package engine

import (
	"strconv"
	"strings"
	"unicode"
	"unicode/utf8"

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

const maxOverrides = 1024

type preparedOverride struct {
	path   Path
	value  *document.Node
	source SourceInfo
	bytes  int64
	nodes  int
}

// preparedOverrideBatch owns all override values and synthetic source records
// needed to apply one CLI batch after its preparation checks succeed.
type preparedOverrideBatch struct {
	overrides []preparedOverride
	sources   []SourceInfo
}

type overridePreparationInput struct {
	root       *document.Node
	inputBytes int64
	inputNodes int
}

// preparePostStructuralOverrides snapshots CLI input for typed assignment after
// structural expansion, when inheritance directives can no longer be supplied.
func preparePostStructuralOverrides(base overridePreparationInput, sources []SourceInfo, overrides []Override, rule *VersionRule, limits importLimits) (preparedOverrideBatch, []Diagnostic) {
	return prepareOverrideBatch(base, sources, overrides, rule, limits)
}

func prepareOverrideBatch(base overridePreparationInput, sources []SourceInfo, overrides []Override, rule *VersionRule, limits importLimits) (preparedOverrideBatch, []Diagnostic) {
	if len(overrides) > maxOverrides || len(sources)+len(overrides) > limits.sources {
		return preparedOverrideBatch{sources: cloneSourceInfos(sources)}, []Diagnostic{{
			Code: CodeOverrideLimitExceeded, Severity: SeverityError,
			Message: "configuration overrides exceed the record or source-count limit",
		}}
	}

	var diagnostics []Diagnostic
	for index, override := range overrides {
		if !validOverrideLabel(override.Flag) {
			diagnostics = append(diagnostics, Diagnostic{
				Code: CodeOverrideInvalidLabel, Severity: SeverityError,
				Message: "override record " + strconv.Itoa(index+1) + " requires a safe nonempty flag name",
			})
		}
	}
	if len(diagnostics) != 0 {
		return preparedOverrideBatch{sources: cloneSourceInfos(sources)}, canonicalDiagnostics(diagnostics)
	}

	prepared := make([]preparedOverride, len(overrides))
	allSources := cloneSourceInfos(sources)
	for index, override := range overrides {
		sourceID := "source-" + strconv.Itoa(len(sources)+index+1)
		info := SourceInfo{ID: sourceID, Label: override.Flag, Layer: LayerCLI, Kind: SourceKindCLI}
		allSources = append(allSources, info)
		prepared[index].source = info
	}

	seen := make(map[string]int, len(overrides))
	var acceptedPaths pathPrefixIndex
	var baseLookup *documentLookup
	if len(overrides) != 0 {
		baseLookup = buildDocumentLookup(base.root)
	}
	var usedBytes int64
	usedNodes := 0
	for index, override := range overrides {
		location := &Location{SourceID: prepared[index].source.ID}
		if issue := validateOverridePath(override.Path, base.root, baseLookup); issue != nil {
			issue.Primary = location
			diagnostics = append(diagnostics, *issue)
			continue
		}
		pointer := override.Path.String()
		if previous, duplicate := seen[pointer]; duplicate {
			diagnostics = append(diagnostics, Diagnostic{
				Code: CodeOverrideDuplicate, Severity: SeverityError, Path: override.Path.clone(),
				Message: "configuration override path is repeated", Primary: location,
				Related: []Location{{SourceID: prepared[previous].source.ID}},
			})
			continue
		}
		seen[pointer] = index
		if conflicting, overlaps := acceptedPaths.earliestIntersectingID(pointer); overlaps {
			diagnostics = append(diagnostics, Diagnostic{
				Code: CodeOverrideOverlap, Severity: SeverityError, Path: override.Path.clone(),
				Message: "configuration override paths overlap", Primary: location,
				Related: []Location{{SourceID: prepared[conflicting].source.ID}},
			})
			continue
		}
		if rule != nil && (pathContains(override.Path, rule.Path) || pathContains(rule.Path, override.Path)) {
			diagnostics = append(diagnostics, Diagnostic{
				Code: CodeOverrideVersion, Severity: SeverityError, Path: override.Path.clone(),
				Message: "configuration overrides cannot replace the schema-version path", Primary: location,
			})
			continue
		}
		if pathContainsDirective(override.Path) || pathContainsInheritanceDirective(override.Path) {
			diagnostics = append(diagnostics, Diagnostic{
				Code: CodeOverrideDirective, Severity: SeverityError, Path: override.Path.clone(),
				Message: "configuration overrides cannot create configuration directives", Primary: location,
			})
			continue
		}
		acceptedPaths.insert(pointer, index)

