.include "macros.s"

.section .init
.global _start
_start:
	jmp _uskel_start

.section .bss
_memory_state:
	cell 0 # bottom of allocation (grows down)
	cell 0 # region start
	cell 0 # region end

.section .text

_uskel_alloc_basic_mem:
	mov $0x100000, %r15 # desired size

	mov $0x9, %rax # mmap
	mov $0, %rdi # addr = NULL
	mov %r15, %rsi # len = %rcx
	mov $0x3, %rdx # prot = PROT_READ 0x1 | PROT_WRITE 0x2
	mov $0x22, %r10 # flags = MAP_PRIVATE 0x2 | MAP_ANONYMOUS 0x20
	mov $-1, %r8 # fd = -1
	mov $0, %r9 # off = 0
	syscall
	mov $_memory_state, %rdi
	mov %rax, (%rdi)
	mov %rax, 0x8(%rdi)
	add %r15, %rax
	mov %rax, 0x10(%rdi)
	retq

_uskel_start:
	call _uskel_alloc_basic_mem
	mov _memory_state, %rdi
	# push a thunk for main
	mov %rdi, %r15 # backup main for later
	movq $main, 0x00(%rdi)
	movq $0, 0x08(%rdi)
	add $0x10, %rdi
	# save the memory ptr
	mov %rdi, _memory_state

	mov $0, %rsi # set continuation to exit
	enter %r15 # run the program

# Simple values and boxed machine integers
# | ptr | value |
CON_evacuate1:
	retq
CON_scavenge1:
	add $0x10, %rsi
	retq
INT_info_table:
	cell CON_evacuate1
	cell CON_scavenge1
	cell 0
INT_code:
	continue

# List
# | ptr | 0 |
# | ptr | 1 | a | b |
LIST_evacuate:
	# [] | a : b
	retq #TODO
LIST_scavenge:
	mov 0x8(%rbp), %rax
	shl $1, %rax
	add $2, %rax
	shl $3, %rax
	add %rax, %rsi
	retq
LIST_info_table:
	cell LIST_evacuate
	cell LIST_scavenge
	cell 0
LIST_code:
	continue

# FUN/PAP combo objects
# | ptr | thunkptr | args | arg[0] | arg[1] | ... | arg[args] |
FUN_evacuate:
	retq #TODO
FUN_scavenge:
	mov 0x10(%rbp), %rax
	add $3, %rax
	shl $3, %rax
	add %rax, %rsi
	retq

# Simple info for n-ary functions
# TODO continue to add as required
fun1_info_table:
	cell FUN_evacuate
	cell FUN_scavenge
	cell 1
fun1_code:
	continue

fun2_info_table:
	cell FUN_evacuate
	cell FUN_scavenge
	cell 2
fun2_code:
	continue

fun3_info_table:
	cell FUN_evacuate
	cell FUN_scavenge
	cell 3
fun3_code:
	continue

# indirection (Q: how to recognize IND and THUNK on return?)
# | ptr | indptr |
IND_evacuate:
	retq #TODO
IND_scavenge:
	add $0x10,%rsi
	retq
IND_info:
	cell IND_evacuate
	cell IND_scavenge
	cell 0
IND_code:
	enter 0x8(%rbp)

# THU objects (gc implementation only, actual THUs are defined by functions)
# | ptr | args | arg[0] | arg[1] | ... | arg[args] |
# args wouldn't need to be here but let's keep them for gc simplicity
THU_evacuate:
	retq #TODO
THU_scavenge:
	mov 0x8(%rbp), %rax
	add $2,%rax
	shl $3,%rax
	add %rax,%rsi
	retq

#
# Actual code!
#

# || -> cont
.makethunk main
	mov _memory_state, %r15

	# push a new integer
	mov %r15, %r11 # backup first arg
	movq $INT_code, 0x00(%r15)
	movq $100, 0x08(%r15)
	add $0x10, %r15

	# push another new integer
	mov %r15, %r12 # backup second arg
	movq $INT_code, 0x00(%r15)
	movq $23, 0x08(%r15)
	add $0x10, %r15

	# push the plus
	mov %r15, %r13 # backup plus
	movq $plus, 0x00(%r15)
	movq $2, 0x08(%r15)
	mov %r11, 0x10(%r15)
	mov %r12, 0x18(%r15)
	add $0x20, %r15

	# push a cont thunk for main_exit
	mov %r15, %r14 # backup cont thunk
	movq $main_exit, 0x00(%r15)
	movq $1, 0x08(%r15)
	mov %rsi, 0x10(%r15)
	add $0x18, %r15

	mov %r15, _memory_state

	# evaluate into main_exit
	mov %r14, %rsi
	enter %r13

# exitcode -> | cont (unused, should be 0) |
.makethunk main_exit
	mov 0x8(%rsi), %rdi
	mov $0x3c, %rax
	syscall # exit %rdi

# | arg1 | arg2 | -> cont
.makethunk plus
	# push a thunk for finishing the plus
	mov _memory_state, %r15
	mov %r15, %r14 # plus_step1 origin
	movq $plus_step1, 0x00(%r15)
	movq $3, 0x08(%r15)
	mov 0x18(%rbp), %rax
	mov %rax, 0x10(%r15)
	mov %rbp, 0x18(%r15)
	mov %rsi, 0x20(%r15)
	add $0x28, %r15
	mov %r15, _memory_state

	# evaluate arg0
	mov %r14, %rsi
	enter 0x10(%rbp)

# arg0 -> | arg1 | ret | cont |
.makethunk plus_step1
	# this is guaranteed to be entered only once (it's a cont), so we can rewrite the thunk in place
	mov 0x10(%rbp), %rax
	movq $plus_fini, 0x00(%rbp)
	mov %rsi, 0x10(%rbp)

	mov %rbp, %rsi # continue on the rewritten thunk
	enter %rax # evaluate arg1

# arg1 -> | arg0 | ret | cont |
.makethunk plus_fini
	mov 0x8(%rsi), %rax # arg1
	mov 0x10(%rbp), %rsi
	add 0x8(%rsi), %rax # + arg0

	mov 0x18(%rbp), %rsi # rewrite the resulting thunk
	movq $INT_code, 0x00(%rsi)
	mov %rax, 0x08(%rsi)
	# result is in rsi already
	enter 0x20(%rbp)

# Q: are there gonna be functions that have both the argument AND the cont?
# A: No, either stuff is entered as return-continuation (takes res) or as forward call (takes cont)
# (needs validation)