/**
 * Numpad Component - Alpine.js component for touch-friendly numeric input
 * Used for measurement data entry in task_execute.html
 */

function numpad(options) {
  var opts = options || {};

  return {
    // State
    value: '',           // String representation of the current value
    negative: false,     // Whether the value is negative
    hasDecimal: false,   // Whether a decimal point has been entered
    unit: 'mm',          // Unit of measurement (can be set externally)
    maxIntDigits: 6,     // Maximum integer digits
    maxDecDigits: 6,     // Maximum decimal digits

    /* Whether a value may be typed at all, as the recipe declares it. When false
       the keypad shows no digits and a value that looks typed is refused here as
       well as by the server: the caliper is the instrument. Defaults to allowed,
       so a caller that says nothing gets the behaviour that came before. */
    allowManual: opts.allowManual !== false,

    // HID burst detection (USB caliper vs manual typing)
    _lastKeyTime: 0,     // Timestamp of last keystroke
    _burstCount: 0,      // Consecutive fast keystrokes
    _enterWasFast: false, // Enter arrived in the same burst as the digits
    _rejected: false,    // Current reading refused (e.g. overflow); ignore the rest of it
    _runStart: null,     // {value, gap} snapshot taken at the first key of the current run

    /**
     * Get the display value with sign
     */
    get displayValue() {
      if (!this.value) return '';
      return (this.negative ? '-' : '') + this.value;
    },

    /**
     * Get the numeric value as a number
     */
    get numericValue() {
      if (!this.value) return null;
      const v = parseFloat(this.value);
      return this.negative ? -v : v;
    },

    /**
     * Check if a valid value has been entered
     */
    get hasValue() {
      return this.value.length > 0 && this.value !== '.';
    },

    /**
     * Add a digit to the current value
     * @param {string} d - The digit to add (0-9)
     */
    addDigit(d) {
      if (this._rejected) return;

      // Validate: don't exceed max digits
      const parts = this.value.split('.');

      if (this.hasDecimal) {
        // Check decimal part length
        if (parts[1] && parts[1].length >= this.maxDecDigits) return;
      } else {
        // Check integer part length
        if (parts[0] && parts[0].length >= this.maxIntDigits) {
          // A caliper reading whose integer part does not fit must not be
          // quietly cut down to something that does: refuse the whole
          // reading instead of saving a truncated number. Manual typing
          // (outside a burst) keeps the old, harmless behaviour of simply
          // not accepting more digits.
          if (this._burstCount >= 2) this._rejectReading('integer_overflow');
          return;
        }
      }

      // Prevent leading zeros (except "0.")
      if (this.value === '0' && d !== '.') {
        this.value = d;
        return;
      }

      this.value += d;
    },

    /**
     * Add a decimal point to the current value
     */
    addDecimal() {
      if (this._rejected) return;

      // Don't add decimal if one already exists
      if (this.hasDecimal) return;

      // If value is empty, start with "0."
      if (!this.value) this.value = '0';

      this.value += '.';
      this.hasDecimal = true;
    },

    /**
     * Toggle the sign of the current value. Works on an empty display too -
     * the manual +/- key is pressed before the first digit as often as after
     * one, and used to be silently dropped in that case.
     */
    toggleSign() {
      this.negative = !this.negative;
    },

    /**
     * Remove the last character from the current value
     */
    backspace() {
      if (!this.value) return;

      const removed = this.value.charAt(this.value.length - 1);

      // If removing decimal point, update flag
      if (removed === '.') this.hasDecimal = false;

      this.value = this.value.slice(0, -1);
    },

    /**
     * Clear all entered data
     */
    clearAll() {
      this.value = '';
      this.negative = false;
      this.hasDecimal = false;
      this._enterWasFast = false;
      this._rejected = false;
      this._runStart = null;
    },

    /**
     * How the value in the display got there.
     *
     * A wedge caliper sends its digits and the Enter that follows them as one
     * burst; a person is slower on both. The Enter is the stronger of the two
     * signals: a short reading like "9.5" is only three keystrokes, too few to
     * judge by count alone, and used to be filed as typed by hand.
     */
    _classifyInput() {
      if (this._enterWasFast) return 'usb_caliper';
      return this._burstCount >= 3 ? 'usb_caliper' : 'manual';
    },

    /**
     * Confirm the current value and dispatch event
     */
    confirm() {
      this._rejected = false;
      if (!this.hasValue) return;

      const val = this.numericValue;
      const inputMethod = this._classifyInput();

