package docfill

import (
	"archive/zip"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"

	_ "modernc.org/sqlite"

	"github.com/xuri/excelize/v2"
)

type config struct {
	Vars     map[string]string `json:"vars"`
	Data     dataConfig        `json:"data"`
	Template templateConfig    `json:"template"`
	Output   outputConfig      `json:"output"`
}

type dataConfig struct {
	Type      string   `json:"type"`
	Path      string   `json:"path"`
	Sheet     string   `json:"sheet"`
	Query     string   `json:"query"`
	Params    []string `json:"params"`
	HeaderRow int      `json:"header_row"`
}

type templateConfig struct {
	Path string `json:"path"`
}

type outputConfig struct {
	Path      string `json:"path"`
	Overwrite bool   `json:"overwrite"`
}

type RunOptions struct {
	Vars map[string]string
}

type RunResult struct {
	Files []string
}

var (
	placeholderPattern    = regexp.MustCompile(`\{\{([^{}<>]+)\}\}`)
	docxParagraphPattern  = regexp.MustCompile(`(?s)<w:p\b[^>]*>.*?</w:p>`)
	docxTextNodePattern   = regexp.MustCompile(`(?s)<w:t\b[^>]*>(.*?)</w:t>`)
	docxGeneratedXMLTypes = map[string]struct{}{
		".xml": {},
	}
)

// Run executes one configured fill task.
func Run(configPath string) error {
	_, err := RunWithOptions(configPath, RunOptions{})
	return err
}

// RunWithOptions executes one configured fill task and returns generated files.
func RunWithOptions(configPath string, opts RunOptions) (RunResult, error) {
	cfg, err := loadConfig(configPath)
	if err != nil {
		return RunResult{}, err
	}
	if err := validateConfig(cfg); err != nil {
		return RunResult{}, err
	}

	vars := mergeVars(cfg.Vars, opts.Vars)
	rows, err := readRowsWithVars(cfg.Data, vars)
	if err != nil {
		return RunResult{}, err
	}
	if len(rows) == 0 {
		return RunResult{}, errors.New("data returned no rows")
	}

	result := RunResult{Files: make([]string, 0, len(rows))}
	for i, row := range rows {
		context := renderContext(vars, row, i+1)
		if err := ensurePlaceholdersAvailable("output path", cfg.Output.Path, context); err != nil {
			return RunResult{}, fmt.Errorf("render row %d: %w", i+1, err)
		}

		outputPath := replacePathPlaceholders(cfg.Output.Path, context)
		if hasPlaceholder(outputPath) {
			return RunResult{}, fmt.Errorf("render row %d: unresolved placeholder in output path %q", i+1, outputPath)
		}
		if !cfg.Output.Overwrite && fileExists(outputPath) {
			return RunResult{}, fmt.Errorf("render row %d: output already exists: %s", i+1, outputPath)
		}
		if err := renderTemplate(cfg.Template.Path, outputPath, context); err != nil {
			return RunResult{}, fmt.Errorf("render row %d: %w", i+1, err)
		}

		result.Files = append(result.Files, outputPath)
	}

	return result, nil
}

func loadConfig(path string) (config, error) {
	if path == "" {
		return config{}, errors.New("config path is required")
	}

	data, err := os.ReadFile(path)
	if err != nil {
		return config{}, fmt.Errorf("read config: %w", err)
	}

	var cfg config
	if err := json.Unmarshal(data, &cfg); err != nil {
		return config{}, fmt.Errorf("parse config json: %w", err)
	}
	resolveConfigPaths(&cfg, filepath.Dir(absPath(path)))
	return cfg, nil
}

func validateConfig(cfg config) error {
	if cfg.Data.Type == "" {
		return errors.New("data.type is required")
	}
	if cfg.Data.Path == "" {
		return errors.New("data.path is required")
	}
	if cfg.Template.Path == "" {
		return errors.New("template.path is required")
	}
	if cfg.Output.Path == "" {
		return errors.New("output.path is required")
	}
	if cfg.Data.HeaderRow < 0 {
		return errors.New("data.header_row must not be negative")
	}
	return nil
}

func readRows(cfg dataConfig) ([]map[string]string, error) {
	return readRowsWithVars(cfg, nil)
}