		builder := valueBuilder{sourceID: prepared[index].source.ID, active: make(map[valueVisit]bool)}
		value, issue := builder.build(override.Value, override.Path, len(override.Path.segments))
		if issue != nil {
			diagnostic := issue.overrideDiagnostic()
			diagnostic.Primary = location
			diagnostics = append(diagnostics, diagnostic)
			continue
		}
		if relative, ok := overrideStructuralDirectivePath(value, Path{}); ok {
			diagnostics = append(diagnostics, Diagnostic{
				Code: CodeOverrideDirective, Severity: SeverityError, Path: appendOverridePath(override.Path, relative),
				Message: "configuration overrides cannot create configuration directives", Primary: location,
			})
			continue
		}
		nodes := builder.nodes + len(override.Path.segments)*2
		if nodes > limits.nodes || base.inputNodes+usedNodes+nodes > limits.nodes {
			diagnostics = append(diagnostics, Diagnostic{
				Code: CodeOverrideLimitExceeded, Severity: SeverityError, Path: override.Path.clone(),
				Message: "configuration overrides exceed the aggregate node limit", Primary: location,
			})
			continue
		}
		if builder.bytes > maxSourceBytes || base.inputBytes+usedBytes+builder.bytes > limits.bytes {
			diagnostics = append(diagnostics, Diagnostic{
				Code: CodeOverrideLimitExceeded, Severity: SeverityError, Path: override.Path.clone(),
				Message: "configuration overrides exceed a record or aggregate string-byte limit", Primary: location,
			})
			continue
		}
		prepared[index].path = override.Path.clone()
		prepared[index].value = value
		prepared[index].bytes = builder.bytes
		prepared[index].nodes = nodes
		usedBytes += builder.bytes
		usedNodes += nodes
	}
	if len(diagnostics) != 0 {
		return preparedOverrideBatch{sources: allSources}, canonicalDiagnostics(diagnostics)
	}

	return preparedOverrideBatch{overrides: prepared, sources: allSources}, nil
}

func validOverrideLabel(label string) bool {
	if label == "" || strings.TrimSpace(label) != label || !utf8.ValidString(label) {
		return false
	}
	for _, character := range label {
		if unicode.IsControl(character) {
			return false
		}
	}
	return true
}

func validateOverridePath(path Path, root *document.Node, lookup *documentLookup) *Diagnostic {
	if !path.valid() || len(path.segments) == 0 {
		return &Diagnostic{Code: CodeOverrideInvalidPath, Severity: SeverityError, Path: path.clone(), Message: "configuration override path must be a valid non-root mapping path"}
	}
	current := root
	for index, segment := range path.segments {
		if segment.kind == pathSegmentIndex {
			return &Diagnostic{Code: CodeOverrideInvalidPath, Severity: SeverityError, Path: path.clone(), Message: "configuration override paths cannot contain sequence indices"}
		}
		if current == nil {
			continue
		}
		if current.Kind != document.Mapping {
			return &Diagnostic{Code: CodeOverrideInvalidPath, Severity: SeverityError, Path: path.clone(), Message: "configuration override path traverses a non-mapping value"}
		}
		position := lookup.find(current, segment.key)
		if index == len(path.segments)-1 {
			continue
		}
		if position < 0 {
			current = nil
			continue
		}
		current = current.Mapping[position].Value
	}
	return nil
}

func pathContainsDirective(path Path) bool {
	for _, segment := range path.segments {
		if segment.key == directiveKey {
			return true
		}
	}
	return false
}

func pathContainsInheritanceDirective(path Path) bool {
	for _, segment := range path.segments {
		if segment.key == inheritanceKey {
			return true
		}
	}
	return false
}

func appendOverridePath(base, relative Path) Path {
	result := base.clone()
	result.segments = append(result.segments, clonePathSegments(relative.segments, 0)...)
	return result
}

func overrideStructuralDirectivePath(node *document.Node, path Path) (Path, bool) {
	return overrideStructuralDirectivePathAt(node, path)
}

func overrideStructuralDirectivePathAt(node *document.Node, path Path) (Path, bool) {
	if node == nil {
		return Path{}, false
	}
	if node.Kind == document.Mapping {
		for _, entry := range node.Mapping {
			child := path.Key(entry.Key)
			if entry.Key == directiveKey || entry.Key == inheritanceKey {
				return child, true
			}
			if found, ok := overrideStructuralDirectivePathAt(entry.Value, child); ok {
				return found, true
			}
		}
	} else if node.Kind == document.Sequence {
		for index, child := range node.Sequence {
			if found, ok := overrideStructuralDirectivePathAt(child, path.Index(index)); ok {
				return found, true
			}
		}
	}
	return Path{}, false
}