// Package config loads and validates YAML configuration for odidere.
package config

import (
	"fmt"
	"net/url"
	"os"
	"regexp"
	"time"

	"gopkg.in/yaml.v3"
)

// TTS holds the configuration for TTS.
type TTS struct {
	// URL is the base URL of kokoro-fastapi.
	// For example, "http://localhost:8880".
	URL string `yaml:"url"`
	// Voice is the default voice ID to use (e.g., "af_heart").
	Voice string `yaml:"voice"`
	// Timeout is the maximum duration for a synthesis request.
	// Defaults to 60s if zero.
	Timeout time.Duration `yaml:"timeout"`
}

func (cfg TTS) Validate() error {
	if cfg.URL == "" {
		return fmt.Errorf("missing URL")
	}
	if _, err := url.Parse(cfg.URL); err != nil {
		return fmt.Errorf("invalid URL %q: %w", cfg.URL, err)
	}
	if cfg.Voice == "" {
		return fmt.Errorf("missing voice")
	}
	if cfg.Timeout < 0 {
		return fmt.Errorf("invalid timeout %v: must not be negative", cfg.Timeout)
	}
	return nil
}

// Database holds the SQLite database configuration.
type Database struct {
	// Path is the filesystem path to the SQLite database file.
	Path string `yaml:"path"`
}

func (cfg Database) Validate() error {
	if cfg.Path == "" {
		return fmt.Errorf("missing path")
	}
	return nil
}

// STT holds the configuration for the frontend-facing speech-to-text server.
type STT struct {
	// URL is the base URL of the whisper-server.
	// For example, "http://localhost:8178".
	URL string `yaml:"url"`
}

func (cfg STT) Validate() error {
	if cfg.URL == "" {
		return fmt.Errorf("missing URL")
	}
	if _, err := url.Parse(cfg.URL); err != nil {
		return fmt.Errorf("invalid URL %q: %w", cfg.URL, err)
	}
	return nil
}

// ProviderConfig holds the configuration for a single LLM provider.
type ProviderConfig struct {
	// Name uniquely identifies this provider (e.g., "llama.cpp", "openrouter").
	Name string `yaml:"name"`
	// URL is the base URL of the OpenAI-compatible API endpoint.
	URL string `yaml:"url"`
	// Key is the API key for authentication.
	Key string `yaml:"key"`
	// Timeout is the maximum duration for a query (e.g., "5m").
	// Defaults to 5 minutes if zero.
	Timeout time.Duration `yaml:"timeout"`
	// Models is an optional whitelist of model IDs for this provider.
	Models []string `yaml:"models,omitempty"`
}

func (cfg ProviderConfig) Validate() error {
	if cfg.Name == "" {
		return fmt.Errorf("missing name")
	}
	if cfg.URL == "" {
		return fmt.Errorf("missing URL")
	}
	if _, err := url.Parse(cfg.URL); err != nil {
		return fmt.Errorf("invalid URL %q: %w", cfg.URL, err)
	}
	if cfg.Timeout < 0 {
		return fmt.Errorf("invalid timeout %v: must not be negative", cfg.Timeout)
	}
	return nil
}

// ModelConfig specifies the provider and model to use.
type ModelConfig struct {
	// Provider is the provider name (e.g., "llama.cpp").
	Provider string `yaml:"provider,omitempty"`
	// Model is the model ID within that provider (e.g., "qwen3.6-27b").
	Model string `yaml:"model,omitempty"`
}

// JobConfig holds the user-facing configuration for a job.
type JobConfig struct {
	// MaxIterations caps the number of agent loop iterations.
	MaxIterations int `yaml:"max_iterations,omitempty"`
	// Name uniquely identifies the job within the config.
	Name string `yaml:"name"`
	// Model is the optional model for this job.
	Model ModelConfig `yaml:"model,omitempty"`
	// Schedule is a cron expression (e.g., "0 9 * * *").
	Schedule string `yaml:"schedule"`
	// SystemMessage overrides the global system message for this job.
	SystemMessage string `yaml:"system_message,omitempty"`
	// Task is the user-level instruction to give the LLM.
	Task string `yaml:"task"`
	// Timeout limits the job execution time (e.g., "10m").
	Timeout time.Duration `yaml:"timeout,omitempty"`
	// UserId identifies the user that owns conversations created by this job.
	UserId string `yaml:"user_id,omitempty"`
}

