local utils = require 'u.utils'

--- @alias Tag { kind: 'tag'; name: string, attributes: table<string, unknown>, children: Tree }
--- @alias Node nil | boolean | string | Tag
--- @alias Tree Node | Node[]
local TagMetaTable = {}

--------------------------------------------------------------------------------
-- Renderer class
--------------------------------------------------------------------------------
--- @alias RendererExtmark { id?: number; start: [number, number]; stop: [number, number]; opts: any; tag: any }

--- @class Renderer
--- @field bufnr number
--- @field ns number
--- @field changedtick number
--- @field old { lines: string[]; extmarks: RendererExtmark[] }
--- @field curr { lines: string[]; extmarks: RendererExtmark[] }
local Renderer = {}
Renderer.__index = Renderer

--- function h(name: string, attributes: table<string, unknown>, children: Node | Node[]): Node
--- @param name string
--- @param attributes? table<string, any>
--- @param children? Node | Node[]
--- @return Tag
function Renderer.h(name, attributes, children)
  return setmetatable({
    kind = 'tag',
    name = name,
    attributes = attributes or {},
    children = children,
  }, TagMetaTable)
end

--- @param x any
--- @return boolean
function Renderer.is_tag(x) return type(x) == 'table' and getmetatable(x) == TagMetaTable end

--- @param x any
--- @return boolean
function Renderer.is_tag_arr(x)
  if type(x) ~= 'table' then return false end
  return #x == 0 or not Renderer.is_tag(x)
end

--- @param bufnr number|nil
function Renderer.new(bufnr)
  if bufnr == nil then bufnr = vim.api.nvim_get_current_buf() end

  if vim.b[bufnr]._renderer_ns == nil then
    vim.b[bufnr]._renderer_ns = vim.api.nvim_create_namespace('my.renderer:' .. tostring(bufnr))
  end

  local self = setmetatable({
    bufnr = bufnr,
    ns = vim.b[bufnr]._renderer_ns,
    changedtick = 0,
    old = { lines = {}, extmarks = {} },
    curr = { lines = {}, extmarks = {} },
  }, Renderer)
  return self
end

--- @param opts {
---   tree: Tree;
---   on_tag?: fun(tag: Tag, start0: [number, number], stop0: [number, number]): any;
--- }
function Renderer.markup_to_lines(opts)
  --- @type string[]
  local lines = {}

  local curr_line1 = 1
  local curr_col1 = 1 -- exclusive: sits one position **beyond** the last inserted text
  --- @param s string
  local function put(s)
    lines[curr_line1] = (lines[curr_line1] or '') .. s
    curr_col1 = #lines[curr_line1] + 1
  end
  local function put_line()
    table.insert(lines, '')
    curr_line1 = curr_line1 + 1
    curr_col1 = 1
  end

  --- @param node Node
  local function visit(node)
    if node == nil or type(node) == 'boolean' then return end

    if type(node) == 'string' then
      local node_lines = vim.split(node, '\n')
      for lnum, s in ipairs(node_lines) do
        if lnum > 1 then put_line() end
        put(s)
      end
    elseif Renderer.is_tag(node) then
      local start0 = { curr_line1 - 1, curr_col1 - 1 }

      -- visit the children:
      if Renderer.is_tag_arr(node.children) then
        for _, child in ipairs(node.children) do
          -- newlines are not controlled by array entries, do NOT output a line here:
          visit(child)
        end
      else
        visit(node.children)
      end

      local stop0 = { curr_line1 - 1, curr_col1 - 1 }
      if opts.on_tag then opts.on_tag(node, start0, stop0) end
    elseif Renderer.is_tag_arr(node) then
      for _, child in ipairs(node) do
        -- newlines are not controlled by array entries, do NOT output a line here:
        visit(child)
      end
    end
  end
  visit(opts.tree)

  return lines
end

--- @param opts {
---   tree: string;
---   format_tag?: fun(tag: Tag): string;
--- }
function Renderer.markup_to_string(opts) return table.concat(Renderer.markup_to_lines(opts), '\n') end

--- @param tree Tree
function Renderer:render(tree)
  local changedtick = vim.b[self.bufnr].changedtick
  if changedtick ~= self.changedtick then
    self.curr = { lines = vim.api.nvim_buf_get_lines(self.bufnr, 0, -1, false) }
    self.changedtick = changedtick
  end

