/**
 * Operators and utilities used for style expressions
 * @module ol/style/expressions
 */

import PaletteTexture from '../webgl/PaletteTexture.js';
import {Uniforms} from '../renderer/webgl/TileLayer.js';
import {asArray, fromString, isStringColor} from '../color.js';

/**
 * Base type used for literal style parameters; can be a number literal or the output of an operator,
 * which in turns takes {@link import("./expressions.js").ExpressionValue} arguments.
 *
 * The following operators can be used:
 *
 * * Reading operators:
 *   * `['band', bandIndex, xOffset, yOffset]` For tile layers only. Fetches pixel values from band
 *     `bandIndex` of the source's data. The first `bandIndex` of the source data is `1`. Fetched values
 *     are in the 0..1 range. {@link import("../source/TileImage.js").default} sources have 4 bands: red,
 *     green, blue and alpha. {@link import("../source/DataTile.js").default} sources can have any number
 *     of bands, depending on the underlying data source and
 *     {@link import("../source/GeoTIFF.js").Options configuration}. `xOffset` and `yOffset` are optional
 *     and allow specifying pixel offsets for x and y. This is used for sampling data from neighboring pixels.
 *   * `['get', 'attributeName', typeHint]` fetches a feature property value, similar to `feature.get('attributeName')`
 *     A type hint can optionally be specified, in case the resulting expression contains a type ambiguity which
 *     will make it invalid. Type hints can be one of: 'string', 'color', 'number', 'boolean', 'number[]'
 *   * `['geometry-type']` returns a feature's geometry type as string, either: 'LineString', 'Point' or 'Polygon'
 *     `Multi*` values are returned as their singular equivalent
 *     `Circle` geometries are returned as 'Polygon'
 *     `GeometryCollection` geometries are returned as the type of the first geometry found in the collection
 *   * `['resolution']` returns the current resolution
 *   * `['time']` returns the time in seconds since the creation of the layer
 *   * `['var', 'varName']` fetches a value from the style variables; will throw an error if that variable is undefined
 *   * `['zoom']` returns the current zoom level
 *
 * * Math operators:
 *   * `['*', value1, value2, ...]` multiplies the values (either numbers or colors)
 *   * `['/', value1, value2]` divides `value1` by `value2`
 *   * `['+', value1, value2, ...]` adds the values
 *   * `['-', value1, value2]` subtracts `value2` from `value1`
 *   * `['clamp', value, low, high]` clamps `value` between `low` and `high`
 *   * `['%', value1, value2]` returns the result of `value1 % value2` (modulo)
 *   * `['^', value1, value2]` returns the value of `value1` raised to the `value2` power
 *   * `['abs', value1]` returns the absolute value of `value1`
 *   * `['floor', value1]` returns the nearest integer less than or equal to `value1`
 *   * `['round', value1]` returns the nearest integer to `value1`
 *   * `['ceil', value1]` returns the nearest integer greater than or equal to `value1`
 *   * `['sin', value1]` returns the sine of `value1`
 *   * `['cos', value1]` returns the cosine of `value1`
 *   * `['atan', value1, value2]` returns `atan2(value1, value2)`. If `value2` is not provided, returns `atan(value1)`
 *   * `['sqrt', value1]` returns the square root of `value1`
 *
 * * Transform operators:
 *   * `['case', condition1, output1, ...conditionN, outputN, fallback]` selects the first output whose corresponding
 *     condition evaluates to `true`. If no match is found, returns the `fallback` value.
 *     All conditions should be `boolean`, output and fallback can be any kind.
 *   * `['match', input, match1, output1, ...matchN, outputN, fallback]` compares the `input` value against all
 *     provided `matchX` values, returning the output associated with the first valid match. If no match is found,
 *     returns the `fallback` value.
 *     `input` and `matchX` values must all be of the same type, and can be `number` or `string`. `outputX` and
 *     `fallback` values must be of the same type, and can be of any kind.
 *   * `['interpolate', interpolation, input, stop1, output1, ...stopN, outputN]` returns a value by interpolating between
 *     pairs of inputs and outputs; `interpolation` can either be `['linear']` or `['exponential', base]` where `base` is
 *     the rate of increase from stop A to stop B (i.e. power to which the interpolation ratio is raised); a value
 *     of 1 is equivalent to `['linear']`.
 *     `input` and `stopX` values must all be of type `number`. `outputX` values can be `number` or `color` values.
 *     Note: `input` will be clamped between `stop1` and `stopN`, meaning that all output values will be comprised
 *     between `output1` and `outputN`.
 *
 * * Logical operators:
 *   * `['<', value1, value2]` returns `true` if `value1` is strictly lower than `value2`, or `false` otherwise.
 *   * `['<=', value1, value2]` returns `true` if `value1` is lower than or equals `value2`, or `false` otherwise.
 *   * `['>', value1, value2]` returns `true` if `value1` is strictly greater than `value2`, or `false` otherwise.
 *   * `['>=', value1, value2]` returns `true` if `value1` is greater than or equals `value2`, or `false` otherwise.
 *   * `['==', value1, value2]` returns `true` if `value1` equals `value2`, or `false` otherwise.
 *   * `['!=', value1, value2]` returns `true` if `value1` does not equal `value2`, or `false` otherwise.
 *   * `['!', value1]` returns `false` if `value1` is `true` or greater than `0`, or `true` otherwise.
 *   * `['all', value1, value2, ...]` returns `true` if all the inputs are `true`, `false` otherwise.
 *   * `['any', value1, value2, ...]` returns `true` if any of the inputs are `true`, `false` otherwise.
 *   * `['between', value1, value2, value3]` returns `true` if `value1` is contained between `value2` and `value3`
 *     (inclusively), or `false` otherwise.
 *   * `['in', needle, haystack]` returns `true` if `needle` is found in `haystack`, and
 *     `false` otherwise.
 *     This operator has the following limitations:
 *     * `haystack` has to be an array of numbers or strings (searching for a substring in a string is not supported yet)
 *     * Only literal arrays are supported as `haystack` for now; this means that `haystack` cannot be the result of an
 *     expression. If `haystack` is an array of strings, use the `literal` operator to disambiguate from an expression:
 *     `['literal', ['abc', 'def', 'ghi']]`
 *
 * * Conversion operators:
 *   * `['array', value1, ...valueN]` creates a numerical array from `number` values; please note that the amount of
 *     values can currently only be 2, 3 or 4.
 *   * `['color', red, green, blue, alpha]` creates a `color` value from `number` values; the `alpha` parameter is
 *     optional; if not specified, it will be set to 1.
 *     Note: `red`, `green` and `blue` components must be values between 0 and 255; `alpha` between 0 and 1.
 *   * `['palette', index, colors]` picks a `color` value from an array of colors using the given index; the `index`
 *     expression must evaluate to a number; the items in the `colors` array must be strings with hex colors
 *     (e.g. `'#86A136'`), colors using the rgba[a] functional notation (e.g. `'rgb(134, 161, 54)'` or `'rgba(134, 161, 54, 1)'`),
 *     named colors (e.g. `'red'`), or array literals with 3 ([r, g, b]) or 4 ([r, g, b, a]) values (with r, g, and b
 *     in the 0-255 range and a in the 0-1 range).
 *
 * Values can either be literals or another operator, as they will be evaluated recursively.
 * Literal values can be of the following types:
 * * `boolean`
 * * `number`
 * * `number[]` (number arrays can only have a length of 2, 3 or 4)
 * * `string`
 * * {@link module:ol/color~Color}
 *
 * @typedef {Array<*>|import("../color.js").Color|string|number|boolean} ExpressionValue
 * @api
 */

