package tools

import (
	"bufio"
	"bytes"
	"encoding/base64"
	"errors"
	"fmt"
	"hash/fnv"
	"io"
	"os"
	"path"
	"sort"
	"strings"
	"unicode"
)

const selfPkg = "code.squareroundforest.org/arpio/wand"

type ExecOptions struct {
	NoCache       bool
	ClearCache    bool
	CacheDir      string
	Import        []string
	ReplaceModule []string
}

func commandReader(in io.Reader) func() ([]string, error) {
	var (
		yieldErr                             error
		currentArg                           []rune
		args                                 []string
		escapeOne, escapePartial, escapeFull bool
	)

	buf := bufio.NewReader(in)
	return func() ([]string, error) {
		if yieldErr != nil {
			return nil, yieldErr
		}

		for {
			r, _, err := buf.ReadRune()
			if errors.Is(err, io.EOF) {
				if len(currentArg) > 0 {
					args = append(args, string(currentArg))
					currentArg = nil
				}

				yield := args
				args = nil
				yieldErr = err
				return yield, nil
			}

			if err != nil {
				yieldErr = fmt.Errorf("failed reading from input: %w", err)
				return nil, yieldErr
			}

			if r == unicode.ReplacementChar {
				if len(currentArg) > 0 {
					yieldErr = errors.New("broken unicode stream")
					return nil, yieldErr
				}

				continue
			}

			if escapeFull {
				if r == '\'' {
					escapeFull = false
					args = append(args, string(currentArg))
					currentArg = nil
					continue
				}

				currentArg = append(currentArg, r)
				continue
			}

			if escapeOne {
				escapeOne = false
				currentArg = append(currentArg, r)
				continue
			}

			if escapePartial {
				if r == '\\' {
					escapeOne = true
					continue
				}

				if r == '"' {
					escapePartial = false
					args = append(args, string(currentArg))
					currentArg = nil
					continue
				}

				currentArg = append(currentArg, r)
				continue
			}

			if r == '\n' {
				if len(currentArg) > 0 {
					args = append(args, string(currentArg))
					currentArg = nil
				}

				yield := args
				args = nil
				return yield, nil
			}

			if unicode.IsSpace(r) {
				if len(currentArg) > 0 {
					args = append(args, string(currentArg))
					currentArg = nil
				}

				continue
			}

			switch r {
			case '\\':
				escapeOne = true
			case '"':
				escapePartial = true
			case '\'':
				escapeFull = true
			default:
				currentArg = append(currentArg, r)
			}
		}
	}
}

func hash(expression string, imports []string) (string, error) {
	h := fnv.New128()
	h.Write([]byte(expression))
	sort.Strings(imports)
	for _, i := range imports {
		h.Write([]byte(i))
	}

	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 expression: %w", err)
	}

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

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

func printGoFile(fn string, expression string, imports []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")
	for _, i := range imports {
		ii := strings.Split(i, "=")
		p := ii[0]
		if len(ii) > 1 {
			p = strings.Join(ii[1:], "=")
		}

		if len(ii) == 1 {
			fprintf("import \"%s\"\n", strings.Split(p, "@")[0])
		} else {
			fprintf("import %s \"%s\"\n", ii[0], strings.Split(p, "@")[0])
		}
	}

	fprintf("import \"%s\"\n", selfPkg)
	fprintf("func main() {\n")
	fprintf("wand.Exec(%s)\n", expression)
	fprintf("}")
	return err
}

func execWand(o ExecOptions, stdin io.Reader, stdout, stderr io.Writer, args []string) error {
	expression, args := args[0], args[1:]
	commandHash, err := hash(expression, o.Import)
	if err != nil {
		return err
	}

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

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

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

	if err := os.MkdirAll(commandDir, 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
	}

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

		return nil
	}

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

	defer os.Chdir(wd)
	gomodPath := path.Join(commandDir, "go.mod")
	if _, err := os.Stat(gomodPath); err != nil {
		if err := execInternal("go mod init", commandHash); err != nil {
			return fmt.Errorf("failed to initialize temporary module: %w", err)
		}

		var hasSelf bool
		for _, pkg := range o.Import {
			pp := strings.Split(pkg, "=")
			p := pp[0]
			if len(pp) > 1 {
				p = strings.Join(pp[1:], "=")
			}

			if err := goGet(p); err != nil {
				return err
			}

			if p == selfPkg {
				hasSelf = true
			}
		}

		if !hasSelf {
			if err := goGet(selfPkg); err != nil {
				return err
			}
		}

		for _, replace := range o.ReplaceModule {
			if err := goReplace(replace); err != nil {
				return err
			}
		}
	}

	goFile := path.Join(commandDir, fmt.Sprintf("%s.go", commandHash))
	if _, err := os.Stat(goFile); err != nil {
		if err := printGoFile(goFile, expression, o.Import); err != nil {
			return fmt.Errorf("failed to create temporary go file: %w", err)
		}
	}

	if err := execc(stdin, stdout, stderr, "go run", append([]string{commandDir}, args...), nil); err != nil {
		return err
	}

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

	return nil
}

func readExec(o ExecOptions, stdin io.Reader, stdout, stderr io.Writer) error {
	readCommand := commandReader(stdin)
	for {
		args, err := readCommand()
		if errors.Is(err, io.EOF) {
			return nil
		}

		if err != nil {
			return err
		}

		if len(args) == 0 {
			continue
		}

		if err := execWand(o, stdin, stdout, stderr, args); err != nil {
			fmt.Fprintln(stderr, err)
		}
	}
}

func execInput(o ExecOptions, stdin io.Reader, stdout, stderr io.Writer, args ...string) error {
	if len(args) == 0 {
		return readExec(o, stdin, stdout, stderr)
	}

	return execWand(o, stdin, stdout, stderr, args)
}

func Exec(o ExecOptions, stdin io.Reader, stdout io.Writer, args ...string) error {
	return execInput(o, stdin, stdout, os.Stderr, args...)
}