package configkit

import (
	"cmp"
	"encoding/json"
	"fmt"
	"io"
	"reflect"
	"slices"
	"strconv"

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

// Secret is an opaque reference to an environment variable. Its name is public
// configuration; its resolved value is available only through Value.
type Secret struct {
	name      string
	value     string
	specified bool
	resolved  bool
}

// SecretEnv constructs an unresolved environment-backed secret reference.
// Invalid names are reported if the reference survives a configuration load.
func SecretEnv(name string) Secret {
	return Secret{name: name, specified: true}
}

// EnvName returns the public environment-variable name.
func (s Secret) EnvName() string {
	return s.name
}

// Value returns the resolved credential, or an empty string when unresolved.
func (s Secret) Value() string {
	if !s.resolved {
		return ""
	}
	return s.value
}

// IsResolved reports whether this reference resolved to a nonempty value during
// its configuration load.
func (s Secret) IsResolved() bool {
	return s.resolved
}

// Format renders only the public reference name for every formatting verb.
func (s Secret) Format(state fmt.State, _ rune) {
	_, _ = io.WriteString(state, "configkit.SecretEnv("+strconv.Quote(s.name)+")")
}

// MarshalJSON emits only the public environment-variable name.
func (s Secret) MarshalJSON() ([]byte, error) {
	return json.Marshal(s.name)
}

type secretLookup func(string) (string, bool)

type secretLookupResult struct {
	value   string
	present bool
}

type secretResolutionResult struct {
	lookups     map[string]secretLookupResult
	references  map[string]string
	diagnostics []Diagnostic
}

func resolveSecretReferences(root reflect.Value, schema *schemaDescriptor, input *document.Node, lookup secretLookup) secretResolutionResult {
	result := secretResolutionResult{
		lookups: make(map[string]secretLookupResult), references: make(map[string]string),
	}
	if schema == nil || schema.root == nil || !root.IsValid() || root.Type() != schema.root.typeOf {
		result.diagnostics = []Diagnostic{{Code: CodeSecretRequired, Severity: SeverityError, Message: "configuration value does not match its secret-reference schema"}}
		return result
	}
	if lookup == nil {
		lookup = func(string) (string, bool) { return "", false }
	}
	resolveSecretValue(root, schema.root, Path{}, false, input, lookup, &result)
	result.diagnostics = canonicalDiagnostics(result.diagnostics)
	return result
}

func resolveSecretValue(value reflect.Value, descriptor *typeDescriptor, path Path, optional bool, input *document.Node, lookup secretLookup, result *secretResolutionResult) {
	if descriptor.kind == descriptorPointer {
		if value.IsNil() {
			return
		}
		resolveSecretValue(value.Elem(), descriptor.element, path, descriptor.element.kind == descriptorSecret, input, lookup, result)
		return
	}

	switch descriptor.kind {
	case descriptorSecret:
		reference := value.Interface().(Secret)
		name := reference.EnvName()
		if name == "" {
			code := CodeSecretRequired
			message := "required secret reference is absent"
			if optional || reference.specified {
				code = CodeSecretInvalidName
				message = "secret environment name is empty"
			}
			result.diagnostics = append(result.diagnostics, secretDiagnostic(code, path, message, input))
			return
		}
		if !validEnvironmentName(name) {
			result.diagnostics = append(result.diagnostics, secretDiagnostic(CodeSecretInvalidName, path, "secret environment name is invalid", input))
			return
		}
		found, exists := result.lookups[name]
		if !exists {
			found.value, found.present = lookup(name)
			result.lookups[name] = found
		}
		if !found.present {
			result.diagnostics = append(result.diagnostics, secretDiagnostic(CodeSecretUnset, path, "secret environment variable is not set", input))
			return
		}
		if found.value == "" {
			result.diagnostics = append(result.diagnostics, secretDiagnostic(CodeSecretEmpty, path, "secret environment variable is empty", input))
			return
		}
		value.Set(reflect.ValueOf(Secret{name: name, value: found.value, specified: true, resolved: true}))
		result.references[path.String()] = name
	case descriptorStruct:
		for _, member := range descriptor.members {
			memberPath := path
			if !member.inline {
				memberPath = path.Key(member.name)
			}
			resolveSecretValue(value.Field(member.index), member.descriptor, memberPath, false, input, lookup, result)
		}
	case descriptorMap:
		if value.IsNil() {
			return
		}
		keys := value.MapKeys()
		slices.SortFunc(keys, func(left, right reflect.Value) int { return cmp.Compare(left.String(), right.String()) })
		for _, key := range keys {
			entry := reflect.New(value.Type().Elem()).Elem()
			entry.Set(value.MapIndex(key))
			resolveSecretValue(entry, descriptor.element, path.Key(key.String()), false, input, lookup, result)
			value.SetMapIndex(key, entry)
		}
	case descriptorSlice, descriptorArray:
		if descriptor.kind == descriptorSlice && value.IsNil() {
			return
		}
		for index := 0; index < value.Len(); index++ {
			resolveSecretValue(value.Index(index), descriptor.element, path.Index(index), false, input, lookup, result)
		}
	}
}

func secretDiagnostic(code Code, path Path, message string, input *document.Node) Diagnostic {
	diagnostic := Diagnostic{Code: code, Severity: SeverityError, Path: path.clone(), Message: message}
	if location, ok := nearestDocumentLocation(input, path); ok {
		diagnostic.Primary = documentLocationPointer(location)
	}
	return diagnostic
}

func changedSecretStates(root reflect.Value, descriptor *typeDescriptor, lookups map[string]secretLookupResult) []Path {
	var changed []Path
	collectChangedSecretStates(root, descriptor, Path{}, lookups, &changed)
	slices.SortFunc(changed, func(left, right Path) int { return cmp.Compare(left.String(), right.String()) })
	return changed
}

func collectChangedSecretStates(value reflect.Value, descriptor *typeDescriptor, path Path, lookups map[string]secretLookupResult, changed *[]Path) {
	if descriptor.kind == descriptorPointer {
		if !value.IsNil() {
			collectChangedSecretStates(value.Elem(), descriptor.element, path, lookups, changed)
		}
		return
	}
	switch descriptor.kind {
	case descriptorSecret:
		reference := value.Interface().(Secret)
		expected, ok := lookups[reference.EnvName()]
		if ok && (!expected.present || expected.value == "" || !reference.resolved || reference.value != expected.value) {
			*changed = append(*changed, path.clone())
		}
	case descriptorStruct:
		for _, member := range descriptor.members {
			memberPath := path
			if !member.inline {
				memberPath = path.Key(member.name)
			}
			collectChangedSecretStates(value.Field(member.index), member.descriptor, memberPath, lookups, changed)
		}
	case descriptorMap:
		if value.IsNil() {
			return
		}
		keys := value.MapKeys()
		slices.SortFunc(keys, func(left, right reflect.Value) int { return cmp.Compare(left.String(), right.String()) })
		for _, key := range keys {
			collectChangedSecretStates(value.MapIndex(key), descriptor.element, path.Key(key.String()), lookups, changed)
		}
	case descriptorSlice, descriptorArray:
		if descriptor.kind == descriptorSlice && value.IsNil() {
			return
		}
		for index := 0; index < value.Len(); index++ {
			collectChangedSecretStates(value.Index(index), descriptor.element, path.Index(index), lookups, changed)
		}
	}
}