package recordmirror

import (
	"go/ast"
	"go/parser"
	"go/token"
	"io/fs"
	"os"
	"path/filepath"
	"slices"
	"strconv"
	"strings"
	"testing"

	"github.com/novox/mesh-controller/internal/broker"
)

// mayNameAMirror are the files of the controller that may name a record mirror's bucket outside their tests:
// where the buckets are defined, asserted and granted (internal/broker), the list a reader names in `reads`
// (internal/catalogue/state.go), and each mirror's own writer (this package and the loop that runs it). The
// audit of a mirror against its store (ADR 0289 §4, issue 419) joins this list when it is built.
var mayNameAMirror = []string{
	"cmd/mesh-controller/record_mirrors.go",
	"internal/broker/controller_buckets.go",
	"internal/broker/writers.go",
	"internal/catalogue/state.go",
}

// The packages whose names stand for a mirror, by import path, and the names in each.
const (
	brokerPath       = "github.com/novox/mesh-controller/internal/broker"
	recordmirrorPath = "github.com/novox/mesh-controller/internal/recordmirror"
)

var mirrorNames = map[string][]string{
	brokerPath: {"AssignmentsBucket", "DeclaredConfigBucket", "MirrorAssignments", "MirrorDeclaredConfig",
		"ControllerMirrors"},
	recordmirrorPath: {"Assignments", "DeclaredConfig", "Mirrors"},
}

// **Nothing in the controller reads a mirror to decide anything** (ADR 0289 §19 as ADR 0356 §2 changes it): no
// file of the controller's packages outside its tests names a mirror's bucket but the audit and a mirror's own
// writer. A reader elsewhere fails here, naming the file and what it named.
//
// **What it catches**: a name that stands for a mirror, qualified by the package it comes from under any
// local name the file imports it as (`broker.AssignmentsBucket`, `b.AssignmentsBucket`); the same names bare
// in a file of package broker or package recordmirror; and a string literal holding a mirror's bucket name.
// **What it does not catch**: a bucket name built at run time, such as `BucketName(ControllerSeat,
// "assignments")` or literals concatenated into one, and a mirror reached through a value passed in from an
// allowed file. Those are deliberate evasions rather than ordinary code; a reviewer judges them.
func TestOnlyTheAuditAndAMirrorsWriterReadAMirror(t *testing.T) {
	var buckets []string
	for _, m := range broker.ControllerMirrors() {
		buckets = append(buckets, broker.BucketName(broker.ControllerSeat, m))
	}
	root := filepath.Join("..", "..")
	found := mirrorReaders(t, root, buckets)
	if len(found) > 0 {
		t.Fatalf("a package of the controller reads a record mirror, which only the audit and the mirror's "+
			"writer may (ADR 0289 §19, ADR 0356 §2):\n  %s", strings.Join(found, "\n  "))
	}
}

