// Package ctxasm 实现上下文组装与预算管理（4.10）：分层管线 + 可观测裁剪记录。
package ctxasm

import (
	"fmt"
	"strings"

	agentllm "agent-native/runtime/llm"
	core "agent-system-core"
)

// Report 记录一次组装的实际构成（可观测：模型看到了什么、裁了什么）。
type Report struct {
	Items      []string `json:"items"`
	Truncations []string `json:"truncations,omitempty"`
	EstChars   int      `json:"estChars"`
}

// AssembleInput 组装模型输入消息。
func AssembleInput(prof core.AgentProfile, eff core.EffectiveSettings, history []core.Message, currentUser core.Message, attachments []core.ParsedDocument, knowledge []core.RetrievalHit) ([]agentllm.Message, *Report) {
	rep := &Report{}
	msgs := []agentllm.Message{{Role: agentllm.RoleSystem, Content: prof.SystemPrompt}}
	rep.Items = append(rep.Items, "system(画像)")

	maxHist := prof.Context.MaxHistoryMessages
	if maxHist <= 0 {
		maxHist = int(eff.GetNumber("context.maxHistoryMessages", 40))
	}
	if maxHist <= 0 {
		maxHist = 40
	}
	// 历史窗口（不含当前轮——当前轮单独注入附件与检索）。
	start := 0
	if len(history) > maxHist {
		start = len(history) - maxHist
		rep.Truncations = append(rep.Truncations, fmt.Sprintf("历史 %d 条超窗口 %d，仅保留最近部分", len(history), maxHist))
	}
	for _, m := range history[start:] {
		if m.ID == currentUser.ID {
			continue
		}
		content := renderMessage(m)
		if content == "" {
			continue
		}
		role := agentllm.RoleUser
		if m.Role == core.RoleAssistant {
			role = agentllm.RoleAssistant
		}
		msgs = append(msgs, agentllm.Message{Role: role, Content: content})
	}
	rep.Items = append(rep.Items, fmt.Sprintf("history(%d)", len(history)-start))

	// 当前轮：文本 + 附件解析结果 + 知识检索注入。
	var sb strings.Builder
	for _, p := range currentUser.Parts {
		if p.Type == core.PartText {
			sb.WriteString(p.Text)
		}
	}
	if len(attachments) > 0 {
		sb.WriteString("\n\n[附件]\n")
		for _, doc := range attachments {
			text := doc.PlainText()
			limit := 16000
			if len(text) > limit {
				text = text[:limit] + "…（附件超长截断）"
				rep.Truncations = append(rep.Truncations, "附件 "+doc.Meta.Filename+" 超长截断")
			}
			fmt.Fprintf(&sb, "### %s\n%s\n", doc.Meta.Filename, text)
		}
		rep.Items = append(rep.Items, fmt.Sprintf("attachments(%d)", len(attachments)))
	}
	if len(knowledge) > 0 {
		sb.WriteString("\n\n[相关知识]\n")
		for i, h := range knowledge {
			fmt.Fprintf(&sb, "[%d] %s（来源 %s）\n%s\n", i+1, h.Doc.Title, h.Doc.Source, h.Doc.Chunk)
		}
		rep.Items = append(rep.Items, fmt.Sprintf("knowledge(%d)", len(knowledge)))
	}
	msgs = append(msgs, agentllm.Message{Role: agentllm.RoleUser, Content: sb.String()})

	for _, m := range msgs {
		rep.EstChars += len(m.Content)
	}
	return msgs, rep
}

// renderMessage 把消息部件渲染为模型可读文本（思考部件不回灌；工具结果给摘要）。
func renderMessage(m core.Message) string {
	var sb strings.Builder
	for _, p := range m.Parts {
		switch p.Type {
		case core.PartText:
			sb.WriteString(p.Text)
			sb.WriteString("\n")
		case core.PartToolCall:
			if p.ToolCall != nil {
				fmt.Fprintf(&sb, "[调用工具 %s(%s)]\n", p.ToolCall.Name, p.ToolCall.Arguments)
			}
		case core.PartToolResult:
			if p.ToolResult != nil {
				fmt.Fprintf(&sb, "[工具结果 %s %s]\n", p.ToolResult.Status, p.ToolResult.Summary)
			}
		case core.PartArtifactRef:
			if p.Artifact != nil {
				fmt.Fprintf(&sb, "[产出工件 %s]\n", p.Artifact.Name)
			}
		case core.PartHITL:
			if p.Hitl != nil && p.Hitl.Resolved {
				fmt.Fprintf(&sb, "[用户确认：%s → %s]\n", p.Hitl.Question, p.Hitl.Answer)
			}
		}
	}
	return strings.TrimSpace(sb.String())
}