local errors = {}

-- Split subject into array of lines (local helper)

local function splitlines(subject)

local lines = {}

local start = 1

while true do

local newline_pos = subject:find("\n", start, true)

if newline_pos then

lines[#lines + 1] = subject:sub(start, newline_pos - 1)

start = newline_pos + 1

else

lines[#lines + 1] = subject:sub(start)

break

end

end

return lines

end

-- Calculate line number and column from byte position (local helper)

-- Returns: line (1-indexed), column (1-indexed)

local function calcline(subject, pos)

if pos <= 1 then return 1, 1 end

local sub = subject:sub(1, pos - 1)

local line = 1

local last_newline = 0

for i = 1, #sub do

if sub:sub(i, i) == "\n" then

line = line + 1

last_newline = i

end

end

local col = pos - last_newline

return line, col

end

-- Get the line of text containing the given position (local helper)

-- Returns: line text, column position within that line

local function getline(subject, pos)

-- Find start of line

local line_start = pos

while line_start > 1 and subject:sub(line_start - 1, line_start - 1) ~= "\n" do

line_start = line_start - 1

end

-- Find end of line

local line_end = pos

while line_end <= #subject and subject:sub(line_end, line_end) ~= "\n" do

line_end = line_end + 1

end

return subject:sub(line_start, line_end - 1), pos - line_start + 1

end

-- Format a complete error message

-- subject: the input string being parsed

-- pos: byte position where error occurred (1-indexed)

-- label: error label from T() or nil

-- opts: optional table with:

-- color: boolean - if true, use ansicolors for colored output

-- context: number - lines to show above and below error line (default: 0)

function errors.format(subject, pos, label, opts)

local line, col = calcline(subject, pos)

local line_text, col_in_line = getline(subject, pos)

local context = opts and opts.context or 0

local msg

if opts and opts.color then

local colors = require("ansicolors")

msg = colors("%{bright red}" .. (label or "error") .. "%{reset}")

msg = msg .. colors(" %{dim}at line " .. line .. ", column " .. col .. ":%{reset}\n")

if context > 0 then

local lines = splitlines(subject)

local start_line = math.max(1, line - context)

local end_line = math.min(#lines, line + context)

local max_line_num = end_line

local line_num_width = #tostring(max_line_num)

for i = start_line, end_line do

local line_num_str = string.format("%" .. line_num_width .. "d", i)

msg = msg .. colors("%{dim}" .. line_num_str .. " |%{reset} ") .. lines[i] .. "\n"

if i == line then

local prefix_width = line_num_width + 3 + col_in_line - 1

msg = msg .. string.rep(" ", prefix_width) .. colors("%{bright red}^%{reset}") .. "\n"

end

end

msg = msg:sub(1, -2) -- remove trailing newline

else

msg = msg .. " " .. line_text .. "\n"

msg = msg .. " " .. string.rep(" ", col_in_line - 1)

msg = msg .. colors("%{bright red}^%{reset}")

end

else

msg = string.format("%s at line %d, column %d:\n",

label or "error", line, col)

if context > 0 then

local lines = splitlines(subject)

local start_line = math.max(1, line - context)

local end_line = math.min(#lines, line + context)

local max_line_num = end_line

local line_num_width = #tostring(max_line_num)

for i = start_line, end_line do

local line_num_str = string.format("%" .. line_num_width .. "d", i)

msg = msg .. line_num_str .. " | " .. lines[i] .. "\n"

if i == line then

local prefix_width = line_num_width + 3 + col_in_line - 1

msg = msg .. string.rep(" ", prefix_width) .. "^\n"

end

end

msg = msg:sub(1, -2) -- remove trailing newline

else

msg = msg .. " " .. line_text .. "\n"

msg = msg .. " " .. string.rep(" ", col_in_line - 1) .. "^"

end

end

return msg

end

return errors