golangで先週の〇〇曜日をtime.Timeで取得するコード

type Weekday struct {
    Now time.Time
    Loc *time.Location
}

func (w Weekday) LastWeekOf(weekday time.Weekday) time.Time {
    levellingOffset := int(w.Now.Weekday())
    weekDiff := 7-(int(weekday))

    return time.
        Date(w.Now.Year(), w.Now.Month(), w.Now.Day(), 0, 0, 0, 0, w.Loc).
        AddDate(0, 0, -levellingOffset).
        AddDate(0, 0, -weekDiff)
}

こう使う

package main

import (
    "fmt"
    "time"
)

func main() {   
    now := time.Date(2020, 11, 27, 0, 0, 0, 0, time.UTC)    
    fmt.Println(now.Year(), now.Month(), now.Day())

    w := Weekday{
        Now: now, 
        Loc: time.UTC,
    }   
    r := w.LastWeekOf(time.Monday) // 先週の月曜日を取得する
    fmt.Println(r.Year(), r.Month(), r.Day())
}

結果

2020 November 27
2020 November 16