/**
 * Custom Footer Extension for pi
 *
 * Replaces the default footer with:
 * - Context shown as absolute tokens (e.g. "120k/524k") instead of percentage
 * - Cache hit rate displayed as "CH94%" instead of raw cache tokens
 * - Thinking level shown next to model name
 * - Same layout: cwd+branch on line 1, stats on line 2, extension statuses on line 3
 */

import type { AssistantMessage } from "@earendil-works/pi-ai";
import type { ExtensionAPI, ExtensionContext } from "@earendil-works/pi-coding-agent";
import { readFileSync } from "node:fs";
import { homedir } from "node:os";
import { join, relative, resolve, sep } from "node:path";
import { truncateToWidth, visibleWidth } from "@earendil-works/pi-tui";

// ── Helpers ──────────────────────────────────────────────────────────────────

function fmtTokens(n: number): string {
	if (n < 1000) return n.toString();
	if (n < 10000) return `${(n / 1000).toFixed(1)}k`;
	if (n < 1000000) return `${Math.round(n / 1000)}k`;
	if (n < 10000000) return `${(n / 1000000).toFixed(1)}M`;
	return `${Math.round(n / 1000000)}M`;
}

function fmtCwd(cwd: string): string {
	const home = process.env.HOME || process.env.USERPROFILE || "";
	if (!home) return cwd;
	const r = resolve(cwd);
	const rel = relative(resolve(home), r);
	if (rel === "") return "~";
	if (rel.startsWith("..")) return cwd;
	return `~${sep}${rel}`;
}

// ── Extension Entry Point ────────────────────────────────────────────────────

export default function (pi: ExtensionAPI) {
	let fCtx: ExtensionContext | null = null;

	// Track thinking level: read default from settings.json, update via events
	let currentThinkingLevel = "";
	try {
		const settingsPath = join(homedir(), ".pi", "agent", "settings.json");
		const settings = JSON.parse(readFileSync(settingsPath, "utf-8"));
		currentThinkingLevel = settings.defaultThinkingLevel ?? "";
	} catch { /* ignore */ }

	pi.on("thinking_level_select", async (event) => {
		currentThinkingLevel = event.level;
	});

	// ── Install Footer ───────────────────────────────────────────────────────

	function installFooter(ctx: ExtensionContext) {
		fCtx = ctx;

		ctx.ui.setFooter((tui, theme, footerData) => {
			const unsub = footerData.onBranchChange(() => tui.requestRender());
			return {
				dispose: unsub,
				invalidate() {},
				render(width: number): string[] {
					if (!fCtx) return [];
					const sm = fCtx.sessionManager;
					const model = fCtx.model;

					// Token stats from all entries
					let tIn = 0, tOut = 0, tCR = 0, tCW = 0, tCost = 0;
					for (const e of sm.getEntries()) {
						if (e.type === "message" && e.message.role === "assistant") {
							const u = (e.message as AssistantMessage).usage;
							tIn += u.input;
							tOut += u.output;
							tCR += u.cacheRead;
							tCW += u.cacheWrite;
							tCost += u.cost.total;
						}
					}

					// Context usage
					const cu = fCtx.getContextUsage();
					const cw = cu?.contextWindow ?? model?.contextWindow ?? 0;
					const ct = cu?.tokens;

					// Build stats parts
					const parts: string[] = [];
					if (tIn) parts.push(`↑${fmtTokens(tIn)}`);
					if (tOut) parts.push(`↓${fmtTokens(tOut)}`);

					// Cache hit rate: cacheRead / (input + cacheRead + cacheWrite)
					const totalPrompt = tIn + tCR + tCW;
					if (totalPrompt > 0) {
						const hitRate = (tCR / totalPrompt) * 100;
						if (hitRate > 0) {
							const hitStr = hitRate >= 99.5 ? "100%" : `${hitRate.toFixed(0)}%`;
							parts.push(`CH${hitStr}`);
						}
					}

					if (tCost) parts.push(`$${tCost.toFixed(3)}`);

					// Context: "120k/524k (auto)" instead of "26.2%/524k (auto)"
					const ctStr = ct != null ? fmtTokens(ct) : "?";
					const ctxDisplay = `${ctStr}/${fmtTokens(cw)} (auto)`;
					const pct = cu?.percent ?? 0;
					if (pct > 90) parts.push(theme.fg("error", ctxDisplay));
					else if (pct > 70) parts.push(theme.fg("warning", ctxDisplay));
					else parts.push(ctxDisplay);

					let left = parts.join(" ");
					let leftW = visibleWidth(left);
					if (leftW > width) {
						left = truncateToWidth(left, width, "...");
						leftW = visibleWidth(left);
					}

					// Right side: model + thinking level
					const mId = model?.id ?? "no-model";
					let right = mId;
					if (model?.reasoning && currentThinkingLevel) {
						right = currentThinkingLevel === "off"
							? `${mId} • thinking off`
							: `${mId} • ${currentThinkingLevel}`;
					}
					const rightW = visibleWidth(right);
					const gap = 2;

					let line: string;
					if (leftW + gap + rightW <= width) {
						line = left + " ".repeat(width - leftW - rightW) + right;
					} else {
						const avail = width - leftW - gap;
						if (avail > 0) {
							const tr = truncateToWidth(right, avail, "");
							line = left + " ".repeat(Math.max(0, width - leftW - visibleWidth(tr))) + tr;
						} else {
							line = left;
						}
					}

					const dimLeft = theme.fg("dim", left);
					const dimRight = theme.fg("dim", line.slice(left.length));

					// Line 1: cwd + branch + session name
					const cwd = fmtCwd(sm.getCwd?.() ?? process.cwd());
					const branch = footerData.getGitBranch();
					const sName = sm.getSessionName?.();
					let pwd = cwd;
					if (branch) pwd = `${pwd} (${branch})`;
					if (sName) pwd = `${pwd} • ${sName}`;
					const pwdLine = truncateToWidth(theme.fg("dim", pwd), width, theme.fg("dim", "..."));

					const lines = [pwdLine, dimLeft + dimRight];

					// Line 3: extension statuses
					const statuses = footerData.getExtensionStatuses();
					if (statuses.size > 0) {
						const sorted = Array.from(statuses.entries())
							.sort(([a], [b]) => a.localeCompare(b))
							.map(([, t]) => t.replace(/[\r\n\t]/g, " ").replace(/ +/g, " ").trim());
						lines.push(truncateToWidth(sorted.join(" "), width, theme.fg("dim", "...")));
					}

					return lines;
				},
			};
		});
	}

	// ── Lifecycle ────────────────────────────────────────────────────────────

	pi.on("session_start", async (_event, ctx) => {
		installFooter(ctx);
	});

	pi.on("session_shutdown", async () => {
		fCtx = null;
	});
}