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use std

use "types"

pkg regex =
	/* regex execution */
	const exec	: (re : regex#, str : byte[:] -> std.option(byte[:][:]))
	const search	: (re : regex#, str : byte[:] -> std.option(byte[:][:]))

	/* regex execution returning indexes */
	const iexec	: (re : regex#, str : byte[:] -> std.option((std.size, std.size)[:]))
	const isearch	: (re : regex#, str : byte[:] -> std.option((std.size, std.size)[:]))

	/* substitution */
	const sub	: (re : regex#, str : byte[:], subst : byte[:][:] -> std.option(byte[:]))
	const sbsub	: (sb : std.strbuf#, re : regex#, str : byte[:], subst : byte[:][:] -> bool)
	const suball	: (re : regex#, str : byte[:], subst : byte[:][:] -> byte[:])
	const sbsuball	: (sb : std.strbuf#, re : regex#, str : byte[:], subst : byte[:][:] -> void)

	const matchfree	: (pat : byte[:][:] -> void)
;;

/* Ugly: for performance. std.option() should be used instead when unions get faster. */
const Zthr = (0 : rethread#)
const Maxfree = 128

const matchfree = {m
	std.slfree(m)
}

const exec = {re, str
	-> getmatches(re, run(re, str, 0, true))
}

const iexec = {re, str
	-> getidxmatches(re, run(re, str, 0, true))
}

const search = {re, str
	var thr = Zthr

	for var i = 0; i < str.len; i++
		thr = run(re, str[i:], 0, false)
		if thr != Zthr
			break
		;;
	;;
	-> getmatches(re, thr)
}

const isearch = {re, str
	var thr = Zthr

	for var i = 0; i < str.len; i++
		thr = run(re, str[i:], 0, false)
		if thr != Zthr
			break
		;;
	;;
	-> getidxmatches(re, thr)
}

const sub = {re, str, subst
	var sb

	sb = std.mksb()
	if sbsub(sb, re, str, subst)
		-> `std.Some std.sbfin(sb)
	;;
	-> `std.None
}

const sbsub = {sb, re, str, subst
	std.assert(re.nmatch == subst.len + 1, "substitution length does not match capture count")
	-> dosubst(sb, re, run(re, str, 0, true), str, subst)
}

const suball = {re, str, subst
	var sb

	sb = std.mksb()
	sbsuball(sb, re, str, subst)
	-> std.sbfin(sb)
}

const sbsuball = {sb, re, str, subst
	var thr, len, i

	std.assert(re.nmatch == subst.len + 1, "substitution length does not match capture count")
	i = 0
	while i < str.len
		thr = run(re, str[i:], 0, false)
		if thr == Zthr
			std.sbputb(sb, str[i])
			i++
		else
			len = thr.mgroup[0][1]
			dosubst(sb, re, thr, str[i:len + i], subst)
			i += len
		;;
		cleanup(re, thr)
	;;
}


const dosubst = {sb, re, thr, str, subst
	var off

	if thr == Zthr
		-> false
	;;
	off = 0
	for var i = 1; i < re.nmatch; i++
		if thr.mgroup[i][0] != -1 && thr.mgroup[i][1] != -1
			std.sbputs(sb, str[off:thr.mgroup[i][0]])
			std.sbputs(sb, subst[i - 1])
			off = thr.mgroup[i][1]
		;;
	;;
	std.sbputs(sb, str[off:])
	-> true
}

const cleanup = {re, result
	lfree(re.runq)
	lfree(re.expired)
	lfree(re.free)
	std.free(result)
	re.runq = Zthr
	re.expired = Zthr
	re.free = Zthr
	re.nfree = 0
	re.nthr = 0
}

const lfree = {thr
	for var next = thr; thr != Zthr; thr = next
		next = thr.next
		std.free(thr)
	;;
}

const getmatches = {re, thr
	var ret, i

	if thr == Zthr
		-> `std.None
	;;

	i = 0
	ret = std.slalloc(re.nmatch)
	for [lo, hi] : thr.mgroup[:re.nmatch]
		if lo != -1 && hi != -1
			ret[i] = re.str[lo : hi]
		;;
		i++
	;;
	cleanup(re, thr)
	-> `std.Some ret
}

const getidxmatches = {re, thr
	var ret

	if thr == Zthr
		-> `std.None
	;;
	ret = std.slalloc(re.nmatch)
	for var i = 0; i < re.nmatch; i++
		ret[i] = (thr.mgroup[i][0], thr.mgroup[i][1])
	;;
	cleanup(re, thr)
	-> `std.Some ret
}

