import type { Theme } from "@earendil-works/pi-coding-agent";
import type { CacheSessionMetrics, CacheUsageTotals } from "./types.js";
import { formatCompact, formatPercent, hitRateColor, summarizeHitPercent } from "./format-utils.js";

/** Width of the label column so the two summary rows align. "Active branch" = 13. */
const LABEL_WIDTH = 13;

/** One metric cell: dim name + plain value, e.g. "prompt 60.0k". */
function metric(theme: Theme, name: string, value: string): string {
  return `${theme.fg("dim", name)} ${value}`;
}

/**
 * One aligned summary row:
 *   Active branch  3 turns · prompt 60.0k · recv 1.5k · hit 33.0k · rate 66.7%
 * Label is accent, metric names dim, values plain, hit rate tier-colored.
 */
function totalsLine(
  theme: Theme,
  label: string,
  totals: CacheUsageTotals,
  hideWrite: boolean,
): string {
  const rate = summarizeHitPercent(totals);
  const parts = [
    theme.fg("accent", label.padEnd(LABEL_WIDTH)),
    theme.fg("dim", `${formatCompact(totals.assistantMessages)} turns`),
    metric(theme, "prompt", formatCompact(totals.input + totals.cacheRead + totals.cacheWrite)),
    metric(theme, "recv", formatCompact(totals.output)),
    metric(theme, "hit", formatCompact(totals.cacheRead)),
  ];
  if (!hideWrite) parts.push(metric(theme, "write", formatCompact(totals.cacheWrite)));
  parts.push(metric(theme, "rate", hitRateColor(theme, rate, theme.bold(formatPercent(rate)))));
  return parts.join(" · ");
}

/** Block title shared by the summary and view sections. */
function blockTitle(theme: Theme, text: string): string {
  return theme.fg("accent", theme.bold(`▎ ${text}`));
}

/** One line: current context occupancy, e.g. "context: 45.2% · 57.8k / 128k". */
function contextLine(
  theme: Theme,
  contextUsage?: { tokens: number | null; contextWindow: number; percent: number | null },
): string[] {
  if (!contextUsage) return [];
  const { tokens, contextWindow, percent } = contextUsage;
  const pct =
    percent === null
      ? "?"
      : percent > 90
        ? theme.fg("error", `${percent.toFixed(1)}%`)
        : percent > 70
          ? theme.fg("warning", `${percent.toFixed(1)}%`)
          : `${percent.toFixed(1)}%`;
  const tokensText = tokens === null ? "?" : formatCompact(tokens);
  return [
    theme.fg("dim", "context:") +
      ` ${pct}` +
      theme.fg("dim", " · ") +
      `${tokensText} / ${formatCompact(contextWindow)}`,
  ];
}

/**
 * Session-wide summary, rendered once in the dialog's fixed header.
 * The delta row appears only when the session tree has side branches.
 */
export function buildSummaryLines(
  theme: Theme,
  metrics: CacheSessionMetrics,
  contextUsage?: { tokens: number | null; contextWindow: number; percent: number | null },
): string[] {
  const tree = metrics.treeTotals;
  const branch = metrics.activeBranchTotals;
  const treeHitRate = summarizeHitPercent(tree);
  const branchHitRate = summarizeHitPercent(branch);
  // Providers without a cache-write bucket (DeepSeek/OpenAI/Gemini) always
  // report 0 here; hide the noise term instead of printing "write 0".
  const hideWrite = tree.cacheWrite === 0 && branch.cacheWrite === 0;

  const deltaPrompt =
    tree.input + tree.cacheRead + tree.cacheWrite - (branch.input + branch.cacheRead + branch.cacheWrite);
  const deltaReceived = tree.output - branch.output;
  const deltaHit = tree.cacheRead - branch.cacheRead;
  const deltaWrite = tree.cacheWrite - branch.cacheWrite;
  const deltaSpread = treeHitRate - branchHitRate;
  // Sessions without forks have tree == branch; hide the all-zero delta row
  // instead of printing zeros (it reappears once the session forks).
  const hasSideBranches =
    tree.assistantMessages !== branch.assistantMessages ||
    deltaPrompt !== 0 ||
    deltaReceived !== 0 ||
    deltaHit !== 0 ||
    deltaWrite !== 0;

  const lines = [
    blockTitle(theme, "Session summary"),
    ...contextLine(theme, contextUsage),
    totalsLine(theme, "Active branch", branch, hideWrite),
    totalsLine(theme, "Whole tree", tree, hideWrite),
  ];
  if (hasSideBranches) {
    const deltaParts = [
      theme.fg("accent", "Delta".padEnd(LABEL_WIDTH)),
      metric(theme, "prompt", formatCompact(deltaPrompt)),
      metric(theme, "recv", formatCompact(deltaReceived)),
      metric(theme, "hit", formatCompact(deltaHit)),
    ];
    if (!hideWrite) deltaParts.push(metric(theme, "write", formatCompact(deltaWrite)));
    deltaParts.push(metric(theme, "spread", formatPercent(deltaSpread)));
    lines.push(deltaParts.join(" · "));
  }
  return lines;
}