/**
 * Possible inferred types from a given value or expression.
 * Note: these are binary flags.
 * @enum {number}
 */
export const ValueTypes = {
  NUMBER: 0b00001,
  STRING: 0b00010,
  COLOR: 0b00100,
  BOOLEAN: 0b01000,
  NUMBER_ARRAY: 0b10000,
  ANY: 0b11111,
  NONE: 0,
};

/**
 * @param {string} typeHint Type hint
 * @return {ValueTypes} Resulting value type (will be a single type)
 */
function getTypeFromHint(typeHint) {
  switch (typeHint) {
    case 'string':
      return ValueTypes.STRING;
    case 'color':
      return ValueTypes.COLOR;
    case 'number':
      return ValueTypes.NUMBER;
    case 'boolean':
      return ValueTypes.BOOLEAN;
    case 'number[]':
      return ValueTypes.NUMBER_ARRAY;
    default:
      throw new Error(`Unrecognized type hint: ${typeHint}`);
  }
}

/**
 * An operator declaration must contain two methods: `getReturnType` which returns a type based on
 * the operator arguments, and `toGlsl` which returns a GLSL-compatible string.
 * Note: both methods can process arguments recursively.
 * @typedef {Object} Operator
 * @property {function(Array<ExpressionValue>): ValueTypes|number} getReturnType Returns one or several types
 * @property {function(ParsingContext, Array<ExpressionValue>, ValueTypes): string} toGlsl Returns a GLSL-compatible string
 * given a parsing context, an array of arguments and an expected type.
 * Note: the expected type can be a combination such as ValueTypes.NUMBER | ValueTypes.STRING or ValueTypes.ANY for instance
 */

/**
 * Operator declarations
 * @type {Object<string, Operator>}
 */
export const Operators = {};

/**
 * Returns the possible types for a given value (each type being a binary flag)
 * To test a value use e.g. `getValueType(v) & ValueTypes.BOOLEAN`
 * @param {ExpressionValue} value Value
 * @return {ValueTypes|number} Type or types inferred from the value
 */
export function getValueType(value) {
  if (typeof value === 'number') {
    return ValueTypes.NUMBER;
  }
  if (typeof value === 'boolean') {
    return ValueTypes.BOOLEAN;
  }
  if (typeof value === 'string') {
    if (isStringColor(value)) {
      return ValueTypes.COLOR | ValueTypes.STRING;
    }
    return ValueTypes.STRING;
  }
  if (!Array.isArray(value)) {
    throw new Error(`Unhandled value type: ${JSON.stringify(value)}`);
  }
  const valueArr = /** @type {Array<*>} */ (value);
  const onlyNumbers = valueArr.every(function (v) {
    return typeof v === 'number';
  });
  if (onlyNumbers) {
    if (valueArr.length === 3 || valueArr.length === 4) {
      return ValueTypes.COLOR | ValueTypes.NUMBER_ARRAY;
    }
    return ValueTypes.NUMBER_ARRAY;
  }
  if (typeof valueArr[0] !== 'string') {
    throw new Error(
      `Expected an expression operator but received: ${JSON.stringify(
        valueArr
      )}`
    );
  }
  const operator = Operators[valueArr[0]];
  if (operator === undefined) {
    throw new Error(
      `Unrecognized expression operator: ${JSON.stringify(valueArr)}`
    );
  }
  return operator.getReturnType(valueArr.slice(1));
}

