package cluster

import (
	"context"
	"fmt"
	"strings"
	"sync"
	"time"
)

type drainFailure struct {
	node    string
	err     error
	details string
}

// drainWorkers runs one orchestration or CLI step.
// Signature: (o *Orchestrator) drainWorkers(ctx context.Context, workers []string) error.
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) drainWorkers(ctx context.Context, workers []string) error {
	total := len(workers)
	if total == 0 {
		return nil
	}
	parallelism := o.cfg.Shutdown.DrainParallelism
	if parallelism <= 0 {
		parallelism = 6
	}
	if parallelism > total {
		parallelism = total
	}

	o.log.Printf("drain workers total=%d parallelism=%d", total, parallelism)
	sem := make(chan struct{}, parallelism)
	var wg sync.WaitGroup
	errCh := make(chan drainFailure, total)

	for idx, node := range workers {
		idx := idx
		node := node
		wg.Add(1)
		go func() {
			defer wg.Done()
			sem <- struct{}{}
			defer func() { <-sem }()

			o.log.Printf("drain worker %d/%d: %s", idx+1, total, node)
			if _, err := o.kubectl(ctx, 20*time.Second, "cordon", node); err != nil {
				o.log.Printf("warning: cordon %s failed: %v", node, err)
			}
			if _, err := o.kubectl(ctx, 3*time.Minute, "drain", node, "--ignore-daemonsets", "--delete-emptydir-data", "--grace-period=30", "--timeout=180s"); err != nil {
				details := o.drainNodeDiagnostics(ctx, node)
				errCh <- drainFailure{
					node:    node,
					err:     fmt.Errorf("drain %s failed: %w", node, err),
					details: details,
				}
				return
			}
		}()
	}

	wg.Wait()
	close(errCh)
	if len(errCh) == 0 {
		return nil
	}
	failures := make([]drainFailure, 0, len(errCh))
	for failure := range errCh {
		failures = append(failures, failure)
	}
	count := len(failures)
	samples := []string{}
	for _, failure := range failures {
		msg := failure.err.Error()
		if strings.TrimSpace(failure.details) != "" {
			msg = fmt.Sprintf("%s (details: %s)", msg, failure.details)
		}
		samples = append(samples, msg)
		if len(samples) >= 4 {
			break
		}
	}
	return fmt.Errorf("drain workers had %d errors (first: %s)", count, strings.Join(samples, " | "))
}

// drainNodeDiagnostics runs one orchestration or CLI step.
// Signature: (o *Orchestrator) drainNodeDiagnostics(ctx context.Context, node string) string.
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) drainNodeDiagnostics(ctx context.Context, node string) string {
	out, err := o.kubectl(
		ctx,
		20*time.Second,
		"get",
		"pods",
		"-A",
		"--field-selector", "spec.nodeName="+node,
		"-o",
		"custom-columns=NS:.metadata.namespace,NAME:.metadata.name,PHASE:.status.phase,OWNER:.metadata.ownerReferences[0].kind",
		"--no-headers",
	)
	if err != nil {
		if strings.TrimSpace(out) == "" {
			return fmt.Sprintf("diagnostics unavailable: %v", err)
		}
		return fmt.Sprintf("diagnostics unavailable: %v (%s)", err, strings.Join(lines(out), "; "))
	}

	blockers := make([]string, 0, 6)
	for _, line := range lines(out) {
		fields := strings.Fields(line)
		if len(fields) < 4 {
			continue
		}
		namespace := fields[0]
		name := fields[1]
		phase := fields[2]
		owner := fields[3]
		if strings.EqualFold(owner, "DaemonSet") {
			continue
		}
		if strings.EqualFold(phase, "Succeeded") || strings.EqualFold(phase, "Failed") {
			continue
		}
		blockers = append(blockers, fmt.Sprintf("%s/%s(phase=%s owner=%s)", namespace, name, phase, owner))
		if len(blockers) >= 6 {
			break
		}
	}
	if len(blockers) == 0 {
		return "no non-daemonset blocking pods found on node"
	}
	return strings.Join(blockers, ", ")
}

