;license:MIT
;(c) 2018-2020 by 4am
;
; Ordered key/value store (6502 compatible)(256+ records compatible)
;
; Public functions
; - okvs_init(address)                          reset (required)
; - okvs_len(address)                           get number of keys
; - okvs_append(address, key, value, max_len)   add new key/value pair
; - okvs_update(address, key, value)            update key/value pair
; - okvs_get(address, key)                      get value by key lookup
; - okvs_find(address, key)                     get key by key lookup
; - okvs_nth(address, n)                        get key by numeric index
; - okvs_next(address, n)                       get next key by numeric index
; - okvs_iter(address, callback)                iterate through keys
; - okvs_iter_values(address, callback)         iterate through values
;
; Call init() once. Call it again to reset the store to 0 records.
;
; Records are maintained in a singly linked list, so most functions are O(n).
; len() and append() are O(1) though.
;
; Record count is stored as a word, so a store can hold 65535 records.
;
; Keys and values are length-prefixed strings (Pascal style), so max length
; of any single key or value is 255 bytes.
;
; Keys are case-sensitive. Lookups are an exact byte-for-byte comparison.
;
; append() has a max_len argument to reserve more space for the value, in case
; you want to update it later. max_len is the total space to reserve, not the
; additional space. One exception: max_len can be 0, and it will be treated as
; length(value) at append time. update() always modifies the value in place.
; There is no range checking because this is assembly.

; All functions take the starting address of the store's data buffer in
; memory, so there can be multiple independent stores at one time. The next-
; record pointers are actual memory addresses, so stores are not easily
; relocatable. append() will happily extend the store's data buffer without
; limit. There is no overflow protection because this is assembly.
;
; There is no sort() function.
;
; There is no delete() function.
;
; Keys can be duplicated, but get() and find() will always return the one that
; was append()ed first.
;
; Structures:
;
; Store
;   +0 number of records (word)
;   +2 free space pointer after last record (word)
;   +4 Record
;   ...Record...
;   ...Record...
;
; Record
;   +0 next-record pointer (word)
;   +2 key length
;   +3 key
; +K+2 value length (actual length, not max length)
; +K+3 value
;  ... filler bytes up to value max length (set at append() time)

;------------------------------------------------------------------------------
; okvs_init
;
; in:    A/Y = handle to storage space
; out:   $00/$01 clobbered
;        $02/$03 clobbered
;        all registers clobbered
;------------------------------------------------------------------------------
okvs_init
         jsr   GetStoreAddressFromAY
                                     ; PTR -> store
                                     ; Y = 0
         tya
         sta   (PTR),y               ; set number of keys in store to 0 (word)
         iny
         sta   (PTR),y

         iny                         ; set next-free-space pointer to store + 4
         ldx   PTR+1
         lda   PTR
         clc
         adc   #$04
         bcc   +
         inx
+        sta   (PTR),y
         iny
         txa
         sta   (PTR),y
         rts

;------------------------------------------------------------------------------
; okvs_len
;
; in:    A/Y = handle to storage space
; out:   $WCOUNT contains number of keys in this store
;        X preserved
;        A, Y clobbered
;        $00/$01 clobbered
;        $02/$03 clobbered
;------------------------------------------------------------------------------
okvs_len
         jsr   GetStoreAddressFromAY
                                     ; PTR -> store
                                     ; Y = 0
         lda   (PTR), y              ; get number of keys in store (word)
         sta   WCOUNT
         iny
         lda   (PTR), y
         sta   WCOUNT+1
         rts

