// Package shared holds the plumbing common to the vault-tools CLIs (vcm and
// vctx): config-file parsing, the on-disk token cache, and a small Vault HTTP
// API client. Both tools read the SAME config file and token cache so a single
// ~/.config/vcm/ configures every tool in the family.
package shared

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"

	"gopkg.in/yaml.v3"
)

const (
	// DefaultMethod is the auth method used when neither the context nor the
	// file-level defaults specify one.
	DefaultMethod = "ldap"

	// appDir is the per-user config/cache subdirectory both tools live under.
	appDir = "vcm"

	configFileName = "config.yaml"
)

// Context is a single vault instance the tools can target. Every field except
// Address is optional and, when empty, falls back to the file-level Defaults
// and finally the built-in defaults.
type Context struct {
	// Address is the Vault API base URL, e.g. https://vault.syd1.au.unkin.net.
	Address string `yaml:"address"`
	// Method is the auth method (ldap, userpass, okta, radius, token, oidc).
	Method string `yaml:"method,omitempty"`
	// User is the login username (LDAP/userpass/...); ignored for token auth.
	User string `yaml:"user,omitempty"`
	// Namespace is the Vault namespace (X-Vault-Namespace) for the context.
	Namespace string `yaml:"namespace,omitempty"`
	// Path overrides the auth mount path (defaults to Method), e.g. "ldap2".
	Path string `yaml:"path,omitempty"`
	// Role is the OIDC role to log in with (empty = the mount's default_role).
	Role string `yaml:"role,omitempty"`
	// OIDCListen is the local OIDC callback listener (default localhost:8250).
	OIDCListen string `yaml:"oidc_listen,omitempty"`
}

// Defaults holds file-level fallbacks applied to every context that does not
// set its own value.
type Defaults struct {
	Method    string `yaml:"method,omitempty"`
	User      string `yaml:"user,omitempty"`
	Namespace string `yaml:"namespace,omitempty"`
}

// Config is the parsed config file: file-level defaults plus a map of named
// contexts. Context names may contain slashes (e.g. "staging/sydney"), which
// map to nested cache paths.
type Config struct {
	Defaults Defaults           `yaml:"defaults"`
	Contexts map[string]Context `yaml:"contexts"`

	// path records the file this config was loaded from (empty if none found).
	path string
}

// ResolvedContext is a Context with all defaults applied, ready to use. Method
// and User are always populated.
type ResolvedContext struct {
	Name       string
	Address    string
	Method     string
	User       string
	Namespace  string
	Path       string
	Role       string
	OIDCListen string
}

// Overrides are CLI-flag values that replace resolved context fields; empty
// fields leave the resolved value untouched.
type Overrides struct {
	Method string
	User   string
	Role   string
	Listen string
}

// ConfigDir returns the XDG_CONFIG_HOME/vcm directory.
func ConfigDir() string {
	base := os.Getenv("XDG_CONFIG_HOME")
	if base == "" {
		home, _ := os.UserHomeDir()
		base = filepath.Join(home, ".config")
	}
	return filepath.Join(base, appDir)
}

// ConfigPath returns the path of the config file, whether or not it exists.
func ConfigPath() string {
	return filepath.Join(ConfigDir(), configFileName)
}

// Load reads and parses the config file. A missing config file is not an
// error: an empty Config is returned so callers can give a helpful "no
// contexts configured" message.
func Load() (*Config, error) {
	cfg := &Config{Contexts: map[string]Context{}}

	p := ConfigPath()
	data, err := os.ReadFile(p)
	if err != nil {
		if os.IsNotExist(err) {
			return cfg, nil
		}
		return cfg, fmt.Errorf("reading config %s: %w", p, err)
	}
	if err := yaml.Unmarshal(data, cfg); err != nil {
		return cfg, fmt.Errorf("parsing config %s: %w", p, err)
	}
	if cfg.Contexts == nil {
		cfg.Contexts = map[string]Context{}
	}
	cfg.path = p
	return cfg, nil
}

// Path returns the file this config was loaded from, or "" if none was found.
func (c *Config) Path() string { return c.path }

// ContextNames returns the configured context names, sorted. Used to drive
// shell completion for the --context flag / context arguments.
func (c *Config) ContextNames() []string {
	names := make([]string, 0, len(c.Contexts))
	for n := range c.Contexts {
		names = append(names, n)
	}
	sort.Strings(names)
	return names
}

// Resolve looks up a context by name and applies the fallback chain for each
// field: context value < file defaults < built-in default. Method and User are
// guaranteed non-empty in the result (User defaults to $USER).
func (c *Config) Resolve(name string) (ResolvedContext, error) {
	ctx, ok := c.Contexts[name]
	if !ok {
		return ResolvedContext{}, fmt.Errorf("no context %q in %s", name, displayPath(c.path))
	}
	if ctx.Address == "" {
		return ResolvedContext{}, fmt.Errorf("context %q has no address", name)
	}

	method := firstNonEmpty(ctx.Method, c.Defaults.Method, DefaultMethod)
	user := firstNonEmpty(ctx.User, c.Defaults.User, os.Getenv("USER"))
	namespace := firstNonEmpty(ctx.Namespace, c.Defaults.Namespace)
	path := firstNonEmpty(ctx.Path, method)

	return ResolvedContext{
		Name:       name,
		Address:    ctx.Address,
		Method:     method,
		User:       user,
		Namespace:  namespace,
		Path:       path,
		Role:       ctx.Role,
		OIDCListen: firstNonEmpty(ctx.OIDCListen, DefaultOIDCListen),
	}, nil
}

// ResolveWithOverrides is Resolve plus explicit CLI-flag overrides. When the
// method is overridden and the context did not pin an explicit auth path, the
// auth path follows the new method.
func (c *Config) ResolveWithOverrides(name string, o Overrides) (ResolvedContext, error) {
	rc, err := c.Resolve(name)
	if err != nil {
		return rc, err
	}
	if o.Method != "" {
		rc.Method = o.Method
		if c.Contexts[name].Path == "" {
			rc.Path = o.Method
		}
	}
	rc.User = firstNonEmpty(o.User, rc.User)
	rc.Role = firstNonEmpty(o.Role, rc.Role)
	rc.OIDCListen = firstNonEmpty(o.Listen, rc.OIDCListen)
	return rc, nil
}

func firstNonEmpty(vals ...string) string {
	for _, v := range vals {
		if v != "" {
			return v
		}
	}
	return ""
}

func displayPath(p string) string {
	if p == "" {
		return ConfigPath() + " (not found)"
	}
	return p
}