package fileedit

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"sort"
	"strings"
	"time"

	batchv1 "k8s.io/api/batch/v1"
	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/kubernetes"
)

// pollInterval is how often the runner re-Lists Pods while waiting for the file
// container to start. It is a POLL rather than a Watch because felis-api holds
// pods:list and NOT pods:watch (internal/platform.APIMinecraftRole) — establishing
// a watch would need a permission this design exists to avoid.
const pollInterval = 150 * time.Millisecond

// maxLogBytes bounds what the runner will buffer from a Pod's log. The payload is
// at most a base64-encoded MaxReadBytes (≈4/3 of 1 MiB) plus the JSON envelope, so
// 4 MiB is generous headroom while still refusing to let a Pod that floods stderr
// pull felis-api's memory down with it.
const maxLogBytes = 4 << 20

// K8sRunner is the production Runner (spec §7, §16). It drives one file operation
// end to end using ONLY the three permissions felis-api already holds in the
// minecraft namespace, which is the entire point of the design:
//
//	jobs:create   → create the file Job
//	pods:list     → find its Pod and observe the phase (no pods:get, no pods:watch)
//	pods/log:get  → read the printed result back
//
// It deliberately takes a typed kubernetes.Interface rather than the
// controller-runtime client that internal/restore's K8sJobs uses: the log
// subresource (GetLogs(...).Stream) exists only on the typed CoreV1 client, and
// the Job create is available on both — so one client covers all three calls
// instead of the binding carrying two.
//
// The transport is tested against the Kubernetes HTTP API shape; the Editor
// tests separately verify orchestration and error mapping against a fake Runner.
type K8sRunner struct {
	cs      kubernetes.Interface
	Browser *Browser
}

// NewK8sRunner builds a Runner over cs. Every per-operation parameter — the
// namespace included — travels in the JobParams the Editor renders, so there is no
// Config to retain here.
func NewK8sRunner(cs kubernetes.Interface) *K8sRunner {
	return &K8sRunner{cs: cs}
}

// Run streams read results as soon as they are printed. Mutations still wait
// for termination so returning success does not leave the next write racing
// the cluster-side world lock.
//
// The Job name carries a fresh random OpID (FilesJobName), so a create collision is
// not an expected condition the way it is for restore — an AlreadyExists here means
// a 64-bit collision inside one TTL window and is reported rather than absorbed,
// because absorbing it would mean returning ANOTHER operation's output.
func (k *K8sRunner) Run(ctx context.Context, p JobParams) ([]byte, error) {
	if k.Browser != nil && !mutates(p.Op) {
		payload, err := k.Browser.Run(ctx, p, k.Start)
		// At capacity, retain the bounded one-shot path instead of starting
		// more idle workers. All reads still use the same containment checks.
		if !errors.Is(err, errBrowserFull) {
			return payload, err
		}
	}
	job, err := FilesJob(p)
	if err != nil {
		return nil, err
	}
	if _, err := k.cs.BatchV1().Jobs(p.Namespace).Create(ctx, job, metav1.CreateOptions{}); err != nil {
		return nil, fmt.Errorf("fileedit: create file job: %w", err)
	}

	pod, err := k.awaitPod(ctx, p)
	if err != nil {
		return nil, err
	}

	stream, err := k.cs.CoreV1().Pods(p.Namespace).GetLogs(pod.Name, &corev1.PodLogOptions{
		Container: containerName, Follow: true,
	}).Stream(ctx)
	if err != nil {
		return nil, fmt.Errorf("fileedit: read file job log: %w", err)
	}
	defer stream.Close()
	sc := bufio.NewScanner(io.LimitReader(stream, maxLogBytes))
	sc.Buffer(make([]byte, 0, 64*1024), maxLogBytes)
	var last string
	for sc.Scan() {
		if payload, ok := strings.CutPrefix(sc.Text(), ResultPrefix); ok {
			return []byte(payload), nil
		}
		last = sc.Text()
	}
	if err := sc.Err(); err != nil {
		return nil, fmt.Errorf("fileedit: read file job result: %w", err)
	}
	return nil, fmt.Errorf("fileedit: file job %s produced no result (phase %s): %s",
		job.Name, pod.Status.Phase, tail(last))
}

