package config

import (
	"fmt"
	"os"
	"time"

	"gopkg.in/yaml.v3"
)

// FileDoc wraps the parsed YAML node tree of a broker config file so that
// database entries can be added, removed, or toggled while leaving the
// rest of the file (formatting, comments, unrelated keys) intact.
type FileDoc struct {
	path string
	root *yaml.Node
}

// databaseFileConfig mirrors DatabaseConfig with duration fields represented
// as strings, which is the form used by the human-edited YAML config. YAML
// unmarshalling does not parse strings into time.Duration automatically.
type databaseFileConfig struct {
	Name            string `yaml:"name"`
	Host            string `yaml:"host"`
	Port            int    `yaml:"port"`
	Database        string `yaml:"database"`
	User            string `yaml:"user"`
	Password        string `yaml:"password"`
	SSLMode         string `yaml:"sslmode"`
	MaxOpenConns    int    `yaml:"max_open_conns"`
	MaxIdleConns    int    `yaml:"max_idle_conns"`
	ConnMaxLifetime string `yaml:"conn_max_lifetime"`
	ConnMaxIdleTime string `yaml:"conn_max_idle_time"`
	QueueCount      int    `yaml:"queue_count"`
	TenantID        string `yaml:"tenant_id"`
	AutoMigrate     bool   `yaml:"auto_migrate"`
	Disabled        bool   `yaml:"disabled"`
}

func decodeDatabase(node *yaml.Node) (DatabaseConfig, error) {
	var raw databaseFileConfig
	if err := node.Decode(&raw); err != nil {
		return DatabaseConfig{}, err
	}
	db := DatabaseConfig{
		Name: raw.Name, Host: raw.Host, Port: raw.Port, Database: raw.Database,
		User: raw.User, Password: raw.Password, SSLMode: raw.SSLMode,
		MaxOpenConns: raw.MaxOpenConns, MaxIdleConns: raw.MaxIdleConns,
		QueueCount: raw.QueueCount, TenantID: raw.TenantID,
		AutoMigrate: raw.AutoMigrate, Disabled: raw.Disabled,
	}
	var err error
	if raw.ConnMaxLifetime != "" {
		db.ConnMaxLifetime, err = time.ParseDuration(raw.ConnMaxLifetime)
		if err != nil {
			return DatabaseConfig{}, fmt.Errorf("conn_max_lifetime: %w", err)
		}
	}
	if raw.ConnMaxIdleTime != "" {
		db.ConnMaxIdleTime, err = time.ParseDuration(raw.ConnMaxIdleTime)
		if err != nil {
			return DatabaseConfig{}, fmt.Errorf("conn_max_idle_time: %w", err)
		}
	}
	return db, nil
}

// LoadFileDoc reads and parses the YAML config file at path for editing.
// A missing file is treated as an empty document so `db add` can be used
// to create a new config file from scratch.
func LoadFileDoc(path string) (*FileDoc, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		if !os.IsNotExist(err) {
			return nil, fmt.Errorf("failed to read config file %s: %w", path, err)
		}
		data = nil
	}

	var root yaml.Node
	if len(data) > 0 {
		if err := yaml.Unmarshal(data, &root); err != nil {
			return nil, fmt.Errorf("failed to parse config file %s: %w", path, err)
		}
	}
	if root.Kind == 0 {
		root.Kind = yaml.DocumentNode
		root.Content = []*yaml.Node{{Kind: yaml.MappingNode, Tag: "!!map"}}
	}

	return &FileDoc{path: path, root: &root}, nil
}

// Save writes the document back to its original path.
func (f *FileDoc) Save() error {
	data, err := yaml.Marshal(f.root)
	if err != nil {
		return fmt.Errorf("failed to marshal config: %w", err)
	}
	if err := os.WriteFile(f.path, data, 0o644); err != nil {
		return fmt.Errorf("failed to write config file %s: %w", f.path, err)
	}
	return nil
}

func (f *FileDoc) mappingRoot() (*yaml.Node, error) {
	if len(f.root.Content) == 0 {
		return nil, fmt.Errorf("config file is empty")
	}
	m := f.root.Content[0]
	if m.Kind != yaml.MappingNode {
		return nil, fmt.Errorf("config file root is not a mapping")
	}
	return m, nil
}

// databasesSeq returns the "databases" sequence node, creating it (and the
// key) if it isn't already present.
func (f *FileDoc) databasesSeq() (*yaml.Node, error) {
	m, err := f.mappingRoot()
	if err != nil {
		return nil, err
	}
	for i := 0; i+1 < len(m.Content); i += 2 {
		if m.Content[i].Value == "databases" {
			seq := m.Content[i+1]
			if seq.Kind != yaml.SequenceNode {
				return nil, fmt.Errorf("'databases' key in config is not a list")
			}
			return seq, nil
		}
	}
	keyNode := &yaml.Node{Kind: yaml.ScalarNode, Value: "databases"}
	seqNode := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq"}
	m.Content = append(m.Content, keyNode, seqNode)
	return seqNode, nil
}

// ListDatabases decodes all database entries currently in the document, in
// file order.
func (f *FileDoc) ListDatabases() ([]DatabaseConfig, error) {
	seq, err := f.databasesSeq()
	if err != nil {
		return nil, err
	}
	dbs := make([]DatabaseConfig, 0, len(seq.Content))
	for _, item := range seq.Content {
		db, err := decodeDatabase(item)
		if err != nil {
			return nil, fmt.Errorf("failed to decode database entry: %w", err)
		}
		dbs = append(dbs, db)
	}
	return dbs, nil
}

