// SPDX-License-Identifier: AGPL-3.0-only

package eventlog

import (
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"syscall"
	"time"
)

const Version = 1

var safeValue = regexp.MustCompile(`^[A-Za-z0-9._:/@+-]{1,256}$`)
var hexDigest = regexp.MustCompile(`^[0-9a-f]{64}$`)
var gitCommit = regexp.MustCompile(`^[0-9a-f]{40}$`)
var operationID = regexp.MustCompile(`^[0-9a-f]{32}$`)

type Event struct {
	Version        int    `json:"version"`
	OperationID    string `json:"operation_id"`
	Service        string `json:"service"`
	ArtifactDigest string `json:"artifact_digest"`
	Commit         string `json:"commit"`
	ReleaseVersion string `json:"release_version"`
	Phase          string `json:"phase"`
	Slot           string `json:"slot,omitempty"`
	DurationMillis int64  `json:"duration_ms"`
	Outcome        string `json:"outcome"`
	ObservedAt     string `json:"observed_at"`
}

func OperationID() (string, error) {
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		return "", errors.New("cryptographic randomness unavailable")
	}
	return hex.EncodeToString(b), nil
}

func Append(path string, event Event) error {
	if err := event.validate(); err != nil {
		return err
	}
	if !filepath.IsAbs(path) || filepath.Clean(path) != path {
		return errors.New("event log path must be absolute and clean")
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o750); err != nil {
		return fmt.Errorf("create event directory: %w", err)
	}
	if info, err := os.Lstat(path); err == nil {
		if !info.Mode().IsRegular() || info.Mode()&os.ModeSymlink != 0 || info.Mode().Perm()&0o022 != 0 {
			return errors.New("event log must be a non-writable regular non-symlink file")
		}
	} else if !errors.Is(err, os.ErrNotExist) {
		return fmt.Errorf("inspect event log: %w", err)
	}
	b, err := json.Marshal(event)
	if err != nil {
		return fmt.Errorf("encode deployment event: %w", err)
	}
	if len(b) > 4096 {
		return errors.New("deployment event exceeds bound")
	}
	b = append(b, '\n')
	fd, err := syscall.Open(path, syscall.O_WRONLY|syscall.O_APPEND|syscall.O_CREAT|syscall.O_CLOEXEC|syscall.O_NOFOLLOW, 0o640)
	if err != nil {
		return fmt.Errorf("open event log: %w", err)
	}
	file := os.NewFile(uintptr(fd), path)
	if file == nil {
		_ = syscall.Close(fd)
		return errors.New("open event log file")
	}
	defer file.Close()
	n, err := file.Write(b)
	if err != nil || n != len(b) {
		return errors.New("write complete deployment event")
	}
	if err := file.Sync(); err != nil {
		return fmt.Errorf("sync deployment event: %w", err)
	}
	return nil
}

func (e Event) validate() error {
	if e.Version != Version || !operationID.MatchString(e.OperationID) {
		return errors.New("deployment event identity is invalid")
	}
	if !hexDigest.MatchString(e.ArtifactDigest) || !gitCommit.MatchString(e.Commit) {
		return errors.New("deployment event provenance is invalid")
	}
	for label, value := range map[string]string{"service": e.Service, "artifact_digest": e.ArtifactDigest, "commit": e.Commit, "release_version": e.ReleaseVersion, "phase": e.Phase, "outcome": e.Outcome} {
		if !safeValue.MatchString(value) || strings.ContainsRune(value, '\x00') {
			return fmt.Errorf("deployment event %s is invalid", label)
		}
	}
	if e.Slot != "" && !safeValue.MatchString(e.Slot) {
		return errors.New("deployment event slot is invalid")
	}
	if e.DurationMillis < 0 {
		return errors.New("deployment event duration is invalid")
	}
	if _, err := time.Parse(time.RFC3339Nano, e.ObservedAt); err != nil {
		return errors.New("deployment event timestamp is invalid")
	}
	return nil
}