package terraform

import (
	"context"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strings"
	"time"

	"github.com/databricks/cli/bundle"
	"github.com/databricks/cli/bundle/config"
	"github.com/databricks/cli/bundle/internal/tf/schema"
	"github.com/databricks/cli/internal/build"
	"github.com/databricks/cli/libs/diag"
	"github.com/databricks/cli/libs/env"
	"github.com/databricks/cli/libs/log"
	"github.com/hashicorp/hc-install/product"
	"github.com/hashicorp/hc-install/releases"
	"github.com/hashicorp/terraform-exec/tfexec"
	"golang.org/x/exp/maps"
)

type initialize struct{}

func (m *initialize) Name() string {
	return "terraform.Initialize"
}

func (m *initialize) findExecPath(ctx context.Context, b *bundle.Bundle, tf *config.Terraform) (string, error) {
	// If set, pass it through [exec.LookPath] to resolve its absolute path.
	if tf.ExecPath != "" {
		execPath, err := exec.LookPath(tf.ExecPath)
		if err != nil {
			return "", err
		}
		tf.ExecPath = execPath
		log.Debugf(ctx, "Using Terraform at %s", tf.ExecPath)
		return tf.ExecPath, nil
	}

	// Load exec path from the environment if it matches the currently used version.
	envExecPath, err := getEnvVarWithMatchingVersion(ctx, TerraformExecPathEnv, TerraformVersionEnv, TerraformVersion.String())
	if err != nil {
		return "", err
	}
	if envExecPath != "" {
		tf.ExecPath = envExecPath
		log.Debugf(ctx, "Using Terraform from %s at %s", TerraformExecPathEnv, tf.ExecPath)
		return tf.ExecPath, nil
	}

	binDir, err := b.CacheDir(context.Background(), "bin")
	if err != nil {
		return "", err
	}

	// If the execPath already exists, return it.
	execPath := filepath.Join(binDir, product.Terraform.BinaryName())
	_, err = os.Stat(execPath)
	if err != nil && !errors.Is(err, fs.ErrNotExist) {
		return "", err
	}
	if err == nil {
		tf.ExecPath = execPath
		log.Debugf(ctx, "Using Terraform at %s", tf.ExecPath)
		return tf.ExecPath, nil
	}

	// Download Terraform to private bin directory.
	installer := &releases.ExactVersion{
		Product:    product.Terraform,
		Version:    TerraformVersion,
		InstallDir: binDir,
		Timeout:    1 * time.Minute,
	}
	execPath, err = installer.Install(ctx)
	if err != nil {
		return "", fmt.Errorf("error downloading Terraform: %w", err)
	}

	tf.ExecPath = execPath
	log.Debugf(ctx, "Using Terraform at %s", tf.ExecPath)
	return tf.ExecPath, nil
}

// This function inherits some environment variables for Terraform CLI.
func inheritEnvVars(ctx context.Context, environ map[string]string) error {
	// Include $HOME in set of environment variables to pass along.
	home, ok := env.Lookup(ctx, "HOME")
	if ok {
		environ["HOME"] = home
	}

	// Include $USERPROFILE in set of environment variables to pass along.
	// This variable is used by Azure CLI on Windows to find stored credentials and metadata
	userProfile, ok := env.Lookup(ctx, "USERPROFILE")
	if ok {
		environ["USERPROFILE"] = userProfile
	}

	// Include $PATH in set of environment variables to pass along.
	// This is necessary to ensure that our Terraform provider can use the
	// same auxiliary programs (e.g. `az`, or `gcloud`) as the CLI.
	path, ok := env.Lookup(ctx, "PATH")
	if ok {
		environ["PATH"] = path
	}

	// Include $TF_CLI_CONFIG_FILE to override terraform provider in development.
	// See: https://developer.hashicorp.com/terraform/cli/config/config-file#explicit-installation-method-configuration
	devConfigFile, ok := env.Lookup(ctx, "TF_CLI_CONFIG_FILE")
	if ok {
		environ["TF_CLI_CONFIG_FILE"] = devConfigFile
	}

	// Map $DATABRICKS_TF_CLI_CONFIG_FILE to $TF_CLI_CONFIG_FILE
	// VSCode extension provides a file with the "provider_installation.filesystem_mirror" configuration.
	// We only use it if the provider version matches the currently used version,
	// otherwise terraform will fail to download the right version (even with unrestricted internet access).
	configFile, err := getEnvVarWithMatchingVersion(ctx, TerraformCliConfigPathEnv, TerraformProviderVersionEnv, schema.ProviderVersion)
	if err != nil {
		return err
	}
	if configFile != "" {
		log.Debugf(ctx, "Using Terraform CLI config from %s at %s", TerraformCliConfigPathEnv, configFile)
		environ["TF_CLI_CONFIG_FILE"] = configFile
	}

	return nil
}

// Example: this function will return a value of TF_EXEC_PATH only if the path exists and if TF_VERSION matches the TerraformVersion.
// This function is used for env vars set by the Databricks VSCode extension. The variables are intended to be used by the CLI
// bundled with the Databricks VSCode extension, but users can use different CLI versions in the VSCode terminals, in which case we want to ignore
// the variables if that CLI uses different versions of the dependencies.
func getEnvVarWithMatchingVersion(ctx context.Context, envVarName string, versionVarName string, currentVersion string) (string, error) {
	envValue := env.Get(ctx, envVarName)
	versionValue := env.Get(ctx, versionVarName)

