/*
 * 728_match_4arm_cross_module — Class A asm-presence + byte-id sentinel
 * for task #31. Pins that the variant tag for each arm of a 4-arm match
 * on a qualified `mod.fn(...)` call matches between cstage and wwstage
 * even when the caller fn shadows the callee's fn-name across modules.
 *
 * Pre-fix wwstage's matchscrutt (selfhost/cmd/wcc/cgenutil.ww:2061-2074)
 * resolved the scrutinee's tagged type via name-only fnretlookup. With
 * `fn next` in two modules, collectfnrets' prepend ordering meant the
 * last-declared `next` sat at the head, so `match (utf8.next(d))`
 * inside a `fn next() (rune | done)` saw the 2-arm tagged instead of
 * the callee's real 4-arm tagged. Arms 2/3 of the match dispatch then
 * silently collapsed to CMPQ $0 (their case bodies were unreachable
 * even when the tag matched). Sister of #27 (aliaslookupmod) and #28
 * (fnparamslookupmod) — the third leaf in the same name-collision trio.
 *
 * Cstage carries module info through the checker-set callee type
 * (cmd/w6c/cgen.c) so its match-scrutinee resolution is correct.
 * Wwstage converges via fnretlookupmod (cgen.ww), called from
 * matchscrutt's N_DOT branch.
 *
 * The repro requires:
 *   1. callee fn declared first in module A, returning a 4+ arm tagged.
 *   2. caller fn in module B, *same fn name*, returning a 2-arm tagged
 *      that is a subset of the callee's arms (so arms 0/1 still resolve
 *      and only 2+ surface the dispatch corruption).
 *   3. The match scrutinee is the qualified `A.fn(...)` call.
 *
 * Asserts each arm of the canonical 4-arm match emits a *distinct*
 * CMPQ tag in the wwstage asm AND cstage-vs-wwstage cmp -s holds.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/wait.h>

static int
runwait(const char *cmd)
{
	int rc = system(cmd);
	if (rc == -1) return -1;
	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
	return -1;
}

struct row {
	const char *label;
	const char *src;
	/* Function whose body holds the match-dispatch to inspect. The
	 * 4 arms must each emit a distinct `CMPQ $K, AX` between
	 * `TEXT <fn>` and the next TEXT directive. */
	const char *fn;
	int arms;
};

static const struct row rows[] = {
	/* Canonical 4-arm: caller `next` in mod B shadows callee `next`
	 * in mod A. Pre-fix arms 2/3 → CMPQ $0; post-fix → $2/$3. */
	{ "4arm_shadowed_callee",
	  "package a;\n"
	  "export type more = void;\n"
	  "export type invalid = !void;\n"
	  "export type done = void;\n"
	  "export fn next() (rune | done | more | invalid) = {\n"
	  "    let r: rune;\n"
	  "    return r;\n"
	  "};\n"
	  "package b;\n"
	  "import a;\n"
	  "type done = void;\n"
	  "fn next() (rune | done) = {\n"
	  "    match (a.next()) {\n"
	  "    case let r: rune       => return r;\n"
	  "    case let dn: a.done    => { let v: done; return v; };\n"
	  "    case let m:  a.more    => { abort(\"i\"); };\n"
	  "    case let e:  a.invalid => { abort(\"i\"); };\n"
	  "    };\n"
	  "};\n"
	  "export fn main() i32 = { return 0; };\n",
	  "b.next", 4 },
	/* Reverse arm order in the match source: pins that the bug
	 * follows variantindex (or in our case, the mod-disambiguated
	 * scrutinee type), not source order — arm 0 stays at idx 3 etc. */
	{ "4arm_shadowed_reverse",
	  "package a;\n"
	  "export type more = void;\n"
	  "export type invalid = !void;\n"
	  "export type done = void;\n"
	  "export fn next() (rune | done | more | invalid) = {\n"
	  "    let r: rune;\n"
	  "    return r;\n"
	  "};\n"
	  "package b;\n"
	  "import a;\n"
	  "type done = void;\n"
	  "fn next() (rune | done) = {\n"
	  "    match (a.next()) {\n"
	  "    case let e:  a.invalid => { abort(\"i\"); };\n"
	  "    case let m:  a.more    => { abort(\"i\"); };\n"
	  "    case let dn: a.done    => { let v: done; return v; };\n"
	  "    case let r: rune       => return r;\n"
	  "    };\n"
	  "};\n"
	  "export fn main() i32 = { return 0; };\n",
	  "b.next", 4 },
	/* 3-arm boundary: confirm the issue is "arms ≥ caller's variant
	 * count collapse", not "≥ 2". Caller `next` returns 2-arm, callee
	 * returns 3-arm. Arm 2 must be CMPQ $2. */
	{ "3arm_shadowed_callee",
	  "package a;\n"
	  "export type more = void;\n"
	  "export type done = void;\n"
	  "export fn next() (rune | done | more) = {\n"
	  "    let r: rune;\n"
	  "    return r;\n"
	  "};\n"
	  "package b;\n"
	  "import a;\n"
	  "type done = void;\n"
	  "fn next() (rune | done) = {\n"
	  "    match (a.next()) {\n"
	  "    case let r: rune    => return r;\n"
	  "    case let dn: a.done => { let v: done; return v; };\n"
	  "    case let m:  a.more => { abort(\"i\"); };\n"
	  "    };\n"
	  "};\n"
	  "export fn main() i32 = { return 0; };\n",
	  "b.next", 3 },
};

static int
slurp(const char *path, char *buf, size_t cap)
{
	FILE *f = fopen(path, "rb");
	if (!f) return -1;
	size_t n = fread(buf, 1, cap - 1, f);
	fclose(f);
	buf[n] = '\0';
	return (int)n;
}

static int
emit_s(const char *w6c, const struct row *r, int i, char *out_s, size_t cap)
{
	char src[64], cmd[1024];
	snprintf(src, sizeof src, "/tmp/m4cm_%d_%d.ww", getpid(), i);
	snprintf(out_s, cap, "/tmp/m4cm_%d_%d_%s.s",
	    getpid(), i, w6c[strlen(w6c) - 1] == 'w' ? "ww" : "c");

