#Bilibili AV/BV Code Conversion

Bilibili AV/BV Code Conversion

#Bilibili AV/BV Code Conversion code-golfconversion

###Background

Bilibili is a China-based video sharing platform, similar to Nico Nico Douga in Japan, and Youtube around the world.

Since the establishment, Bilibili had been using the AV code to reference a video. An AV code is a string of 3 or more characters, starting with av and followed by a natural number, like av82054919.

However, since 23 March 2020, Bilibili introduced a new referencing system called the BV code. This time, the code is a string of exactly 12 characters, starting with BV and followed by 10 alphanumerical characters, like BV1XJ41157tQ. Still, users can use both codes to reference a video, and there is a conversion algorithm between the two.

^{(For your information, the two examples reference the same video)}

###The algorithm

To convert from AV code to BV code:

1. Remove the av part of the AV code.
2. Do a bitwise XOR between the result in step 1 (as a number) and 177451812.
3. Add 8728348608 to the result in step 2.
4. Convert the result in step 3 to a 6-digit base-58 number with digits fZodR9XQDSUm21yCkr6zBqiveYah8bt4xsWpHnJE7jL5VG3guMTKNPAwcF in place of 0, 1, ..., 57 respectively. Here, 0, I, O, l are omitted to eliminate ambiguity. Assume the result is abcdef.
5. The BV code is then BV1db4a1c7ef.

To convert from BV code to AV code:

1. Remove the 1st to 3rd, the 6th, the 8th and the 10th characters. Assume the result is abcdef.
2. Rearrange the result in step 1 to cbdaef.
3. Treat the result in step 2 as a base-58 number with digits fZodR9XQDSUm21yCkr6zBqiveYah8bt4xsWpHnJE7jL5VG3guMTKNPAwcF in place of 0, 1, ..., 57 respectively. Convert this base-58 number into decimal.
4. Subtract 8728348608 from the result in step 3.
5. Do a bitwise XOR between the result in step 4 and 177451812.
6. The AV code is then av followed by the result in step 5.

###Example

To convert av82054919 to BV code:

1. Removing av from the code results in 82054919.
2. \$82054919\text{ XOR }177451812=242727971\$
3. \$242727971+8728348608=8971076579\$
4. \$8971076579_{10} = (13,38,43,6,30,7)_{58}\$ → 1J5XtQ
5. Substituting: BV1[X][J]4[1]1[5]7[t][Q] → BV1XJ41157tQ

To convert BV1XJ41157tQ back to AV code:

1. Remove the bracketed numbers: [BV1]XJ[4]1[1]5[7]tQ → XJ15tQ
2. Rearranging the characters results in 1J5XtQ.
3. 1J5XtQ → \$(13,38,43,6,30,7)_{58} = 8971076579_{10}\$
4. \$8971076579-8728348608=242727971\$
5. \$242727971\text{ XOR }177451812=82054919\$
6. Prepending av to the result, we have av82054919.

###Challenge

Write two independent programs or functions, one receiving the AV code as input and outputting the corresponding BV code, and one receiving the BV code as input and outputting the corresponding AV code. Both the prefixes av and BV are case insensitive, you may choose either upper or lower case to accept or output. Each code should work even without the code from the other.

You may assume that the input for both programs must have a valid format, and the number in its corresponding AV code is between 1 and 2147483647 inclusive.

###Test cases

AV code <-> BV code av82054919 <-> BV1XJ41157tQ av123456789 <-> BV1yn411L7tG av1 <-> BV1xx411c7mQ av2147483647 <-> BV1Fr4k1q7G1 

###Winning condition

The total length of the codes of the two programs (measured in bytes) will be your code length, and since this is a code-golf challenge, the submission with shortest code length for each language wins. No standard loopholes.

#Bilibili AV/BV Code Conversion

Write two independent programs or functions, one receiving the AV code as input and outputting the corresponding BV code, and one receiving the BV code as input and outputting the corresponding AV code. Both the prefixes av and BV are case insensitive, you may choose either upper or lower case to accept or input. Each code should work even without the code from the other.

Write two independent programs or functions, one receiving the AV code as input and outputting the corresponding BV code, and one receiving the BV code as input and outputting the corresponding AV code. Both the prefixes av and BV are case insensitive, you may choose either upper or lower case to accept or output. Each code should work even without the code from the other.