/*
 * Run manages the virtual machine state, and schedules the
 * regex threads. Each linear match runs in its own thread.
 * When a new thread is created, it is carefully scheduled
 * after the current thread, to ensure that match order is
 * preserved.
 */
const run = {re, str, idx, wholestr
	var bestmatch
	var consumed
	var states
	var thr
	var ip

	re.str = str
	re.strp = 0
	re.nexttid = 0

	bestmatch = Zthr
	states = std.mkbs()
	re.runq = mkthread(re, 0)
	if re.debug
		/* 
		  If we're in debug mode, then we keep
		  the traces around, so we can show them
		  to the user. To avoid leaking, we need
		  to free the traces from the last run
		  when we start a new one.
		 */
		for bs : re.traces
			std.bsfree(bs)
		;;
		std.slfree(re.traces)
		re.traces = [][:]
		std.slpush(&re.traces, std.mkbs())
	;;
	for var i = 0; i < re.nmatch; i++
		re.runq.mgroup[i][0] = -1
		re.runq.mgroup[i][1] = -1
	;;
	while re.nthr > 0
		while re.runq != Zthr
			if re.trace
				std.put("switch\n")
			;;
			thr = re.runq
			re.runq = thr.next

			ip = thr.ip
			/* 
			  Stepping continues until the first
			  non-consuming operator is seen. This
			  keeps all the threads in lockstep,
			  which means that when a match is
			  encountered, we know all the other
			  threads have seen what they need
			  to, and we can terminate them.
			 */
			consumed = step(re, thr, -1)
			while !consumed
				consumed = step(re, thr, ip)
			;;

			/*
			 * Because threads have no memory,
			 * their ip (and current input
			 * character, which is the same
			 * thanks to the above mentioned
			 * lockstep) uniquely identify them.
			 * As a result, if we have two
			 * threads with the same ip, one of
			 * them can be culled.
			 */
			if std.bshas(states, thr.ip)
				die(re, thr)
			;;

			if thr.dead
				thrfree(re, thr)
			elif thr.matched
				if bestmatch != Zthr
					thrfree(re, bestmatch)
				;;

				if re.strp == re.str.len
					bestmatch = thr
					goto done
				elif !wholestr
					bestmatch = thr
				else
					thrfree(re, thr)
				;;
			elif !thr.matched
				std.bsput(states, thr.ip)
				if re.expired == Zthr
					re.expired = thr
				;;
				if re.expiredtail != Zthr
					re.expiredtail.next = thr
				;;
				re.expiredtail = thr
				thr.next = Zthr

			;;
		;;
		std.bsclear(states)
		re.runq = re.expired
		re.expired = Zthr
		re.expiredtail = Zthr
		re.strp++
	;;
:done
	std.bsfree(states)
	-> bestmatch
}

/*
 * Step executes a single step of the compiled regex.
 *
 * Operations fall into two overall categories. Consuming
 * operators advance the match, and nonconsuming operators
 * change the state of the regex virtual machine.
 *
 * Consuming operators are simple: They check if the current
 * character matches a criteria, and then advance the regex.
 *
 * Nonconsuming operators can do one of several things. They
 * can fork the vm, record a successful match, or mark a
 * thread as a failure.
 *
 * A thread continues to run forward until a consuming
 * opcode is encountered, after which it must switch.
 * This is in order to keep all threads in lockstep
 * operating over the same characters, and finishing
 * at the same time.
 */
const step = {re, thr, curip var str, nthr, inst

	str = re.str
	inst = re.code[thr.ip]
	if re.trace
		itrace(re, thr, re.prog[thr.ip])
	;;
	if re.debug
		std.bsput(re.traces[thr.tid], thr.ip)
	;;
	match inst & 0xf
	/* Consuming opcodes */
	| OpRange:
		var lo = (inst >>  4 : byte)
		var hi = (inst >> 16 : byte)
		
