// Copyright 2020 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 golang

import (
	"bytes"
	"context"
	"fmt"
	"go/ast"
	"go/doc"
	"go/printer"
	"go/token"
	"go/types"
	"strings"

	"golang.org/x/tools/gopls/internal/cache"
	"golang.org/x/tools/gopls/internal/protocol"
	"golang.org/x/tools/gopls/internal/settings"
	"golang.org/x/tools/gopls/internal/util/bug"
	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/event/tag"
	"golang.org/x/tools/internal/tokeninternal"
	"golang.org/x/tools/internal/typeparams"
)

// FormatType returns the detail and kind for a types.Type.
func FormatType(typ types.Type, qf types.Qualifier) (detail string, kind protocol.CompletionItemKind) {
	if types.IsInterface(typ) {
		detail = "interface{...}"
		kind = protocol.InterfaceCompletion
	} else if _, ok := typ.(*types.Struct); ok {
		detail = "struct{...}"
		kind = protocol.StructCompletion
	} else if typ != typ.Underlying() {
		detail, kind = FormatType(typ.Underlying(), qf)
	} else {
		detail = types.TypeString(typ, qf)
		kind = protocol.ClassCompletion
	}
	return detail, kind
}

type signature struct {
	name, doc                   string
	typeParams, params, results []string
	variadic                    bool
	needResultParens            bool
}

func (s *signature) Format() string {
	var b strings.Builder
	b.WriteByte('(')
	for i, p := range s.params {
		if i > 0 {
			b.WriteString(", ")
		}
		b.WriteString(p)
	}
	b.WriteByte(')')

	// Add space between parameters and results.
	if len(s.results) > 0 {
		b.WriteByte(' ')
	}
	if s.needResultParens {
		b.WriteByte('(')
	}
	for i, r := range s.results {
		if i > 0 {
			b.WriteString(", ")
		}
		b.WriteString(r)
	}
	if s.needResultParens {
		b.WriteByte(')')
	}
	return b.String()
}

func (s *signature) TypeParams() []string {
	return s.typeParams
}

func (s *signature) Params() []string {
	return s.params
}

// NewBuiltinSignature returns signature for the builtin object with a given
// name, if a builtin object with the name exists.
func NewBuiltinSignature(ctx context.Context, s *cache.Snapshot, name string) (*signature, error) {
	builtin, err := s.BuiltinFile(ctx)
	if err != nil {
		return nil, err
	}
	obj := builtin.File.Scope.Lookup(name)
	if obj == nil {
		return nil, fmt.Errorf("no builtin object for %s", name)
	}
	decl, ok := obj.Decl.(*ast.FuncDecl)
	if !ok {
		return nil, fmt.Errorf("no function declaration for builtin: %s", name)
	}
	if decl.Type == nil {
		return nil, fmt.Errorf("no type for builtin decl %s", decl.Name)
	}
	var variadic bool
	if decl.Type.Params.List != nil {
		numParams := len(decl.Type.Params.List)
		lastParam := decl.Type.Params.List[numParams-1]
		if _, ok := lastParam.Type.(*ast.Ellipsis); ok {
			variadic = true
		}
	}
	fset := tokeninternal.FileSetFor(builtin.Tok)
	params, _ := formatFieldList(ctx, fset, decl.Type.Params, variadic)
	results, needResultParens := formatFieldList(ctx, fset, decl.Type.Results, false)
	d := decl.Doc.Text()
	switch s.Options().HoverKind {
	case settings.SynopsisDocumentation:
		d = doc.Synopsis(d)
	case settings.NoDocumentation:
		d = ""
	}
	return &signature{
		doc:              d,
		name:             name,
		needResultParens: needResultParens,
		params:           params,
		results:          results,
		variadic:         variadic,
	}, nil
}