func (cfg JobConfig) Validate() error {
	if cfg.Name == "" {
		return fmt.Errorf("missing name")
	}
	if cfg.Task == "" {
		return fmt.Errorf("missing task")
	}
	if cfg.Schedule == "" {
		return fmt.Errorf("missing schedule")
	}
	if cfg.MaxIterations < 0 {
		return fmt.Errorf("max_iterations must be non-negative")
	}
	if cfg.Timeout < 0 {
		return fmt.Errorf("invalid timeout %v: must not be negative", cfg.Timeout)
	}
	if cfg.UserId == "" {
		return fmt.Errorf("missing user_id")
	}

	return nil
}

// ToolConfig represents an external tool definition.
type ToolConfig struct {
	// Name uniquely identifies the tool within a registry.
	Name string `yaml:"name"`
	// Description explains the tool's purpose for the LLM.
	Description string `yaml:"description"`
	// Command is the executable path or name.
	Command string `yaml:"command"`
	// Arguments defines the arguments passed to Command when the LLM calls
	// this tool. Each entry is a Go text/template template evaluated with the
	// JSON object supplied by the LLM.
	//
	// For example, this configuration:
	//
	//	arguments:
	//	  - "--message"
	//	  - "{{.message}}"
	//	  - "{{if .verbose}}--verbose{{end}}"
	//
	// combines with these tool-call arguments:
	//
	//	{"message":"hello world","verbose":true}
	//
	// to run Command with:
	//
	//	[]string{"--message", "hello world", "--verbose"}
	//
	// Each configured entry becomes one element of that []string. Spaces in
	// "hello world" do not divide it into separate arguments. If verbose were
	// false, its template would produce an empty string, and ParseArguments
	// would leave that entry out, resulting in:
	//
	//	[]string{"--message", "hello world"}
	//
	// Template output is passed directly to the program. It is not interpreted
	// by a shell. Each entry in Arguments adds either zero or one element to
	// the argument vector, regardless of the type of the value it renders.
	//
	// For example, suppose Command is "cat", Arguments contains:
	//
	//	- "{{.files}}"
	//
	// and the tool-call JSON is:
	//
	//	{"files":["one.txt","two.txt"]}
	//
	// The program is invoked with:
	//
	//	[]string{"cat", "[one.txt two.txt]"}
	//
	// This asks cat to read one file named "[one.txt two.txt]". It does not
	// produce the following argument vector, which would ask cat to read two
	// files:
	//
	//	[]string{"cat", "one.txt", "two.txt"}
	//
	// Note that templates may accept missing values without reporting an
	// error. For example, suppose Command is "echo", Arguments contains:
	//
	//	- "--message"
	//	- "{{.message}}"
	//
	// and the tool-call JSON is {}. The program is invoked with:
	//
	//	[]string{"echo", "--message", "<no value>"}
	//
	// The missing message is therefore passed to echo as the text
	// "<no value>"; it does not cause the tool call to fail.
	//
	// Each template is compiled when the tool is constructed, so a template
	// syntax error is reported at configuration load, not on the tool's
	// first call.
	//
	// See https://pkg.go.dev/text/template.
	Arguments []string `yaml:"arguments"`
	// Parameters is the JSON Schema included in the tool definition sent to
	// the LLM. It describes the values the LLM should provide when calling the
	// tool, including their names, types, and which values are required.
	//
	// The schema is not used to validate a tool call before Arguments is
	// evaluated. For example, if Parameters requires "message" but the LLM
	// supplies {}, evaluation continues without first reporting that
	// "message" is missing. Values that do not have the types described by the
	// schema may likewise reach the argument templates.
	Parameters map[string]any `yaml:"parameters"`
	// Timeout limits execution time (e.g., "30s", "5m"). Zero means no limit.
	Timeout time.Duration `yaml:"timeout"`
}

func (cfg ToolConfig) Validate() error {
	if cfg.Name == "" {
		return fmt.Errorf("missing name")
	}
	if cfg.Description == "" {
		return fmt.Errorf("missing description")
	}
	if cfg.Command == "" {
		return fmt.Errorf("missing command")
	}
	if cfg.Timeout < 0 {
		return fmt.Errorf("invalid timeout %v: must not be negative", cfg.Timeout)
	}
	return nil
}

