#include "asm.h"

#include "../../include/std/mem.h"
#include "../../include/std/log.h"
#include <errno.h>
#include <assert.h>
#include <stdio.h>

#include <sys/mman.h>

#define REX_W 0x48

#ifdef DEBUG
#include <stdarg.h>
#include <string.h>

static u8 asm_debug_str_buffer[256];
static usize asm_debug_str_buffer_index = 0;
static usize ins_start_offset = 0;

static void asm_debug_str_append(const char *str) {
    const usize len = strlen(str);
    am_memcpy(asm_debug_str_buffer + asm_debug_str_buffer_index, str, len);
    asm_debug_str_buffer[asm_debug_str_buffer_index + len + 1] = '\0';
    asm_debug_str_buffer_index += len;
}

static void asm_debug_str_append_num(int num) {
    char num_str[32];
    sprintf(num_str, "0x%x", num);
    asm_debug_str_append(num_str);
}

static void ins_start(Asm *self) {
    ins_start_offset = (u8*)self->code_it - (u8*)self->code;
    asm_debug_str_buffer_index = 0;
}

static int max(int a, int b) {
    return a >= b ? a : b;
}

static void ins_end(Asm *self, const char *fmt, ...) {
    usize ins_end_offset;
    usize i;
    va_list args;

    va_start(args, fmt);
    ins_end_offset = (u8*)self->code_it - (u8*)self->code;
    for(i = ins_start_offset; i < ins_end_offset; ++i) {
        fprintf(stderr, "%02x ", ((u8*)self->code)[i]);
    }
    /* Same padding for all instructions, no matter how long they are */
    for(i = 0; i < (usize)max(0, 35 - (ins_end_offset - ins_start_offset)*3); ++i) {
        putc(' ', stderr);
    }
    vfprintf(stderr, fmt, args);
    putc('\n', stderr);
    va_end(args);
}

static const char* reg32_to_str(Reg32 reg) {
    switch(reg) {
        case EAX: return "eax";
        case ECX: return "ecx";
        case EDX: return "edx";
        case EBX: return "ebx";
        case ESP: return "esp";
        case EBP: return "ebp";
        case ESI: return "esi";
        case EDI: return "edi";
    }
    assert(bool_false);
    return NULL;
}

static const char* reg64_to_str(Reg64 reg) {
    switch(reg) {
        case RAX: return "rax";
        case RCX: return "rcx";
        case RDX: return "rdx";
        case RBX: return "rbx";
        case RSP: return "rsp";
        case RBP: return "rbp";
        case RSI: return "rsi";
        case RDI: return "rdi";
    }
    assert(bool_false);
    return NULL;
}

static i32 abs(i32 num) {
    return num >= 0 ? num : -num;
}

static const char* asm_ptr_to_string(AsmPtr *self) {
    const char *buf = (const char*)(asm_debug_str_buffer + asm_debug_str_buffer_index);
    asm_debug_str_append("QWORD PTR [");
    asm_debug_str_append(reg64_to_str(self->base));
    if((int)self->index != -1) {
        asm_debug_str_append(reg64_to_str(self->index));
        asm_debug_str_append(" * ");
        asm_debug_str_append_num(1 << self->scale);
    }
    if(self->disp != 0) {
        if(self->disp < 0)
            asm_debug_str_append(" - ");
        else
            asm_debug_str_append(" + ");
        asm_debug_str_append_num(abs(self->disp));
    }
    asm_debug_str_append("]");
    return buf;
}
#else
static void ins_start(Asm *self) {
    (void)self;
}

static void ins_end(Asm *self, const char *fmt, ...) {
    (void)self;
    (void)fmt;
}

static const char* reg32_to_str(Reg32 reg) {
    (void)reg;
    return NULL;
}

static const char* reg64_to_str(Reg64 reg) {
    (void)reg;
    return NULL;
}

static const char* asm_ptr_to_string(AsmPtr *self) {
    (void)self;
    return NULL;
}
#endif

void asm_ptr_init(AsmPtr *self, Reg64 base) {
    self->base = base;
    self->index = -1;
    self->disp = 0;
    self->scale = 0;
}

void asm_ptr_init_index(AsmPtr *self, Reg64 base, Reg64 index) {
    self->base = base;
    self->index = index;
    self->disp = 0;
    self->scale = 0;
}

