package resource

// Quantity is a fixed-point representation of a number. It provides convenient
// marshaling/unmarshaling in JSON and YAML, in addition to String() and
// AsInt64() accessors.
//
// The serialization format is:
//
// ``` <quantity> ::= <signedNumber><suffix>
//
// (Note that <suffix> may be empty, from the "" case in <decimalSI>.)
//
// <digit> ::= 0 | 1 | ... | 9 <digits> ::= <digit> | <digit><digits> <number>
// ::= <digits> | <digits>.<digits> | <digits>. | .<digits> <sign> ::= "+" |
// "-" <signedNumber> ::= <number> | <sign><number> <suffix> ::= <binarySI> |
// <decimalExponent> | <decimalSI> <binarySI> ::= Ki | Mi | Gi | Ti | Pi | Ei
//
// (International System of units; See: http://physics.nist.gov/cuu/Units/binary.html)
//
// <decimalSI> ::= m | "" | k | M | G | T | P | E
//
// (Note that 1024 = 1Ki but 1000 = 1k; I didn't choose the capitalization.)
//
// <decimalExponent> ::= "e" <signedNumber> | "E" <signedNumber> ```
//
// No matter which of the three exponent forms is used, no quantity may
// represent a number greater than 2^63-1 in magnitude, nor may it have more
// than 3 decimal places. Numbers larger or more precise will be capped or
// rounded up. (E.g.: 0.1m will rounded up to 1m.) This may be extended in the
// future if we require larger or smaller quantities.
//
// When a Quantity is parsed from a string, it will remember the type of suffix
// it had, and will use the same type again when it is serialized.
//
// Before serializing, Quantity will be put in "canonical form". This means that
// Exponent/suffix will be adjusted up or down (with a corresponding increase
// or decrease in Mantissa) such that:
//
// - No precision is lost - No fractional digits will be emitted - The exponent
// (or suffix) is as large as possible.
//
// The sign will be omitted unless the number is negative.
//
// Examples:
//
// - 1.5 will be serialized as "1500m" - 1.5Gi will be serialized as "1536Mi"
//
// Note that the quantity will NEVER be internally represented by a floating
// point number. That is the whole point of this exercise.
//
// Non-canonical values will still parse as long as they are well formed, but
// will be re-emitted in their canonical form. (So always use canonical form,
// or don't diff.)
//
// This format is intended to make it difficult to use these numbers without
// writing some sort of special handling code in the hopes that that will cause
// implementors to also use a fixed point implementation.
#Quantity: number | string