package env

import (
	"errors"
	"fmt"
	"os"

	"github.com/zclconf/go-cty/cty"
	"github.com/zclconf/go-cty/cty/function"
)

var ErrNoEnvKeyProvided = errors.New("no environment lookup key provided")

func GetEnv() function.Function {
	const typeAndName = 2
	return function.New(&function.Spec{
		Description: "Get environment variables",
		Params: []function.Parameter{
			{
				Name:        "key",
				Description: "Environment variable key to lookup",
				Type:        cty.String,
			},
		},
		VarParam: &function.Parameter{
			Name:        "fallbackValue",
			Description: "if no matching environment variable is set the fallback will be returned",
			Type:        cty.String,
		},
		Type: function.StaticReturnType(cty.String),
		Impl: func(args []cty.Value, retType cty.Type) (cty.Value, error) {
			if len(args) < 1 {
				return cty.Value{}, ErrNoEnvKeyProvided
			}

			lookupKey := args[0].AsString()

			value, ok := os.LookupEnv(lookupKey)
			if !ok {
				if len(args) < typeAndName {
					return cty.Value{}, fmt.Errorf("no environment variable with given lookup key %s set", lookupKey)
				}
				return args[1], nil
			}

			return cty.StringVal(value), nil
		},
	})
}