//! A webassembly::Instance object is a stateful, executable instance of a
//! webassembly::Module.  Instance objects contain all the Exported
//! WebAssembly functions that allow calling into WebAssembly code.

//! The webassembly::Instance() constructor function can be called to
//! synchronously instantiate a given webassembly::Module object. However, the
//! primary way to get an Instance is through the asynchronous
//! webassembly::instantiate_streaming() function.
use cranelift_codegen::ir::LibCall;
use cranelift_codegen::{binemit, isa, Context};
use cranelift_entity::EntityRef;
use cranelift_wasm::{FuncIndex, GlobalInit};
use region;
use std::iter::Iterator;
use std::ptr::write_unaligned;
use std::slice;
use std::sync::Arc;

use super::super::common::slice::{BoundedSlice, UncheckedSlice};
use super::errors::ErrorKind;
use super::import_object::ImportObject;
use super::memory::LinearMemory;
use super::module::Export;
use super::module::Module;
use super::relocation::{Reloc, RelocSink, RelocationType};

pub fn protect_codebuf(code_buf: &Vec<u8>) -> Result<(), String> {
    match unsafe {
        region::protect(
            code_buf.as_ptr(),
            code_buf.len(),
            region::Protection::ReadWriteExecute,
        )
    } {
        Err(err) => {
            return Err(format!(
                "failed to give executable permission to code: {}",
                err
            ))
        }
        Ok(()) => Ok(()),
    }
}

fn get_function_addr(
    func_index: &FuncIndex,
    import_functions: &Vec<*const u8>,
    functions: &Vec<Vec<u8>>,
) -> *const u8 {
    let index = func_index.index();
    let len = import_functions.len();
    let func_pointer = if index < len {
        import_functions[index]
    } else {
        (&functions[func_index.index() - len]).as_ptr()
    };
    func_pointer
}

// TODO: To be removed.
// #[derive(Debug)]
// #[repr(C, packed)]
// pub struct VmCtx<'phantom> {
//     pub user_data: UserData,
//     globals: UncheckedSlice<u8>,
//     memories: UncheckedSlice<UncheckedSlice<u8>>,
//     tables: UncheckedSlice<BoundedSlice<usize>>,
//     phantom: PhantomData<&'phantom ()>,
// }

// // TODO: To be removed.
// #[derive(Debug)]
// #[repr(C, packed)]
// pub struct UserData {
//     // pub process: Dispatch<Process>,
//     pub instance: Instance,
// }

/// An Instance of a WebAssembly module
#[derive(Debug)]
pub struct Instance {
    /// WebAssembly table data
    // pub tables: Arc<Vec<RwLock<Vec<usize>>>>,
    pub tables: Arc<Vec<Vec<usize>>>,

    /// WebAssembly linear memory data
    pub memories: Arc<Vec<LinearMemory>>,

    /// WebAssembly global variable data
    pub globals: Vec<u8>,

    /// Webassembly functions
    // functions: Vec<usize>,
    functions: Vec<Vec<u8>>,

    /// Imported functions
    import_functions: Vec<*const u8>,

    /// The module start function
    pub start_func: Option<FuncIndex>,
    // Region start memory location
    // code_base: *const (),

    // C-like pointers to data (heaps, globals, tables)
    pub data_pointers: DataPointers,

    // Default memory bound
    // TODO: Support for only one LinearMemory for now.
    pub default_memory_bound: i32,
}

/// Contains pointers to data (heaps, globals, tables) needed
/// by Cranelift.
#[derive(Debug)]
pub struct DataPointers {
    // Pointer to tables
    pub tables: UncheckedSlice<BoundedSlice<usize>>,

    // Pointer to memories
    pub memories: UncheckedSlice<UncheckedSlice<u8>>,

    // Pointer to globals
    pub globals: UncheckedSlice<u8>,
}

impl Instance {
    /// Create a new `Instance`.
    pub fn new(
        module: &Module,
        import_object: &ImportObject<&str, &str>,
    ) -> Result<Instance, ErrorKind> {
        let mut tables: Vec<Vec<usize>> = Vec::new();
        let mut memories: Vec<LinearMemory> = Vec::new();
        let mut globals: Vec<u8> = Vec::new();
        let mut functions: Vec<Vec<u8>> = Vec::new();
        let mut import_functions: Vec<*const u8> = Vec::new();
        // let mut code_base: *const () = ptr::null();

        debug!("Instance - Instantiating functions");
        // Instantiate functions
        {
            functions.reserve_exact(module.info.functions.len());
            let isa = isa::lookup(module.info.triple.clone())
                .unwrap()
                .finish(module.info.flags.clone());
            let mut relocations = Vec::new();

