import { TERMINAL_PALETTE as palette } from "@berry/util/palette.ts";

function indexedColor(index: number): string | undefined {
  if (!Number.isInteger(index) || index < 0 || index > 255) return undefined;
  if (index < 16) return palette[index];
  if (index >= 232) {
    const gray = 8 + (index - 232) * 10;
    return `rgb(${gray}, ${gray}, ${gray})`;
  }
  const value = index - 16;
  const levels = [0, 95, 135, 175, 215, 255];
  return `rgb(${levels[Math.floor(value / 36)]}, ${levels[Math.floor(value / 6) % 6]}, ${
    levels[value % 6]
  })`;
}

export type AnsiRun = { text: string; style: Record<string, string> };

/** An incremental SGR decoder that hides terminal controls, even across chunk boundaries. */
export function ansiParser() {
  let foreground: string | undefined;
  let background: string | undefined;
  let bold = false;
  let dim = false;
  let italic = false;
  let underline = false;
  let strike = false;
  let inverse = false;
  let mode: "text" | "escape" | "csi" | "osc" | "oscEscape" = "text";
  let parametersText = "";
  let invalid = false;

  return {
    write(source: string): AnsiRun[] {
      const runs: AnsiRun[] = [];
      let offset = 0;
      // discard non-SGR controls, including OSC links and a streaming chunk's unfinished escape
      while (offset < source.length) {
        if (mode === "text") {
          const escape = source.indexOf("\x1b", offset);
          const text = source.slice(offset, escape === -1 ? source.length : escape);
          if (text) {
            const style: Record<string, string> = {};
            const fg = inverse ? background ?? "var(--panel)" : foreground;
            const bg = inverse ? foreground ?? "var(--text)" : background;
            if (fg) style.color = fg;
            if (bg) style["background-color"] = bg;
            if (bold) style["font-weight"] = "bold";
            if (dim) style.opacity = "0.5";
            if (italic) style["font-style"] = "italic";
            const decoration = [underline ? "underline" : "", strike ? "line-through" : ""].filter(
              Boolean,
            );
            if (decoration.length) style["text-decoration"] = decoration.join(" ");
            runs.push({ text, style });
          }
          if (escape === -1) break;
          offset = escape + 1;
          mode = "escape";
          continue;
        }
        const char = source[offset++];
        if (mode === "escape") {
          if (char === "[") {
            mode = "csi";
            parametersText = "";
            invalid = false;
          } else if (char === "]") mode = "osc";
          else if (char !== "\x1b" && !(char >= " " && char <= "/")) mode = "text";
        } else if (mode === "osc") {
          if (char === "\x07") mode = "text";
          else if (char === "\x1b") mode = "oscEscape";
        } else if (mode === "oscEscape") {
          if (char === "\\" || char === "\x07") mode = "text";
          else if (char !== "\x1b") mode = "osc";
        } else if (char >= "@" && char <= "~") {
          mode = "text";
          if (char !== "m" || invalid || !/^[\d;]*$/.test(parametersText)) continue;
          const parameters = parametersText.split(";").map(Number);
          for (let i = 0; i < parameters.length; i++) {
            const parameter = parameters[i];
            if (parameter === 0) {
              foreground = background = undefined;
              bold = dim = false;
              italic = underline = false;
              strike = inverse = false;
            } else if (parameter === 1) bold = true;
            else if (parameter === 2) dim = true;
            else if (parameter === 3) italic = true;
            else if (parameter === 4) underline = true;
            else if (parameter === 7) inverse = true;
            else if (parameter === 9) strike = true;
            else if (parameter === 22) bold = dim = false;
            else if (parameter === 23) italic = false;
            else if (parameter === 24) underline = false;
            else if (parameter === 27) inverse = false;
            else if (parameter === 29) strike = false;
            else if (parameter === 39) foreground = undefined;
            else if (parameter === 49) background = undefined;
            else if (parameter >= 30 && parameter <= 37) foreground = palette[parameter - 30];
            else if (parameter >= 90 && parameter <= 97) foreground = palette[parameter - 82];
            else if (parameter >= 40 && parameter <= 47) background = palette[parameter - 40];
            else if (parameter >= 100 && parameter <= 107) background = palette[parameter - 92];
            else if (parameter === 38 || parameter === 48) {
              const mode = parameters[++i];
              let color: string | undefined;
              if (mode === 5) color = indexedColor(parameters[++i]);
              else if (mode === 2) {
                const rgb = parameters.slice(i + 1, i + 4);
                i += 3;
                if (
                  rgb.length === 3 && rgb.every((n) => Number.isInteger(n) && n >= 0 && n <= 255)
                ) {
                  color = `rgb(${rgb.join(", ")})`;
                }
              } else break;
              if (color !== undefined) {
                if (parameter === 38) foreground = color;
                else background = color;
              }
            }
          }
          parametersText = "";
        } else if (char >= " " && char <= "?") {
          // bound malformed CSI sequences; OSC payloads are never buffered
          if (parametersText.length < 1024 && char >= "0" && !invalid) parametersText += char;
          else invalid = true;
        } else {
          mode = char === "\x1b" ? "escape" : "text";
        }
      }
      return runs;
    },
  };
}

/** Text and SGR styles, without interpreting terminal commands or output as markup. */
export function ansiRuns(source: string): AnsiRun[] {
  return ansiParser().write(source);
}