// UNREVIEWED

// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package noder

import (
	"cmd/compile/internal/base"
	"cmd/compile/internal/syntax"
	"cmd/compile/internal/types2"
	"cmd/internal/src"
)

type pkgReader2 struct {
	pkgDecoder

	env     *types2.Environment
	imports map[string]*types2.Package

	posBases []*syntax.PosBase
	pkgs     []*types2.Package
	typs     []types2.Type
}

func readPackage2(env *types2.Environment, imports map[string]*types2.Package, input pkgDecoder) *types2.Package {
	pr := pkgReader2{
		pkgDecoder: input,

		env:     env,
		imports: imports,

		posBases: make([]*syntax.PosBase, input.numElems(relocPosBase)),
		pkgs:     make([]*types2.Package, input.numElems(relocPkg)),
		typs:     make([]types2.Type, input.numElems(relocType)),
	}

	r := pr.newReader(relocMeta, publicRootIdx, syncPublic)
	pkg := r.pkg()
	r.bool() // has init

	for i, n := 0, r.len(); i < n; i++ {
		// As if r.obj(), but avoiding the Scope.Lookup call,
		// to avoid eager loading of imports.
		r.sync(syncObject)
		assert(!r.bool())
		r.p.objIdx(r.reloc(relocObj))
		assert(r.len() == 0)
	}

	r.sync(syncEOF)

	pkg.MarkComplete()
	return pkg
}

type reader2 struct {
	decoder

	p *pkgReader2

	dict *reader2Dict
}

type reader2Dict struct {
	bounds []typeInfo

	tparams []*types2.TypeParam

	derived      []derivedInfo
	derivedTypes []types2.Type
}

type reader2TypeBound struct {
	derived  bool
	boundIdx int
}

func (pr *pkgReader2) newReader(k reloc, idx int, marker syncMarker) *reader2 {
	return &reader2{
		decoder: pr.newDecoder(k, idx, marker),
		p:       pr,
	}
}

// @@@ Positions

func (r *reader2) pos() syntax.Pos {
	r.sync(syncPos)
	if !r.bool() {
		return syntax.Pos{}
	}

	// TODO(mdempsky): Delta encoding.
	posBase := r.posBase()
	line := r.uint()
	col := r.uint()
	return syntax.MakePos(posBase, line, col)
}

func (r *reader2) posBase() *syntax.PosBase {
	return r.p.posBaseIdx(r.reloc(relocPosBase))
}

func (pr *pkgReader2) posBaseIdx(idx int) *syntax.PosBase {
	if b := pr.posBases[idx]; b != nil {
		return b
	}

	r := pr.newReader(relocPosBase, idx, syncPosBase)
	var b *syntax.PosBase

	filename := r.string()

	if r.bool() {
		b = syntax.NewTrimmedFileBase(filename, true)
	} else {
		pos := r.pos()
		line := r.uint()
		col := r.uint()
		b = syntax.NewLineBase(pos, filename, true, line, col)
	}

	pr.posBases[idx] = b
	return b
}

// @@@ Packages

func (r *reader2) pkg() *types2.Package {
	r.sync(syncPkg)
	return r.p.pkgIdx(r.reloc(relocPkg))
}

func (pr *pkgReader2) pkgIdx(idx int) *types2.Package {
	// TODO(mdempsky): Consider using some non-nil pointer to indicate
	// the universe scope, so we don't need to keep re-reading it.
	if pkg := pr.pkgs[idx]; pkg != nil {
		return pkg
	}

	pkg := pr.newReader(relocPkg, idx, syncPkgDef).doPkg()
	pr.pkgs[idx] = pkg
	return pkg
}

func (r *reader2) doPkg() *types2.Package {
	path := r.string()
	if path == "builtin" {
		return nil // universe
	}
	if path == "" {
		path = r.p.pkgPath
	}

	if pkg := r.p.imports[path]; pkg != nil {
		return pkg
	}

	name := r.string()
	height := r.len()

	pkg := types2.NewPackageHeight(path, name, height)
	r.p.imports[path] = pkg

	// TODO(mdempsky): The list of imported packages is important for
	// go/types, but we could probably skip populating it for types2.
	imports := make([]*types2.Package, r.len())
	for i := range imports {
		imports[i] = r.pkg()
	}
	pkg.SetImports(imports)

	return pkg
}

// @@@ Types

func (r *reader2) typ() types2.Type {
	return r.p.typIdx(r.typInfo(), r.dict)
}

func (r *reader2) typInfo() typeInfo {
	r.sync(syncType)
	if r.bool() {
		return typeInfo{idx: r.len(), derived: true}
	}
	return typeInfo{idx: r.reloc(relocType), derived: false}
}

func (pr *pkgReader2) typIdx(info typeInfo, dict *reader2Dict) types2.Type {
	idx := info.idx
	var where *types2.Type
	if info.derived {
		where = &dict.derivedTypes[idx]
		idx = dict.derived[idx].idx
	} else {
		where = &pr.typs[idx]
	}

	if typ := *where; typ != nil {
		return typ
	}

	r := pr.newReader(relocType, idx, syncTypeIdx)
	r.dict = dict

	typ := r.doTyp()
	assert(typ != nil)

