// Copyright 2022 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 (
	"cmp"
	"context"
	"fmt"
	"go/ast"
	"go/constant"
	"go/token"
	"go/types"
	"slices"
	"strings"

	"golang.org/x/tools/go/ast/inspector"
	"golang.org/x/tools/go/types/typeutil"
	"golang.org/x/tools/gopls/internal/cache"
	"golang.org/x/tools/gopls/internal/cache/parsego"
	"golang.org/x/tools/gopls/internal/file"
	"golang.org/x/tools/gopls/internal/protocol"
	"golang.org/x/tools/gopls/internal/settings"
	"golang.org/x/tools/gopls/internal/util/safetoken"
	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/typeparams"
	"golang.org/x/tools/internal/typesinternal"
)

func InlayHint(ctx context.Context, snapshot *cache.Snapshot, fh file.Handle, pRng protocol.Range) ([]protocol.InlayHint, error) {
	ctx, done := event.Start(ctx, "golang.InlayHint")
	defer done()

	pkg, pgf, err := NarrowestPackageForFile(ctx, snapshot, fh.URI())
	if err != nil {
		return nil, fmt.Errorf("getting file for InlayHint: %w", err)
	}

	// Collect a list of the inlay hints that are enabled.
	inlayHintOptions := snapshot.Options().InlayHintOptions
	var enabledHints []inlayHintFunc
	for hint, enabled := range inlayHintOptions.Hints {
		if !enabled {
			continue
		}
		if fn, ok := allInlayHints[hint]; ok {
			enabledHints = append(enabledHints, fn)
		}
	}
	if len(enabledHints) == 0 {
		return nil, nil
	}

	info := pkg.TypesInfo()
	qual := typesinternal.FileQualifier(pgf.File, pkg.Types())

	// Set the range to the full file if the range is not valid.
	start, end := pgf.File.FileStart, pgf.File.FileEnd

	// TODO(adonovan): this condition looks completely wrong!
	if pRng.Start.Line < pRng.End.Line || pRng.Start.Character < pRng.End.Character {
		// Adjust start and end for the specified range.
		var err error
		start, end, err = pgf.RangePos(pRng)
		if err != nil {
			return nil, err
		}
	}

	var hints []protocol.InlayHint
	if curSubrange, ok := pgf.Cursor().FindByPos(start, end); ok {
		add := func(hint protocol.InlayHint) { hints = append(hints, hint) }
		for _, fn := range enabledHints {
			fn(info, pgf, qual, curSubrange, add)
		}
	}
	return hints, nil
}

type inlayHintFunc func(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint))

var allInlayHints = map[settings.InlayHint]inlayHintFunc{
	settings.AssignVariableTypes:        assignVariableTypes,
	settings.ConstantValues:             constantValues,
	settings.ParameterNames:             parameterNames,
	settings.RangeVariableTypes:         rangeVariableTypes,
	settings.CompositeLiteralTypes:      compositeLiteralTypes,
	settings.CompositeLiteralFieldNames: compositeLiteralFields,
	settings.FunctionTypeParameters:     funcTypeParams,
	settings.IgnoredError:               ignoredError,
}

func parameterNames(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint)) {
	for curCall := range cur.Preorder((*ast.CallExpr)(nil)) {
		callExpr := curCall.Node().(*ast.CallExpr)
		t := info.TypeOf(callExpr.Fun)
		if t == nil {
			continue
		}
		signature, ok := typeparams.CoreType(t).(*types.Signature)
		if !ok {
			continue
		}

		for i, v := range callExpr.Args {
			start, err := pgf.PosPosition(v.Pos())
			if err != nil {
				continue
			}
			params := signature.Params()
			// When a function has variadic params, we skip args after
			// params.Len().
			if i > params.Len()-1 {
				break
			}
			param := params.At(i)
			// param.Name is empty for built-ins like append
			if param.Name() == "" {
				continue
			}
			// Skip the parameter name hint if the arg matches
			// the parameter name.
			if i, ok := v.(*ast.Ident); ok && i.Name == param.Name() {
				continue
			}

			label := param.Name()
			if signature.Variadic() && i == params.Len()-1 {
				label = label + "..."
			}
			add(protocol.InlayHint{
				Position:     start,
				Label:        labelPart(label + ":"),
				Kind:         protocol.Parameter,
				PaddingRight: true,
			})
		}
	}
}

func ignoredError(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint)) {
	ignoreSubstrings := []string{
		"ignore error",
		"discard error",
		"can't fail",
		"cannot fail",
	}

outer:
	for curCall := range cur.Preorder((*ast.ExprStmt)(nil)) {
		stmt := curCall.Node().(*ast.ExprStmt)
		call, ok := stmt.X.(*ast.CallExpr)
		if !ok {
			continue // not a call stmt
		}

