// Package render templates the contents of manifests pulled from pallets and
// defines the total set of valid template variables.
package render

import (
	"fmt"
	"io"

	envsubst "github.com/drone/envsubst/v2"

	"edge-infra.dev/pkg/f8n/warehouse/lift"
	"edge-infra.dev/pkg/lib/uuid"
)

// Render inflates rendering rendering parameters into bytes read from Reader r
// and returns the result.
//
// Parameters are applied right to left, latest wins in the case of conflicting
// key values across maps. Maps can only contain keys present in Parameters
func Render(r io.Reader, palletParams []string, params ...map[string]string) ([]byte, error) {
	// merge the params slice into one. the params slice includes
	// params from the warehouse.yaml and the other rendering params
	// like cluster-provider and pallet-name
	totalParams := make(map[string]string, 0)
	for _, singleParams := range params {
		for key, val := range singleParams {
			totalParams[key] = val
		}
	}
	handled, err := HandleParams(palletParams, totalParams)
	if err != nil {
		return nil, err
	}
	data, err := io.ReadAll(r)
	if err != nil {
		return nil, fmt.Errorf("failed to read manifest data: %w", err)
	}

	out, err := envsubst.Eval(string(data), func(s string) string {
		return handled[s]
	})
	return []byte(out), err
}

func HandleParams(palletParams []string, params map[string]string) (map[string]string, error) {
	var missingParams []string
	for _, necessaryParam := range palletParams {
		switch {
		case necessaryParam == lift.ClusterUUIDRenderingParameter:
			id := uuid.FromUUID(params[lift.ClusterUUIDRenderingParameter])
			if params[lift.ClusterHashRenderingParameter] != "" &&
				params[lift.ClusterHashRenderingParameter] != id.Hash() {
				return nil, fmt.Errorf("rendering parameter %s cannot be manually set",
					lift.ClusterHashRenderingParameter)
			}
			if params[lift.ClusterUUIDRenderingParameter] != "" {
				params[lift.ClusterHashRenderingParameter] = id.Hash()
			}
		}
		if val, ok := params[necessaryParam]; ok {
			if val == "" {
				missingParams = append(missingParams, necessaryParam)
			}
		}
	}
	if len(missingParams) != 0 {
		return nil, fmt.Errorf("missing parameters %s", missingParams)
	}
	return params, nil
}