package runtime

import (
	"context"
	"fmt"
	"os"
	"strings"

	"github.com/evanw/esbuild/pkg/api"
	"github.com/fastschema/qjs"

	"reichard.io/poiesis/internal/functions"
	_ "reichard.io/poiesis/internal/stdlib"
)

type Runtime struct {
	ctx       *qjs.Context
	opts      qjs.Option
	funcs     map[string]functions.Function
	typeDecls map[string]string
}

func New(ctx context.Context, opts ...RuntimeOption) (*Runtime, error) {
	// Create Runtime
	r := &Runtime{opts: qjs.Option{Context: ctx}}
	for _, opt := range opts {
		opt(r)
	}

	// Create QuickJS Context
	rt, err := qjs.New(r.opts)
	if err != nil {
		return nil, err
	}
	r.ctx = rt.Context()

	// Populate Globals
	if err := r.populateGlobals(); err != nil {
		return nil, err
	}

	return r, nil
}

func (r *Runtime) populateGlobals() error {
	// Initialize Maps
	r.funcs = make(map[string]functions.Function)
	r.typeDecls = make(map[string]string)

	// Load Requested Functions
	allFuncs := functions.GetRegisteredFunctions()
	for name, fn := range allFuncs {
		r.funcs[name] = fn
		if err := r.addFunctionTypes(fn); err != nil {
			return fmt.Errorf("failed to add types for function %s: %w", name, err)
		}
	}

	// Register Functions with QuickJS
	for name, fn := range r.funcs {
		if fn.IsAsync() {
			r.ctx.SetAsyncFunc(name, func(this *qjs.This) {
				qjsVal, err := callFunc(this, fn)
				if err != nil {
					_ = this.Promise().Reject(this.Context().NewError(err))
					return
				}
				_ = this.Promise().Resolve(qjsVal)
			})
		} else {
			r.ctx.SetFunc(name, func(this *qjs.This) (*qjs.Value, error) {
				return callFunc(this, fn)
			})
		}
	}

	return nil
}

// addFunctionTypes adds types from a function to the runtime's type declarations.
// Returns an error if there's a type conflict (same name, different definition).
func (r *Runtime) addFunctionTypes(fn functions.Function) error {
	for name, def := range fn.Types() {
		if existing, ok := r.typeDecls[name]; ok && existing != def {
			return fmt.Errorf("type conflict: %s has conflicting definitions (existing: %s, new: %s)",
				name, existing, def)
		}
		r.typeDecls[name] = def
	}
	return nil
}

// GetTypeDeclarations returns all TypeScript type declarations for this runtime.
// Includes both type definitions and function declarations.
func (r *Runtime) GetTypeDeclarations() string {
	var decls []string

	// Add Type Definitions
	for _, def := range r.typeDecls {
		decls = append(decls, def)
	}

	// Add Function Declarations
	for _, fn := range r.funcs {
		decls = append(decls, fn.Definition())
	}

	return strings.Join(decls, "\n\n")
}

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

	return r.RunCode(string(tsFileContent))
}

func (r *Runtime) RunCode(tsCode string) error {
	transformedCode, err := r.transformCode(tsCode)
	if err != nil {
		return err
	}

	result, err := r.ctx.Eval("code.ts", qjs.Code(string(transformedCode)))
	if result != nil {
		result.Free()
	}
	return err
}

func (r *Runtime) transformCode(tsCode string) ([]byte, error) {
	result := api.Transform(tsCode, api.TransformOptions{
		Loader:      api.LoaderTS,
		Target:      api.ES2022,
		Format:      api.FormatIIFE,
		Sourcemap:   api.SourceMapNone,
		TreeShaking: api.TreeShakingFalse,
	})

	if len(result.Errors) > 0 {
		var b strings.Builder
		for i, e := range result.Errors {
			if i > 0 {
				b.WriteString(", ")
			}
			b.WriteString(e.Text)
		}
		return nil, fmt.Errorf("transpilation failed: %s", b.String())
	}

	return result.Code, nil
}

func callFunc(this *qjs.This, fn functions.Function) (*qjs.Value, error) {
	qjsArgs := this.Args()
	fnArgs := fn.Arguments()

	var allArgs []any
	for i := range min(len(fnArgs), len(qjsArgs)) {
		rVal, err := qjs.JsArgToGo(qjsArgs[i], fnArgs[i])
		if err != nil {
			return nil, fmt.Errorf("argument conversion failed: %w", err)
		}
		allArgs = append(allArgs, rVal.Interface())
	}

	result, err := fn.Call(this.Context(), allArgs)
	if err != nil {
		return nil, err
	}

	val, err := qjs.ToJsValue(this.Context(), result)
	if err != nil {
		return nil, err
	}

	return val, nil
}