// **The reader test sees what it says it sees**: in a planted tree, each planted reader is named, and an allowed
// file and a selector on a value are not.
func TestTheReaderTestFindsPlantedReaders(t *testing.T) {
	root := t.TempDir()
	plant := func(path, src string) {
		full := filepath.Join(root, path)
		if err := os.MkdirAll(filepath.Dir(full), 0o755); err != nil {
			t.Fatal(err)
		}
		if err := os.WriteFile(full, []byte(src), 0o644); err != nil {
			t.Fatal(err)
		}
	}
	plant("cmd/mesh-controller/qualified.go", "package main\n\nimport \""+brokerPath+"\"\n\nvar a = broker.AssignmentsBucket\n")
	plant("internal/x/aliased.go", "package x\n\nimport b \""+brokerPath+"\"\n\nvar a = b.DeclaredConfigBucket\n")
	plant("internal/broker/zz_reader.go", "package broker\n\nfunc zzR() string { return AssignmentsBucket }\n")
	plant("internal/inventory/literal.go", "package inventory\n\nvar a = \"mesh-controller_declared-config\"\n")
	plant("internal/y/writer.go", "package y\n\nimport \""+recordmirrorPath+"\"\n\nvar a = recordmirror.Assignments\n")
	// Allowed: a mirror's definition and its writer.
	plant("internal/broker/controller_buckets.go", "package broker\n\nvar AssignmentsBucket = \"x\"\n")
	plant("internal/broker/other.go", "package broker\n\nfunc other() string { return \"nothing\" }\n")
	// A selector on a value (v.AssignmentsBucket) is no use of the mirror, but declaring a field of a mirror's
	// name in package broker is named, on the safe side; and a bare use inside a call under a selector is found.
	plant("internal/broker/field.go", "package broker\n\ntype s struct{ AssignmentsBucket string }\n\nfunc f(v s) string { return v.AssignmentsBucket }\n")
	plant("internal/broker/nested.go", "package broker\n\nfunc g() int { return len(h(DeclaredConfigBucket).x) }\n")
	found := mirrorReaders(t, root, []string{"mesh-controller_assignments", "mesh-controller_declared-config"})
	want := []string{
		"cmd/mesh-controller/qualified.go: broker.AssignmentsBucket",
		"internal/broker/field.go: AssignmentsBucket",
		"internal/broker/nested.go: DeclaredConfigBucket",
		"internal/broker/zz_reader.go: AssignmentsBucket",
		"internal/inventory/literal.go: \"mesh-controller_declared-config\"",
		"internal/x/aliased.go: b.DeclaredConfigBucket",
		"internal/y/writer.go: recordmirror.Assignments",
	}
	slices.Sort(found)
	if !slices.Equal(found, want) {
		t.Errorf("the planted readers were found as\n  %s\nwant\n  %s", strings.Join(found, "\n  "),
			strings.Join(want, "\n  "))
	}
}

// mirrorReaders is every place under root's cmd and internal, outside tests and the allowed files, that names a
// mirror.
func mirrorReaders(t *testing.T, root string, buckets []string) []string {
	t.Helper()
	var found []string
	for _, dir := range []string{"cmd", "internal"} {
		err := filepath.WalkDir(filepath.Join(root, dir), func(path string, e fs.DirEntry, err error) error {
			if err != nil || e.IsDir() || !strings.HasSuffix(path, ".go") || strings.HasSuffix(path, "_test.go") {
				return err
			}
			rel, err := filepath.Rel(root, path)
			if err != nil {
				return err
			}
			rel = filepath.ToSlash(rel)
			if strings.HasPrefix(rel, "internal/recordmirror/") || slices.Contains(mayNameAMirror, rel) {
				return nil
			}
			f, err := parser.ParseFile(token.NewFileSet(), path, nil, 0)
			if err != nil {
				return err
			}
			// Each import's local name, mapped to the package it stands for.
			imported := map[string]string{}
			for _, imp := range f.Imports {
				p, _ := strconv.Unquote(imp.Path.Value)
				if _, ok := mirrorNames[p]; !ok {
					continue
				}
				local := filepath.Base(p)
				if imp.Name != nil {
					local = imp.Name.Name
				}
				imported[local] = p
			}
			// A file of the package that defines the names may use them bare.
			var bare []string
			switch f.Name.Name {
			case "broker":
				bare = mirrorNames[brokerPath]
			case "recordmirror":
				bare = mirrorNames[recordmirrorPath]
			}
			ast.Inspect(f, func(n ast.Node) bool {
				switch n := n.(type) {
				case *ast.SelectorExpr:
					pkg, ok := n.X.(*ast.Ident)
					if !ok {
						return true
					}
					if p, imp := imported[pkg.Name]; imp && slices.Contains(mirrorNames[p], n.Sel.Name) {
						found = append(found, rel+": "+pkg.Name+"."+n.Sel.Name)
					}
					// Neither a selector's own name nor its package is a bare use.
					return false
				case *ast.Ident:
					if slices.Contains(bare, n.Name) {
						found = append(found, rel+": "+n.Name)
					}
				case *ast.BasicLit:
					for _, b := range buckets {
						if n.Kind == token.STRING && strings.Contains(n.Value, b) {
							found = append(found, rel+": "+n.Value)
						}
					}
				}
				return true
			})
			return nil
		})
		if err != nil {
			t.Fatal(err)
		}
	}
	return found
}