  --- @type RendererExtmark[]
  local extmarks = {}

  --- @type string[]
  local lines = Renderer.markup_to_lines {
    tree = tree,

    on_tag = function(tag, start0, stop0)
      if tag.name == 'text' then
        local hl = tag.attributes.hl
        if type(hl) == 'string' then
          tag.attributes.extmark = tag.attributes.extmark or {}
          tag.attributes.extmark.hl_group = tag.attributes.extmark.hl_group or hl
        end

        local extmark = tag.attributes.extmark

        -- Force creating an extmark if there are key handlers. To accurately
        -- sense the bounds of the text, we need an extmark:
        if tag.attributes.on_key or tag.attributes.on_typed then extmark = extmark or {} end

        if extmark then
          table.insert(extmarks, {
            start = start0,
            stop = stop0,
            opts = extmark,
            tag = tag,
          })
        end
      end
    end,
  }

  self.old = self.curr
  self.curr = { lines = lines, extmarks = extmarks }
  self:_reconcile()
end

--- @private
--- @param info string
--- @param start integer
--- @param end_ integer
--- @param strict_indexing boolean
--- @param replacement string[]
function Renderer:_set_lines(info, start, end_, strict_indexing, replacement)
  self:_log { 'set_lines', self.bufnr, start, end_, strict_indexing, replacement }
  vim.api.nvim_buf_set_lines(self.bufnr, start, end_, strict_indexing, replacement)
  self:_log { 'after(' .. info .. ')', vim.api.nvim_buf_get_lines(self.bufnr, 0, -1, false) }
end

--- @private
--- @param info string
--- @param start_row integer
--- @param start_col integer
--- @param end_row integer
--- @param end_col integer
--- @param replacement string[]
function Renderer:_set_text(info, start_row, start_col, end_row, end_col, replacement)
  self:_log { 'set_text', self.bufnr, start_row, start_col, end_row, end_col, replacement }
  vim.api.nvim_buf_set_text(self.bufnr, start_row, start_col, end_row, end_col, replacement)
  self:_log { 'after(' .. info .. ')', vim.api.nvim_buf_get_lines(self.bufnr, 0, -1, false) }
end

--- @private
function Renderer:_log(...)
  --
  -- vim.print(...)
end

--- @private
function Renderer:_reconcile()
  local line_changes = utils.levenshtein(self.old.lines, self.curr.lines)
  self.old = self.curr

  --
  -- Step 1: morph the text to the desired state:
  --
  self:_log { line_changes = line_changes }
  for _, line_change in ipairs(line_changes) do
    local lnum0 = line_change.index - 1

    if line_change.kind == 'add' then
      self:_set_lines('add-line', lnum0, lnum0, true, { line_change.item })
    elseif line_change.kind == 'change' then
      -- Compute inter-line diff, and apply:
      self:_log '--------------------------------------------------------------------------------'
      local col_changes = utils.levenshtein(vim.split(line_change.from, ''), vim.split(line_change.to, ''))

      for _, col_change in ipairs(col_changes) do
        local cnum0 = col_change.index - 1
        self:_log { line_change = col_change, cnum = cnum0, lnum = lnum0 }
        if col_change.kind == 'add' then
          self:_set_text('add-char', lnum0, cnum0, lnum0, cnum0, { col_change.item })
        elseif col_change.kind == 'change' then
          self:_set_text('change-char', lnum0, cnum0, lnum0, cnum0 + 1, { col_change.to })
        elseif col_change.kind == 'delete' then
          self:_set_text('del-char', lnum0, cnum0, lnum0, cnum0 + 1, {})
        else
          -- No change
        end
      end
    elseif line_change.kind == 'delete' then
      self:_set_lines('del-line', lnum0, lnum0 + 1, true, {})
    else
      -- No change
    end
  end
  self.changedtick = vim.b[self.bufnr].changedtick

  --
  -- Step 2: reconcile extmarks:
  --
  -- Clear current extmarks:
  vim.api.nvim_buf_clear_namespace(self.bufnr, self.ns, 0, -1)
  -- Set current extmarks:
  for _, extmark in ipairs(self.curr.extmarks) do
    extmark.id = vim.api.nvim_buf_set_extmark(
      self.bufnr,
      self.ns,
      extmark.start[1],
      extmark.start[2],
      vim.tbl_extend('force', {
        id = extmark.id,
        end_row = extmark.stop[1],
        end_col = extmark.stop[2],
      }, extmark.opts)
    )
  end

