package config

import (
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"

	"gopkg.in/yaml.v3"
)

// Config holds all runtime configuration for the codespace server.
type Config struct {
	Server    ServerConfig    `yaml:"server"`
	Workspace WorkspaceConfig `yaml:"workspace"`
	Process   ProcessConfig   `yaml:"process"`
	Shell     ShellConfig     `yaml:"shell"`
	File      FileConfig      `yaml:"file"`
	Gin       GinConfig       `yaml:"gin"`
	Log       LogConfig       `yaml:"log"`
}

// ServerConfig holds HTTP server settings.
type ServerConfig struct {
	Addr           string
	ReadTimeout    time.Duration
	WriteTimeout   time.Duration
	IdleTimeout    time.Duration
	MaxHeaderBytes int
}

// WorkspaceConfig holds workspace directory settings.
type WorkspaceConfig struct {
	Root string `yaml:"root"`
}

// ProcessConfig holds OpenCode process settings.
type ProcessConfig struct {
	OpenCodeCommand string `yaml:"opencodeCommand"`
}

// ShellConfig holds interactive shell settings.
type ShellConfig struct {
	Command string   `yaml:"command"`
	Args    []string `yaml:"args"`
}

// FileConfig holds file operation limits.
type FileConfig struct {
	MaxWriteBytes int64 `yaml:"maxWriteBytes"`
}

// GinConfig holds Gin framework runtime settings.
type GinConfig struct {
	Mode string `yaml:"mode"`
}

// LogConfig holds structured logging settings.
type LogConfig struct {
	Level  string `yaml:"level"`
	Format string `yaml:"format"`
}

// rawConfig is used for YAML deserialization so that duration strings can be
// parsed explicitly rather than relying on implicit time.Duration unmarshalling.
type rawConfig struct {
	Server    rawServerConfig `yaml:"server"`
	Workspace WorkspaceConfig `yaml:"workspace"`
	Process   ProcessConfig   `yaml:"process"`
	Shell     ShellConfig     `yaml:"shell"`
	File      FileConfig      `yaml:"file"`
	Gin       GinConfig       `yaml:"gin"`
	Log       LogConfig       `yaml:"log"`
}

type rawServerConfig struct {
	Addr           string `yaml:"addr"`
	ReadTimeout    string `yaml:"readTimeout"`
	WriteTimeout   string `yaml:"writeTimeout"`
	IdleTimeout    string `yaml:"idleTimeout"`
	MaxHeaderBytes int    `yaml:"maxHeaderBytes"`
}

// Default returns the built-in default configuration.
func Default() Config {
	return Config{
		Server: ServerConfig{
			Addr:           ":8080",
			ReadTimeout:    15 * time.Second,
			WriteTimeout:   15 * time.Second,
			IdleTimeout:    60 * time.Second,
			MaxHeaderBytes: 1 << 20, // 1 MiB
		},
		Workspace: WorkspaceConfig{Root: "./workspaces"},
		Process:   ProcessConfig{OpenCodeCommand: "opencode"},
		Shell:     ShellConfig{Command: "bash", Args: []string{"-i"}},
		File:      FileConfig{MaxWriteBytes: 1 << 20},
		Gin:       GinConfig{Mode: "release"},
		Log:       LogConfig{Level: "info", Format: "json"},
	}
}

// Load reads configuration from the given YAML file path (if it exists),
// then applies environment variable overrides. Missing files are not an error.
func Load(path string) (Config, error) {
	cfg := Default()

	data, err := os.ReadFile(path)
	if err == nil {
		var raw rawConfig
		if err := yaml.Unmarshal(data, &raw); err != nil {
			return Config{}, err
		}
		if err := applyRaw(&cfg, raw); err != nil {
			return Config{}, err
		}
	} else if !os.IsNotExist(err) {
		return Config{}, err
	}

	if err := applyEnv(&cfg); err != nil {
		return Config{}, err
	}
	if err := validateGinMode(cfg.Gin.Mode); err != nil {
		return Config{}, err
	}
	return cfg, nil
}

