gno.land/p/moul/dynreplacer/v0⧉

1// Package dynreplacer provides a simple template engine for handling dynamic2// content replacement. It is similar to strings.Replacer but with lazy3// execution of replacements, making it more optimization-friendly in several4// cases. While strings.Replacer requires all replacement values to be computed5// upfront, dynreplacer only executes the callback functions for placeholders6// that actually exist in the template, avoiding unnecessary computations.7//8// The package ensures efficient, non-recursive replacement of placeholders in a9// single pass. This lazy evaluation approach is particularly beneficial when:10// - Some replacement values are expensive to compute11// - Not all placeholders are guaranteed to be present in the template12// - Templates are reused with different content13//14// Example usage:15//16//	r := dynreplacer.New(17//	    dynreplacer.Pair{":name:", func() string { return "World" }},18//	    dynreplacer.Pair{":greeting:", func() string { return "Hello" }},19//	)20//	result := r.Replace("Hello :name:!") // Returns "Hello World!"21//22// The replacer caches computed values, so subsequent calls with the same23// placeholder will reuse the cached value instead of executing the callback24// again:25//26//	r := dynreplacer.New()27//	r.RegisterCallback(":expensive:", func() string { return "computed" })28//	r.Replace("Value1: :expensive:") // Computes the value29//	r.Replace("Value2: :expensive:") // Uses cached value30//	r.ClearCache()                   // Force re-computation on next use31package dynreplacer3233import (34	"strings"35)3637// Replacer manages dynamic placeholders, their associated functions, and cached38// values.39type Replacer struct {40	callbacks    map[string]func() string41	cachedValues map[string]string42}4344// Pair represents a placeholder and its callback function45type Pair struct {46	Placeholder string47	Callback    func() string48}4950// New creates a new Replacer instance with optional initial replacements.51// It accepts pairs where each pair consists of a placeholder string and52// its corresponding callback function.53//54// Example:55//56//	New(57//	    Pair{":name:", func() string { return "World" }},58//	    Pair{":greeting:", func() string { return "Hello" }},59//	)60func New(pairs ...Pair) *Replacer {61	r := &Replacer{62		callbacks:    make(map[string]func() string),63		cachedValues: make(map[string]string),64	}6566	for _, pair := range pairs {67		r.RegisterCallback(pair.Placeholder, pair.Callback)68	}6970	return r71}7273// RegisterCallback associates a placeholder with a function to generate its74// content.75func (r *Replacer) RegisterCallback(placeholder string, callback func() string) {76	r.callbacks[placeholder] = callback77}7879// Replace processes the given layout, replacing placeholders with cached or80// newly computed values.81func (r *Replacer) Replace(layout string) string {82	replacements := []string{}8384	// Check for placeholders and compute/retrieve values85	hasReplacements := false86	for placeholder, callback := range r.callbacks {87		if strings.Contains(layout, placeholder) {88			value, exists := r.cachedValues[placeholder]89			if !exists {90				value = callback()91				r.cachedValues[placeholder] = value92			}93			replacements = append(replacements, placeholder, value)94			hasReplacements = true95		}96	}9798	// If no replacements were found, return the original layout99	if !hasReplacements {100		return layout101	}102103	// Create a strings.Replacer with all computed replacements104	replacer := strings.NewReplacer(replacements...)105	return replacer.Replace(layout)106}107108// ClearCache clears all cached values, forcing re-computation on next Replace.109func (r *Replacer) ClearCache() {110	r.cachedValues = make(map[string]string)111}112