66 lines
1.6 KiB
Go
66 lines
1.6 KiB
Go
package config
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import (
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"fmt"
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"reflect"
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)
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// Merge recursively combines a set of config file structures into a single structure
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// according to the following rules:
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//
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// * only values of type struct, slice, map and pointer to simple types are allowed. Other types panic.
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// * when merging two structs the result is the recursive merge of all fields according to the rules below
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// * when merging two slices the result is the second slice appended to the first
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// * when merging two maps the result is the second map overlaid on the first
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// * when merging two pointer values the result is the second value if it is not nil, otherwise the first
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func Merge(files ...Config) Config {
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var a Config
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for _, b := range files {
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a = merge(a, b).(Config)
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}
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return a
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}
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func merge(a, b interface{}) interface{} {
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return mergeValue(reflect.ValueOf(a), reflect.ValueOf(b)).Interface()
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}
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func mergeValue(a, b reflect.Value) reflect.Value {
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switch a.Kind() {
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case reflect.Map:
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r := reflect.MakeMap(a.Type())
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for _, k := range a.MapKeys() {
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v := a.MapIndex(k)
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r.SetMapIndex(k, v)
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}
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for _, k := range b.MapKeys() {
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v := b.MapIndex(k)
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r.SetMapIndex(k, v)
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}
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return r
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case reflect.Ptr:
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if !b.IsNil() {
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return b
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}
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return a
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case reflect.Slice:
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if !a.IsValid() {
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a = reflect.Zero(a.Type())
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}
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return reflect.AppendSlice(a, b)
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case reflect.Struct:
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r := reflect.New(a.Type()) // &struct{}
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for i := 0; i < a.NumField(); i++ {
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v := mergeValue(a.Field(i), b.Field(i))
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r.Elem().Field(i).Set(v)
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}
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return r.Elem() // *struct
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default:
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panic(fmt.Sprintf("unsupported element type: %v", a.Type()))
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}
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}
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