package attributes

import "fmt"

// Attributes is an immutable struct for storing and retrieving generic
// key/value pairs.  Keys must be hashable, and users should define their own
// types for keys.
type Attributes struct {
	m map[interface{}]interface{}
}

// New returns a new Attributes containing all key/value pairs in kvs.  If the
// same key appears multiple times, the last value overwrites all previous
// values for that key.  Panics if len(kvs) is not even.
func New(kvs ...interface{}) *Attributes {
	if len(kvs)%2 != 0 {
		panic(fmt.Sprintf("attributes.New called with unexpected input: len(kvs) = %v", len(kvs)))
	}
	a := &Attributes{m: make(map[interface{}]interface{}, len(kvs)/2)}
	for i := 0; i < len(kvs)/2; i++ {
		a.m[kvs[i*2]] = kvs[i*2+1]
	}
	return a
}

// WithValues returns a new Attributes containing all key/value pairs in a and
// kvs.  Panics if len(kvs) is not even.  If the same key appears multiple
// times, the last value overwrites all previous values for that key.  To
// remove an existing key, use a nil value.
func (a *Attributes) WithValues(kvs ...interface{}) *Attributes {
	if a == nil {
		return New(kvs...)
	}
	if len(kvs)%2 != 0 {
		panic(fmt.Sprintf("attributes.New called with unexpected input: len(kvs) = %v", len(kvs)))
	}
	n := &Attributes{m: make(map[interface{}]interface{}, len(a.m)+len(kvs)/2)}
	for k, v := range a.m {
		n.m[k] = v
	}
	for i := 0; i < len(kvs)/2; i++ {
		n.m[kvs[i*2]] = kvs[i*2+1]
	}
	return n
}

// Value returns the value associated with these attributes for key, or nil if
// no value is associated with key.
func (a *Attributes) Value(key interface{}) interface{} {
	if a == nil {
		return nil
	}
	return a.m[key]
}

func (a *Attributes) For(call func(key interface{}, val interface{})) {
	if a == nil {
		return
	}
	for k, v := range a.m {
		call(k, v)
	}
}