--- `[[wiki-link]]` parsing and following (tech-spec §8).
---
--- The cursor grammar mirrors `heph-core`'s `extract.rs`: a span `[[target]]`
--- or `[[target|display]]`, where the resolvable name is everything left of the
--- first `|`, trimmed. Resolution goes through `node.resolve` (exact, the same
--- mapping that materializes stored `wiki` links) — never fuzzy `search`, which
--- would mis-jump.

local rpc = require("heph.rpc")
local util = require("heph.util")

local M = {}

--- The wiki target under the cursor on the current line, or nil. Scans for the
--- `[[...]]` span that contains the cursor column.
function M.target_under_cursor()
  local line = vim.api.nvim_get_current_line()
  local col = vim.api.nvim_win_get_cursor(0)[2] + 1 -- 1-based byte column
  local from = 1
  while true do
    local open_s, open_e = line:find("[[", from, true)
    if not open_s then
      return nil
    end
    local close_s, close_e = line:find("]]", open_e + 1, true)
    if not close_s then
      return nil
    end
    if col >= open_s and col <= close_e then
      local inner = line:sub(open_e + 1, close_s - 1)
      local target = inner:match("^([^|]*)") or ""
      target = target:gsub("^%s+", ""):gsub("%s+$", "")
      return (#target > 0) and target or nil
    end
    from = close_e + 1
  end
end

--- Follow the `[[link]]` under the cursor to its node, **creating** the target
--- doc if it doesn't exist yet (the zettelkasten follow-or-create gesture). The
--- newly-created doc resolves the source's previously-unresolved wiki-link, so
--- re-saving the source materializes the backlink.
function M.follow()
  local target = M.target_under_cursor()
  if not target then
    util.notify("no [[link]] under cursor", vim.log.levels.WARN)
    return
  end
  local node = rpc.call("node.resolve", { title = target })
  if not node then
    node = rpc.call("node.create", { kind = "doc", title = target, body = "" })
    util.notify("created [[" .. target .. "]]")
    -- Materialize the source's wiki-link to the new doc — it was unresolved when
    -- the source was saved, so extraction skipped it (tech-spec §5). If the
    -- source has unsaved edits, saving re-extracts and materializes it (and
    -- persists the edits); otherwise add the link directly (a no-op re-save
    -- wouldn't re-extract).
    local src = vim.api.nvim_get_current_buf()
    local src_id = vim.b[src].heph_node_id
    if src_id then
      if vim.bo[src].modified then
        pcall(require("heph.node").write, src, vim.api.nvim_buf_get_name(src))
      else
        pcall(rpc.call, "links.add", { src = src_id, dst = node.id, link_type = "wiki" })
      end
    end
  end
  require("heph.node").open(node.id)
end

-- Insert the labelled form `[[id|Name]]` at the cursor (readable + conceal-ready;
-- it collapses to the canonical bare `[[id]]` on save, §8.4).
local function put_link(id, title)
  vim.api.nvim_put({ "[[" .. id .. "|" .. title .. "]]" }, "c", true, true)
end

-- Mint a doc named `title` and insert a link to it.
local function create_and_put(title)
  if title and #title > 0 then
    local node = rpc.call("node.create", { kind = "doc", title = title })
    put_link(node.id, node.title)
  end
end

-- Telescope is available and not explicitly disabled (tests force ui.select).
local function use_telescope()
  return not vim.g.heph_force_ui_select and pcall(require, "telescope")
end

-- A live, fuzzy-filtered Telescope picker over every node: type to narrow,
-- <CR> inserts the highlighted node, <C-x> creates a doc named the current
-- prompt text (so a miss flows straight into "make it"). Telescope only.
-- The markdown body to preview for a picker entry: a doc/journal's own body,
-- or — for a task (which has no body of its own) — its canonical-context doc.
local function preview_body(node)
  local ok, body = pcall(function()
    local id = node.id
    if node.kind == "task" then
      for _, l in ipairs(rpc.call("links.outgoing", { id = node.id }) or {}) do
        if l.link_type == "canonical-context" then
          id = l.dst_id
          break
        end
      end
    end
    local fetched = rpc.call("node.get", { id = id })
    return (fetched and fetched.body) or ""
  end)
  return vim.split(ok and body or "", "\n", { plain = true })
end

local function telescope_insert()
  local pickers = require("telescope.pickers")
  local finders = require("telescope.finders")
  local conf = require("telescope.config").values
  local actions = require("telescope.actions")
  local action_state = require("telescope.actions.state")
  local previewers = require("telescope.previewers")

