#include <stdlib.h>
#include <stdio.h>

#include "interpreter.h"



machine_state_t machine_state_t_new( void * cache_function_data
				, size_t program_size
				, size_t cache_size
				, size_t memory_size
				, size_t (* cache_block)(uint16_t * cache
							, uint16_t offset
							, size_t cache_size
							, void * cache_function_data)
				, dispatch_tree_t method_dispatcher)
{

	machine_state_t state = malloc(sizeof(struct machine_state_s));
	if(!state)
	{
		return NULL;
	}
	uint16_t * cache = calloc(sizeof(uint16_t), cache_size);
	if(!cache)
	{
		free(state);
		return NULL;
	}
	uint16_t * memory = calloc(sizeof(uint16_t), memory_size);
	if(!memory)
	{
		free(state);
		free(cache);
		return NULL;
	}


	state->program_size = program_size;
	state->cache = cache;
	state->cache_block = cache_block;
	state->cache_size = cache_size;
	state->cache_loaded = 0;
	state->cache_offset = 0;
	state->cache_function_data = cache_function_data;

	state->program_counter = 0;
	state->status_reg = 0;
	state->shutdown_reg = 0;
	int i;
	for(i = 0; i < BCI_CORE_NUM_REG; i++)
	{
		state->data_reg[i] = 0;
	}
	state->stack = NULL;

	state->memory = memory;
	state->memory_size = memory_size;

	state->method_dispatcher = method_dispatcher;

	return state;
}

void machine_state_t_del(machine_state_t state)
{
	free(state->cache);
	free(state->memory);
	dispatch_tree_t_del(state->method_dispatcher);
	bci_stack_t_del(&(state->stack));
	free(state);
}


char update_cache(machine_state_t state, uint16_t offset)
{
	// Calculate a clever offset for caching.
	uint16_t cache_offset = offset;
	if((cache_offset + state->cache_size)
		> state->program_size)
	{
		if(state->program_size < state->cache_size)
		{
			cache_offset = 0;
		}
		else
		{
			cache_offset = state->program_size - state->cache_size;
		}
	}
	size_t cached = state->cache_block(state->cache
					, cache_offset
					, state->cache_size
					, state->cache_function_data);

	if(cached != state->cache_size)
	{
		#ifdef DEBUG
		printf("ERROR: should have cached %zu words, but got %zu.\n", state->cache_size, cached);
		#endif
		return 1;
	}
	state->cache_offset = cache_offset;
	state->cache_loaded = 1;
	return 0;
}

char machine_state_t_get_word(machine_state_t state, uint16_t offset, uint16_t * result)
{

	// This would be bad.
	if(offset >= state->program_size)
	{
		return 0b01000000 | 1; 
	}
	
	// Calculate the in-cache offset of the desired offset.
	int32_t in_cache_offset = offset - state->cache_offset;

	// Check if we need to update the cache.
	if( in_cache_offset < 0
		|| !(state->cache_loaded)
		)
	{
		if(update_cache(state, offset))
		{
			#ifdef DEBUG
			printf("ERROR: failed to update cache\n");
			#endif
			state->error = 0b01000000 | 2;
			return 0b01000000 | 2;
		}
		// Re-calculate the in-cache offset
		in_cache_offset = offset - state->cache_offset;
	}

	*result = state->cache[in_cache_offset];
	return 0;

}

char machine_state_t_exec_cycle(machine_state_t state)
{
	char res = 0;
	uint16_t opcode;
	res = machine_state_t_get_word(state, state->program_counter, &opcode);
	
	if(res)
	{
		return res;
	}

#ifdef DEBUG
	printf("MSG: opcode = 0x%x, small_arg = 0x%x\n"
			, opcode & BCI_CORE_OPCODE_MASK
			, opcode & BCI_CORE_SMALL_ARG_MASK);
#endif

	bci_core_method_t method = dispatch_tree_t_dispatch(
					state->method_dispatcher
					, opcode & BCI_CORE_OPCODE_MASK);
	if(!method)
	{
		state->error = res;
		return 0b10000000 | 1;
	}

	return BCI_CORE_RESULT_APPLICATION_BITS 
		& method( opcode & BCI_CORE_SMALL_ARG_MASK
			, state);

}


char machine_state_t_default_afterexec(machine_state_t state, uint8_t argc)
{
	state->program_counter += 1 + argc;
	return 0;
}


char machine_state_t_get_mem(machine_state_t state, uint16_t offset, uint16_t * result)
{
	if(offset > state->memory_size)
	{
		state->error = 0b01000000 | 15;
		return 0b01000000 | 15;
	}

	*result = state->memory[offset];
	return 0;
}
char machine_state_t_set_mem(machine_state_t state, uint16_t offset, uint16_t data)
{
	if(offset > state->memory_size)
	{
		state->error = 0b01000000 | 15;
		return 0b01000000 | 15;
	}

	state->memory[offset] = data;
	return 0;
}




char machine_state_t_exec(machine_state_t state)
{
	char status = 0;
	while((!status) && (!state->shutdown_reg))
	{
		status = machine_state_t_exec_cycle(state);
	}
	state->error = status;
	return status;
}