package contextwindow

import (
	"strings"

	"aichat/message"
	"aichat/stream"

	"github.com/volcengine/volcengine-go-sdk/service/arkruntime/model"
)

type Result struct {
	MaxTokens    int
	BeforeTokens int
	AfterTokens  int
	Removed      int
	Overflow     bool
	BaseOverflow bool
	ChatMessages []message.ChatMessage
	ArkMessages  []*model.ChatCompletionMessage
}

type chatItem struct {
	msg       message.ChatMessage
	tokens    int
	fixed     bool
	protected bool
}

type arkItem struct {
	msg    *model.ChatCompletionMessage
	tokens int
	fixed  bool
}

func ApplyChatWindow(messages []message.ChatMessage, maxTokens int) Result {
	before := stream.EstimateChatMessagesTokens(messages)
	result := Result{MaxTokens: maxTokens, BeforeTokens: before, AfterTokens: before, ChatMessages: append([]message.ChatMessage(nil), messages...)}
	if maxTokens <= 0 || before <= maxTokens {
		result.Overflow = maxTokens > 0 && before > maxTokens
		return result
	}

	items := make([]chatItem, 0, len(messages))
	lastUser := -1
	baseTokens := 0
	for i, msg := range messages {
		item := chatItem{msg: msg, tokens: stream.EstimateChatMessagesTokens([]message.ChatMessage{msg}), fixed: isFixedChatMessage(msg)}
		if item.fixed {
			baseTokens += item.tokens
		} else if strings.EqualFold(msg.Role, "user") {
			lastUser = i
		}
		items = append(items, item)
	}
	if lastUser >= 0 {
		items[lastUser].protected = true
	}
	if baseTokens > maxTokens {
		result.BaseOverflow = true
	}

	result.ChatMessages, result.Removed = pruneChatItems(items, maxTokens)
	result.AfterTokens = stream.EstimateChatMessagesTokens(result.ChatMessages)
	result.Overflow = result.AfterTokens > maxTokens
	return result
}

func ApplyArkWindow(messages []*model.ChatCompletionMessage, maxTokens int) Result {
	before := stream.EstimateArkMessagesTokens(messages)
	result := Result{MaxTokens: maxTokens, BeforeTokens: before, AfterTokens: before, ArkMessages: append([]*model.ChatCompletionMessage(nil), messages...)}
	if maxTokens <= 0 || before <= maxTokens {
		result.Overflow = maxTokens > 0 && before > maxTokens
		return result
	}

	items := make([]arkItem, 0, len(messages))
	lastUser := -1
	baseTokens := 0
	for i, msg := range messages {
		item := arkItem{msg: msg, tokens: stream.EstimateArkMessagesTokens([]*model.ChatCompletionMessage{msg}), fixed: isFixedArkMessage(msg)}
		if item.fixed {
			baseTokens += item.tokens
		} else if msg != nil && msg.Role == model.ChatMessageRoleUser {
			lastUser = i
		}
		items = append(items, item)
	}
	if lastUser >= 0 {
		items[lastUser].fixed = true
	}
	if baseTokens > maxTokens {
		result.BaseOverflow = true
	}

	result.ArkMessages, result.Removed = pruneArkItems(items, maxTokens)
	result.AfterTokens = stream.EstimateArkMessagesTokens(result.ArkMessages)
	result.Overflow = result.AfterTokens > maxTokens
	return result
}

func isFixedChatMessage(msg message.ChatMessage) bool {
	return msg.Hidden || strings.EqualFold(msg.Role, "system")
}

func isFixedArkMessage(msg *model.ChatCompletionMessage) bool {
	if msg == nil {
		return false
	}
	if msg.Role == model.ChatMessageRoleSystem || msg.Role == model.ChatMessageRoleTool {
		return true
	}
	return len(msg.ToolCalls) > 0
}

func pruneChatItems(items []chatItem, maxTokens int) ([]message.ChatMessage, int) {
	removed := make([]bool, len(items))
	total := 0
	for _, item := range items {
		total += item.tokens
	}
	removedCount := 0
	for total > maxTokens {
		idx := -1
		for i, item := range items {
			if removed[i] || item.fixed || item.protected {
				continue
			}
			idx = i
			break
		}
		if idx == -1 {
			break
		}
		removed[idx] = true
		total -= items[idx].tokens
		removedCount++
	}

	messages := make([]message.ChatMessage, 0, len(items)-removedCount)
	for i, item := range items {
		if !removed[i] {
			messages = append(messages, item.msg)
		}
	}
	return messages, removedCount
}

func pruneArkItems(items []arkItem, maxTokens int) ([]*model.ChatCompletionMessage, int) {
	removed := make([]bool, len(items))
	total := 0
	for _, item := range items {
		total += item.tokens
	}
	removedCount := 0
	for total > maxTokens {
		idx := -1
		for i, item := range items {
			if removed[i] || item.fixed {
				continue
			}
			idx = i
			break
		}
		if idx == -1 {
			break
		}
		removed[idx] = true
		total -= items[idx].tokens
		removedCount++
	}

	messages := make([]*model.ChatCompletionMessage, 0, len(items)-removedCount)
	for i, item := range items {
		if !removed[i] {
			messages = append(messages, item.msg)
		}
	}
	return messages, removedCount
}