. `irqn` is the IRQ number (See CMSIS); `irqn` will be a negative
/// number when the handler is servicing a core exception; `irqn` will be a positive number when the
/// handler is servicing a device specific exception (interrupt).
///
/// `#[exception] fn Name(..` overrides the default handler for the exception with the given `Name`.
/// These handlers must have signature `[unsafe] fn() [-> !]`. When overriding these other exception
/// it's possible to add state to them by declaring `static mut` variables at the beginning of the
/// body of the function. These variables will be safe to access from the function body.
///
/// # Properties
///
/// Exception handlers can only be called by the hardware. Other parts of the program can't refer to
/// the exception handlers, much less invoke them as if they were functions.
///
/// `static mut` variables declared within an exception handler are safe to access and can be used
/// to preserve state across invocations of the handler. The compiler can't prove this is safe so
/// the attribute will help by making a transformation to the source code: for this reason a
/// variable like `static mut FOO: u32` will become `let FOO: &mut u32;`.
///
/// # Examples
///
/// - Setting the `HardFault` handler
///
/// ```
/// # extern crate cortex_m_rt;
/// # extern crate cortex_m_rt_macros;
/// # use cortex_m_rt_macros::exception;
/// #[exception]
/// fn HardFault(ef: &cortex_m_rt::ExceptionFrame) -> ! {
///     // prints the exception frame as a panic message
///     panic!("{:#?}", ef);
/// }
///
/// # fn main() {}
/// ```
///
/// - Setting the default handler
///
/// ```
/// # use cortex_m_rt_macros::exception;
/// #[exception]
/// fn DefaultHandler(irqn: i16) {
///     println!("IRQn = {}", irqn);
/// }
///
/// # fn main() {}
/// ```
///
/// - Overriding the `SysTick` handler
///
/// ```
/// extern crate cortex_m_rt as rt;
///
/// use rt::exception;
///
/// #[exception]
/// fn SysTick() {
///     static mut COUNT: i32 = 0;
///
///     // `COUNT` is safe to access and has type `&mut i32`
///     *COUNT += 1;
///
///     println!("{}", COUNT);
/// }
///
/// # fn main() {}
/// ```
#[proc_macro_attribute]
pub fn exception(args: TokenStream, input: TokenStream) -> TokenStream {
    let f = parse_macro_input!(input as ItemFn);

    if !args.is_empty() {
        return parse::Error::new(Span::call_site(), "This attribute accepts no arguments")
            .to_compile_error()
            .into();
    }

    let fspan = f.span();
    let ident = f.ident;

    enum Exception {
        DefaultHandler,
        HardFault,
        Other,
    }

    let ident_s = ident.to_string();
    let exn = match &*ident_s {
        "DefaultHandler" => Exception::DefaultHandler,
        "HardFault" => Exception::HardFault,
        // NOTE that at this point we don't check if the exception is available on the target (e.g.
        // MemoryManagement is not available on Cortex-M0)
        "NonMaskableInt" | "MemoryManagement" | "BusFault" | "UsageFault" | "SecureFault"
        | "SVCall" | "DebugMonitor" | "PendSV" | "SysTick" => Exception::Other,
        _ => {
            return parse::Error::new(ident.span(), "This is not a valid exception name")
                .to_compile_error()
                .into();
        }
    };

    // XXX should we blacklist other attributes?
    let attrs = f.attrs;
    let block = f.block;
    let stmts = block.stmts;
    let unsafety = f.unsafety;

    let hash = random_ident();
    match exn {
        Exception::DefaultHandler => {
            let valid_signature = f.constness.is_none()
                && f.vis == Visibility::Inherited
                && f.abi.is_none()
                && f.decl.inputs.len() == 1
                && f.decl.generics.params.is_empty()
                && f.decl.generics.where_clause.is_none()
                && f.decl.variadic.is_none()
                && match f.decl.output {
                    ReturnType::Default => true,
                    ReturnType::Type(_, ref ty) => match **ty {
                        Type::Tuple(ref tuple) => tuple.elems.is_empty(),
                        Type::Never(..) => true,
                        _ => false,
                    },
                };

            if !valid_signature {
                return parse::Error::new(
                    fspan,
                    "`DefaultHandler` must have signature `[unsafe] fn(i16) [-> !]`",
                )
                .to_compile_error()
                .into();
            }

            let arg = match f.decl.inputs[0] {
                FnArg::Captured(ref arg) => arg,
                _ => unreachable!(),
            };

            quote!(
                #[export_name = #ident_s]
                #(#attrs)*
                pub #unsafety extern "C" fn #hash() {
                    extern crate core;

                    const SCB_ICSR: *const u32 = 0xE000_ED04 as *const u32;

                    let #arg = unsafe { core::ptr::read(SCB_ICSR) as u8 as i16 - 16 };