	FILE *f = fopen(src, "wb");
	if (!f) return -1;
	fputs(r->src, f);
	fclose(f);

	snprintf(cmd, sizeof cmd, "%s -o %s %s 2>/dev/null", w6c, out_s, src);
	int rc = runwait(cmd);
	unlink(src);
	return rc;
}

/* Inside TEXT <fn>, walk every `CMPQ $K, AX` line that precedes the
 * next TEXT directive and assert at least `arms` of them and that
 * the first `arms` such tags are pairwise distinct AND cover [0..arms). */
static int
check_distinct_cmpq(const char *spath, const struct row *r, const char *stage)
{
	char buf[1 << 14];
	if (slurp(spath, buf, sizeof buf) < 0) {
		fprintf(stderr, "row[%s][%s]: cannot read %s\n",
		    r->label, stage, spath);
		return -1;
	}
	char fnhdr[128];
	snprintf(fnhdr, sizeof fnhdr, "TEXT %s", r->fn);
	const char *fn = strstr(buf, fnhdr);
	if (!fn) {
		fprintf(stderr, "row[%s][%s]: no `%s` in %s\n",
		    r->label, stage, fnhdr, spath);
		return -1;
	}
	const char *end = strstr(fn + strlen(fnhdr), "\nTEXT ");
	if (!end) end = buf + strlen(buf);

	int seen[16] = {0};
	int got = 0;
	const char *p = fn;
	while (p < end) {
		const char *m = strstr(p, "CMPQ\t$");
		if (!m || m >= end) break;
		const char *digits = m + strlen("CMPQ\t$");
		if (*digits < '0' || *digits > '9') { p = m + 1; continue; }
		int k = 0;
		while (*digits >= '0' && *digits <= '9') {
			k = k * 10 + (*digits - '0');
			digits++;
		}
		if (strncmp(digits, ", AX", 4) == 0) {
			if (got < 16 && k < 16) seen[got++] = k;
		}
		p = m + 1;
	}
	if (got < r->arms) {
		fprintf(stderr,
		    "row[%s][%s]: only %d `CMPQ $K, AX` in %s body (want %d)\n",
		    r->label, stage, got, r->fn, r->arms);
		return -1;
	}
	int bitmap = 0;
	for (int i = 0; i < r->arms; i++) {
		if (seen[i] < 0 || seen[i] >= r->arms) {
			fprintf(stderr,
			    "row[%s][%s]: arm %d emits CMPQ $%d (out of [0, %d))\n",
			    r->label, stage, i, seen[i], r->arms);
			return -1;
		}
		if (bitmap & (1 << seen[i])) {
			fprintf(stderr,
			    "row[%s][%s]: arm %d repeats tag $%d (collapse)\n",
			    r->label, stage, i, seen[i]);
			return -1;
		}
		bitmap |= 1 << seen[i];
	}
	return 0;
}

int
main(void)
{
	const char *bin = getenv("BIN");
	if (!bin) bin = "out/bin";
	char absbin[512];
	if (bin[0] != '/') {
		char cwd[256];
		if (getcwd(cwd, sizeof cwd) == NULL) return 1;
		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
		bin = absbin;
	}

	char w6c[640], w6c_ww[640];
	snprintf(w6c, sizeof w6c, "%s/w6c", bin);
	snprintf(w6c_ww, sizeof w6c_ww, "%s/w6c_ww", bin);

	int have_ww = (access(w6c_ww, X_OK) == 0);
	int n = (int)(sizeof rows / sizeof rows[0]);
	int total = 0, fail = 0;

	for (int i = 0; i < n; i++) {
		char cs_path[128], ws_path[128];

		if (emit_s(w6c, &rows[i], i, cs_path, sizeof cs_path) != 0) {
			fprintf(stderr,
			    "match_4arm_cross_module[cstage][%s]: w6c failed\n",
			    rows[i].label);
			fail++; total++; continue;
		}
		total++;
		if (check_distinct_cmpq(cs_path, &rows[i], "cstage") != 0)
			fail++;

		if (!have_ww) { unlink(cs_path); continue; }

		if (emit_s(w6c_ww, &rows[i], i, ws_path, sizeof ws_path) != 0) {
			fprintf(stderr,
			    "match_4arm_cross_module[wwstage][%s]: w6c_ww failed\n",
			    rows[i].label);
			fail++; total++;
			unlink(cs_path); continue;
		}
		total++;
		if (check_distinct_cmpq(ws_path, &rows[i], "wwstage") != 0)
			fail++;

		unlink(cs_path); unlink(ws_path);
	}

	if (fail) {
		fprintf(stderr,
		    "match_4arm_cross_module: %d/%d fixtures failed\n",
		    fail, total);
		return 1;
	}
	printf("match_4arm_cross_module: %d/%d ok\n", total, total);
	return 0;
}