      // The recipe forbids typing: say so and keep the value on screen rather than
      // clearing it, so the operator sees what was refused. The server refuses the
      // same request anyway - this is only the earlier, kinder of the two answers.
      if (inputMethod === 'manual' && !this.allowManual) {
        this.$dispatch('numpad-rejected', { reason: 'manual_not_allowed', value: val });
        this._enterWasFast = false;
        this._burstCount = 0;
        this._lastKeyTime = 0;
        return;
      }

      // Dispatch custom event for parent component to handle
      this.$dispatch('numpad-confirm', { value: val, inputMethod: inputMethod });

      // Reset after confirmation
      this.clearAll();
      this._burstCount = 0;
      this._lastKeyTime = 0;
    },

    /**
     * Set a value programmatically (e.g., from USB caliper)
     * @param {number} val - The numeric value to set
     */
    setValue(val) {
      this.clearAll();

      // Handle negative values
      if (val < 0) {
        this.negative = true;
        val = Math.abs(val);
      }

      this.value = val.toString();

      // Update decimal flag if value contains decimal point
      if (this.value.includes('.')) this.hasDecimal = true;
    },

    /**
     * Set the unit of measurement
     * @param {string} newUnit - The unit to set (e.g., 'mm', 'cm', 'in')
     */
    setUnit(newUnit) {
      this.unit = newUnit;
    },

    /**
     * Handle keyboard input for physical keyboard support
     * @param {KeyboardEvent} e - The keyboard event
     */
    handleKeydown(e) {
      // Ignore keystrokes aimed at an editable field (e.g. the supervisor
      // login modal). The numpad has no text inputs of its own, so this
      // window-level capture is only meant for the USB caliper / keyboard
      // wedge when no field is focused. Without this guard the numpad would
      // swallow digits and Backspace inside those inputs.
      const t = e.target;
      if (t && (t.tagName === 'INPUT' || t.tagName === 'TEXTAREA' ||
                t.tagName === 'SELECT' || t.isContentEditable)) {
        return;
      }

      // Number keys
      if (e.key >= '0' && e.key <= '9') {
        e.preventDefault();
        this._trackBurst();
        this.addDigit(e.key);
      }
      // Decimal point (both . and ,)
      else if (e.key === '.' || e.key === ',') {
        e.preventDefault();
        this._trackBurst();
        this.addDecimal();
      }
      // Backspace
      else if (e.key === 'Backspace') {
        e.preventDefault();
        this.backspace();
      }
      // Escape - clear all
      else if (e.key === 'Escape') {
        e.preventDefault();
        this.clearAll();
      }
      // Enter - confirm
      else if (e.key === 'Enter') {
        e.preventDefault();
        // Measured before confirming: an Enter that lands within the burst is the
        // caliper closing its own transmission, not a person reaching for a key.
        const gap = this._lastKeyTime > 0
          ? performance.now() - this._lastKeyTime
          : Infinity;
        this._enterWasFast = gap < 80;
        this.confirm();
      }
      // Minus / plus - the caliper's own sign character. Unlike the manual
      // +/- key (toggleSign(), bound to the on-screen button) these are
      // absolute rather than a toggle: a caliper transmission says which
      // sign the reading is, it never flips one already on screen.
      else if (e.key === '-') {
        e.preventDefault();
        this.negative = true;
      }
      else if (e.key === '+') {
        e.preventDefault();
        this.negative = false;
      }
    },

    /**
     * Refuse the reading in progress: say why with an event the page can show,
     * and wipe the display so the rejected digits do not linger as if valid.
     * Further keystrokes of the same burst are ignored until Enter or a clear.
     */
    _rejectReading(reason) {
      this.$dispatch('numpad-error', { reason: reason });
      this.value = '';
      this.negative = false;
      this.hasDecimal = false;
      this._enterWasFast = false;
      this._rejected = true;
    },

    /**
     * Track keystroke timing for HID burst detection.
     * USB calipers send digits in rapid succession (<80ms apart).
     * Human typing is much slower (>100ms between keys).
     */
    _trackBurst() {
      const now = performance.now();
      const gap = this._lastKeyTime > 0 ? now - this._lastKeyTime : Infinity;

      if (gap < 80) {
        this._burstCount++;
        // The burst is only recognisable from its second character. If the
        // pause before the first one was long enough to be a human keystroke,
        // whatever was on display before this run began was typed by hand:
        // drop it now instead of letting the caliper's own digits
        // concatenate onto it.
        if (this._burstCount === 2 && this._runStart && this._runStart.gap > 300) {
          this.value = this.value.slice(this._runStart.value.length);
          this.hasDecimal = this.value.includes('.');
        }
      } else {
        this._burstCount = 1;
        this._runStart = { value: this.value, gap: gap };
      }

      this._lastKeyTime = now;
    }
  };
}