package app

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/harrybrwn/patterm/internal/preset"
)

// Launcher knows how to turn a preset into a running child. Both the
// palette and the MCP spawn_agent tool route through here so MCP
// injection happens consistently. SPEC §10.
type Launcher struct {
	sess       *Session
	mcpSocket  string
	bin        string // path to this binary (for the mcp-stdio subcommand)
	sizeMu     sync.Mutex
	cols, rows uint16
}

func NewLauncher(sess *Session, mcpSocket string, cols, rows uint16) *Launcher {
	bin, err := os.Executable()
	if err != nil {
		bin = "patterm"
	}
	return &Launcher{sess: sess, mcpSocket: mcpSocket, bin: bin, cols: cols, rows: rows}
}

func (l *Launcher) SetSize(cols, rows uint16) {
	l.sizeMu.Lock()
	defer l.sizeMu.Unlock()
	l.cols, l.rows = cols, rows
}

func (l *Launcher) size() (uint16, uint16) {
	l.sizeMu.Lock()
	defer l.sizeMu.Unlock()
	return l.cols, l.rows
}

// LaunchAgent spawns the agent preset, applies the preset's MCP
// injection, waits for the ready signal, and types initial_prompt into
// the PTY. SPEC §7 spawn_agent, §8 conversation protocol.
func (l *Launcher) LaunchAgent(p *preset.Preset, displayName, initialPrompt, parentID string) (*Child, error) {
	if p.Kind != preset.KindAgent {
		return nil, fmt.Errorf("launch: %q is not an agent preset", p.Name)
	}
	argv := append([]string(nil), p.Argv...)
	env := l.sess.ChildEnv()
	for k, v := range p.Env {
		env = append(env, k+"="+v)
	}

	// Mint a per-spawn MCP config file pointing at the mcp-stdio proxy
	// with the new child's identity. We don't know the identity until
	// we've created the child, but the child needs the env/argv at
	// creation time — so we reserve the identity by pre-creating the
	// MCP config with a placeholder, then patching it post-spawn.
	identity, mcpConfigPath, err := l.writeMCPConfig()
	if err != nil {
		return nil, err
	}

	if p.MCPInjection != nil {
		switch p.MCPInjection.Kind {
		case "flag":
			if p.MCPInjection.Flag == "" {
				return nil, fmt.Errorf("preset %s: mcp_injection.flag required for kind=flag", p.Name)
			}
			argv = append(argv, p.MCPInjection.Flag, mcpConfigPath)
		case "env_var":
			if p.MCPInjection.Var == "" {
				return nil, fmt.Errorf("preset %s: mcp_injection.var required for kind=env_var", p.Name)
			}
			env = append(env, p.MCPInjection.Var+"="+mcpConfigPath)
		case "config_file":
			// SPEC §10 mentions merging into an external config file. We
			// expose the config_path via an env var the user can read
			// at preset-creation time; full merge is deferred.
			env = append(env, "PATTERM_MCP_CONFIG="+mcpConfigPath)
		default:
			return nil, fmt.Errorf("preset %s: unknown mcp_injection.kind %q", p.Name, p.MCPInjection.Kind)
		}
	}

	// Spawn with the chosen identity.
	cols, rows := l.size()
	c, err := l.sess.spawnWithIdentity(displayName, KindAgent, argv, env, cols, rows, parentID, identity)
	if err != nil {
		_ = os.Remove(mcpConfigPath)
		return nil, err
	}

	// Wait for the preset's ready signal, then type the initial prompt.
	idle := time.Duration(1000) * time.Millisecond
	if p.ReadySignal != nil && p.ReadySignal.IdleMS > 0 {
		idle = time.Duration(p.ReadySignal.IdleMS) * time.Millisecond
	}
	go func() {
		waitForIdle(c, idle, 30*time.Second)
		if initialPrompt == "" {
			return
		}
		_ = c.InjectAsOrchestrator([]byte(initialPrompt + "\n"))
	}()
	return c, nil
}

// LaunchProcess spawns a process preset. No MCP injection; just argv.
func (l *Launcher) LaunchProcess(p *preset.Preset, displayName string) (*Child, error) {
	if p.Kind != preset.KindProcess {
		return nil, fmt.Errorf("launch: %q is not a process preset", p.Name)
	}
	env := l.sess.ChildEnv()
	for k, v := range p.Env {
		env = append(env, k+"="+v)
	}
	cols, rows := l.size()
	return l.sess.Spawn(displayName, KindProcess, p.ResolvedArgv(), env, cols, rows, "")
}

func (l *Launcher) writeMCPConfig() (identity, path string, err error) {
	identity = mintIdentity()
	dir, err := preset.ConfigDir()
	if err != nil {
		return "", "", err
	}
	dir = filepath.Join(dir, "mcp")
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return "", "", err
	}
	path = filepath.Join(dir, identity+".json")
	cfg := map[string]any{
		"mcpServers": map[string]any{
			"patterm": map[string]any{
				"command": l.bin,
				"args":    []string{"mcp-stdio", "--socket", l.mcpSocket, "--identity", identity},
			},
		},
	}
	body, err := json.MarshalIndent(cfg, "", "  ")
	if err != nil {
		return "", "", err
	}
	body = append(body, '\n')
	if err := os.WriteFile(path, body, 0o600); err != nil {
		return "", "", err
	}
	return identity, path, nil
}

// waitForIdle polls the child's IdleMS until it exceeds idle, or until
// max elapses.
func waitForIdle(c *Child, idle, max time.Duration) {
	deadline := time.Now().Add(max)
	tick := time.NewTicker(100 * time.Millisecond)
	defer tick.Stop()
	for {
		<-tick.C
		if c.Status() != StatusRunning {
			return
		}
		if c.IdleMS() >= idle.Milliseconds() && c.lastWriteNS.Load() != 0 {
			return
		}
		if time.Now().After(deadline) {
			return
		}
	}
}

// joinArgs flattens an argv slice into a single line (used for display
// hints).
func joinArgs(argv []string) string { return strings.Join(argv, " ") }