void asm_ptr_init_disp(AsmPtr *self, Reg64 base, i32 disp) {
    self->base = base;
    self->index = -1;
    self->disp = disp;
    self->scale = 0;
}

void asm_ptr_init_index_disp(AsmPtr *self, Reg64 base, Reg64 index, i32 disp) {
    self->base = base;
    self->index = index;
    self->disp = disp;
    self->scale = 0;
}

int asm_init(Asm *self) {
    self->allocated_size = am_pagesize();
    amal_log_debug("asm: page size: %u", self->allocated_size);
    self->code = mmap(NULL, self->allocated_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    if(self->code == MAP_FAILED)
        return -errno;
    self->code_it = self->code;
    return 0;
}

void asm_deinit(Asm *self) {
    if(self->code)
        munmap(self->code, self->allocated_size);
    self->code = NULL;
    self->code_it = NULL;
    self->allocated_size = 0;
}

usize asm_get_size(Asm *self) {
    return self->code_it - (u8*)self->code;
}

#if 0
static void asm_print_code_hex(Asm *self) {
    u8 *ptr;
    int off;
    ptr = self->code;
    off = 0;
    while(ptr != self->code_it) {
        printf("%02x", *ptr);
        ++ptr;
        ++off;
        if(off == 8) {
            putc('\n', stdout);
            off = 0;
        } else {
            putc(' ', stdout);
        }
    }
    if(off != 0)
        putc('\n', stdout);
}
#endif

int asm_execute(Asm *self) {
    void (*func)();
    if(mprotect(self->code, self->allocated_size, PROT_READ | PROT_EXEC) != 0)
        return -errno;

    /*asm_print_code_hex(self);*/

    /* TODO: Verify if this is valid on all platforms. According to ISO C standard it isn't? */
    *(void**)(&func) = self->code;
    func();
    return 0;
}

/* TODO: See how this can be optimized */
static CHECK_RESULT int asm_ensure_capacity(Asm *self, usize size) {
    usize current_offset;
    current_offset = (u8*)self->code_it - (u8*)self->code;
    if(current_offset + size > self->allocated_size) {
        void *new_mem;
        usize new_size;
        new_size = self->allocated_size + am_pagesize();
        new_mem = mmap(NULL, new_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        if(self->code == MAP_FAILED)
            return -errno;

        am_memcpy(new_mem, self->code, self->allocated_size);
        self->code = new_mem;
        self->allocated_size = new_size;
        self->code_it = (u8*)self->code + current_offset;
    }
    return 0;
}

#ifdef DEBUG
static isize asm_get_capacity_left(Asm *self) {
    return (isize)self->allocated_size - (isize)((u8*)self->code_it - (u8*)self->code);
}
#endif

int asm_nop(Asm *self) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 1));
    *self->code_it++ = 0x90;
    ins_end(self, "nop");
    return 0;
}

static i32 abs_i32(i32 value) {
    return value >= 0 ? value : -value;
}

/*
TODO: Implement 1 and 2 byte displacement?
There has to be at least 6 bytes left in the asm buffer before calling this function.
*/
static void asm_rm(Asm *self, AsmPtr *mem, Reg64 reg) {
    u8 rm_byte;
    u8 disp_bytes;
    assert(asm_get_capacity_left(self) >= 6);
    if((int)mem->index != -1) {
        u8 sib_offset;
        if(mem->disp == 0) {
            rm_byte = 0x04;
            disp_bytes = 0;
        } else if(abs_i32(mem->disp) <= INT8_MAX) {
            rm_byte = 0x44;
            disp_bytes = 1;
        } else {
            rm_byte = 0x84;
            disp_bytes = 4;
        }

        /* Scale is not valid when index is RSP */
        assert(mem->index != RSP || mem->scale == 0);

        #ifdef DEBUG
        if(mem->scale != 0 && mem->scale != 2 && mem->scale != 4 && mem->scale != 8) {
            amal_log_error("Invalid scale %d, expected 0, 2, 4, or 8", mem->scale);
            assert(bool_false);
        }
        #endif
        assert(mem->base != RBP && "TODO: Implement RBP base for sib byte. RBP is special and requires different logic");
        sib_offset = (mem->scale << 5) + 8*mem->index + mem->base;

