// Copyright 2024 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 (
	"context"
	"encoding/json"
	"fmt"
	"go/ast"
	"go/types"
	"strings"

	"golang.org/x/tools/go/ast/astutil"
	"golang.org/x/tools/gopls/internal/analysis/fillstruct"
	"golang.org/x/tools/gopls/internal/analysis/fillswitch"
	"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/label"
	"golang.org/x/tools/gopls/internal/protocol"
	"golang.org/x/tools/gopls/internal/protocol/command"
	"golang.org/x/tools/gopls/internal/settings"
	"golang.org/x/tools/gopls/internal/util/bug"
	"golang.org/x/tools/gopls/internal/util/slices"
	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/imports"
	"golang.org/x/tools/internal/typesinternal"
)

// CodeActions returns all wanted code actions (edits and other
// commands) available for the selected range.
//
// Depending on how the request was triggered, fewer actions may be
// offered, e.g. to avoid UI distractions after mere cursor motion.
//
// See ../protocol/codeactionkind.go for some code action theory.
func CodeActions(ctx context.Context, snapshot *cache.Snapshot, fh file.Handle, rng protocol.Range, diagnostics []protocol.Diagnostic, want map[protocol.CodeActionKind]bool, trigger protocol.CodeActionTriggerKind) (actions []protocol.CodeAction, _ error) {
	// Only compute quick fixes if there are any diagnostics to fix.
	wantQuickFixes := want[protocol.QuickFix] && len(diagnostics) > 0

	// Note: don't forget to update the allow-list in Server.CodeAction
	// when adding new query operations like GoTest and GoDoc that
	// are permitted even in generated source files

	// Code actions that can be offered based on syntax information alone.
	if wantQuickFixes ||
		want[protocol.SourceOrganizeImports] ||
		want[protocol.RefactorExtract] ||
		want[settings.GoFreeSymbols] {

		pgf, err := snapshot.ParseGo(ctx, fh, parsego.Full)
		if err != nil {
			return nil, err
		}

		// Process any missing imports and pair them with the diagnostics they fix.
		if wantQuickFixes || want[protocol.SourceOrganizeImports] {
			importEdits, importEditsPerFix, err := allImportsFixes(ctx, snapshot, pgf)
			if err != nil {
				event.Error(ctx, "imports fixes", err, label.File.Of(fh.URI().Path()))
				importEdits = nil
				importEditsPerFix = nil
			}

			// Separate this into a set of codeActions per diagnostic, where
			// each action is the addition, removal, or renaming of one import.
			if wantQuickFixes {
				for _, importFix := range importEditsPerFix {
					fixed := fixedByImportFix(importFix.fix, diagnostics)
					if len(fixed) == 0 {
						continue
					}
					actions = append(actions, protocol.CodeAction{
						Title: importFixTitle(importFix.fix),
						Kind:  protocol.QuickFix,
						Edit: protocol.NewWorkspaceEdit(
							protocol.DocumentChangeEdit(fh, importFix.edits)),
						Diagnostics: fixed,
					})
				}
			}

			// Send all of the import edits as one code action if the file is
			// being organized.
			if want[protocol.SourceOrganizeImports] && len(importEdits) > 0 {
				actions = append(actions, protocol.CodeAction{
					Title: "Organize Imports",
					Kind:  protocol.SourceOrganizeImports,
					Edit: protocol.NewWorkspaceEdit(
						protocol.DocumentChangeEdit(fh, importEdits)),
				})
			}
		}

		if want[protocol.RefactorExtract] {
			extractions, err := getExtractCodeActions(pgf, rng, snapshot.Options())
			if err != nil {
				return nil, err
			}
			actions = append(actions, extractions...)
		}

		if want[settings.GoFreeSymbols] && rng.End != rng.Start {
			loc := protocol.Location{URI: pgf.URI, Range: rng}
			cmd, err := command.NewFreeSymbolsCommand("Browse free symbols", snapshot.View().ID(), loc)
			if err != nil {
				return nil, err
			}
			// For implementation, see commandHandler.FreeSymbols.
			actions = append(actions, protocol.CodeAction{
				Title:   cmd.Title,
				Kind:    settings.GoFreeSymbols,
				Command: &cmd,
			})
		}
	}

