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.intel_syntax noprefix

.section .data
    stars_x: .space 800      # x coordinates (100 stars * 8 bytes)
    stars_y: .space 800      # y coordinates  
    stars_z: .space 800      # z coordinates
    screen: .space 500000    # Very large screen buffer for any terminal size
    seed: .quad 12345        # random seed
    term_rows: .quad 24      # Terminal rows (will be detected)
    term_cols: .quad 80      # Terminal cols (will be detected)
    
    clear_seq: .ascii "\033[2J\033[H"
    clear_len = . - clear_seq
    
    newline: .ascii "\n"
    
.section .text
    .global _start

_start:
    # Get terminal size using ioctl
    call get_terminal_size
    
    # Initialize stars
    call init_stars
    
main_loop:
    # Clear screen
    mov rax, 1               # sys_write
    mov rdi, 1               # stdout
    mov rsi, offset clear_seq
    mov rdx, clear_len
    syscall
    
    # Clear screen buffer
    mov rdi, offset screen
    mov rcx, [rip + term_rows]
    mov rax, [rip + term_cols]
    imul rcx, rax
    mov al, 32               # space character
    rep stosb
    
    # Update and draw stars
    call update_stars
    call draw_stars
    
    # Display screen
    mov rax, 1               # sys_write
    mov rdi, 1               # stdout
    mov rsi, offset screen
    mov rdx, [rip + term_rows]
    mov rcx, [rip + term_cols]
    imul rdx, rcx
    syscall
    
    # Small delay
    mov rax, 35              # sys_nanosleep
    mov rdi, offset delay_spec
    mov rsi, 0
    syscall
    
    jmp main_loop

init_stars:
    mov r8, 0                # star index
    
init_loop:
    cmp r8, 100
    jge init_done
    
    # Random x (-cols/2 to cols/2)
    call random
    mov rbx, [rip + term_cols]
    and rax, 0x3FF           # Use more bits for wider range
    xor rdx, rdx
    div rbx                  # rax % term_cols
    mov rax, rdx
    shr rbx, 1
    sub rax, rbx
    mov [stars_x + r8*8], rax
    
    # Random y (-rows/2 to rows/2)
    call random
    mov rbx, [rip + term_rows]
    and rax, 0x1FF           # Use more bits for taller terminals
    xor rdx, rdx
    div rbx                  # rax % term_rows
    mov rax, rdx
    shr rbx, 1
    sub rax, rbx
    mov [stars_y + r8*8], rax
    
    # Random z (1 to 100)
    call random
    and rax, 0x7F
    add rax, 1
    mov [stars_z + r8*8], rax
    
    inc r8
    jmp init_loop
    
init_done:
    ret

update_stars:
    mov r8, 0                # star index
    
update_loop:
    cmp r8, 100
    jge update_done
    
    # Move star closer (decrease z)
    mov rax, [stars_z + r8*8]
    sub rax, 2
    
    # If z <= 0, reset star
    cmp rax, 0
    jle reset_star
    
    mov [stars_z + r8*8], rax
    jmp next_star
    
reset_star:
    # New random position
    call random
    mov rbx, [rip + term_cols]
    and rax, 0x3FF
    xor rdx, rdx
    div rbx
    mov rax, rdx
    shr rbx, 1
    sub rax, rbx
    mov [stars_x + r8*8], rax
    
    call random
    mov rbx, [rip + term_rows]
    and rax, 0x1FF
    xor rdx, rdx
    div rbx
    mov rax, rdx
    shr rbx, 1
    sub rax, rbx
    mov [stars_y + r8*8], rax
    
    mov rax, 100
    mov [stars_z + r8*8], rax
    
next_star:
    inc r8
    jmp update_loop
    
update_done:
    ret

draw_stars:
    mov r8, 0                # star index
    
draw_loop:
    cmp r8, 100
    jge draw_done
    
    # Project 3D to 2D using terminal dimensions
    
    mov rax, [stars_x + r8*8]
    mov rbx, [rip + term_cols]
    shr rbx, 1               # cols/2
    imul rax, rbx
    mov rbx, [stars_z + r8*8]
    cmp rbx, 0
    je next_draw
    cqo
    idiv rbx
    mov rbx, [rip + term_cols]
    shr rbx, 1
    add rax, rbx             # + cols/2
    
    # Check X bounds
    cmp rax, 0
    jl next_draw
    mov rbx, [rip + term_cols]
    dec rbx
    cmp rax, rbx
    jg next_draw
    mov rcx, rax             # screen_x
    
    mov rax, [stars_y + r8*8]
    mov rbx, [rip + term_rows]
    shr rbx, 1               # rows/2
    imul rax, rbx
    mov rbx, [stars_z + r8*8]
    cqo
    idiv rbx
    mov rbx, [rip + term_rows]
    shr rbx, 1
    add rax, rbx             # + rows/2
    
    # Check Y bounds
    cmp rax, 0
    jl next_draw
    mov rbx, [rip + term_rows]
    dec rbx
    cmp rax, rbx
    jg next_draw
    mov rdx, rax             # screen_y
    
    # Calculate screen position
    mov rax, rdx
    mov rbx, [rip + term_cols]
    imul rax, rbx
    add rax, rcx
    
    # Draw star character based on distance
    mov rbx, [stars_z + r8*8]
    cmp rbx, 20
    jl bright_star
    cmp rbx, 50
    jl medium_star
    
    mov byte ptr [screen + rax], 46   # '.'
    jmp next_draw
    
medium_star:
    mov byte ptr [screen + rax], 42   # '*'
    jmp next_draw
    
bright_star:
    mov byte ptr [screen + rax], 35   # '#'
    
next_draw:
    inc r8
    jmp draw_loop
    
draw_done:
    ret

get_terminal_size:
    # Use ioctl TIOCGWINSZ to get terminal size
    sub rsp, 16              # Space for winsize struct
    mov rax, 16              # sys_ioctl
    mov rdi, 0               # stdin
    mov rsi, 0x5413          # TIOCGWINSZ
    mov rdx, rsp             # winsize struct
    syscall
    
    # Extract rows and cols from struct
    movzx eax, word ptr [rsp]     # ws_row (short)
    mov [rip + term_rows], rax
    movzx eax, word ptr [rsp + 2] # ws_col (short)
    mov [rip + term_cols], rax
    
    add rsp, 16
    ret

random:
    mov rax, [rip + seed]
    mov rbx, 1103515245
    imul rax, rbx
    add rax, 12345
    mov [rip + seed], rax
    ret

.section .data
delay_spec:
    .quad 0, 50000000        # 50ms delay

.section .text
exit:
    mov rax, 60              # sys_exit
    mov rdi, 0
    syscall