package main

import (
	"bytes"
	"fmt"
	"io"
	"io/fs"
	"log"
	"os"
	"os/exec"
	pathpkg "path"
	"sort"
	"strings"
	"time"

	"gopkg.in/yaml.v3"
)

// Page represents a page.
type Page struct {
	Title    string                 `yaml:"title"`
	Date     time.Time              `yaml:"date"`
	Weight   int                    `yaml:"weight"`
	Outputs  []string               `yaml:"outputs"`
	Template string                 `yaml:"template"`
	Params   map[string]interface{} `yaml:"params"`
	Path     string                 `yaml:"-"`
	FilePath string                 `yaml:"-"`
	URL      string                 `yaml:"-"`
	Content  string                 `yaml:"-"`
	Prev     *Page                  `yaml:"-"`
	Next     *Page                  `yaml:"-"`
	Pages    []*Page                `yaml:"-"`
	Dirs     []*Page                `yaml:"-"`
	pages    map[string]*Page
	feeds    map[string][]byte
	index    bool
}

// read reads from a directory and indexes the files and directories within it.
func (p *Page) read(srcDir string, task *Task, cfg *Site) error {
	return p._read(os.DirFS(srcDir), ".", task, cfg)
}

func (p *Page) _read(fsys fs.FS, path string, task *Task, cfg *Site) error {
	entries, err := fs.ReadDir(fsys, path)
	if err != nil {
		return err
	}
	for _, entry := range entries {
		name := entry.Name()
		path := pathpkg.Join(path, name)
		if entry.IsDir() {
			// Ignore directories beginning with "_"
			if strings.HasPrefix(name, "_") {
				continue
			}
			// Gather directory data
			dirPath := "/" + path + "/"
			dir := &Page{
				Path:     dirPath,
				FilePath: path,
				URL:      task.URL + dirPath,
			}
			if err := dir._read(fsys, path, task, cfg); err != nil {
				return err
			}
			p.Dirs = append(p.Dirs, dir)
			p.addPage(name, dir)
		} else if ext := pathpkg.Ext(name); task.Match(ext) {
			// Ignore pages beginning with "_" with the exception of _index pages
			namePrefix := strings.TrimSuffix(name, ext)
			if strings.HasPrefix(name, "_") && namePrefix != "_index" {
				continue
			}

			content, err := fs.ReadFile(fsys, path)
			if err != nil {
				return err
			}

			page := &Page{
				FilePath: path,
			}
			if namePrefix == "_index" {
				p.index = true
				page = p
			}

			// Try to parse the date from the page filename
			const layout = "2006-01-02"
			base := pathpkg.Base(path)
			if len(base) >= len(layout) {
				dateStr := base[:len(layout)]
				if time, err := time.Parse(layout, dateStr); err == nil {
					page.Date = time
					// Remove the date from the path
					base = base[len(layout):]
					if len(base) > 0 {
						// Remove a leading dash
						if base[0] == '-' {
							base = base[1:]
						}
						if len(base) > 0 {
							dir := pathpkg.Dir(path)
							if dir == "." {
								dir = ""
							}
							path = pathpkg.Join(dir, base)
						}
					}
				}
			}

			// Extract frontmatter from content
			frontmatter, content := extractFrontmatter(content)
			if len(frontmatter) != 0 {
				if err := yaml.Unmarshal(frontmatter, page); err != nil {
					log.Printf("failed to parse frontmatter for %q: %v", path, err)
				} else if page.Outputs != nil {
					// Enforce page outputs
					if len(page.Outputs) == 0 || task.Name == "" {
						continue
					}
					found := false
					for _, output := range page.Outputs {
						if output == task.Name {
							found = true
							break
						}
					}
					if !found {
						continue
					}
				}

				// Trim leading newlines from content
				content = bytes.TrimLeft(content, "\r\n")
			}

			if cmd, ok := task.preprocess[strings.TrimPrefix(ext, ".")]; ok {
				var buf bytes.Buffer
				if err := execute(cmd, bytes.NewReader(content), &buf); err != nil {
					return err
				}
				content = buf.Bytes()
			}
			page.Content = string(content)

			if !page.index {
				if namePrefix == "index" {
					path = "/" + strings.TrimSuffix(path, name)
				} else {
					path = "/" + strings.TrimSuffix(path, ext)
					if task.UglyURLs {
						path += task.OutputExt
					} else {
						path += "/"
					}
				}
				page.Path = path
				if permalink, ok := task.permalinks[p.Path]; ok {
					var b strings.Builder
					permalink.Execute(&b, page)
					page.Path = b.String()
				}
				page.URL = task.URL + page.Path
				p.Pages = append(p.Pages, page)
				p.addPage(name, page)
			}
		}
	}
	return nil
}

func (p *Page) addPage(name string, page *Page) {
	if p.pages == nil {
		p.pages = map[string]*Page{}
	}
	p.pages[name] = page
}

// process processes the directory's contents.
func (p *Page) process(cfg *Site, task *Task) error {
	// Build feeds before templates are applied to the page contents
	for _, feed := range task.feeds[p.FilePath] {
		b, err := p.buildFeed(cfg, feed)
		if err != nil {
			return err
		}
		p.addFeed(feed.Output, b)
	}

	if task.TemplateExt != "" {
		// Create index
		if p.index {
			tmplName := p.Template
			if tmplName == "" {
				tmplName = "index"
			}
			tmpl, ok := cfg.templates.FindTemplate(p.FilePath, tmplName+task.TemplateExt)
			if !ok && p.Template != "" {
				return fmt.Errorf("failed to generate index page %q: template %q specified in frontmatter but not found", p.Path, tmplName)
			}
			if ok {
				var b strings.Builder
				if err := tmpl.Execute(&b, p); err != nil {
					return err
				}
				p.Content = b.String()
			}
		}