/**
 * Checks if only one value type is enabled in the input number.
 * @param {ValueTypes|number} valueType Number containing value type binary flags
 * @return {boolean} True if only one type flag is enabled, false if zero or multiple
 */
export function isTypeUnique(valueType) {
  return Math.log2(valueType) % 1 === 0;
}

/**
 * Print types as a readable string
 * @param {ValueTypes|number} valueType Number containing value type binary flags
 * @return {string} Types
 */
function printTypes(valueType) {
  const result = [];
  if ((valueType & ValueTypes.NUMBER) > 0) {
    result.push('number');
  }
  if ((valueType & ValueTypes.COLOR) > 0) {
    result.push('color');
  }
  if ((valueType & ValueTypes.BOOLEAN) > 0) {
    result.push('boolean');
  }
  if ((valueType & ValueTypes.NUMBER_ARRAY) > 0) {
    result.push('number[]');
  }
  if ((valueType & ValueTypes.STRING) > 0) {
    result.push('string');
  }
  return result.length > 0 ? result.join(', ') : '(no type)';
}

/**
 * @typedef {Object} ParsingContextExternal
 * @property {string} name Name, unprefixed
 * @property {ValueTypes} type One of the value types constants
 * @property {function(import("../Feature.js").FeatureLike): *} [callback] Function used for computing the attribute value;
 *   if undefined, `feature.get(attribute.name)` will be used
 */

/**
 * Context available during the parsing of an expression.
 * @typedef {Object} ParsingContext
 * @property {boolean} [inFragmentShader] If false, means the expression output should be made for a vertex shader
 * @property {Array<ParsingContextExternal>} variables External variables used in the expression
 * @property {Array<ParsingContextExternal>} attributes External attributes used in the expression
 * @property {Object<string, number>} stringLiteralsMap This object maps all encountered string values to a number
 * @property {Object<string, string>} functions Lookup of functions used by the style.
 * @property {number} [bandCount] Number of bands per pixel.
 * @property {Array<PaletteTexture>} [paletteTextures] List of palettes used by the style.
 * @property {import("../style/literal").LiteralStyle} style The style being parsed
 */

/**
 * @param {string} operator Operator
 * @param {ParsingContext} context Parsing context
 * @return {string} A function name based on the operator, unique in the given context
 */
function computeOperatorFunctionName(operator, context) {
  return `operator_${operator}_${Object.keys(context.functions).length}`;
}

/**
 * Will return the number as a float with a dot separator, which is required by GLSL.
 * @param {number} v Numerical value.
 * @return {string} The value as string.
 */
export function numberToGlsl(v) {
  const s = v.toString();
  return s.includes('.') ? s : s + '.0';
}

/**
 * Will return the number array as a float with a dot separator, concatenated with ', '.
 * @param {Array<number>} array Numerical values array.
 * @return {string} The array as a vector, e. g.: `vec3(1.0, 2.0, 3.0)`.
 */
export function arrayToGlsl(array) {
  if (array.length < 2 || array.length > 4) {
    throw new Error(
      '`formatArray` can only output `vec2`, `vec3` or `vec4` arrays.'
    );
  }
  return `vec${array.length}(${array.map(numberToGlsl).join(', ')})`;
}

/**
 * Will normalize and converts to string a `vec4` color array compatible with GLSL.
 * @param {string|import("../color.js").Color} color Color either in string format or [r, g, b, a] array format,
 * with RGB components in the 0..255 range and the alpha component in the 0..1 range.
 * Note that the final array will always have 4 components.
 * @return {string} The color expressed in the `vec4(1.0, 1.0, 1.0, 1.0)` form.
 */
export function colorToGlsl(color) {
  const array = asArray(color);
  const alpha = array.length > 3 ? array[3] : 1;
  // all components are premultiplied with alpha value
  return arrayToGlsl([
    (array[0] / 255) * alpha,
    (array[1] / 255) * alpha,
    (array[2] / 255) * alpha,
    alpha,
  ]);
}

/**
 * Returns a stable equivalent number for the string literal.
 * @param {ParsingContext} context Parsing context
 * @param {string} string String literal value
 * @return {number} Number equivalent
 */
export function getStringNumberEquivalent(context, string) {
  if (context.stringLiteralsMap[string] === undefined) {
    context.stringLiteralsMap[string] = Object.keys(
      context.stringLiteralsMap
    ).length;
  }
  return context.stringLiteralsMap[string];
}

