package log

import (
	"fmt"
	"io"
	"os"
	"strings"
	"sync"
	"time"

	"golang.org/x/term"

	"hauler.dev/go/hauler/v2/pkg/consts"
)

// spinnerFrames is the braille-dot spinner animation, advanced roughly every
// spinnerInterval by the Renderer's ticker goroutine.
var spinnerFrames = []string{"⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"}

const spinnerInterval = 120 * time.Millisecond

// fallbackWidth is used when out is not an *os.File (e.g. tests writing to a
// *bytes.Buffer) or when the terminal width can't be determined.
const fallbackWidth = 80

// heightMargin is reserved off the raw detected terminal height before it is
// used as a row cap. Writing to a terminal's last row triggers auto-scroll,
// which invalidates eraseLocked's "move cursor up N-1 rows" math and
// corrupts scrollback -- load-bearing, not a tunable optimization. It does
// not help if the cursor was already near the bottom when hauler started.
const heightMargin = 1

// Renderer renders one live row per in-flight job to a terminal, erasing and
// redrawing the whole live region as jobs begin, finish, and log lines are
// emitted through it. A job's row disappears the moment it finishes, but
// whatever it already logged (e.g. a "✓ added ..." line) stays behind in
// permanent scrollback.
//
// Locking: mu guards both the terminal (out) and all status state
// (in-flight names, spinner frame, cached width/height, drawn row count).
// Compose as log.NewLogger(renderer) so NewLogger's zerolog.SyncWriter wraps
// the Renderer, giving strict nesting SyncWriter.mu -> Renderer.mu on the
// log-write path. The spinner ticker writes to the terminal via Renderer.mu
// directly, bypassing SyncWriter entirely, so Renderer.mu is what actually
// prevents a tick-driven redraw from interleaving with an in-progress
// log-line write. Wrapping a second SyncWriter around the real os.Stdout
// inside the Renderer would create an unordered second lock on the same fd.
type Renderer struct {
	out io.Writer

	mu           sync.Mutex
	started      bool
	stopped      bool
	inFlight     []string
	spinnerFrame int
	width        int
	height       int // cached effective terminal height; 0 == no cap
	drawnRows    int // rows currently occupying screen space from the last draw

	done chan struct{}
	wg   sync.WaitGroup
}

// NewRenderer returns a Renderer that writes to out.
func NewRenderer(out io.Writer) *Renderer {
	return &Renderer{out: out}
}

// Start begins a new progress session and launches the spinner ticker
// goroutine. It caches the terminal width and height for the lifetime of the
// session (mid-run resize is out of scope). A call while a session is
// already live (started and not yet stopped) is a no-op: reassigning r.done
// here would orphan the still-running spinner goroutine on the old channel,
// which it holds in its own stack frame. Stop closes only the newest r.done,
// so that goroutine would never observe a close and r.wg.Wait() in Stop
// would block forever.
func (r *Renderer) Start() {
	r.mu.Lock()
	if r.started && !r.stopped {
		r.mu.Unlock()
		return
	}
	r.inFlight = nil
	r.spinnerFrame = 0
	r.width, r.height = r.detectSize()
	r.drawnRows = 0
	r.started = true
	r.stopped = false
	done := make(chan struct{})
	r.done = done
	r.mu.Unlock()

	r.wg.Add(1)
	go r.run(done)
}

// Began records name as in-flight and redraws the live region.
func (r *Renderer) Began(name string) {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.inFlight = append(r.inFlight, name)
	r.redrawLocked()
}

// Finished removes name from the in-flight set and redraws the live region.
// Call it regardless of the job's success or failure so failed jobs are
// removed from the display too.
func (r *Renderer) Finished(name string) {
	r.mu.Lock()
	defer r.mu.Unlock()
	for i, n := range r.inFlight {
		if n == name {
			r.inFlight = append(r.inFlight[:i], r.inFlight[i+1:]...)
			break
		}
	}
	r.redrawLocked()
}

// Write implements io.Writer and is the sink log.NewLogger writes through.
// It erases the current live region, writes the log payload untouched, then
// redraws the region on the fresh line(s) left by the payload's trailing
// newline.
func (r *Renderer) Write(p []byte) (int, error) {
	r.mu.Lock()
	defer r.mu.Unlock()

	r.eraseLocked()
	if _, err := r.out.Write(p); err != nil {
		return 0, err
	}
	r.drawRowsLocked()

	return len(p), nil
}

// Stop synchronously halts and joins the spinner goroutine, then erases the
// live region. Safe to call even if Start was never called; a single call is
// sufficient (double-Stop is not required to be safe).
func (r *Renderer) Stop() {
	r.mu.Lock()
	if !r.started || r.stopped {
		r.mu.Unlock()
		return
	}
	r.stopped = true
	close(r.done)
	r.mu.Unlock()

	r.wg.Wait()

	r.mu.Lock()
	r.eraseLocked()
	r.mu.Unlock()
}

// run advances the spinner frame and redraws roughly every spinnerInterval
// until done closes. done is passed in rather than read from r.done because
// r.done is only ever written under r.mu (by Start), and this goroutine
// otherwise has no synchronized way to observe it.
func (r *Renderer) run(done chan struct{}) {
	defer r.wg.Done()

	ticker := time.NewTicker(spinnerInterval)
	defer ticker.Stop()

	for {
		select {
		case <-done:
			return
		case <-ticker.C:
			r.mu.Lock()
			r.spinnerFrame = (r.spinnerFrame + 1) % len(spinnerFrames)
			r.redrawLocked()
			r.mu.Unlock()
		}
	}
}

