package store

import (
	"bufio"
	"encoding/json"
	"os"
	"path/filepath"
	"strings"
	"time"
)

// FocusEvent is one raw, disposable observation in a session's firehose log.
type FocusEvent struct {
	AtUnixMillis int64  `json:"at_unix_millis"`
	Class        string `json:"class"`
	Title        string `json:"title"` // full, unscrubbed
	Available    bool   `json:"available"`
	Reason       string `json:"reason,omitempty"`
}

func sessionFile(dir, sessionID string) string {
	return filepath.Join(dir, sessionID+".jsonl")
}

// AppendFocus appends one event to dir/<sessionID>.jsonl, creating dir if
// needed. It is best-effort detail, not the state of truth.
func AppendFocus(dir, sessionID string, e FocusEvent) error {
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return err
	}
	line, err := json.Marshal(e)
	if err != nil {
		return err
	}
	f, err := os.OpenFile(sessionFile(dir, sessionID), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o644)
	if err != nil {
		return err
	}
	defer f.Close()
	_, err = f.Write(append(line, '\n'))
	return err
}

// ReplaySession reads all events for a session in append order. A missing file
// yields an empty slice and no error.
func ReplaySession(dir, sessionID string) ([]FocusEvent, error) {
	f, err := os.Open(sessionFile(dir, sessionID))
	if os.IsNotExist(err) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	defer f.Close()
	var out []FocusEvent
	sc := bufio.NewScanner(f)
	sc.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for sc.Scan() {
		line := strings.TrimSpace(sc.Text())
		if line == "" {
			continue
		}
		var e FocusEvent
		if err := json.Unmarshal([]byte(line), &e); err != nil {
			return nil, err
		}
		out = append(out, e)
	}
	return out, sc.Err()
}

// PruneOlderThan deletes session files whose modification time precedes
// now-age. A missing dir is a no-op. now is injected for testability.
func PruneOlderThan(dir string, age time.Duration, now time.Time) error {
	entries, err := os.ReadDir(dir)
	if os.IsNotExist(err) {
		return nil
	}
	if err != nil {
		return err
	}
	cutoff := now.Add(-age)
	for _, entry := range entries {
		if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".jsonl") {
			continue
		}
		info, err := entry.Info()
		if err != nil {
			continue
		}
		if info.ModTime().Before(cutoff) {
			_ = os.Remove(filepath.Join(dir, entry.Name()))
		}
	}
	return nil
}