package pi

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"regexp"
	"sort"
	"strings"
)

var (
	ErrConfirmationRequired = errors.New("update requires --yes after reviewing the planned Pi version")
	ErrActiveSessions       = errors.New("active sessions must be drained before updating Pi; use --drain only after they are complete")
	ErrInterruptedUpdate    = errors.New("a previous Pi update is incomplete; run pi rollback --yes before starting another update")
	versionPattern          = regexp.MustCompile(`^[0-9]+(?:\.[0-9]+){1,3}(?:[-+][0-9A-Za-z.-]+)?$`)
	digestPattern           = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._/:@-]*@sha256:[a-f0-9]{64}$`)
)

// Source chooses whether the candidate is built from this checkout or pulled from an immutable image.
type Source string

const (
	BuildSource Source = "build"
	PullSource  Source = "pull"
)

// Request contains only non-secret operator inputs.
type Request struct {
	StatePath string
	Version   string
	Source    Source
	Image     string
	Confirm   bool
	Drain     bool
}

// Result summarizes the completed, failed, or recovered transaction without command output.
type Result struct {
	Phase     Phase
	StatePath string
}

// Update performs a recoverable core-only Pi update using the default Compose command layout.
func Update(ctx context.Context, runner Runner, request Request) (Result, error) {
	if request.StatePath == "" {
		return Result{}, errors.New("update state path is required")
	}
	if !request.Confirm {
		return Result{StatePath: request.StatePath}, ErrConfirmationRequired
	}
	if !versionPattern.MatchString(request.Version) {
		return Result{StatePath: request.StatePath}, errors.New("Pi version must be an explicit pinned version")
	}
	if request.Source == "" {
		request.Source = BuildSource
	}
	if request.Source != BuildSource && request.Source != PullSource {
		return Result{StatePath: request.StatePath}, errors.New("Pi update source must be build or pull")
	}
	if request.Source == PullSource && !digestPattern.MatchString(request.Image) {
		return Result{StatePath: request.StatePath}, errors.New("pulled Pi image must use an immutable sha256 digest")
	}
	if old, err := readState(request.StatePath); err == nil && old.Phase != PhaseVerified && old.Phase != PhaseRolledBack && old.Phase != PhaseNoop {
		return Result{StatePath: request.StatePath}, ErrInterruptedUpdate
	} else if err != nil && !errors.Is(err, os.ErrNotExist) {
		return Result{StatePath: request.StatePath}, err
	}

	running, err := activeSessions(ctx, runner)
	if err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	if running {
		if !request.Drain {
			return Result{StatePath: request.StatePath}, ErrActiveSessions
		}
		running, err = activeSessions(ctx, runner)
		if err != nil {
			return Result{StatePath: request.StatePath}, err
		}
		if running {
			return Result{StatePath: request.StatePath}, ErrActiveSessions
		}
	}
	if err := Doctor(ctx, runner); err != nil {
		return Result{StatePath: request.StatePath}, err
	}

	currentVersion, err := Status(ctx, runner)
	if err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	if currentVersion == request.Version {
		return Result{Phase: PhaseNoop, StatePath: request.StatePath}, nil
	}
	configured, err := renderedCore(ctx, runner)
	if err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	previous, err := runningImage(ctx, runner, configured.Reference)
	if err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	previous.ConfigurationSHA = configured.ConfigurationSHA
	state := State{Phase: PhasePreflight, Target: Target{Version: request.Version, Source: sourceValue(request)}, Previous: previous}
	if err := writeState(request.StatePath, state); err != nil {
		return Result{StatePath: request.StatePath}, err
	}

