/*
*  Node.js-like module loading framework for Duktape
*
*  https://nodejs.org/api/modules.html
*/

#include "duktape.h"
#include "duk_module_node.h"

#if DUK_VERSION >= 19999
static duk_int_t duk__eval_module_source(duk_context *ctx, void *udata);
#else
static duk_int_t duk__eval_module_source(duk_context *ctx);
#endif
static void duk__push_module_object(duk_context *ctx, const char *id, duk_bool_t main);

static duk_bool_t duk__get_cached_module(duk_context *ctx, const char *id) {
   duk_push_global_stash(ctx);
   (void) duk_get_prop_string(ctx, -1, "\xff" "requireCache");
   if (duk_get_prop_string(ctx, -1, id)) {
	   duk_remove(ctx, -2);
	   duk_remove(ctx, -2);
	   return 1;
   } else {
	   duk_pop_3(ctx);
	   return 0;
   }
}

/* Place a `module` object on the top of the value stack into the require cache
* based on its `.id` property.  As a convenience to the caller, leave the
* object on top of the value stack afterwards.
*/
static void duk__put_cached_module(duk_context *ctx) {
   /* [ ... module ] */

   duk_push_global_stash(ctx);
   (void) duk_get_prop_string(ctx, -1, "\xff" "requireCache");
   duk_dup(ctx, -3);

   /* [ ... module stash req_cache module ] */

   (void) duk_get_prop_string(ctx, -1, "id");
   duk_dup(ctx, -2);
   duk_put_prop(ctx, -4);

   duk_pop_3(ctx);  /* [ ... module ] */
}

static void duk__del_cached_module(duk_context *ctx, const char *id) {
   duk_push_global_stash(ctx);
   (void) duk_get_prop_string(ctx, -1, "\xff" "requireCache");
   duk_del_prop_string(ctx, -1, id);
   duk_pop_2(ctx);
}

static duk_ret_t duk__handle_require(duk_context *ctx) {
   /*
	*  Value stack handling here is a bit sloppy but should be correct.
	*  Call handling will clean up any extra garbage for us.
	*/

   const char *id;
   const char *parent_id;
   duk_idx_t module_idx;
   duk_idx_t stash_idx;
   duk_int_t ret;

   duk_push_global_stash(ctx);
   stash_idx = duk_normalize_index(ctx, -1);

   duk_push_current_function(ctx);
   (void) duk_get_prop_string(ctx, -1, "\xff" "moduleId");
   parent_id = duk_require_string(ctx, -1);
   (void) parent_id;  /* not used directly; suppress warning */

   /* [ id stash require parent_id ] */

   id = duk_require_string(ctx, 0);

   (void) duk_get_prop_string(ctx, stash_idx, "\xff" "modResolve");
   duk_dup(ctx, 0);   /* module ID */
   duk_dup(ctx, -3);  /* parent ID */
   duk_call(ctx, 2);

   /* [ ... stash ... resolved_id ] */

   id = duk_require_string(ctx, -1);

   if (duk__get_cached_module(ctx, id)) {
	   goto have_module;  /* use the cached module */
   }

   duk__push_module_object(ctx, id, 0 /*main*/);
   duk__put_cached_module(ctx);  /* module remains on stack */

   /*
	*  From here on out, we have to be careful not to throw.  If it can't be
	*  avoided, the error must be caught and the module removed from the
	*  require cache before rethrowing.  This allows the application to
	*  reattempt loading the module.
	*/

   module_idx = duk_normalize_index(ctx, -1);

   /* [ ... stash ... resolved_id module ] */

   (void) duk_get_prop_string(ctx, stash_idx, "\xff" "modLoad");
   duk_dup(ctx, -3);  /* resolved ID */
   (void) duk_get_prop_string(ctx, module_idx, "exports");
   duk_dup(ctx, module_idx);
   ret = duk_pcall(ctx, 3);
   if (ret != DUK_EXEC_SUCCESS) {
	   duk__del_cached_module(ctx, id);
	   (void) duk_throw(ctx);  /* rethrow */
   }

   if (duk_is_string(ctx, -1)) {
	   duk_int_t ret;

	   /* [ ... module source ] */

#if DUK_VERSION >= 19999
	   ret = duk_safe_call(ctx, duk__eval_module_source, NULL, 2, 1);
#else
	   ret = duk_safe_call(ctx, duk__eval_module_source, 2, 1);
#endif
	   if (ret != DUK_EXEC_SUCCESS) {
		   duk__del_cached_module(ctx, id);
		   (void) duk_throw(ctx);  /* rethrow */
	   }
   } else if (duk_is_undefined(ctx, -1)) {
	   duk_pop(ctx);
   } else {
	   duk__del_cached_module(ctx, id);
	   (void) duk_type_error(ctx, "invalid module load callback return value");
   }

   /* fall through */

have_module:
   /* [ ... module ] */

   (void) duk_get_prop_string(ctx, -1, "exports");
   return 1;
}

static void duk__push_require_function(duk_context *ctx, const char *id) {
   duk_push_c_function(ctx, duk__handle_require, 1);
   duk_push_string(ctx, "name");
   duk_push_string(ctx, "require");
   duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE);
   duk_push_string(ctx, id);
   duk_put_prop_string(ctx, -2, "\xff" "moduleId");

   /* require.cache */
   duk_push_global_stash(ctx);
   (void) duk_get_prop_string(ctx, -1, "\xff" "requireCache");
   duk_put_prop_string(ctx, -3, "cache");
   duk_pop(ctx);

   /* require.main */
   duk_push_global_stash(ctx);
   (void) duk_get_prop_string(ctx, -1, "\xff" "mainModule");
   duk_put_prop_string(ctx, -3, "main");
   duk_pop(ctx);
}

static void duk__push_module_object(duk_context *ctx, const char *id, duk_bool_t main) {
   duk_push_object(ctx);