// Config holds all application configuration sections.
type Config struct {
	// Address is the host:port to listen on.
	Address string `yaml:"address"`
	// Database configures the SQLite database path.
	Database Database `yaml:"database"`
	// ShutdownTimeout is the maximum time to wait for graceful shutdown.
	ShutdownTimeout time.Duration `yaml:"shutdown_timeout"`
	// SystemMessage is the default system prompt prepended to all conversations.
	SystemMessage string `yaml:"system_message"`
	// DefaultModel specifies the default provider and model.
	DefaultModel ModelConfig `yaml:"default_model"`
	// Providers defines the available LLM providers.
	Providers []ProviderConfig `yaml:"providers"`
	// STT configures the speech-to-text server URL passed to the frontend.
	STT STT `yaml:"stt"`
	// Jobs defines scheduled autonomous tasks.
	Jobs []JobConfig `yaml:"jobs"`
	// Tools defines external commands available to the LLM.
	Tools []ToolConfig `yaml:"tools"`
	// TTS configures the text-to-speech client.
	TTS TTS `yaml:"tts"`
}

// ApplyDefaults sets default values for optional configuration fields.
func (cfg *Config) ApplyDefaults() {
	if cfg.ShutdownTimeout == 0 {
		cfg.ShutdownTimeout = 30 * time.Second
	}
	if cfg.Address == "" {
		cfg.Address = ":8080"
	}
}

// Validate checks that all required fields are present and valid.
func (cfg *Config) Validate() error {
	if cfg.Address == "" {
		return fmt.Errorf("address required")
	}
	if err := cfg.Database.Validate(); err != nil {
		return fmt.Errorf("invalid database config: %w", err)
	}
	if cfg.DefaultModel.Provider == "" {
		return fmt.Errorf("default_model.provider required")
	}
	if cfg.DefaultModel.Model == "" {
		return fmt.Errorf("default_model.model required")
	}
	if len(cfg.Providers) == 0 {
		return fmt.Errorf("at least one provider required")
	}
	for i, p := range cfg.Providers {
		if err := p.Validate(); err != nil {
			return fmt.Errorf("providers[%d] invalid: %w", i, err)
		}
	}
	if err := cfg.STT.Validate(); err != nil {
		return fmt.Errorf("invalid stt config: %w", err)
	}
	if err := cfg.TTS.Validate(); err != nil {
		return fmt.Errorf("invalid tts config: %w", err)
	}
	if cfg.ShutdownTimeout < 0 {
		return fmt.Errorf("invalid shutdown_timeout %v: must not be negative", cfg.ShutdownTimeout)
	}
	for i, jc := range cfg.Jobs {
		if err := jc.Validate(); err != nil {
			return fmt.Errorf("jobs[%d] invalid: %w", i, err)
		}
	}
	for i, tc := range cfg.Tools {
		if err := tc.Validate(); err != nil {
			return fmt.Errorf("tools[%d] invalid: %w", i, err)
		}
	}
	return nil
}

// Load reads a YAML configuration file, expands environment variables,
// applies defaults, and validates the result.
func Load(path string) (*Config, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read file: %w", err)
	}

	// Expand environment variables.
	re := regexp.MustCompile(`\$\{([^}]+)\}`)
	expanded := re.ReplaceAllStringFunc(string(data), func(match string) string {
		v := match[2 : len(match)-1]
		return os.Getenv(v)
	})

	var cfg Config
	if err := yaml.Unmarshal([]byte(expanded), &cfg); err != nil {
		return nil, fmt.Errorf("parse config: %w", err)
	}

	cfg.ApplyDefaults()
	if err := cfg.Validate(); err != nil {
		return nil, fmt.Errorf("invalid config: %v", err)
	}

	return &cfg, nil
}