//! Instantiate a module, call functions, and read exports.

use crate::{
    error::{update_last_error, CApiError},
    export::{wasmer_exports_t, wasmer_import_export_kind, NamedExport, NamedExports},
    import::{wasmer_import_object_t, wasmer_import_t},
    memory::wasmer_memory_t,
    module::wasmer_module_t,
    value::{wasmer_value, wasmer_value_t, wasmer_value_tag},
    wasmer_result_t,
};
use libc::{c_char, c_int, c_void};
use std::{collections::HashMap, ffi::CStr, slice};
use wasmer_runtime::{Ctx, Global, Instance, Memory, Module, Table, Value};
use wasmer_runtime_core::{
    export::Export,
    import::{ImportObject, Namespace},
};

/// Opaque pointer to a `wasmer_runtime::Instance` value in Rust.
///
/// A `wasmer_runtime::Instance` represents a WebAssembly instance. It
/// is generally generated by the `wasmer_instantiate()` function, or by
/// the `wasmer_module_instantiate()` function for the most common paths.
#[repr(C)]
pub struct wasmer_instance_t;

/// Opaque pointer to a `wasmer_runtime::Ctx` value in Rust.
///
/// An instance context is passed to any host function (aka imported
/// function) as the first argument. It is necessary to read the
/// instance data or the memory, respectively with the
/// `wasmer_instance_context_data_get()` function, and the
/// `wasmer_instance_context_memory()` function.
///
/// It is also possible to get the instance context outside a host
/// function by using the `wasmer_instance_context_get()` function.
///
/// Example:
///
/// ```c
/// // A host function that prints data from the WebAssembly memory to
/// // the standard output.
/// void print(wasmer_instance_context_t *context, int32_t pointer, int32_t length) {
///     // Use `wasmer_instance_context` to get back the first instance memory.
///     const wasmer_memory_t *memory = wasmer_instance_context_memory(context, 0);
///
///     // Continue…
/// }
/// ```
#[repr(C)]
pub struct wasmer_instance_context_t;

/// Creates a new WebAssembly instance from the given bytes and imports.
///
/// The result is stored in the first argument `instance` if
/// successful, i.e. when the function returns
/// `wasmer_result_t::WASMER_OK`. Otherwise
/// `wasmer_result_t::WASMER_ERROR` is returned, and
/// `wasmer_last_error_length()` with `wasmer_last_error_message()` must
/// be used to read the error message.
///
/// Example:
///
/// ```c
/// // 1. Read a WebAssembly module from a file.
/// FILE *file = fopen("sum.wasm", "r");
/// fseek(file, 0, SEEK_END);
/// long bytes_length = ftell(file);
/// uint8_t *bytes = malloc(bytes_length);
/// fseek(file, 0, SEEK_SET);
/// fread(bytes, 1, bytes_length, file);
/// fclose(file);
///
/// // 2. Declare the imports (here, none).
/// wasmer_import_t imports[] = {};
///
/// // 3. Instantiate the WebAssembly module.
/// wasmer_instance_t *instance = NULL;
/// wasmer_result_t result = wasmer_instantiate(&instance, bytes, bytes_length, imports, 0);
///
/// // 4. Check for errors.
/// if (result != WASMER_OK) {
///     int error_length = wasmer_last_error_length();
///     char *error = malloc(error_length);
///     wasmer_last_error_message(error, error_length);
///     // Do something with `error`…
/// }
/// ```
#[allow(clippy::cast_ptr_alignment)]
#[no_mangle]
pub unsafe extern "C" fn wasmer_instantiate(
    instance: *mut *mut wasmer_instance_t,
    wasm_bytes: *mut u8,
    wasm_bytes_len: u32,
    imports: *mut wasmer_import_t,
    imports_len: c_int,
) -> wasmer_result_t {
    if wasm_bytes.is_null() {
        update_last_error(CApiError {
            msg: "wasm bytes ptr is null".to_string(),
        });
        return wasmer_result_t::WASMER_ERROR;
    }
    let imports: &[wasmer_import_t] = slice::from_raw_parts(imports, imports_len as usize);
    let mut import_object = ImportObject::new();
    let mut namespaces = HashMap::new();
    for import in imports {
        let module_name = slice::from_raw_parts(
            import.module_name.bytes,
            import.module_name.bytes_len as usize,
        );
        let module_name = if let Ok(s) = std::str::from_utf8(module_name) {
            s
        } else {
            update_last_error(CApiError {
                msg: "error converting module name to string".to_string(),
            });
            return wasmer_result_t::WASMER_ERROR;
        };
        let import_name = slice::from_raw_parts(
            import.import_name.bytes,
            import.import_name.bytes_len as usize,
        );
        let import_name = if let Ok(s) = std::str::from_utf8(import_name) {
            s
        } else {
            update_last_error(CApiError {
                msg: "error converting import_name to string".to_string(),
            });
            return wasmer_result_t::WASMER_ERROR;
        };

