// lib/ww/syntax/sym.ww — port of cmd/wcc/sym.c.
//
// Per-scope hashtable, chained to the parent. Lookup walks up.
// Plan 9 / Hare flavoured. Duplicate definitions in the same scope
// return nil; the caller flags the error.

package syntax;

// Symbol kinds — must stay numerically aligned with cmd/wcc/ww.h Skind.
export type skind = enum i32 {
	SK_NONE  = 0,
	SK_VAR   = 1,
	SK_PARAM = 2,
	SK_DEF   = 3,
	SK_TYPE  = 4,
	SK_FN    = 5,
	SK_USE   = 6,
	SK_FIELD = 7,
};

export type sym = struct {
	name:     str,
	skind:    skind,
	type_:    *tinfo,
	decl:     *node,
	exported: i32,
	is_const: i32,	// const-bound (assignment rejected)
	use_alias: i32,	// #30: this value/type decl ALSO names an imported
			// module (the fnmatch.fnmatch / random.random shape).
			// Set when installtop promotes a same-leaf SK_USE in
			// place; the N_DOT guards treat such a sym as a module
			// for `name.member`. Mirror cstage Sym.use_alias
			// (cmd/wcc/check.c:2831-2951 promote + 87/1337 guards).
	mod:      str,	// importing module's bareword for symbols
			// from a `use`-imported module; "" for primary
			// (root) compilation unit symbols. Used by
			// scopelookupinmodule to disambiguate same-leaf-
			// name types coming from different imports.
	snext:    *sym,	// iteration order
	hashnext: *sym,	// hash bucket chain
	scope:    *scope,
};

def NBUCKETS: i32 = 16;

export type scope = struct {
	parent:   *scope,
	first:    *sym,
	last:     *sym,
	buckets:  **sym,	// length = NBUCKETS
	nbuckets: i32,
};

// FNV-1a 64 — same hash the C side uses, so bucket distribution is
// identical when both walk a scope in declaration order.
fn hashstr(s: str) u64 = {
	let h: u64 = 14695981039346656037u64;
	let i: i32 = 0;
	for (i < s.len) {
		let c: u8 = s[i];
		h = h ^ (c: u64);
		h = h * 1099511628211u64;
		i += 1;
	};
	return h;
};

export fn newscope(parent: *scope) *scope = {
	let buckets_sl: []*sym = alloc([], NBUCKETS: u64)!;
	let s: *scope = alloc(scope{parent=parent, first=nil, last=nil, buckets=buckets_sl.ptr, nbuckets=NBUCKETS})!;
	return s;
};

export fn streq(a: str, b: str) bool = {
	if (a.len != b.len) { return false; };
	let i: i32 = 0;
	for (i < a.len) {
		if (a[i] != b[i]) { return false; };
		i += 1;
	};
	return true;
};

export fn scopelookuplocal(s: *scope, name: str) *sym = {
	if (s == nil) { return nil; };
	let h: u64 = hashstr(name);
	let bi: i32 = (h % (s.nbuckets: u64)): i32;
	let b: *sym = s.buckets[bi];
	for (b != nil) {
		let bn: str = b.name;
		if (streq(bn, name)) { return b; };
		b = b.hashnext;
	};
	return nil;
};

export fn scopelookup(s: *scope, name: str) *sym = {
	for (s != nil) {
		let r: *sym = scopelookuplocal(s, name);
		if (r != nil) { return r; };
		s = s.parent;
	};
	return nil;
};

// scopelookuptype — find an SK_TYPE entry by name, same-module preferred.
//
// Same FNV bucket + hashnext chain + parent walk as scopelookup, with
// an `skind == SK_TYPE` filter. Used to disambiguate the bare-TNAME
// vs imported-module-bareword collision: when scopelookup returns the
// SK_USE sym for a leaf that ALSO names a type (a same-name `import X;`
// SK_USE shadowing a struct X declared in another module), the resolver
// needs the type entry — the struct's mod may differ from the leaf so
// scopelookupinmodule(c, leaf, leaf) won't find it.
//
// #58/#50: within each scope, Pass-1 prefers an SK_TYPE whose `sym.mod`
// matches `mod`; Pass-2 falls back to the first SK_TYPE regardless of
// mod (chain-first, the prior behavior). scopedefineinmodule PREPENDS,
// so chain-first = last-registered — when two modules export the same
// type leaf the bare walk silently picked the newest-installed one,
// install-order-dependent, while cstage is deterministic on cur_mod.
// Mirrors cstage cmd/wcc/sym.c scope_lookup_type(s, mod, name) (the
// kind-filtered + mod-preferring single walk); sole caller passes
// c.curmod. i32-correct: streq throughout, only `.len > 0` guards (the
// reverted attempt compared str.len as u64 — str.len is i32).
export fn scopelookuptype(s: *scope, mod: str, name: str) *sym = {
	let p: *scope = s;
	for (p != nil) {
		let h: u64 = hashstr(name);
		let bi: i32 = (h % (p.nbuckets: u64)): i32;
		let b: *sym = p.buckets[bi];
		let fallback: *sym = nil;
		for (b != nil) {
			if (streq(b.name, name)) {
				if (b.skind == skind.SK_TYPE) {
					if (mod.len > 0) {
						if (b.mod.len > 0) {
							if (streq(b.mod, mod)) {
								return b;
							};
						};
					};
					if (fallback == nil) { fallback = b; };
				};
			};
			b = b.hashnext;
		};
		if (fallback != nil) { return fallback; };
		p = p.parent;
	};
	return nil;
};

