package tui

import (
	"fmt"
	"sort"
	"strings"

	tea "github.com/charmbracelet/bubbletea"
	"github.com/charmbracelet/lipgloss"

	"github.com/lukaszkasprzak/lectio/internal/bible"
	"github.com/lukaszkasprzak/lectio/internal/config"
	"github.com/lukaszkasprzak/lectio/internal/i18n"
)

// readerMode is the reader's screen: the book picker or the chapter view.
type readerMode int

const (
	modePick readerMode = iota
	modeRead
)

// selStyle marks the picker's selected row (reverse video, legible on any theme).
var selStyle = lipgloss.NewStyle().Reverse(true)

// ReaderModel is lectio-ui's --reader mode: a fuzzy book picker over the sigla
// dialect's book names, then a scrolling view of a chapter from the embedded
// corpora with chapter navigation and version cycling. It implements tea.Model
// and reuses the package's styleBlock/styles. It never touches the network.
type ReaderModel struct {
	cfg      config.Config
	dialect  string           // sigla dialect / book-name language ("en"/"pl")
	books    []bible.BookInfo // dialect books, scriptural order
	versions []string         // corpus versions available (wuj/vul/grb/drb subset)
	verIdx   int

	mode readerMode

	// picker
	query   string
	matches []int // indices into books, filtered + ranked
	pickSel int   // selected position within matches
	pickTop int   // first visible match (list scroll)

	// reading
	bookIdx  int   // index into books
	chapters []int // sorted chapters for current book+version
	chapPos  int   // index into chapters
	verses   []bible.Verse
	scroll   int

	width, height int
}

// NewReader builds the reader. tbl supplies the dialect book names/abbrevs
// (cfg.SiglaLang() picks the dialect); versions is the corpus-backed subset of
// cfg.Versions (wuj/vul/grb/drb), since "bt" has no full text to read.
func NewReader(cfg config.Config, tbl *bible.BookTable) ReaderModel {
	dialect := cfg.SiglaLang()
	m := ReaderModel{
		cfg:      cfg,
		dialect:  dialect,
		books:    tbl.Books(dialect),
		versions: corpusVersions(cfg),
		mode:     modePick,
	}
	m.refilter()
	return m
}

// corpusVersions returns the readable (corpus-backed) versions from cfg, in
// config order, never empty: bt is dropped and, if nothing is left, all four
// bundled corpora are offered.
func corpusVersions(cfg config.Config) []string {
	var out []string
	for _, v := range cfg.Versions {
		if config.ValidVersion(v) && v != "bt" {
			out = append(out, v)
		}
	}
	if len(out) == 0 {
		out = []string{"wuj", "vul", "grb", "drb"}
	}
	return out
}

func (m ReaderModel) version() string {
	if m.verIdx < 0 || m.verIdx >= len(m.versions) {
		return ""
	}
	return m.versions[m.verIdx]
}

func (m ReaderModel) Init() tea.Cmd { return nil }

// refilter rebuilds matches from query (fuzzy, ranked); empty query lists all
// books in scriptural order.
func (m *ReaderModel) refilter() {
	m.matches = m.matches[:0]
	q := strings.TrimSpace(m.query)
	if q == "" {
		for i := range m.books {
			m.matches = append(m.matches, i)
		}
	} else {
		type sc struct{ i, score int }
		var scored []sc
		for i, b := range m.books {
			if s, ok := fuzzyScore(q, b.Shortcut+" "+b.Name); ok {
				scored = append(scored, sc{i, s})
			}
		}
		sort.SliceStable(scored, func(a, b int) bool { return scored[a].score > scored[b].score })
		for _, s := range scored {
			m.matches = append(m.matches, s.i)
		}
	}
	if m.pickSel >= len(m.matches) {
		m.pickSel = len(m.matches) - 1
	}
	if m.pickSel < 0 {
		m.pickSel = 0
	}
	m.pickTop = 0
}