// uncordonWorkers runs one orchestration or CLI step.
// Signature: (o *Orchestrator) uncordonWorkers(ctx context.Context, workers []string) error.
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) uncordonWorkers(ctx context.Context, workers []string) error {
	for _, node := range workers {
		if _, err := o.kubectl(ctx, 20*time.Second, "uncordon", node); err != nil {
			o.log.Printf("warning: uncordon %s failed: %v", node, err)
		}
	}
	return nil
}

// stopWorkers runs one orchestration or CLI step.
// Signature: (o *Orchestrator) stopWorkers(ctx context.Context, workers []string).
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) stopWorkers(ctx context.Context, workers []string) {
	o.runSSHAcrossNodes(ctx, workers, "stop k3s-agent", "sudo systemctl stop k3s-agent || true")
}

// startWorkers runs one orchestration or CLI step.
// Signature: (o *Orchestrator) startWorkers(ctx context.Context, workers []string).
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) startWorkers(ctx context.Context, workers []string) {
	o.runSSHAcrossNodes(ctx, workers, "start k3s-agent", "sudo systemctl start k3s-agent || true")
}

// stopControlPlanes runs one orchestration or CLI step.
// Signature: (o *Orchestrator) stopControlPlanes(ctx context.Context, cps []string).
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) stopControlPlanes(ctx context.Context, cps []string) {
	o.runSSHAcrossNodes(ctx, cps, "stop k3s", "sudo systemctl stop k3s || true")
}

// startControlPlanes runs one orchestration or CLI step.
// Signature: (o *Orchestrator) startControlPlanes(ctx context.Context, cps []string).
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) startControlPlanes(ctx context.Context, cps []string) {
	o.runSSHAcrossNodes(ctx, cps, "start k3s", "sudo systemctl start k3s || true")
}

// runSSHAcrossNodes runs one orchestration or CLI step.
// Signature: (o *Orchestrator) runSSHAcrossNodes(ctx context.Context, nodes []string, action, command string).
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) runSSHAcrossNodes(ctx context.Context, nodes []string, action, command string) {
	if len(nodes) == 0 {
		return
	}
	parallelism := o.cfg.Shutdown.SSHParallelism
	if parallelism <= 0 {
		parallelism = 8
	}
	if parallelism > len(nodes) {
		parallelism = len(nodes)
	}

	sem := make(chan struct{}, parallelism)
	var wg sync.WaitGroup
	for _, node := range nodes {
		node := node
		if !o.sshManaged(node) {
			o.log.Printf("skip %s on %s: node not in ssh_managed_nodes", action, node)
			continue
		}
		wg.Add(1)
		go func() {
			defer wg.Done()
			sem <- struct{}{}
			defer func() { <-sem }()
			o.bestEffort(action+" on "+node, func() error {
				_, err := o.ssh(ctx, node, command)
				return err
			})
		}()
	}
	wg.Wait()
}

// takeEtcdSnapshot runs one orchestration or CLI step.
// Signature: (o *Orchestrator) takeEtcdSnapshot(ctx context.Context, node string) error.
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) takeEtcdSnapshot(ctx context.Context, node string) error {
	if !o.sshManaged(node) {
		return fmt.Errorf("cannot run etcd snapshot on %s: node not in ssh_managed_nodes", node)
	}
	name := "pre-shutdown-" + time.Now().UTC().Format("20060102-150405")
	_, err := o.runSudoK3S(ctx, node, "etcd-snapshot", "save", "--name", name)
	return err
}

// latestEtcdSnapshotPath runs one orchestration or CLI step.
// Signature: (o *Orchestrator) latestEtcdSnapshotPath(ctx context.Context, node string) (string, error).
// Why: keeps behavior explicit so startup/shutdown workflows remain maintainable as services evolve.
func (o *Orchestrator) latestEtcdSnapshotPath(ctx context.Context, node string) (string, error) {
	if !o.sshManaged(node) {
		return "", fmt.Errorf("cannot resolve etcd snapshot on %s: node not in ssh_managed_nodes", node)
	}
	out, err := o.runSudoK3S(ctx, node, "etcd-snapshot", "ls")
	if err != nil {
		return "", fmt.Errorf("resolve latest etcd snapshot on %s: %w", node, err)
	}
	snapshot := parseSnapshotPathFromEtcdSnapshotList(out)
	if snapshot == "" {
		return "", fmt.Errorf("no etcd snapshots found on %s under /var/lib/rancher/k3s/server/db/snapshots", node)
	}
	return snapshot, nil
}