// FindDatabase returns the decoded entry with the given name.
func (f *FileDoc) FindDatabase(name string) (DatabaseConfig, bool, error) {
	dbs, err := f.ListDatabases()
	if err != nil {
		return DatabaseConfig{}, false, err
	}
	for i := range dbs {
		db := &dbs[i]
		if db.Name == name {
			return *db, true, nil
		}
	}
	return DatabaseConfig{}, false, nil
}

// LastDatabase returns the last database entry in the file, used to prime
// defaults for a new `db add` when no --from instance is given.
func (f *FileDoc) LastDatabase() (DatabaseConfig, bool, error) {
	dbs, err := f.ListDatabases()
	if err != nil {
		return DatabaseConfig{}, false, err
	}
	if len(dbs) == 0 {
		return DatabaseConfig{}, false, nil
	}
	return dbs[len(dbs)-1], true, nil
}

// AddDatabase appends a new database entry. It fails if an entry with the
// same name already exists.
func (f *FileDoc) AddDatabase(db DatabaseConfig) error {
	seq, err := f.databasesSeq()
	if err != nil {
		return err
	}
	for _, item := range seq.Content {
		existing, err := decodeDatabase(item)
		if err != nil {
			return fmt.Errorf("failed to decode database entry: %w", err)
		}
		if existing.Name == db.Name {
			return fmt.Errorf("a database named %q already exists", db.Name)
		}
	}
	seq.Content = append(seq.Content, dbToNode(db))
	return nil
}

// RemoveDatabase deletes the entry with the given name, reporting whether
// it was found.
func (f *FileDoc) RemoveDatabase(name string) (bool, error) {
	seq, err := f.databasesSeq()
	if err != nil {
		return false, err
	}
	for i, item := range seq.Content {
		existing, err := decodeDatabase(item)
		if err != nil {
			return false, fmt.Errorf("failed to decode database entry: %w", err)
		}
		if existing.Name == name {
			seq.Content = append(seq.Content[:i], seq.Content[i+1:]...)
			return true, nil
		}
	}
	return false, nil
}

// SetDisabled sets (or clears) the disabled flag on the named entry,
// reporting whether the entry was found.
func (f *FileDoc) SetDisabled(name string, disabled bool) (bool, error) {
	seq, err := f.databasesSeq()
	if err != nil {
		return false, err
	}
	for _, item := range seq.Content {
		existing, err := decodeDatabase(item)
		if err != nil {
			return false, fmt.Errorf("failed to decode database entry: %w", err)
		}
		if existing.Name != name {
			continue
		}
		if disabled {
			setMappingKey(item, "disabled", &yaml.Node{Kind: yaml.ScalarNode, Tag: "!!bool", Value: "true"})
		} else {
			removeMappingKey(item, "disabled")
		}
		return true, nil
	}
	return false, nil
}

// setMappingKey sets key to value within a mapping node, appending the
// pair if the key isn't already present.
func setMappingKey(m *yaml.Node, key string, value *yaml.Node) {
	for i := 0; i+1 < len(m.Content); i += 2 {
		if m.Content[i].Value == key {
			m.Content[i+1] = value
			return
		}
	}
	m.Content = append(m.Content, &yaml.Node{Kind: yaml.ScalarNode, Value: key}, value)
}

// removeMappingKey removes key from a mapping node if present.
func removeMappingKey(m *yaml.Node, key string) {
	for i := 0; i+1 < len(m.Content); i += 2 {
		if m.Content[i].Value == key {
			m.Content = append(m.Content[:i], m.Content[i+2:]...)
			return
		}
	}
}

// dbToNode builds a YAML mapping node for a database entry, omitting
// fields left at their zero value so the on-disk defaults from
// applyDatabaseDefaults keep applying (matching broker.example.yaml
// style). Field order mirrors DatabaseConfig / broker.example.yaml.
func dbToNode(db DatabaseConfig) *yaml.Node {
	m := &yaml.Node{Kind: yaml.MappingNode, Tag: "!!map"}

	add := func(key, value string) {
		m.Content = append(m.Content,
			&yaml.Node{Kind: yaml.ScalarNode, Value: key},
			&yaml.Node{Kind: yaml.ScalarNode, Value: value},
		)
	}
	addBool := func(key string, value bool) {
		m.Content = append(m.Content,
			&yaml.Node{Kind: yaml.ScalarNode, Value: key},
			&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!bool", Value: fmt.Sprintf("%t", value)},
		)
	}
	addInt := func(key string, value int) {
		m.Content = append(m.Content,
			&yaml.Node{Kind: yaml.ScalarNode, Value: key},
			&yaml.Node{Kind: yaml.ScalarNode, Tag: "!!int", Value: fmt.Sprintf("%d", value)},
		)
	}

	add("name", db.Name)
	add("host", db.Host)
	if db.Port != 0 {
		addInt("port", db.Port)
	}
	add("database", db.Database)
	add("user", db.User)
	if db.Password != "" {
		add("password", db.Password)
	}
	if db.SSLMode != "" {
		add("sslmode", db.SSLMode)
	}
	if db.MaxOpenConns != 0 {
		addInt("max_open_conns", db.MaxOpenConns)
	}
	if db.MaxIdleConns != 0 {
		addInt("max_idle_conns", db.MaxIdleConns)
	}
	if db.ConnMaxLifetime != 0 {
		add("conn_max_lifetime", db.ConnMaxLifetime.String())
	}
	if db.ConnMaxIdleTime != 0 {
		add("conn_max_idle_time", db.ConnMaxIdleTime.String())
	}
	if db.QueueCount != 0 {
		addInt("queue_count", db.QueueCount)
	}
	if db.TenantID != "" {
		add("tenant_id", db.TenantID)
	}
	if db.AutoMigrate {
		addBool("auto_migrate", db.AutoMigrate)
	}
	if db.Disabled {
		addBool("disabled", db.Disabled)
	}

	return m
}