                    #(#stmts)*
                }
            )
            .into()
        }
        Exception::HardFault => {
            let valid_signature = f.constness.is_none()
                && f.vis == Visibility::Inherited
                && f.abi.is_none()
                && f.decl.inputs.len() == 1
                && match f.decl.inputs[0] {
                    FnArg::Captured(ref arg) => match arg.ty {
                        Type::Reference(ref r) => r.lifetime.is_none() && r.mutability.is_none(),
                        _ => false,
                    },
                    _ => false,
                }
                && f.decl.generics.params.is_empty()
                && f.decl.generics.where_clause.is_none()
                && f.decl.variadic.is_none()
                && match f.decl.output {
                    ReturnType::Default => false,
                    ReturnType::Type(_, ref ty) => match **ty {
                        Type::Never(_) => true,
                        _ => false,
                    },
                };

            if !valid_signature {
                return parse::Error::new(
                    fspan,
                    "`HardFault` handler must have signature `[unsafe] fn(&ExceptionFrame) -> !`",
                )
                .to_compile_error()
                .into();
            }

            let arg = match f.decl.inputs[0] {
                FnArg::Captured(ref arg) => arg,
                _ => unreachable!(),
            };

            let pat = &arg.pat;

            quote!(
                #[export_name = "HardFault"]
                #[link_section = ".HardFault.user"]
                #(#attrs)*
                pub #unsafety extern "C" fn #hash(#arg) -> ! {
                    extern crate cortex_m_rt;

                    // further type check of the input argument
                    let #pat: &cortex_m_rt::ExceptionFrame = #pat;
                    #(#stmts)*
                }
            )
            .into()
        }
        Exception::Other => {
            let valid_signature = f.constness.is_none()
                && f.vis == Visibility::Inherited
                && f.abi.is_none()
                && f.decl.inputs.is_empty()
                && f.decl.generics.params.is_empty()
                && f.decl.generics.where_clause.is_none()
                && f.decl.variadic.is_none()
                && match f.decl.output {
                    ReturnType::Default => true,
                    ReturnType::Type(_, ref ty) => match **ty {
                        Type::Tuple(ref tuple) => tuple.elems.is_empty(),
                        Type::Never(..) => true,
                        _ => false,
                    },
                };

            if !valid_signature {
                return parse::Error::new(
                    fspan,
                    "`#[exception]` handlers other than `DefaultHandler` and `HardFault` must have \
                     signature `[unsafe] fn() [-> !]`",
                )
                .to_compile_error()
                .into();
            }

            let (statics, stmts) = match extract_static_muts(stmts) {
                Err(e) => return e.to_compile_error().into(),
                Ok(x) => x,
            };

            let vars = statics
                .into_iter()
                .map(|var| {
                    let (ref cfgs, ref attrs) = extract_cfgs(var.attrs);
                    let ident = var.ident;
                    let ty = var.ty;
                    let expr = var.expr;

                    quote!(
                        #[allow(non_snake_case)]
                        #(#cfgs)*
                        let #ident: &mut #ty = unsafe {
                            #(#attrs)*
                            #(#cfgs)*
                            static mut #ident: #ty = #expr;

                            &mut #ident
                        };
                    )
                })
                .collect::<Vec<_>>();

            quote!(
                #[export_name = #ident_s]
                #(#attrs)*
                pub #unsafety extern "C" fn #hash() {
                    extern crate cortex_m_rt;

                    // check that this exception actually exists
                    cortex_m_rt::Exception::#ident;

