encodeSpecificVersion method
Implementation
ResultList encodeSpecificVersion(Version version) {
/// A vertex represents a tuple of a position in the input, a mode and a character encoding where position 0
/// denotes the position left of the first character, 1 the position left of the second character and so on.
/// Likewise the end vertices are located after the last character at position stringToEncode.length().
///
/// An edge leading to such a vertex encodes one or more of the characters left of the position that the vertex
/// represents and encodes it in the same encoding and mode as the vertex on which the edge ends. In other words,
/// all edges leading to a particular vertex encode the same characters in the same mode with the same character
/// encoding. They differ only by their source vertices who are all located at i+1 minus the number of encoded
/// characters.
///
/// The edges leading to a vertex are stored in such a way that there is a fast way to enumerate the edges ending
/// on a particular vertex.
///
/// The algorithm processes the vertices in order of their position thereby performing the following:
///
/// For every vertex at position i the algorithm enumerates the edges ending on the vertex and removes all but the
/// shortest from that list.
/// Then it processes the vertices for the position i+1. If i+1 == stringToEncode.length() then the algorithm ends
/// and chooses the the edge with the smallest size from any of the edges leading to vertices at this position.
/// Otherwise the algorithm computes all possible outgoing edges for the vertices at the position i+1
///
/// Examples:
/// The process is illustrated by showing the graph (edges) after each iteration from left to right over the input:
/// An edge is drawn as follows "(" + fromVertex + ") -- " + encodingMode + "(" + encodedInput + ") (" +
/// accumulatedSize + ") --> (" + toVertex + ")"
///
/// Example 1 encoding the string "ABCDE":
/// Note: This example assumes that alphanumeric encoding is only possible in multiples of two characters so that
/// the example is both short and showing the principle. In reality this restriction does not exist.
///
/// Initial situation
/// (initial) -- BYTE(A) (20) --> (1_BYTE)
/// (initial) -- ALPHANUMERIC(AB) (24) --> (2_ALPHANUMERIC)
///
/// Situation after adding edges to vertices at position 1
/// (initial) -- BYTE(A) (20) --> (1_BYTE) -- BYTE(B) (28) --> (2_BYTE)
/// (1_BYTE) -- ALPHANUMERIC(BC) (44) --> (3_ALPHANUMERIC)
/// (initial) -- ALPHANUMERIC(AB) (24) --> (2_ALPHANUMERIC)
///
/// Situation after adding edges to vertices at position 2
/// (initial) -- BYTE(A) (20) --> (1_BYTE)
/// (initial) -- ALPHANUMERIC(AB) (24) --> (2_ALPHANUMERIC)
/// (initial) -- BYTE(A) (20) --> (1_BYTE) -- BYTE(B) (28) --> (2_BYTE)
/// (1_BYTE) -- ALPHANUMERIC(BC) (44) --> (3_ALPHANUMERIC)
/// (initial) -- ALPHANUMERIC(AB) (24) --> (2_ALPHANUMERIC) -- BYTE(C) (44) --> (3_BYTE)
/// (2_ALPHANUMERIC) -- ALPHANUMERIC(CD) (35) --> (4_ALPHANUMERIC)
///
/// Situation after adding edges to vertices at position 3
/// (initial) -- BYTE(A) (20) --> (1_BYTE) -- BYTE(B) (28) --> (2_BYTE) -- BYTE(C) (36) --> (3_BYTE)
/// (1_BYTE) -- ALPHANUMERIC(BC) (44) --> (3_ALPHANUMERIC) -- BYTE(D) (64) --> (4_BYTE)
/// (3_ALPHANUMERIC) -- ALPHANUMERIC(DE) (55) --> (5_ALPHANUMERIC)
/// (initial) -- ALPHANUMERIC(AB) (24) --> (2_ALPHANUMERIC) -- ALPHANUMERIC(CD) (35) --> (4_ALPHANUMERIC)
/// (2_ALPHANUMERIC) -- ALPHANUMERIC(CD) (35) --> (4_ALPHANUMERIC)
///
/// Situation after adding edges to vertices at position 4
/// (initial) -- BYTE(A) (20) --> (1_BYTE) -- BYTE(B) (28) --> (2_BYTE) -- BYTE(C) (36) --> (3_BYTE) -- BYTE(D) (44) --> (4_BYTE)
/// (1_BYTE) -- ALPHANUMERIC(BC) (44) --> (3_ALPHANUMERIC) -- ALPHANUMERIC(DE) (55) --> (5_ALPHANUMERIC)
/// (initial) -- ALPHANUMERIC(AB) (24) --> (2_ALPHANUMERIC) -- ALPHANUMERIC(CD) (35) --> (4_ALPHANUMERIC) -- BYTE(E) (55) --> (5_BYTE)
///
/// Situation after adding edges to vertices at position 5
/// (initial) -- BYTE(A) (20) --> (1_BYTE) -- BYTE(B) (28) --> (2_BYTE) -- BYTE(C) (36) --> (3_BYTE) -- BYTE(D) (44) --> (4_BYTE) -- BYTE(E) (52) --> (5_BYTE)
/// (1_BYTE) -- ALPHANUMERIC(BC) (44) --> (3_ALPHANUMERIC) -- ALPHANUMERIC(DE) (55) --> (5_ALPHANUMERIC)
/// (initial) -- ALPHANUMERIC(AB) (24) --> (2_ALPHANUMERIC) -- ALPHANUMERIC(CD) (35) --> (4_ALPHANUMERIC)
///
/// Encoding as BYTE(ABCDE) has the smallest size of 52 and is hence chosen. The encodation ALPHANUMERIC(ABCD),
/// BYTE(E) is longer with a size of 55.
