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

package asm

import (
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strings"
	"testing"

	"sourcedock.dev/petrbalvin/gasm-sdk/parser"
)

// riscv64ErrorCatalogues are the toolchain's own negative-case files for
// riscv64, relative to cmd/asm's testdata: riscv64error.s carries the
// preprocess-stage rejections and riscv64validation.s the validate-stage
// ones (register banks, compressed constraints, vector shapes).
var riscv64ErrorCatalogues = []string{"riscv64error.s", "riscv64validation.s"}

// riscv64AcceptedErrorShapes lists the toolchain's catalogue spellings gasm
// still accepts, each an acceptance superset with a documented reason.  The
// list only shrinks: every tightening of the encoder moves spellings out of
// it, and a spelling reappearing here means a regression.
var riscv64AcceptedErrorShapes = []string{}

// TestRISCVToolchainErrorParity walks the toolchain's riscv64error.s and
// riscv64validation.s (Go 1.27) and requires gasm to reject every case the
// toolchain rejects, with an equivalent diagnostic, the documented acceptance
// supersets above excepted.  A live Go toolchain is needed for the source
// files; the test skips without one or in -short.
func TestRISCVToolchainErrorParity(t *testing.T) {
	goroot := riscv64Goroot(t)
	dir := filepath.Join(goroot, "src", "cmd", "asm", "internal", "asm", "testdata")
	allowed := map[string]bool{}
	for _, s := range riscv64AcceptedErrorShapes {
		allowed[s] = true
	}
	for _, name := range riscv64ErrorCatalogues {
		data, err := os.ReadFile(filepath.Join(dir, name))
		if err != nil {
			t.Skip(err)
		}
		for raw := range strings.SplitSeq(string(data), "\n") {
			line := strings.TrimSpace(raw)
			if line == "" || strings.HasPrefix(line, "//") || strings.HasPrefix(line, "TEXT") || !strings.Contains(line, "ERROR") {
				continue
			}
			body := line
			if i := strings.Index(body, "//"); i >= 0 {
				body = strings.TrimSpace(body[:i])
			}
			want := ""
			if m := regexp.MustCompile(`ERROR "([^"]*)"`).FindStringSubmatch(line); m != nil {
				want = m[1]
			}
			body = strings.ReplaceAll(body, "\t", " ")
			body = strings.Join(strings.Fields(body), " ")
			// A symbol reference needs the file's own declarations, which a
			// one-line probe cannot carry.
			if strings.Contains(body, "(SB)") {
				continue
			}
			src := "#include \"textflag.h\"\n\nTEXT ·f(SB), NOSPLIT, $0-0\n\t" + body + "\n\tRET\n"
			f, perr := parser.Parse("errorparity.s", src)
			if len(perr) > 0 {
				continue // the parser already rejects the spelling
			}
			_, aerr := AssembleFileRISCV(f)
			if aerr == nil {
				if !allowed[body] {
					t.Errorf("gasm accepts what the toolchain rejects: %s", body)
				}
				continue
			}
			if want != "" && !riscv64DiagEquivalent(want, aerr.Error()) {
				t.Errorf("gasm rejects %s with an inequivalent diagnostic:\n toolchain: %s\n gasm: %s", body, want, aerr)
			}
		}
	}
}

// riscv64DiagEquivalent answers whether gasm's rejection carries the same
// information as the toolchain's expected message.  The two word the same
// facts differently: the toolchain writes "immediate out of range 0 to 31"
// where gasm may spell the field's own name, and gasm prefixes the mnemonic.
// Canonicalisation drops the subjects and connectives and compares the
// remaining token sequence.
func riscv64DiagEquivalent(want, got string) bool {
	return riscv64DiagSubseq(riscv64DiagTokens(want), riscv64DiagTokens(got))
}

// riscv64DiagTokens lower-cases a diagnostic, strips punctuation and the
// connective tokens, and returns its words.  "to" survives only between
// digits, where the range wording uses it.
func riscv64DiagTokens(msg string) []string {
	msg = strings.ToLower(msg)
	for _, r := range []string{"[", "]", ",", ".", ":", "\n", "(", ")"} {
		msg = strings.ReplaceAll(msg, r, " ")
	}
	fields := strings.Fields(msg)
	out := make([]string, 0, len(fields))
	for i, w := range fields {
		switch w {
		case "the", "a", "operand", "immediate", "an", "for":
			// subjects and articles carry no constraint
		case "to":
			if i > 0 && i+1 < len(fields) && riscv64IsNumeric(fields[i-1]) && riscv64IsNumeric(fields[i+1]) {
				continue // the range connective
			}
			out = append(out, w)
		default:
			out = append(out, w)
		}
	}
	return out
}