// scopelookupuselocal — find a same-leaf SK_USE entry within ONE scope.
//
// Same FNV bucket + hashnext chain as scopelookuplocal, with a
// `skind == SK_USE` filter and NO parent walk. The dot-lhs twin of
// scopelookuptype: when a `use mod;` and a colliding top-level
// `fn mod` / `type mod` of the same leaf coexist (random.random,
// fnmatch.fnmatch), the mod-preferring scopelookupprefer returns the
// SK_FN/SK_TYPE whose mod matches the importing unit's package, masking
// the SK_USE. A dot-lhs `mod.x` must resolve `mod` to the SK_USE for the
// module-qualified arm to fire, so the resolver re-resolves through this
// filter — keyed on the scope where scopelookupprefer LANDED — when it
// lands on a non-USE same-leaf entry.
//
// Single-scope (not a parent walk) so a local binding that shares a leaf
// with a top-level `use` keeps value semantics: scopelookupprefer
// resolves the local in its inner scope, whose bucket holds no SK_USE,
// so this returns nil and the dot stays field access. Only a genuine
// same-scope coexistence (top-level use + top-level type/fn) re-resolves.
//
// #30 (design reversal): this serves the DISTINCT-mod two-sym case only —
// a `fn fnmatch` (mod="fnmatch") coexisting with `import fnmatch`'s SK_USE
// (mod=""), where scopelookupprefer lands on the value and the dot re-
// resolves to the SK_USE here. The SAME-mod collision (a primary-package
// decl whose leaf also names a bundled module — `type sym` vs `import sym`,
// `@test fn ascii` vs the fnmatch->ascii bundle floor) is NO LONGER left to
// two coexisting syms: that ripples into every bare-ref resolver (a missed
// site is a byte-id-consistent-but-wrong cat-A risk the gate can't prove
// away). Instead installtop now PROMOTES the SK_USE in place to the value
// kind with use_alias=1 (selfhost/cmd/wcc/check.ww installtop), mirroring
// cstage's Sym.use_alias promote exactly (cmd/wcc/check.c:2831-2951); the
// N_DOT guards honor `skind == SK_USE || use_alias` directly. ONE
// correctly-kinded sym → all resolvers correct by construction. Cite:
// task #30; project memory module_type_name_collision (cstage 2026-05-13).
export fn scopelookupuselocal(s: *scope, name: str) *sym = {
	if (s == nil) { return nil; };
	let h: u64 = hashstr(name);
	let bi: i32 = (h % (s.nbuckets: u64)): i32;
	let b: *sym = s.buckets[bi];
	for (b != nil) {
		if (streq(b.name, name)) {
			if (b.skind == skind.SK_USE) { return b; };
		};
		b = b.hashnext;
	};
	return nil;
};

// scopelookupinmodule — module-filtered chain walk.
//
// Same FNV bucket + hashnext chain + parent walk as scopelookup, plus
// a `b.mod.len > 0 && streq(b.mod, mod)` filter. When `mod` is empty
// we fall back to unfiltered scopelookup semantics, so callers that
// don't care about disambiguation get the default.
//
// Used by the dot-prefixed type-name lookup in selfhost/cmd/wcc/
// check.ww to pick the right same-leaf-name type when two imports
// each export it (`bufio.stream` vs `io.stream`).
export fn scopelookupinmodule(s: *scope, mod: str, name: str) *sym = {
	if (mod.len == 0) { return scopelookup(s, name); };
	for (s != nil) {
		let h: u64 = hashstr(name);
		let bi: i32 = (h % (s.nbuckets: u64)): i32;
		let b: *sym = s.buckets[bi];
		for (b != nil) {
			if (streq(b.name, name)) {
				if (b.mod.len > 0) {
					if (streq(b.mod, mod)) {
						return b;
					};
				};
			};
			b = b.hashnext;
		};
		s = s.parent;
	};
	return nil;
};

