package godocs

import (
	"net/url"
	"regexp"
	"strings"
	"time"

	"github.com/PuerkitoBio/goquery"
)

// Parser parses pkg.go.dev HTML pages into structured documentation.
type Parser struct {
	baseURL string
}

// NewParser creates a new parser for pkg.go.dev content.
func NewParser() *Parser {
	return &Parser{
		baseURL: "https://pkg.go.dev",
	}
}

// ParsePackagePage parses a pkg.go.dev package documentation page.
func (p *Parser) ParsePackagePage(html string, docURL string) (*Package, error) {
	doc, err := goquery.NewDocumentFromReader(strings.NewReader(html))
	if err != nil {
		return nil, err
	}

	pkg := &Package{
		DocURL:    docURL,
		FetchedAt: time.Now(),
	}

	// Extract import path from URL or breadcrumb
	pkg.ImportPath = p.extractImportPath(doc, docURL)
	pkg.Name = p.extractPackageName(doc)

	// Extract synopsis
	pkg.Synopsis = p.extractSynopsis(doc)

	// Extract package documentation
	pkg.Doc = p.extractPackageDoc(doc)

	// Extract version info
	pkg.Version = p.extractVersion(doc)

	// Extract module info
	pkg.Module = p.extractModule(doc)

	// Extract licenses
	pkg.Licenses = p.extractLicenses(doc)

	// Extract imported by count
	pkg.ImportedBy = p.extractImportedBy(doc)

	// Extract repository URL
	pkg.Repository = p.extractRepository(doc)

	// Extract functions
	pkg.Functions = p.extractFunctions(doc)

	// Extract types
	pkg.Types = p.extractTypes(doc)

	// Extract constants
	pkg.Constants = p.extractConstants(doc)

	// Extract variables
	pkg.Variables = p.extractVariables(doc)

	// Extract examples
	pkg.Examples = p.extractPackageExamples(doc)

	return pkg, nil
}

// ParseSearchResults parses pkg.go.dev search results page.
func (p *Parser) ParseSearchResults(html string) ([]*SearchResult, error) {
	doc, err := goquery.NewDocumentFromReader(strings.NewReader(html))
	if err != nil {
		return nil, err
	}

	var results []*SearchResult

	doc.Find(".SearchSnippet").Each(func(i int, s *goquery.Selection) {
		result := &SearchResult{}

		// Extract name and path
		s.Find("h2 a").Each(func(_ int, a *goquery.Selection) {
			result.Name = strings.TrimSpace(a.Text())
			if href, exists := a.Attr("href"); exists {
				result.URL = p.baseURL + href
				result.Path = strings.TrimPrefix(href, "/")
			}
		})

		// Extract path from span
		pathSpan := s.Find(".SearchSnippet-header-path")
		if pathSpan.Length() > 0 {
			result.Path = strings.Trim(pathSpan.Text(), "()")
		}

		// Extract synopsis
		synopsis := s.Find(".SearchSnippet-synopsis")
		if synopsis.Length() > 0 {
			result.Synopsis = strings.TrimSpace(synopsis.Text())
		}

		// Extract imported by count
		infoLabel := s.Find(".SearchSnippet-infoLabel").Text()
		if strings.Contains(infoLabel, "Imported by") {
			re := regexp.MustCompile(`Imported by\s+(\d[\d,]*)`)
			if matches := re.FindStringSubmatch(infoLabel); len(matches) > 1 {
				countStr := strings.ReplaceAll(matches[1], ",", "")
				result.ImportedBy = parseCount(countStr)
			}
		}

		// Extract version
		versionMatch := regexp.MustCompile(`v?\d+\.\d+(?:\.\d+)?`).FindString(infoLabel)
		result.Version = versionMatch

		// Extract license
		license := s.Find("[data-test-id='snippet-license'] a")
		if license.Length() > 0 {
			result.License = strings.TrimSpace(license.Text())
		}

		results = append(results, result)
	})

	return results, nil
}

// extractImportPath extracts the import path from the page.
func (p *Parser) extractImportPath(doc *goquery.Document, docURL string) string {
	// Try to extract from breadcrumb
	var importPath string
	doc.Find(".go-Breadcrumb li a").Each(func(i int, s *goquery.Selection) {
		if i > 0 { // Skip "Discover Packages"
			part := strings.TrimSpace(s.Text())
			if part != "" {
				if importPath != "" {
					importPath += "/"
				}
				importPath += part
			}
		}
	})

	if importPath != "" {
		return importPath
	}

	// Fallback: extract from URL
	if docURL != "" {
		u, err := url.Parse(docURL)
		if err == nil {
			path := strings.TrimPrefix(u.Path, "/")
			// Remove version suffix like @v1.0.0
			if idx := strings.Index(path, "@"); idx > 0 {
				path = path[:idx]
			}
			return path
		}
	}

	return ""
}

// extractPackageName extracts the package name.
func (p *Parser) extractPackageName(doc *goquery.Document) string {
	// Try UnitHeader-title
	title := doc.Find(".UnitHeader-titleHeading").Text()
	title = strings.TrimSpace(title)
	if title != "" {
		return title
	}