  -- First-class targets only (excludes tags + tasks' context/log docs, §8.4).
  local nodes = rpc.call("node.linkable", vim.empty_dict()) or {}
  pickers
    .new({}, {
      prompt_title = "Link to node  (<C-x> = create from prompt)",
      finder = finders.new_table({
        results = nodes,
        entry_maker = function(n)
          return {
            value = n,
            display = n.title .. "  [" .. (n.kind or "node") .. "]",
            ordinal = n.title,
          }
        end,
      }),
      sorter = conf.generic_sorter({}),
      previewer = previewers.new_buffer_previewer({
        title = "Preview",
        define_preview = function(self, entry)
          vim.api.nvim_buf_set_lines(self.state.bufnr, 0, -1, false, preview_body(entry.value))
          vim.bo[self.state.bufnr].filetype = "markdown"
        end,
      }),
      attach_mappings = function(bufnr, map)
        actions.select_default:replace(function()
          local entry = action_state.get_selected_entry()
          actions.close(bufnr)
          if entry then
            put_link(entry.value.id, entry.value.title)
          end
        end)
        local create = function()
          local title = action_state.get_current_line()
          actions.close(bufnr)
          create_and_put(title)
        end
        map("i", "<C-x>", create)
        map("n", "<C-x>", create)
        return true
      end,
    })
    :find()
end

-- Fallback when Telescope isn't available: prompt a query, search, then pick
-- from the results (or a "+ Create" entry). `vim.ui.select` can't filter live.
local function uiselect_insert()
  vim.ui.input({ prompt = "Link to: " }, function(query)
    if not query or query == "" then
      return
    end
    local items = {}
    for _, hit in ipairs(rpc.call("search", { query = query }) or {}) do
      items[#items + 1] = hit
    end
    items[#items + 1] = { __create = true, title = query }
    require("heph.picker").select(items, {
      prompt = "Link to",
      format = function(it)
        if it.__create then
          return "+ Create new doc: " .. it.title
        end
        return it.title .. "  [" .. (it.kind or "node") .. "]"
      end,
    }, function(choice)
      if not choice then
        return
      elseif choice.__create then
        create_and_put(choice.title)
      else
        put_link(choice.id, choice.title)
      end
    end)
  end)
end

--- Insert a canonical `[[NODEID|Name]]` link at the cursor (§8.4) by picking a
--- node — live-filtered via Telescope when available, else a search-then-select
--- prompt. A node id is the only thing that ever enters a stored link.
function M.insert()
  if use_telescope() then
    telescope_insert()
  else
    uiselect_insert()
  end
end

--- Attach the buffer-local follow/insert keymaps and inline-`#hashtag`
--- highlighting (only on heph:// buffers).
function M.attach(buf)
  vim.keymap.set("n", "<CR>", function()
    M.follow()
  end, { buffer = buf, desc = "heph: follow [[link]]" })
  -- Typing `[[` opens the node picker (Obsidian-style), inserting `[[NODEID]]`.
  vim.keymap.set("i", "[[", function()
    M.insert()
  end, { buffer = buf, desc = "heph: insert [[link]]" })

  -- Render inline #hashtags in italics so they stand out — matching the
  -- save-time tag detection (whitespace-prefixed `#word`, never a `# heading`).
  -- `default = true` leaves a user's own `HephHashtag` definition intact.
  vim.api.nvim_set_hl(0, "HephHashtag", { italic = true, default = true })
  vim.api.nvim_buf_call(buf, function()
    vim.cmd([[syntax match HephHashtag /\v%(^|\s)@<=#[0-9A-Za-z_-]+/ containedin=ALL]])
  end)
end

return M