// SPDX-FileCopyrightText: 2026 LINUXexpert-org
// SPDX-License-Identifier: GPL-3.0-or-later

package preflight

import (
	"context"
	"encoding/json"
	"fmt"
	"os/exec"
	"strings"

	"github.com/LINUXexpert-org/stalwart-migrator/internal/checkpoint"
)

// checkFunc is the closure Checker.Run uses to run and checkpoint one
// check. Named here so the container checks can be a method rather than
// another hundred lines inside Run.
type checkFunc func(name string, fn func() (CheckResult, string)) (checkpoint.StepOutcome, error)

// ComposeProjectLabel is set by Docker Compose on every container it
// manages. Its presence is the difference between a container this tool
// could one day recreate and one it must not: recreating a compose-managed
// container out from under compose leaves the running container and the
// compose file disagreeing about what is deployed, and the next
// `compose up` silently reverts the migration.
const ComposeProjectLabel = "com.docker.compose.project"

// Mount is one bind or volume mount as the container sees it. Only the
// fields this tool reasons about are kept; docker inspect returns more.
type Mount struct {
	Type        string `json:"Type"`        // "volume" or "bind"
	Name        string `json:"Name"`        // volume name, empty for binds
	Source      string `json:"Source"`      // host path
	Destination string `json:"Destination"` // path inside the container
	RW          bool   `json:"RW"`
}

// ContainerFacts is what `docker inspect` says about a running Stalwart
// container, reduced to the things that decide whether it can be migrated.
type ContainerFacts struct {
	Name    string
	Image   string // the tag it was started from, e.g. "stalwartlabs/stalwart:v0.15.5"
	ImageID string // the digest actually running, which a tag can drift from
	Labels  map[string]string
	Mounts  []Mount
	Running bool
}

// ComposeProject returns the compose project managing this container, or
// "" if it is a plain `docker run`.
func (f ContainerFacts) ComposeProject() string { return f.Labels[ComposeProjectLabel] }

// WritableMounts are the mounts data could persist in. A container with
// none keeps everything in its own writable layer, which is discarded when
// the container is replaced - and replacing the container is exactly what
// migrating it means.
func (f ContainerFacts) WritableMounts() []Mount {
	var out []Mount
	for _, m := range f.Mounts {
		if m.RW {
			out = append(out, m)
		}
	}
	return out
}

// MountFor returns the mount whose Destination contains path, if any. A
// data directory not covered by one lives in the writable layer.
func (f ContainerFacts) MountFor(path string) (Mount, bool) {
	if path == "" {
		return Mount{}, false
	}
	var best Mount
	var found bool
	for _, m := range f.Mounts {
		if m.Destination == path || strings.HasPrefix(path, strings.TrimSuffix(m.Destination, "/")+"/") {
			// Longest destination wins: /var/lib/stalwart/data is more
			// specific than /var/lib, and it is the specific one that
			// actually holds the bytes.
			if !found || len(m.Destination) > len(best.Destination) {
				best, found = m, true
			}
		}
	}
	return best, found
}

// inspectOutput is the subset of `docker inspect` this parses. Named
// separately from ContainerFacts because docker's shape is docker's to
// change, and the rest of this package should not have to know it.
type inspectOutput struct {
	Name   string `json:"Name"`
	Image  string `json:"Image"`
	Config struct {
		Image  string            `json:"Image"`
		Labels map[string]string `json:"Labels"`
	} `json:"Config"`
	State struct {
		Running bool `json:"Running"`
	} `json:"State"`
	Mounts []Mount `json:"Mounts"`
}

// InspectContainer reads the facts about containerName. An error here is
// an error, not an absent container: callers reach this only after
// DetectDeploymentKind has already established that a container answers to
// this name, so a failure now means docker stopped answering, and guessing
// past that is how a tool ends up migrating something it cannot see.
func InspectContainer(ctx context.Context, containerName string) (ContainerFacts, error) {
	if containerName == "" {
		containerName = "stalwart"
	}
	out, err := exec.CommandContext(ctx, "docker", "inspect", containerName).Output()
	if err != nil {
		return ContainerFacts{}, fmt.Errorf("preflight: docker inspect %s: %w", containerName, err)
	}
	var got []inspectOutput
	if err := json.Unmarshal(out, &got); err != nil {
		return ContainerFacts{}, fmt.Errorf("preflight: parsing docker inspect %s: %w", containerName, err)
	}
	if len(got) == 0 {
		return ContainerFacts{}, fmt.Errorf("preflight: docker inspect %s returned no container", containerName)
	}
	c := got[0]
	return ContainerFacts{
		Name:    strings.TrimPrefix(c.Name, "/"),
		Image:   c.Config.Image,
		ImageID: c.Image,
		Labels:  c.Config.Labels,
		Mounts:  c.Mounts,
		Running: c.State.Running,
	}, nil
}

