#include <assert.h>
#include <stdio.h>
#include <libguile.h>

/**
 * ISO C forbids casting a function pointer to a void pointer because on some
 * architectures they have different sizes. However scm_c_define_gsubr() wants
 * a function pointer as a void pointer, which trips -Wpedantic. Compiling C
 * without pedantic errors is not a reasonable option in my opinion, so instead
 * we'll have to resort to this hack.
 */
#define scm_c_define_gsubr_fix(NAME, REQ, OPT, RST, FN) \
	{ const long int ptr = (long int)FN; scm_c_define_gsubr(NAME, REQ, OPT, RST, (void *)ptr); }

extern SCM layout_demand_handler;
extern SCM user_command_handler;

static SCM install_handler (SCM key, SCM proc)
{
	if ( scm_is_false(scm_symbol_p(key)) == 1 )
	{
		scm_error_scm(
			scm_from_utf8_symbol("wrong-type-arg"),
			scm_from_utf8_string("install-handler"),
			scm_from_utf8_string("First argument must be a symbol."),
			SCM_BOOL_F,
			scm_list_1(key)
		);
		return SCM_UNSPECIFIED;
	}

	// TODO check if the procedure has the right amount of arguments.
	if ( scm_is_false(scm_procedure_p(proc)) == 1 )
	{
		scm_error_scm(
			scm_from_utf8_symbol("wrong-type-arg"),
			scm_from_utf8_string("install-handler"),
			scm_from_utf8_string("Second argument must be a procedure."),
			SCM_BOOL_F,
			scm_list_1(proc)
		);
		return SCM_UNSPECIFIED;
	}

	if (scm_is_eq(scm_from_utf8_symbol("layout-demand"), key))
		layout_demand_handler = proc;
	else if (scm_is_eq(scm_from_utf8_symbol("user-command"), key))
		user_command_handler = proc;
	else
	{
		scm_error_scm(
			// TODO should this be 'misc-error instead?
			scm_from_utf8_symbol("out-of-range"),
			scm_from_utf8_string("install-handler"),
			scm_from_utf8_string("Unknown key: ~A"),
			scm_list_1(key),
			scm_list_1(key)
		);
		return SCM_UNSPECIFIED;
	}

	return SCM_BOOL_T;
}

static void *load_script_inner (void *data)
{
	const char *path = (char *)data;

	/* scm_primitive_load_path() searches guiles load-path when encountering
	 * a relative path. That should never happen here though.
	 */
	assert(path[0] == '/');

	return scm_primitive_load_path(scm_from_utf8_string(path));
}

void *load_script (void *data)
{
	/* Note: All guile objects are garbage collected. */

	scm_c_define_gsubr_fix("install-handler", 2, 0, 0, install_handler);

	/* Continuation barrier causes stack unwind on exceptions to stop here.
	 * Otherwise the entire stack created by scm_with_guile() would be
	 * unwound. This makes responding to exceptions nicer.
	 */
	SCM call_result = scm_c_with_continuation_barrier(
		load_script_inner, data
	);

	if ( call_result == NULL )
		return (void *)"ERROR: Fatal error while loading layout script.\n";

	if ( layout_demand_handler == NULL )
		return (void *)"ERROR: No layout demand handler installed.\n";

	/* Checked in the installer functions. */
	assert(scm_is_true(scm_procedure_p(layout_demand_handler)) == 1);
	if ( user_command_handler != NULL )
		assert(scm_is_true(scm_procedure_p(user_command_handler)) == 1);

	return NULL;
}