                    #(#vars)*

                    #(#stmts)*
                }
            )
            .into()
        }
    }
}

/// Attribute to declare an interrupt (AKA device-specific exception) handler
///
/// **IMPORTANT**: If you are using Rust 1.30 this attribute must be used on reachable items (i.e.
/// there must be no private modules between the item and the root of the crate); if the item is in
/// the root of the crate you'll be fine. This reachability restriction doesn't apply to Rust 1.31
/// and newer releases.
///
/// **NOTE**: This attribute is exposed by `cortex-m-rt` only when the `device` feature is enabled.
/// However, that export is not meant to be used directly -- using it will result in a compilation
/// error. You should instead use the device crate (usually generated using `svd2rust`) re-export of
/// that attribute. You need to use the re-export to have the compiler check that the interrupt
/// exists on the target device.
///
/// # Syntax
///
/// ``` ignore
/// extern crate device;
///
/// // the attribute comes from the device crate not from cortex-m-rt
/// use device::interrupt;
///
/// #[interrupt]
/// fn USART1() {
///     // ..
/// }
/// ```
///
/// where the name of the function must be one of the device interrupts.
///
/// # Usage
///
/// `#[interrupt] fn Name(..` overrides the default handler for the interrupt with the given `Name`.
/// These handlers must have signature `[unsafe] fn() [-> !]`. It's possible to add state to these
/// handlers by declaring `static mut` variables at the beginning of the body of the function. These
/// variables will be safe to access from the function body.
///
/// If the interrupt handler has not been overridden it will be dispatched by the default exception
/// handler (`DefaultHandler`).
///
/// # Properties
///
/// Interrupts handlers can only be called by the hardware. Other parts of the program can't refer
/// to the interrupt handlers, much less invoke them as if they were functions.
///
/// `static mut` variables declared within an interrupt handler are safe to access and can be used
/// to preserve state across invocations of the handler. The compiler can't prove this is safe so
/// the attribute will help by making a transformation to the source code: for this reason a
/// variable like `static mut FOO: u32` will become `let FOO: &mut u32;`.
///
/// # Examples
///
/// - Using state within an interrupt handler
///
/// ``` ignore
/// extern crate device;
///
/// use device::interrupt;
///
/// #[interrupt]
/// fn TIM2() {
///     static mut COUNT: i32 = 0;
///
///     // `COUNT` is safe to access and has type `&mut i32`
///     *COUNT += 1;
///
///     println!("{}", COUNT);
/// }
/// ```
#[proc_macro_attribute]
pub fn interrupt(args: TokenStream, input: TokenStream) -> TokenStream {
    let f: ItemFn = syn::parse(input).expect("`#[interrupt]` must be applied to a function");

    if !args.is_empty() {
        return parse::Error::new(Span::call_site(), "This attribute accepts no arguments")
            .to_compile_error()
            .into();
    }

    let fspan = f.span();
    let ident = f.ident;
    let ident_s = ident.to_string();

    // XXX should we blacklist other attributes?
    let attrs = f.attrs;
    let block = f.block;
    let stmts = block.stmts;
    let unsafety = f.unsafety;

    let valid_signature = f.constness.is_none()
        && f.vis == Visibility::Inherited
        && f.abi.is_none()
        && f.decl.inputs.is_empty()
        && f.decl.generics.params.is_empty()
        && f.decl.generics.where_clause.is_none()
        && f.decl.variadic.is_none()
        && match f.decl.output {
            ReturnType::Default => true,
            ReturnType::Type(_, ref ty) => match **ty {
                Type::Tuple(ref tuple) => tuple.elems.is_empty(),
                Type::Never(..) => true,
                _ => false,
            },
        };

    if !valid_signature {
        return parse::Error::new(
            fspan,
            "`#[interrupt]` handlers must have signature `[unsafe] fn() [-> !]`",
        )
        .to_compile_error()
        .into();
    }

    let (statics, stmts) = match extract_static_muts(stmts) {
        Err(e) => return e.to_compile_error().into(),
        Ok(x) => x,
    };

    let vars = statics
        .into_iter()
        .map(|var| {
            let (ref cfgs, ref attrs) = extract_cfgs(var.attrs);
            let ident = var.ident;
            let ty = var.ty;
            let expr = var.expr;

            quote!(
                #[allow(non_snake_case)]
                #(#cfgs)*
                let #ident: &mut #ty = unsafe {
                    #(#attrs)*
                    #(#cfgs)*
                    static mut #ident: #ty = #expr;

                    &mut #ident
                };
            )
        })
        .collect::<Vec<_>>();

    let hash = random_ident();
    quote!(
        #[export_name = #ident_s]
        #(#attrs)*
        pub #unsafety extern "C" fn #hash() {
            interrupt::#ident;

