open Parser

(* --- Groff escape/formatting stripper --- *)

let strip_groff_escapes s =
  let buf = Buffer.create (String.length s) in
  let len = String.length s in
  let i = ref 0 in
  while !i < len do
    if s.[!i] = '\\' && !i + 1 < len then begin
      let next = s.[!i + 1] in
      match next with
      | 'f' ->
        (* Font escape: \fB, \fI, \fP, \fR, \f(XX, \f[...] *)
        if !i + 2 < len then begin
          if s.[!i + 2] = '(' then
            i := !i + 4  (* \f(XX *)
          else if s.[!i + 2] = '[' then begin
            (* \f[...] - skip to ] *)
            i := !i + 3;
            while !i < len && s.[!i] <> ']' do incr i done;
            if !i < len then incr i
          end else
            i := !i + 3  (* \fX *)
        end else
          i := !i + 2
      | '-' ->
        Buffer.add_char buf '-';
        i := !i + 2
      | '&' | '/' | ',' ->
        (* Zero-width characters *)
        i := !i + 2
      | '(' ->
        (* Two-char named character: \(aq, \(lq, \(rq, etc. *)
        if !i + 3 < len then begin
          let name = String.sub s (!i + 2) 2 in
          (match name with
           | "aq" -> Buffer.add_char buf '\''
           | "lq" | "Lq" -> Buffer.add_char buf '"'
           | "rq" | "Rq" -> Buffer.add_char buf '"'
           | "em" | "en" -> Buffer.add_char buf '-'
           | _ -> ());
          i := !i + 4
        end else
          i := !i + 2
      | '[' ->
        (* Named character: \[...] *)
        i := !i + 2;
        let start = !i in
        while !i < len && s.[!i] <> ']' do incr i done;
        if !i < len then begin
          let name = String.sub s start (!i - start) in
          (match name with
           | "aq" -> Buffer.add_char buf '\''
           | "lq" | "Lq" -> Buffer.add_char buf '"'
           | "rq" | "Rq" -> Buffer.add_char buf '"'
           | _ -> ());
          incr i
        end
      | 's' ->
        (* Size escape: \sN, \s+N, \s-N, \s'N' *)
        i := !i + 2;
        if !i < len && (s.[!i] = '+' || s.[!i] = '-') then incr i;
        if !i < len && s.[!i] >= '0' && s.[!i] <= '9' then incr i;
        if !i < len && s.[!i] >= '0' && s.[!i] <= '9' then incr i
      | 'm' ->
        (* Color escape: \m[...] *)
        i := !i + 2;
        if !i < len && s.[!i] = '[' then begin
          incr i;
          while !i < len && s.[!i] <> ']' do incr i done;
          if !i < len then incr i
        end
      | 'X' ->
        (* Device control: \X'...' *)
        i := !i + 2;
        if !i < len && s.[!i] = '\'' then begin
          incr i;
          while !i < len && s.[!i] <> '\'' do incr i done;
          if !i < len then incr i
        end
      | '*' ->
        (* String variable: \*X or \*(XX or \*[...] *)
        i := !i + 2;
        if !i < len then begin
          if s.[!i] = '(' then
            i := !i + 2
          else if s.[!i] = '[' then begin
            incr i;
            while !i < len && s.[!i] <> ']' do incr i done;
            if !i < len then incr i
          end else
            incr i
        end
      | 'n' ->
        (* Number register: \nX or \n(XX or \n[...] *)
        i := !i + 2;
        if !i < len then begin
          if s.[!i] = '(' then
            i := !i + 2
          else if s.[!i] = '[' then begin
            incr i;
            while !i < len && s.[!i] <> ']' do incr i done;
            if !i < len then incr i
          end else
            incr i
        end
      | 'e' ->
        Buffer.add_char buf '\\';
        i := !i + 2
      | '\\' ->
        Buffer.add_char buf '\\';
        i := !i + 2
      | ' ' ->
        Buffer.add_char buf ' ';
        i := !i + 2
      | _ ->
        (* Unknown escape, skip *)
        i := !i + 2
    end else begin
      Buffer.add_char buf s.[!i];
      incr i
    end
  done;
  Buffer.contents buf