// riscv64DiagSubseq answers whether want is a subsequence of got.
func riscv64DiagSubseq(want, got []string) bool {
	i := 0
	for _, w := range got {
		if i < len(want) && w == want[i] {
			i++
		}
	}
	return i == len(want)
}

// riscv64IsNumeric reports whether s parses as a signed decimal number, the
// token shape the range connective sits between.
func riscv64IsNumeric(s string) bool {
	if s == "" {
		return false
	}
	if s[0] == '-' || s[0] == '+' {
		s = s[1:]
	}
	if s == "" {
		return false
	}
	for _, r := range s {
		if r < '0' || r > '9' {
			return false
		}
	}
	return true
}

// riscv64Goroot resolves the live toolchain root, the environment's own value
// first, `go env GOROOT` as the fallback.
func riscv64Goroot(t *testing.T) string {
	t.Helper()
	if goroot := os.Getenv("GOROOT"); goroot != "" {
		return goroot
	}
	out, err := exec.Command("go", "env", "GOROOT").Output()
	if err != nil {
		t.Skipf("no GOROOT: %v", err)
	}
	return strings.TrimSpace(string(out))
}

// riscv64RejectedNames pins the names the toolchain's riscv64 table carries
// but refuses to encode: each is a "no encoding for instruction" under every
// operand shape GOARCH=riscv64 go tool asm accepts.  gasm rejects them too,
// and the pair of rejections is the parity this catalogue asserts.
var riscv64RejectedNames = []string{"DUFFCOPY", "DUFFZERO", "PCALIGNMAX"}

// TestRISCVBacklogNameParity walks the audit's known-but-unencodable
// backlog: the names go tool asm recognises on riscv64 yet refuses to encode
// must be refused by gasm as well.
func TestRISCVBacklogNameParity(t *testing.T) {
	if testing.Short() {
		t.Skip("live toolchain backlog: skipped in -short mode")
	}
	for _, name := range riscv64RejectedNames {
		if riscv64ProbeAssembles(name + " X5") {
			t.Errorf("gasm encodes %s, which the toolchain refuses under every shape", name)
		}
		if riscv64ProbeAssembles(name) {
			t.Errorf("gasm encodes %s, which the toolchain refuses under every shape", name)
		}
	}
}

// riscv64ProbeAssembles answers whether a single statement wrapped in its
// own function parses and assembles on riscv64.
func riscv64ProbeAssembles(body string) bool {
	src := "#include \"textflag.h\"\n\nTEXT ·probe(SB), NOSPLIT, $0-0\n\t" + body + "\n\tRET\n"
	f, perr := parser.Parse("backlogparity.s", src)
	if len(perr) > 0 {
		return false // the parser already rejects the line
	}
	_, aerr := AssembleFileRISCV(f)
	return aerr == nil
}

// riscv64CatalogueSelfCheck guards the catalogue walk itself: every ERROR
// line in the two files must yield a probe body, so a formatting change in
// the toolchain's files cannot silently empty the parity set.
func TestRISCVErrorCatalogueSelfCheck(t *testing.T) {
	if testing.Short() {
		t.Skip("live toolchain catalogue: skipped in -short mode")
	}
	goroot := riscv64Goroot(t)
	dir := filepath.Join(goroot, "src", "cmd", "asm", "internal", "asm", "testdata")
	total := 0
	for _, name := range riscv64ErrorCatalogues {
		data, err := os.ReadFile(filepath.Join(dir, name))
		if err != nil {
			t.Skip(err)
		}
		n := strings.Count(string(data), "ERROR")
		total += n
		if n == 0 {
			t.Errorf("%s carries no ERROR lines; the catalogue walk is empty", name)
		}
	}
	if total < 1000 {
		t.Errorf("catalogue carries %d ERROR lines, want at least 1000", total)
	}
}