            #(#vars)*

            #(#stmts)*
        }
    )
    .into()
}

/// Attribute to mark which function will be called at the beginning of the reset handler.
///
/// **IMPORTANT**: This attribute can appear at most *once* in the dependency graph. Also, if you
/// are using Rust 1.30 the attribute must be used on a reachable item (i.e. there must be no
/// private modules between the item and the root of the crate); if the item is in the root of the
/// crate you'll be fine. This reachability restriction doesn't apply to Rust 1.31 and newer
/// releases.
///
/// The function must have the signature of `unsafe fn()`.
///
/// The function passed will be called before static variables are initialized. Any access of static
/// variables will result in undefined behavior.
///
/// # Examples
///
/// ```
/// # use cortex_m_rt_macros::pre_init;
/// #[pre_init]
/// unsafe fn before_main() {
///     // do something here
/// }
///
/// # fn main() {}
/// ```
#[proc_macro_attribute]
pub fn pre_init(args: TokenStream, input: TokenStream) -> TokenStream {
    let f = parse_macro_input!(input as ItemFn);

    // check the function signature
    let valid_signature = f.constness.is_none()
        && f.vis == Visibility::Inherited
        && f.unsafety.is_some()
        && f.abi.is_none()
        && f.decl.inputs.is_empty()
        && f.decl.generics.params.is_empty()
        && f.decl.generics.where_clause.is_none()
        && f.decl.variadic.is_none()
        && match f.decl.output {
            ReturnType::Default => true,
            ReturnType::Type(_, ref ty) => match **ty {
                Type::Tuple(ref tuple) => tuple.elems.is_empty(),
                _ => false,
            },
        };

    if !valid_signature {
        return parse::Error::new(
            f.span(),
            "`#[pre_init]` function must have signature `unsafe fn()`",
        )
        .to_compile_error()
        .into();
    }

    if !args.is_empty() {
        return parse::Error::new(Span::call_site(), "This attribute accepts no arguments")
            .to_compile_error()
            .into();
    }

    // XXX should we blacklist other attributes?
    let attrs = f.attrs;
    let ident = f.ident;
    let block = f.block;

    quote!(
        #[export_name = "__pre_init"]
        #(#attrs)*
        pub unsafe fn #ident() #block
    )
    .into()
}

// Creates a random identifier
fn random_ident() -> Ident {
    let secs = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap()
        .as_secs();

    let count: u64 = CALL_COUNT.fetch_add(1, Ordering::SeqCst) as u64;
    let mut seed: [u8; 16] = [0; 16];

    for (i, v) in seed.iter_mut().take(8).enumerate() {
        *v = ((secs >> (i * 8)) & 0xFF) as u8
    }

    for (i, v) in seed.iter_mut().skip(8).enumerate() {
        *v = ((count >> (i * 8)) & 0xFF) as u8
    }

    let mut rng = rand::rngs::SmallRng::from_seed(seed);
    Ident::new(
        &(0..16)
            .map(|i| {
                if i == 0 || rng.gen() {
                    ('a' as u8 + rng.gen::<u8>() % 25) as char
                } else {
                    ('0' as u8 + rng.gen::<u8>() % 10) as char
                }
            })
            .collect::<String>(),
        Span::call_site(),
    )
}

/// Extracts `static mut` vars from the beginning of the given statements
fn extract_static_muts(stmts: Vec<Stmt>) -> Result<(Vec<ItemStatic>, Vec<Stmt>), parse::Error> {
    let mut istmts = stmts.into_iter();

    let mut seen = HashSet::new();
    let mut statics = vec![];
    let mut stmts = vec![];
    while let Some(stmt) = istmts.next() {
        match stmt {
            Stmt::Item(Item::Static(var)) => {
                if var.mutability.is_some() {
                    if seen.contains(&var.ident) {
                        return Err(parse::Error::new(
                            var.ident.span(),
                            format!("the name `{}` is defined multiple times", var.ident),
                        ));
                    }

                    seen.insert(var.ident.clone());
                    statics.push(var);
                } else {
                    stmts.push(Stmt::Item(Item::Static(var)));
                }
            }
            _ => {
                stmts.push(stmt);
                break;
            }
        }
    }

    stmts.extend(istmts);

    Ok((statics, stmts))
}

fn extract_cfgs(attrs: Vec<Attribute>) -> (Vec<Attribute>, Vec<Attribute>) {
    let mut cfgs = vec![];
    let mut not_cfgs = vec![];

    for attr in attrs {
        if eq(&attr, "cfg") {
            cfgs.push(attr);
        } else {
            not_cfgs.push(attr);
        }
    }

    (cfgs, not_cfgs)
}

/// Returns `true` if `attr.path` matches `name`
fn eq(attr: &Attribute, name: &str) -> bool {
    attr.style == AttrStyle::Outer && attr.path.segments.len() == 1 && {
        let pair = attr.path.segments.first().unwrap();
        let segment = pair.value();
        segment.arguments == PathArguments::None && segment.ident.to_string() == name
    }
}