import { randomUUID } from "node:crypto";
import type { CustomMessageEntryDraft } from "@earendil-works/pi-coding-agent";
import type { AgentMessage } from "@earendil-works/pi-agent-core";
import type { CodexDeveloperMessageDetails } from "../developer-messages.ts";

export const CODEX_CONTEXT_WINDOW_MESSAGE_TYPE = "codex-context-window";
export const CONTEXT_WINDOW_COMPACTION_SUMMARY =
	"[Pi Codex context-window boundary; no conversation summary was generated.]";
export const CONTEXT_WINDOW_COMPACTION_STRATEGY =
	"codex-context-window";

export const CONTEXT_WINDOW_REMINDER_PERCENT = 85;
export const CONTEXT_WINDOW_URGENT_PERCENT = 90;

export type ContextManagementMessageKind =
	| "window"
	| "identity"
	| "reminder"
	| "urgent"
	| "fallback";

export interface ContextWindowIdentity {
	agentName?: string | undefined;
	firstWindowId: string;
	currentWindowId: string;
	previousWindowId?: string | undefined;
	windowNumber: number;
}

export interface CodexContextManagementMessageDetails
	extends CodexDeveloperMessageDetails {
	contextManagement: {
		protocol: 1;
		kind: ContextManagementMessageKind;
		agentName?: string | undefined;
		firstWindowId: string;
		currentWindowId: string;
		previousWindowId?: string | undefined;
		trimPreviousWindow?: true | undefined;
		windowNumber: number;
	};
}

export interface ContextWindowCompactionDetails {
	protocol: 1;
	strategy: typeof CONTEXT_WINDOW_COMPACTION_STRATEGY;
	windowId?: string | undefined;
}

const CONTEXT_WINDOW_BACKLOG_GUIDANCE = "Include useful deferred ideas and tasks, even unrelated ones, when checkpointing. Recording is not permission to implement";
const CONTEXT_WINDOW_TASK_GUIDANCE = "After substantial work, save useful new findings, decisions, progress or resumable state in notes as your last tool calls before replying. Skip completion notes for brief clarifications, routine lookups, acknowledgements and unchanged state. Explicit checkpoints and context reminders still apply. Include note paths in agent handoffs";

const CONTEXT_WINDOW_GUIDANCE = `<context_window_guidance>
Checkpoint the active request, known history IDs, decisions, progress, learnings and next steps in notes before new_context. After rollover, read hinted notes. Use history only for a missing detail.
${CONTEXT_WINDOW_TASK_GUIDANCE}
${CONTEXT_WINDOW_BACKLOG_GUIDANCE}
</context_window_guidance>`;

const CONTEXT_WINDOW_EXPLICIT_GUIDANCE = `<context_window_guidance>
Notes persist across windows; history retrieves earlier conversation. Update existing notes with task state, decisions and next steps before new_context. After rollover, read hinted notes and resume; consult history only for missing details. Save enough in notes to resume the task without rereading the conversation.
${CONTEXT_WINDOW_TASK_GUIDANCE}
${CONTEXT_WINDOW_BACKLOG_GUIDANCE}
</context_window_guidance>`;

export function rewriteContextWindowGuidance(content: string, concise: boolean): string {
	return content.replace(/^<context_window_guidance>[\s\S]*?<\/context_window_guidance>/,
		concise ? CONTEXT_WINDOW_GUIDANCE : CONTEXT_WINDOW_EXPLICIT_GUIDANCE);
}

export function renderContextWindowMessage(
	identity: ContextWindowIdentity,
	threadHint?: string,
	agentName = "/root",
): string {
	const lines = [
		"<context_window>",
		`Agent name: ${agentName}`,
		`First context window id: ${identity.firstWindowId}`,
		`Current context window id: ${identity.currentWindowId}`,
	];
	if (identity.previousWindowId)
		lines.push(`Previous context window id: ${identity.previousWindowId}`);
	if (threadHint) lines.push(threadHint);
	lines.push("</context_window>");
	return `${CONTEXT_WINDOW_GUIDANCE}\n\n${lines.join("\n")}`;
}

export function renderContextWindowReminder(remainingPercent: number, urgent: boolean): string {
	return `<context_window_reminder>
${urgent ? "Urgent: " : ""}${remainingPercent}% remaining. Checkpoint the active request, state and known history IDs in notes, then call new_context ${urgent ? "now, before other work" : "before continuing work"}.
</context_window_reminder>`;
}

export function renderManualContextCheckpoint(customInstructions?: string): string {
	return `<context_window_reminder>
Manual context rollover requested. Save the current state with notes, then finish your response. The new window opens after this run settles. Do not call new_context. If saving fails, report the failure without rolling over.
</context_window_reminder>${customInstructions?.trim() ? `\n\nCheckpoint guidance from /compact:\n${customInstructions}` : ""}`;
}

export function isCodexContextManagementMessageDetails(
	value: unknown,
): value is CodexContextManagementMessageDetails {
	if (!value || typeof value !== "object") return false;
	const details = value as Record<string, unknown>;
	if (
		details["protocol"] !== 1 ||
		typeof details["id"] !== "string" ||
		!details["id"]
	)
		return false;
	const context = details["contextManagement"];
	if (!context || typeof context !== "object") return false;
	const record = context as Record<string, unknown>;
	return (
		record["protocol"] === 1 &&
		(record["kind"] === "window" ||
			record["kind"] === "identity" ||
			record["kind"] === "reminder" ||
			record["kind"] === "urgent" ||
			record["kind"] === "fallback") &&
		(record["agentName"] === undefined || typeof record["agentName"] === "string") &&
		typeof record["firstWindowId"] === "string" &&
		record["firstWindowId"] !== "" &&
		typeof record["currentWindowId"] === "string" &&
		record["currentWindowId"] !== "" &&
		(record["previousWindowId"] === undefined ||
			typeof record["previousWindowId"] === "string") &&
		(record["trimPreviousWindow"] === undefined ||
			record["trimPreviousWindow"] === true) &&
		Number.isInteger(record["windowNumber"]) &&
		(record["windowNumber"] as number) >= 0
	);
}

export function isContextWindowBoundary(
	message: AgentMessage,
): message is Extract<AgentMessage, { role: "custom" }> & {
	details: CodexContextManagementMessageDetails;
} {
	return (
		message.role === "custom" &&
		message.customType === CODEX_CONTEXT_WINDOW_MESSAGE_TYPE &&
		isCodexContextManagementMessageDetails(message.details) &&
		message.details.contextManagement.kind === "window"
	);
}

export function isContextWindowCompactionDetails(
	value: unknown,
): value is ContextWindowCompactionDetails {
	return Boolean(
		value &&
			typeof value === "object" &&
			"protocol" in value &&
			value.protocol === 1 &&
			"strategy" in value &&
			value.strategy === CONTEXT_WINDOW_COMPACTION_STRATEGY,
	);
}

export function createContextWindowMessage(
	content: string,
	kind: ContextManagementMessageKind,
	identity: ContextWindowIdentity,
	trimPreviousWindow = false,
): CustomMessageEntryDraft & { details: CodexContextManagementMessageDetails } {
	return {
		type: "custom_message",
		customType: CODEX_CONTEXT_WINDOW_MESSAGE_TYPE,
		content,
		display: true,
		details: {
			protocol: 1,
			id: randomUUID(),
			contextManagement: {
				protocol: 1,
				kind,
				...identity,
				...(trimPreviousWindow ? { trimPreviousWindow: true as const } : {}),
			},
		},
	};
}