   /* Set this as the main module, if requested */
   if (main) {
	   duk_push_global_stash(ctx);
	   duk_dup(ctx, -2);
	   duk_put_prop_string(ctx, -2, "\xff" "mainModule");
	   duk_pop(ctx);
   }

   /* Node.js uses the canonicalized filename of a module for both module.id
	* and module.filename.  We have no concept of a file system here, so just
	* use the module ID for both values.
	*/
   duk_push_string(ctx, id);
   duk_dup(ctx, -1);
   duk_put_prop_string(ctx, -3, "filename");
   duk_put_prop_string(ctx, -2, "id");

   /* module.exports = {} */
   duk_push_object(ctx);
   duk_put_prop_string(ctx, -2, "exports");

   /* module.loaded = false */
   duk_push_false(ctx);
   duk_put_prop_string(ctx, -2, "loaded");

   /* module.require */
   duk__push_require_function(ctx, id);
   duk_put_prop_string(ctx, -2, "require");
}

#if DUK_VERSION >= 19999
static duk_int_t duk__eval_module_source(duk_context *ctx, void *udata) {
#else
static duk_int_t duk__eval_module_source(duk_context *ctx) {
#endif
   const char *src;

   /*
	*  Stack: [ ... module source ]
	*/

#if DUK_VERSION >= 19999
   (void) udata;
#endif

   /* Wrap the module code in a function expression.  This is the simplest
	* way to implement CommonJS closure semantics and matches the behavior of
	* e.g. Node.js.
	*/
   duk_push_string(ctx, "(function(exports,require,module,__filename,__dirname){");
   src = duk_require_string(ctx, -2);
   duk_push_string(ctx, (src[0] == '#' && src[1] == '!') ? "//" : "");  /* Shebang support. */
   duk_dup(ctx, -3);  /* source */
   duk_push_string(ctx, "\n})");  /* Newline allows module last line to contain a // comment. */
   duk_concat(ctx, 4);

   /* [ ... module source func_src ] */

   (void) duk_get_prop_string(ctx, -3, "filename");
   duk_compile(ctx, DUK_COMPILE_EVAL);
   duk_call(ctx, 0);

   /* [ ... module source func ] */

   /* Set name for the wrapper function. */
   duk_push_string(ctx, "name");
   duk_push_string(ctx, "main");
   duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE | DUK_DEFPROP_FORCE);

   /* call the function wrapper */
   (void) duk_get_prop_string(ctx, -3, "exports");   /* exports */
   (void) duk_get_prop_string(ctx, -4, "require");   /* require */
   duk_dup(ctx, -5);                                 /* module */
   (void) duk_get_prop_string(ctx, -6, "filename");  /* __filename */
   duk_push_undefined(ctx);                          /* __dirname */
   duk_call(ctx, 5);

   /* [ ... module source result(ignore) ] */

   /* module.loaded = true */
   duk_push_true(ctx);
   duk_put_prop_string(ctx, -4, "loaded");

   /* [ ... module source retval ] */

   duk_pop_2(ctx);

   /* [ ... module ] */

   return 1;
}

/* Load a module as the 'main' module. */
duk_ret_t duk_module_node_peval_main(duk_context *ctx, const char *path) {
   /*
	*  Stack: [ ... source ]
	*/

   duk__push_module_object(ctx, path, 1 /*main*/);
   /* [ ... source module ] */

   duk_dup(ctx, 0);
   /* [ ... source module source ] */

#if DUK_VERSION >= 19999
   return duk_safe_call(ctx, duk__eval_module_source, NULL, 2, 1);
#else
   return duk_safe_call(ctx, duk__eval_module_source, 2, 1);
#endif
}

void duk_module_node_init(duk_context *ctx) {
   /*
	*  Stack: [ ... options ] => [ ... ]
	*/

   duk_idx_t options_idx;

   duk_require_object_coercible(ctx, -1);  /* error before setting up requireCache */
   options_idx = duk_require_normalize_index(ctx, -1);

   /* Initialize the require cache to a fresh object. */
   duk_push_global_stash(ctx);
#if DUK_VERSION >= 19999
   duk_push_bare_object(ctx);
#else
   duk_push_object(ctx);
   duk_push_undefined(ctx);
   duk_set_prototype(ctx, -2);
#endif
   duk_put_prop_string(ctx, -2, "\xff" "requireCache");
   duk_pop(ctx);

   /* Stash callbacks for later use.  User code can overwrite them later
	* on directly by accessing the global stash.
	*/
   duk_push_global_stash(ctx);
   duk_get_prop_string(ctx, options_idx, "resolve");
   duk_require_function(ctx, -1);
   duk_put_prop_string(ctx, -2, "\xff" "modResolve");
   duk_get_prop_string(ctx, options_idx, "load");
   duk_require_function(ctx, -1);
   duk_put_prop_string(ctx, -2, "\xff" "modLoad");
   duk_pop(ctx);

   /* Stash main module. */
   duk_push_global_stash(ctx);
   duk_push_undefined(ctx);
   duk_put_prop_string(ctx, -2, "\xff" "mainModule");
   duk_pop(ctx);

   /* register `require` as a global function. */
   duk_push_global_object(ctx);
   duk_push_string(ctx, "require");
   duk__push_require_function(ctx, "");
   duk_def_prop(ctx, -3, DUK_DEFPROP_HAVE_VALUE |
								 DUK_DEFPROP_SET_WRITABLE |
								 DUK_DEFPROP_SET_CONFIGURABLE);
   duk_pop(ctx);

   duk_pop(ctx);  /* pop argument */
}