		// Check that type of result (or last component) is error.
		tv, ok := info.Types[call]
		if !ok {
			continue // no type info
		}
		t := tv.Type
		if res, ok := t.(*types.Tuple); ok && res.Len() > 1 {
			t = res.At(res.Len() - 1).Type()
		}
		if !types.Identical(t, errorType) {
			continue
		}

		// Suppress some common false positives.
		obj := typeutil.Callee(info, call)
		if typesinternal.IsFunctionNamed(obj, "fmt", "Print", "Printf", "Println", "Fprint", "Fprintf", "Fprintln") ||
			typesinternal.IsMethodNamed(obj, "bytes", "Buffer", "Write", "WriteByte", "WriteRune", "WriteString") ||
			typesinternal.IsMethodNamed(obj, "strings", "Builder", "Write", "WriteByte", "WriteRune", "WriteString") ||
			typesinternal.IsFunctionNamed(obj, "io", "WriteString") ||
			typesinternal.IsMethodNamed(obj, "hash/maphash", "Hash", "Write", "WriteByte", "WriteString") {
			continue
		}

		// Suppress if comment on same line contains "ignore error" (etc).
		line := func(pos token.Pos) int { return safetoken.Line(pgf.Tok, pos) }
		comments := pgf.File.Comments
		compare := func(cg *ast.CommentGroup, pos token.Pos) int {
			return cmp.Compare(cg.Pos(), pos)
		}
		i, _ := slices.BinarySearchFunc(comments, stmt.End(), compare)
		if i >= 0 && i < len(comments) {
			cg := comments[i]
			if line(cg.Pos()) == line(stmt.End()) {
				for _, sub := range ignoreSubstrings {
					if strings.Contains(cg.Text(), sub) {
						continue outer // suppress
					}
				}
			}
		}

		// Provide a hint.
		pos, err := pgf.PosPosition(stmt.End())
		if err != nil {
			continue
		}
		add(protocol.InlayHint{
			Position: pos,
			Label:    labelPart(" // ignore error"),
		})
	}
}

func funcTypeParams(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint)) {
	for curCall := range cur.Preorder((*ast.CallExpr)(nil)) {
		call := curCall.Node().(*ast.CallExpr)
		var id *ast.Ident
		switch fun := call.Fun.(type) {
		case *ast.Ident:
			id = fun
		case *ast.SelectorExpr: // imported function
			id = fun.Sel
		}
		if id == nil {
			continue
		}
		inst := info.Instances[id]
		if inst.TypeArgs == nil {
			continue
		}
		start, err := pgf.PosPosition(id.End())
		if err != nil {
			continue
		}
		var args []string
		for t := range inst.TypeArgs.Types() {
			args = append(args, types.TypeString(t, qual))
		}
		if len(args) == 0 {
			continue
		}
		add(protocol.InlayHint{
			Position: start,
			Label:    labelPart("[" + strings.Join(args, ", ") + "]"),
			Kind:     protocol.Type,
		})
	}
}

func assignVariableTypes(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint)) {
	for cur := range cur.Preorder((*ast.AssignStmt)(nil), (*ast.ValueSpec)(nil)) {
		switch node := cur.Node().(type) {
		case *ast.AssignStmt:
			if node.Tok == token.DEFINE {
				for _, lhs := range node.Lhs {
					variableType(info, pgf, qual, lhs, add)
				}
			}
		case *ast.ValueSpec:
			if cur.Parent().Node().(*ast.GenDecl).Tok == token.VAR && node.Type == nil { // type not already explicit
				for _, id := range node.Names {
					variableType(info, pgf, qual, id, add)
				}
			}
		}
	}
}

func rangeVariableTypes(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint)) {
	for curRange := range cur.Preorder((*ast.RangeStmt)(nil)) {
		rStmt := curRange.Node().(*ast.RangeStmt)
		variableType(info, pgf, qual, rStmt.Key, add)
		variableType(info, pgf, qual, rStmt.Value, add)
	}
}

func variableType(info *types.Info, pgf *parsego.File, qual types.Qualifier, e ast.Expr, add func(protocol.InlayHint)) {
	typ := info.TypeOf(e)
	if typ == nil {
		return
	}
	end, err := pgf.PosPosition(e.End())
	if err != nil {
		return
	}
	add(protocol.InlayHint{
		Position:    end,
		Label:       labelPart(types.TypeString(typ, qual)),
		Kind:        protocol.Type,
		PaddingLeft: true,
	})
}

