From d4a35b62df56246ef67cbe4f1eb0a24457e70dde Mon Sep 17 00:00:00 2001
From: Lukas Krickl <lukas@krickl.dev>
Date: Tue, 5 Aug 2025 20:21:45 +0200
Subject: [PATCH] unit: Added basic chaser cpu script

---
 src/defs.s     |  3 ++
 src/math.s     |  4 +--
 src/unit_cpu.s | 82 +++++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 86 insertions(+), 3 deletions(-)

diff --git a/src/defs.s b/src/defs.s
index b5f8ae0..7d5fadd 100644
--- a/src/defs.s
+++ b/src/defs.s
@@ -330,3 +330,6 @@
 #define DD_TIME 90 
 #define DD_D0_TILE 0x90 
 #define DD_CROSS_TILE 0xA0
+
+#define DISTANCE_BGTA 1
+#define DISTANCE_AGTB 0
diff --git a/src/math.s b/src/math.s
index 2d1d4b0..4d90eec 100644
--- a/src/math.s
+++ b/src/math.s
@@ -15,7 +15,7 @@ distance:
 	
 	; otherwise a simple sub will do
 	sub a, b
-	ld c, 0
+	ld c, DISTANCE_AGTB 
 	ret
 @b_gt_a:
 	; exchange a and b and sub
@@ -23,5 +23,5 @@ distance:
 	ld a, b
 	ld b, c
 	sub a, b
-	ld c, 1 
+	ld c, DISTANCE_BGTA 
 	ret
diff --git a/src/unit_cpu.s b/src/unit_cpu.s
index 10a5df8..f743617 100644
--- a/src/unit_cpu.s
+++ b/src/unit_cpu.s
@@ -1,15 +1,95 @@
+#define UNIT_SCAN_RANGE_Y MAP_H/4
+#define UNIT_SCAN_RANGE_X MAP_W/4
 
 	; handles cpu inputs
+	; chaser CPU script 
 	; inputs:
 	;		de: actor
 	;	returns:
 	;		bc: next state
 unit_handle_cpu_inputs:
+#define MOVE_MADE scratch 
+	; clear move made buffer
+	xor a, a
+	ld [MOVE_MADE], a
+	
+	; there's a change the
+	; unit will just move randomly anyway
+	call rand
+	and a, 0x7F
+	cp a, 0
+	jp z, @random_move
+
+	; otherwise follow player
+
+	; check y position
+	; and follow player in y direction if player is in range
+	ld hl, player_unit+act_pos_y
+	ld a, [hl]
+	ld b, a ; b = player y pos
+	push de
+	ld hl, act_pos_y
+	add hl, de
+	ld a, [hl] ; a = act y pos
+	call distance
+	pop de
+
+	; are we in scan range?
+	cp a, UNIT_SCAN_RANGE_Y
+	jr nc, @not_in_y_range REL
+	cp a, 1 
+	jr z, @not_in_y_range REL
+
+	; which direction?
+	ld a, c
+	cp a, DISTANCE_BGTA
+	push af
+	call nz, unit_try_move_up
+	pop af
+	call z, unit_try_move_down
+	ld a, 1
+	ld [MOVE_MADE], a
+@not_in_y_range:
+
+	; check x position
+	; and follow player in x direction if player is in range
+	ld hl, player_unit+act_pos_x
+	ld a, [hl]
+	ld b, a ; b = player x pos
+	push de
+	ld hl, act_pos_x
+	add hl, de
+	ld a, [hl] ; a = act x pos
 	call distance
+	pop de
+
+	; are we in scan range?
+	cp a, UNIT_SCAN_RANGE_X
+	jr nc, @not_in_x_range REL
+	cp a, 1 
+	jr z, @not_in_x_range REL
+
+	; which direction?
+	ld a, c
+	cp a, DISTANCE_BGTA
+	push af
+	call nz, unit_try_move_left
+	pop af
+	call z, unit_try_move_right
+	ld a, 1
+	ld [MOVE_MADE], a
+@not_in_x_range:
+@random_move:
+	
+	; call random move if move was not made
+	ld a, [MOVE_MADE]
+	cp a, 0
+	call z, unit_cpu_random_move
 
-	call unit_cpu_random_move
+@move_made:
   ld bc, st_unit_delay_to_active
 	ret
+#undefine MOVE_MADE
 
 	
 	; moves actor into a random direction
-- 
2.30.2