// Copyright 2018 The CUE Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package cue

import (
	"path"
	"strconv"
	"sync"

	"cuelang.org/go/cue/ast"
	"cuelang.org/go/cue/build"
	"cuelang.org/go/cue/errors"
	"cuelang.org/go/cue/token"
	"cuelang.org/go/internal"
)

// A Runtime is used for creating CUE interpretations.
//
// Any operation that involves two Values or Instances should originate from
// the same Runtime.
//
// The zero value of a Runtime is ready to use.
type Runtime struct {
	ctx *build.Context // TODO: remove
	idx *index
}

func init() {
	internal.GetRuntime = func(instance interface{}) interface{} {
		switch x := instance.(type) {
		case Value:
			return &Runtime{idx: x.idx}

		case *Instance:
			return &Runtime{idx: x.index}

		default:
			panic("argument must be Value or *Instance")
		}
	}

	internal.CheckAndForkRuntime = func(runtime, value interface{}) interface{} {
		r := runtime.(*Runtime)
		idx := value.(Value).ctx().index
		if idx != r.idx {
			panic("value not from same runtime")
		}
		return &Runtime{idx: newIndex(idx)}
	}
}

func dummyLoad(token.Pos, string) *build.Instance { return nil }

func (r *Runtime) index() *index {
	if r.idx == nil {
		r.idx = newIndex(sharedIndex)
	}
	return r.idx
}

func (r *Runtime) buildContext() *build.Context {
	ctx := r.ctx
	if r.ctx == nil {
		ctx = build.NewContext()
	}
	return ctx
}

func (r *Runtime) complete(p *build.Instance) (*Instance, error) {
	idx := r.index()
	if err := p.Complete(); err != nil {
		return nil, err
	}
	inst := idx.loadInstance(p)
	inst.ImportPath = p.ImportPath
	if inst.Err != nil {
		return nil, inst.Err
	}
	return inst, nil
}

// Compile compiles the given source into an Instance. The source code may be
// provided as a string, byte slice, io.Reader. The name is used as the file
// name in position information. The source may import builtin packages. Use
// Build to allow importing non-builtin packages.
func (r *Runtime) Compile(filename string, source interface{}) (*Instance, error) {
	ctx := r.buildContext()
	p := ctx.NewInstance(filename, dummyLoad)
	if err := p.AddFile(filename, source); err != nil {
		return nil, p.Err
	}
	return r.complete(p)
}

// CompileFile compiles the given source file into an Instance. The source may
// import builtin packages. Use Build to allow importing non-builtin packages.
func (r *Runtime) CompileFile(file *ast.File) (*Instance, error) {
	ctx := r.buildContext()
	p := ctx.NewInstance(file.Filename, dummyLoad)
	err := p.AddSyntax(file)
	if err != nil {
		return nil, err
	}
	_, p.PkgName, _ = internal.PackageInfo(file)
	return r.complete(p)
}

// CompileExpr compiles the given source expression into an Instance. The source
// may import builtin packages. Use Build to allow importing non-builtin
// packages.
func (r *Runtime) CompileExpr(expr ast.Expr) (*Instance, error) {
	ctx := r.buildContext()
	p := ctx.NewInstance("", dummyLoad)
	switch x := expr.(type) {
	case *ast.StructLit:
		_ = p.AddSyntax(&ast.File{Decls: x.Elts})
	default:
		_ = p.AddSyntax(&ast.File{
			Decls: []ast.Decl{&ast.EmbedDecl{Expr: expr}},
		})
	}
	if p.Err != nil {
		return nil, p.Err
	}
	return r.complete(p)
}

// Parse parses a CUE source value into a CUE Instance. The source code may
// be provided as a string, byte slice, or io.Reader. The name is used as the
// file name in position information. The source may import builtin packages.
//
// Deprecated: use Compile
func (r *Runtime) Parse(name string, source interface{}) (*Instance, error) {
	return r.Compile(name, source)
}

// Build creates an Instance from the given build.Instance. A returned Instance
// may be incomplete, in which case its Err field is set.
func (r *Runtime) Build(instance *build.Instance) (*Instance, error) {
	return r.complete(instance)
}