// fuzzyScore ranks target against query: a substring hit (prefix best) beats a
// subsequence hit; ok=false when query is not even a subsequence.
func fuzzyScore(q, target string) (int, bool) {
	ql, tl := strings.ToLower(q), strings.ToLower(target)
	if i := strings.Index(tl, ql); i >= 0 {
		return 1000 - i, true
	}
	ti := 0
	for _, qc := range ql {
		idx := strings.IndexRune(tl[ti:], qc)
		if idx < 0 {
			return 0, false
		}
		ti += idx + len(string(qc))
	}
	return 100, true
}

func (m ReaderModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	switch msg := msg.(type) {
	case tea.WindowSizeMsg:
		m.width, m.height = msg.Width, msg.Height
		return m, nil
	case tea.KeyMsg:
		if m.mode == modePick {
			return m.updatePick(msg)
		}
		return m.updateRead(msg)
	}
	return m, nil
}

func (m ReaderModel) updatePick(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
	switch msg.Type {
	case tea.KeyCtrlC:
		return m, tea.Quit
	case tea.KeyEsc:
		if m.query != "" {
			m.query = ""
			m.refilter()
			return m, nil
		}
		return m, tea.Quit
	case tea.KeyEnter:
		if len(m.matches) > 0 {
			m.bookIdx = m.matches[m.pickSel]
			m = m.openBook()
			m.mode = modeRead
		}
		return m, nil
	case tea.KeyUp:
		if m.pickSel > 0 {
			m.pickSel--
		}
		return m, nil
	case tea.KeyDown:
		if m.pickSel < len(m.matches)-1 {
			m.pickSel++
		}
		return m, nil
	case tea.KeyBackspace:
		if r := []rune(m.query); len(r) > 0 {
			m.query = string(r[:len(r)-1])
			m.refilter()
		}
		return m, nil
	case tea.KeySpace:
		m.query += " "
		m.refilter()
		return m, nil
	case tea.KeyRunes:
		m.query += string(msg.Runes)
		m.refilter()
		return m, nil
	}
	return m, nil
}

func (m ReaderModel) updateRead(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
	switch msg.String() {
	case "q", "ctrl+c":
		return m, tea.Quit
	case "esc", "backspace":
		m.mode = modePick
		return m, nil
	case "tab":
		return m.cycleVersion(+1), nil
	case "shift+tab":
		return m.cycleVersion(-1), nil
	case "n", "]", "right", "l":
		return m.chapterStep(+1), nil
	case "p", "[", "left", "h":
		return m.chapterStep(-1), nil
	case "j", "down":
		m.scroll = m.clampRead(m.scroll + 1)
		return m, nil
	case "k", "up":
		m.scroll = m.clampRead(m.scroll - 1)
		return m, nil
	case " ", "f":
		m.scroll = m.clampRead(m.scroll + m.readVisible())
		return m, nil
	case "u":
		m.scroll = m.clampRead(m.scroll - m.readVisible())
		return m, nil
	case "g":
		m.scroll = 0
		return m, nil
	case "G":
		m.scroll = m.clampRead(1 << 30)
		return m, nil
	}
	return m, nil
}

// openBook loads the chapter list + first chapter for the selected book in the
// active version.
func (m ReaderModel) openBook() ReaderModel {
	m.chapters = bible.Chapters(m.version(), m.books[m.bookIdx].Canonical)
	m.chapPos = 0
	m.scroll = 0
	return m.loadVerses()
}

func (m ReaderModel) loadVerses() ReaderModel {
	if len(m.chapters) == 0 {
		m.verses = nil
		return m
	}
	if m.chapPos < 0 {
		m.chapPos = 0
	}
	if m.chapPos >= len(m.chapters) {
		m.chapPos = len(m.chapters) - 1
	}
	m.verses = bible.Verses(m.version(), m.books[m.bookIdx].Canonical, m.chapters[m.chapPos])
	return m
}

func (m ReaderModel) chapterStep(d int) ReaderModel {
	if len(m.chapters) == 0 {
		return m
	}
	np := m.chapPos + d
	if np < 0 || np >= len(m.chapters) || np == m.chapPos {
		return m
	}
	m.chapPos = np
	m.scroll = 0
	return m.loadVerses()
}

// cycleVersion moves the active version by d, wrapping. In reading mode it
// recomputes the book's chapter list for the new version and keeps the same
// chapter NUMBER when that version has it (else clamps).
func (m ReaderModel) cycleVersion(d int) ReaderModel {
	n := len(m.versions)
	if n == 0 {
		return m
	}
	curChap := 0
	if len(m.chapters) > 0 && m.chapPos < len(m.chapters) {
		curChap = m.chapters[m.chapPos]
	}
	m.verIdx = ((m.verIdx+d)%n + n) % n
	if m.mode == modeRead {
		m.chapters = bible.Chapters(m.version(), m.books[m.bookIdx].Canonical)
		m.chapPos = 0
		for i, c := range m.chapters {
			if c == curChap {
				m.chapPos = i
				break
			}
		}
		m.scroll = 0
		m = m.loadVerses()
	}
	return m
}

