package runtime

import (
	"context"
	"fmt"
	"io"
	"os"

	"github.com/evanw/esbuild/pkg/api"
	"modernc.org/quickjs"
	"reichard.io/poiesis/internal/functions"
)

type Runtime struct {
	vm  *quickjs.VM
	ctx context.Context

	stdout io.Writer
	stderr io.Writer
}

func New(ctx context.Context) (*Runtime, error) {
	// Create VM
	vm, err := quickjs.NewVM()
	if err != nil {
		return nil, err
	}
	vm.SetCanBlock(true)

	// Create Runtime
	r := &Runtime{vm: vm, ctx: ctx, stdout: os.Stdout, stderr: os.Stderr}
	if err := r.populateGlobals(); err != nil {
		return nil, err
	}

	return r, nil
}

func (r *Runtime) populateGlobals() error {
	// Add Helpers
	if err := r.vm.StdAddHelpers(); err != nil {
		return err
	}

	// Add Log Hook
	if err := r.vm.RegisterFunc("customLog", func(args ...any) {
		for i, arg := range args {
			if i > 0 {
				_, _ = fmt.Fprint(r.stdout, " ")
			}
			_, _ = fmt.Fprint(r.stdout, arg)
		}
		_, _ = fmt.Fprintln(r.stdout)
	}, false); err != nil {
		return err
	}
	if _, err := r.vm.Eval("console.log = customLog;", quickjs.EvalGlobal); err != nil {
		return err
	}

	// Register Custom Functions
	for name, builtin := range functions.GetRegisteredFunctions() {
		// Register Main Function
		if err := r.vm.RegisterFunc(name, builtin.WrapFn(r.ctx), false); err != nil {
			return err
		}

		// Wrap Exception - The QuickJS library does not allow us to throw exceptions, so we
		//                  wrap the function with native JS to appropriately throw on error.
		if _, err := r.vm.Eval(fmt.Sprintf(`
                  (function() {
                    const original = globalThis[%q];
                  
                    globalThis[%q] = function(...args) {
                      const [result, error] = original.apply(this, args);
                      if (error) {
                        throw new Error(error);
                      }
                      return result;
                    };
                  })();
                `, name, name), quickjs.EvalGlobal); err != nil {
			return err
		}
	}

	return nil
}

func (r *Runtime) RunFile(filePath string, stdout, stderr io.Writer) error {
	r.stdout = stdout
	r.stderr = stderr

	content, err := r.transformFile(filePath)
	if err != nil {
		_, _ = fmt.Fprintf(stderr, "Error: %v\n", err)
		return err
	}

	if len(content.errors) > 0 {
		_, _ = fmt.Fprintf(stderr, "Transpilation errors:\n")
		for _, err := range content.errors {
			_, _ = fmt.Fprintf(stderr, "  %s\n", err.Text)
		}
		return fmt.Errorf("transpilation failed")
	}

	_, err = r.vm.Eval(content.code, quickjs.EvalGlobal)
	if err != nil {
		_, _ = fmt.Fprintf(stderr, "Execution error: %v\n", err)
		return err
	}

	return nil
}

func (r *Runtime) RunCode(tsCode string, stdout, stderr io.Writer) error {
	r.stdout = stdout
	r.stderr = stderr

	content := r.transformCode(tsCode)

	if len(content.errors) > 0 {
		_, _ = fmt.Fprintf(stderr, "Transpilation errors:\n")
		for _, err := range content.errors {
			_, _ = fmt.Fprintf(stderr, "  %s\n", err.Text)
		}
		return fmt.Errorf("transpilation failed")
	}

	_, err := r.vm.Eval(content.code, quickjs.EvalGlobal)
	if err != nil {
		_, _ = fmt.Fprintf(stderr, "Execution error: %v\n", err)
		return err
	}

	return nil
}

type transformResult struct {
	code   string
	errors []api.Message
}

func (r *Runtime) transformFile(filePath string) (*transformResult, error) {
	tsFileContent, err := os.ReadFile(filePath)
	if err != nil {
		return nil, fmt.Errorf("error reading file: %w", err)
	}

	return r.transformCode(string(tsFileContent)), nil
}

func (r *Runtime) transformCode(tsCode string) *transformResult {
	// 	wrappedCode := `(async () => {
	// try {
	// 	` + tsCode + `
	// } catch (err) {
	// 	console.error(err);
	// }
	// })()`

	result := api.Transform(tsCode, api.TransformOptions{
		Loader:      api.LoaderTS,
		Target:      api.ES2022,
		Format:      api.FormatIIFE,
		Sourcemap:   api.SourceMapNone,
		TreeShaking: api.TreeShakingFalse,
	})

	return &transformResult{
		code:   string(result.Code),
		errors: result.Errors,
	}
}