package ai

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

// Session 桌面本地会话（落盘 ~/.opsxdb/ai-sessions/<id>.json）。
type Session struct {
	ID        string       `json:"id"`
	Title     string       `json:"title,omitempty"`
	Status    string       `json:"status"` // idle|running|incomplete|completed|failed|cancelled|awaiting_confirm
	CreatedAt string       `json:"createdAt"`
	UpdatedAt string       `json:"updatedAt"`
	Messages  []Message    `json:"messages"`
	Runs      []SessionRun `json:"runs,omitempty"`
}

// SessionRun 一次运行摘要。
type SessionRun struct {
	RunID            string `json:"runId"`
	Outcome          string `json:"outcome"`
	IncompleteReason string `json:"incompleteReason,omitempty"`
	Resumable        bool   `json:"resumable"`
	StepsUsed        int    `json:"stepsUsed"`
	StepsBudget      int    `json:"stepsBudget"`
	FinishedAt       string `json:"finishedAt"`
}

// SessionSummary 列表项（不含 messages）。
type SessionSummary struct {
	ID        string `json:"id"`
	Title     string `json:"title,omitempty"`
	Status    string `json:"status"`
	CreatedAt string `json:"createdAt"`
	UpdatedAt string `json:"updatedAt"`
	MsgCount  int    `json:"msgCount"`
	LastRunID string `json:"lastRunId,omitempty"`
}

func sessionsDir() (string, error) {
	home, err := os.UserHomeDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(home, ".opsxdb", "ai-sessions"), nil
}

// SessionPath 返回会话文件路径。
func SessionPath(id string) (string, error) {
	dir, err := sessionsDir()
	if err != nil {
		return "", err
	}
	id = strings.TrimSpace(id)
	if id == "" || strings.ContainsAny(id, `/\`) {
		return "", fmt.Errorf("invalid session id")
	}
	return filepath.Join(dir, id+".json"), nil
}

// NewSessionID 生成 sess_… 短 id。
func NewSessionID() string {
	var b [8]byte
	_, _ = rand.Read(b[:])
	return "sess_" + hex.EncodeToString(b[:])
}

// SaveSession 脱敏后写入磁盘。
func SaveSession(s Session) error {
	if s.ID == "" {
		return fmt.Errorf("session id required")
	}
	s.Messages = RedactMessages(s.Messages)
	s.UpdatedAt = time.Now().Format(time.RFC3339)
	if s.CreatedAt == "" {
		s.CreatedAt = s.UpdatedAt
	}
	path, err := SessionPath(s.ID)
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
		return err
	}
	b, err := json.MarshalIndent(s, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(path, b, 0600)
}

// LoadSession 读会话；不存在返回 os.ErrNotExist。
func LoadSession(id string) (Session, error) {
	path, err := SessionPath(id)
	if err != nil {
		return Session{}, err
	}
	b, err := os.ReadFile(path)
	if err != nil {
		return Session{}, err
	}
	var s Session
	if err := json.Unmarshal(b, &s); err != nil {
		return Session{}, err
	}
	return s, nil
}

// ListSessions 按 UpdatedAt 倒序；limit<=0 表示全部。
func ListSessions(limit int) ([]SessionSummary, error) {
	dir, err := sessionsDir()
	if err != nil {
		return nil, err
	}
	entries, err := os.ReadDir(dir)
	if err != nil {
		if os.IsNotExist(err) {
			return []SessionSummary{}, nil
		}
		return nil, err
	}
	var out []SessionSummary
	for _, e := range entries {
		if e.IsDir() || !strings.HasSuffix(e.Name(), ".json") {
			continue
		}
		id := strings.TrimSuffix(e.Name(), ".json")
		s, err := LoadSession(id)
		if err != nil {
			continue
		}
		sum := SessionSummary{
			ID: s.ID, Title: s.Title, Status: s.Status,
			CreatedAt: s.CreatedAt, UpdatedAt: s.UpdatedAt,
			MsgCount: len(s.Messages),
		}
		if n := len(s.Runs); n > 0 {
			sum.LastRunID = s.Runs[n-1].RunID
		}
		out = append(out, sum)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].UpdatedAt > out[j].UpdatedAt })
	if limit > 0 && len(out) > limit {
		out = out[:limit]
	}
	return out, nil
}

// DeleteSession 删除会话文件。
func DeleteSession(id string) error {
	path, err := SessionPath(id)
	if err != nil {
		return err
	}
	err = os.Remove(path)
	if os.IsNotExist(err) {
		return nil
	}
	return err
}

// OutcomeToSessionStatus 映射 RunOutcome → Session.Status。
func OutcomeToSessionStatus(outcome string) string {
	switch outcome {
	case OutcomeIncomplete:
		return "incomplete"
	case OutcomeAwaitingConfirm:
		return "awaiting_confirm"
	case OutcomeFailed:
		return "failed"
	case OutcomeCancelled:
		return "cancelled"
	case OutcomeCompleted:
		return "completed"
	default:
		if outcome == "" {
			return "idle"
		}
		return outcome
	}
}

// PersistAgentRun 把本趟轨迹与 outcome 写入会话（真·续跑用）。
func PersistAgentRun(sessionID, title string, trajectory []Message, res AgentRes) (Session, error) {
	sessionID = strings.TrimSpace(sessionID)
	if sessionID == "" {
		sessionID = NewSessionID()
	}
	s, err := LoadSession(sessionID)
	if err != nil {
		if !os.IsNotExist(err) {
			return Session{}, err
		}
		s = Session{ID: sessionID, Status: "idle"}
	}
	if title != "" && s.Title == "" {
		// 标题取首条 user 或短截断
		t := strings.TrimSpace(title)
		r := []rune(t)
		if len(r) > 48 {
			t = string(r[:48]) + "…"
		}
		s.Title = t
	}
	if len(trajectory) > 0 {
		s.Messages = trajectory
	}
	s.Status = OutcomeToSessionStatus(res.Outcome)
	s.Runs = append(s.Runs, SessionRun{
		RunID:            res.RunID,
		Outcome:          res.Outcome,
		IncompleteReason: res.IncompleteReason,
		Resumable:        res.Resumable,
		StepsUsed:        res.Rounds,
		StepsBudget:      res.StepsBudget,
		FinishedAt:       time.Now().Format(time.RFC3339),
	})
	if err := SaveSession(s); err != nil {
		return Session{}, err
	}
	return s, nil
}