// Build creates one Instance for each build.Instance. A returned Instance
// may be incomplete, in which case its Err field is set.
//
// Example:
//	inst := cue.Build(load.Instances(args))
//
func Build(instances []*build.Instance) []*Instance {
	if len(instances) == 0 {
		panic("cue: list of instances must not be empty")
	}
	var r Runtime
	a, _ := r.build(instances)
	return a
}

func (r *Runtime) build(instances []*build.Instance) ([]*Instance, error) {
	index := r.index()

	loaded := []*Instance{}

	var errs errors.Error

	for _, p := range instances {
		_ = p.Complete()
		errs = errors.Append(errs, p.Err)

		i := index.loadInstance(p)
		errs = errors.Append(errs, i.Err)
		loaded = append(loaded, i)
	}

	// TODO: insert imports
	return loaded, errs
}

// FromExpr creates an instance from an expression.
// Any references must be resolved beforehand.
//
// Deprecated: use CompileExpr
func (r *Runtime) FromExpr(expr ast.Expr) (*Instance, error) {
	i := r.index().newInstance(nil)
	err := i.insertFile(&ast.File{
		Decls: []ast.Decl{&ast.EmbedDecl{Expr: expr}},
	})
	if err != nil {
		return nil, err
	}
	return i, nil
}

// index maps conversions from label names to internal codes.
//
// All instances belonging to the same package should share this index.
type index struct {
	labelMap map[string]label
	labels   []string

	loaded        map[*build.Instance]*Instance
	imports       map[value]*Instance // key is always a *structLit
	importsByPath map[string]*Instance

	offset label
	parent *index

	mutex     sync.Mutex
	typeCache sync.Map // map[reflect.Type]evaluated
}

// work around golang-ci linter bug: fields are used.
func init() {
	var i index
	i.mutex.Lock()
	i.mutex.Unlock()
	i.typeCache.Load(1)
}

const sharedOffset = 0x40000000

// sharedIndex is used for indexing builtins and any other labels common to
// all instances.
var sharedIndex = newSharedIndex()

func newSharedIndex() *index {
	// TODO: nasty hack to indicate FileSet of shared index. Remove the whole
	// FileSet idea from the API. Just take the hit of the extra pointers for
	// positions in the ast, and then optimize the storage in an abstract
	// machine implementation for storing graphs.
	token.NewFile("dummy", sharedOffset, 0)
	i := &index{
		labelMap:      map[string]label{"": 0},
		labels:        []string{""},
		imports:       map[value]*Instance{},
		importsByPath: map[string]*Instance{},
	}
	return i
}

// newIndex creates a new index.
func newIndex(parent *index) *index {
	i := &index{
		labelMap:      map[string]label{},
		loaded:        map[*build.Instance]*Instance{},
		imports:       map[value]*Instance{},
		importsByPath: map[string]*Instance{},
		offset:        label(len(parent.labels)) + parent.offset,
		parent:        parent,
	}
	return i
}

func (idx *index) strLabel(str string) label {
	return idx.label(str, false)
}

func (idx *index) nodeLabel(n ast.Node) (f label, ok bool) {
	switch x := n.(type) {
	case *ast.BasicLit:
		name, _, err := ast.LabelName(x)
		return idx.label(name, false), err == nil
	case *ast.Ident:
		name, err := ast.ParseIdent(x)
		return idx.label(name, true), err == nil
	}
	return 0, false
}

func (idx *index) findLabel(s string) (f label, ok bool) {
	for x := idx; x != nil; x = x.parent {
		f, ok = x.labelMap[s]
		if ok {
			break
		}
	}
	return f, ok
}

func (idx *index) label(s string, isIdent bool) label {
	f, ok := idx.findLabel(s)
	if !ok {
		f = label(len(idx.labelMap)) + idx.offset
		idx.labelMap[s] = f
		idx.labels = append(idx.labels, s)
	}
	f <<= 1
	if isIdent && s != "" && s[0] == '_' {
		f |= 1
	}
	return f
}

func (idx *index) labelStr(l label) string {
	l >>= 1
	for ; l < idx.offset; idx = idx.parent {
	}
	return idx.labels[l-idx.offset]
}

