package gen

import (
	"path"
	"strings"

	"google.golang.org/protobuf/reflect/protoreflect"
)

// luaPackagePath returns the dotted Lua require path for a generated file.
//
// Resolution order:
//  1. file option (tarantool.lua_package), used as-is
//  2. proto package + file basename + "_pb"
//     e.g. package=foo.bar, file=baz.proto -> "foo.bar.baz_pb"
//  3. file basename only (when proto package is empty)
//     e.g. file=baz.proto -> "baz_pb"
func luaPackagePath(f protoreflect.FileDescriptor, prefix string) string {
	var p string
	if v := luaPackageOption(f); v != "" {
		p = v
	} else {
		base := strings.TrimSuffix(path.Base(f.Path()), ".proto") + "_pb"
		if pkg := string(f.Package()); pkg != "" {
			p = pkg + "." + base
		} else {
			p = base
		}
	}
	if prefix != "" {
		return prefix + "." + p
	}
	return p
}

// outputFilename returns the on-disk path (relative to the protoc out dir)
// for a generated file. Mirrors the dotted Lua require path with `/`-separators
// and a `.lua` extension.
//
// For example, lua package "myapp.proto.foo" -> "myapp/proto/foo.lua".
func outputFilename(f protoreflect.FileDescriptor, prefix string) string {
	return strings.ReplaceAll(luaPackagePath(f, prefix), ".", "/") + ".lua"
}

// luaTypeName returns the underscore-flattened type name used in generated
// Lua module tables. Strips the leading proto-package prefix.
//
// Examples (assuming file package = "foo.bar"):
//   foo.bar.Person          -> "Person"
//   foo.bar.Outer.Inner     -> "Outer_Inner"
//   foo.bar.Color           -> "Color"
func luaTypeName(fullName protoreflect.FullName, filePkg protoreflect.FullName) string {
	s := string(fullName)
	if filePkg != "" {
		prefix := string(filePkg) + "."
		s = strings.TrimPrefix(s, prefix)
	}
	return strings.ReplaceAll(s, ".", "_")
}

// importAlias produces a stable Lua local-variable name for a required module.
// It dot-separates the module path and joins with underscores, prefixed with
// "_imp_" to avoid clashing with user identifiers.
//
//	"myapp.proto.foo" -> "_imp_myapp_proto_foo"
func importAlias(luaPath string) string {
	return "_imp_" + strings.ReplaceAll(luaPath, ".", "_")
}

// isWellKnownTypeFile reports whether the file declares Google's
// google.protobuf.* well-known types. Those are fulfilled by `pb.wkt`
// at runtime and don't need a separate generated module.
func isWellKnownTypeFile(fd protoreflect.FileDescriptor) bool {
	return string(fd.Package()) == "google.protobuf"
}

// wktTypeName strips the `google.protobuf.` prefix from a WKT type's full
// name. Example: "google.protobuf.Timestamp" -> "Timestamp".
func wktTypeName(full protoreflect.FullName) string {
	return strings.TrimPrefix(string(full), "google.protobuf.")
}