enum dwarf_cfa_op_base {
    DW_CFA_advance_loc = 0x1,
    DW_CFA_offset = 0x2,
    DW_CFA_restore = 0x3
};

enum dwarf_cfa_op {
    DW_CFA_nop = 0x00,
    DW_CFA_set_loc = 0x01,
    DW_CFA_advance_loc1 = 0x02,
    DW_CFA_advance_loc2 = 0x03,
    DW_CFA_advance_loc4 = 0x04,
    DW_CFA_offset_extended = 0x05,
    DW_CFA_restore_extended = 0x06,
    DW_CFA_undefined = 0x07,
    DW_CFA_same_value = 0x08,
    DW_CFA_register = 0x09,
    DW_CFA_remember_state = 0x0a,
    DW_CFA_restore_state = 0x0b,
    DW_CFA_def_cfa = 0x0c,
    DW_CFA_def_cfa_register = 0x0d,
    DW_CFA_def_cfa_offset = 0x0e,
    DW_CFA_def_cfa_expression = 0x0f,
    DW_CFA_expression = 0x10,
    DW_CFA_offset_extended_sf = 0x11,
    DW_CFA_def_cfa_sf = 0x12,
    DW_CFA_def_cfa_offset_sf = 0x13,
    DW_CFA_val_offset = 0x14,
    DW_CFA_val_offset_sf = 0x15,
    DW_CFA_val_expression = 0x16,
    DW_CFA_lo_user = 0x1c,
    DW_CFA_hi_user = 0x3f,
};

struct dwarf_cie_header {
    u32 length;
    u8 version;
    u32 code_alignment;
    s32 data_alignment;
    u32 return_address_register;
    u32 augmentation_data_length;
    u8 *augmentation_data;
};

struct dwarf_fde_header {
    u32 length;
    u64 optional_length;
    struct dwarf_cie_header *cie;
    u64 low_pc;
    u64 high_pc;
    u32 augmentation_data_length;
    u8 *augmentation_data;
};

static u64
iterate_call_frame_instructions(struct dwarf_cie_header header, u8 *data, u8 *original_data)
{
    u64 already_read = data - original_data - 4;
    u64 leftover = header.length - already_read;
    u64 read = 0;
    
    for (;;) {
        u8 op_byte = *data++;
        enum dwarf_cfa_op_base high_two = op_byte >> 6;
        enum dwarf_cfa_op low_six = op_byte & 0x3f;
        
        u32 increment = 0;
        
        if (high_two == DW_CFA_advance_loc) {
            u8 delta = low_six;
        } else if (high_two == DW_CFA_offset) {
            u8 reg = low_six;
            u32 factored_offset;
            increment += decode_leb128(data, &factored_offset);
        } else if (high_two == DW_CFA_restore) {
            u8 reg = low_six;
            
        } else if (high_two == 0) {
            switch (low_six) {
                case DW_CFA_nop: {
                    break;
                }
                
                case DW_CFA_set_loc: {
                    u64 address;
                    memcpy(&address, data, 8);
                    increment = 8;
                    break;
                }
                
                case DW_CFA_advance_loc1: {
                    u8 advance;
                    memcpy(&advance, data, 1);
                    increment = 1;
                    break;
                }
                
                case DW_CFA_advance_loc2: {
                    u16 advance;
                    memcpy(&advance, data, 2);
                    increment = 2;
                    break;
                }
                
                case DW_CFA_advance_loc4: {
                    u32 advance;
                    memcpy(&advance, data, 4);
                    increment = 4;
                    break;
                }
                
                case DW_CFA_offset_extended: {
                    u32 reg;
                    u32 offset;
                    increment += decode_leb128(data, &reg);
                    increment += decode_leb128(data, &offset);
                    break;
                }
                
                case DW_CFA_restore_extended: {
                    u32 reg;
                    increment += decode_leb128(data, &reg);
                    break;
                }
                
                case DW_CFA_undefined: {
                    u32 reg;
                    increment += decode_leb128(data, &reg);
                    break;
                }
                
                case DW_CFA_same_value: {
                    u32 reg;
                    increment += decode_leb128(data, &reg);
                    break;
                }
                
                case DW_CFA_register: {
                    u32 reg;
                    s32 factored_offset;
                    increment += decode_leb128(data, &reg);
                    increment += decode_leb128s(data, &factored_offset);
                    break;
                }
                
                case DW_CFA_remember_state: {
                    break;
                }
                
                case DW_CFA_restore_state: {
                    break;
                }
                
                case DW_CFA_def_cfa: {
                    u32 reg;
                    u32 nonfactored_offset;
                    increment += decode_leb128(data, &reg);
                    increment += decode_leb128(data, &nonfactored_offset);
                    break;
                }
                
                case DW_CFA_def_cfa_register: {
                    u32 reg;
                    increment += decode_leb128(data, &reg);
                    break;
                }
                
