JSON_ToObj.ahk

; Copyright © 2013 VxE. All rights reserved.

; Uses a two-pass iterative approach to deserialize a json string
json_toobj( str ) {

	quot := """" ; firmcoded specifically for readability. Hardcode for (minor) performance gain
	ws := "`t`n`r " Chr(160) ; whitespace plus NBSP. This gets trimmed from the markup
	obj := {} ; dummy object
	objs := [] ; stack
	keys := [] ; stack
	isarrays := [] ; stack
	literals := [] ; queue
	y := nest := 0

; First pass swaps out literal strings so we can parse the markup easily
	StringGetPos, z, str, %quot% ; initial seek
	while !ErrorLevel
	{
		; Look for the non-literal quote that ends this string. Encode literal backslashes as '\u005C' because the
		; '\u..' entities are decoded last and that prevents literal backslashes from borking normal characters
		StringGetPos, x, str, %quot%,, % z + 1
		while !ErrorLevel
		{
			StringMid, key, str, z + 2, x - z - 1
			StringReplace, key, key, \\, \u005C, A
			If SubStr( key, 0 ) != "\"
				Break
			StringGetPos, x, str, %quot%,, % x + 1
		}
	;	StringReplace, str, str, %quot%%t%%quot%, %quot% ; this might corrupt the string
		str := ( z ? SubStr( str, 1, z ) : "" ) quot SubStr( str, x + 2 ) ; this won't

	; Decode entities
		StringReplace, key, key, \%quot%, %quot%, A
		StringReplace, key, key, \b, % Chr(08), A
		StringReplace, key, key, \t, % A_Tab, A
		StringReplace, key, key, \n, `n, A
		StringReplace, key, key, \f, % Chr(12), A
		StringReplace, key, key, \r, `r, A
		StringReplace, key, key, \/, /, A
		while y := InStr( key, "\u", 0, y + 1 )
			if ( A_IsUnicode || Abs( "0x" SubStr( key, y + 2, 4 ) ) < 0x100 )
				key := ( y = 1 ? "" : SubStr( key, 1, y - 1 ) ) Chr( "0x" SubStr( key, y + 2, 4 ) ) SubStr( key, y + 6 )

		literals.insert(key)

		StringGetPos, z, str, %quot%,, % z + 1 ; seek
	}

; Second pass parses the markup and builds the object iteratively, swapping placeholders as they are encountered
	key := isarray := 1

	; The outer loop splits the blob into paths at markers where nest level decreases
	Loop Parse, str, % "]}"
	{
		StringReplace, str, A_LoopField, [, [], A ; mark any array open-brackets

		; This inner loop splits the path into segments at markers that signal nest level increases
		Loop Parse, str, % "[{"
		{
			; The first segment might contain members that belong to the previous object
			; Otherwise, push the previous object and key to their stacks and start a new object
			if ( A_Index != 1 )
			{
				objs.insert( obj )
				isarrays.insert( isarray )
				keys.insert( key )
				obj := {}
				isarray := key := Asc( A_LoopField ) = 93
			}

			; arrrrays are made by pirates and they have index keys
			if ( isarray )
			{
				Loop Parse, A_LoopField, `,, % ws "]"
					if ( A_LoopField != "" )
						obj[key++] := A_LoopField = quot ? literals.remove(1) : A_LoopField
			}
			; otherwise, parse the segment as key/value pairs
			else
			{
				Loop Parse, A_LoopField, `,
					Loop Parse, A_LoopField, :, % ws
						if ( A_Index = 1 )
							key := A_LoopField = quot ? literals.remove(1) : A_LoopField
						else if ( A_Index = 2 && A_LoopField != "" )
							obj[key] := A_LoopField = quot ? literals.remove(1) : A_LoopField
			}
			nest += A_Index > 1
		} ; Loop Parse, str, % "[{"

		If !--nest
			Break

		; Insert the newly closed object into the one on top of the stack, then pop the stack
		pbj := obj
		obj := objs.remove()
		obj[key := keys.remove()] := pbj
		If ( isarray := isarrays.remove() )
			key++

	} ; Loop Parse, str, % "]}"

	Return obj
} ; json_toobj( str )