'use strict';

var fixtures = require('../fixtures');
var fs = require('fs');
var sharp = require('../../index');

sharp.cache(0);


// Constants
var MAX_ALLOWED_IMAGE_MAGICK_MEAN_SQUARED_ERROR = 0.3;

// Helpers
var getPaths = function(baseName, extension) {
  if (typeof extension === 'undefined') {
    extension = 'png';
  }

  var actual = fixtures.path('output.' + baseName + '.' + extension);
  var expected = fixtures.expected(baseName + '.' + extension);
  var expectedMagick = fixtures.expected(baseName + '-imagemagick.' + extension);

  return {
    actual: actual,
    expected: expected,
    expectedMagick: expectedMagick
  };
};

var assertEqual = function (paths, callback) {
  if (typeof callback !== 'function') {
    throw new TypeError('`callback` must be a function');
  }

  fixtures.assertEqual(paths.actual, paths.expected, function (error) {
    if (error) return callback(error);

    sharp.compare(paths.actual, paths.expectedMagick, function (error, info) {
      if (error) return callback(error);

      if (info.meanSquaredError > MAX_ALLOWED_IMAGE_MAGICK_MEAN_SQUARED_ERROR) {
        return callback(new Error('Expected MSE against ImageMagick to be <= ' +
          MAX_ALLOWED_IMAGE_MAGICK_MEAN_SQUARED_ERROR + '. Actual: ' +
          info.meanSquaredError));
      }

      callback();
    });
  });
};

// Test
describe('Overlays', function() {
  it('Overlay transparent PNG on solid background', function(done) {
    var paths = getPaths('alpha-layer-01');

    sharp(fixtures.inputPngOverlayLayer0)
      .overlayWith(fixtures.inputPngOverlayLayer1)
      .toFile(paths.actual, function (error) {
        if (error) return done(error);

        assertEqual(paths, done);
      });
  });

  it('Overlay low-alpha transparent PNG on solid background', function(done) {
    var paths = getPaths('alpha-layer-01-low-alpha');

    sharp(fixtures.inputPngOverlayLayer0)
      .overlayWith(fixtures.inputPngOverlayLayer1LowAlpha)
      .toFile(paths.actual, function (error) {
        if (error) return done(error);

        assertEqual(paths, done);
      });
  });

  it('Composite three transparent PNGs into one', function(done) {
    var paths = getPaths('alpha-layer-012');

    sharp(fixtures.inputPngOverlayLayer0)
      .overlayWith(fixtures.inputPngOverlayLayer1)
      .toBuffer(function (error, data, info) {
        if (error) return done(error);

        sharp(data)
          .overlayWith(fixtures.inputPngOverlayLayer2)
          .toFile(paths.actual, function (error) {
            if (error) return done(error);

            assertEqual(paths, done);
          });
      });
  });

  it('Composite two transparent PNGs into one', function(done) {
    var paths = getPaths('alpha-layer-12');

    sharp(fixtures.inputPngOverlayLayer1)
      .overlayWith(fixtures.inputPngOverlayLayer2)
      .toFile(paths.actual, function (error, data, info) {
        if (error) return done(error);

        assertEqual(paths, done);
      });
  });

  it('Composite two low-alpha transparent PNGs into one', function(done) {
    var paths = getPaths('alpha-layer-12-low-alpha');

    sharp(fixtures.inputPngOverlayLayer1LowAlpha)
      .overlayWith(fixtures.inputPngOverlayLayer2LowAlpha)
      .toFile(paths.actual, function (error, data, info) {
        if (error) return done(error);

        assertEqual(paths, done);
      });
  });

  it('Composite three low-alpha transparent PNGs into one', function(done) {
    var paths = getPaths('alpha-layer-012-low-alpha');

    sharp(fixtures.inputPngOverlayLayer0)
      .overlayWith(fixtures.inputPngOverlayLayer1LowAlpha)
      .toBuffer(function (error, data, info) {
        if (error) return done(error);

        sharp(data)
          .overlayWith(fixtures.inputPngOverlayLayer2LowAlpha)
          .toFile(paths.actual, function (error, data, info) {
            if (error) return done(error);

            assertEqual(paths, done);
          });
      });
  });

  it('Composite transparent PNG onto JPEG', function(done) {
    sharp(fixtures.inputJpg)
      .overlayWith(fixtures.inputPngOverlayLayer1)
      .toBuffer(function (error, data, info) {
        if (error.message !== 'Input image must have an alpha channel') {
          return done(new Error('Unexpected error: ' + error.message));
        }

        done();
      });
  });

});