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// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Paul Buetow
package rpn
import (
"cmp"
"maps"
"math"
"slices"
"sync"
)
// ConstantsProvider defines the interface for reading constant values.
type ConstantsProvider interface {
GetConstant(name string) (float64, bool)
ListConstants() []ConstantInfo
Count() int
HasConstant(name string) bool
SetConstant(name string, value float64) error
ClearConstants()
ReloadBuiltInConstants()
}
// ConstantInfo represents a single constant with its name and value.
type ConstantInfo struct {
Name string
Value float64
}
// Constants stores constant name-value pairs for RPN calculations.
// It provides thread-safe access to constant storage.
type Constants struct {
mu sync.RWMutex
constants map[string]float64
}
// NewConstants creates and initializes a new Constants instance with built-in constants.
func NewConstants() *Constants {
c := &Constants{
constants: make(map[string]float64),
}
c.loadBuiltInConstants()
return c
}
// loadBuiltInConstants loads the standard mathematical constants and returns the set of keys it set.
func (c *Constants) loadBuiltInConstants() map[string]struct{} {
builtIns := make(map[string]struct{})
// Pi (π) - ratio of a circle's circumference to its diameter
c.constants["pi"] = math.Pi
builtIns["pi"] = struct{}{}
c.constants["π"] = math.Pi
builtIns["π"] = struct{}{}
// Euler's number (e) - base of natural logarithm
c.constants["e"] = math.E
builtIns["e"] = struct{}{}
c.constants["euler"] = math.E
builtIns["euler"] = struct{}{}
// Golden ratio (φ)
c.constants["phi"] = 1.618033988749895
builtIns["phi"] = struct{}{}
c.constants["φ"] = 1.618033988749895
builtIns["φ"] = struct{}{}
// Square root of 2
c.constants["sqrt2"] = 1.414213562373095
builtIns["sqrt2"] = struct{}{}
c.constants["√2"] = 1.414213562373095
builtIns["√2"] = struct{}{}
// Square root of 3
c.constants["sqrt3"] = 1.732050807568877
builtIns["sqrt3"] = struct{}{}
c.constants["√3"] = 1.732050807568877
builtIns["√3"] = struct{}{}
// Square root of 5
c.constants["sqrt5"] = 2.23606797749979
builtIns["sqrt5"] = struct{}{}
c.constants["√5"] = 2.23606797749979
builtIns["√5"] = struct{}{}
// Natural logarithm of 2
c.constants["ln2"] = 0.693147180559945
builtIns["ln2"] = struct{}{}
c.constants["log2"] = 0.693147180559945
builtIns["log2"] = struct{}{}
// Natural logarithm of 10
c.constants["ln10"] = 2.302585092994046
builtIns["ln10"] = struct{}{}
c.constants["log10"] = 2.302585092994046
builtIns["log10"] = struct{}{}
// Logarithm of e base 10
c.constants["log_e"] = 0.434294481903252
builtIns["log_e"] = struct{}{}
c.constants["log_e10"] = 0.434294481903252
builtIns["log_e10"] = struct{}{}
// Tau (2π) - circle constant
c.constants["tau"] = 2 * math.Pi
builtIns["tau"] = struct{}{}
c.constants["τ"] = 2 * math.Pi
builtIns["τ"] = struct{}{}
// Fraction 1/π
c.constants["1/π"] = 1 / math.Pi
builtIns["1/π"] = struct{}{}
c.constants["inv_pi"] = 1 / math.Pi
builtIns["inv_pi"] = struct{}{}
// Fraction 1/e
c.constants["1/e"] = 1 / math.E
builtIns["1/e"] = struct{}{}
c.constants["inv_e"] = 1 / math.E
builtIns["inv_e"] = struct{}{}
// Infinity
c.constants["inf"] = math.Inf(1)
builtIns["inf"] = struct{}{}
c.constants["infinity"] = math.Inf(1)
builtIns["infinity"] = struct{}{}
// Negative infinity
c.constants["-inf"] = math.Inf(-1)
builtIns["-inf"] = struct{}{}
c.constants["-infinity"] = math.Inf(-1)
builtIns["-infinity"] = struct{}{}
// NaN (Not a Number)
c.constants["nan"] = math.NaN()
builtIns["nan"] = struct{}{}
return builtIns
}
// SetConstant assigns a value to a constant name.
func (c *Constants) SetConstant(name string, value float64) error {
c.mu.Lock()
defer c.mu.Unlock()
c.constants[name] = value
return nil
}
// GetConstant retrieves the value of a constant.
// Returns the value and true if found, or 0 and false if not found.
func (c *Constants) GetConstant(name string) (float64, bool) {
c.mu.RLock()
defer c.mu.RUnlock()
value, exists := c.constants[name]
return value, exists
}
// ListConstants returns a sorted list of all constant names and their values.
func (c *Constants) ListConstants() []ConstantInfo {
c.mu.RLock()
defer c.mu.RUnlock()
var infos []ConstantInfo
for name, value := range c.constants {
infos = append(infos, ConstantInfo{Name: name, Value: value})
}
// Sort by name for consistent output
slices.SortFunc(infos, func(a, b ConstantInfo) int {
return cmp.Compare(a.Name, b.Name)
})
return infos
}
// ClearConstants removes all constants and reloads the built-in defaults.
// Note: This resets all constants, including any user-defined ones.
func (c *Constants) ClearConstants() {
c.mu.Lock()
defer c.mu.Unlock()
clear(c.constants)
c.loadBuiltInConstants()
}
// ReloadBuiltInConstants restores all built-in constants to their default values.
// It also removes any user-defined constants, effectively resetting the store.
func (c *Constants) ReloadBuiltInConstants() {
c.mu.Lock()
defer c.mu.Unlock()
builtIns := c.loadBuiltInConstants()
maps.DeleteFunc(c.constants, func(k string, _ float64) bool {
_, ok := builtIns[k]
return !ok
})
}
// Count returns the number of defined constants.
func (c *Constants) Count() int {
c.mu.RLock()
defer c.mu.RUnlock()
return len(c.constants)
}
// HasConstant checks if a constant exists.
func (c *Constants) HasConstant(name string) bool {
c.mu.RLock()
defer c.mu.RUnlock()
_, exists := c.constants[name]
return exists
}
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