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

function pad(value: string, width: number, direction: "left" | "right" = "right"): string {
  if (value.length >= width) return value;
  const padding = " ".repeat(width - value.length);
  return direction === "left" ? padding + value : value + padding;
}

function truncate(value: string, width: number): string {
  if (value.length <= width) return value;
  return width <= 1 ? value.slice(0, width) : `${value.slice(0, Math.max(0, width - 1))}…`;
}

function buildRow(
  theme: Theme,
  metric: AssistantUsageMetric,
  cumPrompt: number,
  includeEntryId: boolean,
  includeTimestamp: boolean,
  hideWrite: boolean,
): string {
  const cols = [
    pad(String(metric.sequence), 4, "left"),
    pad(metric.isOnActiveBranch ? "*" : " ", 1),
    pad(truncate(shortModelName(metric.provider, metric.model), 24), 24),
    pad(formatCompact(metric.input + metric.cacheRead + metric.cacheWrite), 9, "left"),
    pad(formatCompact(metric.output), 9, "left"),
    pad(formatCompact(metric.cacheRead), 9, "left"),
  ];
  if (!hideWrite) cols.push(pad(formatCompact(metric.cacheWrite), 9, "left"));
  cols.push(
    hitRateColor(theme, metric.cacheHitPercent, pad(formatPercent(metric.cacheHitPercent), 7, "left")),
  );
  cols.push(pad(formatCompact(cumPrompt), 9, "left"));

  if (includeEntryId) cols.splice(2, 0, pad(truncate(metric.entryId, 8), 8));
  if (includeTimestamp) cols.splice(includeEntryId ? 3 : 2, 0, pad(metric.timestamp.slice(11, 19), 8));

  return cols.join(" ");
}

function buildHeader(includeEntryId: boolean, includeTimestamp: boolean, hideWrite: boolean): string {
  const cols = [
    pad("#", 4, "left"),
    pad("B", 1),
    pad("model", 24),
    pad("prompt", 9, "left"),
    pad("recv", 9, "left"),
    pad("hit", 9, "left"),
  ];
  if (!hideWrite) cols.push(pad("write", 9, "left"));
  cols.push(pad("hit%", 7, "left"));
  cols.push(pad("cumTok", 9, "left"));

  if (includeEntryId) cols.splice(2, 0, pad("entry", 8));
  if (includeTimestamp) cols.splice(includeEntryId ? 3 : 2, 0, pad("time", 8));

  return cols.join(" ");
}

const EDGE_ROWS = 5;

/**
 * Renders the per-message breakdown table. Long sessions show only the first
 * and last EDGE_ROWS messages — the middle is collapsed into a single
 * omission line, so the table stays readable without scrolling.
 * The session-wide summary is rendered once by the dialog header, not here.
 */
export function renderStatsView(theme: Theme, messages: AssistantUsageMetric[], width: number): string[] {
  const lines: string[] = [];

  if (messages.length === 0) {
    lines.push(
      theme.fg("warning", "No assistant messages with usage data are available yet in this session."),
    );
    return lines;
  }

  lines.push(theme.fg("accent", theme.bold("▎ Message table")));
  lines.push(theme.fg("dim", "B = message is on the current active branch"));

  const includeEntryId = width >= 92;
  const includeTimestamp = width >= 104;
  // Providers without a cache-write bucket (DeepSeek/OpenAI/Gemini) always
  // report 0; hide the column instead of printing an all-zero column.
  const hideWrite = messages.every((m) => m.cacheWrite === 0);
  const header = buildHeader(includeEntryId, includeTimestamp, hideWrite);

  lines.push(theme.fg("muted", header));
  lines.push(theme.fg("dim", "-".repeat(Math.min(header.length, Math.max(20, width - 2)))));

  const showAll = messages.length <= EDGE_ROWS * 2;
  if (!showAll) {
    lines.push(
      theme.fg("dim", `Showing first & last ${EDGE_ROWS} of ${messages.length} messages`),
    );
  }

  // Running cumulative prompt tokens (input + cacheRead + cacheWrite).
  const cumPrompt: number[] = [];
  let acc = 0;
  for (const m of messages) {
    acc += m.input + m.cacheRead + m.cacheWrite;
    cumPrompt.push(acc);
  }

  for (const [i, metric] of (showAll ? messages : messages.slice(0, EDGE_ROWS)).entries()) {
    lines.push(buildRow(theme, metric, cumPrompt[i]!, includeEntryId, includeTimestamp, hideWrite));
  }

  if (!showAll) {
    const omitted = messages.length - EDGE_ROWS * 2;
    const firstOmitted = messages[EDGE_ROWS]!;
    const lastOmitted = messages[messages.length - EDGE_ROWS - 1]!;
    lines.push(
      theme.fg(
        "dim",
        `  … ${omitted} messages omitted (seq ${firstOmitted.sequence}–${lastOmitted.sequence}) …`,
      ),
    );
    for (const [i, metric] of messages.slice(-EDGE_ROWS).entries()) {
      lines.push(
        buildRow(theme, metric, cumPrompt[messages.length - EDGE_ROWS + i]!, includeEntryId, includeTimestamp, hideWrite),
      );
    }
  }

  return lines;
}