113 lines
2.5 KiB
Go
113 lines
2.5 KiB
Go
// Copyright (c) 2025 Probo Inc <hello@getprobo.com>.
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice appear in all copies.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
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// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
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// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
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// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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// PERFORMANCE OF THIS SOFTWARE.
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package page
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import (
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"fmt"
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"github.com/jackc/pgx/v5"
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)
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type (
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Cursor struct {
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Size int
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Key *CursorKey
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Position Position
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}
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Position int8
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)
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const (
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DefaultCursorSize = 25
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Tail Position = iota
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Head
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)
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func (p Position) ToDirection() string {
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switch p {
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case Tail:
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return "ASC"
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case Head:
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return "DESC"
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default:
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panic(fmt.Errorf("unknown direction: %d", p))
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}
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}
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func NewCursor(size int, from *CursorKey, pos Position) *Cursor {
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if size == 0 {
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size = DefaultCursorSize
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}
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return &Cursor{
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Size: size,
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Key: from,
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Position: pos,
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}
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}
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func (c *Cursor) SQLFragment() string {
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return `
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CASE
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WHEN @cursor_order = 'DESC' AND @cursor_from_id::TEXT IS NOT NULL THEN (
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(created_at <= @cursor_from_ts) AND NOT (created_at = @cursor_from_ts AND id > @cursor_from_id)
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)
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WHEN @cursor_order = 'ASC' AND @cursor_from_id::TEXT IS NOT NULL THEN (
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(created_at >= @cursor_from_ts) AND NOT (created_at = @cursor_from_ts AND id < @cursor_from_id)
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)
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ELSE TRUE
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END
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ORDER BY
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CASE
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WHEN @cursor_order = 'ASC' THEN created_at
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END ASC,
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CASE
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WHEN @cursor_order = 'ASC' THEN id
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END ASC,
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CASE
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WHEN @cursor_order = 'DESC' THEN created_at
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END DESC,
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CASE
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WHEN @cursor_order = 'DESC' THEN id
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END DESC
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LIMIT @cursor_limit
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`
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}
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func (c *Cursor) SQLArguments() pgx.NamedArgs {
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var size = c.Size
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if c.Key == nil {
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size += 1
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} else {
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size += 2
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}
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arguments := pgx.NamedArgs{
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"cursor_order": c.Position.ToDirection(),
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"cursor_limit": size,
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"cursor_from_id": nil,
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"cursor_from_ts": nil,
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}
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if c.Key != nil {
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arguments["cursor_from_id"] = c.Key.ID()
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arguments["cursor_from_ts"] = c.Key.Timestamp()
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}
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return arguments
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}
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