package engine

import (
	"path"
	"strings"

	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
)

const directiveKey = "configkit"

type rootDirectiveContext uint8

const (
	rootDirectiveContextImportsOnly rootDirectiveContext = iota + 1
	rootDirectiveContextSource
	rootDirectiveContextOverlay
	rootDirectiveContextLayered
)

type rootDirectiveExtraction struct {
	body             *document.Node
	imports          []importDeclarationSpec
	sequences        []sequenceDeclarationSpec
	importsPresent   bool
	sequencesPresent bool
}

func splitImportDirectives(root *document.Node) (*document.Node, []importDeclarationSpec, []Diagnostic) {
	extracted, diagnostics := extractRootDirectives(root, rootDirectiveContextImportsOnly)
	if len(diagnostics) != 0 {
		return nil, nil, diagnostics
	}
	return extracted.body, extracted.imports, nil
}

func extractRootDirectives(root *document.Node, context rootDirectiveContext) (rootDirectiveExtraction, []Diagnostic) {
	if root == nil {
		return rootDirectiveExtraction{}, nil
	}
	body := document.Clone(root)
	directiveIndex := -1
	for index, entry := range body.Mapping {
		if entry.Key != directiveKey {
			continue
		}
		directiveIndex = index
		extracted, diagnostics := parseRootDirectiveBlock(entry.Value, Keys(directiveKey), context)
		if len(diagnostics) != 0 {
			return rootDirectiveExtraction{}, diagnostics
		}
		extracted.body = body
		if directiveIndex >= 0 {
			extracted.body.Mapping = append(extracted.body.Mapping[:directiveIndex], extracted.body.Mapping[directiveIndex+1:]...)
		}
		if diagnostics := nestedDirectiveDiagnostics(extracted.body, Path{}); len(diagnostics) != 0 {
			return rootDirectiveExtraction{}, diagnostics
		}
		return extracted, nil
	}
	if diagnostics := nestedDirectiveDiagnostics(body, Path{}); len(diagnostics) != 0 {
		return rootDirectiveExtraction{}, diagnostics
	}
	return rootDirectiveExtraction{body: body}, nil
}

func parseRootDirectiveBlock(node *document.Node, directivePath Path, context rootDirectiveContext) (rootDirectiveExtraction, []Diagnostic) {
	if node == nil || node.Kind != document.Mapping {
		return rootDirectiveExtraction{}, []Diagnostic{nodeImportDiagnostic(CodeImportInvalid, directivePath, "configuration directive must be a mapping", node)}
	}
	var extracted rootDirectiveExtraction
	var diagnostics []Diagnostic
	for _, entry := range node.Mapping {
		fieldPath := directivePath.Key(entry.Key)
		switch entry.Key {
		case "imports":
			extracted.importsPresent = true
			if context == rootDirectiveContextOverlay {
				diagnostics = append(diagnostics, nodeImportDiagnostic(CodeOverlayDirective, fieldPath, "overlays cannot contain imports", entry.Value))
				continue
			}
			if context != rootDirectiveContextImportsOnly && context != rootDirectiveContextSource && context != rootDirectiveContextLayered {
				diagnostics = append(diagnostics, nodeImportDiagnostic(CodeImportInvalid, fieldPath, "directive extraction context is invalid", entry.Value))
				continue
			}
			parsed, issues := parseImportDeclarations(entry.Value, fieldPath)
			extracted.imports = append(extracted.imports, parsed...)
			diagnostics = append(diagnostics, issues...)
		case "sequences":
			extracted.sequencesPresent = true
			if context == rootDirectiveContextImportsOnly {
				diagnostics = append(diagnostics, sequenceDeclarationDiagnostic(fieldPath, "sequence declarations are not enabled in this extraction context", entry.Value))
				continue
			}
			if context != rootDirectiveContextSource && context != rootDirectiveContextOverlay && context != rootDirectiveContextLayered {
				diagnostics = append(diagnostics, sequenceDeclarationDiagnostic(fieldPath, "directive extraction context is invalid", entry.Value))
				continue
			}
			parsed, issues := parseSequenceDeclarationDirective(entry.Value, fieldPath)
			extracted.sequences = append(extracted.sequences, parsed...)
			diagnostics = append(diagnostics, issues...)
		default:
			diagnostics = append(diagnostics, nodeImportDiagnostic(CodeImportInvalid, fieldPath, "configuration directive field is not recognized", entry.Value))
		}
	}
	if len(diagnostics) != 0 {
		return rootDirectiveExtraction{}, canonicalDiagnostics(diagnostics)
	}
	return extracted, nil
}