// replacer replaces some synthetic "type classes" used in the builtin file
// with their most common constituent type.
var replacer = strings.NewReplacer(
	`ComplexType`, `complex128`,
	`FloatType`, `float64`,
	`IntegerType`, `int`,
)

func formatFieldList(ctx context.Context, fset *token.FileSet, list *ast.FieldList, variadic bool) ([]string, bool) {
	if list == nil {
		return nil, false
	}
	var writeResultParens bool
	var result []string
	for i := 0; i < len(list.List); i++ {
		if i >= 1 {
			writeResultParens = true
		}
		p := list.List[i]
		cfg := printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 4}
		b := &bytes.Buffer{}
		if err := cfg.Fprint(b, fset, p.Type); err != nil {
			event.Error(ctx, "unable to print type", nil, tag.Type.Of(p.Type))
			continue
		}
		typ := replacer.Replace(b.String())
		if len(p.Names) == 0 {
			result = append(result, typ)
		}
		for _, name := range p.Names {
			if name.Name != "" {
				if i == 0 {
					writeResultParens = true
				}
				result = append(result, fmt.Sprintf("%s %s", name.Name, typ))
			} else {
				result = append(result, typ)
			}
		}
	}
	if variadic {
		result[len(result)-1] = strings.Replace(result[len(result)-1], "[]", "...", 1)
	}
	return result, writeResultParens
}

// FormatTypeParams turns TypeParamList into its Go representation, such as:
// [T, Y]. Note that it does not print constraints as this is mainly used for
// formatting type params in method receivers.
func FormatTypeParams(tparams *types.TypeParamList) string {
	if tparams == nil || tparams.Len() == 0 {
		return ""
	}
	var buf bytes.Buffer
	buf.WriteByte('[')
	for i := 0; i < tparams.Len(); i++ {
		if i > 0 {
			buf.WriteString(", ")
		}
		buf.WriteString(tparams.At(i).Obj().Name())
	}
	buf.WriteByte(']')
	return buf.String()
}

// NewSignature returns formatted signature for a types.Signature struct.
func NewSignature(ctx context.Context, s *cache.Snapshot, pkg *cache.Package, sig *types.Signature, comment *ast.CommentGroup, qf types.Qualifier, mq MetadataQualifier) (*signature, error) {
	var tparams []string
	tpList := sig.TypeParams()
	for i := 0; i < tpList.Len(); i++ {
		tparam := tpList.At(i)
		// TODO: is it possible to reuse the logic from FormatVarType here?
		s := tparam.Obj().Name() + " " + tparam.Constraint().String()
		tparams = append(tparams, s)
	}

	params := make([]string, 0, sig.Params().Len())
	for i := 0; i < sig.Params().Len(); i++ {
		el := sig.Params().At(i)
		typ, err := FormatVarType(ctx, s, pkg, el, qf, mq)
		if err != nil {
			return nil, err
		}
		p := typ
		if el.Name() != "" {
			p = el.Name() + " " + typ
		}
		params = append(params, p)
	}

	var needResultParens bool
	results := make([]string, 0, sig.Results().Len())
	for i := 0; i < sig.Results().Len(); i++ {
		if i >= 1 {
			needResultParens = true
		}
		el := sig.Results().At(i)
		typ, err := FormatVarType(ctx, s, pkg, el, qf, mq)
		if err != nil {
			return nil, err
		}
		if el.Name() == "" {
			results = append(results, typ)
		} else {
			if i == 0 {
				needResultParens = true
			}
			results = append(results, el.Name()+" "+typ)
		}
	}
	var d string
	if comment != nil {
		d = comment.Text()
	}
	switch s.Options().HoverKind {
	case settings.SynopsisDocumentation:
		d = doc.Synopsis(d)
	case settings.NoDocumentation:
		d = ""
	}
	return &signature{
		doc:              d,
		typeParams:       tparams,
		params:           params,
		results:          results,
		variadic:         sig.Variadic(),
		needResultParens: needResultParens,
	}, nil
}