	// Code actions requiring type information.
	if want[protocol.RefactorRewrite] ||
		want[protocol.RefactorInline] ||
		want[settings.GoAssembly] ||
		want[settings.GoDoc] ||
		want[settings.GoTest] {
		pkg, pgf, err := NarrowestPackageForFile(ctx, snapshot, fh.URI())
		if err != nil {
			return nil, err
		}
		start, end, err := pgf.RangePos(rng)
		if err != nil {
			return nil, err
		}

		if want[protocol.RefactorRewrite] {
			rewrites, err := getRewriteCodeActions(ctx, pkg, snapshot, pgf, fh, rng, snapshot.Options())
			if err != nil {
				return nil, err
			}
			actions = append(actions, rewrites...)
		}

		// To avoid distraction (e.g. VS Code lightbulb), offer "inline"
		// only after a selection or explicit menu operation.
		if want[protocol.RefactorInline] && (trigger != protocol.CodeActionAutomatic || rng.Start != rng.End) {
			rewrites, err := getInlineCodeActions(pkg, pgf, rng, snapshot.Options())
			if err != nil {
				return nil, err
			}
			actions = append(actions, rewrites...)
		}

		if want[settings.GoTest] {
			fixes, err := getGoTestCodeActions(pkg, pgf, rng)
			if err != nil {
				return nil, err
			}
			actions = append(actions, fixes...)
		}

		if want[settings.GoDoc] {
			// "Browse documentation for ..."
			_, _, title := DocFragment(pkg, pgf, start, end)
			loc := protocol.Location{URI: pgf.URI, Range: rng}
			cmd, err := command.NewDocCommand(title, loc)
			if err != nil {
				return nil, err
			}
			actions = append(actions, protocol.CodeAction{
				Title:   cmd.Title,
				Kind:    settings.GoDoc,
				Command: &cmd,
			})
		}

		if want[settings.GoAssembly] {
			fixes, err := getGoAssemblyAction(snapshot.View(), pkg, pgf, rng)
			if err != nil {
				return nil, err
			}
			actions = append(actions, fixes...)
		}
	}
	return actions, nil
}

func supportsResolveEdits(options *settings.Options) bool {
	return options.CodeActionResolveOptions != nil && slices.Contains(options.CodeActionResolveOptions, "edit")
}

func importFixTitle(fix *imports.ImportFix) string {
	var str string
	switch fix.FixType {
	case imports.AddImport:
		str = fmt.Sprintf("Add import: %s %q", fix.StmtInfo.Name, fix.StmtInfo.ImportPath)
	case imports.DeleteImport:
		str = fmt.Sprintf("Delete import: %s %q", fix.StmtInfo.Name, fix.StmtInfo.ImportPath)
	case imports.SetImportName:
		str = fmt.Sprintf("Rename import: %s %q", fix.StmtInfo.Name, fix.StmtInfo.ImportPath)
	}
	return str
}

// fixedByImportFix filters the provided slice of diagnostics to those that
// would be fixed by the provided imports fix.
func fixedByImportFix(fix *imports.ImportFix, diagnostics []protocol.Diagnostic) []protocol.Diagnostic {
	var results []protocol.Diagnostic
	for _, diagnostic := range diagnostics {
		switch {
		// "undeclared name: X" may be an unresolved import.
		case strings.HasPrefix(diagnostic.Message, "undeclared name: "):
			ident := strings.TrimPrefix(diagnostic.Message, "undeclared name: ")
			if ident == fix.IdentName {
				results = append(results, diagnostic)
			}
		// "undefined: X" may be an unresolved import at Go 1.20+.
		case strings.HasPrefix(diagnostic.Message, "undefined: "):
			ident := strings.TrimPrefix(diagnostic.Message, "undefined: ")
			if ident == fix.IdentName {
				results = append(results, diagnostic)
			}
		// "could not import: X" may be an invalid import.
		case strings.HasPrefix(diagnostic.Message, "could not import: "):
			ident := strings.TrimPrefix(diagnostic.Message, "could not import: ")
			if ident == fix.IdentName {
				results = append(results, diagnostic)
			}
		// "X imported but not used" is an unused import.
		// "X imported but not used as Y" is an unused import.
		case strings.Contains(diagnostic.Message, " imported but not used"):
			idx := strings.Index(diagnostic.Message, " imported but not used")
			importPath := diagnostic.Message[:idx]
			if importPath == fmt.Sprintf("%q", fix.StmtInfo.ImportPath) {
				results = append(results, diagnostic)
			}
		}
	}
	return results
}

