import type { Options } from "./options.ts";
import { type JsonObject, type JsonValue, toJsonValue } from "./parse.ts";

const WIDTH = 80;

function isObject(value: JsonValue): value is JsonObject {
  return typeof value === "object" && value !== null && !Array.isArray(value);
}

/** render an object key (leaving simple identifiers unquoted) */
export function keyText(key: string): string {
  if (/^[$_a-zA-Z][$_a-zA-Z0-9]*$/.test(key)) return key;
  return JSON.stringify(key);
}

function scalar(value: null | boolean | number | string): string {
  if (typeof value === "number") {
    return Number.isFinite(value) ? String(value) : "null";
  }
  return JSON.stringify(value);
}

function flat(value: JsonValue): string | undefined {
  if (Array.isArray(value)) return value.length === 0 ? "[]" : undefined;
  if (isObject(value)) {
    return Object.keys(value).length === 0 ? "{}" : undefined;
  }
  return scalar(value);
}

interface Output {
  text: string;
}

function write(
  value: JsonValue,
  implicit: boolean,
  indent: number,
  out: Output,
): void {
  const single = flat(value);
  if (single !== undefined) {
    out.text += single;
    return;
  }
  if (isObject(value)) {
    const child = implicit ? indent : indent + 2;
    if (!implicit) out.text += "{\n";
    Object.keys(value).forEach((key, index) => {
      if (index > 0) out.text += "\n";
      out.text += `${" ".repeat(child)}${keyText(key)}: `;
      write(value[key], false, child, out);
    });
    if (!implicit) out.text += `\n${" ".repeat(indent)}}`;
    return;
  }
  const items = value as JsonValue[];
  const inline = items.map(flat);
  if (inline.every((text): text is string => text !== undefined)) {
    const text = `[${inline.join(", ")}]`;
    const line = out.text.slice(out.text.lastIndexOf("\n") + 1);
    if ([...line].length + [...text].length <= WIDTH) {
      out.text += text;
      return;
    }
  }
  out.text += "[\n";
  items.forEach((item, index) => {
    if (index > 0) out.text += "\n";
    out.text += " ".repeat(indent + 2);
    write(item, false, indent + 2, out);
  });
  out.text += `\n${" ".repeat(indent)}]`;
}

/**
 * Convert a JavaScript value into a pretty-printed fJSON document: two-space
 * indentation, unquoted identifier keys, implicit nonempty root objects, and
 * newline-separated entries. Short scalar arrays stay inline; longer arrays
 * and nested containers expand toward an 80-column width. No final newline.
 *
 * Values pass through JSON semantics first, so `undefined`, functions,
 * symbols, bigints, and circular structures fail with `TypeError`, and
 * non-finite numbers print as `null`. Values beyond the nesting limit fail
 * with an `FjsonError` of kind `"nesting"` rather than producing text that
 * cannot be parsed back.
 */
export function stringify(value: unknown, options?: Options): string {
  const out: Output = { text: "" };
  write(toJsonValue(value, options), true, 0, out);
  return out.text;
}

/** pretty-print validated JSON */
export function printJson(value: JsonValue, implicit: boolean): string {
  const out: Output = { text: "" };
  write(value, implicit, 0, out);
  return out.text;
}