package guards

import (
	"bufio"
	"os"
	"testing"
)

// maxFileLines is AGENTS.md's per-file cap ("Mechanical rules" and the
// frontend section both cite 300 lines; this test enforces the Go side).
const maxFileLines = 300

// lineCapExempt lists files exempt from the cap, by exact repo-relative
// path — never by pattern or directory, so an exemption is a visible,
// reviewable decision rather than a rule that silently swallows
// whatever lands nearby later. Empty today: nothing vendored or
// generated in this repo's .go tree exceeds the cap yet. Add an entry
// here, dated and justified, the day one does.
var lineCapExempt = map[string]bool{}

// TestFileLineCap enforces the 300-line cap per .go file. It is a floor,
// not a ratchet: it stops a file from ever crossing 300 lines, but does
// not push any file already under the cap any lower.
func TestFileLineCap(t *testing.T) {
	root := repoRoot(t)
	for _, path := range goFiles(t, root) {
		rel := relPath(t, root, path)
		if lineCapExempt[rel] {
			continue
		}
		n, err := countLines(path)
		if err != nil {
			t.Fatalf("guards: count lines in %s: %v", rel, err)
		}
		if n > maxFileLines {
			t.Errorf("%s: %d lines exceeds the %d-line cap (AGENTS.md Mechanical rules: 300-line file cap)", rel, n, maxFileLines)
		}
	}
}

// countLines counts lines the way bufio.Scanner's ScanLines does: each
// newline-terminated line, plus a final line even if it has no trailing
// newline. That is NOT what `wc -l` reports — wc -l counts newline
// characters, so a file whose last line lacks a trailing newline gets
// one fewer from wc than from this. This function's count is the
// stricter of the two (it can only report equal or one higher), and
// gofmt already guarantees a trailing newline on every .go file this
// test walks, so the difference never shows up here in practice.
func countLines(path string) (int, error) {
	f, err := os.Open(path)
	if err != nil {
		return 0, err
	}
	defer f.Close()
	sc := bufio.NewScanner(f)
	sc.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	n := 0
	for sc.Scan() {
		n++
	}
	return n, sc.Err()
}