// Package children manages the creation, lifetime, and shutdown of child
// processes created by the daemon.
package children

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"

	"code.betamike.com/micropelago/pmux/pmuxlib"
	"dev.mediocregopher.com/mediocre-go-lib.git/mlog"

	"isle/bootstrap"
	"isle/daemon/daecommon"
	"isle/secrets"
	"isle/toolkit"
)

// Opts are optional parameters which can be passed in when initializing a new
// Children instance. A nil Opts is equivalent to a zero value.
type Opts struct {
	// Stdout and Stderr are what the associated outputs from child processes
	// will be directed to.
	Stdout, Stderr io.Writer
}

func (o *Opts) withDefaults() *Opts {
	if o == nil {
		o = new(Opts)
	}

	if o.Stdout == nil {
		o.Stdout = os.Stdout
	}

	if o.Stderr == nil {
		o.Stderr = os.Stderr
	}

	return o
}

// Children manages all child processes of a network. Child processes are
// comprised of:
// - nebula
// - dnsmasq
// - garage (0 or more, depending on configured storage allocations)
type Children struct {
	logger     *mlog.Logger
	runtimeDir toolkit.Dir
	opts       Opts

	pmux *pmuxlib.Pmux
}

// New initializes and returns a Children instance. If initialization fails an
// error is returned.
func New(
	ctx context.Context,
	logger *mlog.Logger,
	binDirPath string,
	secretsStore secrets.Store,
	networkConfig daecommon.NetworkConfig,
	runtimeDir toolkit.Dir,
	garageAdminToken string,
	hostBootstrap bootstrap.Bootstrap,
	opts *Opts,
) (
	*Children, error,
) {
	opts = opts.withDefaults()

	logger.Info(ctx, "Loading secrets")
	garageRPCSecret, err := daecommon.GetGarageRPCSecret(ctx, secretsStore)
	if err != nil && !errors.Is(err, secrets.ErrNotFound) {
		return nil, fmt.Errorf("loading garage RPC secret: %w", err)
	}

	c := &Children{
		logger:     logger,
		runtimeDir: runtimeDir,
		opts:       *opts,
	}

	pmuxConfig, err := c.newPmuxConfig(
		ctx,
		garageRPCSecret,
		binDirPath,
		networkConfig,
		garageAdminToken,
		hostBootstrap,
	)
	if err != nil {
		return nil, fmt.Errorf("generating pmux config: %w", err)
	}

	c.pmux = pmuxlib.NewPmux(pmuxConfig, c.opts.Stdout, c.opts.Stderr)

	initErr := c.postPmuxInit(
		ctx, networkConfig, garageAdminToken, hostBootstrap,
	)
	if initErr != nil {
		logger.Warn(ctx, "failed to initialize Children, shutting down child processes", err)
		c.Shutdown()
		return nil, initErr
	}

	return c, nil
}

// TODO block until process has been confirmed to have come back up
// successfully.
func (c *Children) reloadDNSMasq(
	networkConfig daecommon.NetworkConfig,
	hostBootstrap bootstrap.Bootstrap,
) error {
	_, err := dnsmasqWriteConfig(
		c.runtimeDir.Path, networkConfig, hostBootstrap,
	)
	if err != nil {
		return fmt.Errorf("writing new dnsmasq config: %w", err)
	}

	c.pmux.Restart("dnsmasq")
	return nil
}

func (c *Children) reloadNebula(
	ctx context.Context,
	networkConfig daecommon.NetworkConfig,
	hostBootstrap bootstrap.Bootstrap,
) error {
	_, err := nebulaWriteConfig(
		c.runtimeDir.Path, networkConfig, hostBootstrap,
	)
	if err != nil {
		return fmt.Errorf("writing a new nebula config: %w", err)
	}

	c.pmux.Restart("nebula")

	c.logger.Info(ctx, "Waiting for nebula VPN to come online")
	if err := waitForNebula(ctx, c.logger, hostBootstrap); err != nil {
		return fmt.Errorf("waiting for nebula to start: %w", err)
	}

	return nil
}

// Reload applies a ReloadDiff to the Children, using the given bootstrap which
// must be the same one which was passed to CalculateReloadDiff.
func (c *Children) Reload(
	ctx context.Context,
	newNetworkConfig daecommon.NetworkConfig,
	newBootstrap bootstrap.Bootstrap,
	diff ReloadDiff,
) error {
	var errs []error

	if diff.DNSChanged {
		c.logger.Info(ctx, "Reloading dnsmasq to account for bootstrap changes")
		if err := c.reloadDNSMasq(newNetworkConfig, newBootstrap); err != nil {
			errs = append(errs, fmt.Errorf("reloading dnsmasq: %w", err))
		}
	}

	if diff.NebulaChanged {
		c.logger.Info(ctx, "Reloading nebula to account for bootstrap changes")
		err := c.reloadNebula(ctx, newNetworkConfig, newBootstrap)
		if err != nil {
			errs = append(errs, fmt.Errorf("reloading nebula: %w", err))
		}
	}

	return errors.Join(errs...)
}

// Shutdown blocks until all child processes have gracefully shut themselves
// down.
func (c *Children) Shutdown() {
	c.pmux.Stop()
}