// Copyright 2021 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.

// The seeddb command is used to populates a database with an initial set of
// modules.
package main

import (
	"bufio"
	"context"
	"flag"
	"fmt"
	"net/http"
	"os"
	"sort"
	"strings"
	"sync"
	"time"

	_ "github.com/jackc/pgx/v4/stdlib" // for pgx driver
	"golang.org/x/pkgsite/cmd/internal/cmdconfig"
	"golang.org/x/pkgsite/internal/config"
	"golang.org/x/pkgsite/internal/derrors"
	"golang.org/x/pkgsite/internal/log"
	"golang.org/x/pkgsite/internal/postgres"
	"golang.org/x/pkgsite/internal/proxy"
	"golang.org/x/pkgsite/internal/source"
	"golang.org/x/pkgsite/internal/worker"
	"golang.org/x/sync/errgroup"
)

var (
	seedfile = flag.String("static", "cmd/internal/seeddb/seed.txt", "filename containing modules for seeding the database")
)

func main() {
	flag.Parse()

	ctx := context.Background()
	cfg, err := config.Init(ctx)
	if err != nil {
		log.Fatal(ctx, err)
	}
	cfg.Dump(os.Stdout)

	log.SetLevel(cfg.LogLevel)

	db, err := cmdconfig.OpenDB(ctx, cfg, false)
	if err != nil {
		log.Fatal(ctx, err)
	}
	defer db.Close()

	if err := run(ctx, db, cfg.ProxyURL); err != nil {
		log.Fatal(ctx, err)
	}
}

func run(ctx context.Context, db *postgres.DB, proxyURL string) error {
	start := time.Now()

	proxyClient, err := proxy.New(proxyURL)
	if err != nil {
		return err
	}

	sourceClient := source.NewClient(config.SourceTimeout)
	fetchFunc := func(ctx context.Context, modulePath, version string) (int, error) {
		f := &worker.Fetcher{
			ProxyClient:  proxyClient,
			SourceClient: sourceClient,
			DB:           db,
		}
		code, _, err := f.FetchAndUpdateState(ctx, modulePath, version, "")
		return code, err
	}

	seedModules, err := readSeedFile(ctx)
	if err != nil {
		return err
	}

	r := results{}
	g := new(errgroup.Group)
	for _, m := range seedModules {
		m := m

		g.Go(func() error {
			log.Infof(ctx, "Fetch requested: %q %q", m.path, m.version)
			start := time.Now()
			defer func() {
				// Log the duration of this fetch request.
				r.add(m.path, m.version, start)
			}()

			fetchCtx, cancel := context.WithTimeout(ctx, 5*time.Minute)
			defer cancel()

			code, err := fetchFunc(fetchCtx, m.path, m.version)
			if err != nil {
				if code == http.StatusNotFound {
					// We expect
					// github.com/jackc/pgx/pgxpool@v3.6.2+incompatible
					// to fail from seed.txt, so that it will redirect to
					// github.com/jackc/pgx/v4/pgxpool in tests.
					return nil
				}
				return err
			}
			return nil
		})
	}
	if err := g.Wait(); err != nil {
		return err
	}
	log.Infof(ctx, "Successfully fetched all modules: %v", time.Since(start))

	// Print the time it took to fetch these modules.
	var keys []string
	for k := range r.paths {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	for _, k := range keys {
		log.Infof(ctx, "%s | %v", k, r.paths[k])
	}
	return nil
}

type results struct {
	paths map[string]time.Duration
	mu    sync.Mutex
}

func (r *results) add(modPath, version string, start time.Time) {
	r.mu.Lock()
	defer r.mu.Unlock()

	if r.paths == nil {
		r.paths = map[string]time.Duration{}
	}
	r.paths[fmt.Sprintf("%s@%s", modPath, version)] = time.Since(start)
}

type module struct {
	path    string
	version string
}

// readSeedFile reads a file of module versions that we want to fetch for
// seeding the database. Format of the file:
// each line is
//     module@version
func readSeedFile(ctx context.Context) (_ []*module, err error) {
	defer derrors.Wrap(&err, "readSeedFile %q", *seedfile)
	lines, err := readFileLines(*seedfile)
	if err != nil {
		return nil, err
	}
	log.Infof(ctx, "read %d module versions from %s", len(lines), *seedfile)

	var modules []*module
	for _, l := range lines {
		parts := strings.SplitN(l, "@", 2)
		modules = append(modules, &module{
			path:    parts[0],
			version: parts[1],
		})
	}
	return modules, nil
}

// readFileLines reads filename and returns its lines, trimmed of whitespace.
// Blank lines and lines whose first non-blank character is '#' are omitted.
func readFileLines(filename string) ([]string, error) {
	var lines []string
	f, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	scan := bufio.NewScanner(f)
	for scan.Scan() {
		line := strings.TrimSpace(scan.Text())
		if line == "" || line[0] == '#' {
			continue
		}
		lines = append(lines, line)
	}
	if err := scan.Err(); err != nil {
		return nil, err
	}
	return lines, nil
}