package harness

import (
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strings"

	"github.com/hjbdev/patterm/internal/projectkey"
	"github.com/hjbdev/patterm/internal/trust"
)

type Options struct {
	PattermBin string
	Scenario   *Scenario
}

type testEnv struct {
	Root       string `json:"root"`
	ConfigHome string `json:"xdg_config_home"`
	DataHome   string `json:"xdg_data_home"`
	RuntimeDir string `json:"xdg_runtime_dir"`
	BinDir     string `json:"bin_dir"`
	ProjectDir string `json:"project_dir"`
	PattermBin string `json:"patterm_bin"`
	Cols       uint16 `json:"cols"`
	Rows       uint16 `json:"rows"`
}

func prepareEnv(opts Options) (*testEnv, []string, error) {
	sc := opts.Scenario
	root, err := os.MkdirTemp("", "patterm-harness-*")
	if err != nil {
		return nil, nil, err
	}
	env := &testEnv{
		Root:       root,
		ConfigHome: filepath.Join(root, "config"),
		DataHome:   filepath.Join(root, "data"),
		RuntimeDir: filepath.Join(root, "runtime"),
		BinDir:     filepath.Join(root, "bin"),
		Cols:       sc.Cols,
		Rows:       sc.Rows,
		PattermBin: opts.PattermBin,
	}
	if env.ProjectDir = sc.ProjectDir; env.ProjectDir == "" {
		env.ProjectDir = filepath.Join(root, "project")
	}
	for _, dir := range []string{env.ConfigHome, env.DataHome, env.RuntimeDir, env.BinDir, env.ProjectDir} {
		if err := os.MkdirAll(dir, 0o700); err != nil {
			return nil, nil, err
		}
	}
	if env.PattermBin == "" {
		env.PattermBin, err = defaultPattermBin()
		if err != nil {
			return nil, nil, err
		}
	}
	if err := writeScripts(env.BinDir, sc.Scripts); err != nil {
		return nil, nil, err
	}
	if err := writePresets(env.ConfigHome, sc.Presets); err != nil {
		return nil, nil, err
	}
	if err := seedTrust(env, sc.Trust); err != nil {
		return nil, nil, err
	}
	childEnv := append(os.Environ(),
		"XDG_CONFIG_HOME="+env.ConfigHome,
		"XDG_DATA_HOME="+env.DataHome,
		"XDG_RUNTIME_DIR="+env.RuntimeDir,
		"PATTERM_HARNESS=1",
		"PATH="+env.BinDir+string(os.PathListSeparator)+os.Getenv("PATH"),
	)
	for k, v := range sc.Env {
		childEnv = append(childEnv, k+"="+v)
	}
	return env, childEnv, nil
}

func writeScripts(bin string, scripts []ScenarioScript) error {
	for _, script := range scripts {
		if script.Name == "" {
			return fmt.Errorf("script missing name")
		}
		if strings.Contains(script.Name, "/") {
			return fmt.Errorf("script name %q must not contain /", script.Name)
		}
		path := filepath.Join(bin, script.Name)
		if err := os.WriteFile(path, []byte(script.Body), 0o700); err != nil {
			return err
		}
	}
	return nil
}

func writePresets(configHome string, presets ScenarioPresets) error {
	base := filepath.Join(configHome, "patterm", "presets")
	if err := os.MkdirAll(filepath.Join(base, "agents"), 0o700); err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Join(base, "processes"), 0o700); err != nil {
		return err
	}
	for _, p := range presets.Agents {
		if err := writePreset(filepath.Join(base, "agents", p.Name+".json"), p); err != nil {
			return err
		}
	}
	for _, p := range presets.Processes {
		if err := writePreset(filepath.Join(base, "processes", p.Name+".json"), p); err != nil {
			return err
		}
	}
	return nil
}

func writePreset(path string, p ScenarioPreset) error {
	if p.Name == "" {
		return fmt.Errorf("preset missing name")
	}
	b, err := json.MarshalIndent(p, "", "  ")
	if err != nil {
		return err
	}
	b = append(b, '\n')
	return os.WriteFile(path, b, 0o600)
}

func seedTrust(env *testEnv, presets []string) error {
	if len(presets) == 0 {
		return nil
	}
	key, err := projectkey.Key(env.ProjectDir)
	if err != nil {
		return err
	}
	restore := setenv(map[string]string{"XDG_DATA_HOME": env.DataHome})
	defer restore()
	store, err := trust.Open(key)
	if err != nil {
		return err
	}
	for _, p := range presets {
		if err := store.Grant(p); err != nil {
			return err
		}
	}
	return nil
}

func setenv(vals map[string]string) func() {
	type old struct {
		v  string
		ok bool
	}
	prev := map[string]old{}
	for k, v := range vals {
		ov, ok := os.LookupEnv(k)
		prev[k] = old{v: ov, ok: ok}
		_ = os.Setenv(k, v)
	}
	return func() {
		for k, ov := range prev {
			if ov.ok {
				_ = os.Setenv(k, ov.v)
			} else {
				_ = os.Unsetenv(k)
			}
		}
	}
}

func defaultPattermBin() (string, error) {
	if p := os.Getenv("PATTERM_BIN"); p != "" {
		return p, nil
	}
	return buildPattermBinary()
}

func buildPattermBinary() (string, error) {
	root, err := repoRoot()
	if err != nil {
		return "", err
	}
	out := filepath.Join(os.TempDir(), "patterm-harness-bin", "patterm")
	if err := os.MkdirAll(filepath.Dir(out), 0o700); err != nil {
		return "", err
	}
	cmd := exec.Command("go", "build", "-o", out, "./cmd/patterm")
	cmd.Dir = root
	cmd.Env = os.Environ()
	if b, err := cmd.CombinedOutput(); err != nil {
		return "", fmt.Errorf("build patterm: %w\n%s", err, string(b))
	}
	return out, nil
}

func repoRoot() (string, error) {
	_, file, _, ok := runtime.Caller(0)
	if !ok {
		return "", fmt.Errorf("runtime.Caller failed")
	}
	return filepath.Clean(filepath.Join(filepath.Dir(file), "..", "..")), nil
}