/**
 * \file wasmtime/linker.h
 *
 * Wasmtime API for a name-based linker used to instantiate modules.
 */

#ifndef WASMTIME_LINKER_H
#define WASMTIME_LINKER_H

#include <wasm.h>
#include <wasmtime/error.h>
#include <wasmtime/store.h>
#include <wasmtime/extern.h>

#ifdef __cplusplus
extern "C" {
#endif

/**
 * \typedef wasmtime_linker_t
 * \brief Alias to #wasmtime_linker
 *
 * \struct #wasmtime_linker
 * \brief Object used to conveniently link together and instantiate wasm
 * modules.
 *
 * This type corresponds to the `wasmtime::Linker` type in Rust. This
 * type is intended to make it easier to manage a set of modules that link
 * together, or to make it easier to link WebAssembly modules to WASI.
 *
 * A #wasmtime_linker_t is a higher level way to instantiate a module than
 * #wasm_instance_new since it works at the "string" level of imports rather
 * than requiring 1:1 mappings.
 */
typedef struct wasmtime_linker wasmtime_linker_t;

/**
 * \brief Creates a new linker for the specified engine.
 *
 * This function does not take ownership of the engine argument, and the caller
 * is expected to delete the returned linker.
 */
WASM_API_EXTERN wasmtime_linker_t* wasmtime_linker_new(wasm_engine_t* engine);

/**
 * \brief Deletes a linker
 */
WASM_API_EXTERN void wasmtime_linker_delete(wasmtime_linker_t* linker);

/**
 * \brief Configures whether this linker allows later definitions to shadow
 * previous definitions.
 *
 * By default this setting is `false`.
 */
WASM_API_EXTERN void wasmtime_linker_allow_shadowing(wasmtime_linker_t* linker, bool allow_shadowing);

/**
 * \brief Defines a new item in this linker.
 *
 * \param linker the linker the name is being defined in.
 * \param module the module name the item is defined under.
 * \param module_len the byte length of `module`
 * \param name the field name the item is defined under
 * \param name_len the byte length of `name`
 * \param item the item that is being defined in this linker.
 *
 * \return On success `NULL` is returned, otherwise an error is returned which
 * describes why the definition failed.
 *
 * For more information about name resolution consult the [Rust
 * documentation](https://bytecodealliance.github.io/wasmtime/api/wasmtime/struct.Linker.html#name-resolution).
 */
WASM_API_EXTERN wasmtime_error_t* wasmtime_linker_define(
    wasmtime_linker_t *linker,
    const char *module,
    size_t module_len,
    const char *name,
    size_t name_len,
    const wasmtime_extern_t *item
);

/**
 * \brief Defines WASI functions in this linker.
 *
 * \param linker the linker the name is being defined in.
 *
 * \return On success `NULL` is returned, otherwise an error is returned which
 * describes why the definition failed.
 *
 * This function will provide WASI function names in the specified linker. Note
 * that when an instance is created within a store then the store also needs to
 * have its WASI settings configured with #wasmtime_context_set_wasi for WASI
 * functions to work, otherwise an assert will be tripped that will abort the
 * process.
 *
 * For more information about name resolution consult the [Rust
 * documentation](https://bytecodealliance.github.io/wasmtime/api/wasmtime/struct.Linker.html#name-resolution).
 */
WASM_API_EXTERN wasmtime_error_t* wasmtime_linker_define_wasi(
    wasmtime_linker_t *linker
);

/**
 * \brief Defines an instance under the specified name in this linker.
 *
 * \param linker the linker the name is being defined in.
 * \param store the store that owns `instance`
 * \param name the module name to define `instance` under.
 * \param name_len the byte length of `name`
 * \param instance a previously-created instance.
 *
 * \return On success `NULL` is returned, otherwise an error is returned which
 * describes why the definition failed.
 *
 * This function will take all of the exports of the `instance` provided and
 * defined them under a module called `name` with a field name as the export's
 * own name.
 *
 * For more information about name resolution consult the [Rust
 * documentation](https://bytecodealliance.github.io/wasmtime/api/wasmtime/struct.Linker.html#name-resolution).
 */
WASM_API_EXTERN wasmtime_error_t* wasmtime_linker_define_instance(
    wasmtime_linker_t *linker,
    wasmtime_context_t *store,
    const char *name,
    size_t name_len,
    const wasmtime_instance_t *instance
);

