package configs

import (
	"fmt"

	"github.com/hashicorp/hcl2/gohcl"
	"github.com/hashicorp/hcl2/hcl"
	"github.com/hashicorp/hcl2/hcl/hclsyntax"
	"github.com/zclconf/go-cty/cty"
)

// A consistent detail message for all "not a valid identifier" diagnostics.
const badIdentifierDetail = "A name must start with a letter and may contain only letters, digits, underscores, and dashes."

// Variable represents a "variable" block in a module or file.
type Variable struct {
	Name        string
	Description string
	Default     cty.Value
	TypeHint    VariableTypeHint

	DescriptionSet bool

	DeclRange hcl.Range
}

func decodeVariableBlock(block *hcl.Block) (*Variable, hcl.Diagnostics) {
	v := &Variable{
		Name:      block.Labels[0],
		DeclRange: block.DefRange,
	}

	content, diags := block.Body.Content(variableBlockSchema)

	if !hclsyntax.ValidIdentifier(v.Name) {
		diags = append(diags, &hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  "Invalid variable name",
			Detail:   badIdentifierDetail,
			Subject:  &block.LabelRanges[0],
		})
	}

	// Don't allow declaration of variables that would conflict with the
	// reserved attribute and block type names in a "module" block, since
	// these won't be usable for child modules.
	for _, attr := range moduleBlockSchema.Attributes {
		if attr.Name == v.Name {
			diags = append(diags, &hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid variable name",
				Detail:   fmt.Sprintf("The variable name %q is reserved due to its special meaning inside module blocks.", attr.Name),
				Subject:  &block.LabelRanges[0],
			})
		}
	}

	if attr, exists := content.Attributes["description"]; exists {
		valDiags := gohcl.DecodeExpression(attr.Expr, nil, &v.Description)
		diags = append(diags, valDiags...)
		v.DescriptionSet = true
	}

	if attr, exists := content.Attributes["default"]; exists {
		val, valDiags := attr.Expr.Value(nil)
		diags = append(diags, valDiags...)
		v.Default = val
	}

	if attr, exists := content.Attributes["type"]; exists {
		expr, shimDiags := shimTraversalInString(attr.Expr, true)
		diags = append(diags, shimDiags...)

		switch hcl.ExprAsKeyword(expr) {
		case "string":
			v.TypeHint = TypeHintString
		case "list":
			v.TypeHint = TypeHintList
		case "map":
			v.TypeHint = TypeHintMap
		default:
			diags = append(diags, &hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid variable type hint",
				Detail:   "The type argument requires one of the following keywords: string, list, or map.",
				Subject:  expr.Range().Ptr(),
			})
		}
	}

	return v, diags
}

// Output represents an "output" block in a module or file.
type Output struct {
	Name        string
	Description string
	Expr        hcl.Expression
	DependsOn   []hcl.Traversal
	Sensitive   bool

	DescriptionSet bool
	SensitiveSet   bool

	DeclRange hcl.Range
}

func decodeOutputBlock(block *hcl.Block, override bool) (*Output, hcl.Diagnostics) {
	o := &Output{
		Name:      block.Labels[0],
		DeclRange: block.DefRange,
	}

	schema := outputBlockSchema
	if override {
		schema = schemaForOverrides(schema)
	}

	content, diags := block.Body.Content(schema)

	if !hclsyntax.ValidIdentifier(o.Name) {
		diags = append(diags, &hcl.Diagnostic{
			Severity: hcl.DiagError,
			Summary:  "Invalid output name",
			Detail:   badIdentifierDetail,
			Subject:  &block.LabelRanges[0],
		})
	}

	if attr, exists := content.Attributes["description"]; exists {
		valDiags := gohcl.DecodeExpression(attr.Expr, nil, &o.Description)
		diags = append(diags, valDiags...)
		o.DescriptionSet = true
	}

	if attr, exists := content.Attributes["value"]; exists {
		o.Expr = attr.Expr
	}

	if attr, exists := content.Attributes["sensitive"]; exists {
		valDiags := gohcl.DecodeExpression(attr.Expr, nil, &o.Sensitive)
		diags = append(diags, valDiags...)
		o.SensitiveSet = true
	}

	if attr, exists := content.Attributes["depends_on"]; exists {
		deps, depsDiags := decodeDependsOn(attr)
		diags = append(diags, depsDiags...)
		o.DependsOn = append(o.DependsOn, deps...)
	}

	return o, diags
}

// Local represents a single entry from a "locals" block in a module or file.
// The "locals" block itself is not represented, because it serves only to
// provide context for us to interpret its contents.
type Local struct {
	Name string
	Expr hcl.Expression

	DeclRange hcl.Range
}

func decodeLocalsBlock(block *hcl.Block) ([]*Local, hcl.Diagnostics) {
	attrs, diags := block.Body.JustAttributes()
	if len(attrs) == 0 {
		return nil, diags
	}

	locals := make([]*Local, 0, len(attrs))
	for name, attr := range attrs {
		if !hclsyntax.ValidIdentifier(name) {
			diags = append(diags, &hcl.Diagnostic{
				Severity: hcl.DiagError,
				Summary:  "Invalid local value name",
				Detail:   badIdentifierDetail,
				Subject:  &attr.NameRange,
			})
		}

		locals = append(locals, &Local{
			Name:      name,
			Expr:      attr.Expr,
			DeclRange: attr.Range,
		})
	}
	return locals, diags
}

var variableBlockSchema = &hcl.BodySchema{
	Attributes: []hcl.AttributeSchema{
		{
			Name: "description",
		},
		{
			Name: "default",
		},
		{
			Name: "type",
		},
	},
}

var outputBlockSchema = &hcl.BodySchema{
	Attributes: []hcl.AttributeSchema{
		{
			Name: "description",
		},
		{
			Name:     "value",
			Required: true,
		},
		{
			Name: "depends_on",
		},
		{
			Name: "sensitive",
		},
	},
}