func applyRaw(cfg *Config, raw rawConfig) error {
	if raw.Server.Addr != "" {
		cfg.Server.Addr = raw.Server.Addr
	}
	if err := applyDuration(&cfg.Server.ReadTimeout, raw.Server.ReadTimeout, "readTimeout"); err != nil {
		return err
	}
	if err := applyDuration(&cfg.Server.WriteTimeout, raw.Server.WriteTimeout, "writeTimeout"); err != nil {
		return err
	}
	if err := applyDuration(&cfg.Server.IdleTimeout, raw.Server.IdleTimeout, "idleTimeout"); err != nil {
		return err
	}
	if raw.Server.MaxHeaderBytes != 0 {
		cfg.Server.MaxHeaderBytes = raw.Server.MaxHeaderBytes
	}
	if raw.Workspace.Root != "" {
		cfg.Workspace.Root = raw.Workspace.Root
	}
	if raw.Process.OpenCodeCommand != "" {
		cfg.Process.OpenCodeCommand = raw.Process.OpenCodeCommand
	}
	cfg.Shell.Command = raw.Shell.Command
	cfg.Shell.Args = raw.Shell.Args
	if raw.File.MaxWriteBytes != 0 {
		cfg.File.MaxWriteBytes = raw.File.MaxWriteBytes
	}
	if raw.Gin.Mode != "" {
		cfg.Gin.Mode = raw.Gin.Mode
	}
	if raw.Log.Level != "" {
		cfg.Log.Level = raw.Log.Level
	}
	if raw.Log.Format != "" {
		cfg.Log.Format = raw.Log.Format
	}
	return nil
}

func applyDuration(target *time.Duration, value, name string) error {
	if value == "" {
		return nil
	}
	d, err := time.ParseDuration(value)
	if err != nil {
		return fmt.Errorf("invalid duration for %s: %w", name, err)
	}
	*target = d
	return nil
}

func applyEnv(cfg *Config) error {
	if v := os.Getenv("CODESPACE_ADDR"); v != "" {
		cfg.Server.Addr = v
	}
	if v := os.Getenv("CODESPACE_READ_TIMEOUT"); v != "" {
		if err := applyDuration(&cfg.Server.ReadTimeout, v, "CODESPACE_READ_TIMEOUT"); err != nil {
			return err
		}
	}
	if v := os.Getenv("CODESPACE_WRITE_TIMEOUT"); v != "" {
		if err := applyDuration(&cfg.Server.WriteTimeout, v, "CODESPACE_WRITE_TIMEOUT"); err != nil {
			return err
		}
	}
	if v := os.Getenv("CODESPACE_IDLE_TIMEOUT"); v != "" {
		if err := applyDuration(&cfg.Server.IdleTimeout, v, "CODESPACE_IDLE_TIMEOUT"); err != nil {
			return err
		}
	}
	if v := os.Getenv("CODESPACE_MAX_HEADER_BYTES"); v != "" {
		n, err := strconv.Atoi(v)
		if err != nil {
			return fmt.Errorf("invalid integer for CODESPACE_MAX_HEADER_BYTES: %w", err)
		}
		cfg.Server.MaxHeaderBytes = n
	}
	if v := os.Getenv("CODESPACE_WORKSPACE_ROOT"); v != "" {
		cfg.Workspace.Root = v
	}
	if v := os.Getenv("CODESPACE_OPENCODE_COMMAND"); v != "" {
		cfg.Process.OpenCodeCommand = v
	}
	if v := os.Getenv("CODESPACE_SHELL_COMMAND"); v != "" {
		cfg.Shell.Command = v
	}
	if v := os.Getenv("CODESPACE_SHELL_ARGS"); v != "" {
		cfg.Shell.Args = strings.Split(v, ",")
	}
	if v := os.Getenv("CODESPACE_FILE_MAX_WRITE_BYTES"); v != "" {
		n, err := strconv.ParseInt(v, 10, 64)
		if err != nil {
			return fmt.Errorf("invalid integer for CODESPACE_FILE_MAX_WRITE_BYTES: %w", err)
		}
		cfg.File.MaxWriteBytes = n
	}
	if v := os.Getenv("CODESPACE_GIN_MODE"); v != "" {
		cfg.Gin.Mode = v
	}
	if v := os.Getenv("CODESPACE_LOG_LEVEL"); v != "" {
		cfg.Log.Level = v
	}
	if v := os.Getenv("CODESPACE_LOG_FORMAT"); v != "" {
		cfg.Log.Format = v
	}
	return nil
}

func validateGinMode(mode string) error {
	switch mode {
	case "debug", "release", "test":
		return nil
	default:
		return fmt.Errorf("invalid gin mode %q: must be one of debug, release, test", mode)
	}
}