// Package tui is lectio's interactive Bubble Tea reader: a colored,
// scrollable full-day view of the liturgy with version cycling and date
// navigation. It re-styles the same render.GatherVersion data the CLI
// prints as plain text.
package tui

import (
	"fmt"
	"regexp"
	"strings"
	"time"

	tea "github.com/charmbracelet/bubbletea"

	"github.com/lukaszkasprzak/lectio/internal/config"
	"github.com/lukaszkasprzak/lectio/internal/i18n"
	"github.com/lukaszkasprzak/lectio/internal/liturgy"
	"github.com/lukaszkasprzak/lectio/internal/readings"
	"github.com/lukaszkasprzak/lectio/internal/render"
)

// Model is the TUI's state: it implements tea.Model.
type Model struct {
	cfg      config.Config
	versions []string
	verIdx   int
	date     string
	sections []liturgy.Section
	scroll   int
	width    int
	height   int
	loading  bool
	err      error
}

// readingsMsg carries a successful fetch's sections back to Update.
type readingsMsg struct {
	sections []liturgy.Section
}

// errMsg carries a failed fetch's error back to Update.
type errMsg struct {
	err error
}

// New builds the initial model: cfg.Offline drops "pl" from the version
// list (render.OfflineVersions), the active version starts at
// cfg.DefaultVersion (falling back to the first version if not found, or
// "" if there are none), and the date starts at today. The first fetch is
// issued by Init, not here.
func New(cfg config.Config) Model {
	versions := append([]string(nil), cfg.Versions...)
	if cfg.Offline {
		versions = render.OfflineVersions(versions)
	}

	idx := indexOf(versions, cfg.DefaultVersion)
	if idx < 0 {
		idx = 0
	}
	idx = clampIndex(idx, len(versions))

	return Model{
		cfg:      cfg,
		versions: versions,
		verIdx:   idx,
		date:     time.Now().Format("2006-01-02"),
		loading:  true,
	}
}

// version returns the active version code, or "" if there are none.
func (m Model) version() string {
	if m.verIdx < 0 || m.verIdx >= len(m.versions) {
		return ""
	}
	return m.versions[m.verIdx]
}

// cycleVersion moves the active version by d steps, wrapping around the
// list (tab = +1, shift+tab = -1). A pure, unit-tested helper.
func (m Model) cycleVersion(d int) Model {
	n := len(m.versions)
	if n == 0 {
		return m
	}
	m.verIdx = ((m.verIdx+d)%n + n) % n
	return m
}

// indexOf returns the index of v in list, or -1 if not present.
func indexOf(list []string, v string) int {
	for i, s := range list {
		if s == v {
			return i
		}
	}
	return -1
}

// clampIndex clamps i into [0, n-1], returning 0 when n == 0.
func clampIndex(i, n int) int {
	if n == 0 {
		return 0
	}
	if i < 0 {
		return 0
	}
	if i >= n {
		return n - 1
	}
	return i
}

// shiftDate adds days to date (YYYY-MM-DD); an unparsable date is returned
// unchanged.
func shiftDate(date string, days int) string {
	t, err := time.Parse("2006-01-02", date)
	if err != nil {
		return date
	}
	return t.AddDate(0, 0, days).Format("2006-01-02")
}

// fetchCmd issues the readings.Load fetch for the model's current date as a
// tea.Cmd, resolving to readingsMsg or errMsg. It is a full-day reader, so
// All is always true; Offline follows cfg.Offline.
func (m Model) fetchCmd() tea.Cmd {
	cfg := m.cfg
	date := m.date
	return func() tea.Msg {
		secs, err := readings.Load(cfg, readings.Options{
			Date:    date,
			Offline: cfg.Offline,
			All:     true,
		})
		if err != nil {
			return errMsg{err}
		}
		return readingsMsg{secs}
	}
}

// Init issues the first load.
func (m Model) Init() tea.Cmd {
	return m.fetchCmd()
}

// Update handles key input and fetch results.
func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
	switch msg := msg.(type) {
	case tea.WindowSizeMsg:
		m.width = msg.Width
		m.height = msg.Height
		return m, nil

	case readingsMsg:
		m.loading = false
		m.err = nil
		m.sections = msg.sections
		m.scroll = 0
		return m, nil

	case errMsg:
		m.loading = false
		m.err = msg.err
		return m, nil

	case tea.KeyMsg:
		switch msg.String() {
		case "q", "ctrl+c":
			return m, tea.Quit
		case "tab":
			return m.cycleVersion(+1), nil
		case "shift+tab":
			return m.cycleVersion(-1), nil
		case "left":
			m.date = shiftDate(m.date, -1)
			m.loading = true
			m.err = nil
			return m, m.fetchCmd()
		case "right":
			m.date = shiftDate(m.date, +1)
			m.loading = true
			m.err = nil
			return m, m.fetchCmd()
		case "r":
			m.loading = true
			m.err = nil
			return m, m.fetchCmd()
		case "j", "down":
			m.scroll++
			return m, nil
		case "k", "up":
			if m.scroll > 0 {
				m.scroll--
			}
			return m, nil
		case " ":
			m.scroll += pageSize(m.height)
			return m, nil
		case "b":
			m.scroll -= pageSize(m.height)
			if m.scroll < 0 {
				m.scroll = 0
			}
			return m, nil
		case "g":
			m.scroll = 0
			return m, nil
		case "G":
			m.scroll = 1 << 30 // clamped to the last page in View
			return m, nil
		}
	}
	return m, nil
}

