/**
 * KDL composition.
 *
 * A project ships a *fragment* (pane nodes only); sl0ppi wraps it in the tab
 * node that carries identity and cwd. Pure string composition, so there is no
 * KDL parser to keep in step with the fork's dialect, and sl0ppi keeps sole
 * control of the purpose.
 *
 * ALWAYS emit multi-line KDL. On a single line, KDL requires `;` terminators
 * between nodes: `tab x { pane }` is a parse error, which is a genuinely
 * confusing way to lose an afternoon.
 */

import { readFileSync } from "node:fs";
import { join } from "node:path";
import { projectPurpose } from "./purpose.ts";

/** Quote a value for a KDL string property. */
export function kdlString(value: string): string {
  return `"${value.replace(/\\/g, "\\\\").replace(/"/g, '\\"')}"`;
}

/**
 * Pull the `default_tab_template { ... }` block out of a layout file.
 *
 * Without this, a generated session has NO tab bar and NO status bar: our
 * layout replaces the user's default one, so a root with five projects looks
 * exactly like a root with one, and the other tabs are invisible. That was
 * reported as "shouldn't there be a proj_b tab?" -- there was one, with nothing
 * on screen to say so.
 *
 * Brace-matched by hand rather than parsed, but it must respect strings and
 * comments: a zjstatus template is full of `{index}` and `{name}` inside quoted
 * format strings, and counting those as braces truncates the block in the
 * middle and produces a layout that will not parse.
 */
export function extractDefaultTabTemplate(layoutKdl: string): string | undefined {
  const found = extractBlocks(layoutKdl, /(^|\n)[ \t]*default_tab_template[ \t]*\{/g);
  return found[0];
}

/**
 * Find `<head> { ... }` nodes matching `marker`, with their braces balanced.
 *
 * Brace-matched by hand rather than parsed, but it must respect strings and
 * comments: a zjstatus template is full of `{index}` and `{name}` inside quoted
 * format strings, and counting those as braces truncates the block in the
 * middle and produces a layout that will not parse.
 */
function extractBlocks(layoutKdl: string, marker: RegExp): string[] {
  const blocks: string[] = [];
  for (const match of layoutKdl.matchAll(marker)) {
    const head = match[0].replace(/^\n/, "").trim(); // e.g. `pane_template name="x" {`
    const start = (match.index ?? 0) + match[0].length - 1; // at the '{'
    let depth = 0;
    let inString = false;
    let inComment = false;

    for (let i = start; i < layoutKdl.length; i++) {
      const ch = layoutKdl[i] as string;
      const next = layoutKdl[i + 1];

      if (inComment) {
        if (ch === "\n") inComment = false;
        continue;
      }
      if (inString) {
        if (ch === "\\") i++; // skip the escaped character
        else if (ch === '"') inString = false;
        continue;
      }
      if (ch === "/" && next === "/") {
        inComment = true;
        continue;
      }
      if (ch === '"') {
        inString = true;
        continue;
      }
      if (ch === "{") depth++;
      else if (ch === "}") {
        depth--;
        if (depth === 0) {
          const body = layoutKdl.slice(start, i + 1);
          blocks.push(`${head.slice(0, -1).trim()} ${body}`);
          break;
        }
      }
    }
    // unbalanced: better to drop this block than to emit a broken layout
  }
  return blocks;
}

/**
 * The `pane_template` definitions from a layout file.
 *
 * A generated session layout is a FILE OF ITS OWN: it does not inherit
 * anything from `layouts/default.kdl`, so a template body that says `sl0pbar
 * size=3` produces "Invalid tab property: sl0pbar" unless the definition comes
 * along with it. That is exactly how `sl0ppi up` broke the day the status bar
 * became a pane_template -- the tab template referenced a name only the
 * original file knew.
 */
export function extractPaneTemplates(layoutKdl: string): string[] {
  return extractBlocks(layoutKdl, /(^|\n)[ \t]*pane_template[ \t][^\n{]*\{/g);
}

/** The tab template and the pane templates it may reference. */
export interface LayoutTemplates {
  tabTemplate?: string;
  paneTemplates: string[];
}

/** The templates from the user's own default layout, if they have one. */
export function templatesFrom(configDir: string): LayoutTemplates {
  try {
    const kdl = readFileSync(join(configDir, "layouts", "default.kdl"), "utf8");
    return {
      tabTemplate: extractDefaultTabTemplate(kdl),
      paneTemplates: extractPaneTemplates(kdl),
    };
  } catch {
    return { paneTemplates: [] };
  }
}

/** The template from the user's own default layout, if they have one. */
export function defaultTabTemplateFrom(configDir: string): string | undefined {
  return templatesFrom(configDir).tabTemplate;
}

