package controlplane

import (
	"errors"
	"fmt"
	"strings"
	"time"
)

// Multi-turn conversations keep a single Agent's follow-up work in context, so a
// user can say "把它复制到某个目录" without repeating where the previous step put it.
const (
	defaultSessionTurnLimit = 50
	maxSessionTurnLimit     = 200
	// One turn is bounded, and the assembled history has its own budget: the
	// controller always sends plain user/assistant text, never tool transcripts.
	maxSessionTurnChars = 4000
	maxSessionHistory   = 60000
)

// createTaskSession starts an empty conversation with the default turn limit.
func (c *ControlPlane) createTaskSession(agentID string) (string, error) {
	sessionID, err := randomHex(16)
	if err != nil {
		return "", err
	}
	now := time.Now().UTC().Format(time.RFC3339Nano)
	if _, err := c.db.Exec(
		"INSERT INTO task_sessions(session_id, agent_id, turn_limit, created_at, updated_at) VALUES (?, ?, ?, ?, ?)",
		sessionID, agentID, defaultSessionTurnLimit, now, now,
	); err != nil {
		return "", fmt.Errorf("无法创建会话: %w", err)
	}
	return sessionID, nil
}

func normaliseTurnLimit(turnLimit int) int {
	if turnLimit < 1 {
		return defaultSessionTurnLimit
	}
	if turnLimit > maxSessionTurnLimit {
		return maxSessionTurnLimit
	}
	return turnLimit
}

func (c *ControlPlane) sessionTurnCount(sessionID string) (int, error) {
	var turns int
	if err := c.db.QueryRow("SELECT COUNT(*) FROM task_session_messages WHERE session_id = ? AND role = 'user'", sessionID).Scan(&turns); err != nil {
		return 0, fmt.Errorf("无法统计会话轮数: %w", err)
	}
	return turns, nil
}

// ContinueTaskSession dispatches a follow-up turn based on one completed task.
// The one-shot task that starts a thread becomes its first turn, so 单独指派 keeps
// sending context-free tasks while only an explicit follow-up carries context.
func (c *ControlPlane) ContinueTaskSession(taskID, instruction string, timeoutSeconds int, inputs []TaskImageInput) (CreateTaskSessionResult, error) {
	images, err := normalizeTaskImages(inputs)
	if err != nil {
		return CreateTaskSessionResult{}, err
	}
	var agentID, sessionID, previousInstruction, previousOutput, status string
	if err := c.db.QueryRow(
		"SELECT agent_id, COALESCE(session_id, ''), instruction, COALESCE(output, ''), status FROM task_runs WHERE task_id = ?", taskID,
	).Scan(&agentID, &sessionID, &previousInstruction, &previousOutput, &status); err != nil {
		return CreateTaskSessionResult{}, errors.New("未找到要继续的任务")
	}
	if status != "completed" {
		return CreateTaskSessionResult{}, errors.New("只有已完成的任务才能继续对话")
	}
	if sessionID == "" {
		created, createErr := c.createTaskSession(agentID)
		if createErr != nil {
			return CreateTaskSessionResult{}, createErr
		}
		sessionID = created
		c.appendSessionTurn(sessionID, previousInstruction, previousOutput)
		_, _ = c.db.Exec("UPDATE task_runs SET session_id = ? WHERE task_id = ?", sessionID, taskID)
		c.recordAudit("task.session_started", "controller", "agent:"+agentID, "completed", "已基于一条已完成任务开始多轮对话。")
	}
	followUpID, err := c.createTaskWithImages(agentID, instruction, timeoutSeconds, 1, "", images, sessionID)
	if err != nil {
		return CreateTaskSessionResult{}, err
	}
	turns, countErr := c.sessionTurnCount(sessionID)
	if countErr != nil {
		return CreateTaskSessionResult{TaskID: followUpID, SessionID: sessionID, Turns: 1}, nil
	}
	return CreateTaskSessionResult{TaskID: followUpID, SessionID: sessionID, Turns: turns + 1}, nil
}

// TaskSessionTurn is one stored turn of a conversation: exactly the plain
// question/answer text the Agent receives as context.
type TaskSessionTurn struct {
	Instruction string `json:"instruction"`
	Answer      string `json:"answer"`
	CreatedAt   string `json:"createdAt"`
}