	// Fallback to h1
	title = doc.Find("h1").First().Text()
	return strings.TrimSpace(title)
}

// extractSynopsis extracts the package synopsis.
func (p *Parser) extractSynopsis(doc *goquery.Document) string {
	// Synopsis is typically in the first paragraph after the package declaration
	docSection := doc.Find(".Documentation").First()
	if docSection.Length() > 0 {
		// Get the first paragraph
		firstP := docSection.Find("p").First()
		if firstP.Length() > 0 {
			synopsis := strings.TrimSpace(firstP.Text())
			// Limit to reasonable length
			if len(synopsis) > 200 {
				synopsis = synopsis[:197] + "..."
			}
			return synopsis
		}
	}

	return ""
}

// extractPackageDoc extracts the full package documentation.
func (p *Parser) extractPackageDoc(doc *goquery.Document) string {
	var parts []string

	doc.Find(".Documentation").Each(func(_ int, s *goquery.Selection) {
		text := s.Text()
		text = cleanWhitespace(text)
		if text != "" {
			parts = append(parts, text)
		}
	})

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

// extractVersion extracts the version info.
func (p *Parser) extractVersion(doc *goquery.Document) string {
	versionEl := doc.Find("[data-test-id='UnitHeader-version'] a")
	if versionEl.Length() > 0 {
		return strings.TrimSpace(versionEl.Text())
	}
	return ""
}

// extractModule extracts module information.
func (p *Parser) extractModule(doc *goquery.Document) *Module {
	modulePath := ""
	moduleVersion := ""

	// Try to extract from version link
	versionEl := doc.Find("[data-test-id='UnitHeader-version'] a")
	if versionEl.Length() > 0 {
		moduleVersion = strings.TrimSpace(versionEl.Text())
	}

	// Extract module path from breadcrumb
	doc.Find(".go-Breadcrumb li a").Each(func(i int, s *goquery.Selection) {
		text := strings.TrimSpace(s.Text())
		if strings.Contains(text, "/") && i > 0 {
			modulePath = text
		}
	})

	if modulePath != "" {
		return &Module{
			Path:    modulePath,
			Version: moduleVersion,
		}
	}

	return nil
}

// extractLicenses extracts license information.
func (p *Parser) extractLicenses(doc *goquery.Document) []License {
	var licenses []License

	doc.Find("[data-test-id='UnitHeader-license']").Each(func(_ int, s *goquery.Selection) {
		name := strings.TrimSpace(s.Text())
		if name != "" {
			license := License{Name: name}
			if href, exists := s.Attr("href"); exists {
				license.Path = href
			}
			licenses = append(licenses, license)
		}
	})

	return licenses
}

// extractImportedBy extracts the import count.
func (p *Parser) extractImportedBy(doc *goquery.Document) int {
	importEl := doc.Find("[data-test-id='UnitHeader-importedby'] a")
	if importEl.Length() > 0 {
		text := importEl.Text()
		// Extract number from "Imported by: 144,729"
		re := regexp.MustCompile(`[\d,]+`)
		if match := re.FindString(text); match != "" {
			match = strings.ReplaceAll(match, ",", "")
			var count int
			for _, c := range match {
				if c >= '0' && c <= '9' {
					count = count*10 + int(c-'0')
				}
			}
			return count
		}
	}
	return 0
}

// extractRepository extracts the repository URL.
func (p *Parser) extractRepository(doc *goquery.Document) string {
	repoEl := doc.Find(".UnitMeta-repo a")
	if repoEl.Length() > 0 {
		if href, exists := repoEl.Attr("href"); exists {
			return href
		}
	}
	return ""
}

// extractFunctions extracts all function declarations.
func (p *Parser) extractFunctions(doc *goquery.Document) []*Function {
	var functions []*Function

	doc.Find(".Documentation-function").Each(func(_ int, s *goquery.Selection) {
		fn := &Function{}

		// Extract name from the function header
		nameEl := s.Find(".Documentation-functionHeader").First()
		if nameEl.Length() > 0 {
			fn.Name = strings.TrimSpace(nameEl.Text())
		}

		// Extract signature from code block
		sigEl := s.Find("pre").First()
		if sigEl.Length() > 0 {
			fn.Signature = strings.TrimSpace(sigEl.Text())
		}

