package hygiene

import (
	"bufio"
	"go/ast"
	"go/parser"
	"go/token"
	"os"
	"path/filepath"
	"regexp"
	"runtime"
	"sort"
	"strings"
	"testing"
)

const maxGoFileLOC = 500

var goFileNamePattern = regexp.MustCompile(`^[a-z0-9]+(_[a-z0-9]+)*(_test)?\.go$`)

func repoRoot(tb testing.TB) string {
	tb.Helper()
	_, thisFile, _, ok := runtime.Caller(0)
	if !ok {
		tb.Fatalf("unable to resolve caller path")
	}
	return filepath.Clean(filepath.Join(filepath.Dir(thisFile), "..", ".."))
}

func collectGoFiles(tb testing.TB, roots ...string) []string {
	tb.Helper()
	files := make([]string, 0, 128)
	for _, root := range roots {
		err := filepath.WalkDir(root, func(path string, d os.DirEntry, err error) error {
			if err != nil {
				return err
			}
			if d.IsDir() {
				switch d.Name() {
				case ".git", "vendor", "dist", "artifacts", "testdata":
					return filepath.SkipDir
				}
				return nil
			}
			if strings.HasSuffix(path, ".go") {
				files = append(files, path)
			}
			return nil
		})
		if err != nil {
			tb.Fatalf("walk %s: %v", root, err)
		}
	}
	return files
}

// TestHygieneContracts runs one orchestration or CLI step.
// Signature: TestHygieneContracts(t *testing.T).
// Why: Enforces an explicit quality order: doc contracts first, then naming,
// then file-size constraints. That keeps maintainability rules deterministic.
func TestHygieneContracts(t *testing.T) {
	root := repoRoot(t)
	files := collectGoFiles(t, filepath.Join(root, "cmd"), filepath.Join(root, "internal"))
	sort.Strings(files)

	t.Run("doc_contract", func(t *testing.T) {
		checkDocContracts(t, files)
	})
	t.Run("naming_contract", func(t *testing.T) {
		checkNamingContracts(t, files)
	})
	t.Run("loc_limit", func(t *testing.T) {
		checkFileLOCLimits(t, files)
	})
	t.Run("split_module_contract", func(t *testing.T) {
		checkSplitModuleContract(t, root, files)
	})
}

// checkDocContracts runs one orchestration or CLI step.
// Signature: checkDocContracts(t *testing.T, files []string).
// Why: The project requires function-level intent to be explicit so future edits
// preserve behavior and avoid reintroducing drill-time regressions.
func checkDocContracts(t *testing.T, files []string) {
	t.Helper()
	fset := token.NewFileSet()
	for _, file := range files {
		af, err := parser.ParseFile(fset, file, nil, parser.ParseComments)
		if err != nil {
			t.Errorf("parse %s: %v", file, err)
			continue
		}
		for _, decl := range af.Decls {
			fn, ok := decl.(*ast.FuncDecl)
			if !ok {
				continue
			}
			if fn.Doc == nil {
				t.Errorf("%s: function %s is missing doc comment block", file, fn.Name.Name)
				continue
			}
			doc := fn.Doc.Text()
			if !strings.Contains(doc, "Signature:") {
				t.Errorf("%s: function %s doc is missing Signature: contract", file, fn.Name.Name)
			}
			if !strings.Contains(doc, "Why:") {
				t.Errorf("%s: function %s doc is missing Why: contract", file, fn.Name.Name)
			}
		}
	}
}

// checkNamingContracts runs one orchestration or CLI step.
// Signature: checkNamingContracts(t *testing.T, files []string).
// Why: File/module naming consistency is part of maintainability and helps new
// contributors find behavior quickly as the lab and codebase expand.
func checkNamingContracts(t *testing.T, files []string) {
	t.Helper()
	for _, file := range files {
		base := filepath.Base(file)
		if !goFileNamePattern.MatchString(base) {
			t.Errorf("%s: filename %q violates naming contract %s", file, base, goFileNamePattern.String())
		}
	}
}

