/*
 * 762_struct_abi_size — defensive lock for project #78. cstage once
 * folded size(struct{i32,i32,i32}) to 12 while wwstage folded it to
 * 16; the two checkers walked different layout formulas. After
 * d4e500f (#169) introduced structabisize and the cgen ABI sites
 * converged onto a single (off + maxalign - 1) & ~(maxalign - 1)
 * formula on both sides, every layout-edge shape should agree —
 * BOTH at the size(T) fold (cstage check.c:760 / wwstage check.ww
 * astsize N_TSTRUCT) and at the register-RECV/RETURN ABI walker
 * (cgen.c struct_arg_size / structabisize). This probe pins both.
 *
 * The fold and the ABI walker share the formula but live in two
 * different sources: check.c:760 vs check.ww:958 (the language
 * builtin) and cmd/w6c/cgen.c struct_arg_size vs
 * selfhost/cmd/wcc/cgenutil.ww structabisize (the cgen ABI). Either
 * can drift independently — locking only the runtime exit code via
 * size(T) misses an ABI-walker regression that does not change the
 * literal fold; locking only the .s byte-id misses a fold regression
 * the cgen would happily honour. Both gates run per row.
 *
 * Expected size is COMPUTED from a (sz, aln) field table per row,
 * not hardcoded — a stage-internal formula bump (rule 13) lands the
 * change in compute_expected() and every row tracks. The probe must
 * red the moment any source-of-truth drifts from the documented
 * Hare-style layout: align(off, fa); off += fs; size = align(off,
 * maxalign).
 *
 * Shape coverage targets the maxalign edges where the bug class
 * lived:
 *   1. {3xi32}            — #78 canonical, maxalign 4, natural 12,
 *                           ABI 12 (no round-up)
 *   2. {i32,i32,i64}      — maxalign 8, narrow lead, ABI 16
 *   3. {i64,i32,i32}      — maxalign 8 with sub-8 tail, ABI 16
 *                           (the #169 round-up case)
 *   4. {3xi16}            — maxalign 2, natural 6, ABI 6
 *   5. {i16,i64}          — maxalign 8 with mid-record alignment
 *                           padding (f2 must skip off 2→8)
 *   6. {3xi64}            — maxalign 8, all 8-wide, natural==ABI=24
 *
 * GATE POLARITY: this file must stay GREEN. A red here means either
 * d4e500f (#169 structabisize) reverted, or one of the two layout
 * walkers drifted from the formula.
 */
#include <stdio.h>
#include <stdlib.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 field { int sz; int aln; };

struct row {
	const char *label;
	const char *src;	/* must `return size(T): i32` */
	int nfields;
	struct field fields[8];
};

/* Hare / cstage check.c:701-760 / wwstage check.ww astsize N_TSTRUCT
 * formula. Per CLAUDE.md rule 13 the expected size for each row is
 * derived here, not literalled into the row table. */
static int
compute_expected(const struct field *f, int n)
{
	int off = 0, maxalign = 1;
	for (int i = 0; i < n; i++) {
		int a = f[i].aln;
		if (a > maxalign) maxalign = a;
		off = (off + a - 1) & ~(a - 1);
		off += f[i].sz;
	}
	return (off + maxalign - 1) & ~(maxalign - 1);
}

static const struct row rows[] = {
	/* 1. {3xi32} — #78 canonical. cstage check.c:760 returned 12,
	 * wwstage formerly walked a slot-padded ladder yielding 16. The
	 * fold now uses astsize's (off + maxal - 1) & ~(maxal - 1) on
	 * both sides; expect 12. */
	{ "i32_x3_maxalign4",
	  "type t = struct { a: i32, b: i32, c: i32 };\n"
	  "export fn main() i32 = { return size(t): i32; };\n",
	  3, {{4,4},{4,4},{4,4}} },
	/* 2. {i32,i32,i64} — maxalign 8, off lands at 8 before the i64,
	 * total 16. */
	{ "i32_i32_i64_lead_narrow",
	  "type t = struct { a: i32, b: i32, c: i64 };\n"
	  "export fn main() i32 = { return size(t): i32; };\n",
	  3, {{4,4},{4,4},{8,8}} },
	/* 3. {i64,i32,i32} — natural extent 16, maxalign 8: the post-
	 * field-3 round-up is a no-op here, but the #169 commit added
	 * exactly this round-up so the structabisize walker matches
	 * cstage on the maxalign-8 sub-8-tail shape (cf. {i64,i32}). */
	{ "i64_i32_i32_sub8_tail",
	  "type t = struct { a: i64, b: i32, c: i32 };\n"
	  "export fn main() i32 = { return size(t): i32; };\n",
	  3, {{8,8},{4,4},{4,4}} },
	/* 4. {3xi16} — maxalign 2, natural 6. Guards against a future
	 * "round to 8" shortcut creeping back into either walker. */
	{ "i16_x3_maxalign2",
	  "type t = struct { a: i16, b: i16, c: i16 };\n"
	  "export fn main() i32 = { return size(t): i32; };\n",
	  3, {{2,2},{2,2},{2,2}} },
	/* 5. {i16,i64} — exercises a non-trivial mid-record align step:
	 * after f1 off=2, f2 must align off 2→8 before placing the i64.
	 * A missing `off = align(off, fa)` would land f2 at off=2 and
	 * size to 10 (or 16 only via the final maxalign round); either
	 * way it would diverge from the formula. {i32,i32,i64} (rows 2)
	 * already aligns at 8 by the natural off, so the align-step is
	 * a no-op there. */
	{ "i16_i64_mid_pad",
	  "type t = struct { a: i16, b: i64 };\n"
	  "export fn main() i32 = { return size(t): i32; };\n",
	  2, {{2,2},{8,8}} },
	/* 6. {3xi64} — natural==ABI, the maxalign-rounded formula must
	 * not double-round. */
	{ "i64_x3_natural_24",
	  "type t = struct { a: i64, b: i64, c: i64 };\n"
	  "export fn main() i32 = { return size(t): i32; };\n",
	  3, {{8,8},{8,8},{8,8}} },
};

