local config = require('pending.config')
local forge = require('pending.forge')
local parse = require('pending.parse')

---@class pending.ForgeLineMeta
---@field ref pending.ForgeRef
---@field cache? pending.ForgeCache
---@field col_start integer
---@field col_end integer

---@class pending.LineMeta
---@field type 'task'|'header'|'blank'|'filter'
---@field id? integer
---@field due? string
---@field raw_due? string
---@field status? pending.TaskStatus
---@field category? string
---@field overdue? boolean
---@field show_category? boolean
---@field priority? integer
---@field recur? string
---@field forge_spans? pending.ForgeLineMeta[]

---@class pending.views
local M = {}

---@param due? string
---@return string?
local function format_due(due)
  if not due then
    return nil
  end
  local y, m, d, hh, mm = due:match('^(%d%d%d%d)-(%d%d)-(%d%d)T(%d%d):(%d%d)$')
  if not y then
    y, m, d = due:match('^(%d%d%d%d)-(%d%d)-(%d%d)$')
  end
  if not y then
    return due
  end
  local t = os.time({
    year = tonumber(y) --[[@as integer]],
    month = tonumber(m) --[[@as integer]],
    day = tonumber(d) --[[@as integer]],
  })
  local formatted = os.date(config.get().date_format, t) --[[@as string]]
  if hh then
    formatted = formatted .. ' ' .. hh .. ':' .. mm
  end
  return formatted
end

---@param task pending.Task
---@param prefix_len integer
---@return pending.ForgeLineMeta[]?
local function compute_forge_spans(task, prefix_len)
  local refs = forge.find_refs(task.description)
  if #refs == 0 then
    return nil
  end
  local cache = task._extra and task._extra._forge_cache or nil
  local spans = {}
  for _, r in ipairs(refs) do
    table.insert(spans, {
      ref = r.ref,
      cache = cache,
      col_start = prefix_len + r.start_byte,
      col_end = prefix_len + r.end_byte,
    })
  end
  return spans
end

---@type table<string, integer>
local status_rank = { wip = 0, pending = 1, blocked = 2, done = 3 }

---@param task pending.Task
---@return string
local function state_char(task)
  if task.status == 'done' then
    return 'x'
  elseif task.status == 'wip' then
    return '>'
  elseif task.status == 'blocked' then
    return '='
  elseif task.priority > 0 then
    return '!'
  end
  return ' '
end

---@param tasks pending.Task[]
local function sort_tasks(tasks)
  table.sort(tasks, function(a, b)
    local ra = status_rank[a.status] or 1
    local rb = status_rank[b.status] or 1
    if ra ~= rb then
      return ra < rb
    end
    if a.priority ~= b.priority then
      return a.priority > b.priority
    end
    if a.order ~= b.order then
      return a.order < b.order
    end
    return a.id < b.id
  end)
end

---@type table<string, fun(a: pending.Task, b: pending.Task): boolean?>
local sort_key_comparators = {
  status = function(a, b)
    local ra = status_rank[a.status] or 1
    local rb = status_rank[b.status] or 1
    if ra ~= rb then
      return ra < rb
    end
    return nil
  end,
  priority = function(a, b)
    if a.priority ~= b.priority then
      return a.priority > b.priority
    end
    return nil
  end,
  due = function(a, b)
    local a_due = a.due or ''
    local b_due = b.due or ''
    if a_due ~= b_due then
      if a_due == '' then
        return false
      end
      if b_due == '' then
        return true
      end
      return a_due < b_due
    end
    return nil
  end,
  order = function(a, b)
    if a.order ~= b.order then
      return a.order < b.order
    end
    return nil
  end,
  id = function(a, b)
    if a.id ~= b.id then
      return a.id < b.id
    end
    return nil
  end,
  age = function(a, b)
    if a.id ~= b.id then
      return a.id < b.id
    end
    return nil
  end,
}

---@return fun(a: pending.Task, b: pending.Task): boolean
local function build_queue_comparator()
  local log = require('pending.log')
  local keys = config.get().view.queue.sort or { 'status', 'priority', 'due', 'order', 'id' }
  local comparators = {}
  local unknown = {}
  for _, key in ipairs(keys) do
    local cmp = sort_key_comparators[key]
    if cmp then
      table.insert(comparators, cmp)
    else
      table.insert(unknown, key)
    end
  end
  if #unknown > 0 then
    local label = #unknown == 1 and 'unknown queue sort key: ' or 'unknown queue sort keys: '
    log.warn(label .. table.concat(unknown, ', '))
  end
  return function(a, b)
    for _, cmp in ipairs(comparators) do
      local result = cmp(a, b)
      if result ~= nil then
        return result
      end
    end
    return false
  end
end

