package io.prometheus.metrics.model.snapshots;

import static java.lang.Character.MAX_CODE_POINT;
import static java.lang.Character.MAX_LOW_SURROGATE;
import static java.lang.Character.MIN_HIGH_SURROGATE;

import io.prometheus.metrics.config.EscapingScheme;
import java.nio.charset.StandardCharsets;
import javax.annotation.Nullable;

/**
 * Utility for Prometheus Metric and Label naming.
 *
 * <p>Note that this library allows dots in metric and label names. Dots will automatically be
 * replaced with underscores in Prometheus exposition formats. However, if metrics are exposed in
 * OpenTelemetry format the dots are retained.
 */
public class PrometheusNaming {

  /**
   * Test if a metric name is valid. Any non-empty valid UTF-8 string is accepted.
   *
   * <p>Collision detection for suffixes like {@code _total}, {@code _info}, {@code _bucket}, etc.
   * is handled at registration time by the {@link
   * io.prometheus.metrics.model.registry.PrometheusRegistry PrometheusRegistry}, not by name
   * validation.
   *
   * <p>If a metric has a {@link Unit}, the metric name SHOULD end with the unit as a suffix. Note
   * that <a href="https://openmetrics.io/">OpenMetrics</a> requires metric names to have their unit
   * as suffix, and we implement this in {@code prometheus-metrics-core}. However, {@code
   * prometheus-metrics-model} does not enforce Unit suffixes.
   *
   * <p>Example: If you create a Counter for a processing time with Unit {@link Unit#SECONDS
   * SECONDS}, the name should be {@code processing_time_seconds}. When exposed in OpenMetrics Text
   * format, this will be represented as two values: {@code processing_time_seconds_total} for the
   * counter value, and the optional {@code processing_time_seconds_created} timestamp.
   *
   * <p>Use {@link #sanitizeMetricName(String)} to convert arbitrary Strings to valid metric names.
   */
  public static boolean isValidMetricName(String name) {
    return validateMetricName(name) == null;
  }

  /**
   * Same as {@link #isValidMetricName(String)}, but produces an error message.
   *
   * <p>The name is valid if the error message is {@code null}.
   */
  @Nullable
  public static String validateMetricName(String name) {
    if (isValidUtf8(name)) {
      return null;
    }
    return "The metric name contains unsupported characters";
  }

  public static boolean isValidLegacyMetricName(String name) {
    if (name.isEmpty()) {
      return false;
    }
    // First character must be [a-zA-Z_:]
    char first = name.charAt(0);
    if (!((first >= 'a' && first <= 'z')
        || (first >= 'A' && first <= 'Z')
        || first == '_'
        || first == ':')) {
      return false;
    }
    // Remaining characters must be [a-zA-Z0-9_:]
    for (int i = 1; i < name.length(); i++) {
      char c = name.charAt(i);
      if (!((c >= 'a' && c <= 'z')
          || (c >= 'A' && c <= 'Z')
          || (c >= '0' && c <= '9')
          || c == '_'
          || c == ':')) {
        return false;
      }
    }
    return true;
  }

  public static boolean isValidLabelName(String name) {
    return isValidUtf8(name)
        && !(name.startsWith("__")
            || name.startsWith("._")
            || name.startsWith("..")
            || name.startsWith("_."));
  }

  private static boolean isValidUtf8(String name) {
    return !name.isEmpty() && StandardCharsets.UTF_8.newEncoder().canEncode(name);
  }

  public static boolean isValidLegacyLabelName(String name) {
    if (name.isEmpty()) {
      return false;
    }
    // First character must be [a-zA-Z_]
    char first = name.charAt(0);
    if (!((first >= 'a' && first <= 'z') || (first >= 'A' && first <= 'Z') || first == '_')) {
      return false;
    }
    // Remaining characters must be [a-zA-Z0-9_]
    for (int i = 1; i < name.length(); i++) {
      char c = name.charAt(i);
      if (!((c >= 'a' && c <= 'z')
          || (c >= 'A' && c <= 'Z')
          || (c >= '0' && c <= '9')
          || c == '_')) {
        return false;
      }
    }
    return true;
  }

  /** Units may not have illegal characters. */
  public static boolean isValidUnitName(String name) {
    return validateUnitName(name) == null;
  }

  /** Same as {@link #isValidUnitName(String)} but returns an error message. */
  @Nullable
  public static String validateUnitName(String name) {
    if (name.isEmpty()) {
      return "The unit name must not be empty.";
    }
    // Check if all characters are [a-zA-Z0-9_.:]+
    for (int i = 0; i < name.length(); i++) {
      char c = name.charAt(i);
      if (!((c >= 'a' && c <= 'z')
          || (c >= 'A' && c <= 'Z')
          || (c >= '0' && c <= '9')
          || c == '_'
          || c == '.'
          || c == ':')) {
        return "The unit name contains unsupported characters";
      }
    }
    return null;
  }

  /**
   * Get the metric or label name that is used in Prometheus exposition format.
   *
   * @param name must be a valid metric or label name, i.e. {@link #isValidMetricName(String)
   *     isValidMetricName(name)} or {@link #isValidLabelName(String) isValidLabelName(name)} must
   *     be true.
   * @return the name with dots replaced by underscores.
   */
  public static String prometheusName(String name) {
    return escapeName(name, EscapingScheme.UNDERSCORE_ESCAPING);
  }

  /**
   * Convert an arbitrary string to a valid metric name. Since any non-empty valid UTF-8 string is a
   * valid metric name, this simply returns the input unchanged.
   *
   * @throws IllegalArgumentException if the input is empty
   */
  public static String sanitizeMetricName(String metricName) {
    if (metricName.isEmpty()) {
      throw new IllegalArgumentException("Cannot convert an empty string to a valid metric name.");
    }
    return metricName;
  }