;------------------------------------------------------------------------------
; okvs_append
;
; in:    stack contains 7 bytes of parameters:
;          +1 [word] handle to storage space
;          +3 [word] address of key
;          +5 [word] address of value
;          +7 [byte] maximum length of value (or 0 to fit)
; out:   (new record count is not returned because no one cares)
;        all registers clobbered
;        $00/$01 clobbered
;        $02/$03 clobbered
;        $04/$05 has the address of the next available byte after the new record
;        $08/$09 clobbered
;------------------------------------------------------------------------------
okvs_append
         +PARAMS_ON_STACK 7
         jsr   GetStoreAddress
                                     ; PTR -> store
                                     ; Y = 0
         lda   (PTR),y               ; A = number of keys in store
         sta   WINDEX
         iny
         lda   (PTR), y
         sta   WINDEX+1
         inc   WINDEX
         bne   +
         inc   WINDEX+1
+
         dey
         lda   WINDEX
         sta   (PTR),y               ; increment number of keys
         lda   WINDEX+1
         iny
         sta   (PTR),y
         iny
         lda   (PTR),y               ; get address of next free space
         tax
         iny
         lda   (PTR),y
         sta   PTR+1
         sta   SAVE+1
         stx   PTR
         stx   SAVE
                                     ; PTR -> new record
                                     ; SAVE -> new record
         jsr   incptr2
                                     ; PTR -> space for new key
         +LDPARAMPTR 3, SRC          ; SRC -> new key to copy
         ldy   #0
         lda   (SRC),y
         tay
         tax
-        lda   (SRC),y               ; copy new key
         sta   (PTR),y
         dey
         cpy   #$FF
         bne   -

         ;;sec
         txa
         adc   PTR                   ; update PTR to byte after copied key
         sta   PTR
         bcc   +
         inc   PTR+1
+                                    ; PTR -> space for new value
         +LDPARAMPTR 5, SRC          ; SRC -> new value to copy
         iny ;;ldy   #7
         lda   (PARAM),y             ; get max length of value
         tax
         bne   +
         tay
         lda   (SRC),y               ; no max, use actual length instead
         tax
         inx
+        tay
-        lda   (SRC),y
         sta   (PTR),y
         dey
         cpy   #$FF
         bne   -

         txa
         clc
         adc   PTR
         sta   SRC
         bcc   +
         inc   PTR+1
+        lda   PTR+1
         sta   SRC+1                 ; SRC -> byte after this record
         +LD16 SAVE
         +ST16 PTR                   ; PTR -> this record again
         ldy   #0
         lda   SRC                   ; update next-record pointer
         sta   (PTR),y
         iny
         lda   SRC+1
         sta   (PTR),y
         jsr   GetStoreAddress
                                     ; PTR -> store
         ldy   #2
         lda   SRC-2,y
         sta   (PTR),y               ; update next-free-space pointer in head
         iny
         lda   SRC-2,y
         sta   (PTR),y
         rts

;------------------------------------------------------------------------------
; okvs_find / okvs_get
;
; in:    stack contains 4 bytes of parameters:
;          +1 [word] handle to storage space
;          +3 [word] address of key
; out:   if C clear, record was found
;          A/Y = lo/hi address of key (okvs_find) or value (okvs_get)
;          $WINDEX = index of found record (word)
;        if C set, keyrecord was not found and X/Y are clobbered, A=0
;        all other flags clobbered
;        $00/$01 clobbered
;        $02/$03 clobbered
;        $04/$05 clobbered
;------------------------------------------------------------------------------
okvs_find
         lda   #$60
         +HIDE_NEXT_2_BYTES
okvs_get
         lda   #$EA
         sta   @maybeGetValue
         +PARAMS_ON_STACK 4
         jsr   GetStoreAddress
                                     ; PTR -> store
                                     ; Y = 0
         lda   (PTR),y               ; A = number of keys in store
         sta   WCOUNT
         iny
         lda   (PTR),y
         sta   WCOUNT+1
         bne   +
         dey
         lda   (PTR),y
         beq   @fail                 ; no keys, fail immediately
+
         jsr   incptr4
                                     ; PTR -> first record
         +LDPARAMPTR 3, SRC          ; SRC -> key we want to find
         ldy   #0
         sty   WINDEX
         sty   WINDEX+1
         lda   (SRC),y
         tay
         iny
         sty   KEYLEN
@matchRecordLoop
         +LD16 PTR
         clc
         adc   #2
         bcc   +
         iny                         ; DEST -> key of this record
+        +ST16 DEST
         ldy   #0
@matchKeyLoop
         lda   (SRC),y
         cmp   (DEST),y
         bne   @next
         iny
KEYLEN = *+1
         cpy   #$D1                  ; SMC
         bne   @matchKeyLoop
         +LD16 DEST
         clc
@maybeGetValue
         brk                         ; SMC
         jsr   okvs_get_current
         +LD16 PTR
         clc
         rts
@next    jsr   derefptr              ; PTR -> next record
         inc   WINDEX
         bne   +
         inc   WINDEX+1
+
         lda   WINDEX
         cmp   WCOUNT
         bne   @matchRecordLoop
         lda   WINDEX+1
         eor   WCOUNT+1
         bne   @matchRecordLoop
@fail    sec
         rts

