//! Terminal colour theming.
//!
//! tiletopia ships one hard-coded dark palette historically baked into
//! XtermPane. This module turns that into a customisable model:
//!
//!  - a GLOBAL default theme (persisted to localStorage, app-wide), and
//!  - optional PER-PANE overrides (stored on the LeafNode, persisted with the
//!    workspace tree).
//!
//! Only four colours are user-editable — background, foreground, cursor, and
//! selection — the ones that actually move the needle on readability. The
//! rest of xterm's ITheme (the 16-colour ANSI palette, etc.) stays fixed in
//! {@link BASE_XTERM_THEME}: notably `white`/`brightWhite` keep the softened
//! values that tame the Claude TUI's emphasis slots (see XtermPane history).

import type { ITheme } from "@xterm/xterm";

/** The four user-editable colours. All optional: an undefined field on a
 *  per-pane override falls through to the global default; an undefined field
 *  on the global default falls through to {@link DEFAULT_PANE_COLORS}. */
export interface PaneColors {
  /** Terminal background. */
  background?: string;
  /** Default text colour. */
  foreground?: string;
  /** Cursor block colour. */
  cursor?: string;
  /** Selection highlight background. */
  selection?: string;
}

/** Fixed slice of the xterm theme that is NOT user-editable. The softened
 *  white/brightWhite values date back to the original hard-coded theme — they
 *  keep the Claude TUI's emphasis text from hitting glaring pure white. */
const BASE_XTERM_THEME: ITheme = {
  white: "#c5c8c6",
  brightWhite: "#e0e0e0",
};

/** Ground-truth defaults — the historical tiletopia palette. Every editable
 *  field resolves to one of these when nothing overrides it. Also exposed as
 *  the first preset ("Tiletopia Dark"). */
export const DEFAULT_PANE_COLORS: Required<PaneColors> = {
  background: "#0c0c0c",
  foreground: "#c5c8c6",
  cursor: "#ffffff",
  selection: "#3a3a3a",
};

/** A named, ready-to-apply colour set shown as a one-click starting point in
 *  the colour panel. */
export interface ColorPreset {
  name: string;
  colors: Required<PaneColors>;
}

/** Built-in presets. The first is the tiletopia default; the rest are
 *  well-known community palettes (background/foreground/cursor/selection
 *  only — the ANSI ramp is left to {@link BASE_XTERM_THEME}). */
export const COLOR_PRESETS: ColorPreset[] = [
  { name: "Tiletopia Dark", colors: DEFAULT_PANE_COLORS },
  {
    name: "Solarized Dark",
    colors: { background: "#002b36", foreground: "#839496", cursor: "#93a1a1", selection: "#073642" },
  },
  {
    name: "Gruvbox Dark",
    colors: { background: "#282828", foreground: "#ebdbb2", cursor: "#ebdbb2", selection: "#504945" },
  },
  {
    name: "Dracula",
    colors: { background: "#282a36", foreground: "#f8f8f2", cursor: "#f8f8f2", selection: "#44475a" },
  },
  {
    name: "Nord",
    colors: { background: "#2e3440", foreground: "#d8dee9", cursor: "#d8dee9", selection: "#434c5e" },
  },
  {
    name: "Light",
    colors: { background: "#fafafa", foreground: "#1c1c1c", cursor: "#1c1c1c", selection: "#cfe0ff" },
  },
];

/** Merge a per-pane override on top of the global default, then fill any
 *  still-missing field from {@link DEFAULT_PANE_COLORS}. The result always
 *  has all four fields defined. */
export function resolvePaneColors(
  global: PaneColors | undefined,
  override: PaneColors | undefined,
): Required<PaneColors> {
  return {
    background:
      override?.background ?? global?.background ?? DEFAULT_PANE_COLORS.background,
    foreground:
      override?.foreground ?? global?.foreground ?? DEFAULT_PANE_COLORS.foreground,
    cursor: override?.cursor ?? global?.cursor ?? DEFAULT_PANE_COLORS.cursor,
    selection:
      override?.selection ?? global?.selection ?? DEFAULT_PANE_COLORS.selection,
  };
}

/** Build a full xterm ITheme from resolved colours. cursorAccent is pinned to
 *  the background so a block cursor's glyph stays readable. */
export function toXtermTheme(colors: Required<PaneColors>): ITheme {
  return {
    ...BASE_XTERM_THEME,
    background: colors.background,
    foreground: colors.foreground,
    cursor: colors.cursor,
    cursorAccent: colors.background,
    selectionBackground: colors.selection,
  };
}

// ---------------------------------------------------------------------------
// Global-default persistence (localStorage; frontend-only, no backend hop).
// localStorage is shared across all windows of the same origin, so a new
// window picks up the saved theme at startup, and the `storage` event lets
// open windows react live (see App's listener).
// ---------------------------------------------------------------------------

export const GLOBAL_COLORS_STORAGE_KEY = "tiletopia.globalColors.v1";

/** #rgb / #rrggbb hex validator — what `<input type="color">` emits and what
 *  xterm accepts. We reject anything else so a corrupt localStorage value
 *  can't poison the theme. */
const HEX_RE = /^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/;

function sanitizeColors(raw: unknown): PaneColors {
  if (typeof raw !== "object" || raw === null) return {};
  const o = raw as Record<string, unknown>;
  const out: PaneColors = {};
  for (const key of ["background", "foreground", "cursor", "selection"] as const) {
    const v = o[key];
    if (typeof v === "string" && HEX_RE.test(v)) out[key] = v;
  }
  return out;
}

/** Read the saved global theme. Returns {} (→ all defaults) when absent or
 *  unparseable. */
export function loadGlobalColors(): PaneColors {
  try {
    const raw = localStorage.getItem(GLOBAL_COLORS_STORAGE_KEY);
    if (!raw) return {};
    return sanitizeColors(JSON.parse(raw));
  } catch {
    return {};
  }
}

/** Persist the global theme. Empty object is stored as-is (means "all
 *  defaults"), keeping the round-trip lossless. */
export function saveGlobalColors(colors: PaneColors): void {
  try {
    localStorage.setItem(GLOBAL_COLORS_STORAGE_KEY, JSON.stringify(colors));
  } catch (e) {
    console.warn("saveGlobalColors failed:", e);
  }
}