// FormatVarType formats a *types.Var, accounting for type aliases.
// To do this, it looks in the AST of the file in which the object is declared.
// On any errors, it always falls back to types.TypeString.
//
// TODO(rfindley): this function could return the actual name used in syntax,
// for better parameter names.
func FormatVarType(ctx context.Context, snapshot *cache.Snapshot, srcpkg *cache.Package, obj *types.Var, qf types.Qualifier, mq MetadataQualifier) (string, error) {
	// TODO(rfindley): This looks wrong. The previous comment said:
	// "If the given expr refers to a type parameter, then use the
	// object's Type instead of the type parameter declaration. This helps
	// format the instantiated type as opposed to the original undeclared
	// generic type".
	//
	// But of course, if obj is a type param, we are formatting a generic type
	// and not an instantiated type. Handling for instantiated types must be done
	// at a higher level.
	//
	// Left this during refactoring in order to preserve pre-existing logic.
	if typeparams.IsTypeParam(obj.Type()) {
		return types.TypeString(obj.Type(), qf), nil
	}

	if obj.Pkg() == nil || !obj.Pos().IsValid() {
		// This is defensive, though it is extremely unlikely we'll ever have a
		// builtin var.
		return types.TypeString(obj.Type(), qf), nil
	}

	// TODO(rfindley): parsing to produce candidates can be costly; consider
	// using faster methods.
	targetpgf, pos, err := parseFull(ctx, snapshot, srcpkg.FileSet(), obj.Pos())
	if err != nil {
		return "", err // e.g. ctx cancelled
	}

	targetMeta := findFileInDeps(snapshot, srcpkg.Metadata(), targetpgf.URI)
	if targetMeta == nil {
		// If we have an object from type-checking, it should exist in a file in
		// the forward transitive closure.
		return "", bug.Errorf("failed to find file %q in deps of %q", targetpgf.URI, srcpkg.Metadata().ID)
	}

	decl, spec, field := findDeclInfo([]*ast.File{targetpgf.File}, pos)

	// We can't handle type parameters correctly, so we fall back on TypeString
	// for parameterized decls.
	if decl, _ := decl.(*ast.FuncDecl); decl != nil {
		if decl.Type.TypeParams.NumFields() > 0 {
			return types.TypeString(obj.Type(), qf), nil // in generic function
		}
		if decl.Recv != nil && len(decl.Recv.List) > 0 {
			rtype := decl.Recv.List[0].Type
			if e, ok := rtype.(*ast.StarExpr); ok {
				rtype = e.X
			}
			if x, _, _, _ := typeparams.UnpackIndexExpr(rtype); x != nil {
				return types.TypeString(obj.Type(), qf), nil // in method of generic type
			}
		}
	}
	if spec, _ := spec.(*ast.TypeSpec); spec != nil && spec.TypeParams.NumFields() > 0 {
		return types.TypeString(obj.Type(), qf), nil // in generic type decl
	}

	if field == nil {
		// TODO(rfindley): we should never reach here from an ordinary var, so
		// should probably return an error here.
		return types.TypeString(obj.Type(), qf), nil
	}
	expr := field.Type

	rq := requalifier(snapshot, targetpgf.File, targetMeta, mq)

	// The type names in the AST may not be correctly qualified.
	// Determine the package name to use based on the package that originated
	// the query and the package in which the type is declared.
	// We then qualify the value by cloning the AST node and editing it.
	expr = qualifyTypeExpr(expr, rq)

	// If the request came from a different package than the one in which the
	// types are defined, we may need to modify the qualifiers.
	return FormatNodeFile(targetpgf.Tok, expr), nil
}

// qualifyTypeExpr clones the type expression expr after re-qualifying type
// names using the given function, which accepts the current syntactic
// qualifier (possibly "" for unqualified idents), and returns a new qualifier
// (again, possibly "" if the identifier should be unqualified).
//
// The resulting expression may be inaccurate: without type-checking we don't
// properly account for "." imported identifiers or builtins.
//
// TODO(rfindley): add many more tests for this function.
func qualifyTypeExpr(expr ast.Expr, qf func(string) string) ast.Expr {
	switch expr := expr.(type) {
	case *ast.ArrayType:
		return &ast.ArrayType{
			Lbrack: expr.Lbrack,
			Elt:    qualifyTypeExpr(expr.Elt, qf),
			Len:    expr.Len,
		}

	case *ast.BinaryExpr:
		if expr.Op != token.OR {
			return expr
		}
		return &ast.BinaryExpr{
			X:     qualifyTypeExpr(expr.X, qf),
			OpPos: expr.OpPos,
			Op:    expr.Op,
			Y:     qualifyTypeExpr(expr.Y, qf),
		}

