/*
 * Copyright © 2024 Matthew Wozniak <me@woz.blue>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
 * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

#define NO_EXTERNS
#include "api.h"
#undef NO_EXTERNS
#include "os.h"
#include "log.h"
#include "sst/x86.h"

struct engserver *engserver = 0;
struct engclient *engclient = 0;
struct engineapi *engineapi = 0;
struct enginetools *enginetools = 0;
struct cvar *cvar = 0;
struct demoplayer *demoplayer = 0;
struct videomode **videomode = 0;
struct movieinfo *movieinfo = 0;
struct audio_device **audio_device = 0;
struct soundstate *snd = 0;
void (*snd_recordbuffer)(void) = 0;
void (*cbuf_addtext)(char *) = 0;

// This macro is Copyright 2024 Michael Smith under the same license as above.
#define NEXT_INSN(p, tgt) do { \
	int _len = x86_len(p); \
	if (_len == -1) { \
		bail("unknown or invalid instruction looking for %s", tgt); \
		return false; \
	} \
	(p) += _len; \
} while (0)

// TODO: should this be split up?

bool api_init(void) {
	void *engine_dll = os_dlhandle("engine");
	createinterface_func engine_factory =
		(createinterface_func)os_dlsym(engine_dll, "CreateInterface");

	void *vstdlib_dll = os_dlhandle("vstdlib");
	createinterface_func vstdlib_factory =
		(createinterface_func)os_dlsym(vstdlib_dll, "CreateInterface");

	if (!engine_factory) bail("couldn't get engine factory");
	engserver = engine_factory(VENGINE_SERVER_INTERFACE_VERSION, 0);
	if (!engserver) bail("couldn't get IVEngineServer from engine");
	engclient = engine_factory(VENGINE_CLIENT_INTERFACE_VERSION, 0);
	if (!engclient) bail("couldn't get IVEngineClient from engine");
	engineapi = engine_factory(VENGINE_LAUNCHER_INTERFACE_VERSION, 0);
	if (!engineapi) bail("couldn't get IEngineAPI from engine");
	enginetools = engine_factory(VENGINE_TOOL_INTERFACE_VERSION, 0);
	if (!engineapi) bail("couldn't get IEngineTools from engine");
	cvar = vstdlib_factory(VENGINE_CVAR_INTERFACE_VERSION, 0);
	if (!cvar) bail("couldn't get ICVar from vstdlib");

	// find cbuf_addtext
	const u8 *instr = (const u8 *)engserver->vt->server_command;
	// ServerCommand() calls a few small functions before Cbuf_AddText but they
	// get inlined. look for 'push esi' and then a call.
	for (const u8 *p = instr; p - instr < 64;) {
		if (*p == X86_PUSHESI && *++p == X86_CALL) {
			// jump is relative to after the instruction
			cbuf_addtext = (void (*)(char *))(p + 5 + *(i32 *)(p + 1));
		}
		NEXT_INSN(p, "CBuf_AddText");
	}
	if (!cbuf_addtext) bail("couldn't find cbuf_addtext");

	// find demoplayer
	instr = (const u8 *)engclient->vt->is_playing_demo;
	// CEngineClient::IsPlayingDemo is a wrapper around a demoplayer call
	// The first thing it does should be load a ptr to demoplayer into ECX
	if (instr[0] != X86_MOVRMW || instr[1] != X86_MODRM(0, 1, 5))
		bail("couldn't get demoplayer");
	demoplayer = **(struct demoplayer ***)(instr + 2);
	debug("demoplayer = %p", (void *)demoplayer);

	// find videomode
	// CEngineAPI::SetEngineWindow calls videomode->SetGameWindow after
	// detaching the current window with another vcall. Look for the second one.
	// This, like the demoplayer, is a pointer. We need to keep the double
	// pointer because when we get this, it is null. It is set by the engine
	// later.
	instr = (const u8 *)engineapi->vt->set_engine_window;
	int mov_ecx_counter = 0;
	for (const u8 *p = instr; p - instr < 64;) {
		if (p[0] == X86_MOVRMW && p[1] == X86_MODRM(0, 1, 5)
				&& ++mov_ecx_counter == 2) {
			videomode = *(struct videomode ***)(p + 2);
			break;
		}
		NEXT_INSN(p, "videomode");
	}
	debug("videomode = %p", (void *)videomode);

