// Taken and adapted from the stdlib text/template/funcs.go.
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package texttemplate

import (
	"fmt"
	"math"
	"reflect"
)

// indexArg checks if a reflect.Value can be used as an index, and converts it to int if possible.
//
//nolint:revive
func indexArg(index reflect.Value, cap int) (int, error) {
	var x int64
	switch index.Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		x = index.Int()
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		val := index.Uint()
		if val > math.MaxInt64 {
			return -1, fmt.Errorf("index too large: %d", val)
		}

		x = int64(val)
	case reflect.Invalid:
		return 0, fmt.Errorf("cannot index slice/array with nil")
	default:
		return 0, fmt.Errorf("cannot index slice/array with type %s", index.Type())
	}
	if x < 0 || int(x) < 0 || int(x) > cap {
		return 0, fmt.Errorf("index out of range: %d", x)
	}
	return int(x), nil
}

// Slicing.

// slice returns the result of slicing its first argument by the remaining
// arguments. Thus "slice x 1 2" is, in Go syntax, x[1:2], while "slice x"
// is x[:], "slice x 1" is x[1:], and "slice x 1 2 3" is x[1:2:3]. The first
// argument must be a string, slice, or array.
func GoSlice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
	item = indirectInterface(item)
	if !item.IsValid() {
		return reflect.Value{}, fmt.Errorf("slice of untyped nil")
	}
	if len(indexes) > 3 {
		return reflect.Value{}, fmt.Errorf("too many slice indexes: %d", len(indexes))
	}
	var capacity int
	switch item.Kind() {
	case reflect.String:
		if len(indexes) == 3 {
			return reflect.Value{}, fmt.Errorf("cannot 3-index slice a string")
		}
		capacity = item.Len()
	case reflect.Array, reflect.Slice:
		capacity = item.Cap()
	default:
		return reflect.Value{}, fmt.Errorf("can't slice item of type %s", item.Type())
	}
	// set default values for cases item[:], item[i:].
	idx := [3]int{0, item.Len()}
	for i, index := range indexes {
		x, err := indexArg(index, capacity)
		if err != nil {
			return reflect.Value{}, err
		}
		idx[i] = x
	}
	// given item[i:j], make sure i <= j.
	if idx[0] > idx[1] {
		return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[0], idx[1])
	}
	if len(indexes) < 3 {
		return item.Slice(idx[0], idx[1]), nil
	}
	// given item[i:j:k], make sure i <= j <= k.
	if idx[1] > idx[2] {
		return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[1], idx[2])
	}
	return item.Slice3(idx[0], idx[1], idx[2]), nil
}