	case *ast.ChanType:
		return &ast.ChanType{
			Arrow: expr.Arrow,
			Begin: expr.Begin,
			Dir:   expr.Dir,
			Value: qualifyTypeExpr(expr.Value, qf),
		}

	case *ast.Ellipsis:
		return &ast.Ellipsis{
			Ellipsis: expr.Ellipsis,
			Elt:      qualifyTypeExpr(expr.Elt, qf),
		}

	case *ast.FuncType:
		return &ast.FuncType{
			Func:    expr.Func,
			Params:  qualifyFieldList(expr.Params, qf),
			Results: qualifyFieldList(expr.Results, qf),
		}

	case *ast.Ident:
		// Unqualified type (builtin, package local, or dot-imported).

		// Don't qualify names that look like builtins.
		//
		// Without type-checking this may be inaccurate. It could be made accurate
		// by doing syntactic object resolution for the entire package, but that
		// does not seem worthwhile and we generally want to avoid using
		// ast.Object, which may be inaccurate.
		if obj := types.Universe.Lookup(expr.Name); obj != nil {
			return expr
		}

		newName := qf("")
		if newName != "" {
			return &ast.SelectorExpr{
				X: &ast.Ident{
					NamePos: expr.Pos(),
					Name:    newName,
				},
				Sel: expr,
			}
		}
		return expr

	case *ast.IndexExpr:
		return &ast.IndexExpr{
			X:      qualifyTypeExpr(expr.X, qf),
			Lbrack: expr.Lbrack,
			Index:  qualifyTypeExpr(expr.Index, qf),
			Rbrack: expr.Rbrack,
		}

	case *ast.IndexListExpr:
		indices := make([]ast.Expr, len(expr.Indices))
		for i, idx := range expr.Indices {
			indices[i] = qualifyTypeExpr(idx, qf)
		}
		return &ast.IndexListExpr{
			X:       qualifyTypeExpr(expr.X, qf),
			Lbrack:  expr.Lbrack,
			Indices: indices,
			Rbrack:  expr.Rbrack,
		}

	case *ast.InterfaceType:
		return &ast.InterfaceType{
			Interface:  expr.Interface,
			Methods:    qualifyFieldList(expr.Methods, qf),
			Incomplete: expr.Incomplete,
		}

	case *ast.MapType:
		return &ast.MapType{
			Map:   expr.Map,
			Key:   qualifyTypeExpr(expr.Key, qf),
			Value: qualifyTypeExpr(expr.Value, qf),
		}

	case *ast.ParenExpr:
		return &ast.ParenExpr{
			Lparen: expr.Lparen,
			Rparen: expr.Rparen,
			X:      qualifyTypeExpr(expr.X, qf),
		}

	case *ast.SelectorExpr:
		if id, ok := expr.X.(*ast.Ident); ok {
			// qualified type
			newName := qf(id.Name)
			if newName == "" {
				return expr.Sel
			}
			return &ast.SelectorExpr{
				X: &ast.Ident{
					NamePos: id.NamePos,
					Name:    newName,
				},
				Sel: expr.Sel,
			}
		}
		return expr

	case *ast.StarExpr:
		return &ast.StarExpr{
			Star: expr.Star,
			X:    qualifyTypeExpr(expr.X, qf),
		}

	case *ast.StructType:
		return &ast.StructType{
			Struct:     expr.Struct,
			Fields:     qualifyFieldList(expr.Fields, qf),
			Incomplete: expr.Incomplete,
		}

	default:
		return expr
	}
}

func qualifyFieldList(fl *ast.FieldList, qf func(string) string) *ast.FieldList {
	if fl == nil {
		return nil
	}
	if fl.List == nil {
		return &ast.FieldList{
			Closing: fl.Closing,
			Opening: fl.Opening,
		}
	}
	list := make([]*ast.Field, 0, len(fl.List))
	for _, f := range fl.List {
		list = append(list, &ast.Field{
			Comment: f.Comment,
			Doc:     f.Doc,
			Names:   f.Names,
			Tag:     f.Tag,
			Type:    qualifyTypeExpr(f.Type, qf),
		})
	}
	return &ast.FieldList{
		Closing: fl.Closing,
		Opening: fl.Opening,
		List:    list,
	}
}