// TaskSessionTurns returns the stored turns of one conversation, oldest first, so
// the task detail dialog can show what the follow-up request will carry.
func (c *ControlPlane) TaskSessionTurns(sessionID string) ([]TaskSessionTurn, error) {
	turns := make([]TaskSessionTurn, 0)
	sessionID = strings.TrimSpace(sessionID)
	if sessionID == "" {
		return turns, nil
	}
	rows, err := c.db.Query("SELECT role, content, created_at FROM task_session_messages WHERE session_id = ? ORDER BY position", sessionID)
	if err != nil {
		return nil, fmt.Errorf("无法读取会话内容: %w", err)
	}
	defer rows.Close()
	for rows.Next() {
		var role, content, createdAt string
		if err := rows.Scan(&role, &content, &createdAt); err != nil {
			return nil, err
		}
		switch {
		case role == "user":
			turns = append(turns, TaskSessionTurn{Instruction: content, CreatedAt: createdAt})
		case len(turns) > 0 && turns[len(turns)-1].Answer == "":
			turns[len(turns)-1].Answer = content
		}
	}
	return turns, rows.Err()
}

// sessionHistory returns the newest turns that fit the budget, oldest first, so a
// follow-up request carries the context the model needs without unbounded growth.
func (c *ControlPlane) sessionHistory(sessionID string, turnLimit int) ([]map[string]string, error) {
	rows, err := c.db.Query(
		"SELECT role, content FROM task_session_messages WHERE session_id = ? ORDER BY position DESC LIMIT ?",
		sessionID, normaliseTurnLimit(turnLimit)*2,
	)
	if err != nil {
		return nil, fmt.Errorf("无法读取会话历史: %w", err)
	}
	defer rows.Close()
	newestFirst := make([]map[string]string, 0)
	for rows.Next() {
		var role, content string
		if err := rows.Scan(&role, &content); err != nil {
			return nil, err
		}
		if strings.TrimSpace(content) == "" {
			continue
		}
		newestFirst = append(newestFirst, map[string]string{"role": role, "content": content})
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	// Keep the newest messages that fit the character budget.
	budget, kept := maxSessionHistory, make([]map[string]string, 0, len(newestFirst))
	for _, message := range newestFirst {
		budget -= len([]rune(message["content"]))
		if budget < 0 && len(kept) > 0 {
			break
		}
		kept = append(kept, message)
	}
	history := make([]map[string]string, 0, len(kept))
	for index := len(kept) - 1; index >= 0; index-- {
		history = append(history, kept[index])
	}
	return history, nil
}

// appendSessionTurn records one completed turn and trims the oldest turns once the
// conversation exceeds its limit. Failed or cancelled turns never enter history.
func (c *ControlPlane) appendSessionTurn(sessionID, instruction, output string) {
	instruction, output = strings.TrimSpace(instruction), strings.TrimSpace(output)
	if instruction == "" || output == "" {
		return
	}
	var limitValue, messageCount int
	if err := c.db.QueryRow("SELECT turn_limit FROM task_sessions WHERE session_id = ?", sessionID).Scan(&limitValue); err != nil {
		return
	}
	if err := c.db.QueryRow("SELECT COUNT(*) FROM task_session_messages WHERE session_id = ?", sessionID).Scan(&messageCount); err != nil {
		return
	}
	now := time.Now().UTC().Format(time.RFC3339Nano)
	if _, err := c.db.Exec(
		"INSERT INTO task_session_messages(session_id, position, role, content, created_at) VALUES (?, ?, 'user', ?, ?), (?, ?, 'assistant', ?, ?)",
		sessionID, messageCount+1, limit(instruction, maxSessionTurnChars), now,
		sessionID, messageCount+2, limit(output, maxSessionTurnChars), now,
	); err != nil {
		return
	}
	// Drop the oldest turns beyond the configured limit.
	if excess := messageCount + 2 - normaliseTurnLimit(limitValue)*2; excess > 0 {
		_, _ = c.db.Exec(
			"DELETE FROM task_session_messages WHERE session_id = ? AND position <= ?",
			sessionID, excess,
		)
	}
	_, _ = c.db.Exec("UPDATE task_sessions SET updated_at = ? WHERE session_id = ?", now, sessionID)
}