/**
 * What a project gets when it has a `.sl0ppi/` marker but no `layout.kdl`.
 *
 * One suspended agent: every project wants a main agent (agreed), and
 * `start_suspended` is what stops `up` on a twelve-project root from launching
 * twelve of them. The pane exists, focused-and-keypress runs it.
 */
export const DEFAULT_FRAGMENT = `pane purpose="agent:main" start_suspended=true command="pi"`;

export interface TabSpec {
  /** Tab name, shown in the tab bar. Cosmetic; identity is the purpose. */
  name: string;
  /** Project path relative to the root, which the purpose encodes. */
  relPath: string;
  /** Absolute path used as the tab's cwd. */
  cwd: string;
  /** Pane nodes, verbatim from `.sl0ppi/layout.kdl`. */
  fragment?: string;
}

function indent(text: string, spaces: number): string {
  const pad = " ".repeat(spaces);
  return text
    .split("\n")
    .map((line) => (line.trim() === "" ? "" : pad + line))
    .join("\n");
}

/**
 * Fold a tab template around a project's panes.
 *
 * Kept for callers that hand a layout STRING to a running session. The session
 * layout emits `default_tab_template` instead -- see `sessionLayoutKdl`.
 */
export function applyTemplate(fragment: string, template: string): string | undefined {
  const body = template.slice(template.indexOf("{") + 1, template.lastIndexOf("}"));
  const childrenLine = /^([ \t]*)children[ \t]*$/m.exec(body);
  if (!childrenLine) return undefined; // nothing to substitute into; skip the template

  const pad = childrenLine[1] ?? "";
  const replaced = fragment
    .split("\n")
    .map((line) => (line.trim() === "" ? "" : pad + line))
    .join("\n");
  return dedent(body.replace(childrenLine[0], replaced));
}

/** Strip the common leading indentation, so re-indenting is predictable. */
function dedent(text: string): string {
  const lines = text.split("\n").filter((line) => line.trim() !== "");
  const smallest = Math.min(
    ...lines.map((line) => (line.match(/^[ \t]*/)?.[0].length ?? 0)),
    Number.MAX_SAFE_INTEGER,
  );
  return text
    .split("\n")
    .map((line) => line.slice(smallest))
    .join("\n")
    .trim();
}

/** A single `tab { ... }` node, indented for embedding in a `layout` block. */
export function tabKdl(spec: TabSpec, indentBy = 4, template?: string): string {
  let fragment = (spec.fragment ?? DEFAULT_FRAGMENT).trimEnd();
  if (template) fragment = applyTemplate(fragment, template) ?? fragment;
  const head =
    `tab name=${kdlString(spec.name)} ` +
    `purpose=${kdlString(projectPurpose(spec.relPath))} ` +
    `cwd=${kdlString(spec.cwd)} {`;
  return indent(`${head}\n${indent(fragment, 4)}\n}`, indentBy);
}

/**
 * Definitions the generated tabs refer to, emitted once at the top of the
 * layout. Anything a tab body names has to be defined in the same file.
 */
function preamble(paneTemplates?: string[]): string {
  if (!paneTemplates || paneTemplates.length === 0) return "";
  return `${paneTemplates.map((template) => indent(template, 4)).join("\n")}\n`;
}

/**
 * A whole-session layout: what `up` passes to `--layout` when creating.
 *
 * The tab template is EMITTED, not inlined into each tab. It used to be
 * inlined, because a templated tab came back with `purpose=None` and purpose is
 * identity here -- `sl0ppi ls` finds project tabs by it. The fork now keeps a
 * tab's own purpose when a template is applied
 * (`sl0p_a_templated_tab_keeps_its_own_purpose`), which removes that reason and
 * fixes the thing the workaround cost us: a tab created at RUNTIME -- `new-tab`
 * from a keybinding, or the bar's `+` button -- had no template to take a
 * status bar from, and came up bare.
 */
export function sessionLayoutKdl(
  specs: TabSpec[],
  template?: string,
  paneTemplates?: string[],
): string {
  const tabs = specs.map((spec) => tabKdl(spec, 4)).join("\n");
  return `layout {\n${preamble(paneTemplates)}${templateBlock(template)}${tabs}\n}\n`;
}

/** The `default_tab_template { ... }` node, indented into the layout block. */
function templateBlock(template?: string): string {
  if (!template) return "";
  return `${indent(template, 4)}\n`;
}

/**
 * A one-tab layout: what `open` passes to `new-tab --layout-string`.
 *
 * Still inlined: this layout describes ONE tab being added to a session that
 * already exists, and a `default_tab_template` in it would apply to that tab
 * anyway -- but the session's own template (if it has one) would apply first,
 * and the tab would come up with two status bars.
 */
export function singleTabLayoutKdl(
  spec: TabSpec,
  template?: string,
  paneTemplates?: string[],
): string {
  return `layout {\n${preamble(paneTemplates)}${tabKdl(spec, 4, template)}\n}\n`;
}