// getExtractCodeActions returns any refactor.extract code actions for the selection.
func getExtractCodeActions(pgf *parsego.File, rng protocol.Range, options *settings.Options) ([]protocol.CodeAction, error) {
	start, end, err := pgf.RangePos(rng)
	if err != nil {
		return nil, err
	}
	puri := pgf.URI
	var commands []protocol.Command
	if _, ok, methodOk, _ := canExtractFunction(pgf.Tok, start, end, pgf.Src, pgf.File); ok {
		cmd, err := command.NewApplyFixCommand("Extract function", command.ApplyFixArgs{
			Fix:          fixExtractFunction,
			URI:          puri,
			Range:        rng,
			ResolveEdits: supportsResolveEdits(options),
		})
		if err != nil {
			return nil, err
		}
		commands = append(commands, cmd)
		if methodOk {
			cmd, err := command.NewApplyFixCommand("Extract method", command.ApplyFixArgs{
				Fix:          fixExtractMethod,
				URI:          puri,
				Range:        rng,
				ResolveEdits: supportsResolveEdits(options),
			})
			if err != nil {
				return nil, err
			}
			commands = append(commands, cmd)
		}
	}
	if _, _, ok, _ := canExtractVariable(start, end, pgf.File); ok {
		cmd, err := command.NewApplyFixCommand("Extract variable", command.ApplyFixArgs{
			Fix:          fixExtractVariable,
			URI:          puri,
			Range:        rng,
			ResolveEdits: supportsResolveEdits(options),
		})
		if err != nil {
			return nil, err
		}
		commands = append(commands, cmd)
	}
	if canExtractToNewFile(pgf, start, end) {
		cmd, err := command.NewExtractToNewFileCommand(
			"Extract declarations to new file",
			protocol.Location{URI: pgf.URI, Range: rng},
		)
		if err != nil {
			return nil, err
		}
		commands = append(commands, cmd)
	}
	var actions []protocol.CodeAction
	for i := range commands {
		actions = append(actions, newCodeAction(commands[i].Title, protocol.RefactorExtract, &commands[i], nil, options))
	}
	return actions, nil
}

func newCodeAction(title string, kind protocol.CodeActionKind, cmd *protocol.Command, diagnostics []protocol.Diagnostic, options *settings.Options) protocol.CodeAction {
	action := protocol.CodeAction{
		Title:       title,
		Kind:        kind,
		Diagnostics: diagnostics,
	}
	if !supportsResolveEdits(options) {
		action.Command = cmd
	} else {
		data, err := json.Marshal(cmd)
		if err != nil {
			panic("unable to marshal")
		}
		msg := json.RawMessage(data)
		action.Data = &msg
	}
	return action
}

func getRewriteCodeActions(ctx context.Context, pkg *cache.Package, snapshot *cache.Snapshot, pgf *parsego.File, fh file.Handle, rng protocol.Range, options *settings.Options) (_ []protocol.CodeAction, rerr error) {
	// golang/go#61693: code actions were refactored to run outside of the
	// analysis framework, but as a result they lost their panic recovery.
	//
	// These code actions should never fail, but put back the panic recovery as a
	// defensive measure.
	defer func() {
		if r := recover(); r != nil {
			rerr = bug.Errorf("refactor.rewrite code actions panicked: %v", r)
		}
	}()

	var actions []protocol.CodeAction

	if canRemoveParameter(pkg, pgf, rng) {
		cmd, err := command.NewChangeSignatureCommand("remove unused parameter", command.ChangeSignatureArgs{
			RemoveParameter: protocol.Location{
				URI:   pgf.URI,
				Range: rng,
			},
			ResolveEdits: supportsResolveEdits(options),
		})
		if err != nil {
			return nil, err
		}
		actions = append(actions, newCodeAction("Refactor: remove unused parameter", protocol.RefactorRewrite, &cmd, nil, options))
	}

	start, end, err := pgf.RangePos(rng)
	if err != nil {
		return nil, err
	}

	if action, ok := convertStringLiteral(pgf, fh, start, end); ok {
		actions = append(actions, action)
	}

	var commands []protocol.Command
	if _, ok, _ := canInvertIfCondition(pgf.File, start, end); ok {
		cmd, err := command.NewApplyFixCommand("Invert 'if' condition", command.ApplyFixArgs{
			Fix:          fixInvertIfCondition,
			URI:          pgf.URI,
			Range:        rng,
			ResolveEdits: supportsResolveEdits(options),
		})
		if err != nil {
			return nil, err
		}
		commands = append(commands, cmd)
	}

	if msg, ok, _ := canSplitLines(pgf.File, pkg.FileSet(), start, end); ok {
		cmd, err := command.NewApplyFixCommand(msg, command.ApplyFixArgs{
			Fix:          fixSplitLines,
			URI:          pgf.URI,
			Range:        rng,
			ResolveEdits: supportsResolveEdits(options),
		})
		if err != nil {
			return nil, err
		}
		commands = append(commands, cmd)
	}

	if msg, ok, _ := canJoinLines(pgf.File, pkg.FileSet(), start, end); ok {
		cmd, err := command.NewApplyFixCommand(msg, command.ApplyFixArgs{
			Fix:          fixJoinLines,
			URI:          pgf.URI,
			Range:        rng,
			ResolveEdits: supportsResolveEdits(options),
		})
		if err != nil {
			return nil, err
		}
		commands = append(commands, cmd)
	}