            // We walk through the imported functions and set the relocations
            // for each of this functions to be an empty vector (as is defined outside of wasm)
            for (module, field) in module.info.imported_funcs.iter() {
                let function = import_object
                    .get(&module.as_str(), &field.as_str())
                    .ok_or_else(|| {
                        ErrorKind::LinkError(format!(
                            "Imported function {}.{} was not provided in the import_functions",
                            module, field
                        ))
                    })?;
                // println!("GET FUNC {:?}", function);
                import_functions.push(function);
                relocations.push(vec![]);
            }

            debug!("Instance - Compiling functions");
            // Compile the functions (from cranelift IR to machine code)
            for function_body in module.info.function_bodies.values() {
                let mut func_context = Context::for_function(function_body.to_owned());
                // func_context
                //     .verify(&*isa)
                //     .map_err(|e| ErrorKind::CompileError(e.to_string()))?;
                // func_context
                //     .verify_locations(&*isa)
                //     .map_err(|e| ErrorKind::CompileError(e.to_string()))?;
                // let code_size_offset = func_context
                //     .compile(&*isa)
                //     .map_err(|e| ErrorKind::CompileError(e.to_string()))?;
                //     as usize;

                let mut code_buf: Vec<u8> = Vec::new();
                let mut reloc_sink = RelocSink::new();
                let mut trap_sink = binemit::NullTrapSink {};
                // This will compile a cranelift ir::Func into a code buffer (stored in memory)
                // and will push any inner function calls to the reloc sync.
                // In case traps need to be triggered, they will go to trap_sink
                func_context
                    .compile_and_emit(&*isa, &mut code_buf, &mut reloc_sink, &mut trap_sink)
                    .map_err(|e| {
                        debug!("CompileError: {}", e.to_string());
                        ErrorKind::CompileError(e.to_string())
                    })?;
                // We set this code_buf to be readable & executable
                protect_codebuf(&code_buf).unwrap();

                let func_offset = code_buf;
                functions.push(func_offset);

                // context_and_offsets.push(func_context);
                relocations.push(reloc_sink.func_relocs);
                // println!("FUNCTION RELOCATIONS {:?}", reloc_sink.func_relocs)
                // total_size += code_size_offset;
            }

            debug!("Instance - Relocating functions");
            // For each of the functions used, we see what are the calls inside this functions
            // and relocate each call to the proper memory address.
            // The relocations are relative to the relocation's address plus four bytes
            // TODO: Support architectures other than x64, and other reloc kinds.
            for (i, function_relocs) in relocations.iter().enumerate() {
                for ref reloc in function_relocs {
                    let target_func_address: isize = match reloc.target {
                        RelocationType::Normal(func_index) => {
                            get_function_addr(&FuncIndex::new(func_index as usize), &import_functions, &functions) as isize
                        },
                        RelocationType::CurrentMemory => {
                            current_memory as isize
                        },
                        RelocationType::GrowMemory => {
                            grow_memory as isize
                        },
                        RelocationType::LibCall(LibCall::CeilF32) => {
                            _ceilf32 as isize
                        },
                        RelocationType::LibCall(LibCall::FloorF32) => {
                            _floorf32 as isize
                        },
                        RelocationType::LibCall(LibCall::TruncF32) => {
                            _truncf32 as isize
                        },
                        RelocationType::LibCall(LibCall::NearestF32) => {
                            _nearbyintf32 as isize
                        },
                        RelocationType::LibCall(LibCall::CeilF64) => {
                            _ceilf64 as isize
                        },
                        RelocationType::LibCall(LibCall::FloorF64) => {
                            _floorf64 as isize
                        },
                        RelocationType::LibCall(LibCall::TruncF64) => {
                            _truncf64 as isize
                        },
                        RelocationType::LibCall(LibCall::NearestF64) => {
                            _nearbyintf64 as isize
                        },
                        _ => unimplemented!()
                        // RelocationType::Intrinsic(name) => {
                        //     get_abi_intrinsic(name)?
                        // },
                    };

                    let func_addr =
                        get_function_addr(&FuncIndex::new(i), &import_functions, &functions);
                    match reloc.reloc {
                        Reloc::Abs8 => unsafe {
                            let reloc_address = func_addr.offset(reloc.offset as isize) as i64;
                            let reloc_addend = reloc.addend;
                            let reloc_abs = target_func_address as i64 + reloc_addend;
                            write_unaligned(reloc_address as *mut i64, reloc_abs);
                        },
                        Reloc::X86PCRel4 => unsafe {
                            let reloc_address = func_addr.offset(reloc.offset as isize) as isize;
                            let reloc_addend = reloc.addend as isize;
                            // TODO: Handle overflow.
                            let reloc_delta_i32 =
                                (target_func_address - reloc_address + reloc_addend) as i32;
                            write_unaligned(reloc_address as *mut i32, reloc_delta_i32);
                        },
                        _ => panic!("unsupported reloc kind"),
                    }
                }
            }

