// SPDX-License-Identifier: GPL-3.0-or-later

// Package snapshot retains Python-compatible alert snapshot pairs for the Go
// migration service. It intentionally leaves incident grouping and rich
// post-alert enrichment to later parity tranches while preserving the stable
// v1 fields consumed by existing read-only tools.
package snapshot

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"codeberg.org/anassaeneroi/enodia-sentinal/go-agent/internal/model"
)

const Schema = "enodia.alert.snapshot.v1"

type ProcessDetail struct {
	PID       int               `json:"pid"`
	Comm      string            `json:"comm"`
	Exe       string            `json:"exe"`
	CWD       string            `json:"cwd"`
	Cmdline   string            `json:"cmdline"`
	PPID      int               `json:"ppid"`
	PPIDComm  string            `json:"ppid_comm"`
	UID       int               `json:"uid"`
	LDPreload string            `json:"ld_preload"`
	FDs       map[string]string `json:"fds"`
}

type Report struct {
	Schema     string          `json:"schema"`
	Time       string          `json:"time"`
	Host       string          `json:"host"`
	Severity   string          `json:"severity"`
	IncidentID *string         `json:"incident_id"`
	Alerts     []model.Alert   `json:"alerts"`
	Processes  []ProcessDetail `json:"processes"`
	Enrichment map[string]any  `json:"enrichment"`
}

type Stats struct {
	Total     int
	Counts    map[string]int
	LastAlert *string
}

type Store struct {
	Dir        string
	ProcRoot   string
	MaxCount   int
	MaxAgeDays int
	Now        func() time.Time
	Collect    func(int) ProcessDetail

	mu sync.Mutex
}

// New preflights the isolated snapshot directory before service readiness.
func New(dir, procRoot string, maxCount, maxAgeDays int) (*Store, error) {
	if dir == "" {
		return nil, fmt.Errorf("snapshot directory is required")
	}
	if maxCount < 0 || maxAgeDays < 0 {
		return nil, fmt.Errorf("snapshot retention values must be non-negative")
	}
	if procRoot == "" {
		procRoot = "/proc"
	}
	if err := os.MkdirAll(dir, 0o750); err != nil {
		return nil, fmt.Errorf("create snapshot directory: %w", err)
	}
	probe, err := os.CreateTemp(dir, ".snapshot-preflight-*")
	if err != nil {
		return nil, fmt.Errorf("preflight snapshot directory: %w", err)
	}
	probePath := probe.Name()
	if err := probe.Chmod(0o600); err != nil {
		probe.Close()
		os.Remove(probePath)
		return nil, fmt.Errorf("protect snapshot preflight: %w", err)
	}
	if err := probe.Close(); err != nil {
		os.Remove(probePath)
		return nil, fmt.Errorf("close snapshot preflight: %w", err)
	}
	if err := os.Remove(probePath); err != nil {
		return nil, fmt.Errorf("remove snapshot preflight: %w", err)
	}
	store := &Store{Dir: dir, ProcRoot: procRoot, MaxCount: maxCount, MaxAgeDays: maxAgeDays, Now: time.Now}
	store.Collect = func(pid int) ProcessDetail { return collectProcess(procRoot, pid) }
	if err := store.Prune(); err != nil {
		return nil, err
	}
	return store, nil
}

// CaptureEvent merges one alert envelope into its second-granularity snapshot.
// Python filenames use second precision, so merging avoids overwriting sibling
// alerts emitted by one poll sweep or concurrent kernel sources.
func (s *Store) CaptureEvent(event map[string]any) (string, error) {
	if event["event_type"] != "alert" {
		return "", fmt.Errorf("snapshot requires an alert event")
	}
	alert, err := decodeAlert(event["alert"])
	if err != nil {
		return "", err
	}
	timestamp, ok := event["timestamp"].(string)
	if !ok || timestamp == "" {
		return "", fmt.Errorf("snapshot event timestamp is required")
	}
	captured, err := time.Parse(time.RFC3339Nano, timestamp)
	if err != nil {
		return "", fmt.Errorf("parse snapshot timestamp: %w", err)
	}
	host, _ := event["host"].(string)
	base := filepath.Join(s.Dir, "alert-"+captured.Format("20060102-150405"))