/**
 * \brief Instantiates a #wasm_module_t with the items defined in this linker.
 *
 * \param linker the linker used to instantiate the provided module.
 * \param store the store that is used to instantiate within
 * \param module the module that is being instantiated.
 * \param instance the returned instance, if successful.
 * \param trap a trap returned, if the start function traps.
 *
 * \return One of three things can happen as a result of this function. First
 * the module could be successfully instantiated and returned through
 * `instance`, meaning the return value and `trap` are both set to `NULL`.
 * Second the start function may trap, meaning the return value and `instance`
 * are set to `NULL` and `trap` describes the trap that happens. Finally
 * instantiation may fail for another reason, in which case an error is returned
 * and `trap` and `instance` are set to `NULL`.
 *
 * This function will attempt to satisfy all of the imports of the `module`
 * provided with items previously defined in this linker. If any name isn't
 * defined in the linker than an error is returned. (or if the previously
 * defined item is of the wrong type).
 */
WASM_API_EXTERN wasmtime_error_t* wasmtime_linker_instantiate(
    const wasmtime_linker_t *linker,
    wasmtime_context_t *store,
    const wasmtime_module_t *module,
    wasmtime_instance_t *instance,
    wasm_trap_t **trap
);

/**
 * \brief Defines automatic instantiations of a #wasm_module_t in this linker.
 *
 * \param linker the linker the module is being added to
 * \param store the store that is used to instantiate `module`
 * \param name the name of the module within the linker
 * \param name_len the byte length of `name`
 * \param module the module that's being instantiated
 *
 * \return An error if the module could not be instantiated or added or `NULL`
 * on success.
 *
 * This function automatically handles [Commands and
 * Reactors](https://github.com/WebAssembly/WASI/blob/master/design/application-abi.md#current-unstable-abi)
 * instantiation and initialization.
 *
 * For more information see the [Rust
 * documentation](https://bytecodealliance.github.io/wasmtime/api/wasmtime/struct.Linker.html#method.module).
 */
WASM_API_EXTERN wasmtime_error_t* wasmtime_linker_module(
    wasmtime_linker_t *linker,
    wasmtime_context_t *store,
    const char *name,
    size_t name_len,
    const wasmtime_module_t *module
);

/**
 * \brief Acquires the "default export" of the named module in this linker.
 *
 * \param linker the linker to load from
 * \param store the store to load a function into
 * \param name the name of the module to get the default export for
 * \param name_len the byte length of `name`
 * \param func where to store the extracted default function.
 *
 * \return An error is returned if the default export could not be found, or
 * `NULL` is returned and `func` is filled in otherwise.
 *
 * For more information see the [Rust
 * documentation](https://bytecodealliance.github.io/wasmtime/api/wasmtime/struct.Linker.html#method.get_default).
 */
WASM_API_EXTERN wasmtime_error_t* wasmtime_linker_get_default(
    const wasmtime_linker_t *linker,
    wasmtime_context_t *store,
    const char *name,
    size_t name_len,
    wasmtime_func_t *func
);

/**
 * \brief Loads an item by name from this linker.
 *
 * \param linker the linker to load from
 * \param store the store to load the item into
 * \param module the name of the module to get
 * \param module_len the byte length of `module`
 * \param name the name of the field to get
 * \param name_len the byte length of `name`
 * \param item where to store the extracted item
 *
 * \return A nonzero value if the item is defined, in which case `item` is also
 * filled in. Otherwise zero is returned.
 */
WASM_API_EXTERN bool wasmtime_linker_get(
    const wasmtime_linker_t *linker,
    wasmtime_context_t *store,
    const char *module,
    size_t module_len,
    const char *name,
    size_t name_len,
    wasmtime_extern_t *item
);

#ifdef __cplusplus
}  // extern "C"
#endif

#endif // WASMTIME_LINKER_H