// eraseLocked erases the currently-drawn live region. Callers must hold mu.
func (r *Renderer) eraseLocked() {
	if r.drawnRows == 0 {
		return
	}
	if r.drawnRows > 1 {
		fmt.Fprintf(r.out, "\x1b[%dA", r.drawnRows-1)
	}
	fmt.Fprint(r.out, "\r\x1b[0J")
	r.drawnRows = 0
}

// drawRowsLocked writes the current set of rows (see buildRowsLocked).
// Callers must hold mu.
func (r *Renderer) drawRowsLocked() {
	lines := r.buildRowsLocked()
	if len(lines) == 0 {
		return
	}
	fmt.Fprint(r.out, strings.Join(lines, "\n"))
	r.drawnRows = len(lines)
}

// redrawLocked is eraseLocked + drawRowsLocked, used by Began/Finished/the
// spinner tick; Write uses the two halves separately. Callers must hold mu.
func (r *Renderer) redrawLocked() {
	r.eraseLocked()
	r.drawRowsLocked()
}

// buildRowsLocked returns this frame's rows, truncated to width and capped
// to height (with a "+K more" summary row when capped). Callers must hold
// mu.
func (r *Renderer) buildRowsLocked() []string {
	if len(r.inFlight) == 0 {
		return nil
	}

	frame := spinnerFrames[r.spinnerFrame]

	if r.height <= 0 || len(r.inFlight) <= r.height {
		rows := make([]string, len(r.inFlight))
		for i, ref := range r.inFlight {
			rows[i] = r.formatRowLocked(frame, ref)
		}
		return rows
	}

	shown := r.height - 1
	rows := make([]string, 0, r.height)
	for _, ref := range r.inFlight[:shown] {
		rows = append(rows, r.formatRowLocked(frame, ref))
	}
	remaining := len(r.inFlight) - shown
	rows = append(rows, fmt.Sprintf("  +%d more", remaining))
	return rows
}

// ellipsis marks a truncated ref. It is a 3-byte UTF-8 character, so
// truncation math below sizes against len(ellipsis) rather than assuming
// one byte of budget.
const ellipsis = "…"

// levelWidth is the fixed width of zerolog.ConsoleWriter's rendered level
// field ("DBG", "INF", "WRN", "ERR", ...) -- always 3 characters.
const levelWidth = 3

// alignmentWidth pads a progress row to line up under the log *message*
// column rather than the timestamp; it mirrors one rendered log prefix
// (CustomTimeFormat + space + 3-char level + space) and must move if
// CustomTimeFormat's width changes.
var alignmentWidth = len(consts.CustomTimeFormat) + 1 + levelWidth + 1

// alignmentPrefix is alignmentWidth worth of an alternating dot-space guide
// pattern, precomputed once at package init to avoid per-frame allocation.
var alignmentPrefix = buildAlignmentPrefix()

func buildAlignmentPrefix() string {
	var b strings.Builder
	b.Grow(alignmentWidth)
	for i := 0; i < alignmentWidth; i++ {
		if i%2 == 0 {
			b.WriteByte('.')
		} else {
			b.WriteByte(' ')
		}
	}
	return b.String()
}

// formatRowLocked renders "<alignmentPrefix><frame> adding <ref>",
// truncating ref (never the fixed prefix) with a trailing ellipsis so the
// row fits within r.width. Callers must hold mu.
func (r *Renderer) formatRowLocked(frame, ref string) string {
	prefix := alignmentPrefix + frame + " adding "

	budget := r.width - len(prefix)
	if budget < 1 {
		budget = 1
	}
	if len(ref) > budget {
		keep := budget - len(ellipsis)
		if keep < 0 {
			keep = 0
		}
		ref = ref[:keep] + ellipsis
	}

	return prefix + ref
}

// detectSize queries width/height via golang.org/x/term when out is an
// *os.File, else falls back to fallbackWidth/0 (e.g. *bytes.Buffer in
// tests, or a GetSize error). Height's fallback is deliberately 0 (no cap)
// rather than a guessed size, so an unknown height never artificially
// limits rows; see heightMargin for the one-row reduction applied to a
// detected height.
func (r *Renderer) detectSize() (width, height int) {
	width = fallbackWidth
	height = 0

	f, ok := r.out.(*os.File)
	if !ok {
		return width, height
	}

	w, h, err := term.GetSize(int(f.Fd()))
	if err != nil {
		return width, height
	}
	if w > 0 {
		width = w
	}
	if h > 0 {
		if effective := h - heightMargin; effective >= 1 {
			height = effective
		}
		// else: terminal too small after the margin; leave height at 0 (no
		// cap) rather than a degenerate zero/negative-row region.
	}

	return width, height
}