package main

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"strings"

	"github.com/novox/mesh-control/internal/inventory"
	"github.com/novox/mesh-control/internal/link"
)

// following acts on what the catalogue announces.
//
// **It holds the stores, not a copy of the decision.** What to do about an upgrade is read when
// one arrives, so changing it takes effect on the next upgrade rather than on the next restart of
// the control plane.
type following struct{ open *stores }

// Upgraded sends the machines running a module the version the catalogue now considers current —
// or records that they are behind, which is the default and needs no record.
//
// **Recording is not a second code path.** A machine that is not running what the mesh would send
// it is already something the mesh notices and reports; that is what `status` and `push --behind`
// are built on. So "record it" is the absence of an action, and the only thing this has to decide
// is whether to act.
func (f following) Upgraded(ctx context.Context, u link.Upgraded) error {
	inv := f.open.inventory

	decision, err := inv.UpgradeOf(ctx, u.Module)
	if err != nil {
		return err
	}
	on, err := inv.Running(ctx, u.Module)
	if err != nil {
		return err
	}
	if len(on) == 0 {
		fmt.Printf("%s moved to %s; no machine runs it\n", u.Module, shortCommit(u.Commit))
		return nil
	}
	if !decision.RollOut {
		// Named rather than counted, and said even though nothing happens: an upgrade that was
		// deliberately not rolled out and an upgrade that was never noticed look identical in a
		// log that only speaks when it acts.
		fmt.Printf("%s moved to %s; %s %s behind it, and this mesh records upgrades rather than "+
			"rolling them out — `push --behind` when you want them\n",
			u.Module, shortCommit(u.Commit), readableList(on), isAre(len(on)))
		return nil
	}

	if decision.Together {
		fmt.Printf("%s moved to %s; sending %s together\n",
			u.Module, shortCommit(u.Commit), readableList(on))
		return sendTo(ctx, f.open, on)
	}
	// One at a time, and stopping at the first that fails.
	//
	// **Stopping is the point.** The machines are done one after another precisely so that a
	// version that breaks the first one does not reach the rest; carrying on past a failure would
	// make this the same as sending them together, only slower.
	fmt.Printf("%s moved to %s; sending %s one at a time\n",
		u.Module, shortCommit(u.Commit), readableList(on))
	for _, node := range on {
		if err := sendTo(ctx, f.open, []string{node}); err != nil {
			return fmt.Errorf("%s did not take %s, so the machines after it were left alone: %w",
				node, u.Module, err)
		}
	}
	return nil
}

// readableList names machines the way a sentence does, because this is read by a person deciding
// whether an upgrade went where they expected.
func readableList(names []string) string {
	switch len(names) {
	case 0:
		return "nothing"
	case 1:
		return names[0]
	case 2:
		return names[0] + " and " + names[1]
	}
	return strings.Join(names[:len(names)-1], ", ") + " and " + names[len(names)-1]
}

func shortCommit(commit string) string {
	if len(commit) > 8 {
		return commit[:8]
	}
	return commit
}

func isAre(n int) string {
	if n == 1 {
		return "is"
	}
	return "are"
}

// upgradeCommand says what should happen when a module's current version moves.
func upgradeCommand(ctx context.Context, args []string) error {
	set := flag.NewFlagSet("upgrade", flag.ContinueOnError)
	together := set.Bool("together", false,
		"send every machine running it at once, instead of one after another")
	positionals, err := parseAround(set, args)
	if err != nil {
		return err
	}
	if len(positionals) == 0 {
		return errors.New("upgrade <module> [roll-out|record] [--together]")
	}
	module := positionals[0]

	open, err := openStores(ctx)
	if err != nil {
		return err
	}
	defer open.Close()
	inv := open.inventory

	if len(positionals) == 1 {
		decision, err := inv.UpgradeOf(ctx, module)
		if err != nil {
			return err
		}
		fmt.Println(sayUpgrade(module, decision))
		return nil
	}

	var decision inventory.Upgrade
	switch positionals[1] {
	case "roll-out":
		decision = inventory.Upgrade{RollOut: true, Together: *together}
	case "record":
		if *together {
			// Refused rather than ignored: --together only means anything for a roll-out, and
			// accepting it here would store a preference that never applies and looks like it does.
			return errors.New("`--together` says how to roll out, so it cannot be given with " +
				"`record`, which is the choice not to")
		}
		decision = inventory.Upgrade{}
	default:
		return fmt.Errorf("upgrade <module> roll-out|record — not %q", positionals[1])
	}
	if err := inv.SetUpgradeOf(ctx, module, decision); err != nil {
		return err
	}
	fmt.Println(sayUpgrade(module, decision))
	return nil
}

func sayUpgrade(module string, u inventory.Upgrade) string {
	if !u.RollOut {
		return fmt.Sprintf("when %s moves, the mesh records it and the machines running it are "+
			"reported as behind", module)
	}
	if u.Together {
		return fmt.Sprintf("when %s moves, every machine running it is sent the new version "+
			"together", module)
	}
	return fmt.Sprintf("when %s moves, the machines running it are sent the new version one at "+
		"a time, stopping at the first that fails", module)
}