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69 lines
2.1 KiB
Go
69 lines
2.1 KiB
Go
package entity
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import (
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"strings"
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)
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// CombineIds compute a merged Id holding information from both the primary Id
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// and the secondary Id.
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//
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// This allow to later find efficiently a secondary element because we can access
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// the primary one directly instead of searching for a primary that has a
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// secondary matching the Id.
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//
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// An example usage is Comment in a Bug. The interleaved Id will hold part of the
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// Bug Id and part of the Comment Id.
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//
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// To allow the use of an arbitrary length prefix of this Id, Ids from primary
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// and secondary are interleaved with this irregular pattern to give the
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// best chance to find the secondary even with a 7 character prefix.
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//
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// Format is: PSPSPSPPPSPPPPSPPPPSPPPPSPPPPSPPPPSPPPPSPPPPSPPPPSPPPPSPPPPSPPPP
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//
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// A complete interleaved Id hold 50 characters for the primary and 14 for the
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// secondary, which give a key space of 36^50 for the primary (~6 * 10^77) and
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// 36^14 for the secondary (~6 * 10^21). This asymmetry assumes a reasonable number
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// of secondary within a primary Entity, while still allowing for a vast key space
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// for the primary (that is, a globally merged database) with a low risk of collision.
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//
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// Here is the breakdown of several common prefix length:
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//
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// 5: 3P, 2S
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// 7: 4P, 3S
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// 10: 6P, 4S
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// 16: 11P, 5S
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func CombineIds(primary Id, secondary Id) Id {
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var id strings.Builder
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for i := 0; i < idLength; i++ {
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switch {
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default:
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id.WriteByte(primary[0])
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primary = primary[1:]
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case i == 1, i == 3, i == 5, i == 9, i >= 10 && i%5 == 4:
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id.WriteByte(secondary[0])
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secondary = secondary[1:]
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}
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}
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return Id(id.String())
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}
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// SeparateIds extract primary and secondary prefix from an arbitrary length prefix
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// of an Id created with CombineIds.
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func SeparateIds(prefix string) (primaryPrefix string, secondaryPrefix string) {
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var primary strings.Builder
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var secondary strings.Builder
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for i, r := range prefix {
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switch {
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default:
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primary.WriteRune(r)
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case i == 1, i == 3, i == 5, i == 9, i >= 10 && i%5 == 4:
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secondary.WriteRune(r)
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}
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}
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return primary.String(), secondary.String()
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}
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