// ingestion/internal/session/session.go
package session

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"regexp"
	"syscall"
	"time"
)

// Entry is one skill invocation record, appended to the session JSONL log.
type Entry struct {
	SessionID   string          `json:"session_id"`
	Timestamp   time.Time       `json:"timestamp"`
	Skill       string          `json:"skill"`
	Phase       string          `json:"phase,omitempty"`
	ProjectRoot string          `json:"project_root,omitempty"`
	Input       json.RawMessage `json:"input,omitempty"`
	Attempts    []Attempt       `json:"attempts,omitempty"`
	FinalStatus string          `json:"final_status"`
	FilePath    string          `json:"file_path,omitempty"`
	ModelUsed   string          `json:"model_used,omitempty"`
	DurationMs  int64           `json:"duration_ms,omitempty"`
	Message     string          `json:"message,omitempty"`
}

// Attempt represents one subprocess invocation within a skill call.
type Attempt struct {
	Attempt       int    `json:"attempt"`
	Model         string `json:"model"`
	Tier          string `json:"tier"` // local | subagent | managed
	DurationMs    int64  `json:"duration_ms"`
	WarmStart     bool   `json:"warm_start"` // model already loaded in llama-swap
	Verified      bool   `json:"verified"`
	Verdict       string `json:"verdict,omitempty"`  // accept | escalate | error
	Feedback      string `json:"feedback,omitempty"` // verifier feedback on escalation
	OutputSummary string `json:"output_summary,omitempty"`
	RunnerOutput  string `json:"runner_output,omitempty"`
}

// idPattern is a plain file name: session_log takes the id from the caller,
// and a path segment in it created or appended files anywhere the pod could
// write (hyperguild#169).
var idPattern = regexp.MustCompile(`^[A-Za-z0-9_][A-Za-z0-9._-]{0,127}$`)

// ErrInvalidID is returned when a session id is not a plain file name.
var ErrInvalidID = errors.New("session id is not a plain name")

func checkID(sessionID string) error {
	if !idPattern.MatchString(sessionID) {
		return fmt.Errorf("%w: %q", ErrInvalidID, sessionID)
	}
	return nil
}

// Append writes entry as a single JSON line to sessionsDir/{sessionID}.jsonl.
// The open does not follow a final symlink.
func Append(sessionsDir, sessionID string, entry Entry) error {
	if err := checkID(sessionID); err != nil {
		return err
	}
	// Opened through an os.Root on the sessions dir's parent (the brain dir),
	// so a sessions dir swapped for a symlink after the check below can
	// redirect the log only inside that parent, never outside it (#173; the
	// in-brain swap is the #167 residual).
	parentDir, name := filepath.Dir(sessionsDir), filepath.Base(sessionsDir)
	if err := os.MkdirAll(parentDir, 0o755); err != nil {
		return fmt.Errorf("create sessions parent: %w", err)
	}
	root, err := os.OpenRoot(parentDir)
	if err != nil {
		return fmt.Errorf("open sessions parent: %w", err)
	}
	defer func() { _ = root.Close() }()
	if err := root.Mkdir(name, 0o755); err != nil && !errors.Is(err, fs.ErrExist) {
		return fmt.Errorf("create sessions dir: %w", err)
	}
	// The sessions dir itself must be a real directory, not a symlink that
	// redirects the log elsewhere (hyperguild#173).
	if fi, err := root.Lstat(name); err != nil {
		return fmt.Errorf("stat sessions dir: %w", err)
	} else if !fi.IsDir() {
		return fmt.Errorf("sessions dir %s is not a real directory", sessionsDir)
	}
	logRel := name + "/" + sessionID + ".jsonl"
	f, err := root.OpenFile(logRel, os.O_CREATE|os.O_APPEND|os.O_WRONLY|syscall.O_NOFOLLOW|syscall.O_NONBLOCK, 0o644)
	if err != nil {
		return fmt.Errorf("open session log: %w", err)
	}
	// os.Root follows an in-root final symlink even with O_NOFOLLOW, so
	// confirm, before writing, that the path is the regular file we opened.
	hfi, herr := f.Stat()
	lfi, lerr := root.Lstat(logRel)
	if herr != nil || lerr != nil || !lfi.Mode().IsRegular() || !os.SameFile(lfi, hfi) {
		_ = f.Close()
		return fmt.Errorf("session log %s is not a regular file", logRel)
	}

	line, err := json.Marshal(entry)
	if err != nil {
		_ = f.Close()
		return fmt.Errorf("marshal entry: %w", err)
	}
	if _, err = fmt.Fprintf(f, "%s\n", line); err != nil {
		_ = f.Close()
		return fmt.Errorf("write entry: %w", err)
	}
	if err = f.Close(); err != nil {
		return fmt.Errorf("close session log: %w", err)
	}
	return nil
}

// Read returns all entries for sessionID. Returns empty slice if no log exists.
func Read(sessionsDir, sessionID string) ([]Entry, error) {
	if err := checkID(sessionID); err != nil {
		return nil, err
	}
	path := filepath.Join(sessionsDir, sessionID+".jsonl")
	f, err := os.Open(path)
	if errors.Is(err, fs.ErrNotExist) {
		return []Entry{}, nil
	}
	if err != nil {
		return nil, fmt.Errorf("open session log: %w", err)
	}
	defer f.Close() //nolint:errcheck

	var entries []Entry
	scanner := bufio.NewScanner(f)
	scanner.Buffer(make([]byte, 0, 256*1024), 1<<20) // up to 1 MB per line
	for scanner.Scan() {
		line := scanner.Bytes()
		if len(line) == 0 {
			continue
		}
		var e Entry
		if err := json.Unmarshal(line, &e); err != nil {
			return nil, fmt.Errorf("parse entry: %w", err)
		}
		entries = append(entries, e)
	}
	return entries, scanner.Err()
}