; ── SWARM FORAGER ────────────────────────────
; Random walk to find food, dead reckoning to
; navigate home. Pheromone marks food for others.
; Hit play, then try improving it!

; ── Registers ──
.alias dx   r1           ; x displacement from nest
.alias dy   r2           ; y displacement from nest
.alias ret  r3           ; return address for CALL

; ── Pheromone ──
.const PH_FOOD CH_RED      ; marks food locations
.const PH_NEST CH_BLUE
.const PHER_INIT 255
.const PHER_DECAY 2
; ── Roles (visible in simulation viewer) ──
.tag 0 foraging
.tag 1 homing

; ──────────────────────────────────────────────
main:
    set r7 PHER_INIT
loop:
    CARRYING
    JNE r0 0 go_home
    TAG foraging

; ── SEARCH: find food ─────────────────────────
search:
    SENSE FOOD
    JNE r0 0 grab

; if we are too far from the food, dont mark
    JLT r7 PHER_DECAY smell_trail
    SUB r7 PHER_DECAY
; if there is already a trail here, dont mark
    SNIFF PH_NEST HERE r0
    JNE r0 0 smell_trail
    MARK PH_NEST r7

smell_trail:
    SMELL PH_FOOD
    JNE r0 0 step
    SENSE EMPTY
step:
    CALL ret move_track
    JMP loop

grab:
    CALL ret move_track
    PICKUP
    MARK PH_FOOD 255
    SET r6 PHER_INIT
    JMP loop

; ── GO HOME: dead reckon toward nest ──────────
go_home:
    TAG homing
; if we are too far from the food, dont mark
    JLT r6 PHER_DECAY sense_nest
    SUB r6 PHER_DECAY
; if there is already a trail here, dont mark
    SNIFF PH_FOOD HERE r0
    JNE r0 0 sense_nest
    MARK PH_FOOD r6
sense_nest:
    SENSE NEST
    JNE r0 0 deliver
smell_nest:
    SMELL PH_NEST
    JNE r0 0 move_track
    RANDOM r0 4
    JEQ r0 0 wander       ; 25% random to unstick walls
    CALL ret home_dir
    CALL ret move_track
    JMP main
wander:
    SENSE EMPTY
    CALL ret move_track
    JMP main

deliver:
    CALL ret move_track
    DROP
    SET r7 PHER_INIT
    JMP main

; ══════════════════════════════════════════════
; SUBROUTINES — CALL ret <label>, return JMP ret
; ══════════════════════════════════════════════

; home_dir: set r0 = direction toward nest
home_dir:
    SET r4 dx
    JGT dx 0 hd_dxp
    SET r4 0
    SUB r4 dx
hd_dxp:
    SET r5 dy
    JGT dy 0 hd_dyp
    SET r5 0
    SUB r5 dy
hd_dyp:
    JGT r5 r4 hd_y
    JGT dx 0 hd_w
    SET r0 2
    JMP ret
hd_w:
    SET r0 4
    JMP ret
hd_y:
    JGT dy 0 hd_n
    SET r0 3
    JMP ret
hd_n:
    SET r0 1
    JMP ret

; move_track: MOVE r0, then update dx/dy
move_track:
    MOVE r0
    JEQ r0 1 mt_n
    JEQ r0 2 mt_e
    JEQ r0 3 mt_s
    SUB dx 1
    JMP ret
mt_n:
    SUB dy 1
    JMP ret
mt_e:
    ADD dx 1
    JMP ret
mt_s:
    ADD dy 1
    JMP ret