import crypto from 'node:crypto'
import { ChatMessage } from '#package/types/index.js'
import { flattenMessageTextContent } from './flattenMessageTextContent.js'

export interface CalculateContextIdentityOptions {
	messages?: ChatMessage[]
	dropLastUserMessage?: boolean
}

export function calculateChatContextIdentity({
	messages,
	dropLastUserMessage = false,
}: CalculateContextIdentityOptions): string {
	if (!messages?.length) {
		return ''
	}
	const filteredMessages = messages.filter((message, i) => {
		// remove all but the leading system message
		if (message.role === 'system' && i !== 0) {
			return false
		}
		if (message.role === 'tool') {
			return false
		}
		const textContent = flattenMessageTextContent(message.content)
		return !!textContent
	})
	if (dropLastUserMessage && filteredMessages.length > 1) {
		if (filteredMessages[filteredMessages.length - 1].role === 'user') {
			filteredMessages.pop()
		}
	}
	// we dont wanna json stringify because this would make message key order significant
	const serializedMessages = filteredMessages
		.map((message) => {
			return message.role + ': ' + flattenMessageTextContent(message.content)
		})
		.join('\n')
	const contextIdentity = crypto.createHash('sha1').update(serializedMessages).digest('hex')
	return contextIdentity
}