package main

import (
	"bufio"
	"bytes"
	"context"
	"errors"
	"fmt"
	"io/fs"
	"log"
	"os"
	"path/filepath"
	"regexp"
	"strings"

	"ucl.lmika.dev/ucl"
)

const pluginKeyPrefix = "plugin:"

// PluginFilters is the registry of text filters defined by UCL plugin files.
type PluginFilters struct {
	filters map[string]TextProcessor
	errors  []error
}

func newPluginFilters() *PluginFilters {
	return &PluginFilters{
		filters: make(map[string]TextProcessor),
	}
}

// Module returns the "d" UCL module, exposing d:filter.
func (p *PluginFilters) Module() ucl.Module {
	return ucl.Module{
		Name: "d",
		Builtins: map[string]ucl.BuiltinHandler{
			"filter":    p.filterBuiltin,
			"map-lines": p.mapLinesBuiltin,
		},
	}
}

// filterBuiltin implements `d:filter LABEL PROC`. PROC receives the filter input as its only
// argument and its result becomes the filter output.
func (p *PluginFilters) filterBuiltin(ctx context.Context, args ucl.CallArgs) (any, error) {
	var (
		label string
		proc  ucl.Invokable
	)

	if err := args.Bind(&label, &proc); err != nil {
		return nil, fmt.Errorf("d:filter: expected LABEL and PROC: %w", err)
	}
	if strings.TrimSpace(label) == "" {
		return nil, errors.New("d:filter: label must not be empty")
	}
	if proc.IsNil() {
		return nil, errors.New("d:filter: PROC must not be nil")
	}

	p.filters[pluginKeyPrefix+slugify(label)] = TextProcessor{
		Label: label,
		Filter: func(ctx context.Context, input string) (TextFilterResponse, error) {
			res, err := proc.Invoke(ctx, input)
			if err != nil {
				return TextFilterResponse{}, err
			}

			switch v := res.(type) {
			case nil:
				return TextFilterResponse{}, errors.New("filter returned no value")
			case string:
				return TextFilterResponse{Output: v}, nil
			default:
				return TextFilterResponse{Output: fmt.Sprint(v)}, nil
			}
		},
	}
	return nil, nil
}

// mapLinesBuiltin implements `d:map-lines INPUT PROC` which applies a transform for each line of the input.
func (p *PluginFilters) mapLinesBuiltin(ctx context.Context, args ucl.CallArgs) (any, error) {
	var (
		input string
		proc  ucl.Invokable
	)

	if err := args.Bind(&input, &proc); err != nil {
		return nil, fmt.Errorf("d:map-lines: expected INPUT and PROC: %w", err)
	}

	var (
		dst     bytes.Buffer
		dstLine bytes.Buffer
	)

	scnr := bufio.NewScanner(strings.NewReader(input))
	isFirst := true
	for scnr.Scan() {
		dstLine.Reset()
		line := scnr.Text()

		out, err := proc.Invoke(ctx, line)
		if err != nil {
			return TextFilterResponse{}, err
		} else if out == nil {
			continue
		} else if strOut, ok := out.(fmt.Stringer); ok {
			dstLine.WriteString(strOut.String())
		} else {
			dstLine.WriteString(fmt.Sprint(out))
		}

		if isFirst {
			isFirst = false
		} else {
			dst.WriteString("\n")
		}

		dst.WriteString(dstLine.String())
	}

	return dst.String(), nil
}

// LoadDir evaluates every *.ucl file found under dir (recursively, in lexical order). Files
// that fail to load are recorded in Errors() and skipped; loading continues with the rest.
// A missing directory is not an error.
func (p *PluginFilters) LoadDir(ctx context.Context, inst *ucl.Inst, dir string) {
	if _, err := os.Stat(dir); err != nil {
		if !errors.Is(err, fs.ErrNotExist) {
			p.recordError(fmt.Errorf("%s: %w", dir, err))
		}
		return
	}

	_ = filepath.WalkDir(dir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			p.recordError(fmt.Errorf("%s: %w", path, err))
			return nil
		}
		if d.IsDir() || !strings.EqualFold(filepath.Ext(path), ".ucl") {
			return nil
		}

		if err := p.loadFile(ctx, inst, path); err != nil {
			p.recordError(fmt.Errorf("%s: %w", path, err))
		}
		return nil
	})
}

func (p *PluginFilters) loadFile(ctx context.Context, inst *ucl.Inst, path string) error {
	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()

	_, err = inst.Eval(ctx, f)
	return err
}

func (p *PluginFilters) recordError(err error) {
	log.Printf("plugin load error: %v", err)
	p.errors = append(p.errors, err)
}

// Errors returns the errors encountered while loading plugin files.
func (p *PluginFilters) Errors() []error {
	return p.errors
}

// pluginDir returns the plugin directory under macOS Application Support.
func pluginDir() (string, error) {
	home, err := os.UserHomeDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(home, "Library", "Application Support", "dev.lmika.dequoter", "Plugins"), nil
}

func ensurePluginDir() (string, error) {
	dir, err := pluginDir()
	if err != nil {
		return "", err
	}
	if err := os.MkdirAll(dir, 0755); err != nil {
		return "", fmt.Errorf("create plugin directory: %w", err)
	}
	return dir, nil
}

var nonSlugChars = regexp.MustCompile(`[^a-z0-9]+`)

// slugify converts a label into a key-safe slug: lower-cased, with runs of characters other than
// [a-z0-9] replaced by a single hyphen and leading/trailing hyphens removed.
func slugify(label string) string {
	return strings.Trim(nonSlugChars.ReplaceAllString(strings.ToLower(label), "-"), "-")
}