///
/// Example 2 encoding the string "XXYY" where X denotes a character unique to character set ISO-8859-2 and Y a
/// character unique to ISO-8859-3. Both characters encode as double byte in UTF-8:
///
/// Initial situation
/// (initial) -- BYTE(X) (32) --> (1_BYTE_ISO-8859-2)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-8)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-16BE)
///
/// Situation after adding edges to vertices at position 1
/// (initial) -- BYTE(X) (32) --> (1_BYTE_ISO-8859-2) -- BYTE(X) (40) --> (2_BYTE_ISO-8859-2)
/// (1_BYTE_ISO-8859-2) -- BYTE(X) (72) --> (2_BYTE_UTF-8)
/// (1_BYTE_ISO-8859-2) -- BYTE(X) (72) --> (2_BYTE_UTF-16BE)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-8)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-16BE)
///
/// Situation after adding edges to vertices at position 2
/// (initial) -- BYTE(X) (32) --> (1_BYTE_ISO-8859-2) -- BYTE(X) (40) --> (2_BYTE_ISO-8859-2)
/// (2_BYTE_ISO-8859-2) -- BYTE(Y) (72) --> (3_BYTE_ISO-8859-3)
/// (2_BYTE_ISO-8859-2) -- BYTE(Y) (80) --> (3_BYTE_UTF-8)
/// (2_BYTE_ISO-8859-2) -- BYTE(Y) (80) --> (3_BYTE_UTF-16BE)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-8) -- BYTE(X) (56) --> (2_BYTE_UTF-8)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-16BE) -- BYTE(X) (56) --> (2_BYTE_UTF-16BE)
///
/// Situation after adding edges to vertices at position 3
/// (initial) -- BYTE(X) (32) --> (1_BYTE_ISO-8859-2) -- BYTE(X) (40) --> (2_BYTE_ISO-8859-2) -- BYTE(Y) (72) --> (3_BYTE_ISO-8859-3)
/// (3_BYTE_ISO-8859-3) -- BYTE(Y) (80) --> (4_BYTE_ISO-8859-3)
/// (3_BYTE_ISO-8859-3) -- BYTE(Y) (112) --> (4_BYTE_UTF-8)
/// (3_BYTE_ISO-8859-3) -- BYTE(Y) (112) --> (4_BYTE_UTF-16BE)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-8) -- BYTE(X) (56) --> (2_BYTE_UTF-8) -- BYTE(Y) (72) --> (3_BYTE_UTF-8)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-16BE) -- BYTE(X) (56) --> (2_BYTE_UTF-16BE) -- BYTE(Y) (72) --> (3_BYTE_UTF-16BE)
///
/// Situation after adding edges to vertices at position 4
/// (initial) -- BYTE(X) (32) --> (1_BYTE_ISO-8859-2) -- BYTE(X) (40) --> (2_BYTE_ISO-8859-2) -- BYTE(Y) (72) --> (3_BYTE_ISO-8859-3) -- BYTE(Y) (80) --> (4_BYTE_ISO-8859-3)
/// (3_BYTE_UTF-8) -- BYTE(Y) (88) --> (4_BYTE_UTF-8)
/// (3_BYTE_UTF-16BE) -- BYTE(Y) (88) --> (4_BYTE_UTF-16BE)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-8) -- BYTE(X) (56) --> (2_BYTE_UTF-8) -- BYTE(Y) (72) --> (3_BYTE_UTF-8)
/// (initial) -- BYTE(X) (40) --> (1_BYTE_UTF-16BE) -- BYTE(X) (56) --> (2_BYTE_UTF-16BE) -- BYTE(Y) (72) --> (3_BYTE_UTF-16BE)
///
/// Encoding as ECI(ISO-8859-2),BYTE(XX),ECI(ISO-8859-3),BYTE(YY) has the smallest size of 80 and is hence chosen.
/// The encodation ECI(UTF-8),BYTE(XXYY) is longer with a size of 88.
final inputLength = stringToEncode.length;
// Array that represents vertices. There is a vertex for every character, encoding and mode. The vertex contains
// a list of all edges that lead to it that have the same encoding and mode.
// The lists are created lazily
// The last dimension in the array below encodes the 4 modes KANJI, ALPHANUMERIC, NUMERIC and BYTE via the
// function getCompactedOrdinal(Mode)
final List<List<List<Edge?>>> edges = List.generate(
inputLength + 1,
(idx) => List.generate(encoders.length, (idx2) => List.filled(4, null)),
);
addEdges(version, edges, 0, null);
for (int i = 1; i <= inputLength; i++) {
for (int j = 0; j < encoders.length; j++) {
for (int k = 0; k < 4; k++) {
if (edges[i][j][k] != null && i < inputLength) {
addEdges(version, edges, i, edges[i][j][k]);
}
}
}
}
int minimalJ = -1;
int minimalK = -1;
int minimalSize = MathUtils.maxValue;
for (int j = 0; j < encoders.length; j++) {
for (int k = 0; k < 4; k++) {
if (edges[inputLength][j][k] != null) {
final edge = edges[inputLength][j][k];
if (edge != null && edge.cachedTotalSize < minimalSize) {
minimalSize = edge.cachedTotalSize;
minimalJ = j;
minimalK = k;
}
}
}
}
if (minimalJ < 0) {
throw WriterException(
'Internal error: failed to encode "$stringToEncode"',
);
}
return ResultList(version, edges[inputLength][minimalJ][minimalK], this);
}
