1set/gut

package ystring

import (
    "strings"
)

// TrimAfterFirst returns s without the part after the first instance of substr and that instance itself.
// If substr is empty or not present in s, s is returned unchanged.
func TrimAfterFirst(s, substr string) string {
    switch ls, lsub := len(s), len(substr); {
    case ls == 0 || lsub == 0:
        return s
    case ls < lsub:
        return s
    default:
        if idx := strings.Index(s, substr); idx >= 0 {
            return s[0:idx]
        }
    }
    return s
}

// TrimAfterLast returns s without the part after the last instance of substr and that instance itself.
// If substr is empty or not present in s, s is returned unchanged.
func TrimAfterLast(s, substr string) string {
    switch ls, lsub := len(s), len(substr); {
    case ls == 0 || lsub == 0:
        return s
    case ls < lsub:
        return s
    default:
        if idx := strings.LastIndex(s, substr); idx >= 0 {
            return s[0:idx]
        }
    }
    return s
}

// TrimBeforeFirst returns s without the part before the first instance of substr and that instance itself.
// If substr is empty or not present in s, s is returned unchanged.
func TrimBeforeFirst(s, substr string) string {
    switch ls, lsub := len(s), len(substr); {
    case ls == 0 || lsub == 0:
        return s
    case ls < lsub:
        return s
    default:
        if idx := strings.Index(s, substr); idx >= 0 {
            return s[idx+lsub:]
        }
    }
    return s
}

// TrimBeforeLast returns s without the part before the last instance of substr and that instance itself.
// If substr is empty or not present in s, s is returned unchanged.
func TrimBeforeLast(s, substr string) string {
    switch ls, lsub := len(s), len(substr); {
    case ls == 0 || lsub == 0:
        return s
    case ls < lsub:
        return s
    default:
        if idx := strings.LastIndex(s, substr); idx >= 0 {
            return s[idx+lsub:]
        }
    }
    return s
}