	// See comment in pkgReader.typIdx explaining how this happens.
	if prev := *where; prev != nil {
		return prev
	}

	*where = typ
	return typ
}

func (r *reader2) doTyp() (res types2.Type) {
	switch tag := codeType(r.code(syncType)); tag {
	default:
		base.FatalfAt(src.NoXPos, "unhandled type tag: %v", tag)
		panic("unreachable")

	case typeBasic:
		return types2.Typ[r.len()]

	case typeNamed:
		obj, targs := r.obj()
		name := obj.(*types2.TypeName)
		if len(targs) != 0 {
			t, _ := types2.Instantiate(r.p.env, name.Type(), targs, false)
			return t
		}
		return name.Type()

	case typeTypeParam:
		return r.dict.tparams[r.len()]

	case typeArray:
		len := int64(r.uint64())
		return types2.NewArray(r.typ(), len)
	case typeChan:
		dir := types2.ChanDir(r.len())
		return types2.NewChan(dir, r.typ())
	case typeMap:
		return types2.NewMap(r.typ(), r.typ())
	case typePointer:
		return types2.NewPointer(r.typ())
	case typeSignature:
		return r.signature(nil)
	case typeSlice:
		return types2.NewSlice(r.typ())
	case typeStruct:
		return r.structType()
	case typeInterface:
		return r.interfaceType()
	case typeUnion:
		return r.unionType()
	}
}

func (r *reader2) structType() *types2.Struct {
	fields := make([]*types2.Var, r.len())
	var tags []string
	for i := range fields {
		pos := r.pos()
		pkg, name := r.selector()
		ftyp := r.typ()
		tag := r.string()
		embedded := r.bool()

		fields[i] = types2.NewField(pos, pkg, name, ftyp, embedded)
		if tag != "" {
			for len(tags) < i {
				tags = append(tags, "")
			}
			tags = append(tags, tag)
		}
	}
	return types2.NewStruct(fields, tags)
}

func (r *reader2) unionType() *types2.Union {
	terms := make([]*types2.Term, r.len())
	for i := range terms {
		terms[i] = types2.NewTerm(r.bool(), r.typ())
	}
	return types2.NewUnion(terms)
}

func (r *reader2) interfaceType() *types2.Interface {
	methods := make([]*types2.Func, r.len())
	embeddeds := make([]types2.Type, r.len())

	for i := range methods {
		pos := r.pos()
		pkg, name := r.selector()
		mtyp := r.signature(nil)
		methods[i] = types2.NewFunc(pos, pkg, name, mtyp)
	}

	for i := range embeddeds {
		embeddeds[i] = r.typ()
	}

	return types2.NewInterfaceType(methods, embeddeds)
}

func (r *reader2) signature(recv *types2.Var) *types2.Signature {
	r.sync(syncSignature)

	params := r.params()
	results := r.params()
	variadic := r.bool()

	return types2.NewSignature(recv, params, results, variadic)
}

func (r *reader2) params() *types2.Tuple {
	r.sync(syncParams)
	params := make([]*types2.Var, r.len())
	for i := range params {
		params[i] = r.param()
	}
	return types2.NewTuple(params...)
}

func (r *reader2) param() *types2.Var {
	r.sync(syncParam)

	pos := r.pos()
	pkg, name := r.localIdent()
	typ := r.typ()

	return types2.NewParam(pos, pkg, name, typ)
}

// @@@ Objects

func (r *reader2) obj() (types2.Object, []types2.Type) {
	r.sync(syncObject)

	assert(!r.bool())

	pkg, name := r.p.objIdx(r.reloc(relocObj))
	obj := pkg.Scope().Lookup(name)

	targs := make([]types2.Type, r.len())
	for i := range targs {
		targs[i] = r.typ()
	}

	return obj, targs
}

func (pr *pkgReader2) objIdx(idx int) (*types2.Package, string) {
	rname := pr.newReader(relocName, idx, syncObject1)

