package app

import (
	"strings"
	"time"

	"glint/internal/grammar"

	tea "github.com/charmbracelet/bubbletea"
)

// grammarDebounce is how long editing settles before glint sends the buffer to
// harper. Long enough to coalesce a burst of keystrokes into one didChange,
// short enough that underlines feel live.
const grammarDebounce = 400 * time.Millisecond

// grammarDiagMsg carries a fresh batch of diagnostics from the harper listener.
type grammarDiagMsg struct{ diags []grammar.Diag }

// grammarDebounceMsg fires after an edit settles; gen guards against stale ticks.
type grammarDebounceMsg struct{ gen int }

// initGrammar starts harper-ls when grammar is enabled (config not "off") and the
// binary is present, then flags the editor to render grammar underlines. A
// missing binary or a start failure leaves grammar silently off — glint behaves
// exactly as before.
func (a *App) initGrammar() {
	if strings.EqualFold(a.cfg.Grammar, "off") || !grammar.Available() {
		return
	}
	c, err := grammar.Start()
	if err != nil {
		return
	}
	a.grammar = c
	a.editor.SetGrammar(true)
}

// grammarListen returns a command that blocks for the next diagnostic batch. It
// is re-issued after each batch so diagnostics keep flowing; nil when grammar is
// off so Init/Update can compose it unconditionally.
func (a *App) grammarListen() tea.Cmd {
	if a.grammar == nil {
		return nil
	}
	ch := a.grammar.Diagnostics()
	return func() tea.Msg {
		batch, ok := <-ch
		if !ok {
			return nil
		}
		return grammarDiagMsg{diags: batch}
	}
}

// applyGrammarDiags buckets a diagnostic batch by logical line and hands it to
// the editor as green-undercurl ranges.
func (a *App) applyGrammarDiags(diags []grammar.Diag) {
	byLine := map[int][][2]int{}
	for _, d := range diags {
		byLine[d.Line] = append(byLine[d.Line], [2]int{d.StartCol, d.EndCol})
	}
	a.editor.SetGrammarDiags(byLine)
}

// grammarOpen (re)registers the current buffer with harper after the open
// document changes (a load, a new blank buffer, or a save-as that renames it),
// closing the previous document first. No-op without a client.
func (a *App) grammarOpen() {
	if a.grammar == nil {
		return
	}
	if a.grammarOpened {
		a.grammar.DidClose(a.grammarPath)
	}
	a.grammarPath = a.path
	a.grammarOpened = true
	text := string(a.editor.Bytes())
	a.grammarText = text
	a.grammar.DidOpen(a.path, text)
	a.editor.SetGrammarDiags(nil) // drop the previous doc's underlines until harper replies
}

// grammarChanged schedules a debounced didChange after an editor keystroke and
// returns the tick command (nil without a client). Only the latest tick's
// generation survives grammarFlush, so a burst collapses to one sync.
func (a *App) grammarChanged() tea.Cmd {
	if a.grammar == nil {
		return nil
	}
	a.grammarGen++
	gen := a.grammarGen
	return tea.Tick(grammarDebounce, func(time.Time) tea.Msg {
		return grammarDebounceMsg{gen: gen}
	})
}

// grammarFlush sends the buffer to harper when the debounce tick is the latest
// one and the text actually changed since the last sync.
func (a *App) grammarFlush(gen int) {
	if a.grammar == nil || gen != a.grammarGen {
		return
	}
	text := string(a.editor.Bytes())
	if text == a.grammarText {
		return
	}
	a.grammarText = text
	a.grammar.DidChange(a.grammarPath, text)
}

// toggleGrammar flips grammar checking from the spell popup. With no client it
// lazily starts harper (so grammar=off in config can still be enabled at
// runtime), reporting when the binary is missing. It returns the listener
// command to start after a lazy start, else nil.
func (a *App) toggleGrammar() tea.Cmd {
	if a.grammar == nil {
		if !grammar.Available() {
			a.status = "Grammar unavailable — brew install harper"
			return nil
		}
		c, err := grammar.Start()
		if err != nil {
			a.status = "Grammar start failed: " + err.Error()
			return nil
		}
		a.grammar = c
		a.editor.SetGrammar(true)
		a.grammarOpen()
		a.status = "Grammar on"
		return a.grammarListen()
	}
	if on := a.editor.ToggleGrammar(); on {
		a.status = "Grammar on"
	} else {
		a.status = "Grammar off"
	}
	return nil
}

// closeGrammar shuts the harper subprocess down at exit.
func (a *App) closeGrammar() {
	if a.grammar != nil {
		_ = a.grammar.Close()
		a.grammar = nil
	}
}

// Close releases external resources (the harper subprocess). Safe to call more
// than once; run() invokes it after the program loop returns.
func (a *App) Close() { a.closeGrammar() }