// regex — POSIX extended regular expressions. Port of
// ref/hare/regex/regex.ha. Fold 1 = the data model; fold 2a = the
// compile() literal core (lit/any/match + the leading skip); fold 2b
// tranche A = the thread-machine scaffolding (thread/newmatch types,
// result_free, strerror); fold 2b tranche B = the engine leaf fns
// (delete_thread/is_consuming_inst/add_thread — dead until search
// lands, fold-1 precedent). Every other metacharacter arm, the rest
// of the engine (run_thread, see its deferral note below; search on
// F5 element-copy + F2 len-builtin, tranche C) and the exec surface
// (test/find on the C6 multi-success `?` gate, tranche D; replace)
// are DEFERRED behind compiler fixes — probed pre-port, pA*/pB*/PB*
// probes. They land with those fixes.
//
// One fold-1 construct is held back behind a filed compiler/fidelity
// gap (see the charclass_map site below):
//   - charclass_map (regex.ha:74-87) — a module-level const slice of
//     (str, *fn(rune) bool) tuples. Blocked on the array-literal→slice
//     element-coercion checker gap (#25; type.c:402-404 #258 borrow
//     uses exact type_eq, no element decay).
package regex;

import strings;
import encoding.utf8;

// ref/hare/regex/regex.ha:14 — an error string describing a compilation
// error.
export type error = !str;

// ref/hare/regex/regex.ha:16-30.
export type inst_lit = rune;
export type inst_charset = struct { idx: size, is_positive: bool };
export type inst_any = void;
export type inst_split = size;
export type inst_jump = size;
export type inst_skip = void;
export type inst_match = bool;
export type inst_groupstart = size;
export type inst_groupend = void;
export type inst_repeat = struct {
	id: size,
	origin: size,
	min: (void | size),
	max: (void | size),
};

// ref/hare/regex/regex.ha:32-35.
export type inst = (inst_lit | inst_any | inst_split | inst_jump |
	inst_skip | inst_match | inst_charset |
	inst_groupstart | inst_groupend |
	inst_repeat);

// The resulting match of a [[regex]] applied to a string.
//
// The first [[capture]] corresponds to the implicit zeroth capture
// group, i.e. the whole expression.
//
// The rest of the [[capture]]s correspond to the rest of the capture
// groups, i.e. the sub-expressions.
// ref/hare/regex/regex.ha:44.
export type result = []capture;

// A (sub)match corresponding to a regular expression's capture group.
// ref/hare/regex/regex.ha:47-53.
export type capture = struct {
	content: str,
	start: size,
	start_bytesize: size,
	end: size,
	end_bytesize: size,
};

// ref/hare/regex/regex.ha:55-64.
type thread = struct {
	pc: size,
	start_idx: size,
	start_bytesize: size,
	root_capture: capture,
	captures: []capture,
	rep_counters: []size,
	matched: bool,
	failed: bool,
};

// Discriminates a fresh match from plain void at run_thread's return
// boundary. ref/hare/regex/regex.ha:66.
type newmatch = void;

// ref/hare/regex/regex.ha:68-72.
export type charset = [](charset_lit_item | charset_range_item |
	charset_class_item);
export type charset_lit_item = rune;
export type charset_range_item = (u32, u32);
export type charset_class_item = (str, *fn(c: rune) bool);

// ref/hare/regex/regex.ha:74-87 — charclass_map: the const
// [](str, *fn(rune) bool) table mapping POSIX class tokens to the
// matching ascii predicate. DEFERRED: the array-literal→slice
// assignability check (type.c:402-404, the #258 borrow) compares
// element types with exact type_eq and applies NO element coercion, so
// the literal `[(":alnum:]", &ascii.isalnum), ...]` (typed
// `[N](untyped_str, *fn(rune) bool)`) is rejected against the declared
// `[](str, *fn(rune) bool)`. Minimal repro: `let xs: [](size, size) =
// [(1, 2)];`. Reshaping to a fixed `[12](...)` array would compile but
// is an unfaithful workaround (CLAUDE.md rule-7), so the table — and
// the `import ascii;` it needs — land with the consuming fold (compile)
// once the checker gap is fixed.