func nestedDirectiveDiagnostics(node *document.Node, current Path) []Diagnostic {
	if node.Kind == document.Mapping {
		for _, entry := range node.Mapping {
			childPath := current.Key(entry.Key)
			if entry.Key == directiveKey {
				location := publicLocation(entry.KeyLocation)
				return []Diagnostic{{Code: CodeImportInvalid, Severity: SeverityError, Path: childPath, Message: "configuration directives are permitted only at the document root", Primary: &location}}
			}
			if diagnostics := nestedDirectiveDiagnostics(entry.Value, childPath); len(diagnostics) != 0 {
				return diagnostics
			}
		}
	} else if node.Kind == document.Sequence {
		for index, child := range node.Sequence {
			if diagnostics := nestedDirectiveDiagnostics(child, current.Index(index)); len(diagnostics) != 0 {
				return diagnostics
			}
		}
	}
	return nil
}

func fragmentVersionClaim(root *document.Node, rule *VersionRule) *document.Node {
	return fragmentVersionClaimProjected(root, rule, -1, nil)
}

func fragmentVersionClaimProjected(root *document.Node, rule *VersionRule, sourceIndex int, ranges []sequenceRange) *document.Node {
	return fragmentVersionClaimWithIndex(root, rule, sourceIndex, indexSequenceRanges(ranges))
}

func fragmentVersionClaimWithIndex(root *document.Node, rule *VersionRule, sourceIndex int, ranges sequenceRangeIndex) *document.Node {
	if rule == nil {
		return nil
	}
	current := root
	currentPath := Path{}
	if len(rule.Path.segments) == 0 {
		return current
	}
	for _, segment := range rule.Path.segments {
		switch current.Kind {
		case document.Mapping:
			if segment.kind == pathSegmentIndex {
				return current
			}
			index := documentEntryIndex(current.Mapping, segment.key)
			if index < 0 {
				return nil
			}
			current = current.Mapping[index].Value
			currentPath = currentPath.Key(segment.key)
		case document.Sequence:
			index, valid := schemaIndex(segment)
			if !valid {
				return current
			}
			if assigned, found := ranges[sequenceRangeKey{sourceIndex: sourceIndex, path: currentPath.String()}]; found {
				projected, ok := assigned.inputForOutput(index)
				if !ok {
					return nil
				}
				index = projected
			}
			if index < 0 || index >= len(current.Sequence) {
				return nil
			}
			current = current.Sequence[index]
			currentPath = currentPath.Index(index)
		default:
			// A scalar or null at an ancestor replaces the protected subtree.
			return current
		}
	}
	return current
}

func validImportPath(value string) bool {
	if value == "" || strings.TrimSpace(value) != value || path.IsAbs(value) || strings.HasPrefix(value, "//") {
		return false
	}
	return !hasImportScheme(value)
}

func hasImportScheme(value string) bool {
	colon := strings.IndexByte(value, ':')
	slash := strings.IndexByte(value, '/')
	if colon <= 0 || (slash >= 0 && slash < colon) {
		return false
	}
	for index := 0; index < colon; index++ {
		character := value[index]
		if index == 0 {
			if (character < 'a' || character > 'z') && (character < 'A' || character > 'Z') {
				return false
			}
			continue
		}
		if (character < 'a' || character > 'z') && (character < 'A' || character > 'Z') &&
			(character < '0' || character > '9') && character != '+' && character != '-' && character != '.' {
			return false
		}
	}
	return true
}

func nodeImportDiagnostic(code Code, path Path, message string, node *document.Node) Diagnostic {
	location := publicLocation(node.Location)
	return Diagnostic{Code: code, Severity: SeverityError, Path: path, Message: message, Primary: &location}
}