		// Extract documentation
		docEl := s.Find(".Documentation-functionBody p").First()
		if docEl.Length() == 0 {
			docEl = s.Find("p").First()
		}
		if docEl.Length() > 0 {
			fn.Doc = strings.TrimSpace(docEl.Text())
		}

		// Extract examples
		fn.Examples = p.extractExamples(s)

		if fn.Name != "" {
			functions = append(functions, fn)
		}
	})

	return functions
}

// extractTypes extracts all type declarations.
func (p *Parser) extractTypes(doc *goquery.Document) []*Type {
	var types []*Type

	doc.Find(".Documentation-type").Each(func(_ int, s *goquery.Selection) {
		t := &Type{}

		// Extract name from the type header
		nameEl := s.Find(".Documentation-typeHeader").First()
		if nameEl.Length() > 0 {
			t.Name = strings.TrimSpace(nameEl.Text())
		}

		// Determine kind from signature
		sigEl := s.Find("pre").First()
		if sigEl.Length() > 0 {
			sig := sigEl.Text()
			t.Underlying = strings.TrimSpace(sig)

			if strings.Contains(sig, "struct{") {
				t.Kind = TypeKindStruct
				t.Fields = p.extractStructFields(sigEl)
			} else if strings.Contains(sig, "interface{") {
				t.Kind = TypeKindInterface
			} else {
				t.Kind = TypeKindAlias
			}
		}

		// Extract documentation
		docEl := s.Find("p").First()
		if docEl.Length() > 0 {
			t.Doc = strings.TrimSpace(docEl.Text())
		}

		// Extract methods
		t.Methods = p.extractMethods(s)

		// Extract examples
		t.Examples = p.extractExamples(s)

		if t.Name != "" {
			types = append(types, t)
		}
	})

	return types
}

// extractStructFields extracts struct fields from a type definition.
func (p *Parser) extractStructFields(sigEl *goquery.Selection) []*Field {
	var fields []*Field

	sigEl.Find("tr, .Documentation-structField").Each(func(_ int, s *goquery.Selection) {
		text := s.Text()
		text = strings.TrimSpace(text)

		if text == "" || strings.HasPrefix(text, "//") {
			return
		}

		// Parse field: Name Type `tag`
		parts := strings.Fields(text)
		if len(parts) >= 1 {
			field := &Field{
				Name:     parts[0],
				Exported: isExported(parts[0]),
			}

			if len(parts) >= 2 {
				field.Type = strings.Join(parts[1:], " ")
				// Remove tag
				if idx := strings.Index(field.Type, "`"); idx > 0 {
					field.Tag = field.Type[idx:]
					field.Type = field.Type[:idx]
				}
			}

			fields = append(fields, field)
		}
	})

	return fields
}

// extractMethods extracts methods from a type section.
func (p *Parser) extractMethods(typeSection *goquery.Selection) []*Method {
	var methods []*Method

	typeSection.Find(".Documentation-method, .Documentation-function").Each(func(_ int, s *goquery.Selection) {
		m := &Method{}

		// Extract method name
		nameEl := s.Find(".Documentation-functionHeader, .Documentation-methodHeader").First()
		if nameEl.Length() > 0 {
			name := strings.TrimSpace(nameEl.Text())
			// Extract receiver if present: (t *Type) Method(...)
			if strings.HasPrefix(name, "(") {
				if end := strings.Index(name, ")"); end > 0 {
					m.Receiver = name[1:end]
					name = strings.TrimSpace(name[end+1:])
				}
			}
			m.Name = name
		}

		// Extract signature
		sigEl := s.Find("pre").First()
		if sigEl.Length() > 0 {
			m.Signature = strings.TrimSpace(sigEl.Text())
		}

		// Extract documentation
		docEl := s.Find("p").First()
		if docEl.Length() > 0 {
			m.Doc = strings.TrimSpace(docEl.Text())
		}

		if m.Name != "" {
			methods = append(methods, m)
		}
	})

	return methods
}

// extractConstants extracts constant declarations.
func (p *Parser) extractConstants(doc *goquery.Document) []*Value {
	var constants []*Value

	doc.Find(".Documentation-constants").Each(func(_ int, s *goquery.Selection) {
		// Extract constant group
		codeEl := s.Find("pre").First()
		if codeEl.Length() > 0 {
			v := &Value{
				IsConst: true,
			}

			// Parse const declarations
			text := codeEl.Text()
			lines := strings.Split(text, "\n")

			for _, line := range lines {
				line = strings.TrimSpace(line)
				if line == "" || strings.HasPrefix(line, "//") {
					continue
				}