// ref/hare/regex/regex.ha:89-93.
export type regex = struct {
	insts: []inst,
	charsets: []charset,
	n_reps: size,
};

// Frees resources associated with a [[regex]].
//
// ref/hare/regex/regex.ha:96-102, verbatim. The free() builtin is a
// documented no-op (#27 landed): ww is a no-free runtime (rt/alloc.s:30
// — the bump allocator can't reclaim, process-exit does), so each free
// below evaluates its operand and reclaims nothing. Kept verbatim for
// API + source parity with the Hare surface.
export fn finish(re: *regex) void = {
	free(re.insts);
	for (let charset .. re.charsets) {
		free(charset);
	};
	free(re.charsets);
};

// Compiles a regular expression string into a [[regex]].
//
// ref/hare/regex/regex.ha:227-263. Fold 2a ports the literal core:
// inst_lit / inst_any / inst_match plus the leading inst_skip
// (regex.ha:261-263 — unanchored exec depends on it). Every other
// metacharacter arm is one loud not-yet-ported error — the explicit
// fold boundary; falling to literal would be a silent semantic lie.
// State serving only the deferred arms is dropped with them:
// jump_idxs (ha:241-248), the bracket quad (ha:249-252),
// was_prev_rune_pipe / group_level / capture_idx (ha:253-256).
//
// Hare's `defer if (!ok) free(...)` cleanup (ha:231-237) is omitted:
// ww has no `defer if` (cf lib/strings/strings.ww:85), and the free()
// builtin is a no-op anyway (#27 — ww is a no-free runtime), so the
// cleanup would reclaim nothing.
export fn compile(expr: str) (regex | error | nomem) = {
	// Hare `let insts: []inst = [];` — a bare ww slice declaration
	// zeroes the header (cgen.c:9836 no-rhs multi-word composite
	// zero-fill, symmetric in cgenstmt.ww).
	let insts: []inst;
	let charsets: []charset;	// stays empty until the '[' fold
	let iter: strings.iterator = strings.iter(expr);
	let r_idx: size = 0;
	let n_reps: size = 0;

	for (true) {
		let next: (rune | utf8.done) = strings.next(&iter);

		if (r_idx == 0 && next is rune && (next as rune) != '^') {
			// Bare append: ww append returns void; Hare's
			// `append(...)?` nomem propagation is filed #36.
			// Hare appends the bare type name (`inst_skip`) as
			// the void-variant value; in ww that resolves as a
			// symbol ref (cf the alloc(T) rule), so void
			// variants go through a typed let.
			let sk: inst_skip;
			let v: inst = sk;
			append(insts, v);
		};

		// regex.ha:277-284 minus the group_level check (it rides
		// the deferred '(' arm's state).
		let r: rune = match (next) {
		case utf8.done => break;
		case let x: rune => yield x;
		};

		switch (r) {
		case '.': {		// regex.ha:460-461
			let av: inst_any;
			let v: inst = av;
			append(insts, v);
		};
		case ']':		// regex.ha:315-316 — literal outside a bracket
			append(insts, (r: inst_lit));
		case '\\', '^', '$', '[', '(', ')', '|', '{', '?', '*', '+':
			// fold-2a boundary: regex.ha:286-459 arms deferred.
			return "regex: metacharacter not yet ported": error;
		case:			// regex.ha:462-463
			append(insts, (r: inst_lit));
		};
		r_idx += 1;
	};

	// regex.ha:475-477. `$` appends true: inst_match — deferred, so
	// the guard can only see no-match today; kept verbatim.
	if (insts.len == 0 || !(insts[insts.len - 1] is inst_match)) {
		append(insts, (false: inst_match));
	};
	// regex.ha:479-484. The alternation fixup (ha:470-473) drops with
	// jump_idxs.
	return regex {
		insts = insts,
		charsets = charsets,
		n_reps = n_reps,
	};
};

// ref/hare/regex/regex.ha:547-551, verbatim — both free()s are the
// documented no-op (#27; see finish()), kept for source parity. ww
// has no pointer auto-deref, so Hare's `threads[i]` spells
// `(*threads)[i]` (the test-804-pinned delete shape).
fn delete_thread(i: size, threads: *[]thread) void = {
	free((*threads)[i].captures);
	free((*threads)[i].rep_counters);
	delete((*threads)[i]);
};