                case DW_CFA_def_cfa_offset: {
                    u32 offset;
                    increment += decode_leb128(data, &offset);
                    break;
                }
                
                case DW_CFA_def_cfa_expression: {
                    u32 length;
                    increment += decode_leb128(data, &length);
                    increment += length;
                    break;
                }
                
                case DW_CFA_expression: {
                    u32 reg;
                    u32 length;
                    increment += decode_leb128(data, &reg);
                    increment += decode_leb128(data, &length);
                    increment += length;
                    break;
                }
                
                case DW_CFA_offset_extended_sf: {
                    u32 reg;
                    s32 factored_offset;
                    increment += decode_leb128(data, &reg);
                    increment += decode_leb128s(data, &factored_offset);
                    break;
                }
                
                case DW_CFA_def_cfa_sf: {
                    u32 reg;
                    s32 factored_offset;
                    increment += decode_leb128(data, &reg);
                    increment += decode_leb128s(data, &factored_offset);
                    break;
                }
                
                case DW_CFA_def_cfa_offset_sf: {
                    s32 factored_offset;
                    increment += decode_leb128s(data, &factored_offset);
                    break;
                }
                
                case DW_CFA_val_offset: {
                    u32 reg;
                    u32 factored_offset;
                    increment += decode_leb128(data, &reg);
                    increment += decode_leb128(data, &factored_offset);
                    break;
                }
                
                case DW_CFA_val_offset_sf: {
                    u32 reg;
                    s32 factored_offset;
                    increment += decode_leb128(data, &reg);
                    increment += decode_leb128s(data, &factored_offset);
                    break;
                }
                
                case DW_CFA_val_expression: {
                    u32 reg;
                    u32 length;
                    increment += decode_leb128(data, &reg);
                    increment += decode_leb128(data, &length);
                    increment += length;
                    break;
                }
                
                case DW_CFA_lo_user: {
                    break;
                }
                
                case DW_CFA_hi_user: {
                    break;
                }
            }
        }
        
        data += increment;
        read += increment + 1;
        
        if (read >= leftover) {
            break;
        }
    }
    
    return(read);
}

static u64
read_one_cie(u64 length, u8 *data, u8 *original_data)
{
    struct dwarf_cie_header header = { 0 };
    
    header.length = length;
    header.version = *data++;
    
    char *augmenation_string = (char *) data;
    
    // NOTE: null-terminated string
    int has_z = 0;
    int has_L = 0;
    int has_P = 0;
    int has_R = 0;
    
    while (*data) {
        if (*data == 'z') has_z = 1;
        if (*data == 'L') has_L = 1;
        if (*data == 'P') has_P = 1;
        if (*data == 'R') has_R = 1;
        ++data;
    }
    ++data;
    
    (void) has_L;
    (void) has_P;
    (void) has_R;
    
    data += decode_leb128(data, &header.code_alignment);
    data += decode_leb128s(data, &header.data_alignment);
    data += decode_leb128(data, &header.return_address_register);
    
    if (has_z) {
        data += decode_leb128(data, &header.augmentation_data_length);
        header.augmentation_data = data;
        data += header.augmentation_data_length;
    }
    
    data += iterate_call_frame_instructions(header, data, original_data);
    
    return(data - original_data);
}

static u64
read_one_fde(u64 length, u32 cie_offset, u8 *data, u8 *original_data)
{
    struct dwarf_fde_header header = { 0 };
    
    header.length = length;
    header.cie = (struct dwarf_cie_header *) (data - 4 - cie_offset);
    memcpy(&header.low_pc, data, 8);
    data += 8;
    memcpy(&header.high_pc, data, 8);
    data += 8;
    header.high_pc = header.low_pc + header.high_pc;
    
    // if (cie has 'z')
    data += decode_leb128(data, &header.augmentation_data_length);
    header.augmentation_data = data;
    data += header.augmentation_data_length;
    
    
    struct dwarf_cie_header hh = { 0 };
    data += iterate_call_frame_instructions(hh, data, original_data);
    
    return(0);
}

static u64
read_one_call_frame_record(u8 *data)
{
    u8 *original_data = data;
    u64 length;
    u32 length32;
    u32 cie_id;
    
    memcpy(&length32, data, 4);
    length = length32;
    data += 4;
    
    if (length == 0) {
        memcpy(&length, data, 8);
        data += 8;
    }
    
    memcpy(&cie_id, data, 4);
    data += 4;
    
    u64 result;
    
    if (cie_id == 0) {
        result = read_one_cie(length, data, original_data);
    } else {
        result = read_one_fde(length, cie_id, data, original_data);
    }
    
    return(result);
}

static void
parse_eh_frame(u8 *file)
{
    struct elf_section_table_entry_x64 eh_frame = get_section_entry(file, ".eh_frame");
    
    u64 read = 0;
    
    for (;;) {
        u64 size = read_one_call_frame_record(file + eh_frame.offset_in_file + read);
        read += size;
        if (read >= eh_frame.size) {
            break;
        }
    }
}