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71 lines
2.2 KiB
Go
71 lines
2.2 KiB
Go
// Copyright (c) 2020 Shivaram Lingamneni <slingamn@cs.stanford.edu>
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// released under the MIT license
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package history
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import (
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"time"
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)
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// Selector represents a parameter to a CHATHISTORY command
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type Selector struct {
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Msgid string
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Time time.Time
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}
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// Sequence is an abstract sequence of history entries that can be queried;
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// it encapsulates restrictions such as registration time cutoffs, or
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// only looking at a single "query buffer" (DMs with a particular correspondent)
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type Sequence interface {
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Between(start, end Selector, limit int) (results []Item, complete bool, err error)
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Around(start Selector, limit int) (results []Item, err error)
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}
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// This is a bad, slow implementation of CHATHISTORY AROUND using the BETWEEN semantics
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func GenericAround(seq Sequence, start Selector, limit int) (results []Item, err error) {
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var halfLimit int
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halfLimit = (limit + 1) / 2
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initialResults, _, err := seq.Between(Selector{}, start, halfLimit)
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if err != nil {
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return
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} else if len(initialResults) == 0 {
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// TODO: this fails if we're doing an AROUND on the first message in the buffer
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// would be nice to fix this but whatever
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return
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}
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newStart := Selector{Time: initialResults[0].Message.Time}
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results, _, err = seq.Between(newStart, Selector{}, limit)
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return
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}
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// MinMaxAsc converts CHATHISTORY arguments into time intervals, handling the most
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// general case (BETWEEN going forwards or backwards) natively and the other ordering
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// queries (AFTER, BEFORE, LATEST) as special cases.
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func MinMaxAsc(after, before, cutoff time.Time) (min, max time.Time, ascending bool) {
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startIsZero, endIsZero := after.IsZero(), before.IsZero()
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if !startIsZero && endIsZero {
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// AFTER
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ascending = true
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} else if startIsZero && !endIsZero {
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// BEFORE
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ascending = false
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} else if !startIsZero && !endIsZero {
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if before.Before(after) {
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// BETWEEN going backwards
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before, after = after, before
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ascending = false
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} else {
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// BETWEEN going forwards
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ascending = true
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}
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} else if startIsZero && endIsZero {
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// LATEST
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ascending = false
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}
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if after.IsZero() || after.Before(cutoff) {
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// this may result in an impossible query, which is fine
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after = cutoff
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}
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return after, before, ascending
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}
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