            // We only want to allocate in memory if there is more than
            // 0 functions. Otherwise reserving a 0-sized memory region
            // cause a panic error
            // if total_size > 0 {
            //     // Allocate the total memory for this functions
            //     // let map = MmapMut::map_anon(total_size).unwrap();
            //     // let region_start = map.as_ptr() as usize;
            //     // code_base = map.as_ptr() as *const ();

            //     // // Emit this functions to memory
            //     for (ref func_context, func_offset) in context_and_offsets.iter() {
            //         let mut trap_sink = TrapSink::new(*func_offset);
            //         let mut reloc_sink = RelocSink::new();
            //         let mut code_buf: Vec<u8> = Vec::new();

            //         // let mut func_pointer =  as *mut u8;
            //         unsafe {
            //             func_context.emit_to_memory(
            //                 &*isa,
            //                 &mut code_buf,
            //                 &mut reloc_sink,
            //                 &mut trap_sink,
            //             );
            //         };
            //         let func_offset = code_buf.as_ptr() as usize;
            //         functions.push(*func_offset);
            //     }

            //     // Set protection of this memory region to Read + Execute
            //     // so we are able to execute the functions emitted to memory
            //     // unsafe {
            //     //     region::protect(region_start as *mut u8, total_size, region::Protection::ReadExecute)
            //     //         .expect("unable to make memory readable+executable");
            //     // }
            // }
        }

        debug!("Instance - Instantiating tables");
        // Instantiate tables
        {
            // Reserve table space
            tables.reserve_exact(module.info.tables.len());
            for table in &module.info.tables {
                let len = table.entity.size;
                let mut v = Vec::with_capacity(len);
                v.resize(len, 0);
                tables.push(v);
            }
            // instantiate tables
            for table_element in &module.info.table_elements {
                assert!(
                    table_element.base.is_none(),
                    "globalvalue base not supported yet."
                );
                let base = 0;

                let table = &mut tables[table_element.table_index];
                for (i, func_index) in table_element.elements.iter().enumerate() {
                    // since the table just contains functions in the MVP
                    // we get the address of the specified function indexes
                    // to populate the table.

                    // let func_index = *elem_index - module.info.imported_funcs.len() as u32;
                    // let func_addr = functions[func_index.index()].as_ptr();
                    let func_addr = get_function_addr(&func_index, &import_functions, &functions);
                    table[base + table_element.offset + i] = func_addr as _;
                }
            }
        }

        debug!("Instance - Instantiating memories");
        // Instantiate memories
        {
            // Allocate the underlying memory and initialize it to all zeros.
            let total_memories = module.info.memories.len();
            if total_memories > 0 {
                memories.reserve_exact(total_memories);
                for memory in &module.info.memories {
                    let memory = memory.entity;
                    let v = LinearMemory::new(
                        memory.pages_count as u32,
                        memory.maximum.map(|m| m as u32),
                    );
                    memories.push(v);
                }
            } else {
                memories.reserve_exact(1);
                memories.push(LinearMemory::new(0, None));
            }
            for init in &module.info.data_initializers {
                debug_assert!(init.base.is_none(), "globalvar base not supported yet");
                let offset = init.offset;
                let mem_mut = memories[init.memory_index].as_mut();
                let to_init = &mut mem_mut[offset..offset + init.data.len()];
                to_init.copy_from_slice(&init.data);
            }
        }

        debug!("Instance - Instantiating globals");
        // Instantiate Globals
        {
            let globals_count = module.info.globals.len();
            // Allocate the underlying memory and initialize it to zeros
            let globals_data_size = globals_count * 8;
            globals.resize(globals_data_size, 0);