  --
  -- Step 3: setup an updated on_key handler:
  --

  vim.on_key(nil, self.ns)
  vim.on_key(function(key, typed)
    -- Discard if not in the current buffer:
    if
      -- do not capture keys in the wrong buffer:
      vim.api.nvim_get_current_buf() ~= self.bufnr
      -- do not capture keys in COMMAND mode:
      or vim.startswith(vim.api.nvim_get_mode().mode, 'c')
    then
      return
    end

    -- find the tag with the smallest intersection that contains the cursor:
    local pos0 = vim.api.nvim_win_get_cursor(0)
    pos0[1] = pos0[1] - 1 -- make it actually 0-based
    local pos_infos = self:get_pos_infos(pos0)

    -- Check the attributes for each matching_tag and fire events if they are
    -- listening:
    for _, pos_info in ipairs(pos_infos) do
      local tag = pos_info.tag

      -- is the tag listening?
      if tag.attributes.on_key and type(tag.attributes.on_key[key]) == 'function' then
        -- key:
        local result = tag.attributes.on_key[key]()
        if result == '' then return '' end
      elseif tag.attributes.on_typed and type(tag.attributes.on_typed[typed]) == 'function' then
        -- typed:
        local result = tag.attributes.on_typed[typed]()
        if result == '' then return '' end
      end
    end
  end, self.ns)
end

--- Returns pairs of extmarks and tags associate with said extmarks. The
--- returned tags/extmarks are sorted smallest (innermost) to largest
--- (outermost).
---
--- @private (private for now)
--- @param pos0 [number; number]
--- @return { extmark: RendererExtmark; tag: Tag; }[]
function Renderer:get_pos_infos(pos0)
  local cursor_line0, cursor_col0 = pos0[1], pos0[2]

  -- The cursor (block) occupies **two** extmark spaces: one for it's left
  -- edge, and one for it's right. We need to do our own intersection test,
  -- because the NeoVim API is over-inclusive in what it returns:
  --- @type RendererExtmark[]
  local intersecting_extmarks = vim
    .iter(vim.api.nvim_buf_get_extmarks(self.bufnr, self.ns, pos0, pos0, { details = true, overlap = true }))
    --- @return RendererExtmark
    :map(function(ext)
      --- @type number, number, number, { end_row?: number; end_col?: number }|nil
      local id, line0, col0, details = unpack(ext)
      local start = { line0, col0 }
      local stop = { line0, col0 }
      if details and details.end_row ~= nil and details.end_col ~= nil then
        stop = { details.end_row, details.end_col }
      end
      return { id = id, start = start, stop = stop, opts = details }
    end)
    --- @param ext RendererExtmark
    :filter(function(ext)
      if ext.stop[1] ~= nil and ext.stop[2] ~= nil then
        return cursor_line0 >= ext.start[1]
          and cursor_col0 >= ext.start[2]
          and cursor_line0 <= ext.stop[1]
          and cursor_col0 < ext.stop[2]
      else
        return true
      end
    end)
    :totable()

  -- Sort the tags into smallest (inner) to largest (outer):
  table.sort(
    intersecting_extmarks,
    --- @param x1 RendererExtmark
    --- @param x2 RendererExtmark
    function(x1, x2)
      if
        x1.start[1] == x2.start[1]
        and x1.start[2] == x2.start[2]
        and x1.stop[1] == x2.stop[1]
        and x1.stop[2] == x2.stop[2]
      then
        return x1.id < x2.id
      end

      return x1.start[1] >= x2.start[1]
        and x1.start[2] >= x2.start[2]
        and x1.stop[1] <= x2.stop[1]
        and x1.stop[2] <= x2.stop[2]
    end
  )

  -- When we set the extmarks in the step above, we captured the IDs of the
  -- created extmarks in self.curr.extmarks, which also has which tag each
  -- extmark is associated with. Cross-reference with that list to get a list
  -- of tags that we need to fire events for:
  --- @type { extmark: RendererExtmark; tag: Tag }[]
  local matching_tags = vim
    .iter(intersecting_extmarks)
    --- @param ext RendererExtmark
    :map(function(ext)
      for _, extmark_cache in ipairs(self.curr.extmarks) do
        if extmark_cache.id == ext.id then return { extmark = ext, tag = extmark_cache.tag } end
      end
    end)
    :totable()

  return matching_tags
end

return Renderer