  /**
   * Like {@link #sanitizeMetricName(String)}, but also makes sure that the unit is appended as a
   * suffix if the unit is not {@code null}.
   */
  public static String sanitizeMetricName(String metricName, Unit unit) {
    String result = sanitizeMetricName(metricName);
    if (unit != null) {
      if (!result.endsWith("_" + unit) && !result.endsWith("." + unit)) {
        result += "_" + unit;
      }
    }
    return result;
  }

  /**
   * Convert an arbitrary string to a name where {@link #isValidLabelName(String)
   * isValidLabelName(name)} is true.
   */
  public static String sanitizeLabelName(String labelName) {
    if (labelName.isEmpty()) {
      throw new IllegalArgumentException("Cannot convert an empty string to a valid label name.");
    }
    String sanitizedName = labelName;
    while (sanitizedName.startsWith("__")
        || sanitizedName.startsWith("_.")
        || sanitizedName.startsWith("._")
        || sanitizedName.startsWith("..")) {
      sanitizedName = sanitizedName.substring(1);
    }
    return sanitizedName;
  }

  /**
   * Convert an arbitrary string to a valid unit name by replacing illegal characters.
   *
   * @throws IllegalArgumentException if the {@code unitName} cannot be converted, e.g. if you call
   *     {@code sanitizeUnitName("")}.
   * @throws NullPointerException if {@code unitName} is null.
   */
  public static String sanitizeUnitName(String unitName) {
    if (unitName.isEmpty()) {
      throw new IllegalArgumentException("Cannot convert an empty string to a valid unit name.");
    }
    String sanitizedName = replaceIllegalCharsInUnitName(unitName);
    while (sanitizedName.startsWith("_") || sanitizedName.startsWith(".")) {
      sanitizedName = sanitizedName.substring(1);
    }
    while (sanitizedName.endsWith(".") || sanitizedName.endsWith("_")) {
      sanitizedName = sanitizedName.substring(0, sanitizedName.length() - 1);
    }
    if (sanitizedName.isEmpty()) {
      throw new IllegalArgumentException(
          "Cannot convert '" + unitName + "' into a valid unit name.");
    }
    return sanitizedName;
  }

  /** Returns a string with only valid unit name characters [a-zA-Z0-9_.:]. */
  private static String replaceIllegalCharsInUnitName(String name) {
    int length = name.length();
    char[] sanitized = new char[length];
    for (int i = 0; i < length; i++) {
      char ch = name.charAt(i);
      if (ch == ':'
          || ch == '.'
          || (ch >= 'a' && ch <= 'z')
          || (ch >= 'A' && ch <= 'Z')
          || (ch >= '0' && ch <= '9')) {
        sanitized[i] = ch;
      } else {
        sanitized[i] = '_';
      }
    }
    return new String(sanitized);
  }

  /**
   * Escapes the incoming name according to the provided escaping scheme. Depending on the rules of
   * escaping, this may cause no change in the string that is returned (especially NO_ESCAPING,
   * which by definition is a noop). This method does not do any validation of the name.
   */
  public static String escapeName(String name, EscapingScheme scheme) {
    if (name.isEmpty() || !needsEscaping(name, scheme)) {
      return name;
    }

    StringBuilder escaped = new StringBuilder();
    switch (scheme) {
      case ALLOW_UTF8:
        return name;
      case UNDERSCORE_ESCAPING:
        for (int i = 0; i < name.length(); ) {
          int c = name.codePointAt(i);
          if (isValidLegacyChar(c, i)) {
            escaped.appendCodePoint(c);
          } else {
            escaped.append('_');
          }
          i += Character.charCount(c);
        }
        return escaped.toString();
      case DOTS_ESCAPING:
        // Do not early return for legacy valid names, we still escape underscores.
        for (int i = 0; i < name.length(); ) {
          int c = name.codePointAt(i);
          if (c == '_') {
            escaped.append("__");
          } else if (c == '.') {
            escaped.append("_dot_");
          } else if (isValidLegacyChar(c, i)) {
            escaped.appendCodePoint(c);
          } else {
            escaped.append("__");
          }
          i += Character.charCount(c);
        }
        return escaped.toString();
      case VALUE_ENCODING_ESCAPING:
        escaped.append("U__");
        for (int i = 0; i < name.length(); ) {
          int c = name.codePointAt(i);
          if (c == '_') {
            escaped.append("__");
          } else if (isValidLegacyChar(c, i)) {
            escaped.appendCodePoint(c);
          } else if (!isValidUtf8Char(c)) {
            escaped.append("_FFFD_");
          } else {
            escaped.append('_');
            escaped.append(Integer.toHexString(c));
            escaped.append('_');
          }
          i += Character.charCount(c);
        }
        return escaped.toString();
      default:
        throw new IllegalArgumentException("Invalid escaping scheme " + scheme);
    }
  }

  public static boolean needsEscaping(String name, EscapingScheme scheme) {
    return !isValidLegacyMetricName(name)
        || (scheme == EscapingScheme.DOTS_ESCAPING && (name.contains(".") || name.contains("_")));
  }

  static boolean isValidLegacyChar(int c, int i) {
    return (c >= 'a' && c <= 'z')
        || (c >= 'A' && c <= 'Z')
        || c == '_'
        || c == ':'
        || (c >= '0' && c <= '9' && i > 0);
  }

  private static boolean isValidUtf8Char(int c) {
    return (0 <= c && c < MIN_HIGH_SURROGATE) || (MAX_LOW_SURROGATE < c && c <= MAX_CODE_POINT);
  }
}