// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

package lint

import "testing"

// TestABIExpectedArgSize checks the Go ABI0 argument-area size computation
// against hand-verified signatures (the same layouts the go-flac kernels use).
func TestABIExpectedArgSize(t *testing.T) {
	cases := []struct {
		sig  string
		want int64
	}{
		{"func f()", 0},
		{"func f(a int, b int)", 16},
		{"func f(a int32)", 4},            // no results: no word-boundary padding
		{"func f(a int32) (r int32)", 12}, // results begin on a word boundary: 4 -> 8, +4
		{"func f(a int) int", 16},
		{"func f(s []int32, p *[32]uint16) (x uint64, ok bool)", 41},
		{"func f(left, right []int32, sums *[4]uint64)", 56},
		{"func f(src []byte, dst []int32)", 48},
		{"func f(a bool, b int64)", 16}, // bool at 0, int64 aligned to 8
		{"func f(x struct{ a int32; b int64 })", 16},
	}
	for _, c := range cases {
		got, ok := abiExpectedArgSize(c.sig)
		if !ok {
			t.Errorf("%s: could not compute size", c.sig)
			continue
		}
		if got != c.want {
			t.Errorf("%s: size = %d, want %d", c.sig, got, c.want)
		}
	}
}

func TestABIUnknownTypeSkipped(t *testing.T) {
	// A bare named type of unknown size must abort the check rather than guess.
	// (A *pointer* to a named type is still 8 bytes and is fine.)
	if _, ok := abiExpectedArgSize("func f(s Stream)"); ok {
		t.Error("bare named type should make the size undecidable")
	}
	if _, ok := abiExpectedArgSize("func f(s *Stream)"); !ok {
		t.Error("pointer to a named type is decidable (8 bytes)")
	}
}

// TestABIArgSizeRule checks the lint rule end to end.
func TestABIArgSizeRule(t *testing.T) {
	// Matching: the declared arg size agrees with the signature.
	clean := lintSrc(t, "#include \"textflag.h\"\n"+
		"// func f(a int, b int)\n"+
		"TEXT ·f(SB), NOSPLIT, $0-16\n"+
		"\tMOVQ a+0(FP), AX\n"+
		"\tRET\n")
	if codes(clean)[CodeABIArgSize] != 0 {
		t.Fatalf("matching arg size should not warn: %+v", clean)
	}

	// Mismatching: declared 8, signature implies 16.
	bad := lintSrc(t, "#include \"textflag.h\"\n"+
		"// func f(a int, b int)\n"+
		"TEXT ·f(SB), NOSPLIT, $0-8\n"+
		"\tMOVQ a+0(FP), AX\n"+
		"\tRET\n")
	if codes(bad)[CodeABIArgSize] != 1 {
		t.Fatalf("mismatching arg size should warn once: %+v", bad)
	}
}

// TestABIArgSizeSkipsRegisterABI verifies the check does not fire for functions
// that declare a zero arg area (register ABI) or never touch FP.
func TestABIArgSizeSkipsRegisterABI(t *testing.T) {
	diags := lintSrc(t, "#include \"textflag.h\"\n"+
		"// func f(a int, b int)\n"+
		"TEXT ·f(SB), NOSPLIT, $0-0\n"+
		"\tMOVQ AX, BX\n"+
		"\tRET\n")
	if codes(diags)[CodeABIArgSize] != 0 {
		t.Fatalf("register-ABI function must not be checked: %+v", diags)
	}
}

// TestUnreachableCode exercises the dead-code detection and its guard rails.
func TestUnreachableCode(t *testing.T) {
	// Code after a RET is unreachable.
	dead := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tRET\n"+
		"\tMOVQ AX, BX\n")
	if codes(dead)[CodeUnreachable] != 1 {
		t.Fatalf("code after RET should be unreachable: %+v", dead)
	}

	// A label after the RET makes the following code reachable again.
	live := lintSrc(t, "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tRET\n"+
		"again:\n"+
		"\tJMP again\n")
	if codes(live)[CodeUnreachable] != 0 {
		t.Fatalf("code after a label is reachable: %+v", live)
	}
}

// TestUnreachableGuards verifies the analysis is suppressed where reachability
// cannot be determined statically.
func TestUnreachableGuards(t *testing.T) {
	// A PC-relative jump defeats the analysis for the whole function.
	pcrel := lintSrcArch(t, "f_amd64.s", "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tJCC 2(PC)\n"+
		"\tRET\n"+
		"\tMOVQ AX, BX\n")
	if codes(pcrel)[CodeUnreachable] != 0 {
		t.Fatalf("PC-relative functions must be skipped: %+v", pcrel)
	}

	// A register-indirect branch (riscv JALR) defeats the analysis too.
	indirect := lintSrcArch(t, "f_riscv64.s", "#include \"textflag.h\"\n"+
		"TEXT ·f(SB), NOSPLIT, $0\n"+
		"\tJALR X1, X5\n"+
		"\tRET\n"+
		"\tMOV X1, X2\n")
	if codes(indirect)[CodeUnreachable] != 0 {
		t.Fatalf("indirect-branch functions must be skipped: %+v", indirect)
	}
}