            // cast the globals slice to a slice of i64.
            let globals_data = unsafe {
                slice::from_raw_parts_mut(globals.as_mut_ptr() as *mut i64, globals_count)
            };
            for (i, global) in module.info.globals.iter().enumerate() {
                let value: i64 = match global.entity.initializer {
                    GlobalInit::I32Const(n) => n as _,
                    GlobalInit::I64Const(n) => n,
                    GlobalInit::F32Const(f) => f as _, // unsafe { mem::transmute(f as f64) },
                    GlobalInit::F64Const(f) => f as _, // unsafe { mem::transmute(f) },
                    GlobalInit::GlobalRef(_global_index) => {
                        unimplemented!("GlobalInit::GlobalRef is not yet supported")
                    }
                    GlobalInit::Import() => {
                        // Right now (because there is no module/field fields on the Import
                        // https://github.com/CraneStation/cranelift/blob/5cabce9b58ff960534d4017fad11f2e78c72ceab/lib/wasm/src/sections_translator.rs#L90-L99 )
                        // It's impossible to know where to take the global from.
                        // This should be fixed in Cranelift itself.
                        unimplemented!("GlobalInit::Import is not yet supported")
                    }
                };
                globals_data[i] = value;
            }
        }

        let start_func: Option<FuncIndex> =
            module
                .info
                .start_func
                .or_else(|| match module.info.exports.get("main") {
                    Some(Export::Function(index)) => Some(index.to_owned()),
                    _ => None,
                });

        // TODO: Refactor repetitive code
        let tables_pointer: Vec<BoundedSlice<usize>> =
            tables.iter().map(|table| table[..].into()).collect();
        let memories_pointer: Vec<UncheckedSlice<u8>> =
            memories.iter().map(|mem| mem[..].into()).collect();
        let globals_pointer: UncheckedSlice<u8> = globals[..].into();

        let data_pointers = DataPointers {
            memories: memories_pointer[..].into(),
            globals: globals_pointer,
            tables: tables_pointer[..].into(),
        };

        let default_memory_bound = LinearMemory::WASM_PAGE_SIZE as i32;

        Ok(Instance {
            tables: Arc::new(tables.into_iter().collect()), // tables.into_iter().map(|table| RwLock::new(table)).collect()),
            memories: Arc::new(memories.into_iter().collect()),
            globals,
            functions,
            import_functions,
            start_func,
            data_pointers,
            default_memory_bound,
            // code_base: code_base,
        })
    }

    pub fn memory_mut(&mut self, memory_index: usize) -> &mut LinearMemory {
        let memories = Arc::get_mut(&mut self.memories).unwrap_or_else(|| {
            panic!("Can't get memories as a mutable pointer (there might exist more mutable pointers to the memories)")
        });
        memories
            .get_mut(memory_index)
            .unwrap_or_else(|| panic!("no memory for index {}", memory_index))
    }

    pub fn memories(&self) -> Arc<Vec<LinearMemory>> {
        self.memories.clone()
    }

    pub fn get_function_pointer(&self, func_index: FuncIndex) -> *const u8 {
        get_function_addr(&func_index, &self.import_functions, &self.functions)
    }

    pub fn start(&self) {
        if let Some(func_index) = self.start_func {
            let func: fn(&Instance) = get_instance_function!(&self, func_index);
            func(self)
        }
    }

    // TODO: To be removed.
    // pub fn generate_context(&self) -> VmCtx {
    //     let memories: Vec<UncheckedSlice<u8>> =
    //         self.memories.iter().map(|mem| mem[..].into()).collect();
    //     let tables: Vec<BoundedSlice<usize>> =
    //         self.tables.iter().map(|table| table[..].into()).collect();
    //     let globals: UncheckedSlice<u8> = self.globals[..].into();

    //     // println!("GENERATING CONTEXT {:?}", self.globals);

    //     // assert!(memories.len() >= 1, "modules must have at least one memory");
    //     // the first memory has a space of `mem::size_of::<VmCtxData>()` rounded
    //     // up to the 4KiB before it. We write the VmCtxData into that.
    //     let instance = self.clone();
    //     VmCtx {
    //         globals: globals,
    //         memories: memories[..].into(),
    //         tables: tables[..].into(),
    //         user_data: UserData {
    //             // process,
    //             instance: instance,
    //         },
    //         phantom: PhantomData,
    //     }
    //     // let main_heap_ptr = memories[0].as_mut_ptr() as *mut VmCtxData;
    //     // unsafe {
    //     //     main_heap_ptr.sub(1).write(data);
    //     //     &*(main_heap_ptr as *const VmCtx)
    //     // }
    // }

    /// Returns a slice of the contents of allocated linear memory.
    pub fn inspect_memory(&self, memory_index: usize, address: usize, len: usize) -> &[u8] {
        &self
            .memories
            .get(memory_index)
            .unwrap_or_else(|| panic!("no memory for index {}", memory_index))
            .as_ref()[address..address + len]
    }