/**
 * Returns a stable equivalent number for the string literal, for use in shaders. This number is then
 * converted to be a GLSL-compatible string.
 * @param {ParsingContext} context Parsing context
 * @param {string} string String literal value
 * @return {string} GLSL-compatible string containing a number
 */
export function stringToGlsl(context, string) {
  return numberToGlsl(getStringNumberEquivalent(context, string));
}

/**
 * Recursively parses a style expression and outputs a GLSL-compatible string. Takes in a parsing context that
 * will be read and modified during the parsing operation.
 * @param {ParsingContext} context Parsing context
 * @param {ExpressionValue} value Value
 * @param {ValueTypes|number} [expectedType] Expected final type (can be several types combined)
 * If omitted, defaults to ValueTypes.NUMBER
 * @return {string} GLSL-compatible output
 */
export function expressionToGlsl(context, value, expectedType) {
  const returnType =
    expectedType !== undefined ? expectedType : ValueTypes.NUMBER;
  // operator
  if (Array.isArray(value) && typeof value[0] === 'string') {
    const operator = Operators[value[0]];
    if (operator === undefined) {
      throw new Error(
        `Unrecognized expression operator: ${JSON.stringify(value)}`
      );
    }
    return operator.toGlsl(context, value.slice(1), returnType);
  }

  const possibleType = getValueType(value) & returnType;
  assertNotEmptyType(value, possibleType, '');

  if ((possibleType & ValueTypes.NUMBER) > 0) {
    return numberToGlsl(/** @type {number} */ (value));
  }

  if ((possibleType & ValueTypes.BOOLEAN) > 0) {
    return value.toString();
  }

  if ((possibleType & ValueTypes.STRING) > 0) {
    return stringToGlsl(context, value.toString());
  }

  if ((possibleType & ValueTypes.COLOR) > 0) {
    return colorToGlsl(/** @type {Array<number> | string} */ (value));
  }

  if ((possibleType & ValueTypes.NUMBER_ARRAY) > 0) {
    return arrayToGlsl(/** @type {Array<number>} */ (value));
  }

  throw new Error(
    `Unexpected expression ${value} (expected type ${printTypes(returnType)})`
  );
}

function assertNumber(value) {
  if ((getValueType(value) & ValueTypes.NUMBER) === 0) {
    throw new Error(
      `A numeric value was expected, got ${JSON.stringify(value)} instead`
    );
  }
}
function assertNumbers(values) {
  for (let i = 0; i < values.length; i++) {
    assertNumber(values[i]);
  }
}
function assertString(value) {
  if ((getValueType(value) & ValueTypes.STRING) === 0) {
    throw new Error(
      `A string value was expected, got ${JSON.stringify(value)} instead`
    );
  }
}
function assertBoolean(value) {
  if ((getValueType(value) & ValueTypes.BOOLEAN) === 0) {
    throw new Error(
      `A boolean value was expected, got ${JSON.stringify(value)} instead`
    );
  }
}
function assertArgsCount(args, count) {
  if (args.length !== count) {
    throw new Error(
      `Exactly ${count} arguments were expected, got ${args.length} instead`
    );
  }
}
function assertArgsMinCount(args, count) {
  if (args.length < count) {
    throw new Error(
      `At least ${count} arguments were expected, got ${args.length} instead`
    );
  }
}
function assertArgsMaxCount(args, count) {
  if (args.length > count) {
    throw new Error(
      `At most ${count} arguments were expected, got ${args.length} instead`
    );
  }
}
function assertArgsEven(args) {
  if (args.length % 2 !== 0) {
    throw new Error(
      `An even amount of arguments was expected, got ${JSON.stringify(
        args
      )} instead`
    );
  }
}
function assertArgsOdd(args) {
  if (args.length % 2 === 0) {
    throw new Error(
      `An odd amount of arguments was expected, got ${JSON.stringify(
        args
      )} instead`
    );
  }
}
function assertNotEmptyType(args, types, descriptor) {
  if (types === ValueTypes.NONE) {
    throw new Error(
      `No matching type was found for the following expression ${descriptor}: ${JSON.stringify(
        args
      )}`
    );
  }
}
function assertSingleType(args, types, descriptor) {
  assertNotEmptyType(args, types, descriptor);
  if (!isTypeUnique(types)) {
    throw new Error(
      `Expected to have a unique type for the following expression ${descriptor}: ${JSON.stringify(
        args
      )}
Got the following types instead: ${printTypes(types)}`
    );
  }
}
function assertOfType(args, types, expectedTypes, descriptor) {
  if ((types & expectedTypes) === ValueTypes.NONE) {
    throw new Error(
      `Expected the ${descriptor} type of the following expression: ${JSON.stringify(
        args
      )} to be of the following types: ${printTypes(expectedTypes)}
Got these types instead: ${printTypes(types)}`
    );
  }
}