	// fillstruct.Diagnose is a lazy analyzer: all it gives us is
	// the (start, end, message) of each SuggestedFix; the actual
	// edit is computed only later by ApplyFix, which calls fillstruct.SuggestedFix.
	for _, diag := range fillstruct.Diagnose(pgf.File, start, end, pkg.Types(), pkg.TypesInfo()) {
		rng, err := pgf.Mapper.PosRange(pgf.Tok, diag.Pos, diag.End)
		if err != nil {
			return nil, err
		}
		for _, fix := range diag.SuggestedFixes {
			cmd, err := command.NewApplyFixCommand(fix.Message, command.ApplyFixArgs{
				Fix:          diag.Category,
				URI:          pgf.URI,
				Range:        rng,
				ResolveEdits: supportsResolveEdits(options),
			})
			if err != nil {
				return nil, err
			}
			commands = append(commands, cmd)
		}
	}

	for _, diag := range fillswitch.Diagnose(pgf.File, start, end, pkg.Types(), pkg.TypesInfo()) {
		changes, err := suggestedFixToDocumentChange(ctx, snapshot, pkg.FileSet(), &diag.SuggestedFixes[0])
		if err != nil {
			return nil, err
		}
		actions = append(actions, protocol.CodeAction{
			Title: diag.Message,
			Kind:  protocol.RefactorRewrite,
			Edit:  protocol.NewWorkspaceEdit(changes...),
		})
	}
	for i := range commands {
		actions = append(actions, newCodeAction(commands[i].Title, protocol.RefactorRewrite, &commands[i], nil, options))
	}

	return actions, nil
}

// canRemoveParameter reports whether we can remove the function parameter
// indicated by the given [start, end) range.
//
// This is true if:
//   - there are no parse or type errors, and
//   - [start, end) is contained within an unused field or parameter name
//   - ... of a non-method function declaration.
//
// (Note that the unusedparam analyzer also computes this property, but
// much more precisely, allowing it to report its findings as diagnostics.)
func canRemoveParameter(pkg *cache.Package, pgf *parsego.File, rng protocol.Range) bool {
	if perrors, terrors := pkg.ParseErrors(), pkg.TypeErrors(); len(perrors) > 0 || len(terrors) > 0 {
		return false // can't remove parameters from packages with errors
	}
	info, err := findParam(pgf, rng)
	if err != nil {
		return false // e.g. invalid range
	}
	if info.field == nil {
		return false // range does not span a parameter
	}
	if info.decl.Body == nil {
		return false // external function
	}
	if len(info.field.Names) == 0 {
		return true // no names => field is unused
	}
	if info.name == nil {
		return false // no name is indicated
	}
	if info.name.Name == "_" {
		return true // trivially unused
	}

	obj := pkg.TypesInfo().Defs[info.name]
	if obj == nil {
		return false // something went wrong
	}

	used := false
	ast.Inspect(info.decl.Body, func(node ast.Node) bool {
		if n, ok := node.(*ast.Ident); ok && pkg.TypesInfo().Uses[n] == obj {
			used = true
		}
		return !used // keep going until we find a use
	})
	return !used
}

// getInlineCodeActions returns refactor.inline actions available at the specified range.
func getInlineCodeActions(pkg *cache.Package, pgf *parsego.File, rng protocol.Range, options *settings.Options) ([]protocol.CodeAction, error) {
	start, end, err := pgf.RangePos(rng)
	if err != nil {
		return nil, err
	}

	// If range is within call expression, offer to inline the call.
	var commands []protocol.Command
	if _, fn, err := enclosingStaticCall(pkg, pgf, start, end); err == nil {
		cmd, err := command.NewApplyFixCommand(fmt.Sprintf("Inline call to %s", fn.Name()), command.ApplyFixArgs{
			Fix:          fixInlineCall,
			URI:          pgf.URI,
			Range:        rng,
			ResolveEdits: supportsResolveEdits(options),
		})
		if err != nil {
			return nil, err
		}
		commands = append(commands, cmd)
	}