    // Shows the value of a global variable.
    // pub fn inspect_global(&self, global_index: GlobalIndex, ty: ir::Type) -> &[u8] {
    //     let offset = global_index * 8;
    //     let len = ty.bytes() as usize;
    //     &self.globals[offset..offset + len]
    // }

    // pub fn start_func(&self) -> extern fn(&VmCtx) {
    //     self.start_func
    // }
}

impl Clone for Instance {
    fn clone(&self) -> Instance {
        // TODO: Refactor repetitive code
        let tables_pointer: Vec<BoundedSlice<usize>> =
            self.tables.iter().map(|table| table[..].into()).collect();
        let memories_pointer: Vec<UncheckedSlice<u8>> =
            self.memories.iter().map(|mem| mem[..].into()).collect();
        let globals_pointer: UncheckedSlice<u8> = self.globals[..].into();

        let data_pointers = DataPointers {
            memories: memories_pointer[..].into(),
            globals: globals_pointer,
            tables: tables_pointer[..].into(),
        };

        let default_memory_bound = self.memories.get(0).unwrap().current as i32;

        Instance {
            tables: Arc::clone(&self.tables),
            memories: Arc::clone(&self.memories),
            globals: self.globals.clone(),
            functions: self.functions.clone(),
            start_func: self.start_func.clone(),
            import_functions: self.import_functions.clone(),
            data_pointers,
            default_memory_bound,
            // code_base: self.code_base,
        }
    }
}

/// TODO:
///   Need to improve how memories are stored and grown.
///   Dynamic memory is inefficient both for growing and for access
///   Cranelift's dynamic heap assumes a _statically-known_ number of LinearMemories,
///   because it expects a corresponding global variable for each LinearMemory
///
/// Reference:
/// - https://cranelift.readthedocs.io/en/latest/ir.html?highlight=vmctx#heap-examples,
///
extern "C" fn grow_memory(size: u32, memory_index: u32, instance: &mut Instance) -> i32 {
    // TODO: Support for only one LinearMemory for now.
    debug_assert_eq!(
        memory_index, 0,
        "non-default memory_index (0) not supported yet"
    );

    let old_mem_size = instance
        .memory_mut(memory_index as usize)
        .grow(size)
        .unwrap_or(i32::max_value()); // Should be -1 ?

    // Update the default_memory_bound
    instance.default_memory_bound =
        (instance.memories.get(0).unwrap().current as usize * LinearMemory::WASM_PAGE_SIZE) as i32;

    // The grown memory changed so data_pointers need to be updated as well.
    // TODO: Refactor repetitive code
    let tables_pointer: Vec<BoundedSlice<usize>> = instance
        .tables
        .iter()
        .map(|table| table[..].into())
        .collect();
    let memories_pointer: Vec<UncheckedSlice<u8>> =
        instance.memories.iter().map(|mem| mem[..].into()).collect();
    let globals_pointer: UncheckedSlice<u8> = instance.globals[..].into();

    let data_pointers = DataPointers {
        memories: memories_pointer[..].into(),
        globals: globals_pointer,
        tables: tables_pointer[..].into(),
    };

    // Update data_pointers
    instance.data_pointers = data_pointers;

    return old_mem_size;
}

extern "C" fn current_memory(memory_index: u32, instance: &mut Instance) -> u32 {
    let memory = &instance.memories[memory_index as usize];
    memory.current_size() as u32
}

// Because of this bug https://github.com/rust-lang/rust/issues/34123
// We create internal functions for it

use std::intrinsics::{
    ceilf32, ceilf64, floorf32, floorf64, nearbyintf32, nearbyintf64, truncf32, truncf64,
};

// F32
unsafe extern "C" fn _ceilf32(x: f32) -> f32 {
    ceilf32(x)
}

unsafe extern "C" fn _floorf32(x: f32) -> f32 {
    floorf32(x)
}

unsafe extern "C" fn _truncf32(x: f32) -> f32 {
    truncf32(x)
}

unsafe extern "C" fn _nearbyintf32(x: f32) -> f32 {
    nearbyintf32(x)
}

// F64
unsafe extern "C" fn _ceilf64(x: f64) -> f64 {
    ceilf64(x)
}

unsafe extern "C" fn _floorf64(x: f64) -> f64 {
    floorf64(x)
}

unsafe extern "C" fn _truncf64(x: f64) -> f64 {
    truncf64(x)
}

unsafe extern "C" fn _nearbyintf64(x: f64) -> f64 {
    nearbyintf64(x)
}