	state.Phase = PhaseBuilding
	if err := writeState(request.StatePath, state); err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	if err := prepareCandidate(ctx, runner, request, previous.Reference); err != nil {
		state.Phase, state.Error = PhaseFailed, "candidate image preparation failed"
		_ = writeState(request.StatePath, state)
		return Result{Phase: PhaseFailed, StatePath: request.StatePath}, err
	}
	if err := recreateCore(ctx, runner); err != nil {
		state.Phase, state.Error = PhaseFailed, "core recreation failed"
		_ = writeState(request.StatePath, state)
		return Result{Phase: PhaseFailed, StatePath: request.StatePath}, err
	}
	state.Phase = PhaseRecreated
	state.Candidate, _ = runningImage(ctx, runner, previous.Reference)
	if err := writeState(request.StatePath, state); err != nil {
		return Result{Phase: PhaseRecreated, StatePath: request.StatePath}, err
	}
	if err := verifyCandidate(ctx, runner, request.Version, previous.Volumes, previous.ConfigurationSHA); err != nil {
		return rollbackAfterFailure(ctx, runner, request.StatePath, state, err)
	}
	state.Phase, state.Error = PhaseVerified, ""
	if err := writeState(request.StatePath, state); err != nil {
		return Result{Phase: PhaseVerified, StatePath: request.StatePath}, err
	}
	return Result{Phase: PhaseVerified, StatePath: request.StatePath}, nil
}

// Rollback restores the image recorded in durable update state. It is safe for interrupted runs.
func Rollback(ctx context.Context, runner Runner, statePath string, confirm bool) (Result, error) {
	if !confirm {
		return Result{StatePath: statePath}, ErrConfirmationRequired
	}
	state, err := readState(statePath)
	if err != nil {
		return Result{StatePath: statePath}, err
	}
	if err := restore(ctx, runner, state.Previous); err != nil {
		state.Phase, state.Error = PhaseFailed, "rollback failed"
		_ = writeState(statePath, state)
		return Result{Phase: PhaseFailed, StatePath: statePath}, err
	}
	state.Phase, state.Error = PhaseRolledBack, ""
	if err := writeState(statePath, state); err != nil {
		return Result{Phase: PhaseRolledBack, StatePath: statePath}, err
	}
	return Result{Phase: PhaseRolledBack, StatePath: statePath}, nil
}

func rollbackAfterFailure(ctx context.Context, runner Runner, statePath string, state State, cause error) (Result, error) {
	if restoreErr := restore(ctx, runner, state.Previous); restoreErr != nil {
		state.Phase, state.Error = PhaseFailed, "candidate verification and automatic rollback failed"
		_ = writeState(statePath, state)
		return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("candidate verification failed; automatic rollback also failed")
	}
	state.Phase, state.Error = PhaseRolledBack, ""
	_ = writeState(statePath, state)
	return Result{Phase: PhaseRolledBack, StatePath: statePath}, fmt.Errorf("candidate verification failed; previous core image was restored")
}

func sourceValue(request Request) string {
	if request.Source == PullSource {
		return request.Image
	}
	return string(BuildSource)
}

func activeSessions(ctx context.Context, runner Runner) (bool, error) {
	result, err := runCompose(ctx, runner, "exec", "-T", "core", "tht", "session", "list", "--json")
	if err != nil {
		return false, commandError("active-session check", result, err)
	}
	var sessions []struct {
		Status   string `json:"status"`
		Archived bool   `json:"archived"`
	}
	if err := json.Unmarshal([]byte(result.Stdout), &sessions); err != nil {
		return false, errors.New("active-session check returned invalid session data")
	}
	for _, session := range sessions {
		if !session.Archived && session.Status == "open" {
			return true, nil
		}
	}
	return false, nil
}