// checkFileLOCLimits runs one orchestration or CLI step.
// Signature: checkFileLOCLimits(t *testing.T, files []string).
// Why: A strict LOC cap forces focused files and keeps refactors manageable.
func checkFileLOCLimits(t *testing.T, files []string) {
	t.Helper()
	for _, file := range files {
		data, err := os.ReadFile(file)
		if err != nil {
			t.Errorf("read %s: %v", file, err)
			continue
		}
		lineCount := strings.Count(string(data), "\n") + 1
		if lineCount > maxGoFileLOC {
			t.Errorf("%s has %d lines, exceeds %d", file, lineCount, maxGoFileLOC)
		}
	}
}

// checkSplitModuleContract runs one orchestration or CLI step.
// Signature: checkSplitModuleContract(t *testing.T, root string, files []string).
// Why: The long-term test layout requirement is top-level `testing/`; this
// guard freezes the remaining in-tree baseline so new root-module tests cannot
// slip in while the migration continues incrementally and safely.
func checkSplitModuleContract(t *testing.T, root string, files []string) {
	t.Helper()

	allowlistPath := filepath.Join(root, "testing", "hygiene", "in_tree_test_allowlist.txt")
	allowed := loadInTreeTestAllowlist(t, allowlistPath)
	actual := make([]string, 0, len(files))
	for _, file := range files {
		if !strings.HasSuffix(file, "_test.go") {
			continue
		}
		actual = append(actual, mustRepoRelativePath(t, root, file))
	}
	sort.Strings(actual)

	allowedSet := make(map[string]struct{}, len(allowed))
	for _, file := range allowed {
		allowedSet[file] = struct{}{}
	}
	actualSet := make(map[string]struct{}, len(actual))
	for _, file := range actual {
		actualSet[file] = struct{}{}
	}

	unexpected := make([]string, 0)
	for _, file := range actual {
		if _, ok := allowedSet[file]; !ok {
			unexpected = append(unexpected, file)
		}
	}
	missing := make([]string, 0)
	for _, file := range allowed {
		if _, ok := actualSet[file]; !ok {
			missing = append(missing, file)
		}
	}

	if len(unexpected) == 0 && len(missing) == 0 {
		return
	}

	var report strings.Builder
	report.WriteString("split-module contract mismatch\n")
	if len(unexpected) > 0 {
		report.WriteString("unexpected in-tree tests (move them under testing/ or explicitly rebaseline if this is an intentional migration checkpoint):\n")
		for _, file := range unexpected {
			report.WriteString("- " + file + "\n")
		}
	}
	if len(missing) > 0 {
		report.WriteString("stale allowlist entries (remove them from testing/hygiene/in_tree_test_allowlist.txt after a migration):\n")
		for _, file := range missing {
			report.WriteString("- " + file + "\n")
		}
	}
	t.Fatal(report.String())
}

// loadInTreeTestAllowlist runs one orchestration or CLI step.
// Signature: loadInTreeTestAllowlist(t *testing.T, path string) []string.
// Why: The split-module baseline needs one canonical source of truth so the
// gate can distinguish legacy in-tree tests from accidental new ones.
func loadInTreeTestAllowlist(t *testing.T, path string) []string {
	t.Helper()

	f, err := os.Open(path)
	if err != nil {
		t.Fatalf("open in-tree test allowlist %s: %v", path, err)
	}
	defer f.Close()

	entries := make([]string, 0, 64)
	s := bufio.NewScanner(f)
	for s.Scan() {
		line := strings.TrimSpace(s.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		entries = append(entries, filepath.ToSlash(line))
	}
	if err := s.Err(); err != nil {
		t.Fatalf("scan in-tree test allowlist %s: %v", path, err)
	}
	sort.Strings(entries)
	return entries
}

// mustRepoRelativePath runs one orchestration or CLI step.
// Signature: mustRepoRelativePath(t *testing.T, root string, path string) string.
// Why: Relative slash-normalized paths keep split-module hygiene output stable
// across machines and make allowlist diffs easy to review.
func mustRepoRelativePath(t *testing.T, root string, path string) string {
	t.Helper()

	rel, err := filepath.Rel(root, path)
	if err != nil {
		t.Fatalf("make %s relative to %s: %v", path, root, err)
	}
	return filepath.ToSlash(rel)
}