// runContainerChecks adds the checks that only apply to a container. They
// run after deployment-kind has already established there is one.
//
// Both are blocking for `run` and advisory for `rehearse`, on the same
// reasoning as the deployment-kind check itself: rehearse never stops or
// recreates anything, and an operator doing the migration by hand needs
// these facts more than an automated run does.
func (c *Checker) runContainerChecks(ctx context.Context, runCheck checkFunc) error {
	facts, factsErr := InspectContainer(ctx, c.opts.ContainerName)

	if _, err := runCheck("container-inspect", func() (CheckResult, string) {
		if factsErr != nil {
			return CheckResult{Status: StatusFail, Detail: factsErr.Error()}, ""
		}
		return CheckResult{Status: StatusOK, Detail: fmt.Sprintf(
			"container %s runs image %s (%s)", facts.Name, facts.Image, shortID(facts.ImageID))}, facts.Image
	}); err != nil {
		return err
	}
	if factsErr != nil {
		// The two checks below read facts we do not have.
		return nil
	}

	if _, err := runCheck("container-runtime", func() (CheckResult, string) {
		project := facts.ComposeProject()
		if project == "" {
			return CheckResult{Status: StatusOK, Detail: "plain docker container, not compose-managed"}, ""
		}
		status := StatusFail
		if c.opts.DeploymentCheckAdvisory {
			status = StatusWarn
		}
		return CheckResult{Status: status, Detail: fmt.Sprintf(
			"container is managed by docker compose (project %q). Recreating it out from under compose would leave the "+
				"running container and the compose file disagreeing about what is deployed, and the next `compose up` would "+
				"revert the migration. Migrate it by editing the image tag in the compose file and running `compose up -d`",
			project)}, project
	}); err != nil {
		return err
	}

	_, err := runCheck("container-data-volume", func() (CheckResult, string) {
		writable := facts.WritableMounts()
		if len(writable) == 0 {
			status := StatusFail
			if c.opts.DeploymentCheckAdvisory {
				status = StatusWarn
			}
			return CheckResult{Status: status, Detail: "container has no writable volume or bind mount, so its data lives in " +
				"the container's own writable layer - which is discarded when the container is replaced, and replacing it is " +
				"what migrating it means. Move the data onto a volume before migrating"}, ""
		}
		// A data directory named but not covered by a mount is the same
		// problem wearing a disguise, and worth saying separately: the
		// mounts exist, they just are not where the data is.
		if c.opts.DataDir != "" {
			if m, ok := facts.MountFor(c.opts.DataDir); ok {
				return CheckResult{Status: StatusOK, Detail: fmt.Sprintf(
					"data dir %s is on a %s mount (%s)", c.opts.DataDir, m.Type, mountSource(m))}, m.Destination
			}
			status := StatusFail
			if c.opts.DeploymentCheckAdvisory {
				status = StatusWarn
			}
			return CheckResult{Status: status, Detail: fmt.Sprintf(
				"data dir %s is not covered by any of the container's mounts (%s), so it lives in the writable layer and would "+
					"not survive the container being replaced. Check whether --data-dir names the path inside the container",
				c.opts.DataDir, describeMounts(facts.Mounts))}, ""
		}
		return CheckResult{Status: StatusOK, Detail: "container has writable mounts: " + describeMounts(writable)}, ""
	})
	return err
}

func shortID(id string) string {
	id = strings.TrimPrefix(id, "sha256:")
	if len(id) > 12 {
		return id[:12]
	}
	return id
}

func mountSource(m Mount) string {
	if m.Name != "" {
		return m.Name
	}
	return m.Source
}

func describeMounts(mounts []Mount) string {
	if len(mounts) == 0 {
		return "none"
	}
	parts := make([]string, 0, len(mounts))
	for _, m := range mounts {
		parts = append(parts, m.Destination+" <- "+mountSource(m))
	}
	return strings.Join(parts, ", ")
}