// awaitPod polls until the file container has started (or failed). It selects by
// the per-invocation LabelOpID, so it can never observe a different operation's Pod
// — the reason that label exists.
//
// Both Succeeded and Failed are terminal and BOTH return the Pod rather than an
// error, because a caller-fault result (a path that escapes the root, a file that
// is too large) is printed and then exited on cleanly, and even a genuinely failed
// Pod may have printed a diagnosable result first. Deciding what the outcome MEANS
// is the caller's job (Run reads the printed result); this function only decides
// when its log can be opened without a ContainerCreating refusal.
func (k *K8sRunner) awaitPod(ctx context.Context, p JobParams) (*corev1.Pod, error) {
	ticker := time.NewTicker(pollInterval)
	defer ticker.Stop()

	for {
		pods, err := k.cs.CoreV1().Pods(p.Namespace).List(ctx, metav1.ListOptions{
			LabelSelector: LabelOpID + "=" + p.OpID,
		})
		if err != nil {
			return nil, fmt.Errorf("fileedit: find file job pod: %w", err)
		}
		for i := range pods.Items {
			pod := &pods.Items[i]
			if !mutates(p.Op) {
				for _, c := range pod.Status.ContainerStatuses {
					if c.Name == containerName && (c.State.Running != nil || c.State.Terminated != nil) {
						return pod, nil
					}
				}
			}
			switch pod.Status.Phase {
			case corev1.PodSucceeded, corev1.PodFailed:
				return pod, nil
			}
		}

		select {
		case <-ticker.C:
		case <-ctx.Done():
			// The Editor's Timeout (or the client disconnecting) fired. The Job is left
			// alone deliberately: felis-api holds no jobs:delete, and the Job's own
			// activeDeadlineSeconds plus ttlSecondsAfterFinished retire it without help.
			return nil, fmt.Errorf("fileedit: timed out waiting for the file job to finish: %w", ctx.Err())
		}
	}
}

// extractResult finds the marked payload in a Pod log. It scans for the LAST line
// carrying ResultPrefix because pods/log returns stdout and stderr MERGED: a Go
// runtime warning or a libc message can appear anywhere in the stream, so the
// payload must be located by its marker rather than by position. Taking the last
// match rather than the first is the conservative choice — if a marker somehow
// appeared more than once, the final one is the operation's actual outcome.
func extractResult(log string) ([]byte, bool) {
	var payload string
	var found bool
	sc := bufio.NewScanner(strings.NewReader(log))
	sc.Buffer(make([]byte, 0, 64*1024), maxLogBytes)
	for sc.Scan() {
		if rest, ok := strings.CutPrefix(sc.Text(), ResultPrefix); ok {
			payload, found = rest, true
		}
	}
	if !found {
		return nil, false
	}
	return []byte(payload), true
}

// tail returns the last few hundred bytes of a log for an error message, so a
// diagnostic is useful without embedding an entire log in an error string.
func tail(log string) string {
	const n = 512
	log = strings.TrimSpace(log)
	if len(log) <= n {
		return log
	}
	return "..." + log[len(log)-n:]
}

// Start creates the Job for p and returns without waiting on it. Ops reads it
// back.
func (k *K8sRunner) Start(ctx context.Context, p JobParams) error {
	job, err := FilesJob(p)
	if err != nil {
		return err
	}
	if _, err := k.cs.BatchV1().Jobs(p.Namespace).Create(ctx, job, metav1.CreateOptions{}); err != nil {
		return fmt.Errorf("fileedit: create file job: %w", err)
	}
	return nil
}

// maxOps bounds what Ops reports, and so how many Pod logs one call reads. Only
// one background op runs per server at a time (it holds the world volume), so
// this many are the one running and the latest that finished within AsyncTTL.
const maxOps = 10

// opLogLines is how much of an op's log Ops reads: the result line is the last
// thing the Job prints to stdout, the progress lines come before it, and a
// failed run ends with one line on stderr.
const opLogLines = 20

