package terraform

import (
	"fmt"

	"github.com/hashicorp/hcl/v2"
	"github.com/hashicorp/terraform/internal/lang"
	"github.com/hashicorp/terraform/internal/lang/marks"
	"github.com/hashicorp/terraform/internal/tfdiags"
	"github.com/zclconf/go-cty/cty"
)

// evaluateForEachExpression is our standard mechanism for interpreting an
// expression given for a "for_each" argument on a resource or a module. This
// should be called during expansion in order to determine the final keys and
// values.
//
// evaluateForEachExpression differs from evaluateForEachExpressionValue by
// returning an error if the count value is not known, and converting the
// cty.Value to a map[string]cty.Value for compatibility with other calls.
func evaluateForEachExpression(expr hcl.Expression, ctx EvalContext) (forEach map[string]cty.Value, diags tfdiags.Diagnostics) {
	forEachVal, diags := evaluateForEachExpressionValue(expr, ctx, false)
	// forEachVal might be unknown, but if it is then there should already
	// be an error about it in diags, which we'll return below.

	if forEachVal.IsNull() || !forEachVal.IsKnown() || markSafeLengthInt(forEachVal) == 0 {
		// we check length, because an empty set return a nil map
		return map[string]cty.Value{}, diags
	}

	return forEachVal.AsValueMap(), diags
}

// evaluateForEachExpressionValue is like evaluateForEachExpression
// except that it returns a cty.Value map or set which can be unknown.
func evaluateForEachExpressionValue(expr hcl.Expression, ctx EvalContext, allowUnknown bool) (cty.Value, tfdiags.Diagnostics) {
	var diags tfdiags.Diagnostics
	nullMap := cty.NullVal(cty.Map(cty.DynamicPseudoType))

	if expr == nil {
		return nullMap, diags
	}

	refs, moreDiags := lang.ReferencesInExpr(expr)
	diags = diags.Append(moreDiags)
	scope := ctx.EvaluationScope(nil, EvalDataForNoInstanceKey)
	var hclCtx *hcl.EvalContext
	if scope != nil {
		hclCtx, moreDiags = scope.EvalContext(refs)
	} else {
		// This shouldn't happen in real code, but it can unfortunately arise
		// in unit tests due to incompletely-implemented mocks. :(
		hclCtx = &hcl.EvalContext{}
	}
	diags = diags.Append(moreDiags)
	if diags.HasErrors() { // Can't continue if we don't even have a valid scope
		return nullMap, diags
	}

	forEachVal, forEachDiags := expr.Value(hclCtx)
	diags = diags.Append(forEachDiags)

	// If a whole map is marked, or a set contains marked values (which means the set is then marked)
	// give an error diagnostic as this value cannot be used in for_each
	if forEachVal.HasMark(marks.Sensitive) {
		diags = diags.Append(&hcl.Diagnostic{
			Severity:    hcl.DiagError,
			Summary:     "Invalid for_each argument",
			Detail:      "Sensitive values, or values derived from sensitive values, cannot be used as for_each arguments. If used, the sensitive value could be exposed as a resource instance key.",
			Subject:     expr.Range().Ptr(),
			Expression:  expr,
			EvalContext: hclCtx,
		})
	}

	if diags.HasErrors() {
		return nullMap, diags
	}
	ty := forEachVal.Type()

	const errInvalidUnknownDetailMap = "The \"for_each\" map includes keys derived from resource attributes that cannot be determined until apply, and so Terraform cannot determine the full set of keys that will identify the instances of this resource.\n\nWhen working with unknown values in for_each, it's better to define the map keys statically in your configuration and place apply-time results only in the map values.\n\nAlternatively, you could use the -target planning option to first apply only the resources that the for_each value depends on, and then apply a second time to fully converge."
	const errInvalidUnknownDetailSet = "The \"for_each\" set includes values derived from resource attributes that cannot be determined until apply, and so Terraform cannot determine the full set of keys that will identify the instances of this resource.\n\nWhen working with unknown values in for_each, it's better to use a map value where the keys are defined statically in your configuration and where only the values contain apply-time results.\n\nAlternatively, you could use the -target planning option to first apply only the resources that the for_each value depends on, and then apply a second time to fully converge."