func readRowsWithVars(cfg dataConfig, vars map[string]string) ([]map[string]string, error) {
	switch strings.ToLower(cfg.Type) {
	case "excel", "xlsx":
		return readExcelRows(cfg)
	case "sqlite":
		return readSQLiteRows(cfg, vars)
	default:
		return nil, fmt.Errorf("unsupported data.type %q", cfg.Type)
	}
}

func readExcelRows(cfg dataConfig) ([]map[string]string, error) {
	f, err := excelize.OpenFile(cfg.Path)
	if err != nil {
		return nil, fmt.Errorf("open excel data: %w", err)
	}
	defer f.Close()

	sheet := cfg.Sheet
	if sheet == "" {
		sheet = f.GetSheetName(0)
	}
	if sheet == "" {
		return nil, errors.New("excel data has no sheets")
	}

	rawRows, err := f.GetRows(sheet)
	if err != nil {
		return nil, fmt.Errorf("read excel sheet %q: %w", sheet, err)
	}
	if len(rawRows) == 0 {
		return nil, errors.New("excel data has no header row")
	}

	headerRow := cfg.HeaderRow
	if headerRow == 0 {
		headerRow = 1
	}
	if headerRow > len(rawRows) {
		return nil, fmt.Errorf("excel header_row %d is outside sheet %q", headerRow, sheet)
	}

	headers := make([]string, len(rawRows[headerRow-1]))
	for i, header := range rawRows[headerRow-1] {
		headers[i] = strings.TrimSpace(header)
	}

	var rows []map[string]string
	for _, raw := range rawRows[headerRow:] {
		if rowIsEmpty(raw) {
			continue
		}
		row := make(map[string]string)
		for i, header := range headers {
			if header == "" {
				continue
			}
			if i < len(raw) {
				row[header] = raw[i]
			} else {
				row[header] = ""
			}
		}
		rows = append(rows, row)
	}

	return rows, nil
}

func readSQLiteRows(cfg dataConfig, vars map[string]string) ([]map[string]string, error) {
	if cfg.Query == "" {
		return nil, errors.New("data.query is required for sqlite")
	}

	db, err := sql.Open("sqlite", cfg.Path)
	if err != nil {
		return nil, fmt.Errorf("open sqlite data: %w", err)
	}
	defer db.Close()

	args, err := sqliteParams(cfg.Params, vars)
	if err != nil {
		return nil, err
	}

	result, err := db.Query(cfg.Query, args...)
	if err != nil {
		return nil, fmt.Errorf("query sqlite data: %w", err)
	}
	defer result.Close()

	columns, err := result.Columns()
	if err != nil {
		return nil, fmt.Errorf("read sqlite columns: %w", err)
	}

	var rows []map[string]string
	for result.Next() {
		values := make([]any, len(columns))
		scanTargets := make([]any, len(columns))
		for i := range values {
			scanTargets[i] = &values[i]
		}
		if err := result.Scan(scanTargets...); err != nil {
			return nil, fmt.Errorf("scan sqlite row: %w", err)
		}

		row := make(map[string]string)
		for i, column := range columns {
			row[column] = stringify(values[i])
		}
		rows = append(rows, row)
	}
	if err := result.Err(); err != nil {
		return nil, fmt.Errorf("iterate sqlite rows: %w", err)
	}

	return rows, nil
}

func renderTemplate(templatePath, outputPath string, row map[string]string) error {
	if err := validateTemplateFields(templatePath, row); err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(outputPath), 0o755); err != nil {
		return fmt.Errorf("create output directory: %w", err)
	}

	switch strings.ToLower(filepath.Ext(templatePath)) {
	case ".xlsx":
		return renderXLSX(templatePath, outputPath, row)
	case ".docx":
		return renderDOCX(templatePath, outputPath, row)
	default:
		return fmt.Errorf("unsupported template extension %q", filepath.Ext(templatePath))
	}
}

func renderXLSX(templatePath, outputPath string, row map[string]string) error {
	f, err := excelize.OpenFile(templatePath)
	if err != nil {
		return fmt.Errorf("open xlsx template: %w", err)
	}
	defer f.Close()