	objPkg, objName := rname.qualifiedIdent()
	assert(objName != "")

	tag := codeObj(rname.code(syncCodeObj))

	if tag == objStub {
		assert(objPkg == nil || objPkg == types2.Unsafe)
		return objPkg, objName
	}

	dict := pr.objDictIdx(idx)

	r := pr.newReader(relocObj, idx, syncObject1)
	r.dict = dict

	objPkg.Scope().InsertLazy(objName, func() types2.Object {
		switch tag {
		default:
			panic("weird")

		case objAlias:
			pos := r.pos()
			typ := r.typ()
			return types2.NewTypeName(pos, objPkg, objName, typ)

		case objConst:
			pos := r.pos()
			typ := r.typ()
			val := r.value()
			return types2.NewConst(pos, objPkg, objName, typ, val)

		case objFunc:
			pos := r.pos()
			tparams := r.typeParamNames()
			sig := r.signature(nil)
			sig.SetTypeParams(tparams)
			return types2.NewFunc(pos, objPkg, objName, sig)

		case objType:
			pos := r.pos()

			return types2.NewTypeNameLazy(pos, objPkg, objName, func(named *types2.Named) (tparams []*types2.TypeParam, underlying types2.Type, methods []*types2.Func) {
				tparams = r.typeParamNames()

				// TODO(mdempsky): Rewrite receiver types to underlying is an
				// Interface? The go/types importer does this (I think because
				// unit tests expected that), but cmd/compile doesn't care
				// about it, so maybe we can avoid worrying about that here.
				underlying = r.typ().Underlying()

				methods = make([]*types2.Func, r.len())
				for i := range methods {
					methods[i] = r.method()
				}

				return
			})

		case objVar:
			pos := r.pos()
			typ := r.typ()
			return types2.NewVar(pos, objPkg, objName, typ)
		}
	})

	return objPkg, objName
}

func (pr *pkgReader2) objDictIdx(idx int) *reader2Dict {
	r := pr.newReader(relocObjDict, idx, syncObject1)

	var dict reader2Dict

	if implicits := r.len(); implicits != 0 {
		base.Fatalf("unexpected object with %v implicit type parameter(s)", implicits)
	}

	dict.bounds = make([]typeInfo, r.len())
	for i := range dict.bounds {
		dict.bounds[i] = r.typInfo()
	}

	dict.derived = make([]derivedInfo, r.len())
	dict.derivedTypes = make([]types2.Type, len(dict.derived))
	for i := range dict.derived {
		dict.derived[i] = derivedInfo{r.reloc(relocType), r.bool()}
	}

	// function references follow, but reader2 doesn't need those

	return &dict
}

func (r *reader2) typeParamNames() []*types2.TypeParam {
	r.sync(syncTypeParamNames)

	// Note: This code assumes it only processes objects without
	// implement type parameters. This is currently fine, because
	// reader2 is only used to read in exported declarations, which are
	// always package scoped.

	if len(r.dict.bounds) == 0 {
		return nil
	}

	// Careful: Type parameter lists may have cycles. To allow for this,
	// we construct the type parameter list in two passes: first we
	// create all the TypeNames and TypeParams, then we construct and
	// set the bound type.

	r.dict.tparams = make([]*types2.TypeParam, len(r.dict.bounds))
	for i := range r.dict.bounds {
		pos := r.pos()
		pkg, name := r.localIdent()

		tname := types2.NewTypeName(pos, pkg, name, nil)
		r.dict.tparams[i] = types2.NewTypeParam(tname, nil)
	}

	for i, bound := range r.dict.bounds {
		r.dict.tparams[i].SetConstraint(r.p.typIdx(bound, r.dict))
	}

	return r.dict.tparams
}

func (r *reader2) method() *types2.Func {
	r.sync(syncMethod)
	pos := r.pos()
	pkg, name := r.selector()

	rparams := r.typeParamNames()
	sig := r.signature(r.param())
	sig.SetRecvTypeParams(rparams)

	_ = r.pos() // TODO(mdempsky): Remove; this is a hacker for linker.go.
	return types2.NewFunc(pos, pkg, name, sig)
}

func (r *reader2) qualifiedIdent() (*types2.Package, string) { return r.ident(syncSym) }
func (r *reader2) localIdent() (*types2.Package, string)     { return r.ident(syncLocalIdent) }
func (r *reader2) selector() (*types2.Package, string)       { return r.ident(syncSelector) }

func (r *reader2) ident(marker syncMarker) (*types2.Package, string) {
	r.sync(marker)
	return r.pkg(), r.string()
}