        let namespace = namespaces.entry(module_name).or_insert_with(Namespace::new);

        // TODO check that tag is actually in bounds here
        let export = match import.tag {
            wasmer_import_export_kind::WASM_MEMORY => {
                let mem = import.value.memory as *mut Memory;
                Export::Memory((&*mem).clone())
            }
            wasmer_import_export_kind::WASM_FUNCTION => {
                let func_export = import.value.func as *mut Export;
                (&*func_export).clone()
            }
            wasmer_import_export_kind::WASM_GLOBAL => {
                let global = import.value.global as *mut Global;
                Export::Global((&*global).clone())
            }
            wasmer_import_export_kind::WASM_TABLE => {
                let table = import.value.table as *mut Table;
                Export::Table((&*table).clone())
            }
        };
        namespace.insert(import_name, export);
    }
    for (module_name, namespace) in namespaces.into_iter() {
        import_object.register(module_name, namespace);
    }

    let bytes: &[u8] = slice::from_raw_parts_mut(wasm_bytes, wasm_bytes_len as usize);
    let result = wasmer_runtime::instantiate(bytes, &import_object);
    let new_instance = match result {
        Ok(instance) => instance,
        Err(error) => {
            update_last_error(error);
            return wasmer_result_t::WASMER_ERROR;
        }
    };
    *instance = Box::into_raw(Box::new(new_instance)) as *mut wasmer_instance_t;
    wasmer_result_t::WASMER_OK
}

/// Given:
/// * A prepared `wasmer` import-object
/// * A compiled wasmer module
///
/// Instantiates a wasmer instance
#[no_mangle]
pub unsafe extern "C" fn wasmer_module_import_instantiate(
    instance: *mut *mut wasmer_instance_t,
    module: *const wasmer_module_t,
    import_object: *const wasmer_import_object_t,
) -> wasmer_result_t {
    let import_object: &ImportObject = &*(import_object as *const ImportObject);
    let module: &Module = &*(module as *const Module);

    let new_instance: Instance = match module.instantiate(import_object) {
        Ok(instance) => instance,
        Err(error) => {
            update_last_error(error);
            return wasmer_result_t::WASMER_ERROR;
        }
    };
    *instance = Box::into_raw(Box::new(new_instance)) as *mut wasmer_instance_t;

    return wasmer_result_t::WASMER_OK;
}

/// Extracts the instance's context and returns it.
#[allow(clippy::cast_ptr_alignment)]
#[no_mangle]
pub unsafe extern "C" fn wasmer_instance_context_get(
    instance: *mut wasmer_instance_t,
) -> *const wasmer_instance_context_t {
    let instance_ref = &*(instance as *const Instance);

    let ctx: *const Ctx = instance_ref.context() as *const _;

    ctx as *const wasmer_instance_context_t
}

/// Calls an instances exported function by `name` with the provided parameters.
/// Results are set using the provided `results` pointer.
///
/// Returns `wasmer_result_t::WASMER_OK` upon success.
///
/// Returns `wasmer_result_t::WASMER_ERROR` upon failure. Use `wasmer_last_error_length`
/// and `wasmer_last_error_message` to get an error message.
#[allow(clippy::cast_ptr_alignment)]
#[no_mangle]
pub unsafe extern "C" fn wasmer_instance_call(
    instance: *mut wasmer_instance_t,
    name: *const c_char,
    params: *const wasmer_value_t,
    params_len: u32,
    results: *mut wasmer_value_t,
    results_len: u32,
) -> wasmer_result_t {
    if instance.is_null() {
        update_last_error(CApiError {
            msg: "instance ptr is null".to_string(),
        });
        return wasmer_result_t::WASMER_ERROR;
    }
    if name.is_null() {
        update_last_error(CApiError {
            msg: "name ptr is null".to_string(),
        });
        return wasmer_result_t::WASMER_ERROR;
    }
    if params.is_null() {
        update_last_error(CApiError {
            msg: "params ptr is null".to_string(),
        });
        return wasmer_result_t::WASMER_ERROR;
    }

