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

package format

import (
	"os"
	"path/filepath"
	"testing"

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

// FuzzFormatIdempotency hammers the formatter with arbitrary input.  The
// contract: formatting twice equals formatting once, and input that parses
// cleanly still parses cleanly after formatting.  The seed corpus carries the
// repository's kernels, so a plain `go test` run replays every seed as a
// regression case and CI exercises them without any fuzzing budget.
func FuzzFormatIdempotency(f *testing.F) {
	for _, pattern := range []string{
		"../testdata/*.s",
		"../testdata/verify/*.s",
	} {
		files, _ := filepath.Glob(pattern)
		for _, path := range files {
			if b, err := os.ReadFile(path); err == nil {
				f.Add(string(b))
			}
		}
	}
	f.Add("TEXT ·f(SB), NOSPLIT, $0\n\tMOVQ AX, BX\n\tRET\n")
	f.Add("TEXT ·f(SB),NOSPLIT,$0\n\tMOVQ   AX,BX\n\n\n\tRET\n")
	f.Add("garbage ### ???\n")
	// Line-ending whitespace at the edge of a comment: a CR followed by more
	// trailing whitespace once survived the first pass and disappeared on
	// re-lexing, so formatting was not idempotent.
	f.Add("//\r ")
	f.Add("// loop \r\t\nMOVQ AX, BX\n")
	f.Add("TEXT ·f(SB), NOSPLIT, $0 // tail\r\n\tMOVQ AX, BX\r\n\tRET\r\n")

	f.Fuzz(func(t *testing.T, src string) {
		once := Source(src)
		twice := Source(once)
		if once != twice {
			t.Fatalf("formatting is not idempotent:\nfirst:  %q\nsecond: %q", once, twice)
		}
		if _, errs := parser.Parse("in.s", src); len(errs) == 0 {
			if _, errs := parser.Parse("out.s", once); len(errs) > 0 {
				t.Fatalf("formatted output of clean input does not parse: %v\n%s", errs[0], once)
			}
		}
	})
}