		if !within(re, str) || lo > str[re.strp] || hi < str[re.strp]
			die(re, thr)
		else
			thr.ip++
		;;
	| OpByte:
		var b = (inst >> 4 : byte)
		if !within(re, str)
			die(re, thr)
		elif b != str[re.strp]
			die(re, thr)
		else
			thr.ip++
		;;
	| OpFork:
		var lip = ((inst >>  4) & 0x3fffffff : std.size)
		var rip = ((inst >> 34) & 0x3fffffff : std.size)
		if rip != curip
			nthr = mkthread(re, rip)
			nthr.next = re.runq
			nthr.mgroup = thr.mgroup
			re.runq = nthr
		;;
		if re.debug
			std.slpush(&re.traces, std.bsdup(re.traces[thr.tid]))
		;;
		thr.ip = lip
		-> false
	/* Non-consuming opcodes. */
	| OpJmp:
		var ip = (inst >> 4 : std.size)
		thr.ip = ip
		-> false
	| OpMatch:
		var id = (inst >> 4 : std.size)
		re.lastthr = thr.tid
		finish(re, thr)
		-> true
	| OpLbra:
		var m = (inst >> 4 : std.size)
		thr.mgroup[m][0] = re.strp
		thr.ip++
		-> false
	| OpRbra:
		var m = (inst >> 4 : std.size)
		thr.mgroup[m][1] = re.strp
		thr.ip++
		-> false
	| OpBol:
		if re.strp == 0 || str[re.strp - 1] == ('\n' : byte)
			thr.ip++
			-> false
		else
			die(re, thr)
		;;
	| OpEol:
		if re.strp == str.len || str[re.strp] == ('\n' : byte)
			thr.ip++
			-> false
		else
			die(re, thr)
		;;
	| OpBow:
		if iswordchar(str[re.strp:]) && (re.strp == 0 || !iswordchar(prevchar(str, re.strp)))
			thr.ip++
			-> false
		else
			die(re, thr)
		;;
	| OpEow:
		if re.strp == str.len && iswordchar(prevchar(str, re.strp))
			thr.ip++
			-> false
		elif re.strp > 0 && !iswordchar(str[re.strp:]) && iswordchar(prevchar(str, re.strp))
			thr.ip++
			-> false
		else
			die(re, thr)
		;;
	| _:
		std.die("corrupt regex bytecode")
	;;
	-> true
}

const die = {re, thr
        /*
 	  we can have die called on a thread
	  multiple times, eg, if it has a bad
	  range *and* end in a state that another
	  thread is in. We should only decrement
	  the number of threads for that once.
	 */
        if !thr.dead
		re.nthr--
	;;
	re.lastip = thr.ip
	re.lastthr = thr.tid
	thr.dead = true
}

const finish = {re, thr
	thr.matched = true
	re.nthr--
}

const mkthread = {re, ip
	var thr : rethread#

	if re.free != Zthr
		thr = re.free
		re.free = thr.next
		re.nfree--
	else
		thr = std.alloc()
	;;
	thr.next = Zthr
	thr.ip = ip
	thr.tid = re.nexttid++
	thr.dead = false
	thr.matched = false
	re.nthr++

	-> thr
}

const thrfree = {re, thr
	if re.nfree >= Maxfree
		std.free(thr)
	else
		thr.next = re.free
		re.free = thr
		re.nfree++
	;;
}

const within = {re, str 
	-> re.strp < str.len
}

const itrace = {re, thr, inst
	match inst
	| `Ibyte b:	std.put("\t{}.{}:\tByte ({})\n", thr.tid, thr.ip, thr.tid, thr.ip, b)
	| `Irange (lo, hi):	std.put("\t{}.{}:\tRange {}, {}\n", thr.tid, thr.ip, lo, hi)
	| `Ilbra m:	std.put("\t{}.{}:\tLbra {}\n", thr.tid, thr.ip, m)
	| `Irbra m:	std.put("\t{}.{}:\tRbra {}\n", thr.tid, thr.ip, m)
	/* anchors */
	| `Ibol:	std.put("\t{}.{}:\tBol\n", thr.tid, thr.ip)
	| `Ieol:	std.put("\t{}.{}:\tEol\n", thr.tid, thr.ip)
	| `Ibow:	std.put("\t{}.{}:\tBow\n", thr.tid, thr.ip)
	| `Ieow:	std.put("\t{}.{}:\tEow\n", thr.tid, thr.ip)

	/* control flow */
	| `Ifork (l, r):	std.put("\t{}.{}:\tFork {}, {}\n", thr.tid, thr.ip, l, r)
	| `Ijmp	ip:	std.put("\t{}.{}:\tJmp {}\n", thr.tid, thr.ip, ip)
	| `Imatch m:	std.put("\t{}.{}:\tMatch {}\n", thr.tid, thr.ip, m)
	;;
}

const prevchar = {s, i
	std.assert(i != 0, "prevchar must be called with i >= 1\n")
	i--
	while i != 0 && s[i] >= 0x80
		i--
	;;
	-> s[i:]
}

const iswordchar = {s
	var c

	c = std.decode(s)
	-> std.isalpha(c) || std.isdigit(c) || c == '_'
}