package main

import (
	"fmt"
	"strings"
)

// in Go it’s common to provide collection functions if and when they are specifically needed for your program and data types

// Index returns the first index of the target string t, or -1 if no match is found
func Index(vs []string, t string) int {
	for i, v := range vs {
		if v == t {
			return i
		}
	}
	return -1
}

// Include returns true if the target string t is in the slice
func Include(vs []string, t string) bool {
	return Index(vs, t) >= 0
}

// Any returns true if one of the strings in the slice satisfies the predicate f
func Any(vs []string, f func(string) bool) bool {
	for _, v := range vs {
		if f(v) {
			return true
		}
	}
	return false
}

// All returns true if all of the strings in the slice satisfy the predicate f
func All(vs []string, f func(string) bool) bool {
	for _, v := range vs {
		if !f(v) {
			return false
		}
	}
	return true
}

// Filter returns a new slice containing all strings in the slice that satisfy the predicate f
func Filter(vs []string, f func(string) bool) []string {
	vsf := make([]string, 0)
	for _, v := range vs {
		if f(v) {
			vsf = append(vsf, v)
		}
	}
	return vsf
}

// Map returns a new slice containing the results of applying the function f to each string in the original slice
func Map(vs []string, f func(string) string) []string {
	vsm := make([]string, len(vs))
	for i, v := range vs {
		vsm[i] = f(v)
	}
	return vsm
}

func main() {
	// try out various collection functions
	var strs = []string{"peach", "apple", "pear", "plum"}

	fmt.Println(Index(strs, "pear"))

	fmt.Println(Include(strs, "grape"))

	fmt.Println(Any(strs, func(v string) bool {
		return strings.HasPrefix(v, "p")
	}))

	fmt.Println(All(strs, func(v string) bool {
		return strings.HasPrefix(v, "p")
	}))

	fmt.Println(Filter(strs, func(v string) bool {
		return strings.Contains(v, "e")
	}))

	fmt.Println(Map(strs, strings.ToUpper))

}
