// Copyright 2023 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 cmd

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"runtime"
	"strings"
	"sync"
	"time"

	goplsbug "golang.org/x/tools/gopls/internal/bug"
	"golang.org/x/tools/gopls/internal/lsp"
	"golang.org/x/tools/gopls/internal/lsp/command"
	"golang.org/x/tools/gopls/internal/lsp/debug"
	"golang.org/x/tools/gopls/internal/lsp/filecache"
	"golang.org/x/tools/gopls/internal/lsp/protocol"
	"golang.org/x/tools/gopls/internal/lsp/source"
)

type stats struct {
	app *Application
}

func (s *stats) Name() string      { return "stats" }
func (r *stats) Parent() string    { return r.app.Name() }
func (s *stats) Usage() string     { return "" }
func (s *stats) ShortHelp() string { return "print workspace statistics" }

func (s *stats) DetailedHelp(f *flag.FlagSet) {
	fmt.Fprint(f.Output(), `
Load the workspace for the current directory, and output a JSON summary of
workspace information relevant to performance. As a side effect, this command
populates the gopls file cache for the current workspace.

Example:
  $ gopls stats
`)
	printFlagDefaults(f)
}

func (s *stats) Run(ctx context.Context, args ...string) error {

	// This undocumented environment variable allows
	// the cmd integration test to trigger a call to bug.Report.
	if msg := os.Getenv("TEST_GOPLS_BUG"); msg != "" {
		filecache.Start() // effect: register bug handler
		goplsbug.Report(msg)
		return nil
	}

	if s.app.Remote != "" {
		// stats does not work with -remote.
		// Other sessions on the daemon may interfere with results.
		// Additionally, the type assertions in below only work if progress
		// notifications bypass jsonrpc2 serialization.
		return fmt.Errorf("the stats subcommand does not work with -remote")
	}

	stats := GoplsStats{
		GOOS:         runtime.GOOS,
		GOARCH:       runtime.GOARCH,
		GoVersion:    runtime.Version(),
		GoplsVersion: debug.Version,
	}

	opts := s.app.options
	s.app.options = func(o *source.Options) {
		if opts != nil {
			opts(o)
		}
		o.VerboseWorkDoneProgress = true
	}
	var (
		iwlMu    sync.Mutex
		iwlToken protocol.ProgressToken
		iwlDone  = make(chan struct{})
	)

	onProgress := func(p *protocol.ProgressParams) {
		switch v := p.Value.(type) {
		case *protocol.WorkDoneProgressBegin:
			if v.Title == lsp.DiagnosticWorkTitle(lsp.FromInitialWorkspaceLoad) {
				iwlMu.Lock()
				iwlToken = p.Token
				iwlMu.Unlock()
			}
		case *protocol.WorkDoneProgressEnd:
			iwlMu.Lock()
			tok := iwlToken
			iwlMu.Unlock()

			if p.Token == tok {
				close(iwlDone)
			}
		}
	}

	// do executes a timed section of the stats command.
	do := func(name string, f func() error) (time.Duration, error) {
		start := time.Now()
		fmt.Fprintf(os.Stderr, "%-30s", name+"...")
		if err := f(); err != nil {
			return time.Since(start), err
		}
		d := time.Since(start)
		fmt.Fprintf(os.Stderr, "done (%v)\n", d)
		return d, nil
	}

	var conn *connection
	iwlDuration, err := do("Initializing workspace", func() error {
		var err error
		conn, err = s.app.connect(ctx, onProgress)
		if err != nil {
			return err
		}
		select {
		case <-iwlDone:
		case <-ctx.Done():
			return ctx.Err()
		}
		return nil
	})
	stats.InitialWorkspaceLoadDuration = fmt.Sprint(iwlDuration)
	if err != nil {
		return err
	}
	defer conn.terminate(ctx)

	// Gather bug reports produced by any process using
	// this executable and persisted in the cache.
	stats.BugReports = []string{} // non-nil for JSON
	do("Gathering bug reports", func() error {
		for _, report := range filecache.BugReports() {
			stats.BugReports = append(stats.BugReports, string(report))
		}
		return nil
	})

	if _, err := do("Querying memstats", func() error {
		memStats, err := conn.ExecuteCommand(ctx, &protocol.ExecuteCommandParams{
			Command: command.MemStats.ID(),
		})
		if err != nil {
			return err
		}
		stats.MemStats = memStats.(command.MemStatsResult)
		return nil
	}); err != nil {
		return err
	}

	if _, err := do("Querying workspace stats", func() error {
		wsStats, err := conn.ExecuteCommand(ctx, &protocol.ExecuteCommandParams{
			Command: command.WorkspaceStats.ID(),
		})
		if err != nil {
			return err
		}
		stats.WorkspaceStats = wsStats.(command.WorkspaceStatsResult)
		return nil
	}); err != nil {
		return err
	}

	if _, err := do("Collecting directory info", func() error {
		var err error
		stats.DirStats, err = findDirStats(ctx)
		if err != nil {
			return err
		}
		return nil
	}); err != nil {
		return err
	}

	data, err := json.MarshalIndent(stats, "", "  ")
	if err != nil {
		return err
	}
	os.Stdout.Write(data)
	fmt.Println()
	return nil
}

type GoplsStats struct {
	GOOS, GOARCH                 string
	GoVersion                    string
	GoplsVersion                 string
	InitialWorkspaceLoadDuration string // in time.Duration string form
	BugReports                   []string
	MemStats                     command.MemStatsResult
	WorkspaceStats               command.WorkspaceStatsResult
	DirStats                     dirStats
}

type dirStats struct {
	Files         int
	TestdataFiles int
	GoFiles       int
	ModFiles      int
	Dirs          int
}

// findDirStats collects information about the current directory and its
// subdirectories.
func findDirStats(ctx context.Context) (dirStats, error) {
	var ds dirStats
	filepath.WalkDir(".", func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			ds.Dirs++
		} else {
			ds.Files++
			slashed := filepath.ToSlash(path)
			switch {
			case strings.Contains(slashed, "/testdata/") || strings.HasPrefix(slashed, "testdata/"):
				ds.TestdataFiles++
			case strings.HasSuffix(path, ".go"):
				ds.GoFiles++
			case strings.HasSuffix(path, ".mod"):
				ds.ModFiles++
			}
		}
		return nil
	})
	return ds, nil
}