static int
run_driver(const char *driver, const struct row *r, int i)
{
	char src[128], tmpdir[64], outbin[128], rmcmd[160], cmd[1024];
	snprintf(tmpdir, sizeof tmpdir, "/tmp/wcabi_%d_d_%d", getpid(), i);
	mkdir(tmpdir, 0755);
	snprintf(src, sizeof src, "%s/wcabi_%d_%d.ww", tmpdir, getpid(), i);
	snprintf(outbin, sizeof outbin, "%s/wcabi_%d_%d", tmpdir, getpid(), i);
	snprintf(rmcmd, sizeof rmcmd, "rm -rf %s", tmpdir);

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

	/* timeout 180 per repo convention (cf. 760, 761); test/run does
	 * not bound individual binaries. */
	snprintf(cmd, sizeof cmd, "timeout 180 %s build -o %s %s 2>/dev/null",
	    driver, outbin, src);
	if (runwait(cmd) != 0) {
		fprintf(stderr, "row[%s]: build via %s failed\n",
		    r->label, driver);
		runwait(rmcmd);
		return -1;
	}

	int got = runwait(outbin);

	runwait(rmcmd);
	return got;
}

/* asm_byte_identical — diff w6c vs w6c_ww text output. The cgen ABI
 * walker (structabisize since #169 / d4e500f) feeds the struct-
 * return + struct-arg push widths; a divergence on these shapes
 * surfaces as a .s difference even when the size(T) fold still
 * matches (the two walkers are independent SSoTs). */
static int
asm_byte_identical(const char *bin, const struct row *r, int i)
{
	char src[64], cs[64], ws[64], cmd[1024];
	snprintf(src, sizeof src, "/tmp/wcabi_asm_%d_%d.ww", getpid(), i);
	snprintf(cs,  sizeof cs,  "/tmp/wcabi_asm_%d_%d_c.s", getpid(), i);
	snprintf(ws,  sizeof ws,  "/tmp/wcabi_asm_%d_%d_w.s", getpid(), i);

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

	snprintf(cmd, sizeof cmd, "timeout 180 %s/w6c -o %s %s 2>/dev/null",
	    bin, cs, src);
	if (runwait(cmd) != 0) {
		fprintf(stderr, "row[%s]: w6c errored\n", r->label);
		unlink(src);
		return -1;
	}
	snprintf(cmd, sizeof cmd, "timeout 180 %s/w6c_ww -o %s %s 2>/dev/null",
	    bin, ws, src);
	if (runwait(cmd) != 0) {
		fprintf(stderr, "row[%s]: w6c_ww errored\n", r->label);
		unlink(src); unlink(cs);
		return -1;
	}

	FILE *fc = fopen(cs, "rb");
	FILE *fw = fopen(ws, "rb");
	int rc = 0;
	if (!fc || !fw) {
		rc = -1;
	} else {
		for (;;) {
			int a = fgetc(fc);
			int b = fgetc(fw);
			if (a != b) { rc = -1; break; }
			if (a == EOF) break;
		}
	}
	if (fc) fclose(fc);
	if (fw) fclose(fw);
	if (rc != 0)
		fprintf(stderr, "row[%s]: cstage vs wwstage asm differs\n",
		    r->label);
	unlink(src); unlink(cs); unlink(ws);
	return rc;
}

int
main(void)
{
	const char *bin = getenv("BIN");
	if (!bin) bin = "out/bin";
	char absbin[1024];
	if (bin[0] != '/') {
		char cwd[1024];
		if (getcwd(cwd, sizeof cwd) == NULL) return 1;
		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
		bin = absbin;
	}

	char cdrv[1024];
	snprintf(cdrv, sizeof cdrv, "%s/ww", bin);
	char wdrv[1024];
	snprintf(wdrv, sizeof wdrv, "%s/ww_ww", bin);

	struct { const char *name; const char *path; int gated_on_existence; }
	drivers[] = {
		{ "cstage",  cdrv, 0 },
		{ "wwstage", wdrv, 1 },
		{ NULL, NULL, 0 },
	};

	int n = (int)(sizeof rows / sizeof rows[0]);
	int total = 0, fail = 0;

	for (int d = 0; drivers[d].name; d++) {
		if (drivers[d].gated_on_existence
		    && access(drivers[d].path, X_OK) != 0) {
			fprintf(stderr, "struct_abi_size: skip %s (no %s)\n",
			    drivers[d].name, drivers[d].path);
			continue;
		}
		for (int i = 0; i < n; i++) {
			int want = compute_expected(rows[i].fields,
			    rows[i].nfields);
			int got = run_driver(drivers[d].path, &rows[i], i);
			total++;
			if (got != want) {
				fprintf(stderr,
				    "struct_abi_size[%s][%s]: size=%d want=%d\n",
				    drivers[d].name, rows[i].label,
				    got, want);
				fail++;
			}
		}
	}

	if (access(wdrv, X_OK) == 0) {
		for (int i = 0; i < n; i++) {
			total++;
			if (asm_byte_identical(bin, &rows[i], i) != 0)
				fail++;
		}
	}

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