// ref/hare/regex/regex.ha:553-555. Hare's multi-type membership test
// `a is (inst_lit | inst_any | inst_charset)` is loud-rejected by
// design (filed as a Hare-parity task, ww-core #13); the ruled
// spelling is the chained ||.
fn is_consuming_inst(a: inst) bool = {
	return a is inst_lit || a is inst_any || a is inst_charset;
};

// ref/hare/regex/regex.ha:557-587. The dedup scan (ha:560-566) is an
// index loop: ww has no by-ref `&..` range and a by-value range over
// `*threads` miscompiles (F1, ww-core #11). Its bound reads the
// `.len` pseudo-field, not the len() builtin — len(*threads)
// mis-reads the data pointer as the length (FB1, ww-core #41; the
// F2/#10 deref sibling). Hare's `append(...)?` nomem propagation and the
// ok/defer-if unwind (ha:568/573/586) drop together: ww append
// returns void (#36 filed) and free() reclaims nothing (#27), so
// there is nothing to propagate or unwind.
fn add_thread(threads: *[]thread, parent_idx: size, new_pc: size) (void | nomem) = {
	// Do not add this thread if there is already another thread with
	// the same PC
	for (let k: size = 0; k < ((*threads).len: size); k += 1) {
		if ((*threads)[k].pc == new_pc
				&& !(*threads)[k].matched
				&& (*threads)[k].start_idx
				< (*threads)[parent_idx].start_idx) {
			return;
		};
	};

	// Hare dups the parent's captures/rep_counters here
	// (`alloc(threads[parent_idx].captures...)?`, ha:569/572). Every
	// ww route into that dup is blocked today (re-probed post-C3,
	// PB7): the deref-spine spread SOURCE is loud-rejected (#35),
	// the per-element append is loud-rejected (#34 struct element
	// source), and the whole-element let-copy drops bytes (#7/F5).
	// The abort is sound, not a semantic hole: fold-2a's compile()
	// cannot emit inst_groupstart/inst_repeat, so both slices are
	// provably empty in every program this fold can run; the empty
	// case appends honest zeroed headers below. The verbatim dup
	// lands with the group/repeat fold (ww-core #3).
	if ((*threads)[parent_idx].captures.len != 0
			|| (*threads)[parent_idx].rep_counters.len != 0) {
		abort("regex: capture dup not yet portable (#35/#34/#7)");
	};
	let captures: []capture;
	let rep_counters: []size;

	append(*threads, thread {
		pc = new_pc,
		start_idx = (*threads)[parent_idx].start_idx,
		start_bytesize = (*threads)[parent_idx].start_bytesize,
		matched = (*threads)[parent_idx].matched,
		failed = (*threads)[parent_idx].failed,
		captures = captures,
		rep_counters = rep_counters,
		...
	});
	return;
};

// run_thread (regex.ha:589-742) is deferred behind ONE remaining
// compiler boundary: its loop condition
// `is_consuming_inst(re.insts[threads[i].pc])` passes the 56B inst
// BY VALUE from a slice-element source, which the #38b arg wiring
// loud-rejects ("unsupported source kind 12" — ident sources landed
// with #19; the slice-element extension is task #40, in flight).
// Probed pre-port (PB6c); ruled: run_thread lands Hare-VERBATIM once
// #40 wires the source. Every other run_thread shape is probe-proven
// at HEAD (PB6b match-arm store + composed frombytes bound, P7
// composed scrutinee + compound pc step, P8 newmatch return).

// Frees a [[result]].
//
// ref/hare/regex/regex.ha:1113-1116, verbatim — the free() builtin is
// the documented no-op (#27; see finish()).
export fn result_free(s: result) void = {
	free(s);
};

// Converts an [[error]] into a user-friendly string.
//
// ref/hare/regex/regex.ha:1126-1127 (expression-bodied in Hare; ww
// fns take block bodies).
export fn strerror(err: error) str = {
	return err;
};