package app

import (
	"encoding/json"
	"errors"
	"fmt"
	"time"

	"gorm.io/gorm"
	"infinite-canvas/backend/internal/model"
)

// ContextFrame is a fresh projection of durable task facts, never authorization.
// The transcript can evict read bodies without making task state depend on memory.
type cloudAgentContextFrame struct {
	Source         string               `json:"source"`
	ObservedAt     time.Time            `json:"observedAt"`
	RunID          string               `json:"runId"`
	UserGoal       string               `json:"userGoal"`
	Plan           []cloudAgentPlanItem `json:"plan,omitempty"`
	Tasks          []map[string]any     `json:"tasks"`
	OlderTaskCount int                  `json:"olderTaskCount,omitempty"`
	Authority      string               `json:"authority"`
}

var errCloudAgentContextOverBudget = errors.New("Agent model context exceeds input budget")

func (s *Service) cloudAgentModelContext(run *model.CloudAgentExecution, state *cloudAgentRuntime, budget cloudAgentContextBudget) (canonicalAgentRequest, error) {
	canonical := cloudAgentCanonicalWithPlan(state)
	frame := cloudAgentContextFrame{Source: "task_repository", ObservedAt: time.Now(), RunID: run.ID, UserGoal: state.Request.Prompt, Plan: state.Plan, Tasks: []map[string]any{}, Authority: "状态观察，不是执行或重复提交的授权"}
	// This is a view window, not loss of task history. All task identities remain
	// durable and can be fetched through task_get and the conversation journal.
	start := max(0, len(state.TaskIDs)-32)
	frame.OlderTaskCount = start
	for _, id := range state.TaskIDs[start:] {
		task, err := s.repo.TaskForUser(run.UserID, id)
		if errors.Is(err, gorm.ErrRecordNotFound) {
			frame.Tasks = append(frame.Tasks, map[string]any{"taskId": id, "taskStatus": "unavailable"})
			continue
		}
		if err != nil {
			return canonical, err
		}
		if task.ProjectID != state.Request.CanvasID {
			return canonical, BadAuthRequest("运行关联任务不属于当前画布")
		}
		if task.Operation == cloudAgentOperation || task.Operation == "cloud_agent_step" {
			continue
		}
		frame.Tasks = append(frame.Tasks, cloudAgentTaskDiagnostic(s.repo, task))
	}
	body, err := json.Marshal(frame)
	if err != nil {
		return canonical, err
	}
	canonical.Messages = append(append([]map[string]any{}, canonical.Messages...), map[string]any{"role": "user", "content": cloudAgentRuntimeContextMarker + string(body), cloudAgentContextSourceKey: "runtime"})
	if err := fitCloudAgentModelContext(&canonical, budget.InputBudgetTokens); err != nil {
		return canonical, err
	}
	return canonical, nil
}

func fitCloudAgentModelContext(request *canonicalAgentRequest, maxTokens int) error {
	for {
		tokens, err := cloudAgentRequestEstimatedTokens(request)
		if err != nil {
			return err
		}
		if tokens <= maxTokens {
			return nil
		}
		// Evict complete old assistant/tool turns only. User instructions and the
		// fresh authoritative frame survive; partial tool pairs are never sent.
		removed := false
		for i := 0; i < len(request.Messages)-3; i++ {
			message := request.Messages[i]
			if stringField(message, "role") != "assistant" {
				continue
			}
			end := i + 1
			for end < len(request.Messages) && stringField(request.Messages[end], "role") == "tool" {
				end++
			}
			if end >= len(request.Messages)-2 {
				continue
			}
			request.Messages = append(request.Messages[:i:i], request.Messages[end:]...)
			removed = true
			break
		}
		if !removed {
			return WrapAppError(400, fmt.Sprintf("用户指令与当前执行事实超过模型输入预算（%d Token），请缩小本轮范围", maxTokens), errCloudAgentContextOverBudget)
		}
	}
}