1/*
2 * Copyright (C) 2013 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include "utils/autocorrection_threshold_utils.h"
18
19#include <cmath>
20
21#include "defines.h"
22#include "suggest/policyimpl/utils/edit_distance.h"
23#include "suggest/policyimpl/utils/damerau_levenshtein_edit_distance_policy.h"
24
25namespace latinime {
26
27const int AutocorrectionThresholdUtils::MAX_INITIAL_SCORE = 255;
28const int AutocorrectionThresholdUtils::TYPED_LETTER_MULTIPLIER = 2;
29const int AutocorrectionThresholdUtils::FULL_WORD_MULTIPLIER = 2;
30
31/* static */ int AutocorrectionThresholdUtils::editDistance(const int *before,
32        const int beforeLength, const int *after, const int afterLength) {
33    const DamerauLevenshteinEditDistancePolicy daemaruLevenshtein(
34            before, beforeLength, after, afterLength);
35    return static_cast<int>(EditDistance::getEditDistance(&daemaruLevenshtein));
36}
37
38// In dictionary.cpp, getSuggestion() method,
39// When USE_SUGGEST_INTERFACE_FOR_TYPING is true:
40//
41//   // TODO: Revise the following logic thoroughly by referring to the logic
42//   // marked as "Otherwise" below.
43//   SUGGEST_INTERFACE_OUTPUT_SCALE was multiplied to the original suggestion scores to convert
44//   them to integers.
45//     score = (int)((original score) * SUGGEST_INTERFACE_OUTPUT_SCALE)
46//   Undo the scaling here to recover the original score.
47//     normalizedScore = ((float)score) / SUGGEST_INTERFACE_OUTPUT_SCALE
48//
49// Otherwise: suggestion scores are computed using the below formula.
50// original score
51//  := powf(mTypedLetterMultiplier (this is defined 2),
52//         (the number of matched characters between typed word and suggested word))
53//     * (individual word's score which defined in the unigram dictionary,
54//         and this score is defined in range [0, 255].)
55// Then, the following processing is applied.
56//     - If the dictionary word is matched up to the point of the user entry
57//       (full match up to min(before.length(), after.length())
58//       => Then multiply by FULL_MATCHED_WORDS_PROMOTION_RATE (this is defined 1.2)
59//     - If the word is a true full match except for differences in accents or
60//       capitalization, then treat it as if the score was 255.
61//     - If before.length() == after.length()
62//       => multiply by mFullWordMultiplier (this is defined 2))
63// So, maximum original score is powf(2, min(before.length(), after.length())) * 255 * 2 * 1.2
64// For historical reasons we ignore the 1.2 modifier (because the measure for a good
65// autocorrection threshold was done at a time when it didn't exist). This doesn't change
66// the result.
67// So, we can normalize original score by dividing powf(2, min(b.l(),a.l())) * 255 * 2.
68
69/* static */ float AutocorrectionThresholdUtils::calcNormalizedScore(const int *before,
70        const int beforeLength, const int *after, const int afterLength, const int score) {
71    if (0 == beforeLength || 0 == afterLength) {
72        return 0.0f;
73    }
74    const int distance = editDistance(before, beforeLength, after, afterLength);
75    int spaceCount = 0;
76    for (int i = 0; i < afterLength; ++i) {
77        if (after[i] == KEYCODE_SPACE) {
78            ++spaceCount;
79        }
80    }
81
82    if (spaceCount == afterLength) {
83        return 0.0f;
84    }
85
86    if (score <= 0 || distance >= afterLength) {
87        // normalizedScore must be 0.0f (the minimum value) if the score is less than or equal to 0,
88        // or if the edit distance is larger than or equal to afterLength.
89        return 0.0f;
90    }
91    // add a weight based on edit distance.
92    const float weight = 1.0f - static_cast<float>(distance) / static_cast<float>(afterLength);
93
94    // TODO: Revise the following logic thoroughly by referring to...
95    if (true /* USE_SUGGEST_INTERFACE_FOR_TYPING */) {
96        return (static_cast<float>(score) / SUGGEST_INTERFACE_OUTPUT_SCALE) * weight;
97    }
98    // ...this logic.
99    const float maxScore = score >= S_INT_MAX ? static_cast<float>(S_INT_MAX)
100            : static_cast<float>(MAX_INITIAL_SCORE)
101                    * powf(static_cast<float>(TYPED_LETTER_MULTIPLIER),
102                            static_cast<float>(min(beforeLength, afterLength - spaceCount)))
103                    * static_cast<float>(FULL_WORD_MULTIPLIER);
104
105    return (static_cast<float>(score) / maxScore) * weight;
106}
107
108} // namespace latinime
109