	// find cl_movieinfo
	{
		// step 1: find CL_IsRecordingMovie() in
		// CEngineTools::StartMovieRecording
		instr = (const u8 *)enginetools->vt->start_movie_recording;
		void *cl_isrecordingmovie = 0;
		for (const u8 *p = instr; p - instr < 64;) {
			// this is the first call in the function
			if (*p == X86_CALL) {
				cl_isrecordingmovie = (void *)(p + 5 + *(i32 *)(p + 1));
			}
			NEXT_INSN(p, "CL_IsRecordingMovie");
		}
		if (!cl_isrecordingmovie)
			bail("couldn't find cbuf_addtext CL_IsRecordingMovie");

		// step 2: get the pointer to cl_movieinfo
		// should be in the first instruction
		instr = (const u8 *)cl_isrecordingmovie;
		if (instr[0] != X86_ALUMI8 || instr[1] != X86_MODRM(0, 7, 5))
			bail("couldn't get movieinfo");
		movieinfo = *(struct movieinfo **)(instr + 2);
		debug("movieinfo = %p", (void *)movieinfo);
	}
	
	// find SND_RecordBuffer... this is something!
	{
		// step 1: Find S_Init() in snd_restart
		struct concommand *snd_restart = cvar->vt->find_command(cvar, "snd_restart");
		instr = (const u8 *)snd_restart->callback;
		void *s_init = 0;
		// S_Init is the 3rd call in Snd_Restart_f
		int call_count = 0;
		for (const u8 *p = instr; p - instr < 64;) {
			if (*p == X86_CALL && ++call_count == 3)
				s_init = (void *)(p + 5 + *(i32 *)(p + 1));
			NEXT_INSN(p, "S_Init");
		}
		debug("S_Init = %p", (void *)s_init);
		if (!s_init) bail("couldn't find S_Init");
		// step 2: find g_AudioDevice in S_Init
		// g_AudioDevice is the first variable assignment after the check for
		// the -nosound command line arg. look for that.
		instr = (const u8 *)s_init;
		bool nosound_push = false;
		for (const u8 *p = instr; p - instr < 180;) {
			if (p[0] == X86_PUSHIW 
					&& !strcmp(*(const char **)(p + 1), "-nosound"))
				nosound_push = true;
			if (nosound_push && p[0] == X86_MOVIIEAX) {
				audio_device = *(struct audio_device ***)(p + 1);
				break;
			}
			NEXT_INSN(p, "g_AudioDevice");
		}
		debug("g_AudioDevice = %p", (void *)audio_device);
		if (!audio_device) bail("couldn't get ptr to g_AudioDevice");
	}
	return true;
}

bool api_find_snd_recordbuffer(void) {
	// continuation, we must do this part later
	// step 3: Find S_TransferStereo16 in CAudioDirectSound::TransferSamples
	void *transferstereo16 = 0;
	const u8 *instr = (*audio_device)->vt->transfer_samples;
	debug("CAudioDirectSound::TransferSamples = %p", (void *)instr);
	// S_TransferStereo16 is the 8th call in TransferSamples
	int call_count = 0;
	for (const u8 *p = instr; p - instr < 384 /* big func! */;) {
		if (*p == X86_CALL && ++call_count == 8)
			transferstereo16 = (void *)(p + 5 + *(i32 *)(p + 1));
		NEXT_INSN(p, "S_TransferStereo16");
	}
	if (!transferstereo16)
		bail("couldn't find transferstereo16");
	debug("S_TransferStereo16 = %p", transferstereo16);
	// step 4: find SND_RecordBuffer in S_TransferStereo16
	// it should be the next call after an 'add ecx, ecx'
	// We are also going to get Snd_WriteLinearBlastStereo16 to get some other
	// variables we need.
	instr = (const u8 *)transferstereo16;
	bool found_double = false;
	bool found_recbuf = false;
	for (const u8 *p = instr; p - instr < 192;) {
		if (p[0] == X86_ADDRMW && p[1] == X86_MODRM(3, 1, 1))
			found_double = true;
		else if (p[0] == X86_CALL && found_double && !found_recbuf) {
			found_recbuf = true;
			snd_recordbuffer = (void (*)(void))(p + 5 + *(i32 *)(p + 1));
		}
		// this will be the next call
		else if (p[0] == X86_CALL && found_double && found_recbuf) {
			// this looks outrageous! that is because it is.
			snd = (struct soundstate *)(p + 5 + *(i32 *)(p + 1) + 3);
			break;
		}
		NEXT_INSN(p, "SND_RecordBuffer");
	}
	if (!snd_recordbuffer)
		bail("couldn't find snd_recordbuffer");
	debug("SND_RecordBuffer = %p", (void *)snd_recordbuffer);
	debug("Snd_WriteLinearBlastStereo16 + 3 = %p", (void *)snd);
	return true;
}

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