Operators['get'] = {
  getReturnType: function (args) {
    if (args.length === 2) {
      const hint = args[1];
      return getTypeFromHint(/** @type {string} */ (hint));
    }
    return ValueTypes.ANY;
  },
  toGlsl: function (context, args, expectedType) {
    assertArgsMinCount(args, 1);
    assertArgsMaxCount(args, 2);
    assertString(args[0]);
    const outputType = expectedType & Operators['get'].getReturnType(args);
    assertSingleType(['get', ...args], outputType, '');
    const name = args[0].toString();
    const existing = context.attributes.find((a) => a.name === name);
    if (!existing) {
      context.attributes.push({
        name: name,
        type: outputType,
      });
    } else if (outputType !== existing.type) {
      throw new Error(
        `The following attribute was used in different places with incompatible types: ${name}
Types were: ${printTypes(existing.type)} and ${printTypes(outputType)}`
      );
    }
    const prefix = context.inFragmentShader ? 'v_' : 'a_';
    return prefix + name;
  },
};

/**
 * Get the uniform name given a variable name.
 * @param {string} variableName The variable name.
 * @return {string} The uniform name.
 */
export function uniformNameForVariable(variableName) {
  return 'u_var_' + variableName;
}

Operators['var'] = {
  getReturnType: function () {
    return ValueTypes.ANY;
  },
  toGlsl: function (context, args, expectedType) {
    assertArgsCount(args, 1);
    assertString(args[0]);
    const name = args[0].toString();
    if (
      !context.style.variables ||
      context.style.variables[name] === undefined
    ) {
      throw new Error(
        `The following variable is missing from the style: ${name}`
      );
    }
    const initialValue = context.style.variables[name];
    const outputType = expectedType & getValueType(initialValue);
    assertSingleType(['var', ...args], outputType, '');
    const existing = context.variables.find((a) => a.name === name);
    if (!existing) {
      context.variables.push({
        name: name,
        type: outputType,
      });
    } else if (outputType !== existing.type) {
      throw new Error(
        `The following variable was used in different places with incompatible types: ${name}
Types were: ${printTypes(existing.type)} and ${printTypes(outputType)}`
      );
    }
    return uniformNameForVariable(name);
  },
};

export const PALETTE_TEXTURE_ARRAY = 'u_paletteTextures';

// ['palette', index, colors]
Operators['palette'] = {
  getReturnType: function () {
    return ValueTypes.COLOR;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    assertNumber(args[0]);
    const index = expressionToGlsl(context, args[0]);
    const colors = args[1];
    if (!Array.isArray(colors)) {
      throw new Error('The second argument of palette must be an array');
    }
    const numColors = colors.length;
    const palette = new Uint8Array(numColors * 4);
    for (let i = 0; i < numColors; i++) {
      const candidate = colors[i];
      /**
       * @type {import('../color.js').Color}
       */
      let color;
      if (typeof candidate === 'string') {
        color = fromString(candidate);
      } else {
        if (!Array.isArray(candidate)) {
          throw new Error(
            'The second argument of palette must be an array of strings or colors'
          );
        }
        const length = candidate.length;
        if (length === 4) {
          color = candidate;
        } else {
          if (length !== 3) {
            throw new Error(
              `Expected palette color to have 3 or 4 values, got ${length}`
            );
          }
          color = [candidate[0], candidate[1], candidate[2], 1];
        }
      }
      const offset = i * 4;
      palette[offset] = color[0];
      palette[offset + 1] = color[1];
      palette[offset + 2] = color[2];
      palette[offset + 3] = color[3] * 255;
    }
    if (!context.paletteTextures) {
      context.paletteTextures = [];
    }
    const paletteName = `${PALETTE_TEXTURE_ARRAY}[${context.paletteTextures.length}]`;
    const paletteTexture = new PaletteTexture(paletteName, palette);
    context.paletteTextures.push(paletteTexture);
    return `texture2D(${paletteName}, vec2((${index} + 0.5) / ${numColors}.0, 0.5))`;
  },
};

const GET_BAND_VALUE_FUNC = 'getBandValue';

Operators['band'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsMinCount(args, 1);
    assertArgsMaxCount(args, 3);
    const band = args[0];

    if (!(GET_BAND_VALUE_FUNC in context.functions)) {
      let ifBlocks = '';
      const bandCount = context.bandCount || 1;
      for (let i = 0; i < bandCount; i++) {
        const colorIndex = Math.floor(i / 4);
        let bandIndex = i % 4;
        if (i === bandCount - 1 && bandIndex === 1) {
          // LUMINANCE_ALPHA - band 1 assigned to rgb and band 2 assigned to alpha
          bandIndex = 3;
        }
        const textureName = `${Uniforms.TILE_TEXTURE_ARRAY}[${colorIndex}]`;
        ifBlocks += `
          if (band == ${i + 1}.0) {
            return texture2D(${textureName}, v_textureCoord + vec2(dx, dy))[${bandIndex}];
          }
        `;
      }

      context.functions[GET_BAND_VALUE_FUNC] = `
        float getBandValue(float band, float xOffset, float yOffset) {
          float dx = xOffset / ${Uniforms.TEXTURE_PIXEL_WIDTH};
          float dy = yOffset / ${Uniforms.TEXTURE_PIXEL_HEIGHT};
          ${ifBlocks}
        }
      `;
    }

    const bandExpression = expressionToGlsl(context, band);
    const xOffsetExpression = expressionToGlsl(context, args[1] || 0);
    const yOffsetExpression = expressionToGlsl(context, args[2] || 0);
    return `${GET_BAND_VALUE_FUNC}(${bandExpression}, ${xOffsetExpression}, ${yOffsetExpression})`;
  },
};

