package provider

import (
	"context"
	"fmt"

	"github.com/hashicorp/terraform-plugin-framework/path"
	"github.com/hashicorp/terraform-plugin-framework/resource"
	"github.com/hashicorp/terraform-plugin-framework/types"
)

// requiredWhen declares that `attribute` must hold a non-empty value whenever
// `discriminator` equals `value`, and must be absent otherwise.
//
// Terraform's schema language cannot express "required, but only for this
// variant", and Dokploy's Zod schemas accept every combination -- so without a
// provider-side check a nonsensical resource is created without complaint. The
// `dokploy_mount` case is the reason this exists: see mountConfigValidators.
type requiredWhen struct {
	discriminator path.Path
	value         string
	attribute     path.Path
	// rationale explains the consequence of getting it wrong, so the error
	// tells the practitioner why rather than only what.
	rationale string
}

var _ resource.ConfigValidator = &requiredWhen{}

func (v *requiredWhen) Description(ctx context.Context) string {
	return v.MarkdownDescription(ctx)
}

func (v *requiredWhen) MarkdownDescription(_ context.Context) string {
	return fmt.Sprintf("`%s` is required when `%s` is `%s`, and must not be set otherwise.",
		v.attribute, v.discriminator, v.value)
}

func (v *requiredWhen) ValidateResource(
	ctx context.Context,
	req resource.ValidateConfigRequest,
	resp *resource.ValidateConfigResponse,
) {
	var discriminator types.String
	resp.Diagnostics.Append(req.Config.GetAttribute(ctx, v.discriminator, &discriminator)...)
	if resp.Diagnostics.HasError() || discriminator.IsNull() || discriminator.IsUnknown() {
		return
	}

	var attribute types.String
	resp.Diagnostics.Append(req.Config.GetAttribute(ctx, v.attribute, &attribute)...)
	if resp.Diagnostics.HasError() || attribute.IsUnknown() {
		// An unknown value cannot be checked at plan time; it is resolved
		// during apply and Dokploy validates it there.
		return
	}

	matches := discriminator.ValueString() == v.value
	empty := attribute.IsNull() || attribute.ValueString() == ""

	switch {
	case matches && empty:
		detail := fmt.Sprintf("`%s` must be set to a non-empty value when `%s` is `%s`.",
			v.attribute, v.discriminator, v.value)
		if v.rationale != "" {
			detail += "\n\n" + v.rationale
		}
		resp.Diagnostics.AddAttributeError(v.attribute,
			fmt.Sprintf("Missing %s", v.attribute), detail)

	case !matches && !empty:
		resp.Diagnostics.AddAttributeError(v.attribute,
			fmt.Sprintf("Unexpected %s", v.attribute),
			fmt.Sprintf("`%s` only applies when `%s` is `%s`, but it is `%s`. "+
				"Dokploy ignores the value, so leaving it set hides a mistake.",
				v.attribute, v.discriminator, v.value, discriminator.ValueString()))
	}
}