	// return early if the environment variable is not set
	if envValue == "" {
		log.Debugf(ctx, "%s is not defined", envVarName)
		return "", nil
	}

	// If the path does not exist, we return early.
	_, err := os.Stat(envValue)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			log.Debugf(ctx, "%s at %s does not exist", envVarName, envValue)
			return "", nil
		} else {
			return "", err
		}
	}

	// If the version environment variable is not set, we directly return the value of the environment variable.
	if versionValue == "" {
		return envValue, nil
	}

	// When the version environment variable is set, we check if it matches the current version.
	// If it does not match, we return an empty string.
	if versionValue != currentVersion {
		log.Debugf(ctx, "%s as %s does not match the current version %s, ignoring %s", versionVarName, versionValue, currentVersion, envVarName)
		return "", nil
	}
	return envValue, nil
}

// This function sets temp dir location for terraform to use. If user does not
// specify anything here, we fall back to a `tmp` directory in the bundle's cache
// directory
//
// This is necessary to avoid trying to create temporary files in directories
// the CLI and its dependencies do not have access to.
//
// see: os.TempDir for more context
func setTempDirEnvVars(ctx context.Context, environ map[string]string, b *bundle.Bundle) error {
	switch runtime.GOOS {
	case "windows":
		if v, ok := env.Lookup(ctx, "TMP"); ok {
			environ["TMP"] = v
		} else if v, ok := env.Lookup(ctx, "TEMP"); ok {
			environ["TEMP"] = v
		} else {
			tmpDir, err := b.CacheDir(ctx, "tmp")
			if err != nil {
				return err
			}
			environ["TMP"] = tmpDir
		}
	default:
		// If TMPDIR is not set, we let the process fall back to its default value.
		if v, ok := env.Lookup(ctx, "TMPDIR"); ok {
			environ["TMPDIR"] = v
		}
	}
	return nil
}

// This function passes through all proxy related environment variables.
func setProxyEnvVars(ctx context.Context, environ map[string]string, b *bundle.Bundle) error {
	for _, v := range []string{"http_proxy", "https_proxy", "no_proxy"} {
		// The case (upper or lower) is notoriously inconsistent for tools on Unix systems.
		// We therefore try to read both the upper and lower case versions of the variable.
		for _, v := range []string{strings.ToUpper(v), strings.ToLower(v)} {
			if val, ok := env.Lookup(ctx, v); ok {
				// Only set uppercase version of the variable.
				environ[strings.ToUpper(v)] = val
			}
		}
	}
	return nil
}

func setUserAgentExtraEnvVar(environ map[string]string, b *bundle.Bundle) error {
	// Add "cli" to the user agent in set by the Databricks Terraform provider.
	// This will allow us to attribute downstream requests made by the Databricks
	// Terraform provider to the CLI.
	products := []string{fmt.Sprintf("cli/%s", build.GetInfo().Version)}
	if experimental := b.Config.Experimental; experimental != nil {
		if experimental.PyDABs.Enabled {
			products = append(products, "databricks-pydabs/0.0.0")
		}
	}

	userAgentExtra := strings.Join(products, " ")
	if userAgentExtra != "" {
		environ["DATABRICKS_USER_AGENT_EXTRA"] = userAgentExtra
	}

	return nil
}

func (m *initialize) Apply(ctx context.Context, b *bundle.Bundle) diag.Diagnostics {
	tfConfig := b.Config.Bundle.Terraform
	if tfConfig == nil {
		tfConfig = &config.Terraform{}
		b.Config.Bundle.Terraform = tfConfig
	}

	execPath, err := m.findExecPath(ctx, b, tfConfig)
	if err != nil {
		return diag.FromErr(err)
	}

	workingDir, err := Dir(ctx, b)
	if err != nil {
		return diag.FromErr(err)
	}

	tf, err := tfexec.NewTerraform(workingDir, execPath)
	if err != nil {
		return diag.FromErr(err)
	}

	environ, err := b.AuthEnv()
	if err != nil {
		return diag.FromErr(err)
	}

	err = inheritEnvVars(ctx, environ)
	if err != nil {
		return diag.FromErr(err)
	}

	// Set the temporary directory environment variables
	err = setTempDirEnvVars(ctx, environ, b)
	if err != nil {
		return diag.FromErr(err)
	}

	// Set the proxy related environment variables
	err = setProxyEnvVars(ctx, environ, b)
	if err != nil {
		return diag.FromErr(err)
	}

	err = setUserAgentExtraEnvVar(environ, b)
	if err != nil {
		return diag.FromErr(err)
	}

	// Configure environment variables for auth for Terraform to use.
	log.Debugf(ctx, "Environment variables for Terraform: %s", strings.Join(maps.Keys(environ), ", "))
	err = tf.SetEnv(environ)
	if err != nil {
		return diag.FromErr(err)
	}

	b.Terraform = tf
	return nil
}

func Initialize() bundle.Mutator {
	return &initialize{}
}