Operators['time'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 0);
    return 'u_time';
  },
};

Operators['zoom'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 0);
    return 'u_zoom';
  },
};

Operators['resolution'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 0);
    return 'u_resolution';
  },
};

Operators['geometry-type'] = {
  getReturnType: function () {
    return ValueTypes.STRING;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 0);
    const name = 'geometryType';
    const computeType = (geometry) => {
      const type = geometry.getType();
      switch (type) {
        case 'Point':
        case 'LineString':
        case 'Polygon':
          return type;
        case 'MultiPoint':
        case 'MultiLineString':
        case 'MultiPolygon':
          return type.substring(5);
        case 'Circle':
          return 'Polygon';
        case 'GeometryCollection':
          return computeType(geometry.getGeometries()[0]);
        default:
      }
    };
    const existing = context.attributes.find((a) => a.name === name);
    if (!existing) {
      context.attributes.push({
        name: name,
        type: ValueTypes.STRING,
        callback: (feature) => {
          return computeType(feature.getGeometry());
        },
      });
    }
    const prefix = context.inFragmentShader ? 'v_' : 'a_';
    return prefix + name;
  },
};

Operators['*'] = {
  getReturnType: function (args) {
    let outputType = ValueTypes.NUMBER | ValueTypes.COLOR;
    for (let i = 0; i < args.length; i++) {
      outputType = outputType & getValueType(args[i]);
    }
    return outputType;
  },
  toGlsl: function (context, args, expectedType) {
    assertArgsMinCount(args, 2);
    let outputType = expectedType;
    for (let i = 0; i < args.length; i++) {
      outputType = outputType & getValueType(args[i]);
    }
    assertOfType(
      args,
      outputType,
      ValueTypes.NUMBER | ValueTypes.COLOR,
      'output'
    );
    return `(${args
      .map((arg) => expressionToGlsl(context, arg, outputType))
      .join(' * ')})`;
  },
};

Operators['/'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    assertNumbers(args);
    return `(${expressionToGlsl(context, args[0])} / ${expressionToGlsl(
      context,
      args[1]
    )})`;
  },
};

Operators['+'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsMinCount(args, 2);
    assertNumbers(args);
    return `(${args.map((arg) => expressionToGlsl(context, arg)).join(' + ')})`;
  },
};

Operators['-'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    assertNumbers(args);
    return `(${expressionToGlsl(context, args[0])} - ${expressionToGlsl(
      context,
      args[1]
    )})`;
  },
};

Operators['clamp'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 3);
    assertNumbers(args);
    const min = expressionToGlsl(context, args[1]);
    const max = expressionToGlsl(context, args[2]);
    return `clamp(${expressionToGlsl(context, args[0])}, ${min}, ${max})`;
  },
};

Operators['%'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    assertNumbers(args);
    return `mod(${expressionToGlsl(context, args[0])}, ${expressionToGlsl(
      context,
      args[1]
    )})`;
  },
};

Operators['^'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    assertNumbers(args);
    return `pow(${expressionToGlsl(context, args[0])}, ${expressionToGlsl(
      context,
      args[1]
    )})`;
  },
};

Operators['abs'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 1);
    assertNumbers(args);
    return `abs(${expressionToGlsl(context, args[0])})`;
  },
};

Operators['floor'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 1);
    assertNumbers(args);
    return `floor(${expressionToGlsl(context, args[0])})`;
  },
};

Operators['round'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 1);
    assertNumbers(args);
    return `floor(${expressionToGlsl(context, args[0])} + 0.5)`;
  },
};

Operators['ceil'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 1);
    assertNumbers(args);
    return `ceil(${expressionToGlsl(context, args[0])})`;
  },
};

Operators['sin'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 1);
    assertNumbers(args);
    return `sin(${expressionToGlsl(context, args[0])})`;
  },
};

Operators['cos'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 1);
    assertNumbers(args);
    return `cos(${expressionToGlsl(context, args[0])})`;
  },
};

Operators['atan'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsMinCount(args, 1);
    assertArgsMaxCount(args, 2);
    assertNumbers(args);
    return args.length === 2
      ? `atan(${expressionToGlsl(context, args[0])}, ${expressionToGlsl(
          context,
          args[1]
        )})`
      : `atan(${expressionToGlsl(context, args[0])})`;
  },
};

Operators['sqrt'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 1);
    assertNumbers(args);
    return `sqrt(${expressionToGlsl(context, args[0])})`;
  },
};

Operators['>'] = {
  getReturnType: function () {
    return ValueTypes.BOOLEAN;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    assertNumbers(args);
    return `(${expressionToGlsl(context, args[0])} > ${expressionToGlsl(
      context,
      args[1]
    )})`;
  },
};

Operators['>='] = {
  getReturnType: function () {
    return ValueTypes.BOOLEAN;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    assertNumbers(args);
    return `(${expressionToGlsl(context, args[0])} >= ${expressionToGlsl(
      context,
      args[1]
    )})`;
  },
};