(* Strip inline macro formatting: .BI, .BR, .IR, etc.
   These macros alternate between fonts for their arguments.
   We just concatenate the arguments. *)
let strip_inline_macro_args s =
  (* Arguments are separated by spaces, quoted strings are kept together *)
  let buf = Buffer.create (String.length s) in
  let len = String.length s in
  let i = ref 0 in
  while !i < len do
    if s.[!i] = '"' then begin
      incr i;
      while !i < len && s.[!i] <> '"' do
        Buffer.add_char buf s.[!i];
        incr i
      done;
      if !i < len then incr i
    end else if s.[!i] = ' ' || s.[!i] = '\t' then begin
      incr i
    end else begin
      Buffer.add_char buf s.[!i];
      incr i
    end
  done;
  Buffer.contents buf

let strip_groff line =
  let s = strip_groff_escapes line in
  String.trim s

(* --- Line classification --- *)

type groff_line =
  | Macro of string * string   (* e.g. ("SH", "OPTIONS") or ("TP", "") *)
  | Text of string             (* plain text after stroff stripping *)
  | Blank
  | Comment

let classify_line line =
  let len = String.length line in
  if len = 0 then Blank
  else if len >= 2 && line.[0] = '.' && line.[1] = '\\' && (len < 3 || line.[2] = '"') then
    Comment
  else if len >= 3 && line.[0] = '\\' && line.[1] = '"' then
    Comment
  else if line.[0] = '.' || line.[0] = '\'' then begin
    (* Macro line *)
    let rest = String.sub line 1 (len - 1) in
    let rest = String.trim rest in
    (* Split into macro name and arguments *)
    let space_pos =
      try Some (String.index rest ' ')
      with Not_found ->
        try Some (String.index rest '\t')
        with Not_found -> None
    in
    match space_pos with
    | Some pos ->
      let name = String.sub rest 0 pos in
      let args = String.trim (String.sub rest (pos + 1) (String.length rest - pos - 1)) in
      (* Strip quotes from args *)
      let args =
        let alen = String.length args in
        if alen >= 2 && args.[0] = '"' && args.[alen - 1] = '"' then
          String.sub args 1 (alen - 2)
        else args
      in
      Macro (name, args)
    | None ->
      Macro (rest, "")
  end else begin
    let stripped = strip_groff line in
    if String.length stripped = 0 then Blank
    else Text stripped
  end

(* Check for dot-backslash-quote style comments more carefully *)
let is_comment_line line =
  let len = String.length line in
  (len >= 3 && line.[0] = '.' && line.[1] = '\\' && line.[2] = '"')
  || (len >= 2 && line.[0] = '\\' && line.[1] = '"')

let classify_line line =
  if is_comment_line line then Comment
  else classify_line line

(* --- Section extraction --- *)

let extract_options_section lines =
  let classified = List.map classify_line lines in
  let rec collect_until_next_sh lines acc =
    match lines with
    | [] -> List.rev acc
    | Macro ("SH", _) :: _ -> List.rev acc
    | line :: rest -> collect_until_next_sh rest (line :: acc)
  in
  let is_options_section name =
    let s = String.uppercase_ascii (String.trim name) in
    s = "OPTIONS"
    || (String.length s > 0 &&
        try let _ = Str.search_forward (Str.regexp_string "OPTION") s 0 in true
        with Not_found -> false)
  in
  (* First pass: look for OPTIONS section *)
  let rec find_options = function
    | [] -> None
    | Macro ("SH", args) :: rest when is_options_section args ->
      Some (collect_until_next_sh rest [])
    | _ :: rest -> find_options rest
  in
  (* Fallback: DESCRIPTION section *)
  let rec find_description = function
    | [] -> []
    | Macro ("SH", args) :: rest
      when String.uppercase_ascii (String.trim args) = "DESCRIPTION" ->
      collect_until_next_sh rest []
    | _ :: rest -> find_description rest
  in
  match find_options classified with
  | Some section -> section
  | None -> find_description classified

(* --- Strategy-based entry extraction --- *)

(* Collect text lines until next macro or blank *)
let rec collect_text_lines lines acc =
  match lines with
  | Text s :: rest -> collect_text_lines rest (s :: acc)
  | _ -> (String.concat " " (List.rev acc), lines)

(* Parse a tag line to extract entry using the Angstrom switch_parser *)
let parse_tag_to_entry tag desc =
  let tag = strip_groff_escapes tag in
  let tag = String.trim tag in
  match Angstrom.parse_string ~consume:Angstrom.Consume.Prefix
          (Angstrom.lift2 (fun sw p -> (sw, p)) switch_parser param_parser) tag with
  | Ok (switch, param) -> Some { switch; param; desc }
  | Error _ -> None

(* Strategy A: .TP style (most common — GNU coreutils, help2man) *)
let strategy_tp lines =
  let rec walk lines acc =
    match lines with
    | [] -> List.rev acc
    | Macro ("TP", _) :: rest ->
      (* Next text line is the tag *)
      begin match rest with
        | Text tag :: rest2 ->
          let (desc, rest3) = collect_text_lines rest2 [] in
          let entry = parse_tag_to_entry tag desc in
          walk rest3 (match entry with Some e -> e :: acc | None -> acc)
        | _ -> walk rest acc
      end
    | _ :: rest -> walk rest acc
  in
  walk lines []

