package tools

import (
	"bytes"
	"code.squareroundforest.org/arpio/docreflect/generate"
	"encoding/base64"
	"errors"
	"fmt"
	"hash/fnv"
	"io"
	"os"
	"os/exec"
	"path"
	"strings"
)

type ExecOptions struct {
	NoCache    bool
	ClearCache bool
	CacheDir   string
}

func execc(stdin io.Reader, stdout, stderr io.Writer, command string, args []string, env []string) error {
	c := strings.Split(command, " ")
	cmd := exec.Command(c[0], append(c[1:], args...)...)
	cmd.Env = append(os.Environ(), env...)
	cmd.Stdin = stdin
	cmd.Stdout = stdout
	cmd.Stderr = stderr
	return cmd.Run()
}

func execCommandDir(out io.Writer, commandDir string, env ...string) error {
	stderr := bytes.NewBuffer(nil)
	if err := execc(nil, out, stderr, "go run", []string{commandDir}, env); err != nil {
		io.Copy(os.Stderr, stderr)
		return err
	}

	return nil
}

func execInternal(command string, args ...string) error {
	stdout := bytes.NewBuffer(nil)
	stderr := bytes.NewBuffer(nil)
	if err := execc(nil, stdout, stderr, command, args, nil); err != nil {
		io.Copy(os.Stderr, stdout)
		io.Copy(os.Stderr, stderr)
		return err
	}

	return nil
}

func execTransparent(command string, args ...string) error {
	return execc(os.Stdin, os.Stdout, os.Stderr, command, args, nil)
}

func Docreflect(out io.Writer, packageName string, gopaths ...string) error {
	return generate.GenerateRegistry(out, packageName, gopaths...)
}

func Man(out io.Writer, commandDir string) error {
	return execCommandDir(out, commandDir, "wandgenerate=man")
}

func Markdown(out io.Writer, commandDir string) error {
	return execCommandDir(out, commandDir, "wandgenerate=markdown")
}

func splitFunction(function string) (pkg string, expression string, err error) {
	parts := strings.Split(function, "/")
	gopath := parts[:len(parts)-1]
	sparts := strings.Split(parts[len(parts)-1], ".")
	if len(sparts) == 1 && len(gopath) > 1 {
		err = errors.New("function cannot be identified")
		return
	}

	if len(sparts) == 1 {
		expression = sparts[0]
	} else {
		expression = parts[len(parts)-1]
		pkg = strings.Join(append(gopath, sparts[0]), "/")
	}

	return
}

func functionHash(function string) (string, error) {
	h := fnv.New128()
	h.Write([]byte(function))
	buf := bytes.NewBuffer(nil)
	b64 := base64.NewEncoder(base64.RawURLEncoding, buf)
	if _, err := b64.Write(h.Sum(nil)); err != nil {
		return "", fmt.Errorf("failed to encode function: %w", err)
	}

	if err := b64.Close(); err != nil {
		return "", fmt.Errorf("failed to complete encoding of function: %w", err)
	}

	return strings.TrimPrefix(buf.String(), "_"), nil
}

func findGomod(wd string) (string, bool) {
	gomodDir := wd
	for {
		gomodPath := path.Join(gomodDir, "go.mod")
		f, err := os.Stat(gomodPath)
		if err == nil && !f.IsDir() {
			return gomodPath, true
		}

		if gomodDir == "/" {
			return "", false
		}

		gomodDir = path.Dir(gomodDir)
	}
}

func copyGomod(mn, dst, src string) error {
	srcf, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("failed to open file: %s; %w", src, err)
	}

	defer srcf.Close()
	dstf, err := os.Create(dst)
	if err != nil {
		return fmt.Errorf("failed to create file: %s; %w", dst, err)
	}

	defer dstf.Close()
	b, err := io.ReadAll(srcf)
	if err != nil {
		return fmt.Errorf("failed to read go.mod file %s: %w", src, err)
	}

	s := string(b)
	ss := strings.Split(s, "\n")
	for i := range ss {
		if strings.HasPrefix(ss[i], "module ") {
			ss[i] = fmt.Sprintf("module %s", mn)
			break
		}
	}

	if _, err := dstf.Write([]byte(strings.Join(ss, "\n"))); err != nil {
		return fmt.Errorf("failed to write go.mod file %s: %w", dst, err)
	}

	return nil
}

func printFile(fn string, pkg, expression string) error {
	f, err := os.Create(fn)
	if err != nil {
		return err
	}

	defer f.Close()
	fprintf := func(format string, args ...any) {
		if err != nil {
			return
		}

		_, err = fmt.Fprintf(f, format, args...)
	}

	fprintf("package main\n")
	if pkg != "" {
		fprintf("import \"%s\"\n", pkg)
	}

	fprintf("import \"code.squareroundforest.org/arpio/wand\"\n")
	fprintf("func main() {\n")
	fprintf("wand.Exec(%s)\n", expression)
	fprintf("}")
	return err
}

func Exec(o ExecOptions, function string, args ...string) error {
	pkg, expression, err := splitFunction(function)
	if err != nil {
		return err
	}

	functionHash, err := functionHash(function)
	if err != nil {
		return err
	}

	cacheDir := o.CacheDir
	if cacheDir == "" {
		cacheDir = path.Join(os.Getenv("HOME"), ".wand")
	}

	functionDir := path.Join(cacheDir, functionHash)
	if o.NoCache {
		functionDir = path.Join(cacheDir, "tmp", functionHash)
	}

	if o.NoCache || o.ClearCache {
		if err := os.RemoveAll(functionDir); err != nil {
			return fmt.Errorf("failed to clean cache: %w", err)
		}
	}

	if err := os.MkdirAll(functionDir, os.ModePerm); err != nil {
		return fmt.Errorf("failed to ensure cache directory: %w", err)
	}

	wd, err := os.Getwd()
	if err != nil {
		return fmt.Errorf("error identifying current directory: %w", err)
	}

	goGet := func(pkg string) error {
		if err := execInternal("go get", pkg); err != nil {
			return fmt.Errorf("failed to get go module: %w", err)
		}

		return nil
	}

	if err := os.Chdir(functionDir); err != nil {
		return fmt.Errorf("failed to switch to temporary directory: %w", err)
	}

	defer os.Chdir(wd)
	gomodPath, hasGomod := findGomod(wd)
	if hasGomod {
		if err := copyGomod(functionHash, path.Join(functionDir, "go.mod"), gomodPath); err != nil {
			return err
		}
	} else {
		if err := execInternal("go mod init", functionHash); err != nil {
			return fmt.Errorf("failed to initialize temporary module: %w", err)
		}
	}

	// non-robust way of avoiding importing standard library packages:
	if strings.Contains(pkg, ".") {
		if err := goGet(pkg); err != nil {
			return err
		}
	}

	if err := goGet("code.squareroundforest.org/arpio/wand"); err != nil {
		return err
	}

	goFile := path.Join(functionDir, fmt.Sprintf("%s.go", functionHash))
	if _, err := os.Stat(goFile); err != nil {
		if err := printFile(goFile, pkg, expression); err != nil {
			return fmt.Errorf("failed to create temporary go file: %w", err)
		}
	}

	if err := execTransparent("go run", append([]string{functionDir}, args...)...); err != nil {
		return err
	}

	if o.NoCache {
		if err := os.RemoveAll(functionDir); err != nil {
			return fmt.Errorf("failed to clean cache: %w", err)
		}
	}

	return nil
}