        *self->code_it++ = rm_byte;
        *self->code_it++ = sib_offset;
    } else {
        assert(mem->scale == 0); /* Scale isn't valid without index reg */
        if(mem->disp == 0) {
            if(mem->base == RBP) {
                rm_byte = 0x45;
                disp_bytes = 1;
            } else {
                rm_byte = mem->base;
                disp_bytes = 0;
            }
        } else if(abs_i32(mem->disp) <= INT8_MAX) {
            rm_byte = 0x40 + mem->base;
            disp_bytes = 1;
        } else {
            rm_byte = 0x80 + mem->base;
            disp_bytes = 4;
        }

        *self->code_it++ = (reg << 3) | rm_byte;
        /* RSP requires SIB byte */
        if(mem->base == RSP)
            *self->code_it++ = 0x24;
    }

    am_memcpy(self->code_it, &mem->disp, disp_bytes);
    self->code_it += disp_bytes;
}

/* There has to be at least 1 byte left in the asm buffer before calling this function. */
static void asm_rr(Asm *self, Reg64 dst, Reg64 src) {
    assert(asm_get_capacity_left(self) >= 1);
    *self->code_it++ = 0xC0 + dst + 8*src;
}

/* TODO: Implement 1 and 2 byte immediate? */
int asm_mov_mi(Asm *self, AsmPtr *dst, i32 immediate) {
    ins_start(self);
    /* 12 bytes is the maximum size of the instruction. We don't how how large it will be so we prepare for the largest size */
    return_if_error(asm_ensure_capacity(self, 12));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0xC7;
    asm_rm(self, dst, 0);
    am_memcpy(self->code_it, &immediate, sizeof(immediate));
    self->code_it += sizeof(immediate);
    ins_end(self, "mov %s, 0x%x", asm_ptr_to_string(dst), immediate);
    return 0;
}

int asm_mov_mr(Asm *self, AsmPtr *dst, Reg64 src) {
    ins_start(self);
    /* 8 bytes is the maximum size of the instruction. We don't how how large it will be so we prepare for the largest size */
    return_if_error(asm_ensure_capacity(self, 8));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0x89;
    asm_rm(self, dst, src);
    ins_end(self, "mov %s, %s", asm_ptr_to_string(dst), reg64_to_str(src));
    return 0;
}

int asm_mov_rm(Asm *self, Reg64 dst, AsmPtr *src) {
    ins_start(self);
    /* 8 bytes is the maximum size of the instruction. We don't how how large it will be so we prepare for the largest size */
    return_if_error(asm_ensure_capacity(self, 8));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0x8B;
    asm_rm(self, src, dst);
    ins_end(self, "mov %s, %s", reg64_to_str(dst), asm_ptr_to_string(src));
    return 0;
}

/* Note: This shows as instruction movabs in intel assembly format */
int asm_mov_ri(Asm *self, Reg64 dst, i64 immediate) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 10));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0xB8 + dst;
    am_memcpy(self->code_it, &immediate, sizeof(immediate));
    self->code_it += sizeof(immediate);
    ins_end(self, "mov %s, 0x%x", reg64_to_str(dst), immediate);
    return 0;
}

int asm_mov_rr(Asm *self, Reg64 dst, Reg64 src) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 3));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0x89;
    asm_rr(self, dst, src);
    ins_end(self, "mov %s, %s", reg64_to_str(dst), reg64_to_str(src));
    return 0;
}

int asm_add_rr(Asm *self, Reg64 dst, Reg64 src) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 3));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0x01;
    asm_rr(self, dst, src);
    ins_end(self, "add %s, %s", reg64_to_str(dst), reg64_to_str(src));
    return 0;
}

int asm_sub_rr(Asm *self, Reg64 dst, Reg64 src) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 3));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0x29;
    asm_rr(self, dst, src);
    ins_end(self, "sub %s, %s", reg64_to_str(dst), reg64_to_str(src));
    return 0;
}

int asm_imul_rr(Asm *self, Reg64 dst, Reg64 src) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 4));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0x0F;
    *self->code_it++ = 0xAF;
    asm_rr(self, dst, src);
    ins_end(self, "imul %s, %s", reg64_to_str(dst), reg64_to_str(src));
    return 0;
}

int asm_cqo(Asm *self) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 2));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0x99;
    ins_end(self, "cqo");
    return 0;
}

int asm_idiv_rr(Asm *self, Reg64 src) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 4));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0xF7;
    asm_rr(self, src, 0x7);
    ins_end(self, "idiv %s", reg64_to_str(src));
    return 0;
}