	s.mu.Lock()
	defer s.mu.Unlock()
	report := Report{
		Schema: Schema, Time: timestamp, Host: host, Severity: alert.Severity,
		Alerts: []model.Alert{}, Processes: []ProcessDetail{},
		Enrichment: map[string]any{"source": "enodia-sentinel-go"},
	}
	jsonPath := base + ".json"
	if raw, err := os.ReadFile(jsonPath); err == nil {
		if err := json.Unmarshal(raw, &report); err != nil {
			return "", fmt.Errorf("decode existing snapshot: %w", err)
		}
		if report.Schema != Schema {
			return "", fmt.Errorf("existing snapshot has schema %q", report.Schema)
		}
	} else if !os.IsNotExist(err) {
		return "", fmt.Errorf("read existing snapshot: %w", err)
	}
	report.Alerts = append(report.Alerts, alert)
	report.Severity = maxSeverity(report.Severity, alert.Severity)
	report.Processes = s.collectProcesses(report.Alerts)
	if report.Enrichment == nil {
		report.Enrichment = map[string]any{"source": "enodia-sentinel-go"}
	}
	if err := writeJSONAtomic(jsonPath, report); err != nil {
		return "", err
	}
	if err := writeAtomic(base+".log", []byte(formatText(report))); err != nil {
		return "", err
	}
	if err := s.pruneLocked(); err != nil {
		return "", err
	}
	return filepath.Base(base + ".log"), nil
}

func (s *Store) collectProcesses(alerts []model.Alert) []ProcessDetail {
	seen := map[int]bool{}
	var pids []int
	for _, alert := range alerts {
		for _, pid := range alert.PIDs {
			if pid > 0 && !seen[pid] {
				seen[pid] = true
				pids = append(pids, pid)
			}
		}
	}
	sort.Ints(pids)
	result := make([]ProcessDetail, 0, len(pids))
	for _, pid := range pids {
		result = append(result, s.Collect(pid))
	}
	return result
}

// SnapshotStats prunes first, then derives status claims from retained,
// parseable snapshot files. Calling it for every status emission keeps the age
// bound active even when a quiet host produces no new alert snapshots.
func (s *Store) SnapshotStats() (Stats, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if err := s.pruneLocked(); err != nil {
		return Stats{}, err
	}
	stats := Stats{Counts: map[string]int{}}
	paths, _ := filepath.Glob(filepath.Join(s.Dir, "alert-*.json"))
	for _, path := range paths {
		raw, err := os.ReadFile(path)
		if err != nil {
			continue
		}
		var report Report
		if json.Unmarshal(raw, &report) != nil || report.Schema != Schema {
			continue
		}
		stats.Total++
		stats.Counts[report.Severity]++
		if stats.LastAlert == nil || report.Time > *stats.LastAlert {
			value := report.Time
			stats.LastAlert = &value
		}
	}
	return stats, nil
}

// Prune applies count and age limits to JSON/text pairs.
func (s *Store) Prune() error {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.pruneLocked()
}

func (s *Store) pruneLocked() error {
	paths, err := filepath.Glob(filepath.Join(s.Dir, "alert-*.json"))
	if err != nil {
		return fmt.Errorf("list snapshots: %w", err)
	}
	type candidate struct {
		path string
		mod  time.Time
	}
	items := make([]candidate, 0, len(paths))
	for _, path := range paths {
		info, err := os.Stat(path)
		if err == nil {
			items = append(items, candidate{path: path, mod: info.ModTime()})
		}
	}
	sort.Slice(items, func(i, j int) bool { return items[i].mod.After(items[j].mod) })
	cutoff := time.Time{}
	if s.MaxAgeDays > 0 {
		cutoff = s.Now().Add(-time.Duration(s.MaxAgeDays) * 24 * time.Hour)
	}
	kept := 0
	for _, item := range items {
		remove := (!cutoff.IsZero() && item.mod.Before(cutoff)) || (s.MaxCount > 0 && kept >= s.MaxCount)
		if remove {
			if err := removePair(item.path); err != nil {
				return err
			}
			continue
		}
		kept++
	}
	return nil
}

func decodeAlert(value any) (model.Alert, error) {
	raw, err := json.Marshal(value)
	if err != nil {
		return model.Alert{}, fmt.Errorf("encode snapshot alert: %w", err)
	}
	var alert model.Alert
	if err := json.Unmarshal(raw, &alert); err != nil {
		return model.Alert{}, fmt.Errorf("decode snapshot alert: %w", err)
	}
	if alert.SID == 0 || alert.Signature == "" || alert.Severity == "" {
		return model.Alert{}, fmt.Errorf("snapshot alert is incomplete")
	}
	return alert, nil
}

func maxSeverity(left, right string) string {
	rank := map[string]int{"MEDIUM": 1, "HIGH": 2, "CRITICAL": 3}
	if rank[right] > rank[left] {
		return right
	}
	return left
}

