import type { ExtensionAPI, ExtensionCommandContext } from "@earendil-works/pi-coding-agent";
import { collectBreakdown } from "./breakdown";
import { bar, fmt, percent, themeColorFor } from "./format";
import type { Section } from "./types";

/** pi's default compaction reserveTokens (settings.json `compaction.reserveTokens`). */
const RESERVE_TOKENS = 16_384;

/** Renders the context overview + breakdown as a plain-text report. */
export const buildReport = (pi: ExtensionAPI, ctx: ExtensionCommandContext): string => {
	const usage = ctx.getContextUsage();
	const model = ctx.model;
	const theme = ctx.ui.theme;

	const lines: string[] = [];
	lines.push(theme.fg("accent", theme.bold("Context Usage")));
	lines.push("");

	if (!usage) {
		lines.push(theme.fg("dim", "No active model or session yet."));
		return lines.join("\n");
	}

	const { tokens, contextWindow, percent: rawPercent } = usage;
	const threshold = contextWindow - RESERVE_TOKENS;
	const color = themeColorFor(tokens ?? 0, contextWindow, threshold);

	lines.push(
		`${theme.fg("muted", "Model:")}          ${theme.bold(`${model?.provider ?? "?"}/${model?.id ?? "?"}`)}`,
	);
	lines.push(`${theme.fg("muted", "Context window:")}   ${theme.bold(fmt(contextWindow))} tokens`);
	lines.push(
		`${theme.fg("muted", "Used:")}             ${theme.fg(color, `${fmt(tokens ?? 0)} tokens (${rawPercent?.toFixed(1) ?? "?"}%)`)}`,
	);
	if (tokens !== null) {
		lines.push(
			`${theme.fg("muted", "Remaining:")}        ${theme.bold(fmt(Math.max(0, contextWindow - tokens)))} tokens`,
		);
	}
	lines.push("");
	lines.push(`  ${theme.fg(color, bar(tokens ?? 0, contextWindow, threshold))}`);
	lines.push(
		theme.fg(
			"dim",
			`  ┃ = auto-compaction threshold (window − reserve ${fmt(RESERVE_TOKENS)} = ${fmt(threshold)})`,
		),
	);

	if (tokens === null || rawPercent === null) {
		lines.push(theme.fg("dim", "Breakdown unavailable (tokens unknown)."));
		return lines.join("\n");
	}

	const hasReportedUsage = tokens > 0;

	/* --- section breakdown (estimates) --- */
	lines.push("");
	lines.push(theme.fg("accent", theme.bold("Section breakdown (estimated)")));
	if (!hasReportedUsage) {
		lines.push(
			theme.fg(
				"dim",
				"No provider usage yet — sizes below are chars/4 estimates from your session.",
			),
		);
	}

	const breakdown = collectBreakdown(pi, ctx);
	const sections: Section[] = [breakdown.system, breakdown.messages, breakdown.tools];

	for (const section of sections) {
		const sColor = themeColorFor(section.total, tokens, threshold);
		lines.push("");
		const pctLabel = hasReportedUsage
			? ` ${theme.fg("dim", `(${percent(section.total, tokens).toFixed(1)}%)`)}`
			: "";
		lines.push(
			`${theme.bold(section.title)}${" ".repeat(Math.max(1, 16 - section.title.length))}` +
				`${theme.fg("muted", fmt(section.total))} ` +
				`${theme.fg(sColor, bar(section.total, tokens, threshold, 12))} ` +
				pctLabel,
		);
		for (const item of section.lines) {
			const detail = item.detail ? `  ${theme.fg("dim", item.detail)}` : "";
			lines.push(
				`  ${theme.fg("dim", "├")} ${item.label}${" ".repeat(Math.max(1, 22 - item.label.length))}${theme.fg("muted", fmt(item.tokens))}${detail}`,
			);
		}
	}

	if (hasReportedUsage) {
		/* --- reconciliation vs provider-reported total --- */
		const accounted = sections.reduce((a, s) => a + s.total, 0);
		const ratio = (accounted / tokens) * 100;
		const diff = tokens - accounted;
		lines.push("");
		lines.push(
			ratio >= 90
				? theme.fg(
						"success",
						`✓ Breakdown accounts for ${fmt(accounted)} of ${fmt(tokens)} tokens (${ratio.toFixed(0)}%)`,
					)
				: theme.fg(
						"warning",
						`Breakdown accounts for ${fmt(accounted)} of ${fmt(tokens)} tokens (${ratio.toFixed(0)}%); ` +
							`${fmt(diff)} unaccounted (cache markers, encodings, overhead)`,
					),
		);
	}

	lines.push("");
	lines.push(
		theme.fg(
			"dim",
			"Sizes are chars/4 estimates — the provider's own tokenizer may differ.  Subcommands: /context skills · tools · files",
		),
	);

	return lines.join("\n");
};