// FIXME(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
//go:build go1.26

package templates

import (
	"bytes"
	"encoding/json"
	"fmt"
	"reflect"
	"slices"
	"strings"
	"text/template"
)

// basicFunctions are the set of initial
// functions provided to every template.
var basicFunctions = template.FuncMap{
	"json":     formatJSON,
	"split":    strings.Split,
	"join":     joinElements,
	"title":    strings.Title, //nolint:nolintlint,staticcheck // strings.Title is deprecated, but we only use it for ASCII, so replacing with golang.org/x/text is out of scope
	"lower":    strings.ToLower,
	"upper":    strings.ToUpper,
	"pad":      padWithSpace,
	"truncate": truncateWithLength,
}

// HeaderFunctions are used to created headers of a table.
// This is a replacement of basicFunctions for header generation
// because we want the header to remain intact.
// Some functions like `pad` are not overridden (to preserve alignment
// with the columns).
var HeaderFunctions = template.FuncMap{
	"json": func(v string) string {
		return v
	},
	"split": func(v string, _ string) string {
		// we want the table header to show the name of the column, and not
		// split the table header itself. Using a different signature
		// here, and return a string instead of []string
		return v
	},
	"join": func(v string, _ string) string {
		// table headers are always a string, so use a different signature
		// for the "join" function (string instead of []string)
		return v
	},
	"title": func(v string) string {
		return v
	},
	"lower": func(v string) string {
		return v
	},
	"upper": func(v string) string {
		return v
	},
	"truncate": func(v string, _ int) string {
		return v
	},
}

// Parse creates a new anonymous template with the basic functions
// and parses the given format.
func Parse(format string) (*template.Template, error) {
	return template.New("").Funcs(basicFunctions).Parse(format)
}

// New creates a new empty template with the provided tag and built-in
// template functions.
func New(tag string) *template.Template {
	return template.New(tag).Funcs(basicFunctions)
}

// padWithSpace adds whitespace to the input if the input is non-empty
func padWithSpace(source string, prefix, suffix int) string {
	if source == "" {
		return source
	}
	return strings.Repeat(" ", prefix) + source + strings.Repeat(" ", suffix)
}

// truncateWithLength truncates the source string up to the length provided by the input
func truncateWithLength(source string, length int) string {
	if len(source) < length {
		return source
	}
	return source[:length]
}

func formatJSON(v any) string {
	buf := &bytes.Buffer{}
	enc := json.NewEncoder(buf)
	enc.SetEscapeHTML(false)
	err := enc.Encode(v)
	if err != nil {
		panic(err)
	}

	// Remove the trailing new line added by the encoder
	return strings.TrimSpace(buf.String())
}

// joinElements joins a slice of items with the given separator. It uses
// [strings.Join] if it's a slice of strings, otherwise uses [fmt.Sprint]
// to join each item to the output.
func joinElements(elems any, sep string) (string, error) {
	if elems == nil {
		return "", nil
	}

	if ss, ok := elems.([]string); ok {
		return strings.Join(ss, sep), nil
	}

	switch rv := reflect.ValueOf(elems); rv.Kind() { //nolint:exhaustive // ignore: too many options to make exhaustive
	case reflect.Array, reflect.Slice:
		var b strings.Builder
		for i := range rv.Len() {
			if i > 0 {
				b.WriteString(sep)
			}
			_, _ = fmt.Fprint(&b, rv.Index(i).Interface())
		}
		return b.String(), nil

	case reflect.Map:
		out := make([]string, 0, rv.Len())
		for _, k := range rv.MapKeys() {
			out = append(out, fmt.Sprint(rv.MapIndex(k).Interface()))
		}
		// Not ideal, but trying to keep a consistent order
		slices.Sort(out)
		return strings.Join(out, sep), nil

	default:
		return "", fmt.Errorf("expected slice, got %T", elems)
	}
}