	// Convert commands to actions.
	var actions []protocol.CodeAction
	for i := range commands {
		actions = append(actions, newCodeAction(commands[i].Title, protocol.RefactorInline, &commands[i], nil, options))
	}
	return actions, nil
}

// getGoTestCodeActions returns any "run this test/benchmark" code actions for the selection.
func getGoTestCodeActions(pkg *cache.Package, pgf *parsego.File, rng protocol.Range) ([]protocol.CodeAction, error) {
	testFuncs, benchFuncs, err := testsAndBenchmarks(pkg.TypesInfo(), pgf)
	if err != nil {
		return nil, err
	}

	var tests, benchmarks []string
	for _, fn := range testFuncs {
		if protocol.Intersect(fn.rng, rng) {
			tests = append(tests, fn.name)
		}
	}
	for _, fn := range benchFuncs {
		if protocol.Intersect(fn.rng, rng) {
			benchmarks = append(benchmarks, fn.name)
		}
	}

	if len(tests) == 0 && len(benchmarks) == 0 {
		return nil, nil
	}

	cmd, err := command.NewTestCommand("Run tests and benchmarks", pgf.URI, tests, benchmarks)
	if err != nil {
		return nil, err
	}
	return []protocol.CodeAction{{
		Title:   cmd.Title,
		Kind:    settings.GoTest,
		Command: &cmd,
	}}, nil
}

// getGoAssemblyAction returns any "Browse assembly for f" code actions for the selection.
func getGoAssemblyAction(view *cache.View, pkg *cache.Package, pgf *parsego.File, rng protocol.Range) ([]protocol.CodeAction, error) {
	start, end, err := pgf.RangePos(rng)
	if err != nil {
		return nil, err
	}

	// Find the enclosing toplevel function or method,
	// and compute its symbol name (e.g. "pkgpath.(T).method").
	// The report will show this method and all its nested
	// functions (FuncLit, defers, etc).
	//
	// TODO(adonovan): this is no good for generics, since they
	// will always be uninstantiated when they enclose the cursor.
	// Instead, we need to query the func symbol under the cursor,
	// rather than the enclosing function. It may be an explicitly
	// or implicitly instantiated generic, and it may be defined
	// in another package, though we would still need to compile
	// the current package to see its assembly. The challenge,
	// however, is that computing the linker name for a generic
	// symbol is quite tricky. Talk with the compiler team for
	// ideas.
	//
	// TODO(adonovan): think about a smoother UX for jumping
	// directly to (say) a lambda of interest.
	// Perhaps we could scroll to STEXT for the innermost
	// enclosing nested function?
	var actions []protocol.CodeAction
	path, _ := astutil.PathEnclosingInterval(pgf.File, start, end)
	if len(path) >= 2 { // [... FuncDecl File]
		if decl, ok := path[len(path)-2].(*ast.FuncDecl); ok {
			if fn, ok := pkg.TypesInfo().Defs[decl.Name].(*types.Func); ok {
				sig := fn.Type().(*types.Signature)

				// Compute the linker symbol of the enclosing function.
				var sym strings.Builder
				if fn.Pkg().Name() == "main" {
					sym.WriteString("main")
				} else {
					sym.WriteString(fn.Pkg().Path())
				}
				sym.WriteString(".")
				if sig.Recv() != nil {
					if isPtr, named := typesinternal.ReceiverNamed(sig.Recv()); named != nil {
						sym.WriteString("(")
						if isPtr {
							sym.WriteString("*")
						}
						sym.WriteString(named.Obj().Name())
						sym.WriteString(").")
					}
				}
				sym.WriteString(fn.Name())

				if fn.Name() != "_" && // blank functions are not compiled
					(fn.Name() != "init" || sig.Recv() != nil) && // init functions aren't linker functions
					sig.TypeParams() == nil && sig.RecvTypeParams() == nil { // generic => no assembly
					cmd, err := command.NewAssemblyCommand(
						fmt.Sprintf("Browse %s assembly for %s", view.GOARCH(), decl.Name),
						view.ID(),
						string(pkg.Metadata().ID),
						sym.String())
					if err != nil {
						return nil, err
					}
					// For handler, see commandHandler.Assembly.
					actions = append(actions, protocol.CodeAction{
						Title:   cmd.Title,
						Kind:    settings.GoAssembly,
						Command: &cmd,
					})
				}
			}
		}
	}
	return actions, nil
}