// readVisible is how many reading lines fit between the 1-line header and
// 1-line footer, with a sane default before the first WindowSizeMsg.
func (m ReaderModel) readVisible() int {
	chrome := 3 // header + footer + margin
	if m.height <= chrome {
		return 10
	}
	return m.height - chrome
}

func (m ReaderModel) clampRead(s int) int {
	return clampScroll(s, len(m.readBody(m.innerW())), m.readVisible())
}

func (m ReaderModel) innerW() int {
	w := m.width
	if w <= 0 {
		w = 80
	}
	iw := w - 2
	if iw < 20 {
		iw = 20
	}
	return iw
}

// readBody returns the styled, wrapped verse lines for the current chapter.
func (m ReaderModel) readBody(w int) []string {
	ui := i18n.Get(m.cfg.UILanguage)
	if len(m.chapters) == 0 || len(m.verses) == 0 {
		return []string{citationStyle.Render(ui.ReaderNoText)}
	}
	blocks := make([]string, len(m.verses))
	for i, v := range m.verses {
		blocks[i] = fmt.Sprintf("%d:%d  %s", v.Chapter, v.Verse, v.Text)
	}
	numW := maxNumWidth(blocks)
	var lines []string
	for _, b := range blocks {
		lines = append(lines, styleBlock(b, false, w, numW)...)
	}
	return lines
}

func (m ReaderModel) View() string {
	if m.mode == modePick {
		return m.viewPick()
	}
	return m.viewRead()
}

func (m ReaderModel) viewPick() string {
	w := m.width
	if w <= 0 {
		w = 80
	}
	ui := i18n.Get(m.cfg.UILanguage)
	header := headerStyle.Width(w).Render(ui.ReaderTitle)
	footer := footerStyle.Width(w).Render(ui.ReaderPickKeys)
	prompt := headingStyle.Render("› ") + m.query

	// visible list window (header + prompt + footer + margin = 4 chrome lines)
	visible := m.height - 4
	if visible < 3 {
		visible = 3
	}
	// keep selection in view
	top := m.pickTop
	if m.pickSel < top {
		top = m.pickSel
	}
	if m.pickSel >= top+visible {
		top = m.pickSel - visible + 1
	}
	if top < 0 {
		top = 0
	}

	col := shortcutCol(m.books)
	var rows []string
	if len(m.matches) == 0 {
		rows = append(rows, citationStyle.Render(ui.ReaderNoMatch))
	}
	for i := top; i < len(m.matches) && i < top+visible; i++ {
		b := m.books[m.matches[i]]
		pad := col - len([]rune(b.Shortcut))
		if pad < 1 {
			pad = 1
		}
		row := b.Shortcut + strings.Repeat(" ", pad) + b.Name
		if i == m.pickSel {
			row = selStyle.Render("› " + row)
		} else {
			row = "  " + row
		}
		rows = append(rows, row)
	}
	return header + "\n" + prompt + "\n" + strings.Join(rows, "\n") + "\n" + footer
}

// shortcutCol is the width of the shortcut column: widest shortcut + 2.
func shortcutCol(books []bible.BookInfo) int {
	w := 0
	for _, b := range books {
		if n := len([]rune(b.Shortcut)); n > w {
			w = n
		}
	}
	return w + 2
}

func (m ReaderModel) viewRead() string {
	w := m.width
	if w <= 0 {
		w = 80
	}
	ui := i18n.Get(m.cfg.UILanguage)
	b := m.books[m.bookIdx]
	chap := 0
	if len(m.chapters) > 0 && m.chapPos < len(m.chapters) {
		chap = m.chapters[m.chapPos]
	}
	label := m.version()
	if l, ok := ui.Version[m.version()]; ok {
		label = l
	}
	header := headerStyle.Width(w).Render(fmt.Sprintf("%s  %d  [%s]", b.Name, chap, label))
	footer := footerStyle.Width(w).Render(ui.ReaderReadKeys)

	body := m.readBody(m.innerW())
	visible := m.readVisible()
	scroll := clampScroll(m.scroll, len(body), visible)
	end := scroll + visible
	if end > len(body) {
		end = len(body)
	}
	return header + "\n" + strings.Join(body[scroll:end], "\n") + "\n" + footer
}