(* Strategy B: .IP style (curl, hand-written) *)
let strategy_ip lines =
  let rec walk lines acc =
    match lines with
    | [] -> List.rev acc
    | Macro ("IP", tag) :: rest ->
      let tag = strip_groff_escapes tag in
      let (desc, rest2) = collect_text_lines rest [] in
      let entry = parse_tag_to_entry tag desc in
      walk rest2 (match entry with Some e -> e :: acc | None -> acc)
    | _ :: rest -> walk rest acc
  in
  walk lines []

(* Strategy C: .PP + .RS/.RE style (git, DocBook) *)
let strategy_pp_rs lines =
  let rec walk lines acc =
    match lines with
    | [] -> List.rev acc
    | Macro ("PP", _) :: rest ->
      begin match rest with
        | Text tag :: rest2 ->
          (* Look for .RS ... text ... .RE *)
          let rec collect_rs lines desc_acc =
            match lines with
            | Macro ("RS", _) :: rest3 ->
              collect_in_rs rest3 desc_acc
            | Text s :: rest3 ->
              (* Sometimes description follows directly *)
              collect_rs rest3 (s :: desc_acc)
            | _ -> (String.concat " " (List.rev desc_acc), lines)
          and collect_in_rs lines desc_acc =
            match lines with
            | Macro ("RE", _) :: rest3 ->
              (String.concat " " (List.rev desc_acc), rest3)
            | Text s :: rest3 ->
              collect_in_rs rest3 (s :: desc_acc)
            | Macro ("PP", _) :: _ | Macro ("SH", _) :: _ ->
              (String.concat " " (List.rev desc_acc), lines)
            | _ :: rest3 -> collect_in_rs rest3 desc_acc
            | [] -> (String.concat " " (List.rev desc_acc), [])
          in
          let (desc, rest3) = collect_rs rest2 [] in
          let entry = parse_tag_to_entry tag desc in
          walk rest3 (match entry with Some e -> e :: acc | None -> acc)
        | _ -> walk rest acc
      end
    | _ :: rest -> walk rest acc
  in
  walk lines []

(* Strategy D: Deroff fallback — strip all groff, use help text parser *)
let strategy_deroff_lines lines =
  let buf = Buffer.create 256 in
  List.iter (fun line ->
    match line with
    | Text s ->
      Buffer.add_string buf s;
      Buffer.add_char buf '\n'
    | Macro (("BI" | "BR" | "IR" | "B" | "I"), args) ->
      let text = strip_inline_macro_args args in
      let text = strip_groff_escapes text in
      Buffer.add_string buf text;
      Buffer.add_char buf '\n'
    | Blank -> Buffer.add_char buf '\n'
    | _ -> ()
  ) lines;
  let text = Buffer.contents buf in
  match parse_help text with
  | Ok result -> result.entries
  | Error _ -> []

(* Count macros of a given type *)
let count_macro name lines =
  List.fold_left (fun n line ->
    match line with Macro (m, _) when m = name -> n + 1 | _ -> n
  ) 0 lines

(* Auto-detect and try strategies, return the one with most entries *)
let extract_entries lines =
  let results = ref [] in
  (* Try TP if .TP macros present *)
  if count_macro "TP" lines > 0 then
    results := ("TP", strategy_tp lines) :: !results;
  (* Try IP if .IP macros present *)
  if count_macro "IP" lines > 0 then
    results := ("IP", strategy_ip lines) :: !results;
  (* Try PP+RS if both present *)
  if count_macro "PP" lines > 0 && count_macro "RS" lines > 0 then
    results := ("PP+RS", strategy_pp_rs lines) :: !results;
  (* Always try deroff as fallback *)
  results := ("deroff", strategy_deroff_lines lines) :: !results;
  (* Pick the result with the most entries *)
  let best =
    List.fold_left (fun (best_name, best_entries) (name, entries) ->
      if List.length entries >= List.length best_entries then (name, entries)
      else (best_name, best_entries)
    ) ("none", []) !results
  in
  snd best

(* --- Top-level API --- *)

let parse_manpage_lines lines =
  let options_section = extract_options_section lines in
  extract_entries options_section

let parse_manpage_string contents =
  let lines = String.split_on_char '\n' contents in
  parse_manpage_lines lines

let parse_manpage_gzipped_file path =
  let ic = Unix.open_process_in (Printf.sprintf "gzip -dc %s" (Filename.quote path)) in
  let buf = Buffer.create 4096 in
  (try while true do
     let line = input_line ic in
     Buffer.add_string buf line;
     Buffer.add_char buf '\n'
   done with End_of_file -> ());
  let _ = Unix.close_process_in ic in
  parse_manpage_string (Buffer.contents buf)

let parse_manpage_file path =
  if Filename.check_suffix path ".gz" then
    parse_manpage_gzipped_file path
  else begin
    let ic = open_in path in
    let n = in_channel_length ic in
    let s = Bytes.create n in
    really_input ic s 0 n;
    close_in ic;
    parse_manpage_string (Bytes.to_string s)
  end