Operators['<'] = {
  getReturnType: function () {
    return ValueTypes.BOOLEAN;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    assertNumbers(args);
    return `(${expressionToGlsl(context, args[0])} < ${expressionToGlsl(
      context,
      args[1]
    )})`;
  },
};

Operators['<='] = {
  getReturnType: function () {
    return ValueTypes.BOOLEAN;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    assertNumbers(args);
    return `(${expressionToGlsl(context, args[0])} <= ${expressionToGlsl(
      context,
      args[1]
    )})`;
  },
};

function getEqualOperator(operator) {
  return {
    getReturnType: function () {
      return ValueTypes.BOOLEAN;
    },
    toGlsl: function (context, args) {
      assertArgsCount(args, 2);

      // find common type
      let type = ValueTypes.ANY;
      for (let i = 0; i < args.length; i++) {
        type &= getValueType(args[i]);
      }
      if (type === ValueTypes.NONE) {
        throw new Error(
          `All arguments should be of compatible type, got ${JSON.stringify(
            args
          )} instead`
        );
      }

      // Since it's not possible to have color types here, we can leave it out
      // This fixes issues in case the value type is ambiguously detected as a color (e.g. the string 'red')
      type &= ~ValueTypes.COLOR;

      return `(${expressionToGlsl(
        context,
        args[0],
        type
      )} ${operator} ${expressionToGlsl(context, args[1], type)})`;
    },
  };
}

Operators['=='] = getEqualOperator('==');

Operators['!='] = getEqualOperator('!=');

Operators['!'] = {
  getReturnType: function () {
    return ValueTypes.BOOLEAN;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 1);
    assertBoolean(args[0]);
    return `(!${expressionToGlsl(context, args[0], ValueTypes.BOOLEAN)})`;
  },
};

function getDecisionOperator(operator) {
  return {
    getReturnType: function () {
      return ValueTypes.BOOLEAN;
    },
    toGlsl: function (context, args) {
      assertArgsMinCount(args, 2);
      for (let i = 0; i < args.length; i++) {
        assertBoolean(args[i]);
      }
      let result = args
        .map((arg) => expressionToGlsl(context, arg, ValueTypes.BOOLEAN))
        .join(` ${operator} `);
      result = `(${result})`;
      return result;
    },
  };
}

Operators['all'] = getDecisionOperator('&&');

Operators['any'] = getDecisionOperator('||');

Operators['between'] = {
  getReturnType: function () {
    return ValueTypes.BOOLEAN;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 3);
    assertNumbers(args);
    const min = expressionToGlsl(context, args[1]);
    const max = expressionToGlsl(context, args[2]);
    const value = expressionToGlsl(context, args[0]);
    return `(${value} >= ${min} && ${value} <= ${max})`;
  },
};

Operators['array'] = {
  getReturnType: function () {
    return ValueTypes.NUMBER_ARRAY;
  },
  toGlsl: function (context, args) {
    assertArgsMinCount(args, 2);
    assertArgsMaxCount(args, 4);
    assertNumbers(args);
    const parsedArgs = args.map(function (val) {
      return expressionToGlsl(context, val);
    });
    return `vec${args.length}(${parsedArgs.join(', ')})`;
  },
};

Operators['color'] = {
  getReturnType: function () {
    return ValueTypes.COLOR;
  },
  toGlsl: function (context, args) {
    assertArgsMinCount(args, 3);
    assertArgsMaxCount(args, 4);
    assertNumbers(args);
    const parsedArgs = args
      .slice(0, 3)
      .map((val) => `${expressionToGlsl(context, val)} / 255.0`);
    if (args.length === 3) {
      return `vec4(${parsedArgs.join(', ')}, 1.0)`;
    }
    const alpha = expressionToGlsl(context, args[3]);
    return `(${alpha} * vec4(${parsedArgs.join(', ')}, 1.0))`;
  },
};

Operators['interpolate'] = {
  getReturnType: function (args) {
    let type = ValueTypes.COLOR | ValueTypes.NUMBER;
    for (let i = 3; i < args.length; i += 2) {
      type = type & getValueType(args[i]);
    }
    return type;
  },
  toGlsl: function (context, args, expectedType) {
    assertArgsEven(args);
    assertArgsMinCount(args, 6);

    // validate interpolation type
    const type = args[0];
    let interpolation;
    switch (type[0]) {
      case 'linear':
        interpolation = 1;
        break;
      case 'exponential':
        interpolation = type[1];
        break;
      default:
        interpolation = null;
    }
    if (!interpolation) {
      throw new Error(
        `Invalid interpolation type for "interpolate" operator, received: ${JSON.stringify(
          type
        )}`
      );
    }

