import io::{reader, reader_util};

iface to_base64 {
    fn to_base64() -> str;
}

impl of to_base64 for ~[u8] {
    fn to_base64() -> str {
        let chars = str::chars(
            "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
        );

        let len = self.len();
        let mut s = "";
        str::reserve(s, ((len + 3u) / 4u) * 3u);

        let mut i = 0u;

        while i < len - (len % 3u) {
            let n = (self[i] as uint) << 16u |
                    (self[i + 1u] as uint) << 8u |
                    (self[i + 2u] as uint);

            // This 24-bit number gets separated into four 6-bit numbers.
            str::push_char(s, chars[(n >> 18u) & 63u]);
            str::push_char(s, chars[(n >> 12u) & 63u]);
            str::push_char(s, chars[(n >> 6u) & 63u]);
            str::push_char(s, chars[n & 63u]);

            i += 3u;
        }

        alt check len % 3u {
          0u { }
          1u {
            let n = (self[i] as uint) << 16u;
            str::push_char(s, chars[(n >> 18u) & 63u]);
            str::push_char(s, chars[(n >> 12u) & 63u]);
            str::push_char(s, '=');
            str::push_char(s, '=');
          }
          2u {
            let n = (self[i] as uint) << 16u | (self[i + 1u] as uint) << 8u;
            str::push_char(s, chars[(n >> 18u) & 63u]);
            str::push_char(s, chars[(n >> 12u) & 63u]);
            str::push_char(s, chars[(n >> 6u) & 63u]);
            str::push_char(s, '=');
          }
        }

        s
    }
}

impl of to_base64 for str {
    fn to_base64() -> str {
        str::bytes(self).to_base64()
    }
}

iface from_base64 {
    fn from_base64() -> ~[u8];
}

impl of from_base64 for ~[u8] {
    fn from_base64() -> ~[u8] {
        if self.len() % 4u != 0u { fail "invalid base64 length"; }

        let len = self.len();
        let mut padding = 0u;

        if len != 0u {
            if self[len - 1u] == '=' as u8 { padding += 1u; }
            if self[len - 2u] == '=' as u8 { padding += 1u; }
        }

        let mut r = ~[];
        vec::reserve(r, (len / 4u) * 3u - padding);

        let mut i = 0u;
        while i < len {
            let mut n = 0u;

            for iter::repeat(4u) {
                let ch = self[i] as char;
                n <<= 6u;

                if ch >= 'A' && ch <= 'Z' {
                    n |= (ch as uint) - 0x41u;
                } else if ch >= 'a' && ch <= 'z' {
                    n |= (ch as uint) - 0x47u;
                } else if ch >= '0' && ch <= '9' {
                    n |= (ch as uint) + 0x04u;
                } else if ch == '+' {
                    n |= 0x3Eu;
                } else if ch == '/' {
                    n |= 0x3Fu;
                } else if ch == '=' {
                    alt len - i {
                      1u {
                        vec::push(r, ((n >> 16u) & 0xFFu) as u8);
                        vec::push(r, ((n >> 8u ) & 0xFFu) as u8);
                        ret copy r;
                      }
                      2u {
                        vec::push(r, ((n >> 10u) & 0xFFu) as u8);
                        ret copy r;
                      }
                      _ {
                        fail "invalid base64 padding";
                      }
                    }
                } else {
                    fail "invalid base64 character";
                }

                i += 1u;
            };

            vec::push(r, ((n >> 16u) & 0xFFu) as u8);
            vec::push(r, ((n >> 8u ) & 0xFFu) as u8);
            vec::push(r, ((n       ) & 0xFFu) as u8);
        }

        r
    }
}

impl of from_base64 for str {
    fn from_base64() -> ~[u8] {
        str::bytes(self).from_base64()
    }
}

#[cfg(test)]
mod tests {
    #[test]
    fn test_to_base64() {
        assert "".to_base64()       == "";
        assert "f".to_base64()      == "Zg==";
        assert "fo".to_base64()     == "Zm8=";
        assert "foo".to_base64()    == "Zm9v";
        assert "foob".to_base64()   == "Zm9vYg==";
        assert "fooba".to_base64()  == "Zm9vYmE=";
        assert "foobar".to_base64() == "Zm9vYmFy";
    }

    #[test]
    fn test_from_base64() {
        assert "".from_base64() == str::bytes("");
        assert "Zg==".from_base64() == str::bytes("f");
        assert "Zm8=".from_base64() == str::bytes("fo");
        assert "Zm9v".from_base64() == str::bytes("foo");
        assert "Zm9vYg==".from_base64() == str::bytes("foob");
        assert "Zm9vYmE=".from_base64() == str::bytes("fooba");
        assert "Zm9vYmFy".from_base64() == str::bytes("foobar");
    }
}