    let params: &[wasmer_value_t] = slice::from_raw_parts(params, params_len as usize);
    let params: Vec<Value> = params.iter().cloned().map(|x| x.into()).collect();

    let func_name_c = CStr::from_ptr(name);
    let func_name_r = func_name_c.to_str().unwrap();

    let results: &mut [wasmer_value_t] = slice::from_raw_parts_mut(results, results_len as usize);
    let result = (&*(instance as *mut Instance)).call(func_name_r, &params[..]);

    match result {
        Ok(results_vec) => {
            if !results_vec.is_empty() {
                let ret = match results_vec[0] {
                    Value::I32(x) => wasmer_value_t {
                        tag: wasmer_value_tag::WASM_I32,
                        value: wasmer_value { I32: x },
                    },
                    Value::I64(x) => wasmer_value_t {
                        tag: wasmer_value_tag::WASM_I64,
                        value: wasmer_value { I64: x },
                    },
                    Value::F32(x) => wasmer_value_t {
                        tag: wasmer_value_tag::WASM_F32,
                        value: wasmer_value { F32: x },
                    },
                    Value::F64(x) => wasmer_value_t {
                        tag: wasmer_value_tag::WASM_F64,
                        value: wasmer_value { F64: x },
                    },
                    Value::V128(_) => unimplemented!("calling function with V128 parameter"),
                };
                results[0] = ret;
            }
            wasmer_result_t::WASMER_OK
        }
        Err(err) => {
            update_last_error(err);
            wasmer_result_t::WASMER_ERROR
        }
    }
}

/// Gets Exports for the given instance
///
/// The caller owns the object and should call `wasmer_exports_destroy` to free it.
#[allow(clippy::cast_ptr_alignment)]
#[no_mangle]
pub unsafe extern "C" fn wasmer_instance_exports(
    instance: *mut wasmer_instance_t,
    exports: *mut *mut wasmer_exports_t,
) {
    let instance_ref = &mut *(instance as *mut Instance);
    let mut exports_vec: Vec<NamedExport> = Vec::with_capacity(instance_ref.exports().count());
    for (name, export) in instance_ref.exports() {
        exports_vec.push(NamedExport {
            name: name.clone(),
            export: export.clone(),
            instance: instance as *mut Instance,
        });
    }
    let named_exports: Box<NamedExports> = Box::new(NamedExports(exports_vec));
    *exports = Box::into_raw(named_exports) as *mut wasmer_exports_t;
}

/// Sets the `data` field of the instance context. This context will be
/// passed to all imported function for instance.
#[allow(clippy::cast_ptr_alignment)]
#[no_mangle]
pub extern "C" fn wasmer_instance_context_data_set(
    instance: *mut wasmer_instance_t,
    data_ptr: *mut c_void,
) {
    let instance_ref = unsafe { &mut *(instance as *mut Instance) };
    instance_ref.context_mut().data = data_ptr;
}

/// Gets the memory within the context at the index `memory_idx`.
/// The index is always 0 until multiple memories are supported.
#[allow(clippy::cast_ptr_alignment)]
#[no_mangle]
pub extern "C" fn wasmer_instance_context_memory(
    ctx: *const wasmer_instance_context_t,
    _memory_idx: u32,
) -> *const wasmer_memory_t {
    let ctx = unsafe { &*(ctx as *const Ctx) };
    let memory = ctx.memory(0);
    memory as *const Memory as *const wasmer_memory_t
}

/// Gets the `data` field within the context.
#[allow(clippy::cast_ptr_alignment)]
#[no_mangle]
pub extern "C" fn wasmer_instance_context_data_get(
    ctx: *const wasmer_instance_context_t,
) -> *mut c_void {
    let ctx = unsafe { &*(ctx as *const Ctx) };
    ctx.data
}

/// Frees memory for the given Instance
#[allow(clippy::cast_ptr_alignment)]
#[no_mangle]
pub extern "C" fn wasmer_instance_destroy(instance: *mut wasmer_instance_t) {
    if !instance.is_null() {
        unsafe { Box::from_raw(instance as *mut Instance) };
    }
}