/**
 * Pure renderer for `docs/README.md`.
 *
 * The index is intentionally short and mechanical — a stable pointer surface humans (and
 * agents) can use to find the canonical Tier-1 docs + per-layer agent docs. Layout is
 * dictated by the plan's "Index docs/README.md shape" section.
 */

import type { HarnessLayerRule } from "../../types.js";
import {
  attachProvenance,
  computeBodyContentHash,
} from "./provenance.js";

export interface RenderDocsIndexInput {
  layers: readonly HarnessLayerRule[];
  /** Session that produced this index. */
  sessionId: string;
  /** ISO timestamp used in the provenance marker + "Generated by" line. */
  generatedAt: string;
  /** Hard cap on the index LOC (default 50). */
  maxLoc?: number;
}

export const DEFAULT_INDEX_MAX_LOC = 50;

/**
 * Render the index. Deterministic given the same input. The output starts with the
 * provenance marker line and ends with a trailing newline.
 */
export function renderDocsIndex(input: RenderDocsIndexInput): string {
  if (input.layers.length === 0) {
    throw new Error("renderDocsIndex requires at least one layer");
  }
  const maxLoc = input.maxLoc ?? DEFAULT_INDEX_MAX_LOC;

  const sortedLayers = [...input.layers].sort((a, b) => a.layer.localeCompare(b.layer));

  const lines: string[] = [];
  lines.push("# Repo docs");
  lines.push("");
  lines.push(`Generated by /supi:harness on ${input.generatedAt}. Do not edit by hand.`);
  lines.push("");
  lines.push("## Agent contract");
  lines.push("- AGENTS.md — global agent rules");
  lines.push("- docs/architecture.md — layer rules table");
  lines.push("- docs/golden-principles.md — mechanical invariants");
  lines.push("");
  lines.push("## Layer docs");
  lines.push("");
  lines.push("| Layer | Files | Doc |");
  lines.push("|---|---|---|");
  for (const layer of sortedLayers) {
    const globs = layer.globs.map((g) => `\`${g}\``).join(", ");
    lines.push(`| ${layer.layer} | ${globs || "—"} | docs/layers/${layer.layer}.md |`);
  }

  const body = lines.join("\n") + "\n";
  if (countLines(body) + 1 /* marker line */ > maxLoc) {
    // Should be unreachable for any sane layer count; surface as a hard failure so the
    // caller can cap layer count if this ever fires.
    throw new Error(
      `renderDocsIndex output is ${countLines(body) + 1} LOC; max is ${maxLoc} (layers=${input.layers.length})`,
    );
  }

  return attachProvenance(body, {
    sessionId: input.sessionId,
    generatedAt: input.generatedAt,
    contentHash: computeBodyContentHash(body),
  });
}

function countLines(text: string): number {
  if (text.length === 0) return 0;
  let count = 1;
  for (let i = 0; i < text.length; i += 1) {
    if (text.charCodeAt(i) === 10) count += 1;
  }
  if (text.charCodeAt(text.length - 1) === 10) count -= 1;
  return count;
}