	for _, sheet := range f.GetSheetList() {
		rows, err := f.GetRows(sheet)
		if err != nil {
			return fmt.Errorf("read template sheet %q: %w", sheet, err)
		}
		for r, values := range rows {
			for c, value := range values {
				if !strings.Contains(value, "{{") {
					continue
				}
				cell, err := excelize.CoordinatesToCellName(c+1, r+1)
				if err != nil {
					return fmt.Errorf("cell name: %w", err)
				}
				rendered := replacePlaceholders(value, row)
				if hasPlaceholder(rendered) {
					return fmt.Errorf("unresolved placeholder in %s!%s", sheet, cell)
				}
				if err := f.SetCellValue(sheet, cell, rendered); err != nil {
					return fmt.Errorf("set cell %s!%s: %w", sheet, cell, err)
				}
			}
		}
	}

	if err := f.SaveAs(outputPath); err != nil {
		return fmt.Errorf("save xlsx output: %w", err)
	}
	return nil
}

func renderDOCX(templatePath, outputPath string, row map[string]string) error {
	reader, err := zip.OpenReader(templatePath)
	if err != nil {
		return fmt.Errorf("open docx template: %w", err)
	}
	defer reader.Close()

	output, err := os.Create(outputPath)
	if err != nil {
		return fmt.Errorf("create docx output: %w", err)
	}

	writer := zip.NewWriter(output)
	for _, source := range reader.File {
		if err := copyDocxPart(writer, source, row); err != nil {
			_ = writer.Close()
			_ = output.Close()
			return err
		}
	}
	if err := writer.Close(); err != nil {
		_ = output.Close()
		return fmt.Errorf("close docx output: %w", err)
	}
	if err := output.Close(); err != nil {
		return fmt.Errorf("close docx file: %w", err)
	}

	return nil
}

func copyDocxPart(writer *zip.Writer, source *zip.File, row map[string]string) error {
	header := source.FileHeader
	header.Name = source.Name
	header.Method = source.Method

	dest, err := writer.CreateHeader(&header)
	if err != nil {
		return fmt.Errorf("create docx part %s: %w", source.Name, err)
	}

	if source.FileInfo().IsDir() {
		return nil
	}

	src, err := source.Open()
	if err != nil {
		return fmt.Errorf("open docx part %s: %w", source.Name, err)
	}
	defer src.Close()

	data, err := io.ReadAll(src)
	if err != nil {
		return fmt.Errorf("read docx part %s: %w", source.Name, err)
	}
	if isDocxXMLPart(source.Name) {
		rendered, err := renderDocxXML(string(data), row)
		if err != nil {
			return fmt.Errorf("render docx part %s: %w", source.Name, err)
		}
		if docxHasPlaceholder(rendered) {
			return fmt.Errorf("unresolved placeholder in docx part %s", source.Name)
		}
		data = []byte(rendered)
	}

	if _, err := dest.Write(data); err != nil {
		return fmt.Errorf("write docx part %s: %w", source.Name, err)
	}
	return nil
}

func replacePlaceholders(text string, row map[string]string) string {
	return replacePlaceholdersWith(text, row, func(value string) string {
		return value
	})
}

func replaceDocxPlaceholders(text string, row map[string]string) string {
	return replacePlaceholdersWith(text, row, escapeXMLText)
}

func replacePathPlaceholders(text string, row map[string]string) string {
	return replacePlaceholdersWith(text, row, sanitizePathValue)
}

func replacePlaceholdersWith(text string, row map[string]string, transform func(string) string) string {
	return placeholderPattern.ReplaceAllStringFunc(text, func(match string) string {
		key := placeholderKey(match)
		value, ok := row[key]
		if !ok {
			return match
		}
		return transform(value)
	})
}

func rowIsEmpty(row []string) bool {
	for _, cell := range row {
		if strings.TrimSpace(cell) != "" {
			return false
		}
	}
	return true
}

func stringify(value any) string {
	switch v := value.(type) {
	case nil:
		return ""
	case []byte:
		return string(v)
	case string:
		return v
	default:
		return fmt.Sprint(v)
	}
}

func mergeVars(configVars, optionVars map[string]string) map[string]string {
	merged := make(map[string]string)
	for key, value := range configVars {
		merged[key] = value
	}
	for key, value := range optionVars {
		merged[key] = value
	}
	return merged
}