func (idx *index) loadInstance(p *build.Instance) *Instance {
	if inst := idx.loaded[p]; inst != nil {
		if !inst.complete {
			// cycles should be detected by the builder and it should not be
			// possible to construct a build.Instance that has them.
			panic("cue: cycle")
		}
		return inst
	}
	files := p.Files
	inst := idx.newInstance(p)
	if inst.Err == nil {
		// inst.instance.index.state = s
		// inst.instance.inst = p
		inst.Err = resolveFiles(idx, p)
		for _, f := range files {
			err := inst.insertFile(f)
			inst.Err = errors.Append(inst.Err, err)
		}
	}
	inst.ImportPath = p.ImportPath

	inst.complete = true
	return inst
}

func lineStr(idx *index, n ast.Node) string {
	return n.Pos().String()
}

func resolveFiles(idx *index, p *build.Instance) errors.Error {
	// Link top-level declarations. As top-level entries get unified, an entry
	// may be linked to any top-level entry of any of the files.
	allFields := map[string]ast.Node{}
	for _, file := range p.Files {
		for _, d := range file.Decls {
			if f, ok := d.(*ast.Field); ok && f.Value != nil {
				if ident, ok := f.Label.(*ast.Ident); ok {
					allFields[ident.Name] = f.Value
				}
			}
		}
	}
	for _, f := range p.Files {
		if err := resolveFile(idx, f, p, allFields); err != nil {
			return err
		}
	}
	return nil
}

func resolveFile(idx *index, f *ast.File, p *build.Instance, allFields map[string]ast.Node) errors.Error {
	unresolved := map[string][]*ast.Ident{}
	for _, u := range f.Unresolved {
		unresolved[u.Name] = append(unresolved[u.Name], u)
	}
	fields := map[string]ast.Node{}
	for _, d := range f.Decls {
		if f, ok := d.(*ast.Field); ok && f.Value != nil {
			if ident, ok := f.Label.(*ast.Ident); ok {
				fields[ident.Name] = d
			}
		}
	}
	var errs errors.Error

	specs := []*ast.ImportSpec{}

	for _, spec := range f.Imports {
		id, err := strconv.Unquote(spec.Path.Value)
		if err != nil {
			continue // quietly ignore the error
		}
		name := path.Base(id)
		if imp := p.LookupImport(id); imp != nil {
			name = imp.PkgName
		} else if _, ok := builtins[id]; !ok {
			errs = errors.Append(errs,
				nodeErrorf(spec, "package %q not found", id))
			continue
		}
		if spec.Name != nil {
			name = spec.Name.Name
		}
		if n, ok := fields[name]; ok {
			errs = errors.Append(errs, nodeErrorf(spec,
				"%s redeclared as imported package name\n"+
					"\tprevious declaration at %v", name, lineStr(idx, n)))
			continue
		}
		fields[name] = spec
		used := false
		for _, u := range unresolved[name] {
			used = true
			u.Node = spec
		}
		if !used {
			specs = append(specs, spec)
		}
	}

	// Verify each import is used.
	if len(specs) > 0 {
		// Find references to imports. This assumes that identifiers in labels
		// are not resolved or that such errors are caught elsewhere.
		ast.Walk(f, nil, func(n ast.Node) {
			if x, ok := n.(*ast.Ident); ok {
				// As we also visit labels, most nodes will be nil.
				if x.Node == nil {
					return
				}
				for i, s := range specs {
					if s == x.Node {
						specs[i] = nil
						return
					}
				}
			}
		})

		// Add errors for unused imports.
		for _, spec := range specs {
			if spec == nil {
				continue
			}
			if spec.Name == nil {
				errs = errors.Append(errs, nodeErrorf(spec,
					"imported and not used: %s", spec.Path.Value))
			} else {
				errs = errors.Append(errs, nodeErrorf(spec,
					"imported and not used: %s as %s", spec.Path.Value, spec.Name))
			}
		}
	}

	k := 0
	for _, u := range f.Unresolved {
		if u.Node != nil {
			continue
		}
		if n, ok := allFields[u.Name]; ok {
			u.Node = n
			u.Scope = f
			continue
		}
		f.Unresolved[k] = u
		k++
	}
	f.Unresolved = f.Unresolved[:k]
	// TODO: also need to resolve types.
	// if len(f.Unresolved) > 0 {
	// 	n := f.Unresolved[0]
	// 	return ctx.mkErr(newBase(n), "unresolved reference %s", n.Name)
	// }
	return errs
}