From 412be221a733a65057758906ba544fa115a9ce67 Mon Sep 17 00:00:00 2001
From: Vlasta Vesely <vlastavesely@protonmail.ch>
Date: Wed, 1 Jan 2020 22:02:44 +0100
Subject: [PATCH] implement reverse transliteration (latin -> devanagari)

---
 iast.c            |  6 ++--
 tests/translit.c  | 25 ++++++++++++++-
 transliteration.c | 82 +++++++++++++++++++++++++++++++++++++++++++++--
 transliteration.h |  1 +
 4 files changed, 108 insertions(+), 6 deletions(-)

diff --git a/iast.c b/iast.c
index b71ab52..005e801 100644
--- a/iast.c
+++ b/iast.c
@@ -6,6 +6,9 @@
 
 static struct translit_letter table[] = {
 
+	/* Special characters */
+	{0x0950, SPECIAL, "aum"},        /* aum */
+
 	/* Vowels */
 	{0x0910, VOWEL, "ai"},           /* 01 */
 	{0x0914, VOWEL, "au"},           /* 02 */
@@ -62,9 +65,6 @@ static struct translit_letter table[] = {
 	{0x0903, CODA, "\u1e25"},        /* visarga (.h) */
 	{0x093d, CODA, "'"},             /* avagrada (') */
 
-	/* Special characters */
-	{0x0950, SPECIAL, "aum"},        /* aum */
-
 	/* Numbers */
 	{0x0966, NUMBER, "0"},
 	{0x0967, NUMBER, "1"},
diff --git a/tests/translit.c b/tests/translit.c
index 78fa5a5..008d35a 100644
--- a/tests/translit.c
+++ b/tests/translit.c
@@ -1,7 +1,7 @@
+#include "test.h"
 #include "translit.h"
 #include "../transliteration.h"
 
-
 START_TEST(test_translit_devanagari_to_latin)
 {
 	char *latin;
@@ -28,7 +28,30 @@ START_TEST(test_translit_devanagari_to_latin)
 }
 END_TEST
 
+START_TEST(test_translit_latin_to_devanagari)
+{
+	char *devanagari;
+
+	devanagari = transliterate_latin_to_devanagari("saṃskṛtam");
+	ck_assert_str_eq("संस्कृतम्", devanagari);
+	free(devanagari);
+
+	devanagari = transliterate_latin_to_devanagari("bhagavadgītā");
+	ck_assert_str_eq("भगवद्गीता", devanagari);
+	free(devanagari);
+
+	devanagari = transliterate_latin_to_devanagari("āryāvarta");
+	ck_assert_str_eq("आर्यावर्त", devanagari);
+	free(devanagari);
+
+	devanagari = transliterate_latin_to_devanagari("mahābhāratam");
+	ck_assert_str_eq("महाभारतम्", devanagari);
+	free(devanagari);
+}
+END_TEST
+
 void register_translit_tests(TCase *test_case)
 {
 	tcase_add_test(test_case, test_translit_devanagari_to_latin);
+	tcase_add_test(test_case, test_translit_latin_to_devanagari);
 }
diff --git a/transliteration.c b/transliteration.c
index 2dc0066..49a022c 100644
--- a/transliteration.c
+++ b/transliteration.c
@@ -6,6 +6,7 @@
 #include "utf8.h"
 
 #define SCHWA_CHARACTER 'a'
+#define VIRAMA 0x094d
 #define CHUNKSIZE 1024
 
 static struct translit_letter *letter_by_code(struct translit_letter *table,
@@ -22,8 +23,7 @@ static struct translit_letter *letter_by_code(struct translit_letter *table,
 
 char *transliterate_devanagari_to_latin(const char *devanagari)
 {
-	struct translit_letter *table;
-	struct translit_letter *letter;
+	struct translit_letter *table, *letter;
 	unsigned int c, alloc = 0, done = 0, len;
 	const char *src = devanagari;
 	char *latin = NULL;
@@ -70,3 +70,81 @@ char *transliterate_devanagari_to_latin(const char *devanagari)
 
 	return latin;
 }
+
+static struct translit_letter *letter_by_data(struct translit_letter *table,
+					      const char *data)
+{
+	while (table->code != 0) {
+		unsigned int len = strlen(table->data);
+		if (len && strncmp(table->data, data, len) == 0)
+			return table;
+		table++;
+	}
+
+	return NULL;
+}
+
+static struct translit_letter *vowel_sign_by_data(struct translit_letter *table,
+						  const char *data)
+{
+	while (table->code != 0) {
+		unsigned int len = strlen(table->data);
+		if (len && strncmp(table->data, data, len) == 0 &&
+		    table->type == VOWEL_SIGN)
+			return table;
+		table++;
+	}
+
+	return NULL;
+}
+
+char *transliterate_latin_to_devanagari(const char *latin)
+{
+	struct translit_letter *table, *letter, *next;
+	unsigned int alloc = 0, done = 0, len;
+	const char *src = latin;
+	char *devanagari = NULL;
+
+	table = get_iast_transliteration_table();
+
+	while (*src) {
+		if (alloc < done + UNICODE_MAX_LENGTH) {
+			devanagari = realloc(devanagari, alloc + CHUNKSIZE);
+			alloc += CHUNKSIZE;
+		}
+
+		letter = letter_by_data(table, src);
+		if (letter) {
+			utf8_pack_char(devanagari + done, letter->code);
+			len = utf8_char_length(letter->code);
+			done += len;
+			src += strlen(letter->data);
+
+			if (letter->type == VOWEL || letter->type == CODA)
+				continue;
+
+			next = vowel_sign_by_data(table, src);
+			if (next) {
+				utf8_pack_char(devanagari + done, next->code);
+				done += utf8_char_length(next->code);
+				src += strlen(next->data);
+			} else {
+				if (*src == SCHWA_CHARACTER) {
+					src++;
+				} else {
+					if (letter->type == CONSONANT) {
+						utf8_pack_char(devanagari + done, VIRAMA);
+						done += utf8_char_length(VIRAMA);
+					}
+				}
+			}
+		} else {
+			devanagari[done++] = *src++;
+		}
+	}
+
+	if (devanagari)
+		devanagari[done] = '\0';
+
+	return devanagari;
+}
diff --git a/transliteration.h b/transliteration.h
index 9e52b2f..cbdd17d 100644
--- a/transliteration.h
+++ b/transliteration.h
@@ -23,6 +23,7 @@ struct translit_context {
 };
 
 char *transliterate_devanagari_to_latin(const char *text);
+char *transliterate_latin_to_devanagari(const char *text);
 
 static inline int is_devanagari(unsigned int code)
 {