	switch {
	case forEachVal.IsNull():
		diags = diags.Append(&hcl.Diagnostic{
			Severity:    hcl.DiagError,
			Summary:     "Invalid for_each argument",
			Detail:      `The given "for_each" argument value is unsuitable: the given "for_each" argument value is null. A map, or set of strings is allowed.`,
			Subject:     expr.Range().Ptr(),
			Expression:  expr,
			EvalContext: hclCtx,
		})
		return nullMap, diags
	case !forEachVal.IsKnown():
		if !allowUnknown {
			var detailMsg string
			switch {
			case ty.IsSetType():
				detailMsg = errInvalidUnknownDetailSet
			default:
				detailMsg = errInvalidUnknownDetailMap
			}

			diags = diags.Append(&hcl.Diagnostic{
				Severity:    hcl.DiagError,
				Summary:     "Invalid for_each argument",
				Detail:      detailMsg,
				Subject:     expr.Range().Ptr(),
				Expression:  expr,
				EvalContext: hclCtx,
			})
		}
		// ensure that we have a map, and not a DynamicValue
		return cty.UnknownVal(cty.Map(cty.DynamicPseudoType)), diags

	case !(ty.IsMapType() || ty.IsSetType() || ty.IsObjectType()):
		diags = diags.Append(&hcl.Diagnostic{
			Severity:    hcl.DiagError,
			Summary:     "Invalid for_each argument",
			Detail:      fmt.Sprintf(`The given "for_each" argument value is unsuitable: the "for_each" argument must be a map, or set of strings, and you have provided a value of type %s.`, ty.FriendlyName()),
			Subject:     expr.Range().Ptr(),
			Expression:  expr,
			EvalContext: hclCtx,
		})
		return nullMap, diags

	case markSafeLengthInt(forEachVal) == 0:
		// If the map is empty ({}), return an empty map, because cty will
		// return nil when representing {} AsValueMap. This also covers an empty
		// set (toset([]))
		return forEachVal, diags
	}

	if ty.IsSetType() {
		// since we can't use a set values that are unknown, we treat the
		// entire set as unknown
		if !forEachVal.IsWhollyKnown() {
			if !allowUnknown {
				diags = diags.Append(&hcl.Diagnostic{
					Severity:    hcl.DiagError,
					Summary:     "Invalid for_each argument",
					Detail:      errInvalidUnknownDetailSet,
					Subject:     expr.Range().Ptr(),
					Expression:  expr,
					EvalContext: hclCtx,
				})
			}
			return cty.UnknownVal(ty), diags
		}

		if ty.ElementType() != cty.String {
			diags = diags.Append(&hcl.Diagnostic{
				Severity:    hcl.DiagError,
				Summary:     "Invalid for_each set argument",
				Detail:      fmt.Sprintf(`The given "for_each" argument value is unsuitable: "for_each" supports maps and sets of strings, but you have provided a set containing type %s.`, forEachVal.Type().ElementType().FriendlyName()),
				Subject:     expr.Range().Ptr(),
				Expression:  expr,
				EvalContext: hclCtx,
			})
			return cty.NullVal(ty), diags
		}

		// A set of strings may contain null, which makes it impossible to
		// convert to a map, so we must return an error
		it := forEachVal.ElementIterator()
		for it.Next() {
			item, _ := it.Element()
			if item.IsNull() {
				diags = diags.Append(&hcl.Diagnostic{
					Severity:    hcl.DiagError,
					Summary:     "Invalid for_each set argument",
					Detail:      `The given "for_each" argument value is unsuitable: "for_each" sets must not contain null values.`,
					Subject:     expr.Range().Ptr(),
					Expression:  expr,
					EvalContext: hclCtx,
				})
				return cty.NullVal(ty), diags
			}
		}
	}

	return forEachVal, nil
}

// markSafeLengthInt allows calling LengthInt on marked values safely
func markSafeLengthInt(val cty.Value) int {
	v, _ := val.UnmarkDeep()
	return v.LengthInt()
}