// scopelookupprefer — bare-leaf lookup with same-module preference.
//
// Walks the same FNV bucket + hashnext chain + parent walk scopelookup
// uses. Within each scope's bucket: Pass 1 prefers entries whose
// `sym.mod` matches `mod`; Pass 2 falls back to the first match
// regardless of mod (same semantics as scopelookup). We only descend
// to the parent scope when the current scope has no matching entry at
// all — so a local binding in a closer scope still shadows a same-name
// fn from a parent scope, even when the parent entry mod-matches.
//
// When `mod` is empty we just call scopelookup — there's no module
// identity to prefer.
//
// Used at bare-leaf lookup sites inside a known current module so that
// a bare `read` inside lib/os resolves to os.read rather than the
// io.read that happens to hash earlier into the flat scope. Mirrors
// cmd/wcc/sym.c scope_lookup_prefer.
export fn scopelookupprefer(s: *scope, mod: str, name: str) *sym = {
	if (mod.len == 0) { return scopelookup(s, name); };
	let p: *scope = s;
	for (p != nil) {
		let h: u64 = hashstr(name);
		let bi: i32 = (h % (p.nbuckets: u64)): i32;
		let b: *sym = p.buckets[bi];
		let fallback: *sym = nil;
		for (b != nil) {
			if (streq(b.name, name)) {
				if (b.mod.len > 0) {
					if (streq(b.mod, mod)) {
						return b;
					};
				};
				if (fallback == nil) { fallback = b; };
			};
			b = b.hashnext;
		};
		if (fallback != nil) { return fallback; };
		p = p.parent;
	};
	return nil;
};

export fn scopedefine(s: *scope, name: str, k: skind, t: *tinfo, decl: *node) *sym = {
	let empty: str;
	return scopedefineinmodule(s, name, empty, k, t, decl);
};

// scopedefineinmodule — bucket insert with per-mod dedup.
//
// Same insertion as scopedefine, but the duplicate-rejection key is
// (name, mod) rather than name alone. This lets two imports each
// register their own `stream` SK_TYPE in the flat scope, and lets the
// primary register `stream` (mod="") alongside imported `stream`s.
//
// Within a single (name, mod) pair the first registration wins; later
// attempts return nil and the caller can flag the error.
export fn scopedefineinmodule(s: *scope, name: str, mod: str, k: skind, t: *tinfo, decl: *node) *sym = {
	let h: u64 = hashstr(name);
	let bi: i32 = (h % (s.nbuckets: u64)): i32;
	let b: *sym = s.buckets[bi];
	for (b != nil) {
		if (streq(b.name, name)) {
			if (b.mod.len == 0) {
				if (mod.len == 0) { return nil; };
			} else {
				if (mod.len > 0) {
					if (streq(b.mod, mod)) { return nil; };
				};
			};
		};
		b = b.hashnext;
	};
	let sy: *sym = alloc(sym{name=name, skind=k, type_=t, decl=decl, exported=0, is_const=0, use_alias=0, mod=mod, snext=nil, hashnext=s.buckets[bi], scope=s})!;
	s.buckets[bi] = sy;
	if (s.first == nil) { s.first = sy; } else { s.last.snext = sy; };
	s.last = sy;
	return sy;
};

// scopesamekeysym — the entry scopedefineinmodule(name, mod) treats as a
// duplicate (same name, same mod-key), or nil if the key is free. Lets a
// caller that got a nil from scopedefineinmodule learn WHAT it collided
// with (e.g. a pre-seeded builtin vs a genuine user redeclaration). The
// match logic mirrors scopedefineinmodule's reject branch exactly.
export fn scopesamekeysym(s: *scope, name: str, mod: str) *sym = {
	let h: u64 = hashstr(name);
	let bi: i32 = (h % (s.nbuckets: u64)): i32;
	let b: *sym = s.buckets[bi];
	for (b != nil) {
		if (streq(b.name, name)) {
			if (b.mod.len == 0) {
				if (mod.len == 0) { return b; };
			} else {
				if (mod.len > 0) {
					if (streq(b.mod, mod)) { return b; };
				};
			};
		};
		b = b.hashnext;
	};
	return nil;
};