		// Process pages
		for i := range p.Pages {
			tmplName := p.Pages[i].Template
			if tmplName == "" {
				tmplName = "page"
			}
			var b strings.Builder
			tmpl, ok := cfg.templates.FindTemplate(p.FilePath, tmplName+task.TemplateExt)
			if !ok && p.Pages[i].Template != "" {
				return fmt.Errorf("failed to generate page %q: template %q specified in frontmatter but not found", p.Pages[i].Path, tmplName)
			}
			if ok {
				if err := tmpl.Execute(&b, p.Pages[i]); err != nil {
					return err
				}
				p.Pages[i].Content = b.String()
			}
		}
	}

	// Process subdirectories
	for _, d := range p.Dirs {
		if err := d.process(cfg, task); err != nil {
			return err
		}
	}
	return nil
}

// buildFeed build the feed of the directory
func (p *Page) buildFeed(cfg *Site, feed Feed) ([]byte, error) {
	// Feed represents a feed.
	type Feed struct {
		Title string
		Path  string
		URL   string
		Pages []*Page
	}

	tmpl, ok := cfg.templates.FindTemplate(p.FilePath, feed.Template)
	if !ok {
		return nil, fmt.Errorf("failed to generate feed %q: missing feed template %q", feed.Title, feed.Template)
	}

	var b bytes.Buffer
	data := Feed{
		Title: feed.Title,
		Path:  p.Path,
		URL:   p.URL,
		Pages: p.Pages,
	}
	if err := tmpl.Execute(&b, data); err != nil {
		return nil, err
	}
	return b.Bytes(), nil
}

func (p *Page) addFeed(name string, content []byte) {
	if p.feeds == nil {
		p.feeds = map[string][]byte{}
	}
	p.feeds[name] = content
}

// write writes the directory's contents to the provided destination path.
func (p *Page) write(dstDir string, task *Task) error {
	dirPath := pathpkg.Join(dstDir, p.Path)

	// Write pages
	for _, page := range p.Pages {
		dstPath := pathpkg.Join(dstDir, page.Path)
		if !task.UglyURLs {
			dstPath = pathpkg.Join(dstPath, "index"+task.OutputExt)
		}
		if err := page.writeTo(dstPath, task); err != nil {
			return err
		}
	}
	// Write index page
	if p.index {
		dstPath := pathpkg.Join(dstDir, p.Path, "index"+task.OutputExt)
		if err := p.writeTo(dstPath, task); err != nil {
			return err
		}
	}

	// Write feeds
	for name, content := range p.feeds {
		dstPath := pathpkg.Join(dstDir, name)
		os.MkdirAll(dirPath, 0755)
		if err := os.WriteFile(dstPath, content, 0644); err != nil {
			return err
		}
	}

	// Write subdirectories
	for _, dir := range p.Dirs {
		dir.write(dstDir, task)
	}
	return nil
}

func (p *Page) writeTo(dstPath string, task *Task) error {
	var content []byte
	if cmd := task.postprocess; cmd != nil {
		var buf bytes.Buffer
		if err := execute(cmd, strings.NewReader(p.Content), &buf); err != nil {
			return err
		}
		content = buf.Bytes()
	} else {
		content = []byte(p.Content)
	}

	dir := pathpkg.Dir(dstPath)
	os.MkdirAll(dir, 0755)
	if err := os.WriteFile(dstPath, content, 0644); err != nil {
		return err
	}
	return nil
}

// sort sorts the directory's pages by weight, then date, then filepath.
func (p *Page) sort() {
	sortPages(p.Pages)
	sortPages(p.Dirs)

	// Sort subdirectories
	for _, d := range p.Dirs {
		d.sort()
	}
}

func sortPages(pages []*Page) {
	sort.Slice(pages, func(i, j int) bool {
		pi, pj := pages[i], pages[j]
		return pi.FilePath < pj.FilePath
	})

	sort.SliceStable(pages, func(i, j int) bool {
		pi, pj := pages[i], pages[j]
		return pi.Date.After(pj.Date)
	})

	sort.SliceStable(pages, func(i, j int) bool {
		pi, pj := pages[i], pages[j]
		return pi.Weight < pj.Weight
	})

	for i := range pages {
		if i-1 >= 0 {
			pages[i].Prev = pages[i-1]
		}
		if i+1 < len(pages) {
			pages[i].Next = pages[i+1]
		}
	}
}

// execute runs a command.
func execute(command []string, input io.Reader, output io.Writer) error {
	if len(command) == 0 {
		return nil
	}
	cmd := exec.Command(command[0], command[1:]...)
	cmd.Stdin = input
	cmd.Stderr = os.Stderr
	cmd.Stdout = output
	err := cmd.Run()
	if err != nil {
		return err
	}
	return nil
}

// GetPage returns the page with the given path.
func (p *Page) GetPage(path string) *Page {
	path = pathpkg.Clean(path)
	if path == "." {
		return p
	}
	if strings.HasPrefix(path, "/") {
		path = strings.TrimPrefix(path, "/")
		if p.FilePath != "." && !strings.HasPrefix(path, p.FilePath) {
			return nil
		}
		path = strings.TrimPrefix(path, p.FilePath)
		if path == "" {
			return p
		}
		path = strings.TrimPrefix(path, "/")
	}

	page := p
	for _, part := range strings.Split(path, "/") {
		page = page.pages[part]
		if page == nil {
			break
		}
	}
	return page
}