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"
	| "task-boundary"
	| "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_GUIDANCE = `<context_window_guidance>
Notes are recovery state, not a diary. Keep one concise, authoritative note per task or topic at a stable path. Task checkpoints cover request, constraints, decisions, status, next steps and history IDs. Use write_file to replace stale state and mark completion. Link to existing notes instead of copying or summarising their contents. Recording isn't permission to implement.

Batch saves at meaningful milestones, not every reply or intermediate step. Before new_context or handoff, save current state and wait for success; include the checkpoint path in handoffs. After rollover, read the checkpoint, then only needed links. Don't reread notes still in context unless they may have changed. Use history for missing details.

Previous skill reads don’t carry into this window. Read the skills needed for the current task.
</context_window_guidance>`;

export function rewriteContextWindowGuidance(content: string): string {
	return content.replace(/^<context_window_guidance>[\s\S]*?<\/context_window_guidance>/,
		CONTEXT_WINDOW_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: ${identity.previousWindowId}`);
	if (threadHint) lines.push(threadHint, "More notes may be available; list or search notes");
	lines.push("</context_window>");
	return `${CONTEXT_WINDOW_GUIDANCE}\n\n${lines.join("\n")}`;
}

export function renderContextWindowReminder(remainingPercent: number, urgent: boolean): string {
	return `<context_window_reminder>
${urgent ? "Urgent: " : ""}${remainingPercent}% context remaining. Save the task state 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>
Save the task state in notes, then finish your reply. A new window opens automatically after your reply; do not call new_context. If saving fails, report the error.
</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"] === "task-boundary" ||
			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 } : {}),
			},
		},
	};
}