int asm_pushr(Asm *self, Reg64 reg) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 1));
    *self->code_it++ = 0x50 + reg;
    ins_end(self, "push %s", reg64_to_str(reg));
    return 0;
}

int asm_popr(Asm *self, Reg64 reg) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 1));
    *self->code_it++ = 0x58 + reg;
    ins_end(self, "pop %s", reg64_to_str(reg));
    return 0;
}

int asm_callr(Asm *self, Reg64 reg) {
    ins_start(self);
    return_if_error(asm_ensure_capacity(self, 3));
    *self->code_it++ = REX_W;
    *self->code_it++ = 0xFF;
    asm_rr(self, reg, 0x2);
    ins_end(self, "call %s", reg64_to_str(reg));
    return 0;
}

/*
    Note: This is sometimes called with @relative 0 (will print call -5), in which case it's most likely a dummy call until the relative position
    is later changed with @asm_override_call_rel32. TODO: Update the ins_end debug print to take that into account somehow
*/
int asm_call_rel32(Asm *self, i32 relative) {
    ins_start(self);
    relative -= 5; /* In x86, the relative position starts from the next instruction */
    return_if_error(asm_ensure_capacity(self, 5));
    *self->code_it++ = 0xE8;
    am_memcpy(self->code_it, &relative, sizeof(relative));
    self->code_it += sizeof(relative);
    ins_end(self, "call 0x%x", relative);
    return 0;
}

void asm_override_call_rel32(Asm *self, u32 asm_index, i32 new_relative) {
    new_relative -= 5; /* In x86, the relative position starts from the next instruction */
    am_memcpy((u8*)self->code + asm_index + 1, &new_relative, sizeof(new_relative));
}

/* TODO: Remove these !*/

/* /r */
#define DEFINE_INS_RM(mnemonic, opcode)                         \
int asm_##mnemonic##_rmb(Asm *self, Reg32 dst, Reg32 src) {      \
    return_if_error(asm_ensure_capacity(self, 2));              \
    *self->code_it++ = opcode;                                  \
    *self->code_it++ = 0xC0 + 8*dst + src;                      \
    return 0;                                                   \
}                                                               \
                                                                \
int asm_##mnemonic##_rm32(Asm *self, Reg32 dst, Reg32 src) {    \
    int result;                                                 \
    ins_start(self);                                            \
    result = asm_##mnemonic##_rmb(self, (Reg32)dst, (Reg32)src);            \
    ins_end(self, #mnemonic" %s, %s", reg32_to_str(dst), reg32_to_str(src)); \
    return result;                                                           \
}                                                                            \
                                                                \
int asm_##mnemonic##_rm64(Asm *self, Reg64 dst, Reg64 src) {    \
    int result;                                                 \
    ins_start(self);                                            \
    return_if_error(asm_ensure_capacity(self, 1));              \
    *self->code_it++ = REX_W;                                   \
    result = asm_##mnemonic##_rmb(self, (Reg32)dst, (Reg32)src); \
    ins_end(self, #mnemonic" %s, %s", reg64_to_str(dst), reg64_to_str(src)); \
    return result; \
}

DEFINE_INS_RM(mov, 0x8B)
DEFINE_INS_RM(add, 0x03)
DEFINE_INS_RM(sub, 0x2B)
DEFINE_INS_RM(and, 0x23)
DEFINE_INS_RM(or, 0x0B)
DEFINE_INS_RM(xor, 0x33)
DEFINE_INS_RM(cmp, 0x3B)