func renderContext(vars, row map[string]string, rowNumber int) map[string]string {
	context := make(map[string]string)
	for key, value := range vars {
		context[key] = value
	}
	for key, value := range row {
		context[key] = value
	}
	context["_row"] = strconv.Itoa(rowNumber)
	return context
}

func sqliteParams(params []string, vars map[string]string) ([]any, error) {
	args := make([]any, 0, len(params))
	for i, param := range params {
		if err := ensurePlaceholdersAvailable(fmt.Sprintf("sqlite params[%d]", i), param, vars); err != nil {
			return nil, err
		}
		rendered := replacePlaceholders(param, vars)
		if hasPlaceholder(rendered) {
			return nil, fmt.Errorf("unresolved placeholder in sqlite params[%d]", i)
		}
		args = append(args, rendered)
	}
	return args, nil
}

func validateTemplateFields(templatePath string, row map[string]string) error {
	fields, err := templatePlaceholders(templatePath)
	if err != nil {
		return err
	}
	for field := range fields {
		if _, ok := row[field]; !ok {
			return fmt.Errorf("missing template field %q", field)
		}
	}
	return nil
}

func templatePlaceholders(templatePath string) (map[string]struct{}, error) {
	switch strings.ToLower(filepath.Ext(templatePath)) {
	case ".xlsx":
		return xlsxPlaceholders(templatePath)
	case ".docx":
		return docxPlaceholders(templatePath)
	default:
		return nil, fmt.Errorf("unsupported template extension %q", filepath.Ext(templatePath))
	}
}

func xlsxPlaceholders(templatePath string) (map[string]struct{}, error) {
	f, err := excelize.OpenFile(templatePath)
	if err != nil {
		return nil, fmt.Errorf("open xlsx template: %w", err)
	}
	defer f.Close()

	fields := make(map[string]struct{})
	for _, sheet := range f.GetSheetList() {
		rows, err := f.GetRows(sheet)
		if err != nil {
			return nil, fmt.Errorf("read template sheet %q: %w", sheet, err)
		}
		for _, row := range rows {
			for _, value := range row {
				addPlaceholders(fields, value)
			}
		}
	}
	return fields, nil
}

func docxPlaceholders(templatePath string) (map[string]struct{}, error) {
	reader, err := zip.OpenReader(templatePath)
	if err != nil {
		return nil, fmt.Errorf("open docx template: %w", err)
	}
	defer reader.Close()

	fields := make(map[string]struct{})
	for _, file := range reader.File {
		if !strings.HasSuffix(strings.ToLower(file.Name), ".xml") {
			continue
		}
		rc, err := file.Open()
		if err != nil {
			return nil, fmt.Errorf("open docx part %s: %w", file.Name, err)
		}
		data, readErr := io.ReadAll(rc)
		closeErr := rc.Close()
		if readErr != nil {
			return nil, fmt.Errorf("read docx part %s: %w", file.Name, readErr)
		}
		if closeErr != nil {
			return nil, fmt.Errorf("close docx part %s: %w", file.Name, closeErr)
		}
		xml := string(data)
		addPlaceholders(fields, xml)
		addDocxTextPlaceholders(fields, xml)
	}
	return fields, nil
}

func ensurePlaceholdersAvailable(label, text string, row map[string]string) error {
	fields := make(map[string]struct{})
	addPlaceholders(fields, text)
	for field := range fields {
		if _, ok := row[field]; !ok {
			return fmt.Errorf("missing %s field %q", label, field)
		}
	}
	return nil
}

func addPlaceholders(fields map[string]struct{}, text string) {
	matches := placeholderPattern.FindAllStringSubmatch(text, -1)
	for _, match := range matches {
		if len(match) < 2 {
			continue
		}
		key := strings.TrimSpace(match[1])
		if key != "" {
			fields[key] = struct{}{}
		}
	}
}

func placeholderKey(match string) string {
	matches := placeholderPattern.FindStringSubmatch(match)
	if len(matches) < 2 {
		return ""
	}
	return strings.TrimSpace(matches[1])
}

func hasPlaceholder(text string) bool {
	return placeholderPattern.MatchString(text)
}

