// internal/session/session.go
package session

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"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"`
	OutputSummary string `json:"output_summary,omitempty"`
	RunnerOutput  string `json:"runner_output,omitempty"`
	Verified      bool   `json:"verified"`
}

// Append writes entry as a single JSON line to sessionsDir/{sessionID}.jsonl.
func Append(sessionsDir, sessionID string, entry Entry) error {
	if err := os.MkdirAll(sessionsDir, 0o755); err != nil {
		return fmt.Errorf("create sessions dir: %w", err)
	}
	path := filepath.Join(sessionsDir, sessionID+".jsonl")
	f, err := os.OpenFile(path, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		return fmt.Errorf("open session log: %w", err)
	}

	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) {
	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()

	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()
}