    // compute input/output types
    const inputType = ValueTypes.NUMBER;
    const outputType =
      Operators['interpolate'].getReturnType(args) & expectedType;
    assertSingleType(['interpolate', ...args], outputType, 'output');

    const input = expressionToGlsl(context, args[1], inputType);
    const exponent = numberToGlsl(interpolation);

    let result = '';
    for (let i = 2; i < args.length - 2; i += 2) {
      const stop1 = expressionToGlsl(context, args[i], inputType);
      const output1 =
        result || expressionToGlsl(context, args[i + 1], outputType);
      const stop2 = expressionToGlsl(context, args[i + 2], inputType);
      const output2 = expressionToGlsl(context, args[i + 3], outputType);
      let ratio;
      if (interpolation === 1) {
        ratio = `(${input} - ${stop1}) / (${stop2} - ${stop1})`;
      } else {
        ratio = `(pow(${exponent}, (${input} - ${stop1})) - 1.0) / (pow(${exponent}, (${stop2} - ${stop1})) - 1.0)`;
      }
      result = `mix(${output1}, ${output2}, clamp(${ratio}, 0.0, 1.0))`;
    }
    return result;
  },
};

Operators['match'] = {
  getReturnType: function (args) {
    let type = ValueTypes.ANY;
    for (let i = 2; i < args.length; i += 2) {
      type = type & getValueType(args[i]);
    }
    type = type & getValueType(args[args.length - 1]);
    return type;
  },
  toGlsl: function (context, args, expectedType) {
    assertArgsEven(args);
    assertArgsMinCount(args, 4);

    let inputType = getValueType(args[0]);
    for (let i = 1; i < args.length - 1; i += 2) {
      inputType = inputType & getValueType(args[i]);
    }
    assertOfType(
      ['match', ...args],
      inputType,
      ValueTypes.STRING | ValueTypes.NUMBER | ValueTypes.BOOLEAN,
      'input'
    );
    inputType =
      (ValueTypes.STRING | ValueTypes.NUMBER | ValueTypes.BOOLEAN) & inputType;

    const outputType = Operators['match'].getReturnType(args) & expectedType;
    assertSingleType(['match', ...args], outputType, 'output');

    const input = expressionToGlsl(context, args[0], inputType);
    const fallback = expressionToGlsl(
      context,
      args[args.length - 1],
      outputType
    );
    let result = null;
    for (let i = args.length - 3; i >= 1; i -= 2) {
      const match = expressionToGlsl(context, args[i], inputType);
      const output = expressionToGlsl(context, args[i + 1], outputType);
      result = `(${input} == ${match} ? ${output} : ${result || fallback})`;
    }
    return result;
  },
};

Operators['case'] = {
  getReturnType: function (args) {
    let type = ValueTypes.ANY;
    for (let i = 1; i < args.length; i += 2) {
      type = type & getValueType(args[i]);
    }
    type = type & getValueType(args[args.length - 1]);
    return type;
  },
  toGlsl: function (context, args, expectedType) {
    assertArgsOdd(args);
    assertArgsMinCount(args, 3);

    const outputType = Operators['case'].getReturnType(args) & expectedType;
    assertSingleType(['case', ...args], outputType, 'output');
    for (let i = 0; i < args.length - 1; i += 2) {
      assertBoolean(args[i]);
    }

    const fallback = expressionToGlsl(
      context,
      args[args.length - 1],
      outputType
    );
    let result = null;
    for (let i = args.length - 3; i >= 0; i -= 2) {
      const condition = expressionToGlsl(context, args[i], ValueTypes.BOOLEAN);
      const output = expressionToGlsl(context, args[i + 1], outputType);
      result = `(${condition} ? ${output} : ${result || fallback})`;
    }
    return result;
  },
};

Operators['in'] = {
  getReturnType: function (args) {
    return ValueTypes.BOOLEAN;
  },
  toGlsl: function (context, args) {
    assertArgsCount(args, 2);
    const needle = args[0];
    let haystack = args[1];
    if (!Array.isArray(haystack)) {
      throw new Error(
        `The "in" operator expects an array literal as its second argument.`
      );
    }
    if (typeof haystack[0] === 'string') {
      if (haystack[0] !== 'literal') {
        throw new Error(
          `For the "in" operator, a string array should be wrapped in a "literal" operator to disambiguate from expressions.`
        );
      }
      if (!Array.isArray(haystack[1])) {
        throw new Error(
          `The "in" operator was provided a literal value which was not an array as second argument.`
        );
      }
      haystack = haystack[1];
    }

    let inputType = getValueType(needle);
    for (let i = 0; i < haystack.length - 1; i += 1) {
      inputType = inputType & getValueType(haystack[i]);
    }
    assertOfType(
      ['match', ...args],
      inputType,
      ValueTypes.STRING | ValueTypes.NUMBER | ValueTypes.BOOLEAN,
      'input'
    );
    inputType =
      (ValueTypes.STRING | ValueTypes.NUMBER | ValueTypes.BOOLEAN) & inputType;

    const funcName = computeOperatorFunctionName('in', context);
    const tests = [];
    for (let i = 0; i < haystack.length; i += 1) {
      tests.push(
        `  if (inputValue == ${expressionToGlsl(
          context,
          haystack[i],
          inputType
        )}) { return true; }`
      );
    }
    context.functions[funcName] = `bool ${funcName}(float inputValue) {
${tests.join('\n')}
  return false;
}`;
    return `${funcName}(${expressionToGlsl(context, needle, inputType)})`;
  },
};