func runningImage(ctx context.Context, runner Runner, reference string) (Image, error) {
	container, err := runCompose(ctx, runner, "ps", "-q", "core")
	if err != nil || strings.TrimSpace(container.Stdout) == "" {
		return Image{}, commandError("running core image check", container, err)
	}
	id := strings.TrimSpace(container.Stdout)
	image, err := runner.Run(ctx, []string{"inspect", "--format", "{{.Image}}", id}, nil)
	if err != nil || strings.TrimSpace(image.Stdout) == "" {
		return Image{}, commandError("running core image check", image, err)
	}
	mounts, err := runner.Run(ctx, []string{"inspect", "--format", "{{range .Mounts}}{{if eq .Type \"volume\"}}{{.Name}}{{\"\\n\"}}{{end}}{{end}}", id}, nil)
	if err != nil {
		return Image{}, commandError("core volume check", mounts, err)
	}
	volumes := nonEmptyLines(mounts.Stdout)
	if len(volumes) == 0 {
		return Image{}, errors.New("core has no named volumes to preserve")
	}
	return Image{ID: strings.TrimSpace(image.Stdout), Reference: reference, Volumes: volumes}, nil
}

func prepareCandidate(ctx context.Context, runner Runner, request Request, reference string) error {
	if request.Source == BuildSource {
		result, err := runCompose(ctx, runner, "build", "--pull", "--build-arg", "PI_VERSION="+request.Version, "core")
		if err != nil {
			return commandError("Pi image build", result, err)
		}
		return nil
	}
	pull, err := runner.Run(ctx, []string{"pull", request.Image}, nil)
	if err != nil {
		return commandError("Pi image pull", pull, err)
	}
	tag, err := runner.Run(ctx, []string{"image", "tag", request.Image, reference}, nil)
	if err != nil {
		return commandError("Pi image tag", tag, err)
	}
	return nil
}

func recreateCore(ctx context.Context, runner Runner) error {
	result, err := runCompose(ctx, runner, "up", "--detach", "--no-deps", "--force-recreate", "core")
	if err != nil {
		return commandError("core recreation", result, err)
	}
	return nil
}

func verifyCandidate(ctx context.Context, runner Runner, wanted string, previousVolumes []string, configurationSHA string) error {
	health, err := runCompose(ctx, runner, "exec", "-T", "core", "curl", "-fsS", "http://127.0.0.1:8787/health")
	if err != nil {
		return commandError("core health check", health, err)
	}
	version, err := Status(ctx, runner)
	if err != nil {
		return err
	}
	if version != wanted {
		return errors.New("candidate Pi version does not match requested pinned version")
	}
	if err := Test(ctx, runner); err != nil {
		return err
	}
	configured, err := renderedCore(ctx, runner)
	if err != nil {
		return err
	}
	if configured.ConfigurationSHA != configurationSHA {
		return errors.New("external endpoint configuration changed during Pi update")
	}
	after, err := runningImage(ctx, runner, configured.Reference)
	if err != nil {
		return err
	}
	if !sameStrings(previousVolumes, after.Volumes) {
		return errors.New("core volume set changed during Pi update")
	}
	return nil
}

func restore(ctx context.Context, runner Runner, previous Image) error {
	tag, err := runner.Run(ctx, []string{"image", "tag", previous.ID, previous.Reference}, nil)
	if err != nil {
		return commandError("rollback image restore", tag, err)
	}
	if err := recreateCore(ctx, runner); err != nil {
		return err
	}
	configured, err := renderedCore(ctx, runner)
	if err != nil {
		return err
	}
	after, err := runningImage(ctx, runner, configured.Reference)
	if err != nil {
		return err
	}
	if !sameStrings(previous.Volumes, after.Volumes) {
		return errors.New("core volume set changed during rollback")
	}
	return nil
}

func nonEmptyLines(text string) []string {
	var values []string
	for _, value := range strings.Split(text, "\n") {
		if value = strings.TrimSpace(value); value != "" {
			values = append(values, value)
		}
	}
	sort.Strings(values)
	return values
}
func sameStrings(left, right []string) bool {
	left, right = append([]string(nil), left...), append([]string(nil), right...)
	sort.Strings(left)
	sort.Strings(right)
	return strings.Join(left, "\x00") == strings.Join(right, "\x00")
}