okvs_get_current
         +ST16 PTR
         ldy   #0
         lda   (PTR),y
         clc
         adc   PTR
         sta   PTR
         bcc   +
         inc   PTR+1
+        jmp   incptr

;------------------------------------------------------------------------------
; okvs_next
; get (N+1)th key, with wraparound
;
; in:    A/Y = handle to storage space
;        $WINDEX = record index (word)
; out:   A/Y = lo/hi address of ($WINDEX+1)th key, or first key if $WINDEX was the last record
;        $WINDEX = record index of next record
;        see okvs_nth for other exit conditions
;------------------------------------------------------------------------------
okvs_next
         +ST16 PARAM
         inc   WINDEX
         bne   +
         inc   WINDEX+1
+
         jsr   okvs_len
         +LD16 WINDEX
         +CMP16ADDR WCOUNT
         bne   +
         sta   WINDEX
         sta   WINDEX+1
+
         +LD16 PARAM
         ; /!\ execution falls through here to okvs_nth
;------------------------------------------------------------------------------
; okvs_nth
; get (N)th key
;
; in:    A/Y = handle to storage space
;        $WINDEX = record index
; out:   A/Y = lo/hi address of nth key
;        $WINDEX preserved
;        X = 0
;        Z = 0
;        all other flags clobbered
;        $PTR clobbered
;------------------------------------------------------------------------------
okvs_nth
         jsr   GetStoreAddressFromAY
                                     ; PTR -> store
         jsr   incptr4
                                     ; PTR -> first record
         +LD16 WINDEX
         +ST16 SAVE
         jmp   @next
-        jsr   derefptr
@next
         lda   SAVE
         dec   SAVE
         tay
         bne   -
         lda   SAVE+1
         dec   SAVE+1
         tay
         bne   -
         jsr   incptr2
         +LD16 PTR
         ldx   #0
         rts

;------------------------------------------------------------------------------
; okvs_update
;
; in:    stack contains 6 bytes of parameters:
;          +1 [word] handle to storage space
;          +3 [word] address of key
;          +5 [word] address of new value
; out:   if C clear, key was found and value was updated
;        if C set, key was not found
;        all registers are clobbered
;        all other flags clobbered
;        $00/$01 clobbered
;        $02/$03 clobbered
;        $04/$05 clobbered
;------------------------------------------------------------------------------
okvs_update
         +PARAMS_ON_STACK 6
         ldy   #6
         lda   (PARAM),y
         sta   SAVE+1
         dey
         lda   (PARAM),y
         sta   SAVE
         dey
-        lda   (PARAM),y
         sta   @getparams,y
         dey
         bne   -
         jsr   okvs_get
@getparams=*-1
         !word $FDFD                 ; SMC
         !word $FDFD                 ; SMC
         bcs   @exit
         +ST16 DEST
         ldy   #0
         lda   (SAVE),y
         tay
-        lda   (SAVE),y
         sta   (DEST),y
         dey
         cpy   #$FF
         bne   -
         clc
@exit    rts