---@param tasks pending.Task[]
local function sort_tasks_priority(tasks)
  local cmp = build_queue_comparator()
  table.sort(tasks, cmp)
end

---@param tasks pending.Task[]
---@return string[] lines
---@return pending.LineMeta[] meta
function M.category_view(tasks)
  local by_cat = {}
  local cat_order = {}
  local cat_seen = {}
  local done_by_cat = {}

  for _, task in ipairs(tasks) do
    local cat = task.category or config.get().default_category
    if not cat_seen[cat] then
      cat_seen[cat] = true
      table.insert(cat_order, cat)
      by_cat[cat] = {}
      done_by_cat[cat] = {}
    end
    if task.status == 'done' or task.status == 'deleted' then
      table.insert(done_by_cat[cat], task)
    else
      table.insert(by_cat[cat], task)
    end
  end

  local cfg_order = config.get().view.category.order
  if cfg_order and #cfg_order > 0 then
    local ordered = {}
    local seen = {}
    for _, name in ipairs(cfg_order) do
      if cat_seen[name] then
        table.insert(ordered, name)
        seen[name] = true
      end
    end
    for _, name in ipairs(cat_order) do
      if not seen[name] then
        table.insert(ordered, name)
      end
    end
    cat_order = ordered
  end

  for _, cat in ipairs(cat_order) do
    sort_tasks(by_cat[cat])
    sort_tasks(done_by_cat[cat])
  end

  local lines = {}
  local meta = {}

  for i, cat in ipairs(cat_order) do
    if i > 1 then
      table.insert(lines, '')
      table.insert(meta, { type = 'blank' })
    end
    table.insert(lines, '# ' .. cat)
    table.insert(meta, { type = 'header', category = cat })

    local all = {}
    for _, t in ipairs(by_cat[cat]) do
      table.insert(all, t)
    end
    for _, t in ipairs(done_by_cat[cat]) do
      table.insert(all, t)
    end

    for _, task in ipairs(all) do
      local prefix = '/' .. task.id .. '/'
      local state = state_char(task)
      local line = prefix .. '- [' .. state .. '] ' .. task.description
      local prefix_len = #prefix + #('- [' .. state .. '] ')
      table.insert(lines, line)
      table.insert(meta, {
        type = 'task',
        id = task.id,
        due = format_due(task.due),
        raw_due = task.due,
        status = task.status,
        category = cat,
        priority = task.priority,
        overdue = task.status ~= 'done' and task.due ~= nil and parse.is_overdue(task.due) or nil,
        recur = task.recur,
        forge_spans = compute_forge_spans(task, prefix_len),
      })
    end
  end

  return lines, meta
end

---@param tasks pending.Task[]
---@return string[] lines
---@return pending.LineMeta[] meta
function M.priority_view(tasks)
  local pending = {}
  local done = {}

  for _, task in ipairs(tasks) do
    if task.status == 'done' then
      table.insert(done, task)
    else
      table.insert(pending, task)
    end
  end

  sort_tasks_priority(pending)
  sort_tasks_priority(done)

  local lines = {}
  local meta = {}

  local all = {}
  for _, t in ipairs(pending) do
    table.insert(all, t)
  end
  for _, t in ipairs(done) do
    table.insert(all, t)
  end

  for _, task in ipairs(all) do
    local prefix = '/' .. task.id .. '/'
    local state = task.status == 'done' and 'x' or (task.priority > 0 and '!' or ' ')
    local line = prefix .. '- [' .. state .. '] ' .. task.description
    local prefix_len = #prefix + #('- [' .. state .. '] ')
    table.insert(lines, line)
    table.insert(meta, {
      type = 'task',
      id = task.id,
      due = format_due(task.due),
      raw_due = task.due,
      status = task.status,
      category = task.category,
      priority = task.priority,
      overdue = task.status ~= 'done' and task.due ~= nil and parse.is_overdue(task.due) or nil,
      show_category = true,
      recur = task.recur,
      forge_ref = task._extra and task._extra._forge_ref or nil,
      forge_cache = task._extra and task._extra._forge_cache or nil,
      forge_spans = compute_forge_spans(task, prefix_len),
    })
  end

  return lines, meta
end

return M