func overlayDirectiveDiagnostics(node *document.Node, current Path, allowSequences ...bool) []Diagnostic {
	sequencesAllowed := len(allowSequences) != 0 && allowSequences[0]
	if node.Kind == document.Mapping {
		for _, entry := range node.Mapping {
			childPath := current.Key(entry.Key)
			if entry.Key == directiveKey {
				if sequencesAllowed && len(current.segments) == 0 && entry.Value != nil && entry.Value.Kind == document.Mapping && len(entry.Value.Mapping) == 1 && entry.Value.Mapping[0].Key == "sequences" {
					continue
				}
				location := publicLocation(entry.KeyLocation)
				return []Diagnostic{{
					Code: CodeOverlayDirective, Severity: SeverityError, Path: childPath,
					Message: "overlays may contain only root collection sequence declarations", Primary: &location,
				}}
			}
			if diagnostics := overlayDirectiveDiagnostics(entry.Value, childPath, sequencesAllowed); len(diagnostics) != 0 {
				return diagnostics
			}
		}
	} else if node.Kind == document.Sequence {
		for index, child := range node.Sequence {
			if diagnostics := overlayDirectiveDiagnostics(child, current.Index(index), sequencesAllowed); len(diagnostics) != 0 {
				return diagnostics
			}
		}
	}
	return nil
}

func disabledDirectiveDiagnostics(node *document.Node, path Path) []Diagnostic {
	var diagnostics []Diagnostic
	if node.Kind == document.Mapping {
		for _, entry := range node.Mapping {
			childPath := path.Key(entry.Key)
			if entry.Key == directiveKey {
				location := Location{SourceID: entry.KeyLocation.SourceID, Line: entry.KeyLocation.Line, Column: entry.KeyLocation.Column}
				diagnostics = append(diagnostics, Diagnostic{
					Code: CodeImportDisabled, Severity: SeverityError, Path: childPath,
					Message: "configuration directives require imports to be enabled", Primary: &location,
				})
			}
			diagnostics = append(diagnostics, disabledDirectiveDiagnostics(entry.Value, childPath)...)
		}
	} else if node.Kind == document.Sequence {
		for index, child := range node.Sequence {
			diagnostics = append(diagnostics, disabledDirectiveDiagnostics(child, path.Index(index))...)
		}
	}
	return diagnostics
}

func disabledRootImportDiagnostics(node *document.Node) []Diagnostic {
	if node == nil || node.Kind != document.Mapping {
		return nil
	}
	var rootDirective *document.Node
	var rootLocation document.Location
	var foundRootDirective bool
	for index := range node.Mapping {
		if node.Mapping[index].Key == directiveKey {
			rootDirective = node.Mapping[index].Value
			rootLocation = node.Mapping[index].KeyLocation
			foundRootDirective = true
			break
		}
	}
	if foundRootDirective {
		if rootDirective == nil || rootDirective.Kind != document.Mapping {
			return disabledDirectiveDiagnostic(rootLocation)
		}
		for _, directive := range rootDirective.Mapping {
			if directive.Key == "imports" {
				return disabledDirectiveDiagnostic(rootLocation)
			}
		}
	}
	for _, entry := range node.Mapping {
		if entry.Key == directiveKey {
			continue
		}
		if diagnostic := disabledNestedDirectiveDiagnostics(entry.Value, Path{}.Key(entry.Key)); len(diagnostic) != 0 {
			return diagnostic
		}
	}
	return nil
}

func disabledNestedDirectiveDiagnostics(node *document.Node, path Path) []Diagnostic {
	if node.Kind == document.Mapping {
		for _, entry := range node.Mapping {
			childPath := path.Key(entry.Key)
			if entry.Key == directiveKey {
				location := Location{SourceID: entry.KeyLocation.SourceID, Line: entry.KeyLocation.Line, Column: entry.KeyLocation.Column}
				return []Diagnostic{{
					Code: CodeImportDisabled, Severity: SeverityError, Path: childPath,
					Message: "configuration directives require imports to be enabled", Primary: &location,
				}}
			}
			if diagnostics := disabledNestedDirectiveDiagnostics(entry.Value, childPath); len(diagnostics) != 0 {
				return diagnostics
			}
		}
	} else if node.Kind == document.Sequence {
		for index, child := range node.Sequence {
			if diagnostics := disabledNestedDirectiveDiagnostics(child, path.Index(index)); len(diagnostics) != 0 {
				return diagnostics
			}
		}
	}
	return nil
}

func disabledDirectiveDiagnostic(location document.Location) []Diagnostic {
	public := Location{SourceID: location.SourceID, Line: location.Line, Column: location.Column}
	return []Diagnostic{{
		Code: CodeImportDisabled, Severity: SeverityError, Path: Keys(directiveKey),
		Message: "configuration directives require imports to be enabled", Primary: &public,
	}}
}