;------------------------------------------------------------------------------
; okvs_iter / okvs_iter_values
;
; in:    stack contains 4 bytes of parameters:
;          +1 [word] handle to storage space
;          +3 [word] address of callback
; out:   <callback> will be called for each record in the store, in order, with
;          $WINDEX = numeric index of record (word)
;          A/Y = address of key or value (depends on which entry point you call)
;        all registers are clobbered
;        Z=1
;        all other flags clobbered
;        PARAM clobbered
;        PTR clobbered
;        WINDEX clobbered
;        WCOUNT clobbered
;------------------------------------------------------------------------------
okvs_iter
         lda   #$D0                  ; 'BNE' opcode
         +HIDE_NEXT_2_BYTES
okvs_iter_values
         lda   #$24                  ; 'BIT' opcode
         sta   @branch
         +PARAMS_ON_STACK 4
         jsr   GetStoreAddress
                                     ; PTR -> store
                                     ; Y = 0
         lda   (PTR),y               ; get number of keys in store (word)
         sta   WCOUNT
         iny
         lda   (PTR),y
         sta   WCOUNT+1
         bne   +
         dey
         lda   (PTR),y
         beq   @exit                 ; no keys, exit immediately
+
         +LDPARAM 3
         +ST16 @callback
         jsr   incptr4
                                     ; PTR -> first record
         lda   #0
         sta   WINDEX
         sta   WINDEX+1
@loop
         lda   #2                    ; for iter, skip length = 2
@branch  bne   +                     ; SMC (iter_values puts a BIT here, so no branch)
                                     ; for iter_values, skip length = length(key) + 2 + 1
         tay ;;ldy   #2
         lda   (PTR),y               ; A = length of key
         clc
         adc   #3                    ; skip over pointer to next record (2 bytes) + key length (1 byte)
+        sta   @skiplen
         lda   WCOUNT+1              ; save WCOUNT on stack
         pha
         lda   WCOUNT
         pha
         lda   WINDEX+1              ; save WINDEX on stack
         pha
         lda   WINDEX
         pha
         lda   PTR+1
         tay
         pha
         lda   PTR
         pha                         ; save PTR on stack
         clc
@skiplen=*+1
         adc   #$FD                  ; SMC skip over pointer (and possibly key)
         bcc   +
         iny                         ; A/Y -> value
+
@callback=*+1
         jsr   $FDFD                 ; SMC
         pla
         sta   PTR
         pla
         sta   PTR+1                 ; restore PTR from stack
         pla
         sta   WINDEX
         pla
         sta   WINDEX+1
         pla
         sta   WCOUNT
         pla
         sta   WCOUNT+1
         jsr   derefptr              ; PTR -> next record
         inc   WINDEX
         bne   +
         inc   WINDEX+1
+
         lda   WINDEX
         cmp   WCOUNT
         bne   @loop
         lda   WINDEX+1
         cmp   WCOUNT+1
         bne   @loop
@exit    rts

;------------------------------------------------------------------------------
; internal functions

incptr4  jsr   incptr2
incptr2  jsr   incptr
incptr
; preserves A, X, and Y
         inc   PTR
         bne   +
         inc   PTR+1
+        rts

GetStoreAddressFromAY
         +ST16 PTR
         jmp   derefptr

GetStoreAddress
; in:    PARAM = address of stack params (any PARAMS_ON_STACK macro will do this)
; out:   PTR = address of store (always the first parameter on stack)
; preserves X
         ldy   #1
         lda   (PARAM),y
         sta   PTR
         iny
         lda   (PARAM),y
         sta   PTR+1                 ; PTR -> first parameter on stack
                                     ; execution falls through here
derefptr
; out:   Y = 0
;        preserves X
         ldy   #1
         lda   (PTR),y
         pha
         dey
         lda   (PTR),y
         sta   PTR
         pla
         sta   PTR+1
         rts