// Ops lists the server's background Jobs, newest first, with how far each has
// got and how it ended, read from the tail of its Pod's log. A Pod whose log
// cannot be read yet (still pulling its image) or any more (its node went away)
// reports no progress rather than failing the listing.
func (k *K8sRunner) Ops(ctx context.Context, namespace, server string) ([]OpState, error) {
	sel := metav1.ListOptions{LabelSelector: LabelManagedBy + "=" + managedByValue + "," +
		LabelServer + "=" + server + "," + LabelAsync + "=true"}
	jobs, err := k.cs.BatchV1().Jobs(namespace).List(ctx, sel)
	if err != nil {
		return nil, fmt.Errorf("fileedit: list file jobs: %w", err)
	}
	pods, err := k.cs.CoreV1().Pods(namespace).List(ctx, sel)
	if err != nil {
		return nil, fmt.Errorf("fileedit: list file job pods: %w", err)
	}
	// backoffLimit is 0, so a Job has one Pod; the newest wins all the same.
	podOf := map[string]*corev1.Pod{}
	for i := range pods.Items {
		pod := &pods.Items[i]
		id := pod.Labels[LabelOpID]
		if cur := podOf[id]; cur == nil || pod.CreationTimestamp.After(cur.CreationTimestamp.Time) {
			podOf[id] = pod
		}
	}
	items := jobs.Items
	sort.SliceStable(items, func(i, j int) bool {
		return items[i].CreationTimestamp.After(items[j].CreationTimestamp.Time)
	})
	if len(items) > maxOps {
		items = items[:maxOps]
	}
	out := make([]OpState, 0, len(items))
	for i := range items {
		log := ""
		pod := podOf[items[i].Labels[LabelOpID]]
		if pod != nil && pod.Status.Phase != corev1.PodPending {
			log, _ = k.logTail(ctx, namespace, pod.Name)
		}
		out = append(out, opState(&items[i], pod, log))
	}
	return out, nil
}

// logTail reads the last opLogLines lines of a Pod's log.
func (k *K8sRunner) logTail(ctx context.Context, namespace, pod string) (string, error) {
	lines := int64(opLogLines)
	stream, err := k.cs.CoreV1().Pods(namespace).GetLogs(pod, &corev1.PodLogOptions{
		Container: containerName, TailLines: &lines,
	}).Stream(ctx)
	if err != nil {
		return "", err
	}
	defer stream.Close()
	b, err := io.ReadAll(io.LimitReader(stream, maxLogBytes))
	return string(b), err
}

// opState reads one background Job, and the tail of its Pod's log, as an
// OpState. The printed result decides the outcome whatever the Job's condition
// says: a Job killed at its deadline just after printing did finish its work.
// A Job that ended without one failed, and the condition's reason says how
// (DeadlineExceeded, BackoffLimitExceeded), unless its Pod says the kernel
// killed it for memory (ReasonOOMKilled), which the condition does not tell; a
// Job that completed but whose log could not be read has an outcome no one can
// tell, ResultUnavailable.
func opState(job *batchv1.Job, pod *corev1.Pod, log string) OpState {
	st := OpState{
		ID: job.Labels[LabelOpID], Op: job.Labels[LabelMode], Path: job.Annotations[AnnotationPath],
		State: OpRunning, Started: job.CreationTimestamp.Time,
	}
	if p, ok := lastProgress(log); ok {
		st.Done, st.Total = p.Done, p.Total
	}
	ended, reason := false, ""
	for _, c := range job.Status.Conditions {
		if c.Status != corev1.ConditionTrue {
			continue
		}
		switch c.Type {
		case batchv1.JobComplete, batchv1.JobSuccessCriteriaMet:
			ended, reason = true, "ResultUnavailable"
			st.Finished = c.LastTransitionTime.Time
		case batchv1.JobFailed, batchv1.JobFailureTarget:
			ended, reason = true, c.Reason
			st.Finished = c.LastTransitionTime.Time
		}
	}
	if !ended {
		return st
	}
	if payload, ok := extractResult(log); ok {
		var res Result
		if json.Unmarshal(payload, &res) == nil {
			st.Result = &res
		}
	}
	switch {
	case st.Result != nil && st.Result.Code == "":
		st.State = OpSucceeded
	case st.Result != nil:
		st.State = OpFailed
	default:
		st.State, st.Reason = OpFailed, reason
		if killedForMemory(pod) {
			st.Reason = ReasonOOMKilled
		} else if st.Reason == "" {
			st.Reason = "Failed"
		}
	}
	return st
}

// ReasonOOMKilled is an op's Reason when the kernel killed its Job for going over
// the Job's memory limit: an archive of more entries than the Job can hold the
// list of.
const ReasonOOMKilled = "OOMKilled"

// killedForMemory reports whether pod's container was killed for going over its
// memory limit.
func killedForMemory(pod *corev1.Pod) bool {
	if pod == nil {
		return false
	}
	for _, cs := range pod.Status.ContainerStatuses {
		if t := cs.State.Terminated; cs.Name == containerName && t != nil && t.Reason == ReasonOOMKilled {
			return true
		}
	}
	return false
}