package praefect

import (
	"context"
	"flag"
	"fmt"
	"io"
	"log"
	"os"
	"sort"
	"strings"

	"gitlab.com/gitlab-org/gitaly/v15/internal/praefect/config"
	"gitlab.com/gitlab-org/gitaly/v15/proto/go/gitalypb"
)

const datalossCmdName = "dataloss"

type datalossSubcommand struct {
	output                    io.Writer
	virtualStorage            string
	includePartiallyAvailable bool
}

func newDatalossSubcommand() *datalossSubcommand {
	return &datalossSubcommand{output: os.Stdout}
}

func (cmd *datalossSubcommand) FlagSet() *flag.FlagSet {
	fs := flag.NewFlagSet(datalossCmdName, flag.ContinueOnError)
	fs.StringVar(&cmd.virtualStorage, "virtual-storage", "", "virtual storage to check for data loss")
	fs.BoolVar(&cmd.includePartiallyAvailable, "partially-unavailable", false, strings.TrimSpace(`
Additionally include repositories which are available but some assigned replicas
are unavailable. Such repositories are available but are not fully replicated. This
increases the chance of data loss on primary failure`))
	return fs
}

func (cmd *datalossSubcommand) println(indent int, msg string, args ...interface{}) {
	fmt.Fprint(cmd.output, strings.Repeat("  ", indent))
	fmt.Fprintf(cmd.output, msg, args...)
	fmt.Fprint(cmd.output, "\n")
}

func (cmd *datalossSubcommand) Exec(flags *flag.FlagSet, cfg config.Config) error {
	if flags.NArg() > 0 {
		return unexpectedPositionalArgsError{Command: flags.Name()}
	}

	virtualStorages := []string{cmd.virtualStorage}
	if cmd.virtualStorage == "" {
		virtualStorages = make([]string, len(cfg.VirtualStorages))
		for i := range cfg.VirtualStorages {
			virtualStorages[i] = cfg.VirtualStorages[i].Name
		}
	}
	sort.Strings(virtualStorages)

	nodeAddr, err := getNodeAddress(cfg)
	if err != nil {
		return err
	}

	ctx := context.Background()
	conn, err := subCmdDial(ctx, nodeAddr, cfg.Auth.Token, defaultDialTimeout)
	if err != nil {
		return fmt.Errorf("error dialing: %w", err)
	}
	defer func() {
		if err := conn.Close(); err != nil {
			log.Printf("error closing connection: %v", err)
		}
	}()

	client := gitalypb.NewPraefectInfoServiceClient(conn)

	for _, vs := range virtualStorages {
		resp, err := client.DatalossCheck(ctx, &gitalypb.DatalossCheckRequest{
			VirtualStorage:             vs,
			IncludePartiallyReplicated: cmd.includePartiallyAvailable,
		})
		if err != nil {
			return fmt.Errorf("error checking: %w", err)
		}

		cmd.println(0, "Virtual storage: %s", vs)
		if len(resp.Repositories) == 0 {
			msg := "All repositories are available!"
			if cmd.includePartiallyAvailable {
				msg = "All repositories are fully available on all assigned storages!"
			}

			cmd.println(1, msg)
			continue
		}

		cmd.println(1, "Repositories:")
		for _, repo := range resp.Repositories {
			unavailable := ""
			if repo.Unavailable {
				unavailable = " (unavailable)"
			}

			cmd.println(2, "%s%s:", repo.RelativePath, unavailable)

			primary := repo.Primary
			if primary == "" {
				primary = "No Primary"
			}
			cmd.println(3, "Primary: %s", primary)

			cmd.println(3, "In-Sync Storages:")
			for _, storage := range repo.Storages {
				if storage.BehindBy != 0 {
					continue
				}

				cmd.println(4, "%s%s%s",
					storage.Name,
					assignedMessage(storage.Assigned),
					unhealthyMessage(storage.Healthy),
				)
			}

			cmd.println(3, "Outdated Storages:")
			for _, storage := range repo.Storages {
				if storage.BehindBy == 0 {
					continue
				}

				plural := ""
				if storage.BehindBy > 1 {
					plural = "s"
				}

				cmd.println(4, "%s is behind by %d change%s or less%s%s",
					storage.Name,
					storage.BehindBy,
					plural,
					assignedMessage(storage.Assigned),
					unhealthyMessage(storage.Healthy),
				)
			}
		}
	}

	return nil
}

func unhealthyMessage(healthy bool) string {
	if healthy {
		return ""
	}

	return ", unhealthy"
}

func assignedMessage(assigned bool) string {
	assignedMsg := ""
	if assigned {
		assignedMsg = ", assigned host"
	}

	return assignedMsg
}