func renderDocxXML(xml string, row map[string]string) (string, error) {
	rendered := replaceDocxPlaceholders(xml, row)
	return renderDocxSplitTextPlaceholders(rendered, row)
}

func renderDocxSplitTextPlaceholders(xml string, row map[string]string) (string, error) {
	matches := docxParagraphPattern.FindAllStringIndex(xml, -1)
	if len(matches) == 0 {
		return renderDocxTextGroup(xml, row)
	}

	var out strings.Builder
	cursor := 0
	for _, match := range matches {
		out.WriteString(xml[cursor:match[0]])
		rendered, err := renderDocxTextGroup(xml[match[0]:match[1]], row)
		if err != nil {
			return "", err
		}
		out.WriteString(rendered)
		cursor = match[1]
	}
	out.WriteString(xml[cursor:])
	return out.String(), nil
}

func renderDocxTextGroup(xml string, row map[string]string) (string, error) {
	textMatches := docxTextNodePattern.FindAllStringSubmatchIndex(xml, -1)
	if len(textMatches) == 0 {
		return xml, nil
	}

	joined := joinedDocxText(xml, textMatches)
	if !hasPlaceholder(joined) {
		return xml, nil
	}
	if err := ensurePlaceholdersAvailable("docx text", joined, row); err != nil {
		return "", err
	}
	rendered := replaceDocxPlaceholders(joined, row)
	if hasPlaceholder(rendered) {
		return "", errors.New("unresolved placeholder in docx text")
	}

	var out strings.Builder
	cursor := 0
	for i, match := range textMatches {
		out.WriteString(xml[cursor:match[2]])
		if i == 0 {
			out.WriteString(rendered)
		}
		out.WriteString(xml[match[3]:match[1]])
		cursor = match[1]
	}
	out.WriteString(xml[cursor:])
	return out.String(), nil
}

func joinedDocxText(xml string, matches [][]int) string {
	var joined strings.Builder
	for _, match := range matches {
		joined.WriteString(xml[match[2]:match[3]])
	}
	return joined.String()
}

func addDocxTextPlaceholders(fields map[string]struct{}, xml string) {
	matches := docxParagraphPattern.FindAllStringIndex(xml, -1)
	if len(matches) == 0 {
		addPlaceholders(fields, joinedDocxText(xml, docxTextNodePattern.FindAllStringSubmatchIndex(xml, -1)))
		return
	}
	for _, match := range matches {
		paragraph := xml[match[0]:match[1]]
		textMatches := docxTextNodePattern.FindAllStringSubmatchIndex(paragraph, -1)
		addPlaceholders(fields, joinedDocxText(paragraph, textMatches))
	}
}

func docxHasPlaceholder(xml string) bool {
	if hasPlaceholder(xml) {
		return true
	}
	fields := make(map[string]struct{})
	addDocxTextPlaceholders(fields, xml)
	return len(fields) > 0
}

func escapeXMLText(value string) string {
	replacer := strings.NewReplacer(
		"&", "&amp;",
		"<", "&lt;",
		">", "&gt;",
	)
	return replacer.Replace(value)
}

func isDocxXMLPart(name string) bool {
	_, ok := docxGeneratedXMLTypes[strings.ToLower(filepath.Ext(name))]
	return ok
}

func sanitizePathValue(value string) string {
	replacer := strings.NewReplacer(
		"/", "_",
		"\\", "_",
		":", "_",
		"*", "_",
		"?", "_",
		`"`, "_",
		"<", "_",
		">", "_",
		"|", "_",
	)
	return strings.TrimSpace(replacer.Replace(value))
}

func fileExists(path string) bool {
	_, err := os.Stat(path)
	return err == nil
}

func resolveConfigPaths(cfg *config, baseDir string) {
	cfg.Data.Path = resolvePath(baseDir, cfg.Data.Path)
	cfg.Template.Path = resolvePath(baseDir, cfg.Template.Path)
	cfg.Output.Path = resolvePath(baseDir, cfg.Output.Path)
}

func resolvePath(baseDir, path string) string {
	if path == "" || filepath.IsAbs(path) {
		return path
	}
	return filepath.Clean(filepath.Join(baseDir, path))
}

func absPath(path string) string {
	abs, err := filepath.Abs(path)
	if err != nil {
		return path
	}
	return abs
}