file_replace_content.lua

-- MCP Tool: file_replace_content
-- Replace a unique occurrence of text in a file
-- The search text must appear exactly once for safety
-- Entry kind: function.lua

local json = require("json")
local projects = require("projects")

local function call(arguments)
    local vol, err = projects.resolve(arguments.project)
    if err then
        return "Error: " .. err
    end

    local path = arguments.path
    if not path or path == "" then
        return "Error: path is required"
    end

    local search = arguments.search
    if not search or search == "" then
        return "Error: search is required — cannot replace empty content"
    end

    local replace = arguments.replace
    if replace == nil then
        return "Error: replace is required"
    end

    -- Read current content
    local content, read_err = vol:readfile(path)
    if read_err then
        return "Error reading file: " .. tostring(read_err)
    end

    -- Find first occurrence (plain text, no patterns)
    local pos = string.find(content, search, 1, true)
    if not pos then
        return "Error: search text not found in " .. path
            .. ". Verify exact match including whitespace, tabs, and line endings."
            .. " Use file_read tool to see actual file content."
    end

    -- Check uniqueness — must appear exactly once
    local second = string.find(content, search, pos + 1, true)
    if second then
        local count = 2
        local p = second
        while true do
            p = string.find(content, search, p + 1, true)
            if not p then break end
            count = count + 1
        end
        return string.format(
            "Error: search text found %d times in %s."
            .. " Pattern must be unique. Add more surrounding context to make it unique.",
            count, path
        )
    end

    -- Calculate line numbers for reporting
    local before = string.sub(content, 1, pos - 1)
    local _, newlines_before = string.gsub(before, "\n", "\n")
    local line_start = newlines_before + 1

    local _, search_newlines = string.gsub(search, "\n", "\n")
    local _, replace_newlines = string.gsub(replace, "\n", "\n")
    local line_end = line_start + search_newlines
    local new_line_end = line_start + replace_newlines

    -- Perform replacement
    local new_content = string.sub(content, 1, pos - 1)
        .. replace
        .. string.sub(content, pos + #search)

    local _, write_err = vol:writefile(path, new_content)
    if write_err then
        return "Error writing file: " .. tostring(write_err)
    end

    -- Build success message
    local line_info = line_start == line_end
        and ("line " .. line_start)
        or ("lines " .. line_start .. "-" .. line_end)
    local new_info = line_start == new_line_end
        and ("line " .. line_start)
        or ("lines " .. line_start .. "-" .. new_line_end)

    return string.format(
        "Successfully replaced in '%s'.\n"
        .. "Original: %s (%d characters)\n"
        .. "Modified: %s (%d characters)\n"
        .. "Change: %+d characters",
        path,
        line_info, #search,
        new_info, #replace,
        #replace - #search
    )
end

return { call = call }