/*
    /number
    The number is called the extension, a number from 0 to 7;
    It's a number used to extend the opcode type, since the instruction only uses
    one register the other register can be encoded for that.
*/
#define DEFINE_INS_EXT_IMM(mnemonic, extension)                      \
int asm_##mnemonic##_rmb_imm(Asm *self, Reg32 reg, i32 immediate) {  \
    if(abs_i32(immediate) <= INT8_MAX) {                             \
        return_if_error(asm_ensure_capacity(self, 3));               \
        *self->code_it++ = 0x83;                                     \
        *self->code_it++ = 0xC0 + 8*extension + reg;                 \
        *self->code_it++ = (u8)immediate;                            \
    } else {                                                         \
        return_if_error(asm_ensure_capacity(self, 6));               \
        *self->code_it++ = 0x81;                                     \
        *self->code_it++ = 0xC0 + 8*extension + reg;                 \
        am_memcpy(self->code_it, &immediate, sizeof(immediate));     \
        self->code_it += sizeof(immediate);                          \
    }                                                                \
    return 0;                                                        \
}                                                                    \
                                                                     \
int asm_##mnemonic##_rm32_imm(Asm *self, Reg32 reg, i32 immediate) {  \
    int result; \
    ins_start(self); \
    result = asm_##mnemonic##_rmb_imm(self, (Reg32)reg, immediate);   \
    ins_end(self, #mnemonic" %s, 0x%x", reg32_to_str(reg), immediate); \
    return result; \
}\
                                                                     \
int asm_##mnemonic##_rm64_imm(Asm *self, Reg64 reg, i32 immediate) { \
    int result; \
    ins_start(self); \
    return_if_error(asm_ensure_capacity(self, 1));                   \
    *self->code_it++ = REX_W;                                        \
    result = asm_##mnemonic##_rmb_imm(self, (Reg32)reg, immediate);   \
    ins_end(self, #mnemonic" %s, 0x%x", reg64_to_str(reg), immediate); \
    return result; \
}

DEFINE_INS_EXT_IMM(add, 0)
DEFINE_INS_EXT_IMM(or, 1)
DEFINE_INS_EXT_IMM(adc, 2)
DEFINE_INS_EXT_IMM(sbb, 3)
DEFINE_INS_EXT_IMM(and, 4)
DEFINE_INS_EXT_IMM(sub, 5)
DEFINE_INS_EXT_IMM(xor, 6)
DEFINE_INS_EXT_IMM(cmp, 7)

/*
    /number
    The number is called the extension, a number from 0 to 7;
    It's a number used to extend the opcode type, since the instruction only uses
    one register the other register can be encoded for that.
*/
#define DEFINE_INS_SHIFT_IMM8(mnemonic, extension)                  \
int asm_##mnemonic##_rmb_imm(Asm *self, Reg32 reg, i8 immediate) { \
    if(immediate == 1) {                                            \
        return_if_error(asm_ensure_capacity(self, 2));              \
        *self->code_it++ = 0xC1;                                    \
        *self->code_it++ = 0xC0 + 8*reg + extension;                \
    } else {                                                        \
        return_if_error(asm_ensure_capacity(self, 3));              \
        *self->code_it++ = 0xD1;                                    \
        *self->code_it++ = 0xC0 + 8*reg + extension;                \
        *self->code_it++ = immediate;                               \
    }                                                               \
    return 0;                                                       \
}                                                                   \
 \
int asm_##mnemonic##_rm32_imm(Asm *self, Reg32 reg, i8 immediate) { \
    int result; \
    ins_start(self); \
    result = asm_##mnemonic##_rmb_imm(self, (Reg32)reg, immediate);  \
    ins_end(self, #mnemonic" %s, 0x%x", reg32_to_str(reg), immediate); \
    return result; \
} \
                                                                    \
int asm_##mnemonic##_rm64_imm(Asm *self, Reg64 reg, i8 immediate) { \
    int result; \
    ins_start(self); \
    return_if_error(asm_ensure_capacity(self, 1));                  \
    *self->code_it++ = REX_W;                                       \
    result = asm_##mnemonic##_rmb_imm(self, (Reg32)reg, immediate);  \
    ins_end(self, #mnemonic" %s, 0x%x", reg64_to_str(reg), immediate); \
    return result; \
}

DEFINE_INS_SHIFT_IMM8(rol, 0)
DEFINE_INS_SHIFT_IMM8(ror, 1)
DEFINE_INS_SHIFT_IMM8(rcl, 2)
DEFINE_INS_SHIFT_IMM8(rcr, 3)
DEFINE_INS_SHIFT_IMM8(shl, 4)
DEFINE_INS_SHIFT_IMM8(shr, 5)
/*DEFINE_INS_SHIFT_IMM8(shl, 6)*/
DEFINE_INS_SHIFT_IMM8(sar, 7)

int asm_ret(Asm *self, u16 bytes) {
    ins_start(self);
    if(bytes == 0) {
        return_if_error(asm_ensure_capacity(self, 1));
        *self->code_it++ = 0xC3;
        ins_end(self, "ret");
    } else {
        return_if_error(asm_ensure_capacity(self, 3));
        *self->code_it++ = 0xC2;
        am_memcpy(self->code_it, &bytes, sizeof(bytes));
        ins_end(self, "ret 0x%x", bytes);
    }
    return 0;
}