func writeJSONAtomic(path string, value any) error {
	raw, err := json.MarshalIndent(value, "", "  ")
	if err != nil {
		return fmt.Errorf("encode snapshot: %w", err)
	}
	return writeAtomic(path, append(raw, '\n'))
}

func writeAtomic(path string, raw []byte) error {
	temporary := path + ".tmp"
	if err := os.WriteFile(temporary, raw, 0o600); err != nil {
		return fmt.Errorf("write snapshot: %w", err)
	}
	if err := os.Rename(temporary, path); err != nil {
		return fmt.Errorf("replace snapshot: %w", err)
	}
	if err := os.Chmod(path, 0o600); err != nil {
		return fmt.Errorf("protect snapshot: %w", err)
	}
	return nil
}

func removePair(jsonPath string) error {
	base := strings.TrimSuffix(jsonPath, ".json")
	for _, path := range []string{base + ".json", base + ".log"} {
		if err := os.Remove(path); err != nil && !os.IsNotExist(err) {
			return fmt.Errorf("remove expired snapshot: %w", err)
		}
	}
	return nil
}

func formatText(report Report) string {
	var output strings.Builder
	fmt.Fprintln(&output, "=== ENODIA SENTINEL ALERT ===")
	fmt.Fprintln(&output, "Time:    ", report.Time)
	fmt.Fprintln(&output, "Host:    ", report.Host)
	fmt.Fprintln(&output, "Severity:", report.Severity)
	fmt.Fprintln(&output, "\n## Triggering detections")
	for _, alert := range report.Alerts {
		fmt.Fprintf(&output, "  [%s] sid:%d %s (%s) — %s\n", alert.Severity, alert.SID, alert.Signature, alert.Classtype, alert.Detail)
	}
	fmt.Fprintln(&output, "\n## Flagged process detail")
	for _, process := range report.Processes {
		fmt.Fprintf(&output, "  pid:%d comm:%s exe:%s ppid:%d uid:%d cmdline:%s\n", process.PID, process.Comm, process.Exe, process.PPID, process.UID, process.Cmdline)
	}
	if len(report.Processes) == 0 {
		fmt.Fprintln(&output, "  (no specific pid in alerts)")
	}
	return output.String()
}

func collectProcess(procRoot string, pid int) ProcessDetail {
	base := filepath.Join(procRoot, strconv.Itoa(pid))
	detail := ProcessDetail{PID: pid, FDs: map[string]string{}}
	detail.Comm = readText(filepath.Join(base, "comm"))
	detail.Cmdline = strings.TrimSpace(strings.ReplaceAll(readRaw(filepath.Join(base, "cmdline")), "\x00", " "))
	detail.Exe = readLink(filepath.Join(base, "exe"))
	detail.CWD = readLink(filepath.Join(base, "cwd"))
	status := readRaw(filepath.Join(base, "status"))
	for _, line := range strings.Split(status, "\n") {
		fields := strings.Fields(line)
		if len(fields) < 2 {
			continue
		}
		switch fields[0] {
		case "PPid:":
			detail.PPID, _ = strconv.Atoi(fields[1])
		case "Uid:":
			detail.UID, _ = strconv.Atoi(fields[1])
		}
	}
	detail.PPIDComm = readText(filepath.Join(procRoot, strconv.Itoa(detail.PPID), "comm"))
	for _, item := range strings.Split(readRaw(filepath.Join(base, "environ")), "\x00") {
		if strings.HasPrefix(item, "LD_PRELOAD=") {
			detail.LDPreload = strings.TrimPrefix(item, "LD_PRELOAD=")
		}
	}
	entries, _ := os.ReadDir(filepath.Join(base, "fd"))
	sort.Slice(entries, func(i, j int) bool {
		left, leftErr := strconv.Atoi(entries[i].Name())
		right, rightErr := strconv.Atoi(entries[j].Name())
		if leftErr == nil && rightErr == nil {
			return left < right
		}
		return entries[i].Name() < entries[j].Name()
	})
	for _, entry := range entries {
		if len(detail.FDs) >= 40 {
			break
		}
		if target := readLink(filepath.Join(base, "fd", entry.Name())); target != "" {
			detail.FDs[entry.Name()] = target
		}
	}
	return detail
}

func readRaw(path string) string {
	raw, _ := os.ReadFile(path)
	return string(raw)
}

func readText(path string) string { return strings.TrimSpace(readRaw(path)) }

func readLink(path string) string {
	target, _ := os.Readlink(path)
	return target
}