func constantValues(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint)) {
	for curDecl := range cur.Preorder((*ast.GenDecl)(nil)) {
		genDecl := curDecl.Node().(*ast.GenDecl)
		if genDecl.Tok != token.CONST {
			continue
		}

		for _, v := range genDecl.Specs {
			spec, ok := v.(*ast.ValueSpec)
			if !ok {
				continue
			}
			end, err := pgf.PosPosition(v.End())
			if err != nil {
				continue
			}
			// Show hints when values are missing or at least one value is not
			// a basic literal.
			showHints := len(spec.Values) == 0
			checkValues := len(spec.Names) == len(spec.Values)
			var values []string
			for i, w := range spec.Names {
				obj, ok := info.ObjectOf(w).(*types.Const)
				if !ok || obj.Val().Kind() == constant.Unknown {
					continue
				}
				if checkValues {
					switch spec.Values[i].(type) {
					case *ast.BadExpr:
						continue
					case *ast.BasicLit:
					default:
						if obj.Val().Kind() != constant.Bool {
							showHints = true
						}
					}
				}
				values = append(values, fmt.Sprintf("%v", obj.Val()))
			}
			if !showHints || len(values) == 0 {
				continue
			}
			add(protocol.InlayHint{
				Position:    end,
				Label:       labelPart("= " + strings.Join(values, ", ")),
				PaddingLeft: true,
			})
		}
	}
}

func compositeLiteralFields(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint)) {
	for curCompLit := range cur.Preorder((*ast.CompositeLit)(nil)) {
		compLit := curCompLit.Node().(*ast.CompositeLit)
		typ := info.TypeOf(compLit)
		if typ == nil {
			continue
		}
		strct, ok := typeparams.CoreType(typesinternal.Unpointer(typ)).(*types.Struct)
		if !ok {
			continue
		}

		var (
			hints    []protocol.InlayHint
			allEdits []protocol.TextEdit
			label    strings.Builder
		)
		for i, v := range compLit.Elts {
			label.Reset()
			pad := false
			if kv, ok := v.(*ast.KeyValueExpr); ok {
				// keyed field: show implicit field selections
				if id, ok := kv.Key.(*ast.Ident); ok {
					// For some reason an inlayHintFunc
					// doesn't get the current types.Package.
					// Use the package of the explicit field.
					var pkg *types.Package
					if obj, ok := info.Uses[id]; ok {
						pkg = obj.Pkg()
					}

					if seln, ok := types.LookupSelection(strct, true, pkg, id.Name); ok {
						for field := range typesinternal.ImplicitFieldSelections(seln) {
							label.WriteString(field.Name())
							label.WriteByte('.')
						}
					}
				}
			} else {
				// unkeyed field: show key based on index
				if i < strct.NumFields() {
					label.WriteString(strct.Field(i).Name())
					label.WriteByte(':')
					pad = true
				}
			}
			if label.Len() == 0 {
				continue
			}
			labelStr := label.String()

			start, err := pgf.PosPosition(v.Pos())
			if err != nil {
				continue
			}
			hints = append(hints, protocol.InlayHint{
				Position:     start,
				Label:        labelPart(labelStr),
				Kind:         protocol.Parameter,
				PaddingRight: pad,
			})
			allEdits = append(allEdits, protocol.TextEdit{
				Range:   protocol.Range{Start: start, End: start},
				NewText: labelStr,
			})
		}

		// It is not allowed to have a mix of keyed and unkeyed fields, so
		// have the text edits add keys to all fields.
		for i := range hints {
			hints[i].TextEdits = allEdits
			add(hints[i])
		}
	}
}

func compositeLiteralTypes(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint)) {
	for curCompLit := range cur.Preorder((*ast.CompositeLit)(nil)) {
		compLit := curCompLit.Node().(*ast.CompositeLit)
		typ := info.TypeOf(compLit)
		if typ == nil {
			continue
		}
		if compLit.Type != nil {
			continue
		}
		prefix := ""
		if t, ok := typeparams.CoreType(typ).(*types.Pointer); ok {
			typ = t.Elem()
			prefix = "&"
		}
		// The type for this composite literal is implicit, add an inlay hint.
		start, err := pgf.PosPosition(compLit.Lbrace)
		if err != nil {
			continue
		}
		add(protocol.InlayHint{
			Position: start,
			Label:    labelPart(fmt.Sprintf("%s%s", prefix, types.TypeString(typ, qual))),
			Kind:     protocol.Type,
		})
	}
}

func labelPart(s string) []protocol.InlayHintLabelPart {
	const maxLabelLength = 28
	if len(s) > maxLabelLength+len("...") {
		s = s[:maxLabelLength] + "..."
	}
	return []protocol.InlayHintLabelPart{{Value: s}}
}
