/*
 * sym.c — symbol table. Plan 9-flavoured: a per-scope hashtable
 * chained to the parent scope. Lookup walks up. Duplicate definitions
 * within the same scope are flagged by the caller (we just refuse the
 * insert and return the first one).
 */
#include "ww.h"
#include <string.h>

#define INIT_BUCKETS	16

static u64
hashstr(const char *s)
{
	/* FNV-1a 64-bit; small fixed footprint, decent distribution */
	u64 h = 0xcbf29ce484222325ULL;
	for (; *s; s++) {
		h ^= (unsigned char)*s;
		h *= 0x100000001b3ULL;
	}
	return h;
}

Scope *
newscope(Arena *a, Scope *parent)
{
	Scope *s = amalloc(a, sizeof *s);
	s->parent = parent;
	s->a = a;
	s->nbuckets = INIT_BUCKETS;
	s->buckets = amalloc(a, s->nbuckets * sizeof(Sym *));
	return s;
}

Sym *
scope_lookup_local(Scope *s, const char *name)
{
	if (s == NULL) return NULL;
	u64 h = hashstr(name) % s->nbuckets;
	for (Sym *b = s->buckets[h]; b; b = b->hashnext)
		if (strcmp(b->name, name) == 0)
			return b;
	return NULL;
}

Sym *
scope_lookup(Scope *s, const char *name)
{
	for (; s; s = s->parent) {
		Sym *r = scope_lookup_local(s, name);
		if (r) return r;
	}
	return NULL;
}

/*
 * scope_lookup_in_module — module-filtered chain walk.
 *
 * Same FNV bucket + hashnext chain + parent walk as scope_lookup,
 * plus a (b->mod != NULL && strcmp(b->mod, mod) == 0) filter. When
 * `mod` is NULL we fall back to unfiltered scope_lookup semantics,
 * so callers that don't care about disambiguation get the default.
 *
 * Used by resolve_typename and the cexpr N_DOT branch to pick the
 * right same-leaf-name type when two imports each export it
 * (`bufio.stream` vs `io.stream`).
 */
Sym *
scope_lookup_in_module(Scope *s, const char *mod, const char *name)
{
	if (mod == NULL) return scope_lookup(s, name);
	for (; s; s = s->parent) {
		u64 h = hashstr(name) % s->nbuckets;
		for (Sym *b = s->buckets[h]; b; b = b->hashnext) {
			if (strcmp(b->name, name) != 0) continue;
			if (b->mod && strcmp(b->mod, mod) == 0) return b;
		}
	}
	return NULL;
}

/*
 * scope_lookup_prefer — bare-leaf lookup with same-module preference.
 *
 * Walks the same FNV bucket + hashnext chain + parent walk scope_lookup
 * uses. Within each scope's bucket: Pass 1 prefers entries whose
 * `sym.mod` matches the caller's `mod`; Pass 2 falls back to the first
 * match regardless of mod (the existing scope_lookup semantics). 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 NULL we just call scope_lookup — 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.
 * Qualified-lookup paths (`mod.name`) stay on scope_lookup_in_module.
 */
Sym *
scope_lookup_prefer(Scope *s, const char *mod, const char *name)
{
	if (mod == NULL) return scope_lookup(s, name);
	for (Scope *p = s; p; p = p->parent) {
		u64 h = hashstr(name) % p->nbuckets;
		Sym *fallback = NULL;
		for (Sym *b = p->buckets[h]; b; b = b->hashnext) {
			if (strcmp(b->name, name) != 0) continue;
			if (b->mod && strcmp(b->mod, mod) == 0) return b;
			if (fallback == NULL) fallback = b;
		}
		if (fallback) return fallback;
	}
	return NULL;
}

Sym *
scope_define(Scope *s, const char *name, Skind k, Type *t, Node *decl)
{
	return scope_define_in_module(s, name, NULL, k, t, decl);
}

/*
 * scope_define_in_module — bucket insert with per-mod dedup.
 *
 * Same insertion as scope_define, 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=NULL) alongside imported `stream`s.
 *
 * Within a single (name, mod) pair the first registration wins; later
 * attempts return NULL and the caller emits a duplicate-type error.
 */
Sym *
scope_define_in_module(Scope *s, const char *name, const char *mod,
    Skind k, Type *t, Node *decl)
{
	u64 h = hashstr(name) % s->nbuckets;
	for (Sym *b = s->buckets[h]; b; b = b->hashnext) {
		if (strcmp(b->name, name) != 0) continue;
		if (b->mod == NULL && mod == NULL) return NULL;
		if (b->mod && mod && strcmp(b->mod, mod) == 0) return NULL;
	}
	Sym *sy = amalloc(s->a, sizeof *sy);
	sy->name = name;
	sy->mod = mod;
	sy->kind = k;
	sy->type = t;
	sy->decl = decl;
	sy->scope = s;
	sy->hashnext = s->buckets[h];
	s->buckets[h] = sy;
	if (s->first == NULL) s->first = sy;
	else s->last->next = sy;
	s->last = sy;
	return sy;
}