				// Simple const: Name = value
				if strings.Contains(line, "=") {
					parts := strings.SplitN(line, "=", 2)
					if len(parts) == 2 {
						name := strings.TrimSpace(parts[0])
						if v.Names == nil {
							v.Names = []string{}
						}
						v.Names = append(v.Names, name)
						if v.Name == "" {
							v.Name = name
						}
						v.Value = strings.TrimSpace(parts[1])
					}
				}
			}

			// Extract documentation
			docEl := s.Find("p").First()
			if docEl.Length() > 0 {
				v.Doc = strings.TrimSpace(docEl.Text())
			}

			if len(v.Names) > 0 {
				constants = append(constants, v)
			}
		}
	})

	return constants
}

// extractVariables extracts variable declarations.
func (p *Parser) extractVariables(doc *goquery.Document) []*Value {
	var variables []*Value

	doc.Find(".Documentation-variables").Each(func(_ int, s *goquery.Selection) {
		codeEl := s.Find("pre").First()
		if codeEl.Length() > 0 {
			v := &Value{
				IsConst: false,
			}

			text := codeEl.Text()
			// Parse var declarations
			text = strings.TrimPrefix(text, "var ")

			lines := strings.Split(text, "\n")
			for _, line := range lines {
				line = strings.TrimSpace(line)
				if line == "" {
					continue
				}

				// Parse: Name Type = value
				if strings.Contains(line, "=") {
					parts := strings.SplitN(line, "=", 2)
					if len(parts) == 2 {
						nameType := strings.TrimSpace(parts[0])
						v.Name = strings.Fields(nameType)[0]
						v.Value = strings.TrimSpace(parts[1])
						break
					}
				} else {
					// Just name and type
					fields := strings.Fields(line)
					if len(fields) >= 1 {
						v.Name = fields[0]
						if len(fields) >= 2 {
							v.Type = strings.Join(fields[1:], " ")
						}
					}
				}
			}

			// Extract documentation
			docEl := s.Find("p").First()
			if docEl.Length() > 0 {
				v.Doc = strings.TrimSpace(docEl.Text())
			}

			if v.Name != "" {
				variables = append(variables, v)
			}
		}
	})

	return variables
}

// extractExamples extracts examples from a section.
func (p *Parser) extractExamples(section *goquery.Selection) []*Example {
	var examples []*Example

	section.Find(".Documentation-example").Each(func(_ int, s *goquery.Selection) {
		ex := &Example{}

		// Extract example name
		nameEl := s.Find(".Documentation-exampleHeader").First()
		if nameEl.Length() > 0 {
			ex.Name = strings.TrimSpace(nameEl.Text())
		}

		// Extract code
		codeEl := s.Find("pre, code").First()
		if codeEl.Length() > 0 {
			ex.Code = strings.TrimSpace(codeEl.Text())
		}

		// Extract output
		outputEl := s.Find(".Documentation-exampleOutput").First()
		if outputEl.Length() > 0 {
			ex.Output = strings.TrimSpace(outputEl.Text())
		}

		// Extract documentation
		docEl := s.Find("p").First()
		if docEl.Length() > 0 {
			ex.Doc = strings.TrimSpace(docEl.Text())
		}

		if ex.Code != "" {
			examples = append(examples, ex)
		}
	})

	return examples
}

// extractPackageExamples extracts package-level examples.
func (p *Parser) extractPackageExamples(doc *goquery.Document) []*Example {
	var examples []*Example

	doc.Find(".Documentation-example").Each(func(_ int, s *goquery.Selection) {
		ex := &Example{}

		// Extract example name
		nameEl := s.Find(".Documentation-exampleHeader").First()
		if nameEl.Length() > 0 {
			ex.Name = strings.TrimSpace(nameEl.Text())
		}

		// Extract code
		codeEl := s.Find("pre, code").First()
		if codeEl.Length() > 0 {
			ex.Code = strings.TrimSpace(codeEl.Text())
		}

		// Extract output
		outputEl := s.Find(".Documentation-exampleOutput").First()
		if outputEl.Length() > 0 {
			ex.Output = strings.TrimSpace(outputEl.Text())
		}

		if ex.Code != "" {
			examples = append(examples, ex)
		}
	})

	return examples
}

// parseCount parses a count string to int.
func parseCount(s string) int {
	var count int
	for _, c := range s {
		if c >= '0' && c <= '9' {
			count = count*10 + int(c-'0')
		}
	}
	return count
}

// isExported checks if a name is exported (starts with uppercase).
func isExported(name string) bool {
	if len(name) == 0 {
		return false
	}
	return name[0] >= 'A' && name[0] <= 'Z'
}

// cleanWhitespace normalizes whitespace in text.
func cleanWhitespace(text string) string {
	// Replace multiple whitespace with single space
	re := regexp.MustCompile(`\s+`)
	text = re.ReplaceAllString(text, " ")
	return strings.TrimSpace(text)
}