// pageSize is how many reading lines fit between the header and footer bars
// for a given terminal height; it falls back to a sane default before the
// first tea.WindowSizeMsg arrives (height == 0).
func pageSize(height int) int {
	const chrome = 4 // header + blank + footer + margin
	if height <= chrome {
		return 10
	}
	return height - chrome
}

// clampScroll keeps scroll within [0, total-visible] (never negative).
func clampScroll(scroll, total, visible int) int {
	max := total - visible
	if max < 0 {
		max = 0
	}
	if scroll > max {
		scroll = max
	}
	if scroll < 0 {
		scroll = 0
	}
	return scroll
}

// View renders the header (date + active version label), the scrolling
// reading, and the footer keybar.
func (m Model) View() string {
	w := m.width
	if w <= 0 {
		w = 80
	}
	innerW := w - 2
	if innerW < 20 {
		innerW = 20
	}

	header := headerStyle.Width(w).Render(m.headerText())
	footer := footerStyle.Width(w).Render(i18n.Get(m.cfg.UILanguage).FooterKeys)

	bodyLines := m.bodyLines(innerW)

	visible := pageSize(m.height)
	scroll := clampScroll(m.scroll, len(bodyLines), visible)
	end := scroll + visible
	if end > len(bodyLines) {
		end = len(bodyLines)
	}

	return header + "\n" + strings.Join(bodyLines[scroll:end], "\n") + "\n" + footer
}

// headerText is "lectio  DATE  [version label]"; the label comes from the
// active section's render.GatherVersion when sections are loaded, else the
// bare version code.
func (m Model) headerText() string {
	label := m.version()
	if len(m.sections) > 0 {
		if l, _ := render.GatherVersion(m.version(), m.sections[0], m.cfg.Lectionary, m.cfg.UILanguage); l != "" {
			label = l
		}
	}
	return fmt.Sprintf("lectio  %s  [%s]", m.date, label)
}

// bodyLines returns the styled, wrapped lines the reading pane scrolls
// through: a loading/error/empty notice, or each section's heading +
// render.GatherVersion blocks for the active version.
func (m Model) bodyLines(w int) []string {
	ui := i18n.Get(m.cfg.UILanguage)

	switch {
	case m.err != nil:
		return []string{
			errStyle.Render(ui.ErrorPrefix + m.err.Error()),
			"",
			citationStyle.Render(ui.ErrorHint),
		}
	case m.loading:
		return []string{citationStyle.Render(ui.Loading)}
	case len(m.sections) == 0:
		return []string{citationStyle.Render(ui.NoReadingsFor + m.date)}
	}

	ver := m.version()
	var lines []string
	for i, sec := range m.sections {
		if i > 0 {
			lines = append(lines, "")
		}
		heading := render.LocalizeHeading(sec.Heading, sec.PartID, m.cfg.UILanguage)
		lines = append(lines, headingStyle.Render(heading))
		if sec.Subtitle != "" {
			lines = append(lines, citationStyle.Render(sec.Subtitle))
		}
		lines = append(lines, "")

		_, blocks := render.GatherVersion(ver, sec, m.cfg.Lectionary, m.cfg.UILanguage)
		isPsalm := sec.PartID == "psalm"
		for bi, b := range blocks {
			refrain := isPsalm && bi == 0
			lines = append(lines, styleBlock(b, refrain, w)...)
			lines = append(lines, "")
		}
	}
	return lines
}

// verseNumRe matches a bible verse block's "chapter:verse  " prefix, as
// produced by render.GatherVersion (e.g. "3:16  Tak bowiem...").
var verseNumRe = regexp.MustCompile(`^(\d+:\d+)  (.*)$`)

// styleBlock wraps and colors one render.GatherVersion block: a verse
// block gets its "chapter:verse" prefix in the muted verse-number style and
// its text in the default verse style; a psalm's first (refrain) block
// renders italic; everything else renders in the default verse style.
func styleBlock(b string, refrain bool, w int) []string {
	if g := verseNumRe.FindStringSubmatch(b); g != nil {
		num, text := g[1], g[2]
		wrapped := verseTextStyle.Width(w).Render(text)
		wlines := strings.Split(wrapped, "\n")
		wlines[0] = verseNumStyle.Render(num+"  ") + wlines[0]
		return wlines
	}

	style := verseTextStyle
	if refrain {
		style = refrainStyle
	}
	return strings.Split(style.Width(w).Render(b), "\n")
}